CDK6

CDK6 (cyclin-dependent kinase 6) is a serine/threonine kinase that forms active complexes with D-type cyclins and regulates G1-phase progression and the G1/S cell-cycle transition through phosphorylation of the retinoblastoma protein (RB), thereby controlling E2F-dependent transcriptional programs^[1][2]. Mechanistically, CDK6 integrates mitogenic and hormone-derived signals through cyclin D activation, linking extracellular growth cues to cell-cycle entry and cellular proliferation^[1][3]. Beyond canonical cell-cycle regulation, accumulating evidence indicates that CDK6 contributes to tumor development and progression in hematologic malignancies and solid tumors, where dysregulated cyclin D-CDK6 signaling promotes uncontrolled proliferation and therapeutic resistance^[1][4]. In disease models of hormone receptor-positive breast cancer, aberrant CDK4/6 activity drives RB phosphorylation and cell-cycle progression, making this pathway a central therapeutic target^[3][5]. Compared with the closely related isoform CDK4, CDK6 displays distinct regulatory and biological functions, including kinase-dependent and kinase-independent activities that influence transcriptional regulation and tumor adaptation^[4][6]. For experimental applications, selective CDK4/6 inhibitors including palbociclib, ribociclib, and abemaciclib block the G1/S transition by suppressing CDK4/6 activity, although these compounds exhibit different affinities toward CDK4 and CDK6 and produce distinct biological and clinical effects^[3][5]. CDK6 overexpression, CDK6-containing resistant complexes, and alterations in RB-associated pathways have also been implicated in resistance mechanisms, supporting continued investigation of CDK6-selective targeting strategies in cancer research^[5][1].