P3.03-002 Inducible Changes in Cell Morphology and Gene Expression Reflecting the Histological Subtypes of Mesothelioma: Topic: Mesothelioma Transitional

Abstract

Malignant pleural mesothelioma (MPM) represents an aggressive malignancy with dismal prognosis and limited therapeutic options. MPM occurs in three main histological subtypes: epithelioid, sarcomatoid and biphasic, which are characterized by differences in morphological growth pattern, aggressiveness and patient prognosis. However, the mechanisms and causes responsible for the different cell morphologies are poorly understood. Epithelial-mesenchymal transition (EMT) has been implicated in cancer progression and chemoresistance, but its role in MPM is not well understood. Fibroblast growth factor (FGF) signals promote cell growth, survival and aggressiveness in several tumors including mesothelioma. Aim of this study was to characterize growth factor-induced, EMT-like changes with respect to the MPM histological subtypes. Morphological and behavioral changes of treated cell models were analyzed by morphometry, immunoblotting and functional assays. Alterations in gene or microRNA expression were evaluated via qPCR and array hybridization. Pathway enrichment analysis was based on KEGG. In several cell lines established from biphasic MPM, treatment with FGF2 and EGF induced morphological changes reminiscent of EMT and aggressive behavior such as scattering, increased migration, proliferation and invasiveness. Inhibition of the fibroblast growth factor receptors (FGFR) or the MAPK axis via small-molecule inhibitors could prevent these changes and, in cell lines with sarcomatoid-like shape, reverse scattering and induce a more epithelioid morphology. Comparable results were obtained using an engineered FGFR1 enabling contactless activation via blue light. Analyses of genes and microRNAs regulated by FGF2 or EGF showed an overlap with previously established EMT markers but also identified several novel potential markers such as MMP1, ESM1, ETV4, PDL1, ITGA6 or BDKRB2. Blocking the FGFR or MAPK pathways resulted in the opposite regulation of these genes. Inhibition of MMP1 via siRNAs or pharmacological inhibitors prevented FGF2-induced scattering and invasiveness. In unsupervised clustering, the gene expression profiles of solvent- or cytokine-treated cells were associated with those of epithelioid and sarcomatoid MPM, respectively. Immunohistochemistry showed an association of MMP1 as well as phospho-ERK with the sarcomatoid part of tissue specimens from biphasic tumors. Pathway enrichment analysis of differentially expressed genes as well as the targets of altered microRNAs after FGF2 treatment showed that the regulated genes are assigned to categories important for cell growth and aggressive behavior. Our data characterize FGFR-mediated signals as important players in MPM aggressiveness and the morphological and behavioral plasticity of mesothelioma cells, leading to a better understanding of the link between the MPM histological subtypes and their influence on patient outcome.