Cyclin-dependent kinase inhibitor 1 (p21) (p21)

Cyclin-dependent kinase inhibitor 1 (p21) is a critical regulatory protein that functions as a universal inhibitor of cyclin-dependent kinases (CDKs), particularly CDK1, CDK2, and CDK4/6 [1, 3, 20]. Encoded by the CDKN1A gene, p21 is a primary downstream mediator of p53-dependent cell cycle arrest in response to DNA damage and other cellular stress signals, acting mainly at the G1/S and G2/M checkpoints [1, 5, 13]. Beyond its role in cell cycle control, p21 interacts with the proliferating cell nuclear antigen (PCNA) to inhibit DNA replication and plays complex roles in apoptosis, senescence, and DNA repair [1, 10, 11]. In human disease, p21 exhibits a dual role as both a tumor suppressor and a potential oncogene, with its function often dictated by its cellular localization; while nuclear p21 generally inhibits tumor growth, cytoplasmic p21 can promote cell survival, anti-apoptotic signaling, and resistance to chemotherapy [2, 3, 11, 15]. This protein is a major target in oncology research, with therapeutic strategies focusing on either inducing its expression to trigger growth arrest or specifically inhibiting its oncogenic cytoplasmic activity [2, 4, 14, 16].

Other names

p21p21Cip1p21Waf1CDK-interacting protein 1Wild-type p53-activated fragment 1CIP1WAF1SDI1CAP20CDKN1Melanoma differentiation-associated protein 6MDA-6

Binds to and inhibits cyclin-dependent kinase (CDK) complexes to block cell cycle progression and interacts with PCNA to prevent DNA replication [1, 3, 10].