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

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.