Cyclin-dependent kinase 4 (CDK4)

Ser/Thr-kinase part of cyclin D-CDK4 (DC) complexes that phosphorylate and inhibit members of the retinoblastoma (RB) protein family including RB1 and regulate the cell-cycle during G(1)/S transition. Phosphorylation of RB1 allows dissociation of the transcription factor E2F from the RB/E2F complexes and the subsequent transcription of E2F target genes which are responsible for the progression through the G(1) phase.

Hypophosphorylates RB1 in early G(1) phase. Cyclin D-CDK4 complexes are important integrators of various mitogenenic and antimitogenic signals.