Involvement of UVB-induced reactive oxygen species in TGF-β biosynthesis and activation in keratinocytes

TGF-β produced by keratinocytes in response to UVB (290-320 nm) is a potential mediator for effects of acute and chronic solar radiation on skin. This study was designed to determine whether reactive oxygen species (ROS) mediate UVB-induced TGF-β biosynthesis in keratinocytes and the subsequent activation of the latent TGF-β complex. UVB irradiation elevated both total (latent plus active) and active TGF-β in the keratinocyte supernatants, with a greater increase in the active form. UVB irradiation induced up to a 30% increase in ROS, and the ROS were detected up to 90 min after irradiation. NAC and Trolox, cytoplasmic ROS scavengers, abolished the UVB-induced TGF-β and intracellular ROS, suggesting that UVB-induced ROS are involved in TGF-β regulation. Inhibitors of NADPH oxidase activity, DPI and apocynin, decreased UVB-induced ROS. The increase in NADPH oxidase activity was mediated by EGFR activation. UVB-induced ROS also activated latent TGF-β complex by stimulating MMP-2 and -9 activities. In summary, physiological doses of UVB increase intracellular ROS, which upregulate TGF-β biosynthesis and activation of TGF-β through increased activity of MMPs.