p21

The CDK inhibitor p21 promotes cell cycle arrest and belongs to the family of CDK inhibitors that includes p21, p27 and p57. In association with CDK2 complexes, it serves to inhibit kinase activity and block progression through G1/S. P21 inhibits cell cycle progression primarily through the inhibition of CDK2 activity and is activated in response to a variety of cellular and environmental signals to promote tumor suppressor activities.