A defect in the p53 response pathway induced by de novo purine synthesis inhibition

Area of Science:

• Cellular Biology
• Molecular Biology
• Cancer Research

Background:

• p53 protein is crucial for sensing cellular stress and initiating cell cycle arrest.
• The p53 pathway typically responds to DNA damage and other cellular stresses.
• p53-mediated G1 cell cycle arrest is critical for preventing the proliferation of damaged cells.

Purpose of the Study:

• To investigate the p53 pathway's response to inhibition of de novo purine synthesis.
• To elucidate the mechanism by which glycinamide ribonucleotide formyltransferase (GART) inhibition affects p53.
• To determine why the p53-dependent G1 checkpoint is blocked under these conditions.

Main Methods:

• Utilized human carcinoma cell lines (HCT116, MCF7, A549).
• Inhibited de novo purine synthesis using folate analogs targeting GART.
• Analyzed p53 accumulation, phosphorylation, acetylation, and binding to the p21 promoter.
• Assessed histone acetylation at p53 binding sites within the p21 promoter.

Main Results:

• GART inhibition led to p53 accumulation in carcinoma cells.
• Despite p53 accumulation and promoter binding, p53 target gene transcription (e.g., p21) was impaired.
• Accumulated p53 lacked critical post-translational modifications (phosphorylation, acetylation).
• Histone acetylation at the p21 promoter was not induced, preventing chromatin remodeling.

Conclusions:

• The p53-dependent G1 checkpoint is blocked by GART inhibitors in human carcinoma cells.
• Impaired p53 post-translational modifications and failure in chromatin structure opening prevent transcriptional propagation of the p53 response.
• This study reveals a novel mechanism of p53 pathway dysregulation impacting cancer cell cycle control.