MiR-155 is overexpressed in patients with atopic dermatitis and modulates T-cell proliferative responses by targeting cytotoxic T lymphocyte–associated antigen 4.

Background: MicroRNAs (miRNAs) are short noncoding RNAs that suppress gene expression at the posttranscriptional level. Atopic dermatitis is a common chronic inflammatory skin disease characterized by the presence of activated T cells within the skin. Objective: We sought to explore the role of miRNAs in the pathogenesis of atopic dermatitis. Methods: Global miRNA expression in healthy and lesional skin of patients with atopic dermatitis was compared by using TaqMan MicroRNA Low Density Arrays. miR-155 expression in tissues and cells was quantified by means of quantitative real-time PCR. The cellular localization of miR-155 was analyzed by means of in situ hybridization. The regulation of cytotoxic T lymphocyte–associated antigen (CTLA-4) by miR-155 was investigated by using luciferase reporter assays and flow cytometry. CTLA-4 expression and functional assays were performed on T_H cells overexpressing miR-155. Results: miR-155 was one of the highest-ranked upregulated miRNAs in patients with atopic dermatitis. In the skin miR-155 was predominantly expressed in infiltrating immune cells. miR-155 was upregulated during T-cell differentiation/activation and was markedly induced by T-cell activators in PBMCs in vitro and by superantigens and allergens in the skin in vivo. CTLA-4, an important negative regulator of T-cell activation, was identified as a direct target of miR-155. Overexpression of miR-155 in T_H cells resulted in decreased CTLA-4 levels accompanied by an increased proliferative response. Conclusion: miR-155 is significantly overexpressed in patients with atopic dermatitis and might contribute to chronic skin inflammation by increasing the proliferative response of T_H cells through the downregulation of CTLA-4. [Copyright &y& Elsevier]