HGF Regulates Expression Of SRD5A1 Through Egr1 In HepG2

Hepatocyte growth factor (HGF), also known as a scatter factor, is a multifunctional cytokine. By binding to the receptor tyrosine kinase Met, HGF triggers intracellular signals resulting in cell mitogenesis, motogenesis, morphogenesis and metastogenesis in a variety of cells and plays key roles in cancer invasion. In the present study, we investigated the altered gene expression profile in human hepatoma HepG2 cells treated with HGF for an hour using representational difference analysis (RDA). An HGF-induced gene named SRD5A1 (Steroid 5a-reductase) was isolated and its induction by HGF was confirmed by RT-PCR and Northern blot. Previous studies suggest that SRD5A1 can catalyze steroid hormones to active metablities and its aberrant expression is closely related with several endocrine abnormalities and tumorgenesis. But up to now, its function in hepatoma and the regulation mechamism in the HGF induction are still obscure.Here, we have isolated the 5'-flanking fragments of 2.7kb of the human SRD5A1 and have characterized a promoter fragment extending 79 base pairs upstream from the transcriptional start site, which, in transfection experiments, was sufficient to direct the inducible expression by HGF in HepG2 cells. In this fragment, we have identified two potential Egr 1-binding sites that are essential to the promoter activity as demonstrated by point mutation experiments. Overexpression of Egr-1 functionally stimulated SRD5A1 promoter activity. Consistently, Egr-1 is dramatically increased when cells were treated with HGF. These results suggest that Egr1 transcription factor plays critical roles in the expression of SRD5A1 induced by HGF.in HepG2.