MED1 Downregulation Contributes to TGFβ-Induced Metastasis by Inhibiting SMAD2 Ubiquitination Degradation in Cutaneous Melanoma

Metastasis is the main reason for the high mortality of patients and indeed a difficult task in the treatment of cutaneous melanoma. Therefore, it is of great clinical value to explore the molecular mechanism of cutaneous metastatic melanoma and develop novel therapies. MED1, acting as a factor required for activator-dependent transcription, is reported to be involved in carcinogenesis and progression. In this study, we found that MED1 was highly expressed in patients with cutaneous melanoma. MED1 downregulation could induce cellular epithelial-to-mesenchymal transition and promote migration, invasion, and metastasis of cutaneous melanoma in vivo and in vitro. Further analysis showed that in Med1 knockdown cells, the TGFβ/SMAD2 signaling pathway mediated an increase in epithelial-to-mesenchymal transition phenotype and migration. The opposite results were observed after treatment with TGFβ inhibitors. To further explore the mechanism, we found that MED1 interacted with SMAD2, and MED1 downregulation could protect SMAD2 from degradation by inhibiting SMAD2 ubiquitination. Together, these results suggest that MED1 inhibited TGFβ signaling pathway to reduce cell epithelial-to-mesenchymal transition phenotype and migration through SMAD2 ubiquitination in the metastasis of cutaneous melanoma. Our findings elucidated the role of MED1 in the metastasis of cutaneous melanoma and provided a target for the therapeutic strategies of cutaneous melanoma.