Epithelial deletion of CUL4B increased myeloid-derived suppressor cells-mediated immunosuppression to promote ApcMin/+ tumor formation

Cullin 4B (CUL4B) is a scaffold protein of E3 ubiquitin ligase complex and has been found frequently overexpressed in various types of cancer. By repressing tumor suppressors, CUL4B is indicated as pro-oncogenic gene in oncogenesis. Reversely, recent studies reveal that deletion of CUL4B in hematopoietic system exerts tumor suppressive effect in tumor bearing hosts. However, the role of CUL4B in tumor initiation remains unknown. Here we report that CUL4B deficiency in the intestinal epithelium accelerates ApcMin/+ tumor formation. CUL4B in cancer cells restricts the accumulation of tumor-infiltrating CD11b+Gr-1+ MDSCs to prohibit the adenoma permissive microenvironment and thus increases the number of antitumor CD8+ T cells. Addition of MDSCs to ex vivo cultured ApcMin/+; Cul4bΔIEC tumor organoids rescues their phenotypic alteration in stemness, suggesting a reciprocally strengthened immunosuppressive effect between CUL4B deficient tumor cells and MDSCs. Mechanistically, inhibiting CUL4B epigenetically activates the expression of secreted chemokines and proteins including G-CSF to enroll MDSCs. Our findings suggest that epithelial deletion of CUL4B creates a tumor-prone microenvironment during ApcMin/+ tumor formation and provide a potential strategy to overcome colon cancer initiation and progress in the Wnt-disturbed context.