Inflammatory cytokines regulate microRNA-155 expression in human retinal pigment epithelial cells by activating JAK/STAT pathway

► Combination of IFN-γ, TNF-α and IL-1β increased microRNA-155 expression in human retinal pigment epithelial cells. ► Two putative STAT1 binding elements are present in the MIR155 gene promoter region. ► Increase in miR-155 expression was associated with increase in STAT1 activation. ► Increase in miR-155 expression was associated with increase in protein binding to putative STAT1 binding elements. ► Increases in miR-155 expression, STAT1 activation and protein binding were blocked by JAK inhibitor 1. Inflammatory response of the retinal pigment epithelium plays a critical role in the pathogenesis of retinal degenerative diseases such as age-related macular degeneration. Our previous studies have shown that human retinal pigment epithelial (HRPE) cells, established from adult donor eyes, respond to inflammatory cytokines by enhancing the expression of a number of cytokines and chemokines. To investigate the role of microRNA (miRNA) in regulating this response, we performed microarray analysis of miRNA expression in HRPE cells exposed to inflammatory cytokine mix (IFN-γ + TNF-α + IL-1β). Microarray analysis revealed ∼11-fold increase in miR-155 expression, which was validated by real-time PCR analysis. The miR-155 expression was enhanced when the cells were treated individually with IFN-γ, TNF-α or IL-1β, but combinations of the cytokines exaggerated the effect. The increase in miR-155 expression by the inflammatory cytokines was associated with an increase in STAT1 activation as well as an increase in protein binding to putative STAT1 binding elements present in the MIR155 gene promoter region. All these activities were effectively blocked by JAK inhibitor 1. Our results show that the inflammatory cytokines increase miR-155 expression in human retinal pigment epithelial cells by activating the JAK/STAT signaling pathway.