RORα binds to E2F1 to inhibit cell proliferation and regulate mammary gland branching morphogenesis

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Retinoic acid receptor-related orphan nuclear receptor alpha (RORα) acts as a tumor suppressor, inhibiting cell proliferation and tumor growth.
• The precise molecular mechanisms underlying RORα's anti-proliferative effects are not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism by which RORα inhibits cell proliferation.
• To investigate the interaction between RORα and E2F1 in regulating cell cycle progression.

Main Methods:

• Demonstrated RORα binding to E2F1 in epithelial cells.
• Assessed the impact of RORα on E2F1-regulated transcription and acetylation.
• Utilized histone deacetylase 1 (HDAC1) recruitment assays.
• Performed RORα knockdown and HDAC1 inhibition experiments.
• Analyzed RORα expression in mammary ducts versus terminal end buds and correlated with E2F1 target genes and proliferation.

Main Results:

• RORα binds to the heptad repeat and marked box region of E2F1, suppressing its transcriptional activity.
• RORα binding inhibits E2F1 acetylation and DNA-binding by recruiting HDAC1.
• HDAC1 knockdown or inhibition partially restored E2F1 activity repressed by RORα.
• RORα levels are higher in mammary ducts than terminal end buds, inversely correlating with E2F1 target gene expression and proliferation.
• RORα silencing in mammary epithelial cells increased proliferation and promoted ductal side branching.

Conclusions:

• Revealed a noncanonical nuclear receptor pathway where RORα directly inhibits E2F1 activity via HDAC1 recruitment.
• Established a novel link between RORα and E2F1 in controlling cell cycle progression.
• Demonstrated the role of the RORα-E2F1-HDAC1 axis in mammary tissue morphogenesis and tumor suppression.