Knockdown of circZMIZ1 enhances the anti-tumor activity of CD8+ T cells to alleviate hepatocellular carcinoma.

ABSTRACT

ZMIZ1 acts as an oncogene in hepatocellular carcinoma (HCC). circZMIZ1 (hsa_circ_0018964) derives from ZMIZ1; its underlying mechanism in HCC has not been reported. Peripheral blood and peripheral blood mononuclear cells (PBMCs) were obtained from HCC patients and healthy volunteers. CD8+ T cells were sorted from PBMCs of HCC patients. Applying flow cytometry, cell apoptosis and the proportion of KCNJ2/CD8+ T cells were examined. The cytotoxicity of CD8+ T cells against HCC cells was evaluated. The interaction among circZMIZ1, miR-15a-5p, and KCNJ2 was investigated by dual luciferase assay, RNA immunoprecipitation, and RNA pull-down assay. An orthotopic mouse model of HCC was constructed by intrahepatic injection of H22 cells. Upregulation of circZMIZ1 and KCNJ2 and downregulation of miR-15a-5p were observed in peripheral blood and PBMCs of HCC patients. The proportion of KCNJ2/CD8+ T cells was also increased in HCC patients. circZMIZ1 knockdown restrained apoptosis of CD8+ T cells and elevated cytotoxicity of CD8+ T cells. Mechanically speaking, circZMIZ1 elevated KCNJ2 expression by sponging miR-15a-5p. miR-15a-5p inhibitor reversed circZMIZ1 silencing-mediated inhibition of apoptosis and promotion of cytotoxicity in CD8+ T cells. In vivo, orthotopic mice of HCC exhibited increased expression of circZMIZ1 and KCNJ2, elevated proportion of KCNJ2/CD8+ T cells, and decreased expression of miR-15a-5p. This work demonstrated that circZMIZ1 inhibited the anti-tumor activity of CD8+ T cells in HCC by regulating the miR-15a-5p/KCNJ2 axis. This provides a theoretical basis for the development of effective circZMIZ1 in tumor immunotherapy.