Repression of glucocorticoid-stimulated angiopoietin-like 4 gene transcription by insulin

• Published in: Journal of lipid research Vol. 55; no. 5; pp. 919 - 928
• Main Authors: Kuo, Taiyi, Chen, Tzu-Chieh, Yan, Stephanie, Foo, Fritz, Ching, Cecilia, McQueen, Allison, Wang, Jen-Chywan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2014; The American Society for Biochemistry and Molecular Biology; Elsevier
• Subjects: Angiopoietin-like 4 Protein; Angiopoietins - genetics; Animals; Base Sequence; Cell Line, Tumor; chromatin immunoprecipitation; forkhead box protein O1; Forkhead Transcription Factors - genetics; Forkhead Transcription Factors - metabolism; Gene Expression Regulation - drug effects; glucocorticoid receptor; glucocorticoid response element; Glucocorticoids - pharmacology; Humans; Insulin - pharmacology; Lipid Metabolism - drug effects; Male; Mice; Mutation; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Protein Transport - drug effects; Rats; Receptors, Glucocorticoid - metabolism; Response Elements - genetics; Signal Transduction - drug effects; Transcription, Genetic - drug effects; forkhead box protein O1; glucocorticoid receptor; glucocorticoid response element; chromatin immunoprecipitation
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1194/jlr.M047860

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.