Eicosapentaenoic acid inhibits UV-induced MMP-1 expression in human dermal fibroblasts

Ultraviolet (UV) irradiation regulates UV-responsive genes, including matrix metalloproteinases (MMPs). Moreover, UV-induced MMPs cause connective tissue damage and the skin to become wrinkled and aged. Here, we investigated the effect of eicosapentaenoic acid (EPA), a dietary omega-3 fatty acid, on UV-induced MMP-1 expression in human dermal fibroblasts (HDFs). We found that UV radiation increases MMP-1 expression and that this is mediated by p44 and p42 MAP kinase (ERK) and Jun-N-terminal kinase (JNK) activation but not by p38 activation. Pretreatment of HDFs with EPA inhibited UV-induced MMP-1 expression in a dose-dependent manner and also inhibited the UV-induced activation of ERK and JNK by inhibiting ERK kinase (MEK1) and SAPK/ERK kinase 1 (SEK1) activation, respectively. Moreover, inhibition of ERK and JNK by EPA resulted in the decrease of c-Fos expression and c-Jun phosphorylation/expression induced by UV, respectively, which led to the inhibition of UV-induced activator protein-1 DNA binding activity. This inhibitory effect of EPA on MMP-1 was not mediated by an antioxidant effect. We also found that EPA inhibited 12-O-tetradecanoylphorbol-13-acetate- or tumor necrosis factor-alpha-induced MMP-1 expression in HDFs and UV-induced MMP-1 expression in HaCaT cells. In conclusion, our results demonstrate that EPA can inhibit UV-induced MMP-1 expression by inhibiting the MEK1/ERK/c-Fos and SEK1/JNK/c-Jun pathways. Therefore, EPA is a potential agent for the prevention and treatment of skin aging.     

The effect of 2',4',7-trihydroxyisoflavone on ultraviolet-induced matrix metalloproteinases-1 expression in human skin fibroblasts

UV-induced matrix metalloproteinases (MMPs) cause connective tissue damage and the skin to become wrinkled and aged. Here, we investigated the effect of 2',4',7-trihydroxyisoflavone (THF) on UV-induced MMP-1 expression in human skin fibroblasts (HSFs). We found that UV irradiation increases MMP-1 expression and that this is mediated by ERK and JNK activation, but not by p38 activation. Pretreatment of HSFs with 2',4',7-THF inhibited UV-induced MMP-1 expression in a dose-dependent manner, and also inhibited the UV-induced activations of ERK and JNK by inhibiting MEK1 and SEK1 activation, respectively. Moreover, inhibitions of ERK and JNK by 2',4',7-THF resulted in the decrease of c-Fos expression and c-Jun phosphorylation/expression induced by UV, respectively, which led to the inhibition of UV-induced AP-1 DNA binding activity. This inhibitory effect of 2',4',7-THF on MMP-1 was not mediated by an antioxidant effect. In conclusion, our results demonstrate that 2',4',7-THF can inhibit UV-induced MMP-1 expression by inhibiting the MEK1/ERK/c-Fos and SEK1/JNK/c-Jun pathways. Therefore, 2',4',7-THF is a potential agent for the prevention and treatment of skin aging.     

JunB forms the majority of the AP-1 complex and is a target for redox regulation by receptor tyrosine kinase and G protein-coupled receptor agonists in smooth muscle cells

To understand the role of redox-sensitive mechanisms in vascular smooth muscle cell (VSMC) growth, we have studied the effect of N-acetylcysteine (NAC), a thiol antioxidant, and diphenyleneiodonium (DPI), a potent NADH/NADPH oxidase inhibitor, on serum-, platelet-derived growth factor BB-, and thrombin-induced ERK2, JNK1, and p38 mitogen-activated protein (MAP) kinase activation; c-Fos, c-Jun, and JunB expression; and DNA synthesis. Both NAC and DPI completely inhibited agonist-induced AP-1 activity and DNA synthesis in VSMC. On the contrary, these compounds had differential effects on agonist-induced ERK2, JNK1, and p38 MAP kinase activation and c-Fos, c-Jun, and JunB expression. NAC inhibited agonist-induced ERK2, JNK1, and p38 MAP kinase activation and c-Fos, c-Jun, and JunB expression except for platelet-derived growth factor BB-induced ERK2 activation. In contrast, DPI only inhibited agonist-induced p38 MAP kinase activation and c-Fos and JunB expression. Antibody supershift assays indicated the presence of c-Fos and JunB in the AP-1 complex formed in response to all three agonists. In addition, cotransfection of VSMC with expression plasmids for c-Fos and members of the Jun family along with the AP-1-dependent reporter gene revealed that AP-1 with c-Fos and JunB composition exhibited a higher transactivating activity than AP-1 with other compositions tested. All three agonists significantly stimulated reactive oxygen species production, and this effect was inhibited by both NAC and DPI. Together, these results strongly suggest a role for redox-sensitive mechanisms in agonist-induced ERK2, JNK1, and p38 MAP kinase activation; c-Fos, c-Jun, and JunB expression; AP-1 activity; and DNA synthesis in VSMC. These results also suggest a role for NADH/NADPH oxidase activity in some subset of early signaling events such as p38 MAP kinase activation and c-Fos and JunB induction, which appear to be important in agonist-induced AP-1 activity and DNA synthesis in VSMC.     

Mitogen activated protein kinase-dependent activation of c-Jun and c-Fos is required for neuronal differentiation but not for growth and stress response in PC12 cells

MAPK-dependent activation of AP-1 protein c-Jun is involved in PC12 cell differentiation and apoptosis. However, the role of other AP-1 proteins and their connection to MAPKs during growth, differentiation and apoptosis has remained elusive. Here we studied the activation of AP-1 proteins in response to ERK, JNK, and p38 signaling upon NGF, EGF and anisomycin exposures. All treatments caused different kinetics and strength of MAPK and AP-1 activities. NGF induced persistent ERK and AP-1 activities, whereas upon EGF and anisomycin exposures, their activities were only weakly and transiently induced. The sustained AP-1 activity was associated with concomitant c-Fos and c-Jun expression and phoshorylation, which were JNK and ERK dependent. While inhibition of the ERK, JNK, and p38 activities partially prevented AP-1 activity and suppressed differentiation, none of them was required for anisomycin-induced apoptosis. The importance of c-Fos and c-Jun as mediators of differentiation was demonstrated by the findings that the corresponding siRNAs suppressed NGF-induced neurite outgrowth. However, the capacity of c-Fos to promote differentiation required cooperation with Jun proteins. In contrast, Fra-2 expression was not required for the differentiation response. Together, the results show that sustained c-Jun and c-Fos activities mediate MAPK signaling and are essential for differentiation of PC12 cells.     

Activation of c-Jun N-terminal kinase 1 by UV irradiation is inhibited by wortmannin without affecting c-iun expression

Activation of c-Jun N-terminal kinases (JNKs)/stress-activated protein kinases is an early response of cells upon exposure to DNA-damaging agents. JNK-mediated phosphorylation of c-Jun is currently understood to stimulate the transactivating potency of AP-1 (e.g., c-Jun/c-Fos; c-Jun/ATF-2), thereby increasing the expression of AP-1 target genes. Here we show that stimulation of JNK1 activity is not a general early response of cells exposed to genotoxic agents. Treatment of NIH 3T3 cells with UV light (UV-C) as well as with methyl methanesulfonate (MMS) caused activation of JNK1 and an increase in c-Jun protein and AP-1 binding activity, whereas antineoplastic drugs such as mafosfamide, mitomycin C, N-hydroxyethyl-N-chloroethylnitrosourea, and treosulfan did not elicit this response. The phosphatidylinositol 3-kinase inhibitor wortmannin specifically blocked the UV-stimulated activation of JNK1 but did not affect UV-driven activation of extracellular regulated kinase 2 (ERK2). To investigate the significance of JNK1 for transactivation of c-jun, we analyzed the effect of UV irradiation on c-jun expression under conditions of wortmannin-mediated inhibition of UV-induced stimulation of JNK1. Neither the UV-induced increase in c-jun mRNA, c-Jun protein, and AP-1 binding nor the activation of the collagenase and c-jun promoters was affected by wortmannin. In contrast, the mitogen-activated protein kinase/ERK kinase inhibitor PD98056, which blocked ERK2 but not JNK1 activation by UV irradiation, impaired UV-driven c-Jun protein induction and AP-1 binding. Based on the data, we suggest that JNK1 stimulation is not essential for transactivation of c-jun after UV exposure, whereas activation of ERK2 is required for UV-induced signaling leading to elevated c-jun expression.