COPS6 and melanoma: To investigate whether CDK9 expression is influenced by CSN6, a western blot assay was performed and demonstrated that the protein level of CDK9 was remarkably reduced in CSN6-knockdown melanoma cells and recovered after overexpression of CSN6 in CSN6-knockdown cells (Fig. 4C), while the CDK9 mRNA level was not significantly affected by the CSN6 status (Fig. S2), indicating that CSN6 may regulate the expression of CDK9 via posttranscriptional regulation.