title: GLUT4 repression in response to oxidative stress is associated with reciprocal alterations in C/EBP alpha and delta isoforms in 3T3-L1 adipocytes.
abstract: Insulin responsiveness of adipocytes is acquired during normal adipogenesis, and is essential for maintaining whole-body insulin sensitivity. Differentiated adipocytes exposed to oxidative stress become insulin resistant, exhibiting decreased expression of genes like the insulin-responsive glucose transporter GLUT4. Here we assessed the effect of oxidative stress on DNA binding capacity of C/EBP isoforms known to participate in adipocyte differentiation, and determine the relevance for GLUT4 gene regulation. By electrophoretic mobility shift assay, nuclear proteins from oxidized adipocytes exhibited decreased binding of C/EBPalpha-containing dimers to a DNA oligonucleotide harboring the C/EBP binding sequence from the murine GLUT4 promoter. C/EBPdelta-containing dimers were increased, while C/EBPbeta-dimers were unchanged. These alterations were mirrored by a 50% decrease and a 2-fold increase in the protein content of C/EBPalpha and C/EBPdelta, respectively. In oxidized cells, GLUT4 protein and mRNA levels were decreased, and a GLUT4 promoter segment containing the C/EBP binding site partially mediated oxidative stress-induced repression of a reported gene. The antioxidant lipoic acid protected against oxidation-induced decrease in GLUT4 and C/EBPalpha mRNA, but did not prevent the increase in C/EBPdelta mRNA. We propose that oxidative stress induces adipocyte insulin resistance partially by affecting the expression of C/EBPalpha and delta, resulting in altered C/EBP-dimer composition potentially occupying the GLUT4 promoter.
authors.affiliation: Department of Clinical Biochemistry, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
authors.forename: Dorit
authors.initials: D
authors.lastname: Pessler-Cohen
authors.forename: Phillip H
authors.initials: PH
authors.lastname: Pekala
authors.forename: Julia
authors.initials: J
authors.lastname: Kovsan
authors.forename: Asnat
authors.initials: A
authors.lastname: Bloch-Damti
authors.forename: Assaf
authors.initials: A
authors.lastname: Rudich
authors.forename: Nava
authors.initials: N
authors.lastname: Bashan
mesh_terms: D041721:3T3-L1 Cells / Q000187:drug effects / Q000378:metabolism; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D050156:Adipogenesis / Q000502:physiology; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism*; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D015536:Down-Regulation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000235:genetics; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007333:Insulin Resistance; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D051275:Glucose Transporter Type 4; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta; D006861:Hydrogen Peroxide