Growth hormone pretranslationally regulates the sexually dimorphic expression of the prolactin receptor gene in rat liver

The female-specific expression of the rat liver PRL receptor (PRL-R) gene was investigated by Northern analysis of hypophysectomized rats after two alternative human GH treatments that were to mimic either 1) the continuous female-specific or 2) the discontinuous male-specific serum GH patterns. The former (female-specific) pattern was shown to result in a dramatic increase in PRL-R mRNA in both males and females, while the latter (male-specific) pattern failed to evoke this response. A similar inductive effect in hypophysectomized females was shown after continuous administration of bovine GH and was found to constitute an approximately 60-fold increase in PRL-R mRNA levels. This effect by bovine GH, which, unlike the human isoform, is devoid of lactogenic properties, thus indicates the somatogenic origin of the signal resulting in this inductive response. These observations in conjunction with previous data obtained for other GH-regulated non-receptor genes are interpreted to support the proposal of GH serum patterns being an eaerly signal in a more general mechanism for pretranslational regulation of sex-specific gene expression. In contrast to GH, only a slight elevation of PRL-R mRNA was evoked by the ligand ovine PRL, while coadministration of ovine PRL with bovine GH failed to enhance the mRNA level found with bovine GH alone. The detection of previously unreported PRL-R mRNAs in liver of approximately 3.0, 3.8, and 5 kilobases in addition to the major 2.2-kilobase form was also evident after continuous GH administration.