CD47 destabilization via manipulating the SPOP-USP2 axis augments macrophage phagocytosis and cancer immunotherapy.

[BACKGROUND] Macrophages can eliminate cancer cells through phagocytosis via the CD47/signal regulatory protein α axis, which provides promising targets for cancer immunotherapy as innate immune checkpoints. Although CD47 is overexpressed in multiple cancer types, it remains largely unknown whether and how CD47 can be targeted by manipulating its protein stability.

[EXPERIMENTAL DESIGN] Multiple human cancer cell lines were used to identify the function of the ubiquitin-specific protease 2 (USP2) /speckle-type POZ protein (SPOP) axis and the USP2 inhibitor on CD47 protein stability by immunoblot and immunoprecipitation, real-time quantitative PCR, in vitro deubiquitination assay, cell fractionation assay, flow cytometry, and phagocytosis assay. We investigated the antitumor immune response and immunotherapy effects of the USP2 inhibitor using multiple syngeneic and orthotopic mouse tumor models, bioluminescence imaging, immune cell depletion, tumor-infiltrating lymphocyte (TIL) isolation, and flow cytometry.

[RESULTS] Here, we report that ML364, an inhibitor of the USP2 deubiquitinase, reduces the protein abundance of CD47. Mechanistically, USP2 deubiquitinates and protects CD47 from proteasome-mediated degradation. Furthermore, we reveal that USP2 itself can be ubiquitinated by the SPOP ubiquitin E3 ligase, which leads to USP2 degradation and decreased CD47 protein abundance. Functionally, ML364 promotes macrophage phagocytosis of cancer cells by reducing the expression of CD47 and enhances the efficacy of anti-programmed cell death protein-1 (PD-1) immunotherapy, thereby inhibiting tumor growth and improving the overall survival rate in multiple syngeneic and orthotopic mouse tumor models. Bioinformatic analyses indicate that low USP2 expression or high SPOP expression predicts a better response to anti-PD-1 treatment.

[CONCLUSION] Hence, our findings reveal a pivotal role of the SPOP/USP2 axis in regulating CD47 protein stability and advocate for combining USP2 inhibitors with anti-PD-1 immunotherapy to combat cancer.