<p>MDM2-C Functions as an E3 Ubiquitin Ligase</p>

Abstract

Background Mouse double minute 2 (MDM2) is an E3 ubiquitin ligase that is over-expressed in many cancers and regulates target proteins through ubiquitination. Full-length MDM2 (MDM2-FL) is best known for targeting wild-type p53 for degradation by the proteasome, but the functions of the many splice variants of MDM2 are under-explored. The three well-studied alternative MDM2 isoforms are MDM2-A/ALT2, MDM2-B/ALT1, and MDM2-C/ALT3. MDM2-A and MDM2-B are capable of down-regulating MDM2-FL activity and have transforming activity in cancers with mutant p53. The MDM2 isoform MDM2-C is over-expressed in breast cancer and correlates with decreased survival in the context of mutant p53 expression. Therefore, MDM2-C requires further study to determine if it has biochemical activities similar to MDM2-FL. Hypothesis: We hypothesized that like MDM2-FL, the MDM2-C isoform (lacking exons 5–9 and containing a full C-terminal RING finger sequence) would maintain E3 ubiquitin ligase activity. Materials and Methods In order to explore the biochemical function of MDM2-C, we used an in vitro ubiquitination assay and a glutaraldehyde cross-linking assay. Results Here we report, for the first time, that MDM2-C has E3 auto-ubiquitin ligase activity, which can promote ubiquitination of wild-type p53 and mutant p53 R273H, and also can form a protein–protein interaction with p53 proteins. Conclusion This information strongly positions MDM2-C as a protein with biochemical activities that may explain the varied outcomes observed in patients with high-level expression of MDM2-C in the presence of wild-type p53 versus mutant p53.

circNUDT21 promotes bladder cancer progression by modulating the miR-16-1-3p/MDM2/p53 axis

“…As the T24 cell line contains the mutant p53, while the EJ cell line expresses the wild-type p53, the results suggested that circNUDT21 may exert its oncogenic function through the MDM2-p53 pathway in bladder cancer, regardless of the p53 mutation status. Our finding is supported by Kim and colleagues, 30 who found that MDM2-C has E3 auto-ubiquitin ligase activity, which can promote the ubiquitination of both wild-type and mutant p53.…”

Angiotensin-Converting Enzyme 2 Posttranslational Modifications and Implications for Hypertension and SARS-CoV-2: 2023 Lewis K. Dahl Memorial Lecture

“…91 MDM2 is highly expressed in various types of cancer with specific isoforms such as MDM2-C being present in breast cancer and liposarcoma tissue and cell lines. 90 Expression of MDM2 is also increased in lung tissue of patients with idiopathic pulmonary arterial hypertension and mice with induced pulmonary hypertension. 72 This upregulation of MDM2 is associated with a downregulation in ACE2 levels in lung tissues and the mechanism seems to involve binding to ACE2 at lysine site K788.…”

“…87,88 One mechanism by which MDM2 dampens p53 levels is through the ubiquitin-proteasome system. 89 MDM2 is composed of 491 amino acids 90 and the RING domain at the C terminus is the region that performs the E3 ligase functions. 91 MDM2 is highly expressed in various types of cancer with specific isoforms such as MDM2-C being present in breast cancer and liposarcoma tissue and cell lines.…”

Regulation of p53 by E3s

“…Of note, despite the increase in p53 ubiquitination, heterodimers of MDM2-B and full-length MDM2 even increased p53 activity [ 99 , 100 ]. More recently, it was found that MDM2-C also has E3 activity and ubiquitinates wild-type and mutated (R273H) p53 [ 101 ]. However, it was not determined whether this ubiquitination of p53 by MDM-C leads to p53 degradation.…”