UBR5 and melanoma: The E3 ubiquitin ligase UBR5 has shown the ability to ubiquitinate CDK938, so we hypothesized that CSN6 stabilizes the expression of CDK9 by regulating the E3 ligase UBR5.A co-IP assay was performed and demonstrated that CSN6 interacted with UBR5 in A375 and MV3 melanoma cells (Fig. 5A).