Oxidative stress impairs insulin but not platelet-derived growth factor signalling in 3T3-L1 adipocytes.
Activation of phosphatidylinositol 3-kinase (PI 3-kinase) is a common event in both insulin and platelet-derived growth factor (PDGF) signalling, but only insulin activates this enzyme in the high-speed pellet (HSP), and induces GLUT4 translocation. Recently, we have demonstrated that exposure of 3T3-L1 adipocytes to oxidative stress impairs insulin-stimulated GLUT4 translocation and glucose transport, associated with impaired PI 3-kinase translocation and activation in the HSP [Tirosh, Potashnik, Bashan and Rudich (1999) J. Biol. Chem. 274, 10595-10602]. In this study the effect of a 2 h exposure to approximately 30 microM H(2)O(2) on insulin versus PDGF-BB signalling and metabolic effects was compared. PDGF-stimulated p85-associated PI 3-kinase activity in total cell lysates, as well as co-precipitation of the PDGF receptor, were unaffected by oxidative stress. Additionally, the increase in p85 association with the plasma-membrane lawns by PDGF remained intact following oxidation, whereas the insulin effect was decreased. PDGF significantly increased protein kinase B (PKB) activity in early differentiated cells, and that of p70 S6-kinase in both early and fully differentiated 3T3-L1 adipocytes. Following oxidation the effect of PDGF on PKB and p70 S6-kinase activation remained intact, whereas significant inhibition of insulin-stimulated activation of those enzymes was observed. In accordance, in both early and fully differentiated cells, oxidative stress completely blunted insulin- but not PDGF-stimulated protein synthesis. In conclusion, oxidative stress impairs insulin, but not PDGF, signalling and metabolic actions in both early and fully differentiated 3T3-L1 adipocytes. This emphasizes compartment-specific activation of PI 3-kinase as an oxidation-sensitive step specifically leading to insulin resistance.
Tirosh
A
A
Department of Clinical Biochemistry, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Rudich
A
A
Potashnik
R
R
Bashan
N
N
D016475:3T3 Cells; D017667:Adipocytes / Q000201:enzymology / Q000378:metabolism*; D000818:Animals; D004789:Enzyme Activation; D007328:Insulin / Q000378:metabolism*; D051379:Mice; D018384:Oxidative Stress / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism
D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases