In vivo transfection of rat liver discloses binding sites conveying GH-dependent and female-specific gene expression.

The sexually dimorphic mode of GH secretion leads to a sex-differentiated expression of many hepatic target genes. Expression of the a1bg gene in rat liver is specifically induced by the female pattern of GH secretion. In this study, we have used the a1bg promoter in in vivo transfection experiments to investigate molecular mechanisms of GH-mediated female-specific hepatic gene regulation. Rat liver transfection was achieved by rapid tail vein injection of large volumes of plasmid solution. Expression of reporter constructs showed that the 160 bp proximal part of the a1bg promoter contained elements directing sex-specific expression. In vitro footprinting analysis and electromobility shift assays identified binding of hepatic nuclear factor 6 (HNF6), signal transducer and activator of transcriptions (Stat5) and nuclear factor 1 (NF1) in liver nuclear extracts to the 160 bp proximal promoter. Transfection of mutated and/or deletion constructs showed that HNF6 and NF1 binding markedly enhanced expression in female livers, whereas Stat5 reduces the sex difference by enhancing expression more strongly in male than in female rat liver. Based on our present results, we propose that adjacent binding sites for NF1 and HNF6 constitute a gene regulatory unit of importance for transducing the female-specific effect of GH in rat liver.