GCAP‐II: Isolation and characterization of the circulating form of human uroguanylin

Abstract

The systematic isolation of circulating regulatory peptides which generate cGMP as second messenger resulted in the identification of a novel member of the gnanylin family. In the present study we describe the purification and amino acid sequence of a new guanylate cyclase C activating peptide (GCAP-II). GCAP-II contains 24 amino acids in the following sequence: FKTLRTIANDDCELCVNVACTGCL. Its molecular mass is 2597.7 Da. The 16 C-terminal amino acids are identical to uroguanylin from human urine. Native and synthetic GCAP-II activate GC-C, the specific gnanylate cyclase receptor, of cultured human colon carcinoma (T84) cells. GCAP-II stimulates chloride secretion in isolated human intestinal mucosa mediated by intracellular cGMP increase. GCAP-II specific antibodies were used to localize the peptide by immunohistochemistry in entero-endocrine cells of the colonic mucosa. Key words':Guanylate cyclase activating peptide II; Uroguanylin; Guanylin; cGMP; Intestinal chloride secretion; Entero-endocrine cell intestinal tissues, such as kidney, liver, reproductive tract, adrenals, airway epithelia, and pancreas [4,5]. In addition, a larger molecular form of this peptide, namely guanylin-22-115, circulates as a bioactive peptide in human blood, suggesting that this peptide regulates the function of different target organs by an endocrine interaction [8].Uroguanylin, a second ligand of the GC-C receptor, has been recently purified from human and opossum urine [9,10]. The structural homology and the similar biological activity of guanylin and uroguanylin suggest that they are members of a peptide family, the main function of which is the activation of GC-C in the intestine and in other tissues. With regard to putative endocrine interactions of this system we initiated a systematic search for further endogenous activators of GC-C circulating in human blood. Here we report the isolation, the biochemical and functional characterization, and the immunohistochemical localization of a new GCAP related to uroguanylin.

Expression of type II cGMP-dependent protein kinase in rat kidney is regulated by dehydration and correlated with renin gene expression.

“…However, the full repertoire of activators of cGMP in the kidney, which no doubt include also urodilatin and uroguanylin, etc. (43), and their locations are not known. ANP and cGMP do, however, inhibit angiotensin-stimulated proximal tubule sodium and water reabsorption (44), an effect recently shown to be blocked by a cGK inhibitor (45).…”

Uroguanylin knockout mice have increased blood pressure and impaired natriuretic response to enteral NaCl load

“…There is now additional evidence that guanylin and uroguanylin have both local intestinal (paracrine) and endocrine functions, forming a potential enteric-renal link to coordinate salt ingestion with natriuresis (for reviews, see Forte et al,. Circumstantial evidence suggests that both peptides, particularly uroguanylin, function as endocrine intestinal natriuretic hormones because (a) both circulate in the bloodstream (6)(7)(8); (b) high-salt intake increases uroguanylin and guanylin mRNA (9,10), as well as urinary excretion of uroguanylin (11); and (c) uroguanylin levels are increased in the circulation of patients with renal disease and congestive heart failure (12,13). In addition, the cellular localization of uroguanylin in enterocytes of the proximal small intestine is consistent with the luminal and systemic secretion of enteric uroguanylin (11,(14)(15)(16).…”

Guanylin peptides: cyclic GMP signaling mechanisms

“…Uroguanylin mRNAs are most abundant in the small intestine compared to guanylin mRNA levels, which peak in the large intestine. Uroguanylin and prouroguanylin are also found in the circulation and it is likely that the gastrointestinal (GI) tract is a main source of the plasma peptides (7,33,34). Secretion of uroguanylin from GI mucosa into the plasma in response to oral NaCl may explain the prolonged increase in urinary sodium excretion that occurs following a high salt meal (26,27).…”