Overexpression of Phospholipid-hydroperoxide Glutathione Peroxidase in Human Dermal Fibroblasts Abrogates UVA Irradiation-induced Expression of Interstitial Collagenase/Matrix Metalloproteinase-1 by Suppression of Phosphatidylcholine Hydroperoxide-mediated NFκB Activation and Interleukin-6 Release

Abstract

Phospholipid-hydroperoxide glutathione peroxidase (PHGPx) exhibits high specific activity in reducing phosphatidylcholine hydroperoxides (PCOOHs) and thus may play a central role in protecting the skin against UV irradiation-triggered detrimental long term effects like cancer formation and premature skin aging. Here we addressed the role of PHGPx in the protection against UV irradiation-induced expression of matrix metalloproteinase-1 (MMP-1). For this purpose, we created human dermal fibroblast cell lines overexpressing human PHGPx. Overexpression led to a significant increase in PHGPx activity. In contrast to a maximal 4.5-fold induction of specific MMP-1 mRNA levels in vector-transfected cells at 24 h after UVA irradiation, no MMP-1 induction occurred at any studied time point after UVA treatment of PHGPxoverexpressing fibroblasts. As interleukin-6 (IL-6) was earlier shown to mediate the UVA induction of MMP-1, we studied whether PHGPx overexpression might interfere with the NFB-mediated IL-6 induction and downstream signaling. Using transient transfections of IL-6 promoter constructs containing NFB binding sites, we observed a high induction of the reporter gene luciferase in vectortransfected control cells and a significantly lower induction in PHGPx-overexpressing fibroblasts following UVA irradiation. Consistently both UVA irradiation and treatment of fibroblasts with PCOOHs led to phosphorylation and nuclear translocation of the p65 subunit, whereas cells overexpressing PHGPx exhibited impaired NFB activation, p65 phosphorylation, and nuclear translocation. In line with this, the PHGPx-overexpressing fibroblasts showed a reduced constitutive and UVA irradiation-induced IL-6 release. After incubating PHGPx-overexpressing cells with PCOOHs a reduced induction of IL-6 was observed. This together with the suppression of UVA irradiation-induced IL-6 release in the presence of Trolox, a chain breaker of PCOOH-initiated lipid peroxidation, indicates that UVA irradiation-induced PCOOHs and subsequent lipid peroxides initiate the NFB-mediated induction of IL-6, which mediates the induction of MMP-1. Our finding is particularly relevant in light of the already available small molecule mimetics of PHGPx. Although reactive oxygen species (ROS)1 and intermediates thereof are part of normal regulatory circuits, imbalance or loss of cellular redox homeostasis results in oxidative stress (1-3), causing severe damage of cellular components. The damage is mainly conferred by phosphatidylcholine hydroperoxides (PCOOHs), among other peroxides, which initiate the chain reaction of lipid peroxidation. Apart from permanent genetic changes involving protooncogenes and tumor suppressor genes, reactive oxygen species and phosphatidylcholine hydroperoxides activate cytoplasmic signal transduction pathways that are related to growth, differentiation, senescence, and tissue degradation. Therefore, ROS and PCOOHs have been implicated to play a causal role in cancer, aging, and other degenerative diseases like arteriosclerosis, osteoa...

Inhibition of IκB Kinase Activity by Acetyl-boswellic Acids Promotes Apoptosis in Androgen-independent PC-3 Prostate Cancer Cells in Vitro and in Vivo

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