title: Repression of glucocorticoid-stimulated angiopoietin-like 4 gene transcription by insulin.
abstract: Angiopoietin-like 4 (Angptl4) is a glucocorticoid receptor (GR) primary target gene in hepatocytes and adipocytes. It encodes a secreted protein that inhibits extracellular LPL and promotes adipocyte lipolysis. In Angptl4 null mice, glucocorticoid-induced adipocyte lipolysis and hepatic steatosis are compromised. Markedly, insulin suppressed glucocorticoid-induced Angptl4 transcription. To unravel the mechanism, we utilized small molecules to inhibit insulin signaling components and found that phosphatidylinositol 3-kinase and Akt were vital for the suppression in H4IIE cells. A forkhead box transcription factor response element (FRE) was found near the 15 bp Angptl4 glucocorticoid response element (GRE). Mutating the Angptl4 FRE significantly reduced glucocorticoid-induced reporter gene expression in cells. Moreover, chromatin immunoprecipitation revealed that GR and FoxO1 were recruited to Angptl4 GRE and FRE in a glucocorticoid-dependent manner, and cotreatment with insulin abolished both recruitments. Furthermore, in 24 h fasted mice, significant occupancy of GR and FoxO1 at the Angptl4 GRE and FRE was found in the liver. In contrast, both occupancies were diminished after 24 h refeeding. Finally, overexpression of dominant negative FoxO1 mutant abolished glucocorticoid-induced Angptl4 expression, mimicking the insulin suppression. Overall, we demonstrate that both GR and FoxO1 are required for Angptl4 transcription activation, and that FoxO1 negatively mediates the suppressive effect of insulin.
authors.affiliation: Endocrinology Graduate Program, University of California, Berkeley, Berkeley, CA 94720-3104.
authors.forename: Taiyi
authors.initials: T
authors.lastname: Kuo
authors.forename: Tzu-Chieh
authors.initials: TC
authors.lastname: Chen
authors.forename: Stephanie
authors.initials: S
authors.lastname: Yan
authors.forename: Fritz
authors.initials: F
authors.lastname: Foo
authors.forename: Cecilia
authors.initials: C
authors.lastname: Ching
authors.forename: Allison
authors.initials: A
authors.lastname: McQueen
authors.forename: Jen-Chywan
authors.initials: JC
authors.lastname: Wang
mesh_terms: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D050356:Lipid Metabolism / Q000187:drug effects; D008297:Male; D051379:Mice; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects*; D000071161:Forkhead Box Protein O1
chemical_list: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins; D051858:Forkhead Transcription Factors; D005938:Glucocorticoids; D007328:Insulin; D009419:Nerve Tissue Proteins; D011965:Receptors, Glucocorticoid; C407088:Angptl4 protein, mouse; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1
keywords: chromatin immunoprecipitation; forkhead box protein O1; glucocorticoid receptor; glucocorticoid response element