BACE2 Promotes Bladder Cancer Chemoresistance Through Proteolytic Activation of JAG1‐Notch Signaling

Abstract

ABSTRACT Background Chemoresistance to platinum‐based regimens, primarily gemcitabine plus cisplatin, remains a major obstacle in the treatment of advanced bladder cancer. Identifying the underlying molecular mechanisms is critical for developing effective therapeutic strategies to improve clinical outcomes. Methods Integrative analysis of transcriptomic profiles from chemoresistant bladder cancer models and clinical data sets from The Cancer Genome Atlas was performed to identify candidate resistance drivers. The biological function of the candidate gene was evaluated in vitro using bladder cancer cell lines. Mechanistic investigations, including transcriptomic analyses and immunoprecipitation, were conducted to elucidate downstream signaling. The therapeutic potential of targeting this axis was assessed in vitro and in an in vivo xenograft model using a small‐molecule inhibitor combined with chemotherapy. Results We identified β‐secretase 2 (BACE2) as a candidate mediator of cisplatin resistance. BACE2 is significantly upregulated in gemcitabine‐ and cisplatin‐resistant models, including patient‐derived organoids. Its elevated baseline expression correlates with advanced pathologic stage, poor prognosis, and diminished clinical benefit from platinum‐based therapy. Functionally, BACE2 promotes resistance to both gemcitabine and cisplatin. Mechanistically, BACE2 interacts with Jagged1 (JAG1) and promotes the generation of a soluble JAG1 fragment in a catalytic activity‐dependent manner. Mutation of the catalytic Asp303 residue markedly reduced JAG1 fragment generation and restored gemcitabine sensitivity, supporting a functional requirement for BACE2 enzymatic activity in this process. This fragment is associated with Notch signaling activation through autocrine and paracrine mechanisms, which concomitantly induces endogenous JAG1 expression, establishing a positive feedback loop that sustains chemoresistance. Pharmacologic inhibition of β‐secretase activity with verubecestat disrupted JAG1 cleavage, reduced downstream Notch signaling and enhanced chemotherapy efficacy in vitro without inducing apparent cytotoxicity alone. Furthermore, combination treatment with verubecestat and gemcitabine produced stronger tumor growth inhibition than either monotherapy in vivo. Conclusions These results define a novel BACE2‐JAG1‐Notch signaling axis that contributes to bladder cancer chemoresistance. Importantly, our findings identify BACE2 as a potential prognostic biomarker and a therapeutically actionable target to improve clinical outcomes in this disease.