CDK4 and colorectal carcinoma: To examine the potential mechanism by which SelK regulates CDK4, ITCH (an E3 ubiquitin ligase of CDK4 that destabilizes CDK4 and inhibits CRC cell survival [29]) and E6AP (which ubiquitin CDK4 in HEK293 cells as determined by orthogonal ubiquitin transfer (OUT) method [30]) were also evaluated in the cell lines.