ANKRD22 is a potential novel target for reversing the immunosuppressive effects of PMN-MDSCs in ovarian cancer

BACKGROUND: Ovarian cancer is the deadliest type of malignant gynecological tumor. Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are involved ovarian cancer and are closely related to adverse outcomes. However, the immunosuppressive mechanism of PMN-MDSCs remains elusive. METHODS: The types and numbers of ANKRD22-expressing cells were investigated by bioinformatics analysis and immunohistochemical staining. Ankrd22(-/-) C57BL/6 mice were constructed with CRISPR-Cas9 technology. Mouse PMN-MDSCs were obtained from bone marrow (BM)-derived CD11b(+)Ly6G(+)Ly6C(low) cells sorted by fluorescence-activated cell sorting with treatment of GM-CSF and IL-6, and the immunosuppressive activity of PMN-MDSCs was evaluated by flow cytometry (FCM) and ELISA. The expression level of CCR2 and the exogenous glucose uptake capacity were determined by FCM. RT-qPCR was used to detect ANKRD22 expression in CD11b(+)HLA-DR(-)CD14(-)CD15(+) cells from human ovarian cancer tissues, and the correlations of ANKRD22 expression with the clinical characteristics and prognosis of patients were evaluated by the χ(2) test. RESULTS: We identified a novel protein involved in regulating the immunosuppressive ability of PMN-MDSCs, ANKRD22. Ankrd22 expression was high in mouse CD11b(+)Ly6G(+)Ly6C(low) cells and could be significantly downregulated after exposure to a simulated microenvironmental stimulus. Knockout of Ankrd22 increased the expression level of CCR2 of CD11b(+)Ly6G(+)Ly6C(low) cells and the immunosuppressive activity of PMN-MDSCs. BM-derived CD11b(+)Ly6G(+)Ly6C(low) cells of Ankrd22(-/-) mice significantly promoted the proliferation of ovarian cancer cells in tumor xenograft mouse models. Mechanistically, RNA sequencing showed that Wdfy1 expression was obviously increased in Ankrd22-knockout BM-derived CD11b(+)Ly6G(+) Ly6C(low) cells and that ectopic expression of Wdfy1 increased the levels of Arg1, Inos, Ido and Pdl1 in Ankrd22(+/+) PMN-MDSCs derived from BM-derived CD11b(+)Ly6G(+)Ly6C(low) cells. Surprisingly, an ANKRD22-activating candidate small-molecule compound attenuated the immunosuppressive activity of Ankrd22(+/+) PMN-MDSCs. Finally, we found that low ANKRD22 levels in CD11b(+)HLA-DR(-)CD14(-)CD15(+) cells derived from primary ovarian tissues were associated with a more advanced International Federation of Gynecology and Obstetrics stage, a higher recurrence rate, and a higher neutrophil-to-lymphocyte ratio. CONCLUSIONS: These results suggest that ANKRD22 is a potential novel target for reversing the immunosuppressive effects of PMN-MDSCs.