Disease relevance of Guca2a

• Guanylin and E. coli heat-stable enterotoxin induce chloride secretion through direct interaction with basolateral compartment of rat and human colonic cells [1].
• BACKGROUND & AIMS: Guanylin and heat-stable enterotoxin (STa) stimulate intestinal Cl- secretion via activation of the cystic fibrosis transmembrane regulator (CFTR)-encoded Cl- channel [2].
• We now show that two assays previously used to examine the activity of purified beta gamma subunits--namely, to support either rhodopsin-catalyzed guanyl nucleotide exchange on Gt alpha or pertussis toxin-catalyzed ADP-ribosylation of Gt alpha--can be used with detergent extracts of cells [3].
• Complementary DNAs encoding three subtypes of the alpha subunit (alpha i-1, alpha o and alpha s) of rat guanyl nucleotide regulatory proteins were used to construct recombinant baculoviruses which direct high-level expression of the corresponding proteins in cultured Sf9 insect cells [4].
• Moreover, guanylin induced intense edema in the mucosa and submucosa of the small intestine 5 min after the injection, which disappeared after 30 min [5].

High impact information on Guca2a

• Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide [6].
• RasGRP, a guanyl nucleotide-releasing protein for the small guanosine triphosphatase Ras, was characterized [7].
• The aim of the present study was to identify cellular sites of uroguanylin expression in the rat gastrointestinal tract and resolve the guanylin localization controversy [8].
• CONCLUSIONS: Previous results showing guanylin expression in enterochromaffin cells appear to be a consequence of antibody cross-reactivity for epitopes conserved between proguanylin and prouroguanylin [8].
• Prostaglandin E2 and 8-bromo-cAMP but not STa/guanylin also transiently increased paracellular permeability [2].

Chemical compound and disease context of Guca2a

• Moreover, pertussis toxin (100 ng/ml) reversed the inhibition of insulin release due to vasopressin, indicating the possible involvement of a guanyl-nucleotide regulatory protein in the inhibitory effect [9].
• Pertussis toxin eliminated ANF-dependent inhibition of adenylate cyclase by catalyzing ADP-ribosylation of membrane-bound Ni protein (41-kDa alpha subunit of the inhibitory guanyl-nucleotide-binding protein of adenylate cyclase) [10].
• gamma-Hydroxybutyrate receptor binding in rat brain is inhibited by guanyl nucleotides and pertussis toxin [11].
• The effects of non-hydrolyzable guanyl nucleotide analogue GTP-gamma S on CCKB receptor binding in human and guinea-pig cortex, Jurkat T-cells, rat pituitary GH3 cells, rat glioma C6 cells and human small cell lung cancer NCI-H69 cells were investigated by using [3H]CCK-8S saturation and competition binding studies [12].
• PZG's downregulation of lipolysis and cyclic AMP concentrations was unaffected by adenosine deaminase or pertussis toxin, suggesting that PZG did not activate Gi, the inhibitory guanyl nucleotide regulatory protein [13].

Biological context of Guca2a

• This peptide, which we have termed guanylin, is composed of 15 amino acids and has the following amino acid sequence, PNTCEICAYAACTGC, as determined by automated Edman degradation sequence analysis and electrospray mass spectrometry [14].
• Transfection of COS-7 cells with the guanylin cDNA resulted in the expression of a secreted protein of M(r) 10,000 [15].
• Because guanylin circulates in the bloodstream, we tested the hypothesis that it modulates intestinal ion transport by acting on the serosal side of intestinal cells [1].
• In the duct cells guanylin immunoreactivity spread after the duct system developed, whereas in acinar cells it disappeared after cell differentiation [16].
• Guanylin-stimulated HCO3- secretion was independent of luminal Cl-, inhibited by the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate, and additive to the HCO3- secretory rate stimulated by glucagon and carbachol but not by the tested adenosine 3',5'-cyclic monophosphate (cAMP)-dependent agonists [2].

Anatomical context of Guca2a

• Guanylyl cyclase C, the apparent guanylin receptor, was found in abundant amounts in the intestine by Northern analysis, and by the polymerase chain reaction or cDNA cloning it was also found in adrenal gland, airway epithelial cells, brain, and olfactory and tracheal mucosa [15].
• Guanylin mRNA was prevalent in rat intestine but was also found in low abundance in adrenal gland, kidney, and uterus/oviduct [15].
• We previously detected specific binding activity of Escherichia coli heat-stable enterotoxin (ST), the guanylin exogenous ligand, in rat colonic basolateral membranes [1].
• Guanylin addition to either side of Caco-2 cells induced the same effects as ST, although to a lesser extent [1].
• Clones have been isolated which demonstrate that the guanylin peptide is contained within a 115 amino acid apparent preprohormone encoded by a 600 base messenger RNA in rat jejunum [17].

Associations of Guca2a with chemical compounds

• Guanylin: an endogenous activator of intestinal guanylate cyclase [14].
• Guanylin required oxidation for expression of bioactivity and subsequent reduction of the oxidized peptide eliminated the effect on cyclic GMP, indicating a requirement for cysteine disulfide bond formation [14].
• The expressed proguanylin failed to elevate cyclic GMP concentrations in human colonic T84 cells, but acetic acid treatment of pro-guanylin activated it and resulted in large elevations of cyclic GMP [15].
• The carboxyl-terminal region of the predicted polypeptide contained a sequence identical to guanylin, but the 15-amino acid peptide likely represents an artifact of previous acetic acid extraction methods, since an aspartate residue precedes the amino-terminal proline [15].
• Guanylin strongly stimulates rat duodenal HCO3- secretion: proposed mechanism and comparison with other secretagogues [2].

Physical interactions of Guca2a

• Endothelin receptor subtypes are coupled to adenylate cyclase via different guanyl nucleotide-binding proteins in vasculature [18].
• Furthermore, our data clearly show that an accelerating AMPA receptor endocytosis by stimulating the formation of guanyl nucleotide dissociation inhibitor-Rab5 complex is a potential downstream processing of p38 MAPK activation to mediate DHPG-LTD [19].
• A growing body of evidence suggests a role for guanyl nucleotide binding proteins (G proteins) in GnRH action [20].
• Regulation of thyrotropin-releasing hormone binding by monovalent cations and guanyl nucleotides [21].
• The results suggest a role of the regulatory guanyl nucleotide-binding protein in diabetes leading to an increased dose response relationship of the hepatic adenylate cyclase system to glucagon [22].

Regulatory relationships of Guca2a

• It is concluded that occupancy of the guanyl nucleotide binding site that activates the catalytic moiety of the system is not sufficient to promote hormone-receptor coupling to adenylyl cyclase and that occupancy of a second site by guanyl nucleotides is essential to effect stimulation of adenylyl cyclase by the glucagon-receptor complex [23].
• CRF stimulates adenylate cyclase activity at least partly through a guanyl nucleotide-dependent mechanism [24].
• Binding of thyrotropin-releasing hormone (TRH) to specific receptors on membranes isolated from GH4C1 pituitary cells was inhibited by monovalent cations and guanyl nucleotides [21].
• We conclude that calmodulin influences the activity of the guanyl nucleotide-dependent adenylate cyclase in rat thymocytes and ultimately mediates the stimulation of enzyme activity that T3 produces [25].
• Guanyl nucleotides failed to influence the KD and Bmax parameters of [3H]WAY-100635 binding to 5-HT1A receptors [26].

Other interactions of Guca2a

• We have studied whether endothelin (ET) isopeptides have any effects on adenylate cyclase activity via different guanyl nucleotide-binding proteins (G-proteins) in cultured rat vascular smooth muscle cells (VSMC) and bovine endothelial cells (EC) [18].
• Binding of 125I-GRP1-27 was sensitive to GTP analogues, suggesting that the GRP receptor is functionally linked to a guanyl regulatory protein; however, the wheat germ agglutinin-agarose purified receptor had lost this G-protein activity [27].
• Effects of glucagon and guanyl nucleotides on the rat liver plasma membrane adenylyl cyclase were studied [23].
• Coupling of glucagon receptor to adenylyl cyclase. Requirement of a receptor-related guanyl nucleotide binding site for coupling of receptor to the enzyme [23].
• In competition studies, guanyl 5'-yl imidodiphosphate decreased the IC50 s of unlabeled galanin which were homogenized around 4 nM in most telencephalic and hypothalamic regions [28].

Analytical, diagnostic and therapeutic context of Guca2a

• RESULTS: By every criterion, the low-salt diet reduced expression of guanylin to 30%-40% of the level found in control animals [29].
• Western blotting analyses in hypophyseal tissue extracts identified the expected 12.5-kDa immunoreactive peptide by using two different region-specific guanylin antisera [30].
• Since the latter protein is also expressed in airway epithelia, we investigated the lung of three mammalian species for the presence and cellular localization of guanylin by immunoblot (Western blot) analyses and light and electron microscopical immunocytochemistry [31].
• Synthetic uroguanylin-(2-15) (i.e., EDCELCINVACTGC) was 10-fold more potent than synthetic rat guanylin, but both peptides were less potent than Escherichia coli ST in the T84 cell cGMP bioassay [32].
• Guanylin was localized to secretory granules underneath the apical membrane of Clara cells and was, in addition, detected in high concentrations in bronchoalveolar lavage fluid, predicting release of the peptide luminally into the bronchiolar airways [33].

References