Glucocorticoids activate TGF-β induced PAI-1 and CTGF expression in rat hepatocytes

By examining PAI-1 and CTGF mRNA and protein expression in cell lysates and cell-conditioned media under the influence of TGF-β and dexamethasone, we analysed signalling pathways controlling their expression. TGF-β and dexamethasone significantly co-induce PAI-1 and CTGF protein expression. On the other hand, we showed that TGF-β diminished a glucocorticoid receptor dependent luciferase reporter signal in Hep-G2. Inhibition of Erk downstream activation decreased TGF-β induced CTGF and PAI-1 expression to a basal level. PAI-1 was directly secreted by hepatocytes, whereas secretion of CTGF was retarded.The data provide evidence that beside the TGF-β-Smad 3 pathway CTGF and PAI-1 expression is additionally dependent on Erk activity in hepatocytes giving new insights into regulation of the profibrogenic proteins.Hepatocytes fulfil several complex functions, which are regulated by a fine network of transcriptional regulators. Particularly glucocorticoids govern crucial functions in hepatocytes such as glucose metabolism, cell proliferation and differentiation. Once bound to their cytoplasmic receptors (GR) the glucocorticoid-receptor-complex is translocated to the nucleus and binds after dimerization to a cis-active response element to regulate target genes [1,2]. Additionally, ligand-bound GR can interact DNA-independently with transcription factors such as AP-1 or NFκB, resulting in anti-inflammatory effects [3]. These properties were pharmaceutically utilised [4]. In liver injury, the fibrogenetic master cytokine TGF-β activates hepatic stellate cells (HSC) and induces them to produce extra cellular matrix (ECM). Further, TGF-β severely impaired viability and function of hepatocytes [5]. For this, active TGF-β binds and phosphorylates transmembrane receptors with a serine-threonine kinase activity, which in turn propagates the signal via Smads to the nucleus in order to bind corresponding promoter elements [6-8].PAI-1, a member of the serpin superfamily, is regulated