OTUD7B is a new deubiquitinase targeting p53

Area of Science:

• Oncology
• Molecular Biology
• Biochemistry

Background:

• The tumor suppressor p53 is crucial for preventing cellular transformation.
• p53 stability is regulated by post-translational modifications, including polyubiquitination by Mdm2 leading to proteasomal degradation.
• The deubiquitinases (DUBs) that regulate p53 are not fully characterized, particularly in hepatocellular carcinoma (HCC).

Purpose of the Study:

• To investigate the role of the deubiquitinase OTUD7B in hepatocellular carcinoma (HCC).
• To determine if OTUD7B interacts with and deubiquitinates p53.
• To elucidate the functional consequences of OTUD7B-p53 interaction on HCC growth and identify therapeutic potential.

Main Methods:

• Mass spectrometry and co-immunoprecipitation assays to identify and confirm OTUD7B-p53 interaction.
• Assays to measure p53 polyubiquitination and degradation.
• In vitro and xenograft models with genetic manipulation (shRNA, CRISPR-Cas9) to assess OTUD7B function.
• Luciferase reporter and ChIP assays to explore regulatory mechanisms.
• Immunohistochemistry and immunoblotting to analyze OTUD7B expression in HCC tissues.

Main Results:

• OTUD7B directly binds to both wild-type and mutant p53 in HCC cells.
• OTUD7B removes polyubiquitin chains from p53, inhibiting Mdm2-mediated proteasomal degradation and stabilizing p53.
• OTUD7B overexpression suppresses HCC growth and xenograft progression via p53-dependent apoptosis (PUMA, BAX induction).
• OTUD7B knockdown promotes HCC growth, while its absence in p53-null cells negates these effects.
• OTUD7B expression is transcriptionally repressed by p53, forming a mutual feedback loop.
• A positive correlation between OTUD7B and p53 protein levels was observed in HCC tissues.

Conclusions:

• OTUD7B stabilizes both wild-type and mutant p53 in HCC, acting as a tumor suppressor.
• A mutual feedback loop between p53 and OTUD7B regulates their expression and function.
• OTUD7B's tumor-suppressive role is supported by its downregulation in HCC tissues and positive correlation with p53.
• OTUD7B represents a promising therapeutic target for modulating the p53 pathway in HCC.