Activation of MAL2 by RAD21 inhibits the expression of MHC-I in immune evasion of endometrial cancer.

CD8(+) T cells are the primary mediators of anticancer immunity, and modulation of the CD8(+) T cell response has been a central focus of immunotherapy to treat cancer. When CD8(+) T cells specifically recognize antigenic peptides presented by the MHC-I on tumor cells, they become activated and kill the tumor cells. However, one pivotal mechanism through which tumor cells evade immune surveillance is to reduce their antigen presentation. To identify novel immunotherapeutic targets, we specifically focused on the role of MAL2 in immune evasion in endometrial cancer (EC) and the underlying mechanism. MAL2 was overexpressed in EC tissues and cells and its transcription was enhanced by RAD21. Knockdown of MAL2 or RAD21 inhibited malignant behavior and immune evasion of EC cells by repressing MHC-I expression and the cytotoxic effects of CD8(+) cells. Conversely, MAL2 promoted immune evasion of EC cells and tumor growth in mice in the presence of RAD21 knockdown. These results indicate that RAD21 activation of MAL2 inhibits antigen processing and presentation of MHC-I, thereby inducing immune evasion of EC cells. We further suggest that RAD21 and MAL2 may serve as novel targets for EC immunotherapy.