CHIP chaperones wild type p53 tumor suppressor protein

Area of Science:

• Molecular Biology
• Protein Biochemistry
• Cellular Stress Response

Background:

• Wild type p53 (WT53) protein exists in a dynamic equilibrium between wild type and mutant conformations.
• Elevated temperatures induce conformational changes in p53, potentially leading to thermal inactivation and altered function.
• The co-chaperone carboxyl terminus of Hsp70-interacting protein (CHIP) is known to suppress misfolded protein aggregation and promote proteasomal degradation.

Purpose of the Study:

• To investigate the role of CHIP in modulating p53 conformation and activity, particularly under thermal stress.
• To determine if CHIP can prevent thermal inactivation of wild type p53 and restore function to heat-denatured p53.
• To elucidate the mechanism by which CHIP interacts with p53 and influences its conformational state.

Main Methods:

• Demonstration of physical interaction between CHIP and the amino terminus of WT53.
• Assessment of CHIP's effect on p53 aggregation and proteasomal degradation.
• Analysis of CHIP's ability to restore DNA binding activity to heat-denatured p53.
• Investigation of CHIP's role in maintaining p53 conformation in cells under elevated temperatures using geldanamycin and CHIP-small interfering RNA.
• Subcellular localization studies of CHIP and p53 under thermal stress.
• Chromatin immunoprecipitation to identify p53 and CHIP binding to p21 and p53 promoters.

Main Results:

• CHIP physically interacts with WT53 and prevents its irreversible thermal inactivation.
• CHIP preferentially binds to the p53 mutant phenotype and restores DNA binding activity of heat-denatured p53 independently of ATP.
• CHIP promotes the native-like conformation of p53 under elevated temperatures, while CHIP depletion increases the mutant form.
• Both CHIP and p53 show increased nuclear localization under elevated temperatures.
• p53 and CHIP co-occupy DNA binding sites in the p21 and p53 promoters.

Conclusions:

• CHIP functions as a direct chaperone for WT53, aiding in maintaining its native conformation under physiological conditions.
• CHIP can rescue p53 mutant phenotypes, restoring a folded native state under cellular stress conditions.
• These findings suggest a crucial role for CHIP in p53 stability and function, particularly in response to thermal stress.