CLONING OF THE PROMOTER-REGULATORY REGION OF THE MURINE GROWTH-HORMONE RECEPTOR GENE - IDENTIFICATION OF A DEVELOPMENTALLY-REGULATED ENHANCER ELEMENT

The growth hormone (GH) receptor is essential for the actions of GH on postnatal growth and metabolism. To identify DNA sequences involved in the regulation of transcription of the murine GH receptor gene, a 17-kilobase genomic clone containing the 5'-flanking region, exon 1, and part of intron 1 of the murine GH receptor gene was isolated. Utilizing primer extension and ribonuclease protection assays, two major transcription start sites were identified in RNA from liver of male, female, and pregnant mice. Transient transfection stud ies using a reporter gene demonstrated promoter activity in a variety of eukaryotic cells. Deletional analysis and DNA protein binding assays led to the identification of a 30-base pair enhancer element located about 3.4 kilobases upstream of the transcription start sites. Computer analysis of the nucleotide sequence of the enhancer element did not reveal any potential DNA binding motifs for known transcription factors, and this DNA element failed to exhibit binding activity for some common transcription factors. Analysis of both functional activity and DNA-protein binding activity of this enhancer element in adult and fetal hepatocytes suggests that this DNA element may play a role in the developmental expression of the GH receptor gene.