A role for TRIP12 in regulating the E3 ligase network under proteotoxic stress

Cellular proteostasis relies on the coordinated action of molecular chaperones and protein degradation pathways to maintain protein folding and turnover. While the roles of chaperones and the proteasome are well established, how ubiquitin E3 ligases contribute to the proteostasis network remains incompletely understood. Here, we analyzed proteostasis in melanoma cells using quantitative proteomics under mild protein folding stress induced by HSP90 and proteasome inhibition. We identified the HECT-type E3 ligase TRIP12 as a proteostasis-responsive factor that was upregulated upon proteasome inhibition. Depletion of TRIP12 led to protein accumulation of a distinct group of epigenetic and transcriptional regulators, suggesting that these proteins may constitute a novel class of TRIP12 targets. Notably, the loss of TRIP12 led to a widespread reduction in the abundance of many other proteins, including components of the proteostasis network, particularly ubiquitin E3 ligases. These changes occurred largely without corresponding mRNA alterations, indicating post-transcriptional regulation. HSP90 inhibition similarly reduced protein abundance and acted in an additive manner with TRIP12 depletion to further destabilize the proteome. Together, our findings suggest that TRIP12 functions as a regulator of the E3 ligase network and proteostasis capacity, and that its loss, particularly under folding stress, causes a reduction of global protein content. These results reveal an unexpected role for TRIP12 in maintaining proteome stability and support the functional interplay between ubiquitin ligases and molecular chaperones in buffering proteotoxic stress.