TRIM28 orchestrates SUMO-ubiquitin crosstalk to stabilize PPARG and drive bladder cancer progression
Bladder cancer (BLCA) is a growing health burden with rising incidence and limited therapeutic options. To define the role of the Tripartite Motif (TRIM) family in BLCA, we integrated multi-cohort transcriptomic analyses with functional and mechanistic validation. TRIM28 was identified as the most consistently upregulated TRIM member in BLCA and correlated with poor prognosis. TRIM28 depletion suppressed, whereas its overexpression enhanced, BLCA cell proliferation. Mechanistically, TRIM28 directly bound to PPARG and acted as a SUMO E3 ligase to catalyze SUMOylation of PPARG at Lys94 within a noncanonical YKYD motif. This modification impaired PPARG recognition by the E3 ubiquitin ligase STUB1, reduced ubiquitin–proteasome degradation, and stabilized PPARG protein. Stabilized PPARG transcriptionally activated cholesterol biosynthetic genes, including DHCR7 and DHCR24, reprogramming cholesterol metabolism to promote BLCA progression. In summary, we identify a TRIM28-PPARG SUMO-ubiquitin crosstalk axis that drives metabolic remodeling and tumor growth in BLCA, highlighting TRIM28-mediated PPARG SUMOylation as a potential therapeutic target for metabolic intervention. Overall design: Bladder cancer cells were transfected with TRIM28-targeting siRNA (siTRIM28) or a non-targeting negative control siRNA (siNC). Total RNA was extracted after knockdown and subjected to RNA-seq to profile transcriptome-wide changes induced by TRIM28 depletion. Differential gene expression analysis was performed by comparing siTRIM28 versus siNC samples, followed by pathway/gene set enrichment analyses to identify TRIM28-regulated biological processes (with emphasis on metabolic pathways such as cholesterol biosynthesis).