Visit our Expo - Redox and Inflammation signaling 2012

Session XIV : Transcriptional and translational control Poster XIV, 19
Transcriptional Regulation of Human Plasminogen Activator Inhibitor-1 Gene
Expression by IGF-1 and Insulin: Role of HIF-1 and Forkhead transcription factor
Elitsa Y. Dimova, Daniela Fluegel and Thomas Kietzmann
Department of Biochemistry, Faculty of Chemistry, University of Kaiserslautern, D-
67663 Kaiserslautern, Germany. E-mail: edimova@gwdg.de
One risk factor for pathological conditions associated with hypoxia or hyperinsulinemia is
plasminogen activator inhibitor-1 (PAI-1). IGF-1 and insulin have been shown to induce PAI-
1 expression but the molecular mechanisms behind these effects have not been fully
elucidated. Therefore, we searched for putative IGF-1- and insulin-responsive element(s),
transcription factor(s) and signalling components mediating the IGF-1 and insulin-dependent
human PAI-1 expression, using HepG2 cells as a model system. IGF-1 and insulin treatment
enhanced PAI-1 expression and promoter activity. Mutation of the hypoxia responsive
element (HRE), which could bind hypoxia-inducible factor-1 (HIF-1), nearly abolished the
induction by IGF-1 and insulin. Mutation of E-boxes E4 and E5 did not affect the IGF-1- and
insulin-dependent activation of the PAI-1 promoter constructs under normoxia but abolished
the effects of IGF-1 and insulin under hypoxia. Additionally, mutation of a putative Forkhead
binding site abolished the insulin-dependent activation under normoxia, but not under
hypoxia. Overexpression of Forkhead transcription factor resulted in suppression of the
hypoxia–mediated response of the human PAI-1 promoter constructs, but not in abolishment
of the insulin effect. Further the IGF-1 and insulin-induced up-regulation of PAI-1 was
associated with activation of HIF-1alpha IGF-1 enhanced HIF-1alpha protein levels and
HIF-1 DNA-binding to each HRE, E4 and E5 as shown by EMSAs. Inhibition of the PI(3)K
and MAPK pathways by specific inhibitors or by overexpression of the key enzymes e.g.
dominant-negative PDK1, TRB3 which inhibits Akt/PKB or dominant-negative Raf-1
revealed that IGF-1 activates human PAI-1 gene expression through activation of PI(3)K and
ERK1/2 whereas insulin-induced PAI-1 gene expression occurred mainly via the MAPK
pathway.
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