Merkel cell carcinoma-derived exosome-shuttle miR-375 induces fibroblast polarization by inhibition of RBPJ and p53

Abstract

Merkel cell carcinoma (MCC) is a highly invasive and metastatic skin cancer. While high expression of miR-375 is a characteristic of MCC, it seems not to contribute to the malignant phenotype of MCC cells. miR-375 enrichment in MCC-derived extracellular vesicles suggests its intercellular signaling function. Here, we demonstrate that horizontally transferred miR-375 causes fibroblast polarization toward cancer-associated fibroblasts (CAFs). The polarization is evidenced by phenotypic changes and induction of α-SMA, CXCL2, and IL-1β. Fibroblast polarization is inhibited by specific antagomirs and mimicked by experimental miR-375 expression. Mechanistically, miR-375 downregulates RBPJ and p53, two key players regulating fibroblast polarization. In clinical MCC samples, in situ hybridization located miR-375 in CAFs, which correlated with high α-SMA protein and low RBPJ and TP53 expression; single-cell RNAseq revealed a disparate fibroblast polarization negatively correlating with p53 pathway-related gene expression. Thus, the functional role of miR-375 in MCC is to generate a pro-tumorigenic microenvironment by inducing fibroblast polarization.

Cancer-associated fibroblasts exert a pro-angiogenic activity in Merkel cell carcinoma

“…Given that very few studies have thoroughly addressed the biological significance of stromal cells in MCC progression, our investigation is the first to provide evidence that these cells may play a relevant role in modulating tumor growth, particularly angiogenesis. This new paradigm would be consistent with a recent report showing that intercellular communication between MCC cells and stromal fibroblasts is required for the generation of activated/polarized CAFs (Fan et al ., 2021). Consistent with our findings, variability/heterogeneity of stromal components populating MCC lesions has been reported, a phenomenon also observed in many other cancers.…”

“…A more recent study provided evidence of exosome transmitted cargo on the TME in MCC. Exosome transmitted miRNA-375 induced activation of αSMA-1, CXCL2, and IL- 1β genes, suggesting that horizontally transferred miR-375 is critical for polarizing fibroblasts toward a CAF phenotype in MCC (Fan et al , 2021).…”

Role of Virus-Induced Host Cell Epigenetic Changes in Cancer

“…Becker and his group showed that extracellular vesicle-mediated transmission of miR-375 to fibroblasts caused phenotypic changes toward cancer-associated fibroblasts. This observation suggests that miR-375 may contribute to generating a tumor microenvironment [ 276 ].…”

Mutational Landscape of Virus- and UV-Associated Merkel Cell Carcinoma Cell Lines Is Comparable to Tumor Tissue

“…The self-renewal medium was further supplemented with chicken embryo extract containing HBSS, PBS (PAN Biotech), MEM with Earle's salts and L-glutamine (Thermo Fischer) and Hyaluronidase specs (Sigma Aldrich) [42]. Primary cutaneous fibroblasts (F 1.15) were generated and maintained as previously described [43].…”