Abstract 2995: The ectopic expression of miR-380-5p interferes with the aggressive traits of diffuse malignant peritoneal mesothelima cells

Abstract Telomerase activity (TA) and the alternative lengthening of telomere (ALT) pathway are two telomere maintenance mechanisms (TMM) yet identified in human cancers. Although the activation of either TMM seems to be equivalent in supporting tumor cell immortalization (a hallmark of cancer), the contribution of TA and ALT to tumor progression and aggressiveness may be different. Mounting evidence suggests that cancer cell aggressiveness could be associated with a TA↔ALT shift that would allow the acquisition of distinct aggressive traits. We previously showed that an ALT-like phenotype emerged in diffuse malignant peritoneal mesothelioma (DMPM) cells upon miR-380-5p-dependent inhibition of TA (Cimino-Reale G, et al. J Hematol Oncol. 2017). To analyze the transcriptomic changes associated with the emergence of such a phenotype, gene expression profiling was carried out. Results showed that 3331 genes were differentially expressed (FDR0. 05, adjusted for multiple hypothesis testing) in miR-380-5p- vs. preNeg-transfected DMPM cells, out of which 1673 genes were up-regulated and 1658 genes down-regulated. To get biological meaning about the molecular events occurring upon miR-380-5p reconstitution, Gene Set Enrichment Analysis was performed. Results showed a positive enrichment of 188 gene sets, restricted for an FDR 0. 05, out of which signatures related to DNA replication, DNA recombination and telomere maintenance via recombination were present. Conversely, only 1 gene set (GO: positive regulation of blood vessel endothelial cell migration) was negatively enriched at significant level. Notably, among the leading edge genes, PTGS2, which encodes for cyclooxygenase-2 (COX-2) and represents a predicted target of miR-380-5p (miRWalk), was the most significantly down-regulated gene (FDR 0. 000001; log (fold-change): -2. 15). Notably, a complete abrogation of PTGS2 expression levels and COX-2 protein amounts was observed in miR-380-5p- compared to preNeg-transfected cells upon validation by qRT-PCR and western blotting, respectively. This evidence was paralleled by reduced amounts of phospho-FAK (focal adhesion kinase) and impaired migrating/invading capabilities of cells ectopically expressing miR-380-5p. Moreover, a reduction of Vimentin and a slight increase in P-Cadherin protein levels were also observed in cells ectopically expressing miR-380-5p, likely indicating the occurrence of a reverse-EMT program. Finally, a pronounced increase in the sensitivity to Cisplatin and Doxorubicin was also appreciable in miR-380-5p- vs. preNeg-transfected cells, suggesting that miRNA-mediated induction of a reverse-EMT may, at least in part, contribute to improve the response of DMPM cells to chemotherapeutic drugs. Citation Format: Stefano Percio, Lorenzo Di Pietro, Eisa Naghshineh, Marcello Deraco, Nadia Zaffaroni, Marco Folini. The ectopic expression of miR-380-5p interferes with the aggressive traits of diffuse malignant peritoneal mesothelima cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2995.