Chemical proteomic identification of STUB1 as a direct target of benzophenone-3 reveals disrupted NRF2 signaling in chondrocytes.

Osteoarthritis (OA) is a common age-related degenerative joint disease, and emerging evidence implicates environmental chemical exposures as potential contributors. Benzophenone-3 (BP-3), a widely used ultraviolet filter frequently detected in human biospecimens, has been associated with increased OA risk, yet its direct molecular targets and mechanisms of cartilage toxicity remain unclear. Here, we applied an alkyne-tagged BP-3 probe combined with click chemistry-enabled chemical proteomics (SILAC-ABPP), transcriptomics, network toxicology, and experimental validation to investigate the molecular mechanisms underlying BP-3-induced cartilage toxicity. SILAC-ABPP identified the E3 ubiquitin ligase STUB1 as a direct cellular target of BP-3, which was further supported by cellular thermal shift assays and LC-MS/MS analysis. BP-3 exposure significantly increased STUB1 expression both in vivo and in vitro. Network toxicology and transcriptomic integration further implicated NRF2 in the STUB1-associated response to BP-3. BP-3-induced suppression of NRF2 was substantially attenuated by STUB1 knockdown, supporting a functional relationship between STUB1 and NRF2 in the cellular response to BP-3. STUB1 knockdown also attenuated BP-3-induced extracellular matrix disruption and ferroptosis-associated alterations, whereas NRF2 deficiency further aggravated these stress responses in chondrocytes. Chronic BP-3 exposure in mice recapitulated key pathological changes, including increased MMP13 expression, loss of collagen II, and altered ferroptosis-associated markers in articular cartilage. Collectively, these findings identify STUB1 as a direct molecular target of BP-3 and implicate STUB1-associated disruption of NRF2-dependent antioxidant responses in BP-3-induced cartilage toxicity.