Retinoblastoma protein 1–E2F transcription factor 1 pathway (RB1–E2F1 pathway)

The Retinoblastoma protein 1 (RB1)–E2F transcription factor 1 (E2F1) pathway is a critical regulator of the mammalian cell cycle, specifically governing the transition from the G1 to the S phase (Source: UniProt P06400, Q01094). In its active, hypophosphorylated state, RB1 binds to E2F1, preventing the transcription of genes required for DNA synthesis. Upon phosphorylation by Cyclin-dependent kinases (CDK4/6), RB1 releases E2F1, which then initiates the expression of S-phase genes and promotes cell proliferation. Dysregulation of this pathway is a hallmark of many cancers, often occurring through RB1 loss, Cyclin D overexpression, or inactivation of CDK inhibitors like p16 (Source: PubMed PMID: 29476153). Therapeutic strategies primarily focus on CDK4/6 inhibitors, such as Palbociclib and Ribociclib, which restore the inhibitory function of RB1 on E2F1 to induce cell cycle arrest in tumor cells (Source: PubMed PMID: 30104354). Monitoring RB1 status is essential for predicting treatment response, as its loss is a major mechanism of resistance to these therapies. Additionally, the pathway's role in apoptosis and DNA repair makes it a complex but vital target for precision oncology.

Other names

RB-E2F pathwaypRb-E2F axisRetinoblastoma-E2F signaling pathwayRB1-E2F1 axis

Inhibition of Cyclin-dependent kinases 4 and 6 (CDK4/6) prevents the phosphorylation of RB1, maintaining it in a hypophosphorylated state that sequesters E2F1 transcription factors, thereby arresting the cell cycle at the G1 phase.