CAMK2D: a novel molecular target for BAP1-deficient malignant mesothelioma

Our plain-English summary of CAMK2D: a novel molecular target for BAP1-deficient malignant mesothelioma, by S. Karnan, A. Ota, H. Murakami, et al (Cell Death Discovery, 2023).

The study

• Authors: S. Karnan, A. Ota, H. Murakami, M.L. Rahman, M. Wahiduzzaman, M.N. Hasan, L.Q. Vu, I. Hanamura, A. Inoko, M. Riku, H. Ito, Y. Kaneko, T. Hyodo, H. Konishi, S. Tsuzuki, Y. Hosokawa
• Journal: Cell Death Discovery
• Published: 2023;9(1):257
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MMe) is a rare but aggressive malignancy. Although the molecular genetics of MMe is known, including BRCA1-associated protein-1 (BAP1) gene alterations, the prognosis of MMe patients remains poor. Here, we generated BAP1 knockout (BAP1-KO) human mesothelial cell clones to develop molecular-targeted therapeutics based on genetic alterations in MMe. cDNA microarray and quantitative RT-PCR (qRT-PCR) analyses revealed high expression of a calcium/calmodulin-dependent protein kinase type II subunit delta (CAMK2D) gene in the BAP1-KO cells. CAMK2D was highly expressed in 70% of the human MMe tissues (56/80) and correlated with the loss of BAP1 expression, making it a potential diagnostic and therapeutic target for BAP1-deficient MMe. We screened an anticancer drugs library using BAP1-KO cells and successfully identified a CaMKII inhibitor, KN-93, which displayed a more potent and selective antiproliferative effect against BAP1-deficient cells than cisplatin or pemetrexed. KN-93 significantly suppressed the tumor growth in mice xenografted with BAP1-deficient MMe cells. This study is the first to provide a potential molecular-targeted therapeutic approach for BAP1-deficient MMe.

© 2023. The Author(s).

In plain English

This laboratory study used cell lines, human tumour tissue and mice, not asbestos-exposed people. The authors used CRISPR/Cas9 to knock out the BAP1 gene in two immortalised human mesothelial cell lines, MeT-5A and HOMC-D4. Microarray analysis found seven genes upregulated more than 3-fold in BAP1-knockout cells; the number of genes below 0.1-fold is printed inconsistently (91 in the text, 40 in the Figure 1 legend). The authors focused on CAMK2D, whose protein was higher in BAP1-knockout cells and fell when BAP1 was restored. In immunohistochemistry of 80 mesothelioma tissue samples, 8 were scored strong, 34 moderate and 14 weak for CAMK2D, while positivity by BAP1 status was given as 56 of 59 BAP1-negative versus 7 of 21 BAP1-positive tissues (94% versus 33%); these totals do not agree. Screening 363 compounds identified the CaMKII inhibitor KN-93; average IC50 was 7.5 micromolar in BAP1-negative cells versus 20 micromolar in BAP1-positive cells. KN-93 reduced tumour growth in mice xenografted with BAP1-deficient Y-MESO-9 cells; the authors concluded that CAMK2D might be a diagnostic and therapeutic target.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study: CRISPR/Cas9 gene-knockout cell lines, gene expression profiling, drug library screening, immunohistochemistry of tissue arrays, and mouse xenograft experiments
• Who was studied: Two immortalised human mesothelial cell lines (MeT-5A, HOMC-D4) and human mesothelioma cell lines; 80 human malignant mesothelioma tissue samples on commercial tissue arrays; TCGA mesothelioma data (58 BAP1-intact, 23 BAP1-mutated); female SCID and BALB/c mice; work done at Aichi Medical University, Japan
• Exposure: Not an asbestos exposure study; the exposures tested were genetic (BAP1 knockout) and pharmacological (363 library compounds at 10 micromolar, KN-93, cisplatin, pemetrexed; KN-93 15 mg/kg in mice)
• Main results:
  • Microarray of BAP1-knockout versus control mesothelial cells: seven genes upregulated more than 3-fold; downregulated genes given as 91 in the Results text but as 40 in the Fig. 1c legend, at the same less-than-0.1-fold threshold
  • Figure 1c legend gives a different count of downregulated genes
  • CAMK2D staining in the 80 mesothelioma tissues: 8 strong (3+), 34 moderate (2+), 14 weak (1+), totalling 56 positive
  • CAMK2D positivity by BAP1 status, as printed by the authors (these counts total 63, which does not match the 56 positives above)
  • KN-93 average IC50: 20 micromolar in BAP1+/+ cells, 7.5 micromolar in BAP1−/− cells
  • In TCGA data, CAMK2D mRNA was higher in mesothelioma patients with BAP1 somatic mutations (n = 23) than in those with intact BAP1 (n = 58), p less than 0.05
  • In mice xenografted with BAP1-deficient Y-MESO-9 cells, KN-93 suppressed tumour growth without weight loss; it did not reduce growth of BAP1-WT MSTO-211H tumours
• The authors' conclusion: The authors concluded that loss of BAP1 is closely associated with CAMK2D expression and that CAMK2D, and the CaMKII inhibitor KN-93, are potential diagnostic and therapeutic targets for BAP1-deficient malignant mesothelioma
• Limitations the authors state:
  • The cell lines used had been immortalised with SV40 and/or hTERT, and the authors did not test whether this affected CAMK2D expression
  • Further functional experiments are needed to confirm that BAP1 loss causes CAMK2D upregulation in mesothelioma cells
  • The authors stated the molecular mechanism behind CAMK2D upregulation after BAP1 loss remains unclear

Topics

Medical terms in this study, explained in our Lexicon: BAP1, Mesothelioma, Prognosis, Mesothelial Cells, Cisplatin, Pemetrexed (Alimta).

Related studies

• Targeting fatty acid synthase suppresses tumor development in NF2/CDKN2A-deficient pleural mesothelioma — S. Karnan, A. Ota, et al. (2026)
• Identification of CD24 as a potential diagnostic and therapeutic target for malignant pleural mesothelioma — S. Karnan, A. Ota, et al. (2020)
• Establishment and characterization of CRISPR/Cas9-mediated NF2-/- human mesothelial cell line: Molecular insight into fibroblast growth factor receptor 2 in malignant pleural mesothelioma — M. Wahiduzzaman, S. Karnan, et al. (2019)
• Novel ATP-competitive Akt inhibitor afuresertib suppresses the proliferation of malignant pleural mesothelioma cells — M. Yamaji, A. Ota, et al. (2017)
• Editorial: Moving beyond the molecular mechanisms of malignant pleural mesothelioma: Cues for novel biomarkers and drug targets — I. Cavallari, F. Cerciello, et al. (2023)
• Selective killing of tumors deficient in methylthioadenosine phosphorylase: a novel strategy — M. Lubin, A. Lubin (2009)

Browse more research in Cell Death Discovery, or return to medical research.