Inhibition of plasminogen activator inhibitor type-1 expression in HepG2 cells by fenofibrate may be associated with Smad signaling

Abstract

BackgroundWe investigated the molecular mechanism underlying the effect of fenofibrate on expression of plasminogen activator inhibitor type-1 (PAI-1) in HepG2 cells. MethodsLuciferase reporter gene plasmids containing four sequentially truncated fragments of the PAI-1 promoter region (−804 to +17) were constructed and plasmids carrying constructs of Smad binding element (SBE)-site-directed deletions in the PAI-1 promoter were also generated and then transfected to HepG2 cells prior to fenofibrate treatment. Smad3 and Smad4 protein levels were measured by Western blotting. ResultsThe decreased expression of PAI-1 mRNA and protein was detected in HepG2 cells after exposure to fenofibrate. PAI-1 transcription activities were also down-regulated following exposure to fenofibrate in HepG2 cells when they were transfected with the luciferase reporter gene plasmid containing a full-length of PAI-1 promoter. However, with the truncation of PAI-1 promoter, the inhibitory effect of fenofibrate on the transcription activity of PAI-1 gradually diminished. Furthermore, the transcription activity of PAI-1 was significantly up-regulated by fenofibrate in HepG2 cells when they were transfected with plasmids of the SBEs-deleted PAI-1 promoter. The expression of both Smad3 and Smad4 proteins was suppressed by fenofibrate. ConclusionFenofibrate exerts its inhibitory effect on PAI-1 transcription in HepG2 cells presumably involving Smad signaling pathways.