p21 Waf1/Cip1 Recombinant Rabbit mAb (S-3909-60)

p21 Waf1/Cip1, also known as CDKN1A, is a potent cyclin-dependent kinase inhibitor that serves as a critical downstream effector of the tumor suppressor p53 in response to DNA damage and cellular stress. Functioning primarily as a molecular brake on the cell cycle, p21 binds to and inhibits the activity of cyclin-CDK complexes, particularly those involving CDK2, CDK4, and CDK6, thereby preventing the phosphorylation of the retinoblastoma protein (Rb) and arresting cell progression at the G1/S checkpoint to allow time for DNA repair or to initiate senescence. Beyond its canonical role in cell cycle regulation, p21 exhibits complex, context-dependent functions by interacting with proliferating cell nuclear antigen (PCNA) to modulate DNA replication and repair mechanisms, while also influencing apoptosis through interactions with pro-apoptotic factors like ASK1 and caspases; notably, its expression can be induced via both p53-dependent and p53-independent pathways, making it a pivotal node in maintaining genomic stability and preventing tumorigenesis, although its overexpression in certain cancer contexts has been paradoxically associated with poor prognosis due to its potential anti-apoptotic effects.