CDK3

Cyclin-dependent kinase 3 (CDK3) is a serine/threonine kinase that functions in cell-cycle control, particularly during the G₀/G₁ transition and early G₁ phase progression^[1][2]. CDK3 forms an active complex with cyclin C, and this complex phosphorylates retinoblastoma protein (pRB) at Ser807/811, thereby promoting Rb-dependent exit from cellular quiescence and facilitating re-entry into the proliferative cycle^[1]. Mechanistically, CDK3 contributes to cell-cycle progression through regulation of the Rb-E2F signaling axis, a pathway that coordinates transcriptional programs required for G₁ entry and subsequent DNA synthesis^[1][2]. In disease models, aberrant CDK3 activity has been linked to oncogenic transformation through phosphorylation-dependent activation of transcription factors, including ATF1, c-Jun, and NFAT3, which enhance proliferation, anchorage-independent growth, and tumor development^[3][4]. Elevated expression of CDK3 and its downstream signaling components has been reported in several cancer models, including skin cancer and nasopharyngeal carcinoma, supporting its relevance to tumor-associated cell-cycle deregulation^[3][5]. Compared with closely related cell-cycle kinases such as CDK2, CDK3 exhibits distinct functions during G₀ exit that cannot be fully compensated by CDK2, indicating nonredundant regulatory roles within the CDK family^[5][6]. For experimental applications, CDK3 is frequently investigated as a regulator of quiescence-to-proliferation transitions and as a potential target for development of isoform-selective CDK inhibitors, although achieving kinase selectivity remains a major challenge because of structural similarities among CDK family members^[2].