Hemin upregulates Egr-1 expression in vascular smooth muscle cells via reactive oxygen species ERK-1/2-Elk-1 and NF-kappaB.
Reactive oxygen species (ROS) and oxidant stress are important mediators of cardiovascular pathologies including atherosclerosis. One source of ROS in the vasculature is free heme released from hemoglobin. Because Egr-1, the regulator of cell proliferation and apoptosis, is also induced by oxidant stress and is likewise implicated in atherosclerosis, we examined the regulation of Egr-1 by heme in vascular smooth muscle cells (SMCs). Hemin increased Egr-1 expression (mRNA, protein) within 30 minutes and ERK-1/2 phosphorylation and nuclear translocation within 5 minutes. Inhibiting hemin-induced ERK-1/2 activation by U0126 (MAPK-inhibitor), the antioxidant N-acetyl cysteine, the NADPH oxidase inhibitors apocynin and diphenyleneiodonium chloride, the superoxide scavenger tiron, or tricarbonyldichlororuthenium(II)-dimer (carbon-monoxide donor; CORM-2) blocked hemin-induced Egr-1 expression. Hemin activated Elk-1, SRF, and NF-kappaB and promoted their interaction with the Egr-1 promoter. Downregulating Elk-1 (via siRNA) or blocking NF-kappaB activation (via BAY-11-7082) abolished hemin induction of Egr-1. Finally, hemin-induced Egr-1 bound the promoters of tissue factor (TF), Plasminogen Activator Inhibitor (PAI)-1, and NGF-1A Binding (NAB)-2, upregulating their expression, and increased the biochemical activity of TF and PAI-1. Upregulation of Egr-1 and its target genes by heme-induced oxidant stress may be an important event in the initiation and progression of inflammatory vascular diseases such as atherosclerosis.
Hasan
Rukhsana N
RN
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, USA.
Schafer
Andrew I
AI
D002478:Cells, Cultured; D051766:Early Growth Response Protein 1 / Q000187:drug effects / Q000235:genetics*; D006427:Hemin / Q000494:pharmacology*; D006801:Humans; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D011401:Promoter Regions, Genetic; D017382:Reactive Oxygen Species; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism*
C494112:ELK1 protein, human; D051766:Early Growth Response Protein 1; D016328:NF-kappa B; D017382:Reactive Oxygen Species; D050807:ets-Domain Protein Elk-1; D006427:Hemin; D048052:Mitogen-Activated Protein Kinase 3