Identification of microRNA-31 as a novel regulator contributing to impaired IL-2 production in T cells from patients with systemic lupus erythematosus.
ABSTRACT OBJECTIVE.: MicroRNAs (miRNAs) function to fine-tune the control of immune cell signaling. It is well established that there are abnormalities in the interleukin-2 (IL-2)-related signaling pathways in lupus. miR-31 has been identified as being markedly under-expressed in lupus patients. Here, we investigated the role of miR-31 in IL-2 defect in lupus patients. METHODS.: miR-31 expression levels were quantitated using TaqMan miRNA assays. Transfection and stimulation of cultured cells followed by TaqMan quantitative PCR, ELISA and reporter gene assays were conducted to determine the biological function of miR-31. NF-AT nuclear translocation and expression were quantitatively measured using ImageStream cytometer. Bioinformatic analysis, siRNA knockdown and western blotting were performed to validate miR-31 targets and effects. RESULTS.: miR-31 expression was significantly decreased and positively correlated with IL-2 expression in lupus T cells. Over-expression of miR-31 in T cells increased IL-2 production by altering nuclear NF-AT expression and IL-2 promoter activity, while knockdown of endogenous miR-31 reduced it. RhoA was directly repressed by miR-31 in T cells. Of note, small interfering RNA-mediated knockdown of RhoA enhanced IL-2 promoter activity and consequently up-regulated IL-2 production. Consistently, RhoA expression was up-regulated and was negatively correlated with miR-31 levels in lupus T cells. Importantly, manipulation of miR-31 expression in lupus T cells restored IL-2 expression at both the mRNA and protein levels. CONCLUSION.: miR-31 is a novel enhancer of IL-2 production during T cell activation. Dysregulation of miR-31 and its target RhoA could be a novel molecular mechanism underlying the IL-2 deficiency in lupus patients.