Lymphoguanylin: Cloning and characterization of a unique member of the guanylin peptide family

Guanylin and uroguanylin are small peptides containing two disulfide bonds that activate membrane guanylate cyclase-receptors in the intestine, kidney and other epithelia. Hybridization assays with a uroguanylin complementary DNA (cDNA) detected uroguanylin-like messenger RNAs (mRNAs) in the opossum spleen and testis, but these transcripts are larger than uroguanylin mRNAs . RT of RNA from spleen to produce cDNAs for amplification in the PCR follo wed by cloning and sequencing revealed a novel lymphoid-derived cDNA contai ning an open reading frame encoding a 109-amino acid polypeptide. This prot ein shares 84% and 40% of its residues with preprouroguanylin and preprogua nylin, respectively. A 15-amino acid, uroguanylin-like peptide occurs at th e COOH-terminus of the precursor polypeptide. However, this peptide is uniq ue in having only three cysteine residues. We named the gene and its peptid e product lymphoguanylin because the source of the first cDNA isolated was spleen and its mRNA is expressed in all of the lymphoid tissues tested. A 1 5-amino acid form of lymphoguanylin containing a single disulfide bond was synthesized that activates the guanylate cyclase receptors of human T84 int estinal and opossum kidney (OK) cells, although with less potency than urog uanylin and guanylin. Northern and/or RT-PCR assays detected lymphoguanylin mRNA transcripts in many tissues and organs of opossums, including those w ithin the lymphoid/immune, cardiovascular/renal, reproductive, and central nervous organ systems. Lymphoguanylin joins guanylin and uroguanylin in a g rowing family of peptide agonists that activate transmembrane guanylate cyc lase receptors, thus influencing target cell function via the intracellular second messenger, cGMP.