Differential gene induction of human β-defensins (hBD-1, -2, -3, and -4) in keratinocytes is inhibited by retinoic acid

Human skin is able to mount a fast response against invading harmful bacteria through the rapid production of inducible peptide antibiotics such as the human beta-defensins (hBD). To gain more insight into the role and regulation of inducible beta-defensins in the innate immunity of human skin, we investigated whether gene induction of the human beta-defensins hBD-1, -2, -3, and -4 in keratinocytes is regulated in a similar manner. Therefore, we performed a comparative study of gene expression of these four hBD in primary cultured keratinocytes using real-time PCR. A basal mRNA expression was observed for all four hBD in primary keratinocytes, which strongly increased for hBD-2, -3, and -4 during Ca2+-induced differentiation of the keratinocytes. This effect was completely abolished when the keratinocytes were pre-treated with all-trans-retinoic acid (RA). Furthermore, the differential induction of hBD-2, -3, and -4 gene expression in keratinocytes by proinflammatory cytokines, phorbol-myristate-acetate (PMA), and bacteria was inhibited by more than 90% when the keratinocytes were pre-incubated with RA. Inhibition of IL-1beta-mediated hBD-2 induction through RA was further confirmed by gene reporter assays and western-blot analysis. We conclude that RA is a potent inhibitor of beta-defensin induction in keratinocytes and might downregulate the inducible innate chemical defense system of human skin.