title: Oxidative stress posttranslationally regulates the expression of Ha-Ras and Ki-Ras in cultured astrocytes.
abstract: Addition of hydrogen peroxide to cultured astrocytes induced a rapid and transient increase in the expression of Ha-Ras and Ki-Ras. Pull-down experiments with the GTP-Ras-binding domain of Raf-1 showed that oxidative stress substantially increased the activation of Ha-Ras, whereas a putative farnesylated activated form of Ki-Ras was only slightly increased. The increase in both Ha-Ras and Ki-Ras was insensitive to the protein synthesis inhibitor, cycloheximide, and was occluded by the proteasomal inhibitor, MG-132. In addition, exposure to hydrogen peroxide reduced the levels of ubiquitinated Ras protein, indicating that oxidative stress leads to a reduced degradation of both isoforms through the ubiquitin/proteasome pathway. Indeed, the late reduction in Ha-Ras and Ki-Ras was due to a recovery of proteasomal degradation because it was sensitive to MG-132. The late reduction of Ha-Ras levels was abrogated by compound PD98059, which inhibits the MAP kinase pathway, whereas the late reduction of Ki-Ras was unaffected by PD98059. We conclude that oxidative stress differentially regulates the expression of Ha-Ras and Ki-Ras in cultured astrocytes, and that activation of the MAP kinase pathway by oxidative stress itself or by additional factors may act as a fail-safe mechanism limiting a sustained expression of the potentially detrimental Ha-Ras.
authors.affiliation: Department of Human Sciences, Society, and Health, University of Cassino and Southern Lazio, 03043 Cassino, Italy. samantha.messina@uniroma1.it
authors.forename: Samantha
authors.initials: S
authors.lastname: Messina
authors.forename: Luigi
authors.initials: L
authors.lastname: Frati
authors.forename: Antonio
authors.initials: A
authors.lastname: Porcellini
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D006160:Guanosine Triphosphate / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D025801:Ubiquitin; D006160:Guanosine Triphosphate; D006861:Hydrogen Peroxide; D020928:Mitogen-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex; D016283:Proto-Oncogene Proteins p21(ras)