Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The guanylin family of bioactive peptides consists of three endogenous peptides, including guanylin, uroguanylin and lymphoguanylin, and one exogenous peptide toxin produced by enteric bacteria. These small cysteine-rich peptides activate cell-surface receptors, which have intrinsic guanylate cyclase activity, thus modulating cellular function via the intracellular second messenger, cyclic GMP. Membrane guanylate cyclase-C is an intestinal receptor for guanylin and uroguanylin that is responsible for stimulation of Cl- and HCO3- secretion into the intestinal lumen. Guanylin and uroguanylin are produced within the intestinal mucosa to serve in a paracrine mechanism for regulation of intestinal fluid and electrolyte secretion. Enteric bacteria secrete peptide toxin mimics of uroguanylin and guanylin that activate the intestinal receptors in an uncontrolled fashion to produce secretory diarrhea. Opossum kidney guanylate cyclase is a key receptor in the kidney that may be responsible for the diuretic and natriuretic actions of uroguanylin in vivo. Uroguanylin serves in an endocrine axis linking the intestine and kidney where its natriuretic and diuretic actions contribute to the maintenance of Na+ balance following oral ingestion of NaCl. Lymphoguanylin is highly expressed in the kidney and myocardium where this unique peptide may act locally to regulate cyclic GMP levels in target cells. Lymphoguanylin is also produced in cells of the lymphoid-immune system where other physiological functions may be influenced by intracellular cyclic GMP. Observations of nature are providing insights into cellular mechanisms involving guanylin peptides in intestinal diseases such as colon cancer and diarrhea and in chronic renal diseases or cardiac disorders such as congestive heart failure where guanylin and/or uroguanylin levels in the circulation and/or urine are pathologically elevated. Guanylin peptides are clearly involved in the regulation of salt and water homeostasis, but new findings indicate that these novel peptides have diverse physiological roles in addition to those previously documented for control of intestinal and renal function.
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PMID:Guanylin regulatory peptides: structures, biological activities mediated by cyclic GMP and pathobiology. 1039 5

The enteric peptides, guanylin and uroguanylin, are local regulators of intestinal secretion by activation of receptor-guanylate cyclase (R-GC) signaling molecules that produce cyclic GMP (cGMP) and stimulate the cystic fibrosis transmembrane conductance regulator-dependent secretion of Cl- and HCO3-. Our experiments demonstrate that mRNA transcripts for guanylin and uroguanylin are markedly reduced in colon polyps and adenocarcinomas. In contrast, a specific uroguanylin-R-GC, R-GCC, is expressed in polyps and adenocarcinomas at levels comparable with normal colon mucosa. Activation of R-GCC by uroguanylin in vitro inhibits the proliferation of T84 colon cells and elicits profound apoptosis in human colon cancer cells, T84. Therefore, down-regulation of gene expression and loss of the peptides may interfere with renewal and/or removal of the epithelial cells resulting in the formation of polyps, which can progress to malignant cancers of the colon and rectum. Oral replacement therapy with human uroguanylin was used to evaluate its effects on the formation of intestinal polyps in the Min/+ mouse model for colorectal cancer. Uroguanylin significantly reduces the number of polyps found in the intestine of Min/+ mice by approximately 50% of control. Our findings suggest that uroguanylin and guanylin regulate the turnover of epithelial cells within the intestinal mucosa via activation of a cGMP signaling mechanism that elicits apoptosis of target enterocytes. The intestinal R-GC signaling molecules for guanylin regulatory peptides are promising targets for prevention and/or therapeutic treatment of intestinal polyps and cancers by oral administration of human uroguanylin.
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PMID:Uroguanylin treatment suppresses polyp formation in the Apc(Min/+) mouse and induces apoptosis in human colon adenocarcinoma cells via cyclic GMP. 1101 42

In vitro competitive binding studies of In-DOTA-NCS-6-Ahx-Phe(19)-ST[1-19] vs. 125I-Tyr(5)-6-Ahx-Phe(19)-ST[1-19] with guanylate cyclase -C (GC-C) receptors on human colon cancer LS-180 cells revealed an IC(50) value of 7.7 +/- 0.1.6 nM. The in vitro cellular residualization studies of the 111In-DOTA-NCS-ST peptide and GC-C receptor mediated stimulated cGMP production with LS-180 cells demonstrates that this peptide selectively binds to LS-180 cells in an agonistic fashion. In vivo biodistribution studies in LS-180 tumor bearing SCID mice demonstrates that the 111In-DOTA-NCS-ST peptide targets the tumor with a specific uptake of 0.94 +/- 0.31%ID/g at 1 hr p.i. and approximately 23% was retained by the tumor at 4 hrs p.i. The radioactivity cleared rapidly from the blood stream with 84.5 +/- 3.4%ID at 1h p.i. found in the urine. High activity in urine and kidney, and minimal activity in liver and intestines, demonstrates preferential clearance of the radioactivity through the renal/urinary pathway. The specific in vitro and in vivo accumulation of the radioactivity by LS-180 human colonic cancer cells highlights the potential of radiometallated-DOTA-ST analogs as diagnostic/therapeutic radiopharmaceuticals.
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PMID:In vivo evaluation of an 111In-labeled ST-peptide analog for specific-targeting of human colon cancers. 1171 9

New human Escherichia coli heat-stable peptide (ST(h)) analogues containing a DOTA chelating group were synthesized by sequential and selective formation of disulfides bonds in the peptide. This synthetic approach utilizes three orthogonal thiol-protecting groups, Trt, Acm, and t-Bu, to form three disulfide bonds by successive reactions using 2-PDS, iodine, and silyl chloride-sulfoxide systems. The DOTA-ST(h) conjugates exhibiting high guanylin/guanylate cyclase-C (GC-C) receptor binding affinities were obtained with >98% purity. In vitro competitive binding assays, employing T-84 human colon cancer cells, demonstrated the IC(50) values of <2 nM for GC-C receptor binding suggesting that the new synthetic ST(h) analogues are biologically active. In vitro stability studies of the (111)In-DOTA-Phe(19)-ST(h) conjugate incubated in human serum at 37 degrees C under 5% CO(2) atmosphere revealed that this conjugate is extremely stable with no observable decomposition at 24 h postincubation. HPLC analysis of mouse urine at 1 h pi of the (111)In-DOTA-Phe(19)-ST(h) conjugate showed only about 15% decomposition suggesting that the (111)In-DOTA-Phe(19)-ST(h) conjugate is highly stable, even under in vivo conditions. In vivo pharmacokinetic studies of the (111)In-DOTA-Phe(19)-ST(h) conjugate in T-84 human colon cancer derived xenografts in SCID mice conducted at 1 h pi showed an initial tumor uptake of 2.04 +/- 0.30% ID/g at 1 h pi with efficient clearance from the blood pool (0.23 +/- 0.14% ID/g, 1 h pi) by excretion mainly through the renal/urinary pathway (95.8 +/- 0.2% ID, 1 h pi). High tumor/blood, tumor/muscle, and tumor/liver ratios of approximately 9:1, 68:1, and 26:1, respectively, were achieved at 1 h pi The specific in vitro and in vivo uptake of the radioactivity by human colonic cancer cells highlights the potential of radiometalated-DOTA-ST(h) conjugates as diagnostic/therapeutic radiopharmaceuticals.
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PMID:Chemical synthesis of Escherichia coli ST(h) analogues by regioselective disulfide bond formation: biological evaluation of an (111)In-DOTA-Phe(19)-ST(h) analogue for specific targeting of human colon cancers. 1190 59

Recent studies provide evidence that exisulind and two potent derivatives, CP461 and CP248, induce apoptosis in colon cancer cells by inhibiting cyclic GMP (cGMP)-specific phosphodiesterases (phosphodiesterases 2 and 5). This causes an increase in intracellular levels of cGMP, thus activating the cGMP-dependent protein kinase G (PKG), which then activates pathways that lead to apoptosis. To further examine this mechanism and to provide a potential in vivo biomarker for activation of this pathway, we examined phosphorylation of the vasodilator-stimulated phosphoprotein (VASP), a ubiquitously expressed endogenous substrate for PKG. We found that VASP was phosphorylated after treating SW480 colon cancer cells with exisulind, CP461, or CP248. CP248-induced VASP phosphorylation was inhibited by a specific PKG inhibitor but not by a protein kinase A inhibitor. The drug 3-(5'-hydroxymethyl-2'-furyl)-benzylindazole and nitric oxide donors that activate cellular guanylyl cyclase and thus increase cellular levels of cGMP also caused VASP phosphorylation. With all of these agents, the phosphorylation of VASP was associated with increased intracellular levels of cGMP and the induction of apoptosis. We also demonstrated direct in vivo phosphorylation of VASP with constitutively activated mutants of PKG. These results suggest that VASP phosphorylation can provide a useful endogenous cellular biomarker for anticancer agents that cause cGMP-mediated apoptosis.
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PMID:Vasodilator-stimulated phosphoprotein (VASP) phosphorylation provides a biomarker for the action of exisulind and related agents that activate protein kinase G. 1249 13

Guanylin, uroguanylin, and the bacterial heat-stable enterotoxin (ST) peptides comprise a new family of cyclic guanosine 3'-5' monophosphate (cGMP)-regulating agonists. The discovery of guanylin and uroguanylin peptides stems from studies of cellular mechanisms underlying a form of secretory diarrhea caused by enteric bacteria. Guanylin, uroguanylin, and microbial ST peptides activate a common apical membrane receptor-guanylate cyclase (R-GC) that elicits large increases in the intestinal secretion of chloride and bicarbonate via the intracellular second messenger, cGMP. Guanylin and uroguanylin were isolated from rat jejunum and opossum urine, respectively. These peptides are endogenous peptide hormones that physiologically regulate R-GC signaling proteins in target cells. Physiological roles for these peptides include the regulation of epithelial cell balance in the intestinal epithelium and modulation of sodium balance through actions in the kidney. The guanylin-uroguanylin-ST peptides are candidate therapeutic agents targeting receptors in the intestine, kidney, and other epithelia. For example, uroguanylin has anti-tumor actions in an animal model for human colon cancer. The ST peptides can be used as diagnostic agents to detect secondary colon cancers by single photon-emitting computed tomography (SPECT) imaging, thus localizing metastatic forms of colon cancer. Other examples of potential therapeutic applications for the guanylin family of cGMP-regulating agonists are: (1) the irritable bowel syndrome (IBS) with constipation, (2) salt-dependent forms of high blood pressure, (3) liver regeneration and repair, and (4) respiratory diseases such as asthma. Competitive pharmacological antagonists of bacterial ST peptides offer a means for treating the diarrhea caused by ST-secreting strains of enteric bacteria.
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PMID:Uroguanylin and guanylin peptides: pharmacology and experimental therapeutics. 1551 84

We recently reported that proteinase-activated receptors type I (PAR-1) are coupled to both negative and positive invasion pathways in colonic and kidney cancer cells cultured on collagen type I gels. Here, we found that treatments with the cell-permeant analog 8-Br-cGMP and the soluble guanylate cyclase activator BAY41-2272, and Rho kinase (ROK) inhibition by Y27632 or a dominant negative form of ROK lead to PAR-1-mediated invasion through differential Rac1 and Cdc42 signaling. Hypoxia or the counteradhesive matricellular protein SPARC/BM-40 (SPARC: secreted protein acidic rich in cysteine) overexpressed during cancer progression also commutated PAR-1 to cellular invasion through the cGMP/protein kinase G (PKG) cascade, RhoA inactivation, and Rac1-dependent or -independent signaling. Cultured primary cancer cells isolated from peritoneal and pleural effusions from patients with colon cancer or other malignant tumors harbored PAR-1, as shown by RT-PCR and FACS analyses. These malignant effusions also contained high levels of activated thrombin and fibrin, and induced a proinvasive response in HCT8/S11 human colorectal cancer cells. Our data underline the essential role of the tumor microenvironment and of several commutators targeting cGMP/PKG signaling and the RhoA-ROK axis in the control of PAR-1 proinvasive activity and metastatic potential of cancer cells in distant organs and peritoneal or pleural cavities. We also add new insights into the mechanisms linking the coagulation mediators thrombin and PAR-1 in the context of blood coagulation disorders and venous thrombosis often observed in cancer patients, as described in 1865 by Armand Trousseau.
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PMID:Commutators of PAR-1 signaling in cancer cell invasion reveal an essential role of the Rho-Rho kinase axis and tumor microenvironment. 1609 33

Recent studies indicate that the induction of apoptosis in human colon cancer cells by certain nonsteroidal antiinflammatory drugs involves increased expression of 15-LOX-1 and synthesis of its major product 13-S-hydroxyoctadecadienoic acid (13-S-HODE). Evidence was obtained that this occurs via a cyclooxygenase-2 (COX-2)-independent mechanism, but the actual mechanism of induction of 15-LOX-1 by these compounds is not known. There is extensive evidence that treatment of SW480 human colon cancer cells with sulindac sulfone (Exisulind, Aptosyn) or the related derivative OSI-461, both of which inhibit cyclic GMP (cGMP)-phosphodiesterases but lack COX-2 inhibitory activity, causes an increase in intracellular levels of cGMP, thus activating protein kinase G (PKG), which then activates pathways that lead to apoptosis. Therefore, in the present study, we examined the effects of various agents that cause increased cellular levels of cGMP on the expression of 15-LOX-1 in SW480 human colon cancer cells. Treatment of the cells with Exisulind, sulindac sulfide, OSI-461, the guanylyl cyclase activator YC-1, or the cell-permeable cGMP compound 8-para-chlorophenylthio-cGMP (8-pCPT-cGMP) caused an increase in cellular levels of 15-LOX-1. Exisulind, OSI-461, and 8-pCPT-cGMP also increased mRNA levels of 15-LOX-1, suggesting that the effects were at the level of transcription. The cGMP-phosphodiesterase inhibitors and YC-1 increased the production of 13-S-HODE, which is the linoleic acid metabolite of 15-LOX-1. Treatment of SW480 cells with the PKG inhibitor Rp-8-pCPT-cGMP blocked Exisulind-induced 15-LOX-1 expression. Furthermore, derivatives of SW480 cells that were engineered to stably overexpress wild-type PKG Ibeta displayed increased cellular levels of 15-LOX-1 when compared with vector control cells. Taken together, these results provide evidence that the cGMP/PKG pathway can play an important role in the induction of 15-LOX-1 expression by nonsteroidal antiinflammatory drugs and related agents.
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PMID:Activation of protein kinase G up-regulates expression of 15-lipoxygenase-1 in human colon cancer cells. 1616 23

The human E. coli heat-stable enterotoxin (ST(h), amino acid sequence N1SSNYCCELCCNPACTGCY19) binds specifically to the guanylate cyclase C (GC-C) receptor, which is present in high density on the apical surface of normal intestinal epithelial cells as well as on the surface of human colon cancer cells. Analogs of ST(h) are currently being used as vectors targeting human colon cancers. Previous studies in our laboratory have focused on development of 111Indium-labeled ST(h) analogs for in vivo imaging applications. Here, we extend the scope of this work to include targeting of the therapeutic radionuclides 90Y and 177Lu. The peptide DOTA-F19-ST(h)(1-19) was synthesized using conventional Fmoc-based solid-phase techniques and refolded in dilute aqueous solution. The peptide was purified by RP-HPLC and characterized by MALDI-TOF MS and in vitro receptor binding assay. The DOTA-conjugate was metallated with nonradioactive Lu(III)Cl3 and Y(III)Cl3, and IC50 values of 2.6+/-0.1 and 4.2+/-0.9 nM were determined for the Lu- and Y-labeled peptides, respectively. 177Lu(III)Cl3 and 90Y(III)Cl3 labeling yielded tracer preparations that were inseparable by C18 RP-HPLC, indicating that putative differences between Lu-, Y- and In coordination spheres are not observed in the context of labeled ST(h) peptides. In vivo biodistribution studies of the 177Lu-labeled peptide in severe combined immunodeficient (SCID) mice bearing T-84 human cancer tumor xenografts showed rapid clearance from the bloodstream, with >90 %ID in the urine at 1 h pi. Localization of the tracer within tumor xenografts was 1.86+/-0.91 %ID/g at 1 h pi, a value higher than for all other tissues with the exception of kidney (2.74+/-0.24 %ID/g). At 24 h pi, >98 %ID was excreted into the urine, and 0.35+/-0.23 %ID/g remained in tumor, again higher than in all other tissues except kidney (0.91+/-0.46 %ID/g). Biodistribution results at 24 h pi for the 90Y-labeled peptide mirrored those for the 177Lu analog, in agreement with the identical behavior of the labeled analogs by C18 RP-HPLC. These results demonstrate the ability of 177Lu- and 90Y-labeled ST(h) molecules to specifically target GC-C receptors expressed on T-84 human colon cancer cells.
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PMID:In vitro and in vivo evaluation of 177Lu- and 90Y-labeled E. coli heat-stable enterotoxin for specific targeting of uroguanylin receptors on human colon cancers. 1672 Feb 39

Research into the interaction between the E. coli heat-stable enterotoxin (STh) and the guanylin receptor guanylate cyclase C (GC-C) has generated >100 synthetic analogs of the peptide, several of which have been investigated as imaging or therapeutic agents for colorectal cancers. The evidence presented here suggests that in addition to STh binding to GC-C expressing cell lines derived from human colon, STh also specifically binds to an as yet unidentified receptor expressed in high densities on the surface of cell lines derived from human breast cancers. In vitro whole-cell crosslinking studies using 125I-labeled F19-STh(1-19) demonstrate that the putative STh binding protein migrates as an approximately 120-125 kDa species by SDS-PAGE, significantly smaller than the glycosylated GC-C molecule found in the T84 human colon cancer cell line. RT-PCR using total RNA isolated from breast and colon cancer cell lines indicates that GC-C transcripts are undetectable in human breast cancer cell lines and abundant in human colon cancer cell lines. In vitro competitive binding studies using STh analogs and the estrogen receptor positive (ER+) T-47D cell line demonstrated IC50 values between 2.6 and 8.5 nM. Similar studies on the estrogen receptor negative (ER-) cell line MDA-MB-231 showed IC50's between 5.6 and 9.9 nM. Saturation binding analysis revealed receptor expression to fall between 40,000 and 120,000 sites per cell in these cell lines, receptor abundances equal to or greater than the abundance of GC-C in colorectal cancer cell lines. STh binding to these cells, although of similar affinity to STh binding to GC-C, is distinguishable from it on the basis of its ligand specificity. The characteristics of STh analogs as radiopharmaceutical agents were tested in an in vivo model utilizing T-47D human breast cancer cell xenografts in SCID mice. Clearance of STh analogs was rapid, primarily via renal excretion into the urine, with >85% ID excreted into the urine at 1 h p.i. Tumor uptake at 1 h p.i. in T-47D tumor cell xenografts was 0.67+/-0.23% ID/g, and was significantly decreased (p<0.05) upon co-administration of 4 mg/kg unlabeled STh. These results suggest that STh may find application for the imaging and treatment of breast cancer.
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PMID:In vitro and in vivo evaluation of 111In-labeled E. coli heat-stable enterotoxin analogs for specific targeting of human breast cancers. 1672 66


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