The oxidative stressor arsenite activates vascular endothelial growth factor mRNA transcription by an ATF4-dependent mechanism.
Aberrant retinal expression of vascular endothelial growth factor (VEGF) leading to neovascularization is a central feature of age-related macular degeneration and diabetic retinopathy, two leading causes of vision loss. Oxidative stress is suggested to occur in retinal tissue during age-related macular degeneration and diabetic retinopathy and is suspected in the mechanism of VEGF expression in these diseases. Arsenite, a thiol-reactive oxidative stressor, induces VEGF expression by a HIF-1alpha-independent mechanism. Previously, we demonstrated that homocysteine, an endoplasmic reticulum stressor, increases VEGF transcription by a mechanism dependent upon activating transcription factor ATF4. Because ATF4 is expressed in response to oxidative stress, we hypothesized that ATF4 was also responsible for increased VEGF transcription in response to arsenite. We now show that arsenite increased steady state levels of VEGF mRNA and activated transcription from a VEGF promoter construct. Arsenite induced eIF2alpha phosphorylation, resulting in increased ATF4 protein levels. Inactivation or loss of ATF4 greatly diminished the VEGF response to arsenite treatment. Overexpression of ATF4 was sufficient to activate the VEGF promoter, and arsenite cooperated with exogenous ATF4 to further activate the promoter. A complex containing ATF4 binds a DNA element at +1767 bp relative to the VEGF transcription start site, and DNA binding activity is increased by arsenite treatment. In addition, the ability of a thiol antioxidant, N-acetylcysteine, to inhibit the effect of arsenite on VEGF expression coincided with its ability to inhibit phosphorylation of eIF2alpha and ATF4 protein expression. Thus, arsenite-induced up-regulation of VEGF gene transcription occurs by an ATF4-dependent mechanism.
Roybal
C Nathaniel
CN
Department of Biochemistry and Molecular Biology, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131-0001, USA.
Hunsaker
Lucy A
LA
Barbash
Olena
O
Vander Jagt
David L
DL
Abcouwer
Steve F
SF
D000111:Acetylcysteine / Q000494:pharmacology; D051701:Activating Transcription Factor 4; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D018053:Arsenites / Q000494:pharmacology*; D001665:Binding Sites; D002460:Cell Line; D002461:Cell Line, Transformed; D004247:DNA / Q000378:metabolism; D004622:Embryo, Mammalian; D000091342:Endoplasmic Reticulum Chaperone BiP; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005347:Fibroblasts; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000187:drug effects*; D006360:Heat-Shock Proteins / Q000235:genetics; D006419:Heme Oxygenase (Decyclizing); D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D018832:Molecular Chaperones / Q000235:genetics; D018384:Oxidative Stress; D010105:Oxygenases / Q000235:genetics; D010766:Phosphorylation; D010857:Pigment Epithelium of Eye; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
C497109:ATF4 protein, human; D000975:Antioxidants; D018053:Arsenites; C081452:Atf4 protein, mouse; C497110:Atf4 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP; D015852:Eukaryotic Initiation Factor-2; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D051701:Activating Transcription Factor 4; D004247:DNA; D010105:Oxygenases; D006419:Heme Oxygenase (Decyclizing); C491523:Hmox1 protein, rat; C015001:arsenite; D000111:Acetylcysteine