Hyperactivation of β-catenin signal in hepatocellular carcinoma recruits myeloid-derived suppressor cells through PF4-CXCR3 axis.

The high mutation rate of CTNNB1 (37 %) and Wnt-β-catenin signal-associated genes (54 %) has been notified in hepatocellular carcinoma (HCC). The activation of Wnt-β-catenin signal pathway was reported to be associated with an immune "desert" phenotype, but the underlying mechanism remains unclear. Here we mainly employed orthotopic HCC models to explore on it. Mass cytometry depicted the immune contexture of orthotopic HCC syngeneic grafts, unveiling that the exogenous expression of β-catenin significantly increased the percentage of myeloid-derived suppressor cells (MDSCs) and decreased the percentage of CD8+ T-cells. Flow cytometry and immunohistochemistry further confirmed the findings. The protein microarray analysis, Western blot and PCR identified PF4 as its downstream regulating cytokine. Intratumorally injection of cytokine PF4 enhanced the accumulation of MDSCs. Knockout of PF4 abolished the effect of β-catenin on recruiting MDSCs. Chromatin immunoprecipitation and luciferase reporter assay demonstrated that β-catenin increases the mRNA level of PF4 via binding to PF4's promoter region. In vitro chemotaxis assay and in vivo administration of specific inhibitors identified CXCR3 on MDSCs as receptor for recruiting PF4. Lastly, the significant correlations across β-catenin, PF4 and MDSCs and CD8+ T-cells infiltration were verified in HCC clinical samples. Our results unveiled HCC tumor cell intrinsic hyperactivation of β-catenin can recruit MDSC through PF4-CXCR3, which contributes to the formation of immune "desert" phenotype. Our study provided new insights into the development of immunotherapeutic strategy of HCC with CTNNB1 mutation. SIGNIFICANCE: This study identifies PF4-CXCR3-MDSCs as a downstream mechanism underlying CTNNB1 mutation associated immune "desert" phenotype.