STRUCTURE AND FUNCTIONAL EXPRESSION OF A COMPLEMENTARY-DNA FOR PORCINE GROWTH HORMONE-RELEASING HORMONE-RECEPTOR

Growth hormone-releasing hormone (GHRH) belongs to the family of gut-neuropeptide hormones which also includes glucagon, secretin and vasoactive intestinal peptide (VIP). All receptors for this peptide hormone family seem to involve similar signal transduction pathways. Upon hormone binding, these receptors interact with guanine nucleotide binding protein 'Gs' and cause the stimulation of adenylate cyclase. The secretin and VIP receptor cDNAs have recently been cloned and found to be homologous to those of calcitonin and parathyroid hormone receptors. Based on cDNA sequences of these receptors, we designed several oligonucleotide primers which were used to amplify two novel porcine pituitary cDNA fragments by the polymerase chain reaction. One novel receptor cDNA fragment was used to screen a porcine pituitary cDNA library and a full-length cDNA encoding a putative porcine GHRH receptor of 451 amino acids was isolated. This putative receptor mRNA is present specifically in porcine anterior pituitary cells and not in eight other porcine tissues as shown by Northern hybridization analysis. The receptor cDNA was subsequently cloned into a mammalian cell expression vector containing the cytomegalovirus promoter. A human kidney tumor cell line (293) stably transfected with this vector was found to express the receptor efficiently and to bind [I-125]-GHRH specifically. Furthermore, challenge of the 293 cells expressing the receptor by GHRH leads to efficient stimulation of cytoplasmic cAMP production.