MIIP downregulates PD-L1 expression through HDAC6 in cutaneous melanoma

Abstract Purpose Immune checkpoint inhibitors have improved the objective response rate and survival of melanoma patients. However, there are still many melanoma patients suffering from disease progression due to primary or secondary immune checkpoint inhibitor resistance, as is observed in the failure of anti-PD1/PD-L1 therapy. While the expression of valuable markers, such as TMB, MSI, and PD-L1, could serve as effective predictors of anti-checkpoint inhibitor therapies, tumor cell PD-L1 expression and its regulating mechanism would significantly affect the anti-PD-1 immunotherapy response and efficacy. Therefore, it is urgent to determine the function of PD-1/PD-L1 expression in melanoma and its associated pathways to enhance the efficacy of anti-PD-1 therapies. Methods A cohort of 133 patients with histologically confirmed melanoma from Tianjin Medical University Cancer Institute & Hospital were included in this study. We performed immunohistochemical staining to detect the expression of Migration and invasion inhibitory protein (MIIP), HDAC6 and PD-L1. Kaplan–Meier and log-rank test were used for survival analysis. As for vitro, Western blot was used in melanoma cell lines to verify the signaling pathway that MIIP regulates PD-L1 expression. Results MIIP expression was decreased in melanoma and that the negative expression of MIIP was correlated with worse overall survival. The positive expression of HDAC6, a molecule that is downstream of MIIP, had a positive trend with decreased overall survival. At the same time, the positive expression of PD-L1, a crucial costimulatory molecule, was associated with decreased overall survival. Furthermore, there was a positive association between HDAC6 and PD-L1 protein expression (p  Conclusions Our findings highlight the immunomodulatory effects of MIIP in the inhibition of PD-L1 expression by downregulating HDAC6 in melanoma. Methods for targeting MIIP-HDAC6-PD-L1 pathways might be new therapeutic approaches for enhancing immune checkpoint inhibitor therapies in melanoma.