Abstract
MMP‐9, a member of the matrix metalloproteinase family that degrades collagen IV and processes chemokines and cytokines, participates in epidermal remodeling in response to stress and injury. Limited activity of MMP‐9 is essential while excessive activity is deleterious to the healing process. Tumor necrosis factor (TNFα), a key mediator of cutaneous inflammation, is a powerful inducer of MMP‐9. Calcitriol, the hormonally active vitamin D metabolite, and its analogs are known to attenuate epidermal inflammation. We aimed to examine the modulation of MMP‐9 by calcitriol in TNFα‐treated keratinocytes. The immortalized HaCaT keratinocytes were treated with TNFα in the absence of exogenous growth factors or active ingredients. MMP‐9 production was quantified by gelatin zymography and real‐time RT‐PCR. Activation of signaling cascades was assessed by western blot analysis and DNA‐binding activity of transcription factors was determined by EMSA. Exposure to TNFα markedly increased the protein and mRNA levels of MMP‐9, while pretreatment with calcitriol dose dependently reduced this effect. Employing specific inhibitors we established that the induction of MMP‐9 by TNFα was dependent on the activity of the epidermal growth factor receptor, c‐Jun‐N‐terminal kinase (JNK), NFκB and extracellular signal‐regulated kinase‐1/2. The effect of calcitriol was associated with inhibition of JNK activation and reduction of DNA‐binding activities of the transcription factors activator protein‐1 (AP‐1) and NFκB following treatment with TNFα. By down‐regulating MMP‐9 levels active vitamin D derivatives may attenuate deleterious effects due to excessive TNFα‐induced proteolytic activity associated with cutaneous inflammation. J. Cell. Physiol. 222: 729–737, 2010. © 2009 Wiley‐Liss, Inc.