Characterization of human uroguanylin: a member of the guanylin peptide family

Abstract

Guanylin, a peptide homologue of the bacterial heat-stable enterotoxins (ST), is an endogenous activator of guanylate cyclase C (GC-C). We have initiated a search for other members of the guanylin peptide family and in the current study describe a "guanylin-like peptide" from human urine. Bioactivity was monitored by determining the effect of urine extracts on T84 cell guanosine 3',5'-cyclic monophosphate (cGMP) levels. Purification yielded two bioactive peaks of peptides that, when sequenced by NH2-terminal analysis, possessed 15 and 16 amino acids. The sequence of the smaller peptide represented an NH2-terminal truncation of the larger peptide. We have termed the larger peptide human uroguanylin; it has the following amino acid sequence: NDDCELCVNVACTGCL. Human uroguanylin shares amino acid sequence homology with guanylin and ST. Synthetic uroguanylin increased cGMP levels in T84 cells, competed with 125I-labeled ST for receptors, and stimulated Cl- secretion as reflected by an increased short-circuit current. Thus we report the isolation from human urine of a unique peptide, uroguanylin, that behaves in a manner similar to guanylin and appears to be a new member of this peptide family.

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

“…In contrast, synthetic uroguanylin was somewhat more potent than guanylin in the stimulation of GC-C activity in T84 cells [9,10]. Possible explanations for this discrepancy are passage-related differences in the responsiveness of T84 cells, the different incubation times used for experimentation (60 min in our study and 30 rain in the study of Kita and coworkers [10]) and differences in the receptor affinity of GCAP-II and the shorter uroguanylin. Recently, the uroguanylin cDNA has been cloned [15].…”

“…Northern blot analysis using total RNA showed a very high expression of the GCAP-II-gene in human colon [15]. With regard to the high levels of uroguanylin in urine it has been postulated that the kidney may be the main source of this peptide [10]. However, our attempts to demonstrate a significant gene expression in extraintestinal tissues, even in kidney, were unsuccessful.…”

“…Comparison of the sequence of this second circulating guanylate cyclase C activating peptide (GCAP-II) with other proteins in the SwissProt and EMBL databases showed that the sequence is new and that the 16 amino acids from position 9 to position 24 of GCAP-II are identical to those of human uroguanylin, the peptide isolated from urine by Kita and coworkers [10] (see Fig. 3).…”

“…It contains 24 amino acids and represents an N-terminally extended form of uroguanylin, the 16-amino acid peptide recently isolated from urine [10]. As a source for human plasma peptides we used hemofiltrate collected from patients with renal insufficiency, in analogy to our previous study demonstrating the molecular form of circulating guanylin [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.…”