Retinoblastoma protein–E2F transcription factor pathway (RB1–E2F pathway)

The Retinoblastoma protein–E2F transcription factor (RB1–E2F) pathway is a fundamental regulatory circuit that controls the G1-to-S phase transition of the eukaryotic cell cycle (Giacinti & Giordano, 2006, PMID: 16474627). Under normal physiological conditions, the hypophosphorylated form of the RB1 protein acts as a gatekeeper by binding to E2F transcription factors, thereby inhibiting the expression of genes necessary for DNA replication and cell division (Dick & Rubin, 2013, PMID: 23303117). Upon mitogenic stimulation, Cyclin D-dependent kinases (CDK4 and CDK6) phosphorylate RB1, triggering the release of E2F and the subsequent initiation of the S-phase program (Sherr et al., 2016, PMID: 26912533). Dysregulation of this pathway is a near-universal feature of human cancer, often occurring through RB1 mutation, Cyclin D1 amplification, or the loss of endogenous inhibitors like p16INK4a, resulting in uncontrolled cellular proliferation (O'Leary et al., 2016, PMID: 27071704). Therapeutic strategies primarily focus on CDK4/6 inhibitors, which restore the pathway's inhibitory function to induce senescence or apoptosis in malignant cells. These agents have significantly improved outcomes in hormone receptor-positive breast cancer, although the emergence of resistance through RB1 loss remains a significant clinical challenge (Finn et al., 2016, PMID: 27906088).

Other names

RB-E2F axispRb-E2F pathwayRetinoblastoma pathwayCyclin D-CDK4/6-INK4-RB pathwayG1/S checkpoint pathway

Drugs targeting this pathway, specifically CDK4/6 inhibitors, prevent the phosphorylation of the Retinoblastoma protein (RB1) by Cyclin D-CDK4/6 complexes. This maintains RB1 in its hypophosphorylated, active state, which sequesters E2F transcription factors and prevents the transcription of genes required for the transition from G1 to S phase, thereby inducing cell cycle arrest (Sherr et al., 2016, PMID: 26912533).