p300 is required for orderly G1/S transition in human cancer cells

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• The role of transcriptional coactivator p300 in cell cycle control is not fully understood due to limited experimental models.
• p300 is crucial for various cellular processes, including gene transcription and cell growth.

Purpose of the Study:

• To investigate the precise role of p300 in regulating cell cycle progression, specifically the G1/S transition.
• To elucidate the mechanism by which p300 influences retinoblastoma (RB) protein phosphorylation and E2F target gene activation.

Main Methods:

• Utilized p300-deficient cancer cell lines created via gene targeting (p300(-)) and RNA interference (RNAi).
• Analyzed cell cycle progression, RB hyperphosphorylation, E2F target activation, and p300/RB interactions using co-immunoprecipitation and in vitro kinase assays.

Main Results:

• p300-deficient cells exhibited significant proliferation defects but accelerated G1/S transition with premature S-phase entry.
• Accelerated G1/S transition correlated with early RB hyperphosphorylation and E2F target activation.
• p300 directly inhibits cdk6-mediated RB phosphorylation in early G1, preventing premature S-phase entry. p300's acetylase activity was not required for this function.
• p300-deficient cells showed paradoxical continued cycling despite serum depletion, linked to persistent RB hyperphosphorylation.

Conclusions:

• p300 plays a critical role in G1/S phase control by modulating RB phosphorylation.
• p300 acts as a negative regulator of RB phosphorylation in early G1, delaying S-phase entry.
• Dysregulation of p300 function contributes to aberrant cell cycle progression, potentially impacting cancer development.