MOLECULAR-CLONING AND EXPRESSION OF A HUMAN SECRETIN RECEPTOR

Secretin is a 27-amino acid neuroendocrine peptide that stimulates flu id and electrolyte secretion in the gastrointestinal tract, activates tyrosine hydroxylase activity in the central nervous system, and affec ts cardiac and renal function. Specific receptors for secretin have be en previously characterized on neuroblastoma cells, pancreatic acini, gastric glands, and liver cholangiocytes. We report here the isolation of a 1616-base pair cDNA from human lung tissue that encodes a 440-am ino acid, 50-kDa, G protein-coupled human secretin receptor (HSR), wit h homology of 80% with the rat secretin receptor and 37% with the huma n type I vasoactive intestinal peptide receptor. Northern blot analysi s of human tissue mRNA revealed that the relative intensity for expres sion of a 2.1-kilobase HSR transcript was pancreas > kidney > small in testine > lung > liver, with trace levels in brain, heart, and ovary. Stable transfectants of HSR in human embryonic kidney 293 cells, terme d 293S12, expressed 10(5) binding sites/cell for I-125-secretin, with an apparent K-d of 3.2 nM. Vasoactive intestinal peptide, pituitary ad enylyl cyclase-activating peptide-38, and glucagon were less potent (b y 3 orders of magnitude) than secretin in competitively inhibiting I-1 25-secretin binding to 293S12 cells. Secretin evoked concurrent dose-d ependent increases in intracellular cAMP and calcium levels in 293S12 cells and stimulated a 4-fold increase in phosphatidytinositol hydroly sis. Thus, the HSR expressed by stable transfectants can couple to two distinct intracellular signaling pathways.