miR-4516, a microRNA downregulated in psoriasis inhibits keratinocyte motility by targeting fibronectin/integrin α9 signaling.

Psoriasis is recognized as a T cell mediated inflammatory hyperproliferative skin disorder. Several microRNAs (miRNAs) have been implicated in the pathogenesis of psoriasis however, understanding of their mechanistic involvement remains unclear. Previously, we have shown that PUVA induced miR-4516 downregulates signal transducer and activator of transcription 3 (STAT3) by direct binding to its 3' untranslated region (3'UTR) and suppresses STAT3 downstream genes (Bcl xl, Cyclin D1). Here, we demonstrate for the first time that expression of miR-4516 is significantly downregulated in psoriatic skin. We additionally validated extracellular matrix protein fibronectin 1 (FN1) and integrin subunit α9 (ITGA9) as direct targets of miR-4516. Interestingly, ITGA9 expression was found to be increased in the suprabasal psoriatic epidermis. We further showed that ectopic expression of miR-4516 in human keratinocytes not only suppresses cell motility and proliferation via significant downregulation of genes orchestrating cytoskeletal reorganization (Rac1, RhoA, Cdc42), but also inhibits F-actin assembly and induces terminal differentiation. Collectively, our results provide evidence that loss of expression of miR-4516 in psoriatic skin might be contributing to accelerated migration, resistance to apoptosis and differentiation as seen in psoriasis lesional keratinocytes and also highlight its potential as a novel small molecule for therapeutic intervention in psoriasis.