Regulation of prolactin receptor (PRLR) gene expression in insulin-producing cells - Prolactin and growth hormone activate one of the rat PRLR gene promoters via STAT5a and STAT5b

Expression of the prolactin receptor (PRLR) gene is increased in pancreatic islets during pregnancy and in vitro in insulin-producing cells by growth hormone (GH) and prolactin (PRL), The 5'-region of the rat PRLR gene contai ns at least three alternative first exons that are expressed tissue-specifi cally because of differential promoter usage. We show by reverse transcript ion-polymerase chain reaction analysis that both exon 1A- and exon 1C-conta ining PRLR transcripts are expressed in rat islets and that human (h)GH, ov ine (o)PRL, and bovine (b)GH increase exon 1A expression 6.5 +/- 0.8-fold, 6.8 +/- 0.7-fold, and 3.9 +/- 0.7-fold and exon le expression 4.8 +/- 0.4-f old, 4.4 +/- 0.6-fold, and 2.5 +/- 0.7-fold, respectively. Expression of ex on 1B was not detectable. The transcriptional activities of reporter constr ucts containing the 1A, 1B, or 1C promoter were found to be 22.8-fold, 2.7- fold, and 8.0-fold, respectively, above that of a promoterless reporter con struct when transfected into the insulin-producing INS-1 cells. The transcr iptional activity of the 1A promoter construct was increased 8.9 +/- 1.9-fo ld by 0.5 mu g/ml hGH. Responsiveness to hGH of the 1A promoter was localiz ed to the region from -225 to +81 with respect to the transcription start s ite. This region contains the sequence TTCTAGGAA that by gel retardation ex periments was shown to bind the transcription factors STAT5a and STAT5b in response to stimulation by hGH, oPRL, or bGH. Mutation of this gamma-activa ted sequence-like element completely abolished transcriptional induction of the 1A promoter by hGH, Our results suggest that GH and PRL increase the l evels of exon 1A- and 1C-containing PRLR mRNA species and furthermore that the transcriptional activity of the 1A promoter is increased via activation of STAT5a and STAT5b.