Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that critically supports the physicochemical and mechanical properties of the skin. Here, we demonstrate that mycosporine-like amino acids (MAAs), which typically function as UV-absorbing compounds, can stimulate HA secretion from normal human fibroblasts. MAA-stimulated HA secretion was associated with significantly increased and decreased levels of mRNAs encoding HA synthase 2 (HAS2) and HA-binding protein involved in HA depolymerization (HYBID), respectively. Using immunoblotting, we found that MAAs at 10 μg/ml and at 25 μg/ml stimulate the phosphorylation of the mitogen-activated protein kinase (MAPK) p38, extracellular signal–regulated kinase (ERK)/c-Jun, mitogen- and stress-activated protein kinase 1 (MSK1) (at Thr-581, Ser-360, and Ser-376, respectively) and activation of cAMP -responsive element–binding protein (CREB) and activating transcription factor 2 (ATF2), but not phosphorylation of JUN N-terminal kinase (JNK) or NFkB (at Ser-276 or Ser-536, respectively), and increased c-Fos protein levels. Moreover, a p38-specific inhibitor, but not inhibitors of MAPK/ERK kinase (MEK), JNK, or NFkB, significantly abrogated the increased expression of HAS2 mRNA, accompanied by significantly decreased MAA-stimulated HA secretion. These results suggested that the p38–MSK1–CREB–c-Fos–transcription factor AP-1 (AP-1) or the p38–ATF2 signaling cascade is responsible for the MAA-induced stimulation of HAS2 gene expression. Of note, siRNA-mediated ATF2 silencing failed to abrogate MAA-stimulated HAS2 expression, and c-Fos silencing abolished the increased expression of HAS2 mRNA. Our findings suggest that MAAs stimulate HA secretion by up-regulating HAS2 mRNA levels through activation of an intracellular signaling cascade consisting of p38, MSK1, CREB, c-Fos, and AP-1.
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