Expression profiling identifies genes that continue to respond to insulin in adipocytes made insulin-resistant by treatment with tumor necrosis factor-alpha.
We have employed microarray technology using RNA from normal 3T3-L1 adipocytes and from 3T3-L1 adipocytes made insulin-resistant by treatment with tumor necrosis factor-alpha to identify a new class of insulin-responsive genes. These genes continued to respond normally to insulin even though the adipocytes themselves were metabolically insulin-resistant, i.e. they displayed a significantly decreased rate of insulin-stimulated glucose uptake. Approximately 12,000 genes/expressed sequence tags (ESTs) were screened. Of these, 40 genes/ESTs were identified that became insulin-resistant as expected (e.g. Socs-3, junB, and matrix metalloproteinase-11). However, 61 genes/ESTs continued to respond normally to insulin. Although some of these genes were previously shown to be regulated by insulin (e.g. Glut-1 and beta3-adrenergic receptor), other novel insulin-sensitive genes were also identified (e.g. Egr-1, epiregulin, Fra-1, and ABCA1). Real-time reverse transcription-PCR analysis confirmed the expression patterns of several of the differentially expressed genes. One gene that remained insulin-sensitive in the insulin-resistant adipocytes is the transcription factor Egr-1. Using an antisense strategy, we show that tissue factor and macrophage colony-stimulating factor, two cardiovascular risk factors, are downstream EGR-1 target genes in the adipocyte. Taken together, these data support the hypothesis that some signaling pathways remain insulin-sensitive in metabolically insulin-resistant adipocytes. These pathways may promote abnormal gene expression in hyperinsulinemic states like obesity and type II diabetes and thus may contribute to pathologies associated with these conditions.
Sartipy
Peter
P
Department of Cell Biology, Division of Vascular Biology, Scripps Research Institute, La Jolla, California 92037, USA.
Loskutoff
David J
DJ
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D051766:Early Growth Response Protein 1; D020224:Expressed Sequence Tags; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D016376:Oligonucleotides, Antisense / Q000737:chemistry / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012307:Risk Factors; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D015854:Up-Regulation
D016895:Culture Media, Serum-Free; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D017874:Immediate-Early Proteins; D007328:Insulin; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D012313:RNA; D016173:Macrophage Colony-Stimulating Factor