Oncogene

Our medical research library holds 43 studies published in Oncogene (1997–2024). Each entry links to the study's record on PubMed and, where there is one, to the publisher's page and a free full text. 43 have an abstract, the authors' own summary as PubMed records it: open "Abstract" to read it.

About the journal

• Publisher: Nature Publishing Group
• Published: 1987 to the present, England
• Language: English
• ISSN: 0950-9232 (print), 1476-5594 (electronic)
• Its record in the NLM Catalog

2020s

• The BAP1 nuclear deubiquitinase is involved in the nonhomologous end-joining pathway of double-strand DNA repair through interaction with DNA-PK. H. Sato, T. Ito, T. Hayashi, et al. 2024;43(15):1087-1097. PubMed · Publisher · Free full text

  Abstract

  BRCA1-associated protein 1 (BAP1) has emerged as a major tumor suppressor gene in diverse cancer types, notably in malignant pleural mesothelioma (DPM), and has also been identified as a germline cancer predisposition gene for DPM and other select cancers. However, its role in the response to DNA damage has remained unclear. Here, we show that BAP1 inactivation is associated with increased DNA damage both in Met-5A human mesothelial cells and human DPM cell lines. Through proteomic analyses, we identified PRKDC as an interaction partner of BAP1 protein complexes in DPM cells and 293 T human embryonic kidney cells. PRKDC encodes the catalytic subunit of DNA protein kinase (DNA-PKcs) which functions in the nonhomologous end-joining (NHEJ) pathway of DNA repair. Double-stranded DNA damage resulted in prominent nuclear expression of BAP1 in DPM cells and phosphorylation of BAP1 at serine 395. A plasmid-based NHEJ assay confirmed a significant effect of BAP1 knockdown on cellular NHEJ activity. Combination treatment with X-ray irradiation and gemcitabine (as a radiosensitizer) strongly suppressed the growth of BAP1-deficient cells. Our results suggest reciprocal positive interactions between BAP1 and DNA-PKcs, based on phosphorylation of BAP1 by the latter and deubiquitination of DNA-PKcs by BAP1. Thus, functional interaction of BAP1 with DNA-PKcs supports a role for BAP1 in NHEJ DNA repair and may provide the basis for new therapeutic strategies and new insights into its role as a tumor suppressor.

  © 2024. The Author(s), under exclusive licence to Springer Nature Limited.

• BAP1 loss induces mitotic defects in mesothelioma cells through BRCA1-dependent and independent mechanisms. A. Singh, S. Busacca, A. Gaba, et al. 2023;42(8):572-585. PubMed · Publisher · Free full text

  Abstract

  The tumour suppressor BRCA1-associated protein 1 (BAP1) is the most frequently mutated cancer gene in mesothelioma. Here we report novel functions for BAP1 in mitotic progression highlighting the relationship between BAP1 and control of genome stability in mesothelioma cells with therapeutic implications. Depletion of BAP1 protein induced proteasome-mediated degradation of BRCA1 in mesothelioma cells while loss of BAP1 correlated with BRCA1 loss in mesothelioma patient tumour samples. BAP1 loss also led to mitotic defects that phenocopied the loss of BRCA1 including spindle assembly checkpoint failure, centrosome amplification and chromosome segregation errors. However, loss of BAP1 also led to additional mitotic changes that were not observed upon BRCA1 loss, including an increase in spindle length and enhanced growth of astral microtubules. Intriguingly, these consequences could be explained by loss of expression of the KIF18A and KIF18B kinesin motors that occurred upon depletion of BAP1 but not BRCA1, as spindle and astral microtubule defects were rescued by re-expression of KIF18A and KIF18B, respectively. We therefore propose that BAP1 inactivation causes mitotic defects through BRCA1-dependent and independent mechanisms revealing novel routes by which mesothelioma cells lacking BAP1 may acquire genome instability and exhibit altered responses to microtubule-targeted agents.

  © 2022. The Author(s).

• H3K9me3 represses G6PD expression to suppress the pentose phosphate pathway and ROS production to promote human mesothelioma growth. C. Lu, D. Yang, J.D. Klement, et al. 2022;41(18):2651-2662. PubMed · Publisher · Free full text

  Abstract

  The role of glucose-6-phosphate dehydrogenase (G6PD) in human cancer is incompletely understood. In a metabolite screening, we observed that inhibition of H3K9 methylation suppressed aerobic glycolysis and enhances the PPP in human mesothelioma cells. Genome-wide screening identified G6PD as an H3K9me3 target gene whose expression is correlated with increased tumor cell apoptosis. Inhibition of aerobic glycolysis enzyme LDHA and G6PD had no significant effects on tumor cell survival. Ablation of G6PD had no significant effect on human mesothelioma and colon carcinoma xenograft growth in athymic mice. However, activation of G6PD with the G6PD-selective activator AG1 induced tumor cell death. AG1 increased tumor cell ROS production and the resultant extrinsic and intrinsic death pathways, mitochondrial processes, and unfolded protein response in tumor cells. Consistent with increased tumor cell death in vitro, AG1 suppressed human mesothelioma xenograft growth in a dose-dependent manner in vivo. Furthermore, AG1 treatment significantly increased tumor-bearing mouse survival in an intra-peritoneum xenograft athymic mouse model. Therefore, in human mesothelioma and colon carcinoma, G6PD is not essential for tumor growth. G6PD acts as a metabolic checkpoint to control metabolic flux towards the PPP to promote tumor cell apoptosis, and its expression is repressed by its promotor H3K9me3 deposition.

  © 2022. The Author(s), under exclusive licence to Springer Nature Limited.

• Generation of human embryonic stem cell models to exploit the EWSR1-CREB fusion promiscuity as a common pathway of transformation in human tumors. F. Vanoli, B. Meskauskaite, L. Herviou, et al. 2021;40(32):5095-5104. PubMed · Publisher · Free full text

  Abstract

  Chromosomal translocations constitute driver mutations in solid tumors and leukemias. The mechanisms of how related or even identical gene fusions drive the pathogenesis of various tumor types remain elusive. One remarkable example is the presence of EWSR1 fusions with CREB1 and ATF1, members of the CREB family of transcription factors, in a variety of sarcomas, carcinomas and mesotheliomas. To address this, we have developed in vitro models of oncogenic fusions, in particular, EWSR1-CREB1 and EWSR1-ATF1, in human embryonic stem (hES) cells, which are capable of multipotent differentiation, using CRISPR-Cas9 technology and HDR together with conditional fusion gene expression that allows investigation into the early steps of cellular transformation. We show that expression of EWSR1-CREB1/ATF1 fusion in hES cells recapitulates the core gene signatures, respectively, of angiomatoid fibrous histiocytoma (AFH) and gastrointestinal clear cell sarcoma (GI-CCS), although both fusions lead to cell lethality. Conversely, expression of the fusions in hES cells differentiated to mesenchymal progenitors is compatible with prolonged viability while maintaining the core gene signatures. Moreover, in the context of a mesenchymal lineage, the proliferation of cells expressing the EWSR1-CREB1 fusion is further extended by deletion of the tumor suppressor TP53. We expect the generation of isogenic lines carrying oncogenic fusions in various cell lineages to expand our general understanding of how those single genetic events drive tumorigenesis while providing valuable resources for drug discovery.

  © 2021. The Author(s), under exclusive licence to Springer Nature Limited.

2010s

• ADAM10 mediates malignant pleural mesothelioma invasiveness. C. Sépult, M. Bellefroid, N. Rocks, et al. 2019;38(18):3521-3534. PubMed · Publisher · Free full text

  Abstract

  Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited therapeutic options and treatment efficiency. Even if the latency period between asbestos exposure, the main risk factor, and mesothelioma development is very long, the local invasion of mesothelioma is very rapid leading to a mean survival of one year after diagnosis. ADAM10 (A Disintegrin And Metalloprotease) sheddase targets membrane-bound substrates and its overexpression is associated with progression in several cancers. However, nothing is known about ADAM10 implication in MPM. In this study, we demonstrated higher ADAM10 expression levels in human MPM as compared to control pleural samples and in human MPM cell line. This ADAM10 overexpression was also observed in murine MPM samples. Two mouse mesothelioma cell lines were used in this study including one primary cell line obtained by repeated asbestos fibre injections. We show, in vitro, that ADAM10 targeting through shRNA and pharmacological (GI254023X) approaches reduced drastically mesothelioma cell migration and invasion, as well as for human mesothelioma cells treated with siRNA targeting ADAM10. Moreover, ADAM10 downregulation in murine mesothelioma cells significantly impairs MPM progression in vivo after intrapleural cell injection. We also demonstrate that ADAM10 sheddase downregulation decreases the production of a soluble N-cadherin fragment through membrane N-cadherin, which stimulated mesothelioma cell migration. Taken together, we demonstrate that ADAM10 is overexpressed in MPM and takes part to MPM progression through the generation of N-cadherin fragment that stimulates mesothelioma cell migration. ADAM10 inhibition is worth considering as a therapeutic perspective in mesothelioma context.

• Identification of a novel EphB4 phosphodegron regulated by the autocrine IGFII/IRA axis in malignant mesothelioma. P. Scalia, G. Pandini, V. Carnevale, et al. 2019;38(31):5987-6001. PubMed · Publisher · Free full text

  Abstract

  Malignant mesothelioma is a deadly disease with limited therapeutic options. EphB4 is an oncogenic tyrosine kinase receptor expressed in malignant mesothelioma as well as in a variety of cancers. It is involved in tumor microenvironment mediating angiogenesis and invasive cellular effects via both EphrinB2 ligand-dependent and independent mechanisms. The molecular network underlying EphB4 oncogenic effects is still unclear. Here we show that EphB4 expression in malignant mesothelioma cells is markedly decreased upon neutralization of cancer-secreted IGF-II. In particular, we demonstrate that EphB4 protein expression in malignant mesothelioma cells depend upon a degradation rescue mechanism controlled by the autocrine IGF-II-insulin receptor-A specific signaling axis. We show that the regulation of EphB4 expression is linked to a competing post-translational modification of its carboxy-terminal tail via phosphorylation of its tyrosine 987 by the Insulin receptor isoform-A kinase-associated activity in response to the autocrine IGF-II stimuli. Neutralization of this autocrine-induced EphB4-phosphorylation by IGF-II associates with the increased ubiquitination of EphB4 carboxy-terminal tail and with its rapid degradation. We also describe a novel Ubiquitin binding motif in the targeted region as part of the identified EphB4 phosphodegron and provide 3D modeling data supporting a possible model for the acute EphB4 PTM-driven regulation by IGF-II. Altogether, these findings disclose a novel molecular mechanism for the maintenance of EphB4-expression in malignant mesothelioma cells and other IGF-II-secreting cancers (IGF2omas).

• TAZ activation by Hippo pathway dysregulation induces cytokine gene expression and promotes mesothelial cell transformation. A. Matsushita, T. Sato, S. Mukai, et al. 2019;38(11):1966-1978. PubMed · Publisher

  Abstract

  Malignant mesothelioma (MM) constitutes a very aggressive tumor that is caused by asbestos exposure after long latency. The NF2 tumor suppressor gene is mutated in 40-50% of MM; moreover, one of its downstream signaling cascades, the Hippo signaling pathway, is also frequently inactivated in MM cells. Although the YAP transcriptional coactivator, which is regulated by the Hippo pathway, can function as a pro-oncogenic protein, the role of TAZ, a paralog of YAP, in MM cells has not yet been clarified. Here, we show that TAZ is expressed and underphosphorylated (activated) in the majority of MM cells compared to immortalized mesothelial cells. ShRNA-mediated TAZ knockdown highly suppressed cell proliferation, anchorage-independent growth, cell motility, and invasion in MM cells harboring activated TAZ. Conversely, transduction of an activated form of TAZ in immortalized mesothelial cells enhanced these in vitro phenotypes and conferred tumorigenicity in vivo. Microarray analysis determined that activated TAZ most significantly enhanced the transcription of genes related to "cytokine-cytokine receptor interaction." Among selected cytokines, we found that IL-1 signaling activation plays a major role in proliferation in TAZ-activated MM cells. Both IL1B knockdown and an IL-1 receptor antagonist significantly suppressed malignant phenotypes of immortalized mesothelial cells and MM cells with activated TAZ. Overall, these results indicate an oncogenic role for TAZ in MMs via transcriptional induction of distinct pro-oncogenic genes including cytokines. Among these, IL-1 signaling appears as one of the most important cascades, thus potentially serving as a target pathway in MM cells harboring Hippo pathway inactivation.

• Differential regulation of the sphere formation and maintenance of cancer-initiating cells of malignant mesothelioma via CD44 and ALK4 signaling pathways. Y. Ohno, S. Shingyoku, S. Miyake, et al. 2018;37(49):6357-6367. PubMed · Publisher · Free full text

  Abstract

  Malignant mesothelioma (MM) has a poor prognosis and is largely resistant to standard treatments, so it is important to seek novel therapeutic strategies for this disease. Cancer-initiating cells (CICs) were previously identified in MM using stem cell-associated markers in combination with spheroid cultures. However, the mechanisms underlying the induction and maintenance of CICs in MM remain to be fully explored. Here we showed that the CICs, which had high aldehyde dehydrogenase levels (ALDHbright) and stem cell-associated genes, were expanded in MM cells cultured under sphere-forming conditions. The MM spheroids also initiated tumors in immunodeficient mice more efficiently than did conventional adherent MM cells. In the MM spheroids, the expression of hyaluronan (HA) synthases was upregulated. Inhibiting the HA synthesis or CD44 functions by gene knockdown or neutralizing antibody abolished the formation of large-sized spheroids and the expansion of ALDHbright CICs. The expression of activin-A was also increased in the spheroids, and type I activin-A receptor subunit (ALK4) was upregulated in the ALDHbright CICs. The neutralization of activin-A or functional inactivation of ALK4 diminished the ALDHbright CICs without affecting spheroid formation. The knockdown of CD44 or ALK4 strongly suppressed the tumor growth in immunodeficient mice. These results together suggest that the HA-CD44 and activin-A-ALK4 pathways differentially regulate the spheroid formation and maintenance of ALDHbright CICs in MM cells, and that both pathways play critical roles in tumor growth in immunodeficient hosts. Our findings provide a novel therapeutic option for MM that targets signaling pathways that promote the CIC compartment through CD44 and ALK4.

• How asbestos drives the tissue towards tumors: YAP activation, macrophage and mesothelial precursor recruitment, RNA editing, and somatic mutations. H. Rehrauer, L. Wu, W. Blum, et al. 2018;37(20):2645-2659. PubMed · Publisher · Free full text

  Abstract

  Chronic exposure to intraperitoneal asbestos triggered a marked response in the mesothelium well before tumor development. Macrophages, mesothelial precursor cells, cytokines, and growth factors accumulated in the peritoneal lavage. Transcriptome profiling revealed YAP/TAZ activation in inflamed mesothelium with further activation in tumors, paralleled by increased levels of cells with nuclear YAP/TAZ. Arg1 was one of the highest upregulated genes in inflamed tissue and tumor. Inflamed tissue showed increased levels of single-nucleotide variations, with an RNA-editing signature, which were even higher in the tumor samples. Subcutaneous injection of asbestos-treated, but tumor-free mice with syngeneic mesothelioma tumor cells resulted in a significantly higher incidence of tumor growth when compared to naïve mice supporting the role of the environment in tumor progression.

• HSP90 inhibition alters the chemotherapy-driven rearrangement of the oncogenic secretome. S. di Martino, C.A. Amoreo, B. Nuvoli, et al. 2018;37(10):1369-1385. PubMed · Publisher

  Abstract

  Adaptive resistance to therapy is a hallmark of cancer progression. To date, it is not entirely clear how microenvironmental stimuli would mediate emergence of therapy-resistant cell subpopulations, although a rearrangement of the cancer cell secretome following therapy-induced stress can be pivotal for such a process. Here, by using the highly chemoresistant malignant pleural mesothelioma (MPM) as an experimental model, we unveiled a key contribution of the chaperone HSP90 at assisting a chemotherapy-instigated Senescence-Associated-Secretory-Phenotype (SASP). Thus, administration of a clinical trial grade, HSP90, inhibitor blunted the release of several cytokines by the chemotherapy-treated MPM cells, including interleukin (IL)-8. Reduction of IL-8 levels hampered the FAK-AKT signaling and inhibited 3D growth and migration. This correlated with downregulation of key EMT and chemoresistance genes and affected the survival of chemoresistant ALDHbright cell subpopulations. Altogether, inhibition of HSP90 provoked a switch from a pro-tumorigenic SASP to a pro-apoptotic senescence status, thus resulting in chemosensitizing effects. In mouse xenografts treated with first-line agents, inhibiting HSP90 blunted FAK activation and reduced the expression of ALDH1A3 and the levels of circulating human IL-8, these latter strongly correlating with the effect on tumor growth. We validated the above findings in primary mesothelioma cultures, a more clinically relevant model. We unveiled here a key contribution of the chaperone HSP90 at assisting the secretory stress in chemotherapy-treated cells, which may warrant further investigation in combinatorial therapeutic settings.

• RBL2/p130 is a direct AKT target and is required to induce apoptosis upon AKT inhibition in lung cancer and mesothelioma cell lines. F. Pentimalli, I.M. Forte, L. Esposito, et al. 2018;37(27):3657-3671. PubMed · Publisher

  Abstract

  The retinoblastoma (RB) protein family includes RB1/p105, RBL1/p107, and RBL2/p130, which are key factors in cell-cycle regulation and stand at the crossroads of multiple pathways dictating cell fate decisions. The role of RB proteins in apoptosis is controversial because they can inhibit or promote apoptosis depending on the context, on the apoptotic stimuli and on their intrinsic status, impacting on the response to antitumoral treatments. Here we identified RBL2/p130 as a direct substrate of the AKT kinase, a key antiapoptotic factor hyperactive in multiple cancer types. We showed that RBL2/p130 and AKT1 physically interact and AKT phosphorylates RBL2/p130 Ser941, located in the pocket domain, but not when this residue is mutated into Ala. We found that pharmacological inhibition of AKT, through the highly selective AKT inhibitor VIII (AKTiVIII), impairs RBL2/p130 Ser941 phosphorylation and increases RBL2/p130 stability, mRNA expression and nuclear levels in both lung cancer and mesothelioma cell lines, mirroring the more extensively studied effects on the p27 cell-cycle inhibitor. Consistently, AKT inhibition reduced cell viability, induced cell accumulation in G0/G1, and triggered apoptosis, which proved to be largely dependent on RBL2/p130 itself, as shown upon RBL2/p130 silencing. AKT inhibition induced RBL2/p130-dependent apoptosis also in HEK-293 cells, in which re-expression of a short hairpin-resistant RBL2/p130 was able to rescue AKTiVIII-induced apoptosis upon RBL2/p130 silencing. Our data also showed that the combination of AKT and cyclin-dependent kinases (CDK) inhibitors, which converge on the re-activation of RBL2/p130 antitumoral potential, could be a promising anticancer strategy.

• E-cadherin expression is correlated with focal adhesion kinase inhibitor resistance in Merlin-negative malignant mesothelioma cells. T. Kato, T. Sato, K. Yokoi, et al. 2017;36(39):5522-5531. PubMed · Publisher

  Abstract

  Malignant mesothelioma (MM) is an aggressive tumor commonly caused by asbestos exposure after a long latency. Focal adhesion kinase (FAK) inhibitors inhibit the cell growth of Merlin-deficient MM cells; however, their clinical efficacy has not been clearly determined. The aim of this study was to evaluate the growth inhibitory effect of the FAK inhibitor VS-4718 on MM cell lines and identify biomarkers for its efficacy. Although most Merlin-deficient cell lines were sensitive to VS-4718 compared with control MeT-5A cells, a subset of these cell lines exhibited resistance to this drug. Microarray and qRT-PCR analyses using RNA isolated from Merlin-deficient MM cell lines revealed a significant correlation between E-cadherin mRNA levels and VS-4718 resistance. Merlin- and E-cadherin-negative Y-MESO-22 cells underwent apoptosis upon treatment with a low concentration of VS-4718, whereas Merlin-negative, E-cadherin-positive Y-MESO-9 cells did not undergo VS-4718-induced apoptosis. Furthermore, E-cadherin knockdown in Merlin-negative MM cells significantly sensitized cells to VS-4718 and induced apoptotic cell death upon VS-4718 treatment. Together, our results suggest that E-cadherin serves as a predictive biomarker for molecular target therapy with FAK inhibitors for patients with mesothelioma and that its expression endows MM cells with resistance to FAK inhibitors.

• Inhibition of the spindle assembly checkpoint kinase Mps-1 as a novel therapeutic strategy in malignant mesothelioma. A. Szymiczek, M. Carbone, S. Pastorino, et al. 2017;36(46):6501-6507. PubMed · Publisher · Free full text

  Abstract

  Malignant mesothelioma (MM) is an aggressive malignancy, highly resistant to current medical and surgical therapies, whose tumor cells characteristically show a high level of aneuploidy and genomic instability. We tested our hypothesis that targeting chromosomal instability in MM would improve response to therapy. Thr/Tyr kinase (TTK)/monopolar spindle 1 kinase (Mps-1) is a kinase of the spindle assembly checkpoint that controls cell division and cell fate. CFI-402257 is a novel, selective inhibitor of Mps-1 with antineoplastic activity. We found that CFI-402257 suppresses MM growth. We found that Mps-1 is overexpressed in MM and that its expression correlates with poor patients' outcome. In vitro, CFI-402257-mediated inhibition of Mps-1 resulted in abrogation of the mitotic checkpoint, premature progression through mitosis, marked aneuploidy and mitotic catastrophe. In vivo, CFI-402257 reduced MM growth in an orthotopic, syngeneic model, when used as a single agent, and more so when used in combination with cisplatin+pemetrexed, the current standard of care. Our preclinical findings indicate that CFI-402257 is a promising novel therapeutic agent to improve the efficacy of the current chemotherapeutic regimens for MM patients.

• Minimal asbestos exposure in germline BAP1 heterozygous mice is associated with deregulated inflammatory response and increased risk of mesothelioma. A. Napolitano, L. Pellegrini, A. Dey, et al. 2016;35(15):1996-2002. PubMed · Publisher · Free full text

  Abstract

  Germline BAP1 mutations predispose to several cancers, in particular malignant mesothelioma. Mesothelioma is an aggressive malignancy generally associated with professional exposure to asbestos. However, to date, we found that none of the mesothelioma patients carrying germline BAP1 mutations were professionally exposed to asbestos. We hypothesized that germline BAP1 mutations might influence the asbestos-induced inflammatory response that is linked to asbestos carcinogenesis, thereby increasing the risk of developing mesothelioma after minimal exposure. Using a BAP1(+/-) mouse model, we found that, compared with their wild-type littermates, BAP1(+/-) mice exposed to low-dose asbestos fibers showed significant alterations of the peritoneal inflammatory response, including significantly higher levels of pro-tumorigenic alternatively polarized M2 macrophages, and lower levels of several chemokines and cytokines. Consistent with these data, BAP1(+/-) mice had a significantly higher incidence of mesothelioma after exposure to very low doses of asbestos, doses that rarely induced mesothelioma in wild-type mice. Our findings suggest that minimal exposure to carcinogenic fibers may significantly increase the risk of malignant mesothelioma in genetically predisposed individuals carrying germline BAP1 mutations, possibly via alterations of the inflammatory response.

• Role of Merlin/NF2 inactivation in tumor biology. A.M. Petrilli, C. Fernández-Valle. 2016;35(5):537-48. Review PubMed · Publisher · Free full text

  Abstract

  Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

• LIM-domain protein AJUBA suppresses malignant mesothelioma cell proliferation via Hippo signaling cascade. I. Tanaka, H. Osada, M. Fujii, et al. 2015;34(1):73-83. PubMed · Publisher

  Abstract

  Malignant mesothelioma (MM) is one of the most aggressive neoplasms usually associated with asbestos exposure and is highly refractory to current therapeutic modalities. MMs show frequent activation of a transcriptional coactivator Yes-associated protein (YAP), which is attributed to the neurofibromatosis type 2 (NF2)-Hippo pathway dysfunction, leading to deregulated cell proliferation and acquisition of a malignant phenotype. However, the whole mechanism of disordered YAP activation in MMs has not yet been well clarified. In the present study, we investigated various components of the NF2-Hippo pathway, and eventually found that MM cells frequently showed downregulation of LIM-domain protein AJUBA, a binding partner of large tumor suppressor type 2 (LATS2), which is one of the last-step kinases of the NF2-Hippo pathway. Although loss of AJUBA expression was independent of the alteration status of other Hippo pathway components, MM cell lines with AJUBA inactivation showed a more dephosphorylated (activated) level of YAP. Immunohistochemical analysis showed frequent downregulation of AJUBA in primary MMs, which was associated with YAP constitutive activation. We found that AJUBA transduction into MM cells significantly suppressed promoter activities of YAP-target genes, and the suppression of YAP activity by AJUBA was remarkably canceled by knockdown of LATS2. In connection with these results, transduction of AJUBA-expressing lentivirus significantly inhibited the proliferation and anchorage-independent growth of the MM cells that harbored ordinary LATS family expression. Taken together, our findings indicate that AJUBA negatively regulates YAP activity through the LATS family, and inactivation of AJUBA is a novel key mechanism in MM cell proliferation.

• Protumorigenic effects of mir-145 loss in malignant pleural mesothelioma. M. Cioce, F. Ganci, V. Canu, et al. 2014;33(46):5319-31. PubMed · Publisher · Free full text

  Abstract

  We identified a discrete number of microRNAs differentially expressed in benign or malignant mesothelial tissues. We focused on mir-145 whose levels were significantly downregulated in malignant mesothelial tissues and malignant pleural mesothelioma (MPM) cell lines as compared to benign tissues (pleura, peritoneum or cysts). We show that promoter hyper-methylation caused very low levels in MPM cell lines and specimens. Treatment of MPM cell lines with mir-145 agonists negatively modulated some protumorigenic properties of MPM cells, such as clonogenicity, cell migration and resistance to pemetrexed treatment. The main effector mechanism of the clonogenic death induced by mir-145 was that of accelerated senescence. We found that mir-145 targeted OCT4 via specific binding to its 3'-UTR. Increased intracellular levels of mir-145 decreased the levels of OCT4 and its target gene ZEB1, thereby counteracting the increase of OCT4 induced by pemetrexed treatment which is known to favor the development of chemoresistant cells. In line with this, reintroduction of OCT4 into mimic-145 treated cells counteracted the effects on clonogenicity and replicative senescence. This further supports the relevance of the mir-145-OCT4 interaction for the survival of MPM cells. The potential use of mir-145 expression levels to classify benign vs malignant mesothelial tissues and the differences between pemetrexed-induced senescence and that induced by the re-expression of mir-145 are discussed.

• Tsc1-Tp53 loss induces mesothelioma in mice, and evidence for this mechanism in human mesothelioma. Y. Guo, L.R. Chirieac, R. Bueno, et al. 2014;33(24):3151-60. PubMed · Publisher · Free full text

  Abstract

  Mesothelioma is diagnosed in ∼2500 patients in the United States every year, most often arising in the pleural space, but also occurring as primary peritoneal mesothelioma. The vast majority of patients with mesothelioma die of their disease within 3 years. We developed a new mouse model of mesothelioma by bladder or intraperitoneal injection of adenovirus Cre into mice with conditional alleles of each of Tp53 and Tsc1. Such mice began to develop malignant ascites about 6 months after injection, which was due to peritoneal mesothelioma, on the basis of tumor morphology and immunohistochemical staining. Mesothelioma cell lines were established, which showed loss of both Tsc1 and Tp53, with mammalian target of rapamycin complex (mTORC)1 activation. Treatment of mice with malignant ascites due to mesothelioma with rapamycin led to a marked reduction in ascites, extended survival and a 95-99% reduction in the mesothelioma tumor volume, in comparison with vehicle-treated mice. To see whether TSC1/TSC2 loss was a common genetic event in human mesothelioma, we examined nine human mesothelioma cell lines, and found that four of nine showed persistent activation of mTORC1, although none had loss of TSC1 or TSC2. A tissue microarray analysis of 198 human mesothelioma specimens showed that 33% of cases had reduced TSC2 expression and 60% showed activation of mTOR, indicating that mTOR activation is common in human mesothelioma, suggesting that it is a potential therapeutic target.

• AXL regulates mesothelioma proliferation and invasiveness. W.B. Ou, J.M. Corson, D.L. Flynn, et al. 2011;30(14):1643-52. PubMed · Publisher

  Abstract

  Mesothelioma is an asbestos-associated and notoriously chemotherapy-resistant neoplasm. Activation of the receptor tyrosine kinases (RTKs), epidermal growth factor receptor and MET, has been described in subsets of mesothelioma, suggesting that TKs might represent therapeutic targets in this highly lethal disease. We employed proteomic screening by phosphotyrosine immunoaffinity purification and tandem mass spectrometry to characterize RTK activation in mesothelioma cell lines. These assays demonstrated expression and activation of the AXL protein, which is an RTK with known oncogenic properties in non-mesothelial cancer types. AXL was expressed and activated strongly in 8 of 9 mesothelioma cell lines and 6 of 12 mesothelioma biopsies, including each of 12 mesotheliomas with spindle-cell histology. Somatic AXL mutations were not found, but all mesotheliomas expressed an alternatively spliced AXL transcript with in-frame deletion of exon 10, and six of seven mesothelioma cell lines expressed the AXL ligand, growth arrest-specific 6 (GAS6). GAS6 expression appeared to be functionally relevant, as indicated by modulation of AXL tyrosine phosphorylation by knockdown of endogeneous GAS6, and by administration of exogenous GAS6. AXL silencing by lentivirus-mediated short hairpin RNA suppressed mesothelioma migration and cellular proliferation due to G1 arrest. The AXL inhibitor DP-3975 inhibited cell migration and proliferation in mesotheliomas with strong AXL activation. DP-3975 response in these tumors was characterized by inhibition of PI3-K/AKT/mTOR and RAF/MAPK signaling. AXL inhibition suppressed mesothelioma anchorage-independent growth, with reduction in colony numbers and size. These studies suggest that AXL inhibitors warrant clinical evaluation in mesothelioma.

• Onconase mediated NFKβ downregulation in malignant pleural mesothelioma. C.M. Goparaju, J.D. Blasberg, S. Volinia, et al. 2011;30(24):2767-77. PubMed · Publisher · Free full text

  Abstract

  Treatment of malignant pleural mesothelioma (MPM) with Ranpirnase (Onconase) results in disruption of protein translation and cell apoptosis. We hypothesize that Onconase exerts an effect via downregulation of nuclear factor kappa B (NFKβ) by specific microRNAs (miRNAs) and that interference of this pathway could have implications for MPM resistance to chemotherapy. Three immortalized MPM cell lines (H2959, H2373 and H2591) were exposed to Onconase at 0-20 μg/ml. Cell counts were measured at 48 and 72 h. Gene expression in miRNA-enriched RNA was validated by reverse transcription-PCR (RT-PCR). The functional implications of miRNA expression were evaluated by transfecting miRNA mimics or inhibitors into MPM cell lines, and performing Matrigel invasion, cell proliferation, soft agar colony formation and scratch closure assays. Effects on NFKβ expression and downstream targets including ABC transporters, BCL-xl and IAP were assessed by RT-PCR and western blotting. Treatment with 20 μg/ml of Onconase significantly decreased cell count and invasion. Hsa-miR-17* was significantly upregulated and hsa-miR-30c was significantly downregulated by Onconase treatment in all cell lines. Forced expression of hsa-miR-17* mimic and hsa-miR-30c inhibitor each significantly decreased functional activity of Onconase in all assays. NFKB1 (p50) expression and downstream targets were also decreased with Onconase treatment, as well as with forced expression of miRNA mimic and inhibitors. Onconase treatment caused a significant decrease in cell proliferation, invasion and in expression of certain miRNAs. Recapitulation of the resultant miRNA expression pattern with hsa-miR-17* mimic and hsa-miR-30c inhibitor resulted in downregulation of NFKB1 and reduced malignant behavior in functional assays. Thus, Onconase likely exerts its antitumor effect through these miRNAs.

• A novel translational approach for human malignant pleural mesothelioma: heparanase-assisted dual virotherapy. Y. Watanabe, T. Kojima, S. Kagawa, et al. 2010;29(8):1145-54. PubMed · Publisher

  Abstract

  Malignant pleural mesothelioma (MPM) is a highly aggressive tumor that is related to asbestos exposure. MPM is characterized by rapid and diffuse local growth in the thoracic cavity, and it has a poor prognosis because it is often refractory to conventional therapy. Although MPM is an extraordinarily challenging disease to treat, locoregional virotherapy may be useful against this aggressive disease because of the accessibility by intrapleural virus delivery. In this study, we show that telomerase-specific, replication-selective adenovirus OBP-301 can efficiently infect and kill human mesothelioma cells by viral replication. Intrathoracic administration of virus significantly reduced the number and size of human mesothelioma tumors intrathoracically implanted into nu/nu mice. A high-definition, fluorescence optical imaging system with an ultra-thin, flexible fibered microprobe clearly detected intracellular replication of green fluorescent protein-expressing oncolytic virus in intrathoracically established mesothelioma tumors. As the extracellular matrix (ECM) may contribute to the physiological resistance of a solid tumor by preventing the penetration of therapeutic agents (including oncolytic viruses), we also examined whether the co-expression of heparanase, an endoglucuronidase capable of specifically degrading heparan sulfate, that influences the physiological barrier to macromolecule penetration, can modify the permeability of the ECM, resulting in profound therapeutic efficacy. Co-injection of OBP-301 and a replication-defective adenovirus (Ad-S/hep)-expressing heparanase resulted in more profound antitumor effects without apparent toxicity in an orthotopic pleural dissemination model. Our results suggest that intrathoracic dual virotherapy with telomerase-specific oncolytic adenovirus in combination with heparanase-expressing adenovirus may be efficacious in the prevention and treatment of pleural dissemination of human malignant mesothelioma.

• The promyelocytic leukemia zinc-finger gene, PLZF, is frequently downregulated in malignant mesothelioma cells and contributes to cell survival. M. Cheung, J. Pei, Y. Pei, et al. 2010;29(11):1633-40. PubMed · Publisher · Free full text

  Abstract

  DNA copy number analysis was performed, using single-nucleotide polymorphism mapping arrays, to fine map genomic imbalances in human malignant mesothelioma (MM) cell lines derived from primary tumors. Chromosomal losses accounted for the majority of genomic imbalances. All 22 cell lines examined showed homozygous deletions of 9p21.3, centering at the CDKN2A/ARF and CDKN2B loci. Other commonly underrepresented segments included 1p36, 1p22, 3p21-22, 4q13, 4q34, 11q23, 13q12-13, 14q32, 15q15, 18q12, and 22q12, each observed in 55-90% of cell lines. Focal deletions of 11q23 encompassed the transcriptional repressor gene promyelocytic leukemia zinc finger (PLZF), which was validated by analysis of genomic DNA using real-time polymerase chain reaction (PCR). Semi-quantitative RT-PCR and immunoblot analysis revealed that PLZF is greatly downregulated in MM cell lines compared with non-malignant mesothelial cells. Ectopic expression of PLZF in PLZF-deficient MM cells resulted in decreased cell viability, reduced colony formation, as well as increased apoptosis, the latter based on results of various cell death assays and the observation of increased cleavage of caspase 3, PARP, and Mcl-1. These data indicate that deletions of PLZF are a common occurrence in MM and that downregulation of PLZF may contribute to MM pathogenesis by promoting cell survival.

2000s

• Eighth international mesothelioma interest group. M. Carbone, S.M. Albelda, V.C. Broaddus, et al. 2007;26(49):6959-67. PubMed · Publisher

  Abstract

  The eighth International Mesothelioma Interest Group (IMIG) meeting was held in Chicago, IL, United States, in 19-22 October 2006 to discuss mesothelioma - the cancer often linked to asbestos exposure. It is a very aggressive malignancy with a median survival of less than 1 year from diagnosis. Millions of people have been exposed worldwide to asbestos, especially during the second half of the twentieth century when asbestos use increased significantly. The tons of asbestos utilized in the past remain a health hazard for current and future generations because asbestos is difficult to be disposed off. This makes asbestos and mesothelioma research a public health issue in addition to a medical problem. Moreover, the very high costs of asbestos litigation have a significant impact on the whole economy. In the United States, up until 2001, defendant companies had paid 54 billion dollars in claims and estimated future liabilities ranged from 145 to 210 billion. Therefore, asbestos research is of great interest to a large audience that includes patients, millions of asbestos-exposed individuals, scientists, physicians, public health officials, politicians, unions of asbestos workers, lawyers and the public at large. During the past few years, there has been significant progress in understanding the process of mineral fiber carcinogenesis and mesothelioma pathogenesis. With improved understanding of the pathogenesis of mesothelioma, new diagnostic, preventive and therapeutic options are being developed. A total of 247 papers were presented at the IMIG: the abstracts of these presentations were published in Lung Cancer, Supplement 1, October 2006. Here, experts in different disciplines critically review some of the most exciting presentations of the IMIG meeting. The result is a comprehensive review of the research field of asbestos carcinogenesis and mesothelioma, and of the progress that has been made in recent years in both basic and clinical sciences.

• Gene expression and copy number profiling suggests the importance of allelic imbalance in 19p in asbestos-associated lung cancer. H. Wikman, S. Ruosaari, P. Nymark, et al. 2007;26(32):4730-7. PubMed · Publisher

  Abstract

  Asbestos is a pulmonary carcinogen known to give rise to DNA and chromosomal damage, but the exact carcinogenic mechanisms are still largely unknown. In this study, gene expression arrays were performed on lung tumor samples from 14 heavily asbestos-exposed and 14 non-exposed patients matched for other characteristics. Using a two-step statistical analysis, 47 genes were revealed that could differentiate the tumors of asbestos-exposed from those of non-exposed patients. To identify asbestos-associated regions with DNA copy number and expressional changes, the gene expression data were combined with comparative genomic hybridization microarray data. As a result, a combinatory profile of DNA copy number aberrations and expressional changes significantly associated with asbestos exposure was obtained. Asbestos-related areas were detected in 2p21-p16.3, 3p21.31, 5q35.2-q35.3, 16p13.3, 19p13.3-p13.1 and 22q12.3-q13.1. The most prominent of these, 19p13, was further characterized by microsatellite analysis in 62 patients for the differences in allelic imbalance (AI) between the two groups of lung tumors. 79% of the exposed and 45% of the non-exposed patients (P=0.008) were found to be carriers of AI in their lung tumors. In the exposed group, AI in 19p was prevalent regardless of the histological tumor type. In adenocarcinomas, AI in 19p appeared to occur independently of the asbestos exposure.

• Retracted. Aberrant methylation profile of human malignant mesotheliomas and its relationship to SV40 infection. M. Suzuki, S. Toyooka, N. Shivapurkar, et al. 2005;24(7):1302-8. PubMed · Publisher

  Abstract

  Malignant mesothelioma (MM) is associated with asbestos exposure and the presence of SV40 viral sequences. Recently, we reported that SV40 infection of human mesothelial cells (HM) causes aberrant methylation of the tumor suppressor gene (TSG) RASSF1A. We investigated methylation of 12 genes by methylation-specific PCR in 63 MMs, six MM cell lines, and two foci of SV40-infected HM. Methylation percentages of the tested genes ranged from 3 to 65%. The frequencies of HPP1, RASSF1A, Cyclin D2, and RRAD methylation, and the value of the methylation index, were significantly higher in SV40 sequence-positive MMs than in SV40-negative MMs. Methylation of TMS1 and HIC-1 was associated with shortened survival. SV40-infected HM showed progressive aberrant methylation of seven genes (RASSF1A, HPP1, DcR1, TMS1, CRBP1, HIC-1, and RRAD) during serial passage. Our results demonstrate a relationship between SV40 and methylation of multiple genes in MM, indicating that the virus plays a role in the pathogenesis of MM.

• Human and mouse mesotheliomas exhibit elevated AKT/PKB activity, which can be targeted pharmacologically to inhibit tumor cell growth. D.A. Altomare, H. You, G.H. Xiao, et al. 2005;24(40):6080-9. PubMed · Publisher

  Abstract

  Malignant mesotheliomas (MMs) are very aggressive tumors that respond poorly to standard chemotherapeutic approaches. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway has been implicated in tumor aggressiveness, in part by mediating cell survival and reducing sensitivity to chemotherapy. Using antibodies recognizing the phosphorylated/activated form of AKT kinases, we observed elevated phospho-AKT staining in 17 of 26 (65%) human MM specimens. In addition, AKT phosphorylation was consistently observed in MMs arising in asbestos-treated mice and in MM cell xenografts. Consistent with reports implicating hepatocyte growth factor (HGF)/Met receptor signaling in MM, all 14 human and murine MM cell lines had HGF-inducible AKT activity. One of nine human MM cell lines had elevated AKT activity under serum-starvation conditions, which was associated with a homozygous deletion of PTEN, the first reported in MM. Treatment of this cell line with the mTOR inhibitor rapamycin resulted in growth arrest in G1 phase. Treatment of MM cells with the PI3K inhibitor LY294002 in combination with cisplatin had greater efficacy in inhibiting cell proliferation and inducing apoptosis than either agent alone. Collectively, these data indicate that MMs frequently express elevated AKT activity, which may be targeted pharmacologically to enhance chemotherapeutic efficacy. These findings also suggest that mouse models of MM may be useful for future preclinical studies of pharmaceuticals targeting the PI3K/AKT pathway.

• The Human mineral dust-induced gene, mdig, is a cell growth regulating gene associated with lung cancer. Y. Zhang, Y. Lu, B.Z. Yuan, et al. 2005;24(31):4873-82. PubMed · Publisher

  Abstract

  Environmental or occupational exposure to mineral dusts, mainly silica and asbestos, is associated with an increased incidence of lung inflammation, fibrosis, and/or cancer. To better understand the molecular events associated with these pulmonary diseases, we attempted to identify genes that are regulated by mineral dusts. Using a differential display reverse transcription polymerase chain reaction technique and mRNAs of alveolar macrophages from both normal individuals and coal miners, we identified a novel mineral dust-induced gene named mdig, which had not been fully characterized. The expression of mdig mRNA was detected in alveolar macrophages from coal miners but not from normal subjects. The inducible expression of mdig could be observed in A549 cells exposed to silica particles in a time-dependent manner. The full-length mdig mRNA was expressed in human lung cancer tissues but was barely detectable in the adjacent normal tissues. In addition, a number of lung cancer cell lines constitutively express mdig. Alternative spliced transcripts of mdig were detected in some lung cancer cell lines. Silencing mdig mRNA expression in A549 lung cancer cells by siRNA-mediated RNA interference inhibits cell proliferation and sensitizes the cells to silica-induced cytotoxicity. These results suggest that the mdig gene may be involved in the regulation of cell growth and possibly the development of cancer.

• Cell type-specific effects of asbestos on intracellular ROS levels, DNA oxidation and G1 cell cycle checkpoint. P.B. Kopnin, I.V. Kravchenko, V.A. Furalyov, et al. 2004;23(54):8834-40. PubMed · Publisher

  Abstract

  Exposure to asbestos fibers increases the risk of development of mesotheliomas and lung carcinomas, but not fibrosarcomas. We present data suggesting that resistance of fibroblasts to asbestos-induced carcinogenesis is likely to be connected with their lower ability to generate reactive oxygen species (ROS) in response to asbestos exposure and stricter control of proliferation of cells bearing asbestos/ROS-induced injuries. In fact, chrysotile (Mg6Si4O10(OH)8) asbestos exposure (5-10 microg/cm2) increased intracellular ROS and 8-oxo-guanine contents in rat pleural mesothelial cells, but not in lung fibroblasts. Simultaneously, moderate dosages of chrysotile and other agents increasing ROS levels (hydrogen peroxide, H2O2 and ethyl-methanesulfonate, EMS) inhibited cell cycle progression, in particular G1-to-S transition, in fibroblasts, but not in mesothelial cells. The arrested fibroblasts underwent cell death, while the majority of chrysotile-treated mesothelial cells survived. The differences in cell cycle response to asbestos/ROS-induced injuries correlated with distinct activity of p53-p21Cip1/Waf1 pathway in the two cell types. Chrysotile, H2O2 and EMS caused p53 upregulation in both cell types, but mesothelial cells, unlike fibroblasts, showed no accumulation of p21Cip1/Waf1. Of note, treatment with doxorubicin caused similar p53-dependent p21Cip1/Waf1 upregulation and cell cycle arrest in both cell types. This suggests differential response of fibroblasts and mesothelial cells specifically to asbestos/ROS exposure rather than to all DNA-damaging insults.

• Epidemiology of environmental and occupational cancer. P. Boffetta. 2004;23(38):6392-403. Review PubMed · Publisher

  Abstract

  Environmental carcinogens, in a strict sense, include outdoor and indoor air pollutants, as well as soil and drinking water contaminants. An increased risk of mesothelioma has consistently been detected among individuals experiencing residential exposure to asbestos, while results for lung cancer are less consistent. Several good-quality studies have investigated lung cancer risk from outdoor air pollution based on measurement of specific agents. Their results tend to show an increased risk in the categories at highest exposure, with relative risks in the range 1.5. A causal association has been established between exposure to environmental tobacco smoke and lung cancer, with a relative risk in the order of 1.2. Radon is another carcinogen present in indoor air, with a relative risk in the order of 1.06 for exposure at 100 Bq/m3. In several Asian populations, an increased risk of lung cancer results among women from indoor pollution from cooking and heating. There is strong evidence of an increased risk of bladder, skin and lung cancers following consumption of water with high arsenic contamination; results for other drinking water contaminants, including chlorination by-products, are inconclusive. A total of 29 occupational agents are established human carcinogens, and another 30 agents are suspected carcinogens. In addition, at least 12 exposure circumstances entail exposure to carcinogens. Exposure is still widespread for many important occupational carcinogens, such as asbestos, coal tar, arsenic and silica, in particular in developing countries. Although estimates of the global burden of occupational and environmental cancer result in figures in the order of 2% and less than 1%, respectively, these cancers concentrate in subgroups of the population; furthermore, exposure is involuntary and can, to a large extent, be avoided.

• Growth inhibition and induction of apoptosis in mesothelioma cells by selenium and dependence on selenoprotein SEP15 genotype. S. Apostolou, J.O. Klein, Y. Mitsuuchi, et al. 2004;23(29):5032-40. PubMed · Publisher

  Abstract

  Malignant mesotheliomas (MMs) are aggressive tumors derived from mesothelial cells lining the lungs, pericardium and peritoneum, and are often associated with occupational asbestos exposure. Suppression subtractive hybridization was used to identify genes differentially expressed in MM cells compared to normal mesothelial cells. A gene, SEP15, encoding a 15-kDa selenium-containing protein was isolated using this approach and was subsequently shown to be downregulated in approximately 60% of MM cell lines and tumor specimens. A SEP15 polymorphic variant, 1125A, resides in the SECIS recognition element in the 3'-UTR and may influence the efficiency of Sec incorporation into the protein during translation. Since previous studies have implicated a potential role of the trace element selenium as a chemopreventive agent in animal models and in several types of human cancer, we investigated the effect of selenium on MM cells and its dependence on SEP15 genotype. Selenium was shown to inhibit cell growth and induce apoptosis in a dose-dependent manner in MM cells but had minimal effect on normal mesothelial cells. However, MM cells with downregulated SEP15 or the 1125A variant were somewhat less responsive to the growth inhibitory and apoptotic effects of selenium than MM cells expressing wild-type protein. RNAi-based knockdown studies demonstrated that SEP15 inhibition makes sensitive MM cells more resistant to selenium. These data imply that selenium may be useful as a chemopreventive agent in individuals at high risk of MM due to asbestos exposure, although those with the 1125A polymorphism may be less responsive to the protective benefits of dietary selenium supplementation.

• Src-dependent ERK5 and Src/EGFR-dependent ERK1/2 activation is required for cell proliferation by asbestos. L. Scapoli, M.E. Ramos-Nino, M. Martinelli, et al. 2004;23(3):805-13. PubMed · Publisher

  Abstract

  Crocidolite asbestos elicits oxidative stress and cell proliferation, but the signaling cascades linked to these outcomes are unclear. To determine the role of mitogen-activated protein kinases (MAPK) in asbestos-induced cell signaling, we evaluated the effects of crocidolite asbestos, EGF and H2O2, on MAPK activation in murine lung epithelial cells (C10 line). In contrast to rapid and transient activation of extracellular signal-regulated kinase 5 (ERK5) by EGF or H2O2, asbestos caused protracted oxidant-dependent ERK5 activation that was inhibited by an Src kinase inhibitor (PP2), but not by an inhibitor of epidermal growth factor receptor (EGFR) phosphorylation (AG1478). ERK1/2 activation by asbestos was inhibited by either PP2 or AG1478. To confirm the involvement of Src in ERK1/2 and ERK5 activation, a dominant-negative Src construct was used. These experiments showed that Src was essential for ERK1/2 and also ERK5 phosphorylation by asbestos. Time frame studies indicated immediate activation of Src by asbestos fibers, whereas EGFR phosphorylation occurred subsequently. Data suggest that asbestos causes activation of ERK5 through an EGFR-independent pathway, whereas ERK1/2 activation is dependent on Src through a mechanism involving phosphorylation of the EGFR. Furthermore, Src, ERK1/2 and ERK5 activation are essential for cell proliferation by asbestos. The use of a dominant-negative ERK5 construct caused selective downregulation of c-jun expression, whereas inhibition of Src by PP2 or MEK1 by PD98059 caused decreases in c-fos, fra-1 and c-jun expression in asbestos-exposed C10 cells. These observations may have broad relevance to cell proliferation by carcinogenic mineral fibers and oxidants.

• beta1-integrin mediates asbestos-induced phosphorylation of AKT and ERK1/2 in a rat pleural mesothelial cell line. A. Berken, J. Abel, K. Unfried. 2003;22(52):8524-8. PubMed · Publisher

  Abstract

  Integrin-mediated signalling has been implicated in asbestos-induced carcinogenesis. In studies here, we examined signal transduction events associated with integrin-directed cell reactions triggered by crocidolite asbestos in the pleural mesothelial cell line 4/4 RM-4. Crocidolite fibres induced a significant time- and dose-dependent activation of the extracellular-signal-regulated kinases ERK1 and ERK2. ERK activation was specifically inhibited by integrin-blocking agents, that are integrin-binding peptides containing the sequence arginine-glycine-aspartic acid (RGD), and monoclonal antibodies against the integrin beta1-chain. Integrin-dependent activation of ERK1/2 in response to asbestos appeared to be independent of focal adhesion kinase pp125FAK (FAK) since FAK autophosphorylation remained unaffected in crocidolite-exposed mesothelial cells. Instead, we observed striking similarities in the kinetics of asbestos-induced ERK1/2 responses and phosphorylation of protein kinase B (AKT) at serine 473, a possible target residue for integrin-linked kinase. As with ERK activation, asbestos-induced AKT stimulation was significantly blocked by both the RGD-peptide and the beta1-integrin antibodies. These studies are the first to establish that in mesothelial cells ERK1/2 and AKT are simultaneously phosphorylated upon asbestos exposure in a beta1-integrin-dependent manner.

• Hemizygosity of Nf2 is associated with increased susceptibility to asbestos-induced peritoneal tumours. J. Fleury-Feith, C. Lecomte, A. Renier, et al. 2003;22(24):3799-805. PubMed · Publisher

  Abstract

  Biallelic NF2 gene inactivation is frequently found in human malignant mesothelioma. In order to assess whether NF2 hemizygosity may enhance susceptibility to asbestos fibres, we investigated the Nf2 status in mesothelioma developed in mice presenting a heterozygous mutation of the Nf2 gene (Nf2(KO3/+)), after intraperitoneal inoculation of crocidolite fibres. Asbestos-exposed Nf2(KO3/+) mice developed tumoural ascites and mesothelioma at a higher frequency than their wild-type (WT) counterparts (P&<0.05). Six out of seven mesothelioma cell lines established from neoplastic ascitic fluids of Nf2(KO3/+) mice exhibited loss of the WT Nf2 allele and no neurofibromatosis type 2 protein expression was found in these cells. The results show the importance of the NF2 gene in mesothelial oncogenesis, the potential association of asbestos exposure and tumour suppressor gene inactivation, and suggest that NF2 gene mutation may be a susceptibility factor to asbestos.

• Downregulation of Betaig-h3 gene is causally linked to tumorigenic phenotype in asbestos treated immortalized human bronchial epithelial cells. Y.L. Zhao, C.Q. Piao, T.K. Hei. 2002;21(49):7471-7. PubMed · Publisher

  Abstract

  Although Betaig-h3 gene has been suggested to modulate cell adhesion and tumor formation, its physiological functions are not well understood. Using human papillomavirus immortalized human bronchial epithelial (BEP2D) cells, we found that Betaig-h3 expression was markedly decreased in asbestos-induced tumorigenic cells. Fusion of tumorigenic and control BEP2D cells resulted in the recovery of Betaig-h3 gene expression to control level and the loss of tumorigenic phenotype. Furthermore, ectopic expression of Betaig-h3 gene in asbestos-induced tumorigenic cells inhibited cell growth in vitro, anchorage independent phenotype, as well as tumorigenicity in nude mice. Betaig-h3 gene is ubiquitously expressed in various normal human tissues, with the exception of the brain, where there is little or no expression. In contrast, there was a decrease or absence in expression of the Betaig-h3 gene in 14 human tumor cell lines of diverse histological types examined, when compared with normal human cells or tissues. The result strongly suggests that loss of Betaig-h3 expression is a frequent event in human cancer and causally related to acquisition of tumorigenic phenotype in asbestos-treated BEP2D cells.

• Progressive aberrant methylation of the RASSF1A gene in simian virus 40 infected human mesothelial cells. S. Toyooka, M. Carbone, K.O. Toyooka, et al. 2002;21(27):4340-4. PubMed · Publisher

  Abstract

  Mesotheliomas are tumors arising from mesothelial cells and are associated with asbestos exposure and approximately 50% contain simian virus 40 (SV40) DNA sequences. SV40 infection of human mesothelial cells (HM) causes early cellular immortalization and late transformation. Aberrant methylation is a major mech-anism for loss of function of tumor suppressor genes (TSGs). We recently reported that of seven genes frequently methylated in epithelial tumors, only RASSF1A gene was frequently methylated in mesotheliomas, and its methylation was correlated with loss of RASSF1A expression and the presence of SV40. We studied whether SV40 infection of normal HM induces aberrant methylation of the genes previously studied in mesotheliomas. Of six infected foci examined at early passages (passages 8-30) there was no methylation of the seven genes examined. Of two foci examined at late passages (passages 51-86) after the appearance of morphological changes suggestive of transformation, methylation and loss of expression of RASSF1A was detected. Sequencing of the CpG dense region around the transcription start site and semi-quantitative real-time methylation specific PCR (MSP) assay for RASSF1A methylation demonstrated progressive methylation during late passages. Exposure to the demethylating agent 5-aza-2'-deoxycytidine restored RASSF1A expression, while exposure to the histone deacetylation inhibitor trichostatin A had no effect. These data, together with our previous findings, support a causal relationship between SV40 infection, progressive RASSF1A methylation and its silencing, and the pathogenesis of mesothelioma.

• SV40 infection induces telomerase activity in human mesothelial cells. R. Foddis, A. De Rienzo, D. Broccoli, et al. 2002;21(9):1434-42. PubMed · Publisher

  Abstract

  Mesotheliomas are malignant tumors of the pleural and peritoneal membranes which are often associated with asbestos exposure and with Simian virus 40 (SV40) infection. Telomerase activity is repressed in somatic cells and tissues but is activated in immortal and malignant cells. We evaluated telomerase activity in seven primary malignant mesothelioma biopsies and matched lung specimens and 20 mesothelioma cell lines and eight corresponding primary tumor cultures. All the tumor biopsies, and nearly all primary cell mesothelioma cultures and cell lines were telomerase positive. The findings in cell lines paralleled those observed in primary cultures in cases where paired samples were available. Next, we found that SV40, a DNA tumor virus present in approximately 50% of mesothelioma biopsies in the USA, induced telomerase activity in primary human mesothelial cells, but not in primary fibroblasts. Telomerase activity became detectable as early as 72 h following wild-type (strain 776) SV40 infection, and a clear DNA ladder was detectable 1 week after infection. The amount of telomerase activity increased during passage in cell culture and appeared to parallel increases in the cellular amounts of the SV40 large T-antigen. Thus, SV40 infection leads to telomerase activity before the infected mesothelial cells become transformed and immortalized. SV40 infection of human fibroblasts did not cause detectable telomerase activity. We also determined that the SV40 small t-antigen (tag) plays an important role in inducing telomerase activity because this activity was undetectable or minimal in mesothelial cells infected and/or transformed by SV40 tag mutants. Asbestos alone did not induce telomerase activity, and asbestos did not influence telomerase activity in mesothelial cells infected with SV40. Induction of telomerase activity by SV40 may be related to the very high rate of mesothelial cell immortalization that is characteristically associated with SV40 infection of mesothelial cells.

• The molecular epidemiology of asbestos and tobacco in lung cancer. H.H. Nelson, K.T. Kelsey. 2002;21(48):7284-8. Review PubMed · Publisher

  Abstract

  Asbestos is a well-known toxin and lung carcinogen. Epidemiologic studies have established tobacco smoke and asbestos exposures synergistically interact to enhance lung cancer risk. The biologic mechanism responsible for this interaction has been the subject of considerable debate. Studies have suggested that asbestos may act as a carcinogen by generating free radical and reactive oxygen species, by inducing tissue injury and subsequent cellular growth, via large-scale chromosome loss and by enhancing delivery of tobacco carcinogens to the respiratory epithelium. Recent molecular epidemiologic approaches further suggest that asbestos enhances the mutagenicity of tobacco carcinogens and that it acts, at least in part, independent of the tissue damage responsible for fibrosis.

• Analysis of p16 and p21(Cip1) expression in tumorigenic human bronchial epithelial cells induced by asbestos. C.Q. Piao, Y.L. Zhao, T.K. Hei. 2001;20(50):7301-6. PubMed · Publisher

  Abstract

  Although asbestos is carcinogenic to humans, the mechanism(s) by which it induces cancer is unknown. Using tumor cell lines generated previously by asbestos treatment of immortalized human bronchial epithelial (BEP2D) cells, we examined alterations in p16 and p21(Cip1) genes together with their protein levels. Results were compared with untreated BEP2D cells, normal human bronchial epithelial cells (NHBE), as well as non-tumorigenic fusion cell lines generated by fusing tumor cells with BEP2D cells. No deletion in the p16 gene was found in any of the tumor cell lines examined. Although p16 protein was expressed at a similar level in tumor and BEP2D cells, there was a fourfold decrease in its expression among NHBE cells. In contrast, both the protein and mRNA expression levels of p21(Cip1) were decreased by about threefold in tumor cell lines when compared with either BEP2D or NHBE cells, which had a similar expression level. Expression of p21(Cip1) mRNA was restored to the control level in all the fusion cell lines examined. The results suggested that down regulation of p21(Cip1) expression is linked to the tumorigenic conversion of BEP2D cells by asbestos.

• Promoter methylation of DAP-kinase: association with advanced stage in non-small cell lung cancer. D.H. Kim, H.H. Nelson, J.K. Wiencke, et al. 2001;20(14):1765-70. PubMed · Publisher

  Abstract

  Death associated protein (DAP)-kinase is a 16 kDa calmodulin-dependent serine/threonine kinase that carries a death domain at its C-terminus. DAP-kinase functions as a positive mediator of apoptosis that is induced by interferon-gamma. Recent studies suggest that DAP-kinase is involved in tumor metastasis and that it can be inactivated by methylation of CpG islands in the promoter region of the gene in some human tumors. However, little is known about the factors that are associated with the occurrence of DAP-kinase promoter methylation. We investigated both the possible associations of tobacco carcinogen and asbestos exposure with DAP-kinase promoter methylation, and the demographic and clinical factors associated with DAP-kinase promoter methylation in non-small cell lung cancer (NSCLC). One hundred and eighty-five patients diagnosed with NSCLC undergoing surgical resection from June, 1992 through December, 1996 at Massachusetts General Hospital participated in this study. Methylation-Specific PCR (MSP), performed using fresh-frozen tissue, was used to determine the methylation status of the promoter region of the DAP-kinase gene. Forty-seven (25%) of 185 tumors showed DAP-kinase promoter methylation. There was a significant association between methylation and an advanced pathologic stage (P=0.003, Fisher's exact test). Methylation of the DAP-kinase promoter was also associated with an increase in tumor size (P=0.009, Fisher's exact test) and lymph node involvement (P=0.04). No association was found between promoter methylation of DAP-kinase and k-ras or p53 mutation. In addition there was no association with a history of exposure to tobacco or asbestos. Controlling for age, sex, and histology, the odds ratios describing the association of DAP-kinase hypermethylation with stage were 2.70 (1.13--6.45), 3.11 (1.37--7.08) and 7.77 (1.21--50.03) in stages II, III and IV, respectively. Stage I cases with DAP-kinase promoter methylation had worse overall survival, but with the small sample size and limited follow-up this did not reach statistical significance. Our findings suggest that methylation of the promoter region of the DAP-kinase gene is not associated with exposure to tobacco or asbestos. However, they strongly suggest that DAP-kinase may be important in the progression of non-small cell lung cancer from early to late stage disease.

• Repression of GADD153/CHOP by NF-kappaB: a possible cellular defense against endoplasmic reticulum stress-induced cell death. S. Nozaki, G.W. Sledge, H. Nakshatri. 2001;20(17):2178-85. PubMed · Publisher

  Abstract

  Exposure of mammalian cells to ultraviolet light, nutrient deprived culture media, hypoxia, environmental toxicants such as methyl mercury, methyl methanesulfonate, crocodilite asbestos or the agents that disrupt the function of endoplasmic reticulum (ER) leads to activation of the pro-apoptotic transcription factor GADD153/CHOP. Paradoxically, several of these agents also induce the anti-apoptotic transcription factor NF-kappaB. In this report, we demonstrate that NF-kappaB inhibits GADD153 activation in breast cancer cells exposed to nutrient deprived media, tunicamycin (which blocks protein folding in ER) or calcium ionopore (which depletes calcium stores in ER). Basal and calcium ionopore-induced GADD153 expression was more pronounced in fibroblasts obtained from mouse embryos lacking in p65 subunit of NF-kappaB compared to fibroblasts from wild type littermate embryos. Moreover, p65-/- fibroblasts were killed more efficiently by calcium ionopore and tunicamycin but not hydrogen peroxide compared to wild type fibroblasts. We also show that parthenolide, a NF-kappaB inhibitor, sensitizes breast cancer cells to tunicamycin. Transient transfection assay revealed that the p65 subunit but not the p50 subunit of NF-kappaB represses GADD153 promoter activity. These results establish a correlation between repression of pro-apoptotic genes by NF-kappaB and increased cell survival during ER stress as well as identify a distinct NF-kappaB regulated cell survival pathway.

• Expression of GPC3, an X-linked recessive overgrowth gene, is silenced in malignant mesothelioma. S.S. Murthy, T. Shen, A. De Rienzo, et al. 2000;19(3):410-6. PubMed · Publisher

  Abstract

  Gene expression changes in rat asbestos-induced malignant mesothelioma (MM) cells were investigated by differential mRNA display. A mRNA transcript identified by this approach was abundant in normal rat mesothelial cells but not expressed in rat MM cell lines. Northern blot analysis confirmed that this transcript is uniformly silenced in rat MM cell lines and primary tumors. Nucleotide sequence analysis revealed that this transcript is encoded by the rat glypican 3 gene (GPC3), whose human homolog is mutated in the Simpson-Golabi-Behmel overgrowth syndrome. Allelic loss at the GPC3 locus was infrequent (6.9%) in MM cell lines, and no mutations were found. GPC3 transcript levels were markedly decreased in 16 of 18 primary tumors and 17 of 22 human MM cell lines. Most of the cell lines were shown to have aberrant methylation of the GPC3 promoter region. In two of four human MM cell lines tested, GPC3 expression was restored after 2-deoxy 5-azacytidine (DAC)-mediated demethylation of its promoter region. Ectopic expression of GPC3 inhibited in vitro colony formation of human MM cells. Collectively, these data suggest that down-regulation of GPC3 is a common occurrence in MM and that GPC3, an X-linked recessive overgrowth gene, may encode a negative regulator of mesothelial cell growth.

1990s

• Effect of simian virus large T antigen expression on cell cycle control and apoptosis in rat pleural mesothelial cells exposed to DNA damaging agents. V. Levresse, S. Moritz, A. Renier, et al. 1998;16(8):1041-53. PubMed · Publisher

  Abstract

  Cell cycle progression and apoptosis are controlled by regulatory proteins, including p53, of which functional alterations are linked to carcinogenesis. Recently, malignant mesothelioma (MM), a primary tumour related to asbestos exposure, alternatively to post therapeutic radiations, has proven to be an important problem in oncogenesis. The p53 protein does not seem mutated or deleted in MM but a possible inactivation by binding to other proteins [mdm2; SV40 large T antigen (Tag)] has been suggested. The present work investigated cell cycle regulation in normal rat pleural mesothelial cells (RPMC) and in RPMC expressing Tag (RPMC-TSV40), under exposure to asbestos and radiations. In RPMC, these agents induced activation of cell cycle checkpoints located at G1/S and G2/M and/or mitosis but a lack of control at G1/S was found in RPMC-TSV40. A loss of G2/M control may account for the formation of micronuclei observed after exposure of RPMC-TSV40 to radiations. In RPMC-TSV40 the enhancement of abnormal mitoses and apoptosis after asbestos exposure, in comparison with RPMC, suggests a loss of mitotic control and a p53-independent mechanism of apoptosis. Thus Tag expression in mesothelial cells might have both adverse and beneficial effects by impairing the control of DNA integrity and enhancing apoptosis respectively.

• Simian virus 40, poliovaccines and human tumors: a review of recent developments. M. Carbone, P. Rizzo, H.I. Pass. 1997;15(16):1877-88. Review PubMed · Publisher

  Abstract

  Recently, wild-type SV40 and/or DNA sequences indistinguishable from SV40 have been detected in specific types of human tumors: ependymoma and choroid plexus tumors, mesothelioma, osteosarcoma and sarcoma. The same tumor types will develop in hamsters after injection with SV40. These findings are interesting in themselves for they could shed light on the pathogenesis of these tumors. These findings also have public health implications. SV40 was found to have contaminated the poliovaccines and the adenovaccines from 1955 until 1963, therefore resulting in the inadvertent injection of millions of people with this tumor virus. Moreover, our society pays a high cost for asbestos causality, a carcinogen associated with the development of mesothelioma. In addition to asbestos, the potential impact of finding another possible cause for mesothelioma (i.e., SV40), as well as the possible pathogenic role of the contaminated poliovaccines, has generated considerable public interest and concern. To discuss these recent findings, the NIH (National Institutes of Health) and the FDA (Food and Drug Administration), organized an International Conference at the NIH, Bethesda, MD, January 27-28, 1997. The association of SV40 with human mesothelioma was also discussed in a special session at the IV International Mesothelioma Conference that was held at the University of Pennsylvania, Philadelphia, PA, May 13-16, 1997. The purpose of this review is to summarize data, from the discovery of the contaminated poliovaccines, to the most recent findings presented at the meetings in Bethesda and Philadelphia, to discuss technical and other problems associated with this research, and the potential for using these findings to develop new diagnostic and therapeutic approaches for SV40-associated malignancies.

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