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Published on: January 21, 2012
Negative regulation of p53 by Ras superfamily protein RBEL1A
Ki Lui1, Jie An, Joanne Montalbano
1Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, New York 13210, USA.
Abstract:
We had previously reported that RBEL1A, a novel Ras-like GTPase, was overexpressed in multiple human malignancies and that its depletion suppressed cell growth. However, the underlying molecular mechanism remained to be elucidated. Here we report that depletion of endogenous RBEL1A results in p53 accumulation due to increased p53 half-life whereas increased expression of RBEL1A reduces p53 levels under unstressed and genotoxic stress conditions. RBEL1A directly interacts with p53 and MDM2, and strongly enhances MDM2-dependent p53 ubiquitylation and degradation. We also found that RBEL1A modulation of p53 ubiquitylation by MDM2 does not depend on its GTPase activity. We have also defined the p53 oligomeric domain and RBEL1A GTPase domain to be the crucial regions for p53-RBEL1A interactions. Importantly, we have found that RBEL1A strongly interferes with p53 transactivation function; thus our results indicate that RBEL1A appears to function as a novel p53 negative regulator that facilitates MDM2-dependent p53 ubiquitylation and degradation.
Insights
RBEL1A, a novel Ras-like GTPase, regulates the tumor suppressor p53. RBEL1A enhances p53 degradation via MDM2, impacting cancer cell growth and p53 levels.
Area of Science:
- Molecular Biology
- Oncology
- Biochemistry
Background:
- RBEL1A (Ras-like GTPase 1A) is overexpressed in human malignancies, and its depletion inhibits cancer cell growth.
- The molecular mechanisms by which RBEL1A influences cancer progression were previously unclear.
Purpose of the Study:
- To elucidate the molecular mechanism of RBEL1A's role in cancer by investigating its interaction with the tumor suppressor p53.
- To determine how RBEL1A affects p53 stability, ubiquitylation, and transactivation function.
Main Methods:
- Investigated RBEL1A's effect on p53 levels and half-life under varying conditions.
- Utilized co-immunoprecipitation to assess direct interactions between RBEL1A, p53, and MDM2.
- Analyzed the impact of RBEL1A on MDM2-dependent p53 ubiquitylation and degradation.
- Mapped critical interaction domains between RBEL1A and p53.
Main Results:
- RBEL1A depletion leads to p53 accumulation by increasing its half-life.
- RBEL1A overexpression reduces p53 levels under both unstressed and genotoxic conditions.
- RBEL1A directly interacts with p53 and MDM2, enhancing MDM2-mediated p53 ubiquitylation and degradation.
- RBEL1A interferes with p53 transactivation function, independent of its GTPase activity.
Conclusions:
- RBEL1A acts as a novel negative regulator of p53.
- RBEL1A facilitates MDM2-dependent p53 ubiquitylation and degradation, contributing to cancer progression.
- Targeting RBEL1A may offer a therapeutic strategy for cancers with altered p53 pathway activity.
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