title: The oxazolidinedione CP-92,768-2 partially protects insulin receptor substrate-1 from dexamethasone down-regulation in 3T3-L1 adipocytes.
abstract: Oxazolidinediones are a class of oral antidiabetic agents that are closely related structurally and pharmacologically to thiazolidinediones. The thiazolidinediones have been shown to partially reverse the loss in insulin-responsive glucose uptake caused by chronic treatment with dexamethasone. This study was conducted to determine certain aspects of the mechanism of thiazolidinedione and oxazolidinedione action. We selected the oxazolidinedione CP-92,768-2 (5-[2-[(5-methyl2-phenyl-4-oxazolyl)methyl]5-benzofuranyl methyl]2,4- oxazolidinedione) to determine whether these agents could reverse the dexamethasone-induced down-regulation of IRS-1, the insulin receptor substrate-1. In 3T3-L1 adipocytes, dexamethasone treatment resulted in down-regulation of IRS-1 to 60% of control values. Simultaneous treatment with CP-92,768-2 significantly increased IRS-1 to 78% of the control value (EC50, < 10 nM), although it did not completely reverse the dexamethasone effect at any concentration tested. CP-92,768-2 alone did not have any effect on IRS-1. CP-92,768-2 did not affect the stability of IRS-1 protein in the presence or absence of dexamethasone, as measured by [35S]methionine pulse-chase labeling. Dexamethasone decreased messenger RNA (mRNA) for IRS-1 after 24 h of treatment to 40% of the control value. CP-92,768-2 partially reversed this decrease in IRS-1 mRNA to 65% of the control value after 24 h of treatment, but had no effect on IRS-1 mRNA in the absence of dexamethasone. Dexamethasone down-regulated the insulin stimulation of [3H]thymidine incorporation to 68% of the control value. Dexamethasone in the presence of CP-92,768-2 down-regulated insulin stimulation of thymidine incorporation by only 9%. Dexamethasone also down-regulated the expression of phosphoenolpyruvate carboxykinase (PEPCK) protein by 50%. CP-92,768-2 partially protected PEPCK from the dexamethasone down-regulation. Conversely, the up-regulation of expression of PEPCK and IRS-1 produced by dexamethasone in KRC-7 hepatoma cells was not affected by CP-92,768-2. One contribution of oxazolidinediones to an increase in insulin responsiveness in the presence of glucocorticoids may be the up-regulation of IRS-1 in adipose cells.
authors.affiliation: Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock 79430.
authors.forename: M A
authors.initials: MA
authors.lastname: Turnbow
authors.forename: L K
authors.initials: LK
authors.lastname: Smith
authors.forename: C W
authors.initials: CW
authors.lastname: Garner
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D015735:Mifepristone / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology*; D023303:Oxazolidinones; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000378:metabolism
chemical_list: D001572:Benzofurans; C092660:CP 92768-2; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010080:Oxazoles; D023303:Oxazolidinones; D010750:Phosphoproteins; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D015735:Mifepristone; D003907:Dexamethasone; D010729:Phosphoenolpyruvate Carboxykinase (GTP)