Biological activities of two porcine growth hormone-releasing hormone receptor isoforms.
Binding of growth hormone-releasing hormone (GHRH) to two isoforms (G3R and G5R) of the porcine GHRH receptor was studied. Both G3R- and G5R-cDNA were isolated from a porcine anterior pituitary cDNA library and have an identical primary structure from aa 1 to 418 and a different aa sequence from aa 419 to 423. In addition, the G5R isoform contains an extra C-terminal tail of 28 aa. The G3R and G5R mRNAs arise from alternative splicing of a single precursor mRNA for GHRH receptors. A mammalian cell expression vector containing either G3R or G5R cDNA under the regulation of a strong human cytomegalovirus promoter was constructed and used to transfect a human embryonic kidney 293 cell line. Two stable transfectants (293/G3R-4 and 293/G5R-12) were isolated on the basis of high expression of the receptor mRNAs. Both G3R and G5R mRNAs were expressed at similarly high levels in 293/G3R-4 and 293/G5R-12 cells; however, GHRH binding to 293/G3R-4 cells was much greater than that observed for 293/G5R-12 cells. Basal as well as GHRH-stimulated GTPase activity and intracellular cAMP concentration are also significantly greater in 293/G3R-4 cells as compared to 293/G5R-12 cells. We conclude that the modification of GHRH receptor at the C-terminal region hindered GHRH binding to the receptor and thus attenuates its biological activities.
Hassan
H A
HA
Department of Biology, Faculty of Science, United Arab Emirates University, Al-Ain. kataya@uaeu.ac.ae
D000595:Amino Acid Sequence; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D018013:Receptors, Neuropeptide / Q000235:genetics / Q000378:metabolism*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015290:Second Messenger Systems; D013552:Swine
D020033:Protein Isoforms; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C048250:somatotropin releasing hormone receptor