Three newly established immortalized mesothelial cell lines exhibit morphological phenotypes corresponding to malignant mesothelioma epithelioid, intermediate, and sarcomatoid types, respectively

Our plain-English summary of Three newly established immortalized mesothelial cell lines exhibit morphological phenotypes corresponding to malignant mesothelioma epithelioid, intermediate, and sarcomatoid types, respectively, by T. Sato, H. Nakanishi, K. Akao, et al (Cancer Cell International, 2021).

The study

• Authors: T. Sato, H. Nakanishi, K. Akao, M. Okuda, S. Mukai, T. Kiyono, Y. Sekido
• Journal: Cancer Cell International
• Published: 2021;21(1):546
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Malignant mesothelioma (MM) is a very aggressive tumor that develops from mesothelial cells, mainly due to asbestos exposure. MM is categorized into three major histological subtypes: epithelioid, sarcomatoid, and biphasic, with the biphasic subtype containing both epithelioid and sarcomatoid components. Patients with sarcomatoid mesothelioma usually show a poorer prognosis than those with epithelioid mesothelioma, but it is not clear how these morphological phenotypes are determined or changed during the oncogenic transformation of mesothelial cells.

Methods: We introduced the E6 and E7 genes of human papillomavirus type 16 and human telomerase reverse transcriptase gene in human peritoneal mesothelial cells and established three morphologically different types of immortalized mesothelial cell lines.

Results: HOMC-B1 cells exhibited epithelioid morphology, HOMC-A4 cells were fibroblast-like, spindle-shaped, and HOMC-D4 cells had an intermediate morphology, indicating that these three cell lines closely mimicked the histological subtypes of MM. Gene expression profiling revealed increased expression of NOD-like receptor signaling-related genes in HOMC-A4 cells. Notably, the combination treatment of HOMC-D4 cells with TGF-β and IL-1β induced a morphological change from intermediate to sarcomatoid morphology.

Conclusions: Our established cell lines are useful for elucidating the fundamental mechanisms of mesothelial cell transformation and mesothelial-to-mesenchymal transition.

© 2021. The Author(s).

In plain English

This laboratory study established three new immortalized human mesothelial cell lines from primary mesothelial cells taken from the greater omentum of a 51-year-old Japanese man operated on for early gastric cancer. The cells were retrovirally transduced with human papillomavirus 16 E6/E7 and human TERT genes, then selected and cloned. The resulting lines, called HOMCs, differed in shape: HOMC-B1 showed cobblestone-like epithelioid morphology, HOMC-A4 an elongated fibroblast-like morphology, and HOMC-D4 an intermediate shape. Short tandem repeat and SNP analyses showed the lines came from the same patient. All three expressed the mesothelioma-related tumour suppressor proteins merlin, BAP1 and p16. B1 and D4 expressed the mesothelial markers podoplanin, calretinin, mesothelin and WT-1, while A4 kept calretinin, mesothelin and WT1 but at much weaker levels. Gene set enrichment analysis showed the NOD-like receptor signalling pathway differed between HOMC-A4 and HOMC-D4. Treating HOMC-D4 with TGF-beta and IL-1beta together (2 ng/mL each, 24 hours) changed the cells to a fibroblast-like shape, while either factor alone did not. None of the lines formed tumours in nude mice.

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 cell-line establishment and characterization study (in vitro, with mouse transplantation experiments)
• Who was studied: Primary mesothelial cells from the greater omentum of one 51-year-old Japanese male patient operated on for early gastric cancer at Aichi Cancer Center Hospital; comparison lines MeT-5A, NCI-H2052, NCI-H2452, NCCIT; 6-week-old KSN (nu/nu) female nude mice
• Exposure: Retroviral transduction with human papillomavirus 16 E6/E7 and human TERT genes to immortalize the cells; later treatment of HOMC-D4 cells with TGF-beta and IL-1beta at 2 ng/mL each for 24 h, alone or in combination. No asbestos exposure was studied.
• Main results:
  • Three immortalized lines with distinct morphologies were obtained: HOMC-B1 epithelioid, HOMC-A4 fibroblast-like, HOMC-D4 intermediate
  • HOMC-A4 cells had fewer microvilli and poorly developed primary cilia, consistent with fibroblastic morphology
  • All three HOMC lines, like MeT-5A, expressed merlin, BAP1 and p16Ink4a, unlike the two malignant mesothelioma lines used as controls
  • Mesothelial lineage markers (podoplanin, calretinin, mesothelin, WT-1) were all detected in HOMC-D4 and HOMC-B1; HOMC-A4 maintained calretinin, mesothelin and WT1, but much more weakly than the other cells
  • Gene set enrichment analysis found the NOD-like receptor signalling pathway differed significantly between HOMC-A4 and HOMC-D4
  • E-cadherin was high in HOMC-B1; Snail and CTGF were higher in HOMC-A4 than in the other two HOMC lines; vimentin was similar across the three
  • TGF-beta and IL-1beta given together, but not separately, changed HOMC-D4 cells to a fibroblast-like morphology, with reduced E-cadherin and increased Snail and CTGF
  • The induced sarcomatoid morphology did not revert after one week of culture without the factors
  • No tumours formed after subcutaneous transplantation: HOMC-B1 0/6 (0%), HOMC-D4 0/3 (0%), HOMC-A4 0/3 (0%)
  • Proliferation of HOMC-D4 was almost identical to MeT-5A, while HOMC-B1 and HOMC-A4 grew slightly more slowly
• The authors' conclusion: The authors concluded that they had established three immortalized mesothelial cell lines with distinct morphologies that could be useful for studying the causes of mesothelioma cell transformation and for drug screening.
• Limitations the authors state:
  • The authors noted that chromosomal changes were present in all the lines and were probably introduced artificially during their establishment
  • The authors noted the lines came from a single patient, so genetic backgrounds were nearly uniform, and they only suspected (did not show) that epigenetic modifications explain the three morphologies

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Malignant Mesothelioma, Epithelioid, Sarcomatoid, Asbestos Exposure, Histological Subtype, Biphasic Mesothelioma, Mesothelioma.

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