Involvement of Egr-1 in HGF-induced elevation of the human 5α-R1 gene in human hepatocellular carcinoma cells

Abstract

Steroid 5α-reductase 1 (5α-R1), a key enzyme in the conversion of steroids into their respective 5α-reduced derivatives, plays a key role in some hormone-dependent tumours and is abundant in the liver, although it is also widely distributed throughout the body. HGF (hepatocyte growth factor) is a pleiotropic cytokine/growth factor involved in the progression of hepatocellular carcinoma. In the present paper, we report the stimulatory effect of HGF on human 5α-R1 transcription in hepatocellular carcinoma cells. Pre-treatment with actinomycin D or cycloheximide blocked the up-regulation of 5α-R1 mRNA expression by HGF, indicating that the increased level of 5α-R1 mRNA expression is regulated by transcriptional activation and was dependent on de novo protein synthesis. Functional analysis of the 5′-flanking region of the 5α-R1 gene by transfection analysis showed that the −79 to −50 region functioned as the HGF-responsive region. Mutagenesis and electrophoretic mobility-shift assays demonstrated that induction of 5a-R1 by HGF is mediated by an Egr-1 (early growth-response gene 1)-binding site at −60/−54. In addition, overexpression of Egr-1 was sufficient to transactivate 5α-R1 promoter activity, and knockdown of Egr-1 with gene-specific small interfering RNA resulted in inhibition of HGF-induced up-regulation of endogenous 5α-R1 expression. These data provide the first evidence that HGF stimulates 5α-R1 expression through up-regulation of the transcription factor Egr-1, thus suggesting the possibility that regulation of steroid metabolism by HGF represents a mechanism for high risk of hepatocellular carcinogenesis in males.