miR-342-5p: A promising tumor suppressor in diffuse pleural mesothelioma

Diffuse pleural mesothelioma (DPM) is an incurable, aggressive neoplasm with limited therapies. Moving beyond conventional approaches, we posit that microRNAs (miRNA), short, non-coding RNA that coherently regulate gene expression, can uniquely disrupt the molecular networks involved in DPM. In this study, we identified miR-342-5p as a novel DPM-associated miRNA. We used a human miRNA mimic library to screen for miRNAs with antiproliferative effects on a panel of DPM cell lines. Among the most potent candidates was miR-342-5p. We profiled the downregulation of miR-342-5p in DPM patient specimens compared to normal pleura (Normal=22, Tumor=50). TCGA-MESO analysis revealed that miR-342-5p downregulation is significantly associated with poor survival outcomes. Our results demonstrated that the re-expression of miR-342-5p significantly impaired DPM cell viability, reduced 2D colony foci formation, and inhibited anchorage-independent cell growth in soft-agar and sphere assays. Additionally, Annexin-V assays showed a significant increase in early and late apoptotic cells in miR-342-5p transfected DPM cells compared to controls. Furthermore, we confirmed the induction of apoptosis in miR-342-5p-treated DPM cells through PARP cleavage and the activation of caspase-3/7. Importantly, no significant biological effects were observed when normal human mesothelial cells (NP1 line) were treated with miR-342-5p. Next, we performed a Biotin-miRNA (Bi-miR) pull-down assay, a direct binding assay in which a biotin-tagged miR-342-5p probe captures its associated mRNA transcripts in a pooled lysate. Then, RNA-seq analysis is conducted to identify direct target genes associated with apoptosis and cell death pathways in DPM. We identified the top transcripts targeted by miR-342-5p that are also involved in its tumor-suppressive activity in DPM. Overall, our findings highlight the tumor suppressive effects and therapeutic potential of miR-342-5p for DPM treatment.