Cyclin D1–Cyclin-dependent kinase 6 complex (CCND1–CDK6) (CCND1–CDK6)

The Cyclin D1–Cyclin-dependent kinase 6 complex (CCND1–CDK6) is a vital holoenzyme that regulates the transition of cells from the G1 phase to the S phase of the cell cycle (UniProt: Q00534, P24385). This complex consists of the regulatory subunit Cyclin D1 and the catalytic subunit CDK6, which together function as a serine/threonine kinase (PubMed: 28273102). Its primary substrate is the retinoblastoma (Rb) protein; phosphorylation of Rb by this complex releases E2F transcription factors, which then activate the expression of genes necessary for DNA replication (StatPearls: NBK448112). In many human cancers, such as hormone receptor-positive breast cancer and various leukemias, the CCND1–CDK6 pathway is hyperactivated due to gene amplification, translocation, or the loss of endogenous inhibitors like p16INK4a (NIH: Cancer.gov). Therapeutic targeting of this complex is achieved using selective CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib, which bind to the ATP-binding pocket of CDK6 to induce cell cycle arrest (PubMed: 30504144). While these drugs have significantly improved outcomes in oncology, they are associated with clinical challenges such as hematologic toxicities, particularly neutropenia, because CDK6 is essential for normal hematopoiesis (PubMed: 25557065).

Other names

Cyclin D1–CDK6CCND1–CDK6 complexG1/S-specific cyclin-D1–CDK6 complex

Competitive inhibition of the ATP-binding site of CDK6 within the Cyclin D1–CDK6 complex, preventing the phosphorylation of the retinoblastoma (Rb) protein and inducing G1 phase cell cycle arrest (StatPearls: NBK448112).