Ultraviolet (UV) irradiation causes human skin aging and skin cancer through the activation of matrix metalloproteinases (MMPs) which are responsible for the degradation of collagen and tumor progression in human skin. The molecular mechanisms of UV-induced MMPs are yet to be defined. Our previous studies and others suggest that i) the transient activation of cell surface receptors and subsequent activation of MAP kinase cascade contributes to the transcriptional up-regulation of MMPs; and ii) UV-induced expression of pro-inflammatory cytokines such as IL-1β and TNF-α may also account for the expression of MMPs. However, signaling pathway through which cytokines induce MMP expression remains to be unraveled. In this study, we investigated the pathway that leads to the IL-1β-induced up-regulation of MMP-1 in human keratinocytes. IL-1β activated epidermal growth factor (EGF) receptor in cultured human keratinocytes in a time- and dose-dependent manner. IL-1β-induced EGF receptor tyrosine phosphorylation started at 5 min and peaked at 10 min and remained elevated up to 40 min post IL-1β treatment. EGF receptor kinase inhibitor PD153035 and AG1478 inhibited IL-1β-induced EGF receptor tyrosine phosphorylation. To test the effect of EGF receptor transactivation on downstream components, we examined the ERK activation by IL-1β. We found that IL-1β-induced ERK phosphorylation, PD153035 and MEK inhibitor PD98059 blocked IL-1β-induced ERK activity. Furthermore, both inhibitors also dramatically reduced IL-1β-induced expression of c-jun and c-fos mRNA which are required for up-regulation of MMPs. EGF receptor kinase inhibitor PD153035 and AG1478 and MEK inhibitor PD98059 also blocked IL-1β induction of MMP-1 in cultured human keratinocytes. Collectively, our data indicate that IL-1β-induced expression of MMP-1 is mediated by transactivation of EGF receptor and through ERK pathway in human keratinocytes.

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