Targeting MAN1B1 potently enhances bladder cancer antitumor immunity via deglycosylation of CD47

Abstract

Background: Only a few bladder cancer patients benefit from anti-programmed cell death protein 1/programmed cell death ligand 1 immunotherapy. The cluster of differentiation 47 (CD47) plays an important role in tumor immune evasion. CD47 is a highly glycosylated protein, however, the mechanisms governing CD47 glycosylation and its potential role in immunosuppression are unclear. Therefore, this study aimed to evaluate the function of CD47 glycosylation in bladder cancer.

Methods: Western blotting, immunohistochemistry, and flow cytometry were used to measure protein expression, protein-protein interactions, and phagocytosis in bladder cancer. A murine model was employed to investigate the impact of mannosidase alpha class 1B member 1 (MAN1B1) modification of CD47 on anti-phagocytosis in vivo. An ex vivo model, patient-derived tumor-like cell clusters, was used to examine the effect of targeting MAN1B1 on phagocytosis.

Results: Our research identified that aberrant CD47 glycosylation was responsible for its immunosuppression. The glycosyltransferase MAN1B1 responsible for CD47 glycosylation was highly expressed in bladder cancer. Abnormal activation of extracellular signal-regulated kinase (ERK) was significantly associated with MAN1B1 stability by regulating the interaction between MAN1B1 and the E3 ubiquitin ligase HMG-CoA reductase degradation 1 (HRD1). Mechanistically, abnormally activated ERK stabilized MAN1B1, resulting in the glycosylation of CD47 and facilitating immune evasion by enhancing its interaction with signal-regulatory protein alpha (SIRP-α). In vitro and in vivo experiments demonstrated that MAN1B1 knockout weakened CD47-mediated anti-phagocytosis. MAN1B1 inhibitors promoted phagocytosis without causing anemia, offering a safe alternative to anti-CD47 therapy.

Conclusions: This comprehensive analysis uncovered that ERK activation stabilizes MAN1B1 by regulating the interaction between MAN1B1 and HRD1, facilitates immune evasion via CD47 glycosylation, and presents new potential targets and strategies for cancer immunotherapy that do not cause anemia.

Keywords: Bladder cancer; HMG‐CoA reductase degradation 1; cluster of differentiation 47; extracellular signal‐regulated kinase; immunotherapy; macrophage; mannosidase alpha class 1B member 1; phagocytosis.