PURIFICATION, CDNA SEQUENCE, AND TISSUE DISTRIBUTION OF RAT UROGUANYLIN

Guanylin, a peptide purified from rat jejunum, is thought to regulate water and electrolyte balance in the intestine. We show here, using a combination of Northern blots, Western blots, and functional assays, t hat guanylin and its receptor (GCC) are not distributed in parallel wi thin the rat intestine. To investigate the possibility that there migh t be a second intestinal peptide that serves as a ligand for GCC, we a ssayed tissue extracts for the ability to stimulate cyclic GMP synthes is in a GCC-expressing cell line. Duodenal extracts display a peak of biological activity that is not present in colon and that does not com igrate with guanylin or proguanylin. The activity co-purifies with a n ovel peptide (TIATDECELCINVACTGC) that has high homology with uroguany lin, a peptide initially purified from human and opossum urine. A rat uroguanylin cDNA clone was found to encode a propeptide whose C-termin us corresponds to our purified peptide. Northern blots with probes gen erated from this clone reveal that prouroguanylin mRNA is strongly exp ressed in proximal small intestine, but. virtually absent from colon, corroborating our biochemical measurements. Taken together, these stud ies demonstrate an intestinal origin for uroguanylin, and show that wi thin the intestine its distribution is complementary to that of guanyl in. (C) 1997 Elsevier Science B.V.