scholarly journals Mutants in the ADP-ribosyltransferase Cleft of Cholera Toxin Lack Diarrheagenicity but Retain Adjuvanticity

1997 ◽  
Vol 185 (7) ◽  
pp. 1203-1210 ◽  
Author(s):  
Shingo Yamamoto ◽  
Yoshifumi Takeda ◽  
Masafumi Yamamoto ◽  
Hisao Kurazono ◽  
Koichi Imaoka ◽  
...  
Keyword(s):  
Cholera Toxin ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Site Directed Mutagenesis ◽  
T Helper ◽  
Th2 Cell ◽  
A Subunit ◽  
Adp Ribosyltransferase ◽  
Type Response

Cholera toxin (CT), the most commonly used mucosal adjuvant in experimental animals, is unsuitable for humans because of potent diarrhea-inducing properties. We have constructed two CT-A subunit mutants, e.g., serine→ phenylalanine at position 61 (S61F), and glutamic acid→ lysine at 112 (E112K) by site-directed mutagenesis. Neither mutant CT (mCT), in contrast to native CT (nCT), induced adenosine diphosphate-ribosylation, cyclic adenosine monophosphate formation, or fluid accumulation in ligated mouse ileal loops. Both mCTs retained adjuvant properties, since mice given ovalbumin (OVA) subcutaneously with mCTs or nCT, but not OVA alone developed high-titered serum anti-OVA immunoglobulin G (IgG) antibodies (Abs) which were largely of IgG1 and IgG2b subclasses. Although nCT induced brisk IgE Ab responses, both mCTs elicited lower anti-OVA IgE Abs. OVA-specific CD4+ T cells were induced by nCT and by mCTs, and quantitative analysis of secreted cytokines and mRNA revealed a T helper cell 2 (Th2)-type response. These results now show that the toxic properties of CT can be separated from adjuvanticity, and the mCTs induce Ab responses via a Th2 cell pathway.

scholarly journals A genetically detoxified derivative of heat-labile Escherichia coli enterotoxin induces neutralizing antibodies against the A subunit.

1994 ◽  
Vol 180 (6) ◽  
pp. 2147-2153 ◽  
Author(s):  
M Pizza ◽  
M R Fontana ◽  
M M Giuliani ◽  
M Domenighini ◽  
C Magagnoli ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cholera Toxin ◽  
Neutralizing Antibodies ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
E Coli ◽  
Heat Labile ◽  
A Subunit ◽  
Adp Ribosyltransferase ◽  
Derivatives Of

Escherichia coli enterotoxin (LT) and the homologous cholera toxin (CT) are A-B toxins that cause travelers' diarrhea and cholera, respectively. So far, experimental live and killed vaccines against these diseases have been developed using only the nontoxic B portion of these toxins. The enzymatically active A subunit has not been used because it is responsible for the toxicity and it is reported to induce a negligible titer of toxin neutralizing antibodies. We used site-directed mutagenesis to inactivate the ADP-ribosyltransferase activity of the A subunit and obtained nontoxic derivatives of LT that elicited a good titer of neutralizing antibodies recognizing the A subunit. These LT mutants and equivalent mutants of CT may be used to improve live and killed vaccines against cholera and enterotoxinogenic E. coli.

scholarly journals Increased intracellular cyclic adenosine monophosphate inhibits T lymphocyte-mediated cytolysis by two distinct mechanisms.

1988 ◽  
Vol 167 (6) ◽  
pp. 1963-1968 ◽  
Author(s):  
L S Gray ◽  
J Gnarra ◽  
E L Hewlett ◽  
V H Engelhard
Keyword(s):  
Cholera Toxin ◽  
T Lymphocyte ◽  
Pertussis Toxin ◽  
Target Cell ◽  
Cyclic Adenosine Monophosphate ◽  
Second Messenger ◽  
Adenosine Monophosphate ◽  
Dose Dependent Fashion ◽  
Dose Dependent ◽  
Stimulation Of

Cholera toxin (CT), but not pertussis toxin (PT), treatment of cloned murine CTL inhibited target cell lysis in a dose-dependent fashion. The effects of CT were mimicked by forskolin and cyclic adenosine monophosphate (cAMP) analogues. Inhibition of cytotoxicity by CT and cAMP analogs was mediated in part by attenuation of conjugate formation. Additionally, both CT and cAMP analogs blocked the increase in intracellular Ca2+ induced by stimulation of the TCR complex by mAbs. These findings indicate that cAMP inhibits the activity of CTL by two distinct mechanisms and suggests a role for this second messenger in CTL-mediated cytolysis.

scholarly journals Effects of Site-Directed Mutagenesis ofEscherichia coli Heat-Labile Enterotoxin on ADP-Ribosyltransferase Activity and Interaction with ADP-Ribosylation Factors

1999 ◽  
Vol 67 (1) ◽  
pp. 259-265 ◽  
Author(s):  
Linda A. Stevens ◽  
Joel Moss ◽  
Martha Vaughan ◽  
Mariagrazia Pizza ◽  
Rino Rappuoli
Keyword(s):  
Cholera Toxin ◽  
Nucleotide Binding ◽  
Catalytic Site ◽  
Site Directed Mutagenesis ◽  
Guanine Nucleotide ◽  
Adp Ribosylation ◽  
Heat Labile ◽  
Guanine Nucleotide Binding ◽  
Catalyzed Reactions ◽  
Adp Ribosyltransferase

ABSTRACT Escherichia coli heat-labile enterotoxin (LT), an oligomeric protein with one A subunit (LTA) and five B subunits, exerts its effects via the ADP-ribosylation of Gsα, a guanine nucleotide-binding (G) protein that activates adenylyl cyclase. LTA also ADP-ribosylates simple guanidino compounds (e.g., arginine) and catalyzes its own auto-ADP-ribosylation. All LTA-catalyzed reactions are enhanced by ADP-ribosylation factors (ARFs), 20-kDa guanine nucleotide-binding proteins. Replacement of arginine-7 (R7K), valine-53 (V53D), serine-63 (S63K), valine 97 (V97K), or tyrosine-104 (Y104K) in LTA resulted in fully assembled but nontoxic proteins. S63K, V53D, and R7K are catalytic-site mutations, whereas V97K and Y104K are amino acid replacements adjacent to and outside of the catalytic site, respectively. The effects of mutagenesis were quantified by measuring ADP-ribosyltransferase activity (i.e., auto-ADP-ribosylation and ADP-ribosylagmatine synthesis) and interaction with ARF (i.e., inhibition of ARF-stimulated cholera toxin ADP-ribosyltransferase activity and effects of ARF on mutant auto-ADP-ribosylation). All mutants were inactive in the ADP-ribosyltransferase assay; however, auto-ADP-ribosylation in the presence of recombinant human ARF6 was detected, albeit much less than that of native LT (Y104K > V53D > V97K > R7K, S63K). Based on the lack of inhibition by free ADP-ribose, the observed auto-ADP-ribosylation activity was enzymatic and not due to the nonenzymatic addition of free ADP-ribose. V53D, S63K, and R7K were more effective than Y104K or V97K in blocking ARF stimulation of cholera toxin ADP-ribosyltransferase. Based on these data, it appears that ARF-binding and catalytic sites are not identical and that a region outside the NAD cleft may participate in the LTA-ARF interaction.

scholarly journals The effect of pharmacologic inhibition of phospholipid methylation on human platelet function

Blood ◽  
1982 ◽  
Vol 59 (5) ◽  
pp. 906-912
Author(s):  
SJ Shattil ◽  
JA Montgomery ◽  
PK Chiang
Keyword(s):  
Platelet Activation ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Serotonin Release ◽  
Platelet Phospholipid ◽  
Biochemical Effect ◽  
Methylation Pathway ◽  
Pharmacologic Inhibition

Human platelets are capable of synthesizing their major membrane phospholipid, phosphatidylcholine, by a methylation pathway. This involves the sequential transfer of methyl groups from S-adenosyl-L- methionine (AdoMet) to phosphatidylethanolamine, and in the process, AdoMet is converted to S-adenosylhomocysteine (AdoHcy). The activity of this methylation pathway is decreased upon stimulation of platelets by various agonists. We inhibited methylation reactions pharmacologically to see whether this inhibition plays any role in the process of platelet activation. Two inhibitors of AdoHcy hydrolase, 3-deaza- adenosine and 3-deaza-(+/-)aristeromycin (500 microM each), were effective in increasing platelets levels of AdoHcy and preventing turnover of AdoMet. Also, these compounds were equipotent in inhibiting platelet phospholipid methylation. However, while 3-deaza-adenosine potentiated platelet aggregation and 14C-serotonin release induced by epinephrine or adenosine diphosphate (ADP) (p less than 0.01), 3-deaza- aristeromycin had no such effect. Neither compound affected platelet responses to thrombin or collagen. Inhibition of methylation reactions was not the only biochemical effect of 3-deaza-adenosine since it also blunted significantly the elevation of platelet cyclic adenosine monophosphate (AMP) levels induced by prostaglandin E1 (p less than 0.02). Therefore, these studies demonstrate that inhibition of platelet phospholipid methylation, per se, has no discernable effect on the function of human platelets. The methylation pathway, though active in platelets, does not appear to be primarily involved in membrane events responsible for platelet activation.

scholarly journals Differential requirements for platelet aggregation and inhibition of adenylate cyclase by epinephrine. Studies of a familial platelet alpha 2-adrenergic receptor defect

Blood ◽  
1988 ◽  
Vol 71 (2) ◽  
pp. 494-501 ◽  
Author(s):  
AK Rao ◽  
J Willis ◽  
MA Kowalska ◽  
YT Wachtfogel ◽  
RW Colman
Keyword(s):  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Adrenergic Receptors ◽  
Adrenergic Receptor ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Normal Subjects ◽  
Camp Levels ◽  
Epinephrine Concentration

Abstract We describe a family whose members have impaired platelet aggregation and secretion responses to epinephrine with normal responses to adenosine diphosphate and collagen. Platelet alpha 2-adrenergic receptors (measured using 3H methyl-yohimbine) were diminished in the propositus (78 sites per platelet), his two sisters (70 and 27 sites per platelet), and parents (37 and 63 sites per platelet), but not in two maternal aunts (12 normal subjects, 214 +/- 18 sites per platelet; mean +/- SE). However, the inhibition of cyclic adenosine monophosphate (cAMP) levels by epinephrine in platelets exposed to 400 nmol/L PGI2 was similar in the patients and five normal subjects (epinephrine concentration for 50% inhibition, 0.04 +/- 0.01 mumol/L v 0.03 +/- 0.01 mumol/L; P greater than .05). In normal platelets, the concentration of yohimbine (0.18 mumol/L) required for half maximal inhibition of aggregation induced by 2 mumol/L epinephrine was lower than that for inhibition of its effect on adenylate cyclase (1.6 mumol/L). In quin2 loaded platelets, thrombin (0.1 U/mL) stimulated rise in cytoplasmic Ca2+ concentration, [Ca2+]i, was normal in the two patients studied. The PGI2 analog ZK 36,374 completely inhibited thrombin-induced rise in [Ca2+]i; the reversal of this inhibition by epinephrine was normal in the two patients. Thus, despite the impaired aggregation response to epinephrine, platelets from these patients have normal ability to inhibit PGI2-stimulated cAMP levels. These patients with an inherited receptor defect provide evidence that fewer platelet alpha 2-adrenergic receptors are required for epinephrine-induced inhibition of adenylate cyclase than for aggregation.

scholarly journals Adenosine and Forskolin Inhibit Platelet Aggregation by Collagen but not the Proximal Signalling Events

2019 ◽  
Vol 119 (07) ◽  
pp. 1124-1137 ◽  
Author(s):  
Joanne C. Clark ◽  
Deirdre M. Kavanagh ◽  
Stephanie Watson ◽  
Jeremy A. Pike ◽  
Robert K. Andrews ◽  
...  
Keyword(s):  
Adenylyl Cyclase ◽  
G Protein ◽  
Platelet Activation ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Receptor Activation ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Adenosine Receptor Agonist

Background The G protein-coupled receptor, adenosine A2A, signals through the stimulatory G protein, Gs, in platelets leading to activation of adenylyl cyclase and elevation of cyclic adenosine monophosphate (cAMP) and inhibition of platelet activation. Objective This article investigates the effect of A2A receptor activation on signalling by the collagen receptor glycoprotein (GP) VI in platelets. Methods Washed human platelets were stimulated by collagen or the GPVI-specific agonist collagen-related peptide (CRP) in the presence of the adenosine receptor agonist, 5′-N-ethylcarboxamidoadenosine (NECA) or the adenylyl cyclase activator, forskolin and analysed for aggregation, adenosine triphosphate secretion, protein phosphorylation, spreading, Ca2+ mobilisation, GPVI receptor clustering, cAMP, thromboxane B2 (TxB2) and P-selectin exposure. Results NECA, a bioactive adenosine analogue, partially inhibits aggregation and secretion to collagen or CRP in the absence or presence of the P2Y12 receptor antagonist, cangrelor and the cyclooxygenase inhibitor, indomethacin. The inhibitory effect in the presence of the three inhibitors is largely overcome at higher concentrations of collagen but not CRP. Neither NECA nor forskolin altered clustering of GPVI, elevation of Ca2+ or spreading of platelets on a collagen surface. Further, neither NECA nor forskolin, altered collagen-induced tyrosine phosphorylation of Syk, LAT nor PLCγ2. However, NECA and forskolin inhibited platelet activation by the TxA2 mimetic, U46619, but not the combination of adenosine diphosphate and collagen. Conclusion NECA and forskolin have no effect on the proximal signalling events by collagen. They inhibit platelet activation in a response-specific manner in part through inhibition of the feedback action of TxA2.

scholarly journals Antiplatelet Effects of Qishen Yiqi Dropping Pill in Platelets Aggregation in Hyperlipidemic Rabbits

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
Yi Wang ◽  
Jie Wang ◽  
Liping Guo ◽  
Xiumei Gao
Keyword(s):  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Camp Level ◽  
High Fat ◽  
Platelet Factor ◽  
Aggregation Effect ◽  
Antiplatelet Aggregation ◽  
Prostaglandin F ◽  
Camp Metabolism

We investigated the effects of Qishen Yiqi Dropping Pill (QSYQ) on platelets aggregation and its possible mechanisms. Hyperlipidemic model in rabbits was produced by a high fat/cholesterol diet for 6 weeks, the therapeutic effect of QSYQ with 2.0 g/kg, 1.0 g/kg, and 0.5 g/kg was observed. Fourteen days after drug treatment, platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA), and collagen (COLL) was significantly reduced in rabbits of model group. Moreover,β-thromboglobulin (β-TG) level decreased obviously but no significant change in P-selectin and platelet factor 4 (PF4) level, while QSYQ significantly decreased the ratio of thromboxane B2 (TXB2) to 6-keto-prostaglandin F1α(6-Keto-PGF1α) and increased cyclic adenosine monophosphate (cAMP) level in rabbits. In summary, QSYQ can improve platelets aggregation and inhibit the over-release ofβ-TG in hyperlipidemic rabbits; and the increased cAMP level may be involved in this process. These results suggest that the antiplatelet aggregation effect of QSYQ may be due to its ability to increase cAMP level for improving cAMP metabolism.

scholarly journals Requirement for guanosine triphosphate for cholera-toxin-catalysed incorporation of adenosine diphosphate ribose into rat liver plasma membranes and for activation of adenylate cyclase

1980 ◽  
Vol 186 (3) ◽  
pp. 749-754 ◽  
Author(s):  
C A Doberska ◽  
A J S MacPherson ◽  
B R Martin
Keyword(s):  
Plasma Membrane ◽  
Adenylate Cyclase ◽  
Cholera Toxin ◽  
Rat Liver ◽  
Plasma Membranes ◽  
Adenosine Diphosphate ◽  
Activation Process ◽  
Liver Plasma Membrane ◽  
Adp Ribosylation ◽  
A Subunit

1. Cholera toxin was shown to require the presence of GTP to activate rat liver plasma-membrane adenylate cyclase. ATP did not affect the activation process. 2. Cholera toxin catalysed the incorporation of 32P from NAD labelled in the alpha-phosphate group of the ADP moiety into a rat liver plasma-membrane protein with a subunit mol.wt. of 42 500. This is taken to demonstrate ADP-ribosylation. The ADP-ribosylation of this protein also required GTP and was unaffected by ATP. 3. Nicotinamide inhibited both the activation of adenylate cyclase by cholera toxin and the ADP-ribosylation of the protein of 42 500 subunit mol wt. Neither the activation nor the ADP-ribosylation could be reversed by treatment with nicotinamide in the presence of cholera toxin.

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