Induction of the plasminogen activator inhibitor-1 gene expression by mildhypoxia via a hypoxia response element binding the hypoxia-inducible factor-1 in rat hepatocytes

Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhi bitor of both tissue-type and urokinase-type plasminogen activators. The ba lance between plasminogen activators and PAI-1 plays an important role in s everal physiological and pathophysiological processes such as atheroscleros is or thrombosis. Because these conditions are associated with hypoxia, it was the aim of the present study to investigate the influence of low O-2 te nsion on the expression of PAI-1 mRNA and protein using primary cultured ra t hepatocytes as a model system. We found that PAI-1 mRNA and protein were induced by mild hypoxia (8% O-2) The hypoxia-dependent PAI-1 mRNA induction was transcriptionally regulated because it was inhibited by actinomycin D (ActD), Luciferase (LUC) reporter gene constructs driven by about 800 bp of the 5'-flanking region of the rat PAI-1 gene were transiently transfected into primary rat hepatocytes; mild hypoxia caused a 3-fold induction, which was mediated by the PAI-1 promoter region -175/-158 containing 2 putative hypoxia response elements (HRE) binding the hypoxia-inducible factor (HIF-1 ), Mutation of the HRE-1 (-175/-168) or HRE-2 (-165/-158) also abolished th e induction by mild hypoxia. Cotransfection of a HIF-1 alpha vector and the PAI-1-LUC constructs, as well as gel shift assays, showed that the HRE-2 o f the PAI-1 promoter was most critical for induction by hypoxia acid HIF-1 binding. Thus, PAI-1 induction by mild hypoxia via a HIF-1 binding HRE in t he rat PAI-I promoter appears to be the mechanism causing the increase in P AI-1 in many clinical conditions associated with O-2 deficiency. (C) 1999 b y The American Society of Hematology.