Transcriptional repression by p53 involves molecular interactions distinct from those with the TATA box binding...

Area of Science:

• Molecular Biology
• Gene Regulation
• Cancer Research

Background:

• The p53 protein acts as a transcriptional activator but can also repress gene expression.
• p53-mediated repression of promoters lacking p53 binding sites is hypothesized to involve interactions with TATA box binding protein (TBP).

Purpose of the Study:

• To investigate the in vivo relevance of the p53-TBP interaction in transcriptional repression.
• To elucidate the specific mechanisms underlying p53-mediated transcriptional repression.

Main Methods:

• Transient transfection assays were conducted in Drosophila Schneider cells.
• Expression levels were analyzed from promoters containing TATA box or initiator (Inr) elements, activated by various transcription factors (GAL4-VP16, GAL4-ftzQ, Sp1).
• Mutant p53 proteins with defects in DNA binding, transcriptional activation, or TBP-associated factor (TAF) interaction were utilized.

Main Results:

• Wild-type p53 repressed TATA box-dependent transcription but not Inr-dependent transcription.
• A DNA-binding deficient p53 mutant also repressed Sp1-activated TATA-dependent transcription.
• p53 failed to repress basal TATA promoter transcription upon TBP overexpression, and TBP overexpression did not rescue p53-mediated repression.
• A p53 mutant defective in TAF interaction could not repress activated transcription.

Conclusions:

• The interaction between p53 and TBP is necessary but not sufficient for p53-mediated transcriptional repression.
• Repression likely involves p53 interactions with TAFs, which are crucial for activated but not basal transcription.
• p53-mediated repression may occur through squelching of a transcription factor limiting activated transcription from TATA-containing promoters.