SREBP2-RAB11A-ZDHHC20 axis orchestrates FGFR3 palmitoylation and membrane retention to drive bladder cancer progression

Non-muscle-invasive bladder cancer (NMIBC) accounts for approximately 75% of all bladder cancer cases and is characterized by a high recurrence rate, requiring long-term surveillance and repeated treatments that impose substantial clinical burdens. While aberrant fibroblast growth factor receptor 3 (FGFR3) signaling is a well-established driver in the majority of NMIBC cases, the precise molecular mechanisms regulating FGFR3 plasma membrane stability and trafficking remain poorly defined, limiting targeted therapeutic development. This study aims to elucidate the molecular pathway sustaining FGFR3 at the plasma membrane and its clinical relevance. RAB11A expression was analyzed in NMIBC datasets and correlated with survival. In FGFR3-high RT4 cells, RAB11A was knocked down to assess effects on proliferation, apoptosis, and FGFR3 membrane localization via functional assays and immunoblotting. Mechanistic interactions were examined through co-immunoprecipitation and promoter-reporter assays. A phase-separation-defective SREBP2 mutant (F178A) was used to validate transcriptional activation. In vivo tumor growth and FGFR3 membrane localization were evaluated in xenograft models following RAB11A or ZDHHC20 knockdown. Statistical analyses included Student’s t-test and log-rank test. RAB11A was significantly up-regulated in NMIBC, correlated with FGFR3 mRNA expression, and predicted poorer recurrence-free survival. RAB11A knockdown suppressed proliferation, induced apoptosis, and reduced membrane FGFR3 without altering transcript levels. RAB11A acted as a scaffold recruiting ZDHHC20 to promote FGFR3 palmitoylation and inhibit FGFR3 degradation. SREBP2 directly activated RAB11A transcription, dependent on its liquid–liquid phase separation capability. In vivo, knockdown of RAB11A or ZDHHC20 attenuated tumor growth and reduced membrane FGFR3. We identify a novel SREBP2-RAB11A-ZDHHC20 axis essential for FGFR3 palmitoylation, membrane retention, and oncogenic signaling in NMIBC. Targeting this pathway may offer a therapeutic strategy for FGFR3-driven bladder cancer.