The MAPK pathway and HIF-1 are involved in the induction of the human PAI-1 gene expression by insulin in the human hepatoma cell line HepG2.
Enhanced levels of plasminogen activator inhibitor-1 (PAI-1) are considered to be a risk factor for pathological conditions associated with hypoxia or hyperinsulinemia. The expression of the PAI-1 gene is increased by insulin in different cells, although, the molecular mechanisms behind insulin-induced PAI-1 expression are not fully known yet. Here, we show that insulin upregulates human PAI-1 gene expression and promoter activity in HepG2 cells and that mutation of the hypoxia-responsive element (HRE)-binding hypoxia-inducible factor-1 (HIF-1) abolished the insulin effects. Mutation of E-boxes E4 and E5 abolished the insulin-dependent activation of the PAI-1 promoter only under normoxia, but did not affect it under hypoxia. Furthermore, the insulin effect was associated with activation of HIF-1alpha via mitogen-activated protein kinases (MAPKs) but not PDK1 and PKB in HepG2 cells. Furthermore, mutation of a putative FoxO1 binding site which was supposed to be involved in insulin-dependent PAI-1 gene expression influenced the insulin-dependent activation only under normoxia. Thus, insulin-dependent PAI-1 gene expression might be regulated by the action of both HIF-1 and FoxO1 transcription factors.
Dimova
Elitsa Y
EY
University of Kaiserslautern, Faculty of Chemistry, Department of Biochemistry, Erwin-Schroedinger Strasse 54, 67663 Kaiserslautern, Germany. edimova@gwdg.de
Kietzmann
Thomas
T
D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology*; D007328:Insulin / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D020935:MAP Kinase Signaling System; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007328:Insulin; D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger