Suppression of hypoxia-associated vascular endothelial growth factor gene expression by nitric oxide via cGMP.
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PURPOSE: To investigate the suppressive effect of nitric oxide (NO) on vascular endothelial growth factor (VEGF) gene expression and to elucidate its mechanism of action. METHODS: Immortalized human retinal epithelial (RPE) cells, H-ras-transfected murine capillary endothelial cells, and nuclear factor-kappaB (NF-kappaB) RelA knockout 3T3 fibroblasts had VEGF gene expression stimulated by hypoxia, TPA (phorbol ester 12-O-tetradecanoylphorbol-13 acetate), and ras-transfection. The dose response and time course of inhibition of VEGF gene expression by NO were characterized by northern blot analysis, ribonuclease protection assay, and enzyme-linked immunosorbent assay. The effects of NF-kappaB and cGMP in the NO-induced suppression of VEGF gene expression were quantitated. cGMP production was inhibited by LY 83583 (6-anilino-5,8-quinolinedione), a specific inhibitor of guanylate cyclase production, and cGMP accumulation was quantitated by immunoassay. RelA knockout 3T3 fibroblasts were used to assess the contribution of NF-kappaB to the downregulation of VEGF by NO. RESULTS: The NO donor sodium nitroprusside (SNP) decreased hypoxia-induced VEGF gene expression in a dose- and time-dependent manner. One hundred fifty micromolar SNP completely suppressed hypoxia-induced VEGF mRNA levels for at least 24 hours. Constitutive VEGF expression was not altered by SNP. The SNP-mediated decreases in VEGF expression were associated with increases in intracellular cGMP and were blocked by LY 83583. Sodium nitroprusside was able to decrease hypoxia-induced VEGF mRNA increases in fibroblasts deficient in the RelA subunit of NF-kappaB. Nitric oxide was also effective at suppressing increased VEGF expression secondan, to mutant ras and TPA. CONCLUSIONS: These data indicate that NO decreases hypoxia-induced VEGF via a cGMP-dependent mechanism and suggest that NO may serve as an endogenous inhibitor of both hypoxia- and non- hypoxia-enhanced VEGF expression in vivo. (+info)
Generating new ligand-binding RNAs by affinity maturation and disintegration of allosteric ribozymes.
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Allosteric ribozymes are engineered RNAs that operate as molecular switches whose rates of catalytic activity are modulated by the binding of specific effector molecules. New RNA molecular switches can be created by using "allosteric selection," a molecular engineering process that combines modular rational design and in vitro evolution strategies. In this report, we describe the characterization of 3',5'-cyclic nucleotide monophosphate (cNMP)-dependent hammerhead ribozymes that were created using allosteric selection (Koizumi et al., Nat Struct Biol, 1999, 6:1062-1071). Artificial phylogeny data generated by random mutagenesis and reselection of existing cGMP-, cCMP-, and cAMP-dependent ribozymes indicate that each is comprised of distinct effector-binding and catalytic domains. In addition, patterns of nucleotide covariation and direct mutational analysis both support distinct secondary-structure organizations for the effector-binding domains. Guided by these structural models, we were able to disintegrate each allosteric ribozyme into separate ligand-binding and catalytic modules. Examinations of the independent effector-binding domains reveal that each retains its corresponding cNMP-binding function. These results validate the use of allosteric selection and modular engineering as a means of simultaneously generating new nucleic acid structures that selectively bind ligands. Furthermore, we demonstrate that the binding affinity of an allosteric ribozyme can be improved through random mutagenesis and allosteric selection under conditions that favor tighter binding. This "affinity maturation" effect is expected to be a valuable attribute of allosteric selection as future endeavors seek to apply engineered allosteric ribozymes as biosensor components and as controllable genetic switches. (+info)
Phenanthrolines--a new class of CFTR chloride channel openers.
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1. A number of phenanthrolines and benzoquinolines were examined for their ability to activate epithelial chloride secretion by measuring short circuit current (SCC) using the mouse colon epithelium. 1,10 phenanthroline stimulated electrogenic chloride secretion with an EC(50) of 612+/-10 microM and a Hill slope of 4.9+/-0.3. A similar pharmacology was demonstrated by both 1,7 and 4,7 phenanthrolines, 7,8 benzoquinoline and phenanthridine. 2. Evidence that the increase in SCC caused by 1,10 phenanthroline was due to chloride secretion is based upon (a) inhibition of the current by furosemide, (b) failure of cystic fibrosis (CF) colons to respond and (c) an associated net flux of (36)Cl(-). 3. 1,10 Phenanthroline affected neither the generation of cyclic AMP or the concentration of intracellular Ca(2+) in colonic epithelial cells. 4. 1,10 phenanthroline affected the chloride conductance of the apical membrane, as shown by an increase in chloride current in 'apical membrane only' preparations in the presence of an apical to basolateral chloride gradient. The increase in chloride current was inhibited by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and was not present in CF colons. 5. Additionally, 1,10 phenanthroline activated basolateral K(+) channels, both Ca(2+)- and cyclic AMP-sensitive channels, as shown by inhibitor studies with charybdotoxin (ChTX) and XE991, and after the apical membrane was permeabilized with nystatin. 6. The phenanthrolines and benzoquinolines described here, with dual actions affecting CFTR and basolateral K(+) channels, may constitute useful lead compounds for adjunct therapy in CF. (+info)
Contribution of Gln9 and Phe80 to substrate binding in ribonuclease MC1 from bitter gourd seeds.
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Ribonuclease MC1 (RNase MC1) isolated from bitter gourd (Momordica charantia) seeds specifically cleaves phosphodiester bonds on the 5'-side of uridine. The crystal structures of RNase MC1 in complex with 2'-UMP or 3'-UMP reveal that Gln9, Asn71, Leu73, and Phe80 are involved in uridine binding by hydrogen bonding and hydrophobic interactions [Suzuki et al. (2000) Biochem. Biophys. Res. Commun. 275, 572-576]. To evaluate the contribution of Gln9 and Phe80 to uridine binding, Gln9 was replaced with Ala, Phe, Glu, or His, and Phe80 with Ala by site-directed mutagenesis. The kinetic properties of the resulting mutant enzymes were characterized using cytidylyl-3',5'-uridine (CpU) as a substrate. The mutant Q9A exhibited a 3.7-fold increased K(m) and 27.6-fold decreased k(cat), while three other mutations, Q9F, Q9E, and Q9H, predominantly affected the k(cat) value. Replacing Phe80 with Ala drastically reduced the catalytic efficiency (k(cat)/K(m)) with a minimum K(m) value equal to 8 mM. It was further found that the hydrolytic activities of the mutants toward cytidine-2',3'-cyclic monophosphate (cCMP) were reduced. These results demonstrate that Gln9 and Phe80 play essential roles not only in uridine binding but also in hydrolytic activity. Moreover, we produced double Ala substituted mutants at Gln9, Asn71, Leu73, and Phe80, and compared their kinetic properties with those of the corresponding single mutants. The results suggest that these four residues may contribute to uridine binding in a mutually independent manner. (+info)
The HD domain of the Escherichia coli tRNA nucleotidyltransferase has 2',3'-cyclic phosphodiesterase, 2'-nucleotidase, and phosphatase activities.
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In all mature tRNAs, the 3'-terminal CCA sequence is synthesized or repaired by a template-independent nucleotidyltransferase (ATP(CTP):tRNA nucleotidyltransferase; EC 2.7.7.25). The Escherichia coli enzyme comprises two domains: an N-terminal domain containing the nucleotidyltransferase activity and an uncharacterized C-terminal HD domain. The HD motif defines a superfamily of metal-dependent phosphohydrolases that includes a variety of uncharacterized proteins and domains associated with nucleotidyltransferases and helicases from bacteria, archaea, and eukaryotes. The C-terminal HD domain in E. coli tRNA nucleotidyltransferase demonstrated Ni(2+)-dependent phosphatase activity toward pyrophosphate, canonical 5'-nucleoside tri- and diphosphates, NADP, and 2'-AMP. Assays with phosphodiesterase substrates revealed surprising metal-independent phosphodiesterase activity toward 2',3'-cAMP, -cGMP, and -cCMP. Without metal or in the presence of Mg(2+), the tRNA nucleotidyltransferase hydrolyzed 2',3'-cyclic substrates with the formation of 2'-nucleotides, whereas in the presence of Ni(2+), the protein also produced some 3'-nucleotides. Mutations at the conserved His-255 and Asp-256 residues comprising the C-terminal HD domain of this protein inactivated both phosphodiesterase and phosphatase activities, indicating that these activities are associated with the HD domain. Low concentrations of the E. coli tRNA (10 nm) had a strong inhibiting effect on both phosphatase and phosphodiesterase activities. The competitive character of inhibition by tRNA suggests that it might be a natural substrate for these activities. This inhibition was completely abolished by the addition of Mg(2+), Mn(2+), or Ca(2+), but not Ni(2+). The data suggest that the phosphohydrolase activities of the HD domain of the E. coli tRNA nucleotidyltransferase are involved in the repair of the 3'-CCA end of tRNA. (+info)
Cofactor fingerprinting with STD NMR to characterize proteins of unknown function: identification of a rare cCMP cofactor preference.
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Proteomics efforts have created a need for better strategies to functionally categorize newly discovered proteins. To this end, we have employed saturation transfer difference NMR with pools of closely related cofactors, to determine cofactor preferences. This approach works well for dehydrogenases and has also been applied to cyclic nucleotide-binding proteins. In the latter application, a protein (radial spoke protein-2, RSP2) that plays a central role in forming the radial spoke of Chlamydomonas reinhardtii flagella was shown to bind cCMP. cCMP-binding proteins are rare, although previous reports of their presence in sperm and flagella suggest that cCMP may have a more general role in flagellar function. 31P NMR was used to monitor the preferential hydrolysis of ATP versus GTP, suggesting that RSP2 is a kinase. (+info)
Hypertonicity regulates the aquaporin-2 promoter independently of arginine vasopressin.
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BACKGROUND: Aquaporin-2 (AQP-2) is an arginine vasopressin (AVP)-regulated water channel in kidney collecting duct cells. The present study was undertaken to determine whether a change in tonicity could directly regulate the AQP-2 gene in an in vitro experiment. METHODS: Various fragments of the 5'-flanking region of the murine AQP-2 gene up to -9.5 kb were cloned into a luciferase (Luc) reporter plasmid, and they were transiently transfected into Madin-Darby canine kidney cells. RESULTS: Hypertonicity significantly increased the Luc activity of the constructs containing >6.1 kb of the 5'-flanking region of the AQP-2 gene (-6.1AQP2). However, promoter regions <4.3 kb in length containing the tonicity-responsive enhancer (TonE) at bp -570 to -560 were not stimulated by hypertonicity. The TonE-deleted construct which contains -9.5 to -1.1 kb of the 5' side of the AQP-2 gene, 8.4AQP2, was also stimulated by hypertonicity. Mitogen-activated protein (MAP) kinase inhibitors SB203580 and U0126 did not affect the Luc activity of -6.1AQP2 induced by hypertonicity. In addition, the vector expressing dominant-negative TonE-binding protein (TonEBP) did not affect the hypertonicity-induced Luc activity of -6.1AQP2. The Luc activity of -6.1AQP2 was stimulated by the overexpression of TonEBP. Hypertonicity further increased the Luc activity of -6.1AQP2 under the overexpression of TonEBP. CONCLUSION: These findings indicate that hypertonicity regulates AQP-2 promoter activity via an AVP-independent mechanism, and that the tonicity-responsive element resides between the -6.1 and -4.3 kb 5'-flanking region of the AQP-2 gene, in which the structure and mechanism of response to hypertonicity could be distinct from those of TonE. (+info)
A comparison of the diagnostic accuracy and prognostic value of the first and second anti-cyclic citrullinated peptides (CCP1 and CCP2) autoantibody tests for rheumatoid arthritis.
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OBJECTIVES: To compare the diagnostic performance and prognostic value of the anti-cyclic citrullinated peptide (CCP1) and anti-CCP2 autoantibody tests in a clinical setting. METHODS: Anti-CCP1 and anti-CCP2 antibody tests were performed on the same serum samples obtained from 467 patients with early arthritis from the Leiden Arthritis Cohort. The sensitivity, specificity, positive predictive value, and negative predictive value for discriminating between rheumatoid arthritis (RA) and non-RA at 1 year's follow up were calculated for both tests. Results were graphically presented using receiver operating characteristic curves. Progression of radiological joint damage was assessed over 4 years in patients with RA and used to assess the prognostics values of the CCP tests. RESULTS: At a similar specificity the CCP2 test had a higher sensitivity than the CCP1 test. Both tests identified a subgroup of patients with RA with an increased rate of joint damage progression. The anti-CCP2 test identified more patients with an increased rate of joint damage progression than the anti-CCP1 test, and in multiple regression analysis CCP2 was the better predictor of joint damage. CONCLUSIONS: The CCP2 test had better diagnostic and prognostic ability than the CCP1 test. (+info)