Asbestos exposure induces carcinogenesis via minority MOMP and displays characteristics of drug-tolerant persister cells

Background Pleural mesothelioma (PM) occurs many years after asbestos fiber exposure; yet the mechanism that converts chronic damage into malignancy remains unclear. Asbestos fibers induce persistent oxidative and genomic stress that should activate apoptosis via mitochondrial outer membrane permeabilization (MOMP); however, these cells do not undergo apoptosis and instead develop into malignancy. MOMP normally triggers cytochrome c (cyt c) release as well as mitochondrially derived damage-associated molecular patterns (DAMPs), resulting in caspase activation and cell death. Sublethal activation of MOMP can lead to a phenomenon known as Incomplete or Minority mMOMP, in which cells survive and develop somatic mutations which contribute to carcinogenesis. In this study, we evaluated whether minority MOMP induced carcinogenesis in PM cells. Methods We investigated whether prolonged exposure to asbestos fibers drives mMOMP in non-transformed, pleural mesothelial cells (MeT-5A). Cells were cultured for six months with chrysotile (Chry-Asb) or crocidolite (Croc-Asb) asbestos fibers. Cellular phenotypes were assessed by clonogenicity, migration, and invasion assays to evaluate malignant transformation. Reactive oxygen species (ROS) production, cytochrome (cyt) c release, gammaH2AX phosphorylation, and caspase 3 activation were measured to evaluate mitochondrial and apoptotic responses. Results Chronic asbestos exposure increased clonogenicity, migration, and invasion of MeT-5A cells, suggesting transformation toward a malignant phenotype. Additionally, we observed the phenotypic characteristics of minority MOMP, including elevated ROS, cyt c release, an increase in the MOMP effector proteins (Bax/Bak), caspase activation, and gammaH2AX phosphorylation while lacking induction of apoptosis. Furthermore, the anti-apoptotic mitochondrial protein Myeloid Cell Leukemia-1 (MCL-1) was upregulated by asbestos, facilitating minority MOMP by preventing a shift to complete MOMP. Metabolomic analysis revealed a Warburg effect. Consistent with the Warburg effect, both Seahorse analysis and Gene Set Enrichment Analysis showed increased glycolysis in both cell lines. Additionally, asbestos-induced minority MOMP was associated with characteristics of drug-tolerant persister cells (DTPs) including slower proliferation, change in cell phenotype, and resistance to cisplatin. Conclusion Minority MOMP promotes malignant transformation of mesothelial cells while enabling resistance to apoptosis. Our findings suggest that minority MOMP contributes to carcinogenesis by altering mitochondrial dynamics and metabolic reprogramming, reprogramming cells to a DTP phenotype. Targeting mitochondrial pathways to convert Minority MOMP into complete MOMP may represent a novel therapeutic strategy to overcome treatment resistance in pleural mesothelioma.