MOLECULAR-CLONING, FUNCTIONAL EXPRESSION, AND SIGNAL-TRANSDUCTION OF THE GIP-RECEPTOR CLONED FROM A HUMAN INSULINOMA

Glucose-dependent insulinotropic polypeptide (GIP) plays an important role in the regulation of postprandial insulin secretion and proinsuli n gene expression of pancreatic beta-cells. This study demonstrates th e molecular cloning of a cDNA for the GIP-receptor from a human insuli noma lambda gt11 cDNA library, The cloned cDNA encoded a seven transme mbrane domain protein of 466 amino acids which showed high homology (4 1%) to the human glucagon-like peptide 1 (GLP-1) receptor, Homology to the GIP receptor from rat or hamster was 79% and 81%, respectively, W hen transfected stably into fibroblast CHL-cells a high affinity recep tor was expressed which coupled to the adenylate cyclase with normal b asal cAMP and increasing intracellular cAMP levels under stimulation w ith human GIP-1-42 (EC(50) = 1.29 x 10(-13) M). The receptor accepted only human GIP 1-42 (K-d = 1.93 +/- 0.2 x 10(-8) M) and porcine trunca ted GIP 1-30 (K-d = 1.13 +/- 0.1 x 10(-8) M) as high affinity ligands, At 1 mu M, exendin-4 and (9-39)amide weakly reduced GLP-binding (25%) whereas secretin, glucagon, glucagon-like peptide-1, vasoactive intes tinal polypeptide, peptide histidine-isoleucine, and pituitary adenyly l cyclase activating peptide mere without effect, In transfected CHL c ells, GIP-1-42 did not increase intracellular calcium, Northern analys is revealed one transcript of human GIP receptor mRNA with an apparent size of 5.5 kb. The exact understanding of GIP receptor regulation an d signal transduction mill aid in the understanding of the incretin ho rmone's failure to exert its biological action at the pancreatic B-cel l in type IT diabetes mellitus,