Src phosphorylation converts Mdm2 from a ubiquitinating to a neddylating E3 ligase

Area of Science:

• Molecular Biology
• Oncology
• Biochemistry

Background:

• Murine double minute-2 protein (Mdm2) regulates proteins, including the tumor suppressor p53, through ubiquitin or Nedd8 conjugation.
• The regulation of Mdm2's neddylating activity is not well understood, unlike its E3 ubiquitin ligase activity.

Purpose of the Study:

• To investigate the regulation of Mdm2's neddylating activity.
• To elucidate the mechanism by which Mdm2 neutralizes p53 in proliferating cells.

Main Methods:

• Investigated the effect of c-Src kinase on Mdm2 phosphorylation at Y281 and Y302.
• Assessed Mdm2 stability and its association with Ubc12, the E2 enzyme for neddylation.
• Examined the impact of Mdm2-dependent Nedd8 conjugation on p53 transcriptional activity.
• Utilized small molecule inhibitors targeting Src and Ubc12.

Main Results:

• Activated c-Src kinase phosphorylates Mdm2 at Y281 and Y302, enhancing Mdm2 stability.
• Phosphorylation increases Mdm2 association with Ubc12, facilitating Nedd8 conjugation to p53.
• Mdm2-mediated Nedd8 conjugation of p53 leads to transcriptionally inactive p53.
• Inhibitors of Src or Ubc12 reversed the inactivation of p53.

Conclusions:

• c-Src kinase regulates Mdm2 neddylating activity through phosphorylation, impacting p53 stability and function.
• This pathway provides a mechanism for p53 neutralization in proliferating cells.
• Targeting the Nedd8 pathway presents a potential therapeutic strategy for wild-type p53 tumors.