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

The Cyclin-dependent kinase 4–cyclin D complex comprises CDK4, a serine/threonine kinase, and a D-type cyclin (primarily cyclin D1, D2, or D3). This complex forms in early G1 phase and is essential for driving cells through the G1/S checkpoint of the cell cycle by phosphorylating substrates such as the retinoblastoma protein (Rb), thereby promoting cell cycle progression and proliferation[2][3][7]. The activity of CDK4 is tightly controlled by its association with cyclin D, regulatory phosphorylation (especially at Thr172), and inhibition by proteins like p21 and p27[1][3][6]. Dysregulation or overactivation of the CDK4–cyclin D pathway is a hallmark of many cancers, making it a validated therapeutic target, especially in breast cancer and other tumor types[2][5][6]. Clinically approved drugs such as abemaciclib, palbociclib, and ribociclib inhibit its kinase activity to prevent cancer cell proliferation[6][5]. Safety concerns mainly relate to hematological side effects and the potential for acquired resistance through Rb loss or other compensatory pathways[5][6].

Other names

CDK4/cyclin D complexCyclin D/CDK4 complexCyclin-dependent kinase 4–cyclin D1 complexCyclin-dependent kinase 4–cyclin D3 complexCyclin D–CDK4 complex

ATP-competitive inhibition of kinase activity; Allosteric inhibition by conformational stabilization; Displacement of endogenous CDK inhibitors (e.g., p21); Blockade of Rb phosphorylation to prevent cell cycle progression