The RB1 gene product (pRb) normally restrains the cell cycle by binding to which transcription factor, preventing S-phase entry?
- A E2F family of transcription factors ✓
- B p53
- C c-Myc oncoprotein
- D PCNA (proliferating cell nuclear antigen)
Explanation
The retinoblastoma protein (pRb) is a tumor suppressor that, in its hypophosphorylated (active) form, binds and inhibits the E2F family of transcription factors. E2F proteins, when free, transcriptionally activate genes required for S-phase entry (DNA synthesis). In normal cells, cyclin D-CDK4/6 phosphorylates pRb, releasing E2F and permitting cell cycle progression. Loss-of-function mutations in both RB1 alleles (Knudson's two-hit hypothesis) lead to constitutively free E2F and unregulated proliferation. Retinoblastoma uniquely arises in Rb-deficient cells because photoreceptor precursors in developing retina depend on this pathway for cell cycle exit during differentiation.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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