IFN-γ downregulates miR-4319 to enhance NLRC5 and MHC-I expression in MHC-I-deficient breast cancer cells.

Sufficient MHC-I expression on cancer cells is essential for the recognition and killing of cancer cells by immune effector cytotoxic T-lymphocyte (CTL). An important mechanism of cancer immune escape is loss or down-regulation of MHC-I. This is frequently associated with reduced expression of NOD-like receptor (NLR) caspase recruitment domain containing protein 5 (NLRC5), genetically and epigenetically. NLRC5, a regulator of MHC-I, has been identified as a potential target of miR-4319 due to its complementary binding site for miR-4319, according to prediction by TargetScan (http://www.targetscan.org/). Inhibition of miR-4319 by IFN-γ (known as MHC-I increasing agent) to upregulate NLRC5 with upregulation of MHC-I in MHC-I-deficient breast cancer cells, however, remains unclear. After treatment with IFN-γ, miR-4319 was detected with qRT-PCR; NLRC5 protein was detected with western-blot; and MHC-I mRNA and protein were detected with qRT-PCR and western-blot, respectively. It was found statistically that miR-4319 was lower and NLRC5 protein was higher in groups of 50 U/ml and 100 U/ml IFN-γ, and MHC-I mRNA and protein were higher in all groups of different concentrations of IFN-γ, except for HLA-A protein in 25 U/ml IFN-γ group, with dose dependent tendency, compared with the control group. IFN-γ inhibits miR-4319 and upregulates NLRC5, thereby enhancing expression of MHC-I in SKBR3 breast cancer cells, while limitations include the absence of functional rescue experiments and in vivo validation. Along with direct cytotoxicity on tumor cells, IFN-γ's immunomodulatory effect strengthens tumor immunogenicity, counteracts immune evasion mechanisms, and potentially improves the efficacy of cancer immunotherapy.