Regulatory activity of the tumor suppressor gene ras association domain family member 1 isoform A (RASSF1A) on the Merkel cell carcinoma cell proliferation and apoptosis

Ras association domain family member 1 isoform A(RASSF1A) is a tumor suppressor gene, which plays a key role in multiple pathways such as cell proliferation and apoptosis. Although hypermethylation-induced loss of RASSF1A frequently occurs in cancer, the involvement of this gene in the malignant phenotype of Merkel cell carcinoma (MCC), a rare but highly aggressive skin neoplasm, is unclear. The purpose of this study was to investigate the functional role of RASSF1A in the MCC cell phenotype. RASSF1A transcript expression was evaluated in MCC cells MCC13, MCC26, WaGa and PeTa cells and in various epithelial and fibroblast control cells. RASSF1A mimic and inhibitor transfections were carried out to assess the involvement of RASSF1A in regulating MCC cell proliferation and apoptosis. MCC cell viability was investigated in GFP-transfected RASSF1A knock-out/-in WaGa and PeTa cells. To assess whether RASSF1A expression is under epigenetic regulation through promoter hypermethylation in MCC cells, gene transcript levels were assessed in cells treated with the hypomethylating agent guadecitabine and compared to corresponding untreated cells. RASSF1A tested downregulated in MCC13, MCC26, WaGa and PeTa cells compared to epithelial and fibroblast control cells. Functional experiments indicated that forced RASSF1A expression dramatically inhibited cell proliferation and favored apoptosis in MCC13, MCC26, WaGa and PeTa cells, while strongly reduced cell viability in WaGa-GFP and PeTa-GFP cells. The expression of RASSF1A transcript was restored in all tested MCC cells following treatments with guadecitabine, thus suggesting that this gene might be under epigenetic regulation in MCC. Overall, our data suggest a potential tumor suppressor activity for RASSF1A in MCC cells by regulating cell proliferation and apoptosis.