Inhibition of IFN-β-Induced Nitric Oxide Dependent Antimycobacterial Activity by miR-155 and C/EBPβ

miR-155 (microRNA-155) is an important non-coding RNA in regulating host crucial biological regulators. However, its regulatory function in mycobacterium infection remains unclear. Our study demonstrates that miR-155 expression is significantly increased in macrophages after Mycobacterium marinum (M. m) infection. Transfection with anti-miR-155 enhances nitric oxide (NO) synthesis and decreases the mycobacterium burden, and vice versa, in interferon gamma (IFN-gamma) activated macrophages. More importantly, miR-155 can directly bind to the 3'UTR of CCAAT/enhancer binding protein beta (C/EBP beta), a positive transcriptional regulator of nitric oxide synthase (NOS2), and regulate C/EBP beta expression negatively. Knockdown of C/EBP beta inhibit the production of nitric oxide synthase and promoted mycobacterium survival. Collectively, these data suggest that M. m-induced upregulation of miR-155 downregulated the expression of C/EBP beta, thus decreasing the production of NO and promoting mycobacterium survival, which may provide an insight into the function of miRNA in subverting the host innate immune response by using mycobacterium for its own profit. Understanding how miRNAs partly regulate microbicidal mechanisms may represent an attractive way to control tuberculosis infectious.