title: RasGRF Couples Nox4-Dependent Endoplasmic Reticulum Signaling to Ras.
abstract: In response to endoplasmic reticulum (ER) stress, endothelial cells initiate corrective pathways such as the unfolded protein response. Recent studies suggest that reactive oxygen species produced on the ER may participate in homeostatic signaling through Ras in response to ER stress. We sought to identify mechanisms responsible for this focal signaling pathway.
  
  
  
  In endothelial cells, we found that ER stress induced by tunicamycin activates the NADPH (nicotinamide adenine dinucleotide phosphate) oxidase Nox4 focally on the ER surface but not on the plasma membrane. Ras activation is also restricted to the ER, occurs downstream of Nox4, and is required for activation of the unfolded protein response. In contrast, treatment with the growth factor VEGF (vascular endothelial growth factor) results in Ras activation and reactive oxygen species production confined instead to the plasma membrane and not to the ER, demonstrating local coupling of reactive oxygen species and Ras signals. We further identify the calcium-responsive, ER-resident guanyl exchange factors RasGRF1 and RasGRF2 as novel upstream mediators linking Nox4 with Ras activation in response to ER stress. Oxidation of the sarcoendoplasmic reticulum calcium ATPase and increases in cytosolic calcium caused by ER stress are blocked by Nox4 knockdown, and reduction in cytosolic free calcium prevents both Ras activation and the unfolded protein response.
  
  
  
  ER stress triggers a localized signaling module on the ER surface involving Nox4-dependent calcium mobilization, which directs local Ras activation through ER-associated, calcium-responsive RasGRF.
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas.
authors.forename: Ru Feng
authors.initials: RF
authors.lastname: Wu
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas.
authors.forename: Chengxu
authors.initials: C
authors.lastname: Liao
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas.
authors.forename: Hadi
authors.initials: H
authors.lastname: Hatoum
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas.
authors.forename: Guosheng
authors.initials: G
authors.lastname: Fu
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas.
authors.forename: Cristhiaan D
authors.initials: CD
authors.lastname: Ochoa
authors.affiliation: From the Division of Pulmonary and Critical Care, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas. lance.terada@utsouthwestern.edu.
authors.forename: Lance S
authors.initials: LS
authors.lastname: Terada
mesh_terms: D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000201:enzymology*; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D014162:Transfection; D014415:Tunicamycin / Q000494:pharmacology; D056811:Unfolded Protein Response; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology; D020663:ras Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D020666:ras-GRF1 / Q000235:genetics / Q000378:metabolism*
chemical_list: C117307:KRAS protein, human; C513039:RASGRF1 protein, human; C504490:RASGRF2 protein, human; D017382:Reactive Oxygen Species; D042461:Vascular Endothelial Growth Factor A; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1; D014415:Tunicamycin; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D016283:Proto-Oncogene Proteins p21(ras)
keywords: RasGRF1; apoptosis; autophagy; calcium; tunicamycin