IL-22-induced miR-122-5p promotes keratinocyte proliferation by targeting Sprouty2

Psoriasis is a common inflammatory skin disease, but the exact pathogenesis is largely unknown. Interleukin-22 (IL-22) has demonstrated its vital role in T-cell-mediated immune response by interacting with keratinocytes in the pathogenesis of psoriasis. Here, we showed the differentially expressed miRNAs and their potential targets in HaCaT cells stimulated by IL-22 using miRNA and mRNA microarrays. We revealed a total of 20 significantly changed (more than twofold) miRNAs in HaCaT cells and validated the results with quantitative reverse transcriptase PCR (qRT-PCR). We demonstrated that miR-122-5p was up-regulated both in HaCaT cells stimulated by IL-22 and in psoriatic lesions. Then, we aimed to investigate the biological roles and potential mechanism of miR-122-5p in keratinocytes. As a result, CCK-8 assay indicated that overexpression of miR-122-5p in keratinocytes promoted proliferation and conversely inhibition of endogenous miR-122-5p suppressed proliferation. According to the microarray analysis, we assumed that Sprouty2 (Spry2), a negative regulator of extracellular signal regulated kinase/mitogen-activated protein kinase signalling pathway, was a direct target gene of miR-122-5p. We found that the staining of Spry2 in cytoplasm was mainly localized in both basal and suprabasal layers of epidermis and showed a markedly decreased expression in psoriasis than in normal control by immunohistochemistry. Luciferase reporter and Western blot assays in HaCaT cells demonstrated that Spry2 was a direct target gene of miR-122-5p. In conclusion, IL-22-induced miR-122-5p promotes keratinocyte proliferation possibly by downregulating the expression of Spry2 thus playing important roles in the pathogenesis of psoriasis.