p21CIP1 Protein

CIP 1 (Cyclin-Dependent Kinase Inhibitor 1A) regulates cell cycle progression, terminal differentiation, and apoptosis (1). CIP1 was shown to be induced by p53 and to be a potent inhibitor of cyclin-dependent kinase (CDK) activity. DNA damage leads to increased expression of CIP1 in cyclin E-containing complexes and to an associated decrease in cyclin-dependent kinase activity. CIP1 is a critical downstream effector in the p53-specific pathway of growth control in mammalian cells (2).