Ubiquitylation of p53 by the APC/C inhibitor Trim39

Area of Science:

• Molecular Biology
• Cell Biology
• Oncology

Background:

• Tripartite motif 39 (Trim39) is an E3 ubiquitin ligase that can inhibit the anaphase-promoting complex (APC/C).
• The tumor suppressor protein p53 plays a critical role in cell cycle control and apoptosis.
• Murine double minute 2 (MDM2) is a well-characterized E3 ligase targeting p53 for degradation.

Purpose of the Study:

• To investigate the role of Trim39 in cell cycle regulation and apoptosis, particularly in relation to p53.
• To determine if Trim39 directly interacts with and degrades p53.
• To evaluate Trim39 as a potential therapeutic target in cancer.

Main Methods:

• Analysis of Trim39 function in p53-positive and p53-negative cell lines.
• Assessment of cell cycle progression and etoposide-induced apoptosis.
• In vitro and in vivo ubiquitylation and degradation assays for p53.
• Evaluation of Trim39 and MDM2 roles in different cell types.
• Assessment of apoptosis induction by Trim39 knockdown in cells treated with an MDM2 inhibitor (nutlin-3a).

Main Results:

• Trim39 depletion inhibited G1/S transition in p53-positive cells, independent of APC/C.
• Trim39 loss enhanced etoposide-induced apoptosis in p53-positive cells but inhibited it in p53-negative cells.
• Trim39 directly binds and ubiquitylates p53, leading to its degradation.
• Depletion of Trim39 increased p53 protein levels and caused cell growth retardation.
• Trim39 knockdown enhanced apoptosis in cells resistant to MDM2 inhibition.

Conclusions:

• Trim39 directly targets p53 for degradation, influencing cell cycle and apoptosis.
• The functional significance of Trim39 versus MDM2 in p53 regulation varies by cell type.
• Trim39 represents a potential therapeutic target for cancers with wild-type p53, especially when MDM2-targeted therapies are insufficient.