Cyclin D1–cyclin-dependent kinase 4 complex (Cyclin D1–CDK4)

Cyclin D1–cyclin-dependent kinase 4 is a bipartite enzymatic complex vital to the regulation of cell cycle progression. Cyclin D1 (encoded by CCND1) serves as the regulatory subunit, binding to CDK4 and activating its kinase activity, which specifically phosphorylates the retinoblastoma protein (RB1) at the G1/S boundary[1][3][7]. Phosphorylated RB1 releases E2F transcription factors, permitting transcription of genes required for DNA replication and S phase entry[1][3][5]. Overactivation or amplification of cyclin D1–CDK4 is a common event in diverse human cancers, establishing its role as a prominent therapeutic target, with pharmacologic inhibitors approved for clinical use in several malignancies[1][5][6]. Structural studies delineate unique regulatory and conformational features, differentiating it from other cyclin/CDK complexes, for example, substrate-assisted activation and stability dependencies[1][2][6]. Safety concerns with CDK4/6 inhibitors include myelosuppression, variable resistance mechanisms, and the complexity of compensatory pathways due to broad cyclin/CDK network redundancies[6].

Other names

Cyclin D1/CDK4 complexD-type cyclin/CDK4 complexCCND1–CDK4

Drugs inhibit CDK4/6 kinase activity, block phosphorylation of RB1, arrest cell cycle in G1, and suppress cell proliferation