Transcriptional Regulation of Plasminogen Activator Inhibitor Type 1 Gene by Insulin: Insights into the Signaling Pathway

Cristina Banfi, Per Eriksson, Giovanna Giandomenico, Luciana Mussoni, Luigi Sironi, Anders Hamsten, Elena Tremoli

Research output: Contribution to journalArticle

Abstract

Impairment of the fibrinolytic system, caused primarily by increases in the plasma levels of plasminogen activator inhibitor (PAI) type 1, are frequently found in diabetes and the insulin-resistance syndrome. Among the factors responsible for the increases of PAI-1, insulin has recently attracted attention. In this study, we analyzed the effects of insulin on PAI-1 biosynthesis in HepG2 cells, paying particular attention to the signaling network evoked by this hormone. Experiments performed in CHO cells overexpressing the insulin receptor indicate that insulin increases PAI-1 gene transcription through interaction with its receptor. By using inhibitors of the different signaling pathways evoked by insulin-receptor binding, it has been shown that the biosynthesis of PAI-1 is due to phosphatidylinositol (PI) 3-kinase activation, followed by protein kinase C and ultimately by mitogen-activated protein (MAP) kinase activation and extracellular signal-regulated kinase 2 phosphorylation. We also showed that this pathway is Ras-independent. Transfection of HepG2 cells with several truncations of the PAI-1 promoter coupled to a CAT gene allowed us to recognize two major response elements located in the regions between -804 and -708 and between -211 and -54. Electrophoretic mobility shift assay identified three binding sites for insulin-induced factors, all colocalized with putative Sp1 binding sites. Using supershifting antibodies, the binding of Sp1 could only be confirmed at the binding site located just upstream from the transcription start site of the PAI-1 promoter. A construct comprising four tandem repeat copies of the -93/-62 region of the PAI-1 promoter linked to CAT was transcriptionally activated in Hep62 cells by insulin. These results outline the central role of MAP kinase activation in the regulation of PAI-1 induced by insulin.

Original languageEnglish
Pages (from-to)1522-1530
Number of pages9
JournalDiabetes
Volume50
Issue number7
Publication statusPublished - Jul 2001

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Internal Medicine

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