Catalyzes the hydrolytic deamination of adenosine and 2-deoxyadenosine. Plays an important role in purine metabolism and in adenosine homeostasis. Modulates signaling by extracellular adenosine, and so contributes indirectly to cellular signaling events. Acts as a positive regulator of T-cell coactivation, by binding DPP4. Its interaction with DPP4 regulates lymphocyte-epithelial cell adhesion.
The extra-enzymic function of cell-surface adenosine deaminase (ADA), an enzyme mainly localized in the cytosol but also found on the cell surface of monocytes, B cells and T cells, has lately been the subject of numerous studies. Cell-surface ADA is able to transduce co-stimulatory signals in T cells via its interaction with CD26, an integral membrane protein that acts as ADA-binding protein. The aim of the present study was to explore whether ADA-CD26 interaction plays a role in the adhesion of lymphocyte cells to human epithelial cells. To meet this aim, different lymphocyte cell lines (Jurkat and CEM T) expressing endogenous, or overexpressing human, CD26 protein were tested in adhesion assays to monolayers of colon adenocarcinoma human epithelial cells, Caco-2, which express high levels of cell-surface ADA. Interestingly, the adhesion of Jurkat and CEM T cells to a monolayer of Caco-2 cells was greatly dependent on CD26. An increase by 50% in the cell-to-cell adhesion was found in cells containing higher levels of CD26. Incubation with an anti-CD26 antibody raised against the ADA-binding site or with exogenous ADA resulted in a significant reduction (50-70%) of T-cell adhesion to monolayers of epithelial cells. The role of ADA-CD26 interaction in the lymphocyte-epithelial cell adhesion appears to be mediated by CD26 molecules that are not interacting with endogenous ADA (ADA-free CD26), since SKW6.4 (B cells) that express more cell-surface ADA showed lower adhesion than T cells. Adhesion stimulated by CD26 and ADA is mediated by T cell lymphocyte function-associated antigen. A role for ADA-CD26 interaction in cell-to-cell adhesion was confirmed further in integrin activation assays. FACS analysis revealed a higher expression of activated integrins on T cell lines in the presence of increasing amounts of exogenous ADA. Taken together, these results suggest that the ADA-CD26 interaction on the cell surface has a role in lymphocyte-epithelial cell adhesion.
Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.
We have shown recently that adenosine deaminase (ADA)-deficient mice die perinatally with severe liver cell degeneration. In addition to enzyme substitution, we report the restoration of viability through introduction of the human ADA gene. The ADA gene is subject to complex developmental and tissue-specific regulation. To include the cis-regulatory elements necessary for correct regulation of the human ADA gene, a large transgenic locus constituting the human ADA gene with 10 kb of 5' and 4 kb of 3' flanking sequences was generated by co-injection of two overlapping DNA fragments into murine zygotes. Probably as a result of extrachromosomal (homologous) recombination between the fragments, one of the two transgenic lines contained a reconstituted, functional human ADA gene. As in man, human ADA expression generally was low in these transgenic mice, but high in the thymus, spleen and gastro-duodenal part of the gut. Apparently, all cis-regulatory elements essential for a human expression pattern were incorporated in the transgene and were functional in the murine background. Similarly to man, the upper alimentary tract of the transgenic mice revealed low human ADA activity in contrast to extremely high levels of murine ADA. The human gene probably lacks the cis-regulatory elements that target high level murine ADA expression to the murine upper alimentary tract. ADA-deficient mice rescued by introduction of the human ADA transgene appeared histologically and immunologically normal. Apparently, human ADA can complement murine ADA in all tissues, even in the epithelium of the upper alimentary tract where human ADA activity is as much as 70-fold lower than murine ADA activity in wild-type mice. Clearly, the lethal phenotype of ADA-deficient mice is due to the absence of ADA.
J. Biol. Chem. 263, 16291-16296 (1988)[PubMed:3182793]
Adenosine deaminase (ADA) deficiency in humans is one cause of severe combined immunodeficiency disease. Single base mutations affecting the ADA protein have been identified for both alleles of the ADA-deficient cell line GM2606 and for one allele of the ADA-deficient cell line GM2825A. One allele of GM2606 has a mutation altering amino acid 101 from Arg to Trp, and the other allele has a mutation altering amino acid 211 from Arg to His. As previously reported, one ADA allele of GM2825A has a single base mutation changing Ala-329 to Val-329, and the other allele has a mutation which eliminates exon 4 from the mature mRNA. Sequence analysis of polymerase chain reaction-amplified GM2825A DNA showed a single base change of A to G within the invariant bases of the 3' splice site of intron 3 that can account for the mis-splicing of exon 4. To test the effect on ADA catalytic activity of these mutations and the mutations previously found in the ADA-deficient line GM2756, expression vectors containing normal and mutant ADA-coding sequences under transcriptional regulation of the Rous sarcoma virus long terminal repeat were constructed and transfected into human fibroblasts. All transfected cells had levels of ADA mRNA 15-25 times higher than the endogenous ADA message. Yet, cells transfected with the normal ADA-coding sequences had ADA enzymatic levels 40 times higher than cells transfected with any of the mutant ADA sequences. This analysis demonstrates that while the mutant ADA-coding sequences are transcribed, they do not encode a functional ADA protein.
Adenosine deaminase (ADA) is an enzyme involved in purine metabolism and has a major role in the development and function of lymphoid cells. Congenital deficiency of ADA results in severe immunodeficiency. Patients with congenital ADA deficiency treated with polyethylene glycol-conjugated bovine ADA develop antibodies to ADA. This leads us to investigate the role of anti-ADA antibodies in patients with systemic rheumatic diseases. Commercially available ADA was used in ELISA and immunoblots for detection of anti-ADA antibodies. Four out of 100 patients examined were positive for anti-ADA antibodies. Two of them had peripheral blood lymphopenia but the antibody levels did not appear to correlate with the lymphocyte counts. Immunoblotting revealed that the antibodies recognized a 40 kDa peptide of ADA, corresponding to ADA1, the major component of ADA. Affinity-purified antibodies were used to locate the distribution of ADA on Hep-2 cells and lymphocytes by indirect immunofluorescence. Anti-ADA antibodies gave a distinct nuclear speckled pattern on acetone-fixed cells. With viable cell immunofluorescence, anti-ADA antibodies also stained the cell surface of HEp-2 cells and lymphocytes, indicating surface expression of ADA. The anti-ADA antibodies failed to gain access into the cytoplasm or nuclei when added to the cultures of HEp-2 cells. In summary, this is the first report of detection of anti-ADA1 autoantibody which is a new type of ANA with discrete, speckled nuclear staining, but which may not be associated with lymphopenia.
Biochem. J. 290 ( Pt 2), 457-462 (1993)[PubMed:8452534]
Human fibroblast lysosomes, purified on Percoll density gradients, contain an adenosine deaminase (ADA) activity that accounts for approximately 10% of the total ADA activity in GM0010A human fibroblasts. In assays of lysosomal ADA, the conversion of [3H]adenosine into [3H]inosine was proportional to incubation time and the amount of lysosomal material added to reaction mixtures. Maximal activity was observed between pH 7 and 8, and lysosomal ADA displayed a Km of 37 microM for adenosine at 25 degrees C and pH 5.5. Lysosomal ADA was completely inhibited by 2.5 mM Cu2+ or Hg2+ salts, but not by other bivalent cations (Ba2+, Cd2+, Ca2+, Fe2+, Mg2+, Mn2+ and Zn2+). Coformycin (2.5 mM), deoxycoformycin (0.02 mM), 2'-deoxyadenosine (2.5 mM), 6-methylaminopurine riboside (2.5 mM), 2'-3'-isopropylidene-adenosine (2.5 mM) and erythro-9-(2-hydroxy-3-nonyl)adenine (0.2 mM) inhibited lysosomal ADA by > 97%. In contrast, 2.5 mM S-adenosyl-L-homocysteine and cytosine were poor inhibitors. Nearly all lysosomal ADA activity is eluted as a high-molecular-mass protein (> 200 kDa) just after the void volume on a Sephacryl S-200 column, and is very heat-stable, retaining 70% of its activity after incubation at 65 degrees C for 80 min. We speculate that compartmentalization of ADA within lysosomes would allow deamination of adenosine to occur without competition by adenosine kinase, which could assist in maintaining cellular energy requirements under conditions of nutritional deprivation.
Genetic deficiency of the purine salvage enzyme adenosine deaminase (ADA) results in varying degrees of immunodeficiency, ranging from neonatal onset Severe Combined Immunodeficiency (SCID) to an adult onset immunodeficiency disorder. Multiple different mutations have now been identified in these immunodeficient patients. Additional mutations, initially identified in healthy individuals, abolish ADA in erythrocytes but retain 10-80% of activity in non-erythroid cells ('partial deficiency mutations'). In general, severity of disease correlates inversely with the amount of residual ADA expressed by the mutant enzymes and directly with the accumulation of the toxic metabolites deoxyATP and deoxyadenosine. We report two newly identified mutations (Y97C and L106V), both carried on the same allele of an immunodeficient patient who was diagnosed prenatally and successfully transplanted with haploidentical bone marrow. Based on the ability of mutant cDNAs to express ADA in vitro , the L106V mutation resulted in activity similar to 'partial' mutations (30% of normal) while the Y97C mutation resulted in detectable but markedly reduced activity (1.5% of normal). However, the presence of both mutations on the same allele virtually abolished detectable enzyme activity. Analysis of the crystallographic structure of ADA to understand the marked deleterious effect of the Y97C mutation suggested a previously unappreciated role of salt bridges in the catalytic mechanism of ADA. The patient was also heteroallelic for a previously described deletion of the promoter and exon 1. Testing of additional patients in whom we had not identified a mutation on the second allele revealed presence of this deletion in three of four patients tested. This deletion is therefore relatively common, accounting for 10% of almost 100 chromosomes studied by this and other laboratories, but is easily missed by currently used methods of mutation detection. Lastly, the finding of two mutations on the same allele that interact to reduce residual enzyme function emphasizes hazards in evaluating potential genotype-phenotype correlations in individuals analyzed only for the presence of single specific mutations.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionUniProtKB
The expression of surface adenosine deaminase (ADA) and CD26 in activated human T cells was studied by flow cytometry. PBLs and CD3+ or CD4+ cells, when subjected to a variety of stimuli (anti-CD3 Abs plus IL-2 or phorbol esters), presented two structurally different cell populations, which differed in size and cellular complexity (populations B1 and B2). In PBLs triggered by an anti-CD3 mAb there was no significant increase of expression of either surface ADA or CD26 in cells of population B1, whose structure is similar to that of nonstimulated cells. In contrast, there was a significant increase in the percentage of expression of ADA and CD26 in the population B2, which corresponds to structurally more complex and larger cells. In the case of activation via TCR-CD3 but in the presence of IL-2 or via phorbol esters, the increase was found in cells from both populations, but B2 cells always showed a higher percentage of expression than B1 cells. The results of increased expression of surface ADA and CD26 were similar in whole T cells or in purer preparations such as CD3+ or CD4+ lymphocytes. Polyclonal Abs against ADA were not able to induce an activation response in T cells even when cross-linked by a secondary Ab. Interestingly, these Abs produced anergy in CD4+ cells subjected to an anti-CD3 stimulus. In contrast, addition of ADA produced an enzyme-independent synergism in the response through the TCR-CD3 complex. In T cells, ADA and CD26 colocalized on the surface of T cells; thus, the effect of exogenous ADA seems to be mediated by CD26 molecules that are not interacting with endogenous ADA (spare CD26 molecules). The presence of spare CD26 molecules on the surface of CD4+ cells was demonstrated by flow cytometry in the presence of exogenous ADA and also by confocal microscopy. The set of results strongly indicates that ADA binding to CD26 produces a costimulatory response in T cell activation events.
Evidence
2:
Inferred from Physical InteractionUniProtKB
The specific binding of adenosine deaminase to the multifunctional membrane glycoprotein dipeptidyl peptidase IV is thought to be immunologically relevant for certain regulatory and co-stimulatory processes. In this study we present the 3D structure of the complete CD26-ADA complex obtained by single particle cryo-EM at 22A resolution. ADA binding occurs at the outer edges of the beta-propeller of CD26. Docking calculations of available CD26 and ADA crystal data into the obtained EM density map revealed that the ADA-binding site is stretched across CD26 beta-propeller blades 4 and 5 involving the outermost distal hydrophobic amino acids L294 and V341 but not T440 and K441 as suggested by antibody binding. Though the docking of the ADA orientation appears less significant due to the lack of distinct surface features, non-ambiguous conclusions can be drawn in the combination with earlier indirect non-imaging methods affirming the crucial role of the ADA alpha2-helix for binding.
Evidence
3:
Inferred from Physical InteractionUniProtKB
CD26, the T cell activation molecule dipeptidyl peptidase IV (DPPIV), associates with a 43-kilodalton protein. Amino acid sequence analysis and immunoprecipitation studies demonstrated that this 43-kilodalton protein was adenosine deaminase (ADA). ADA was coexpressed with CD26 on the Jurkat T cell lines, and an in vitro binding assay showed that the binding was through the extracellular domain of CD26. ADA deficiency causes severe combined immunodeficiency disease (SCID) in humans. Thus, ADA and CD26 (DPPIV) interact on the T cell surface, and this interaction may provide a clue to the pathophysiology of SCID caused by ADA deficiency.
Three new missense mutations (H15D, A83D, and A179D) and a new splicing defect (573 + IG-->A) in the 5' splice site of intron 5 were among six mutant adenosine deaminase (ADA) alleles found in three unrelated patients with severe combined immunodeficiency disease, the most common phenotype associated with ADA deficiency. When expressed in vitro, the H15D, A83D, and A179D proteins lacked detectable ADA activity. The splicing defect caused skipping of exon 5, resulting in premature termination of translation and a reduced level of mRNA. H15D is the first naturally occurring mutation of a residue that coordinates directly with the enzyme-associated zinc ion. Molecular modeling based on the atomic coordinates of murine ADA suggests that the D15 mutation would create a cavity or gap between the zinc ion and the side chain carboxylate of D15. This could alter the ability of zinc to activate a water molecule postulated to play a role in the catalytic mechanism. A83 and A179 are not directly involved in the active site, but are conserved residues located respectively in alpha helix 4 and beta strand 4 of the alpha/beta barrel. Replacement of these small hydrophobic Ala residues with the charged, more bulky Asp side chain may distort ADA structure and affect enzyme stability or folding.
The chemical reactions and pathways resulting in the breakdown of adenosine, adenine riboside, a ribonucleoside found widely distributed in cells of every type as the free nucleoside and in combination in nucleic acids and various nucleoside coenzymes.
Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.
We have shown recently that adenosine deaminase (ADA)-deficient mice die perinatally with severe liver cell degeneration. In addition to enzyme substitution, we report the restoration of viability through introduction of the human ADA gene. The ADA gene is subject to complex developmental and tissue-specific regulation. To include the cis-regulatory elements necessary for correct regulation of the human ADA gene, a large transgenic locus constituting the human ADA gene with 10 kb of 5' and 4 kb of 3' flanking sequences was generated by co-injection of two overlapping DNA fragments into murine zygotes. Probably as a result of extrachromosomal (homologous) recombination between the fragments, one of the two transgenic lines contained a reconstituted, functional human ADA gene. As in man, human ADA expression generally was low in these transgenic mice, but high in the thymus, spleen and gastro-duodenal part of the gut. Apparently, all cis-regulatory elements essential for a human expression pattern were incorporated in the transgene and were functional in the murine background. Similarly to man, the upper alimentary tract of the transgenic mice revealed low human ADA activity in contrast to extremely high levels of murine ADA. The human gene probably lacks the cis-regulatory elements that target high level murine ADA expression to the murine upper alimentary tract. ADA-deficient mice rescued by introduction of the human ADA transgene appeared histologically and immunologically normal. Apparently, human ADA can complement murine ADA in all tissues, even in the epithelium of the upper alimentary tract where human ADA activity is as much as 70-fold lower than murine ADA activity in wild-type mice. Clearly, the lethal phenotype of ADA-deficient mice is due to the absence of ADA.
A developmental process that is a deterioration and loss of function over time. Aging includes loss of functions such as resistance to disease, homeostasis, and fertility, as well as wear and tear. Aging includes cellular senescence, but is more inclusive. May precede death (GO:0016265) and may succeed developmental maturation (GO:0021700).
The process whose specific outcome is the progression of the gut over time, from its formation to the mature structure during embryonic development. The gut is the region of the digestive tract extending from the beginning of the intestines to the anus.
The process in which a B cell in the spleen acquires the specialized features of a germinal center B cell. Germinal center B cells are rapidly cycling B cells which have downregulated IgD expression and exhibit high levels of binding by peanut agglutinin (PNA).
The regulated release of histamine by a cell or group of cells. It is formed by decarboxylation of histidine and it acts through receptors in smooth muscle and in secretory systems.
The chemical reactions and pathways resulting in the formation of inosine, hypoxanthine riboside, a nucleoside found free but not in combination in nucleic acids except in the anticodons of some tRNAs.
We have shown recently that adenosine deaminase (ADA)-deficient mice die perinatally with severe liver cell degeneration. In addition to enzyme substitution, we report the restoration of viability through introduction of the human ADA gene. The ADA gene is subject to complex developmental and tissue-specific regulation. To include the cis-regulatory elements necessary for correct regulation of the human ADA gene, a large transgenic locus constituting the human ADA gene with 10 kb of 5' and 4 kb of 3' flanking sequences was generated by co-injection of two overlapping DNA fragments into murine zygotes. Probably as a result of extrachromosomal (homologous) recombination between the fragments, one of the two transgenic lines contained a reconstituted, functional human ADA gene. As in man, human ADA expression generally was low in these transgenic mice, but high in the thymus, spleen and gastro-duodenal part of the gut. Apparently, all cis-regulatory elements essential for a human expression pattern were incorporated in the transgene and were functional in the murine background. Similarly to man, the upper alimentary tract of the transgenic mice revealed low human ADA activity in contrast to extremely high levels of murine ADA. The human gene probably lacks the cis-regulatory elements that target high level murine ADA expression to the murine upper alimentary tract. ADA-deficient mice rescued by introduction of the human ADA transgene appeared histologically and immunologically normal. Apparently, human ADA can complement murine ADA in all tissues, even in the epithelium of the upper alimentary tract where human ADA activity is as much as 70-fold lower than murine ADA activity in wild-type mice. Clearly, the lethal phenotype of ADA-deficient mice is due to the absence of ADA.
The process whose specific outcome is the progression of the liver over time, from its formation to the mature structure. The liver is an exocrine gland which secretes bile and functions in metabolism of protein and carbohydrate and fat, synthesizes substances involved in the clotting of the blood, synthesizes vitamin A, detoxifies poisonous substances, stores glycogen, and breaks down worn-out erythrocytes.
The process whose specific outcome is the progression of the alveolus over time, from its formation to the mature structure. The alveolus is a sac for holding air in the lungs; formed by the terminal dilation of air passageways.
Any process that stops, prevents, or reduces the frequency, rate or extent of the adenosine receptor signaling pathway. The adenosine receptor pathway is the series of molecular signals generated as a consequence of an adenosine receptor binding to one of its physiological ligands.
Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.
Any process that increases the rate, frequency or extent of penile erection. Penile erection is the hardening, enlarging and rising of the penis which often occurs in the sexually aroused male and enables sexual intercourse. Achieved by increased inflow of blood into the vessels of erectile tissue, and decreased outflow.
The process whose specific outcome is the progression of Peyer's patches over time, from their formation to the mature structure. Peyer's patches are typically found as nodules associated with gut epithelium with distinct internal structures including B- and T-zones for the activation of lymphocytes.
The process whose specific outcome is the progression of the placenta over time, from its formation to the mature structure. The placenta is an organ of metabolic interchange between fetus and mother, partly of embryonic origin and partly of maternal origin.
Any process that activates or increases the frequency, rate or extent of signaling pathways initiated by the cross-linking of an antigen receptor on a T cell.
Genetic deficiency of the purine salvage enzyme adenosine deaminase (ADA) results in varying degrees of immunodeficiency, ranging from neonatal onset Severe Combined Immunodeficiency (SCID) to an adult onset immunodeficiency disorder. Multiple different mutations have now been identified in these immunodeficient patients. Additional mutations, initially identified in healthy individuals, abolish ADA in erythrocytes but retain 10-80% of activity in non-erythroid cells ('partial deficiency mutations'). In general, severity of disease correlates inversely with the amount of residual ADA expressed by the mutant enzymes and directly with the accumulation of the toxic metabolites deoxyATP and deoxyadenosine. We report two newly identified mutations (Y97C and L106V), both carried on the same allele of an immunodeficient patient who was diagnosed prenatally and successfully transplanted with haploidentical bone marrow. Based on the ability of mutant cDNAs to express ADA in vitro , the L106V mutation resulted in activity similar to 'partial' mutations (30% of normal) while the Y97C mutation resulted in detectable but markedly reduced activity (1.5% of normal). However, the presence of both mutations on the same allele virtually abolished detectable enzyme activity. Analysis of the crystallographic structure of ADA to understand the marked deleterious effect of the Y97C mutation suggested a previously unappreciated role of salt bridges in the catalytic mechanism of ADA. The patient was also heteroallelic for a previously described deletion of the promoter and exon 1. Testing of additional patients in whom we had not identified a mutation on the second allele revealed presence of this deletion in three of four patients tested. This deletion is therefore relatively common, accounting for 10% of almost 100 chromosomes studied by this and other laboratories, but is easily missed by currently used methods of mutation detection. Lastly, the finding of two mutations on the same allele that interact to reduce residual enzyme function emphasizes hazards in evaluating potential genotype-phenotype correlations in individuals analyzed only for the presence of single specific mutations.
The chemical reactions and pathways resulting in the formation of purine ribonucleoside monophosphate, a compound consisting of a purine base linked to a ribose sugar esterified with phosphate on the sugar.
The extra-enzymic function of cell-surface adenosine deaminase (ADA), an enzyme mainly localized in the cytosol but also found on the cell surface of monocytes, B cells and T cells, has lately been the subject of numerous studies. Cell-surface ADA is able to transduce co-stimulatory signals in T cells via its interaction with CD26, an integral membrane protein that acts as ADA-binding protein. The aim of the present study was to explore whether ADA-CD26 interaction plays a role in the adhesion of lymphocyte cells to human epithelial cells. To meet this aim, different lymphocyte cell lines (Jurkat and CEM T) expressing endogenous, or overexpressing human, CD26 protein were tested in adhesion assays to monolayers of colon adenocarcinoma human epithelial cells, Caco-2, which express high levels of cell-surface ADA. Interestingly, the adhesion of Jurkat and CEM T cells to a monolayer of Caco-2 cells was greatly dependent on CD26. An increase by 50% in the cell-to-cell adhesion was found in cells containing higher levels of CD26. Incubation with an anti-CD26 antibody raised against the ADA-binding site or with exogenous ADA resulted in a significant reduction (50-70%) of T-cell adhesion to monolayers of epithelial cells. The role of ADA-CD26 interaction in the lymphocyte-epithelial cell adhesion appears to be mediated by CD26 molecules that are not interacting with endogenous ADA (ADA-free CD26), since SKW6.4 (B cells) that express more cell-surface ADA showed lower adhesion than T cells. Adhesion stimulated by CD26 and ADA is mediated by T cell lymphocyte function-associated antigen. A role for ADA-CD26 interaction in cell-to-cell adhesion was confirmed further in integrin activation assays. FACS analysis revealed a higher expression of activated integrins on T cell lines in the presence of increasing amounts of exogenous ADA. Taken together, these results suggest that the ADA-CD26 interaction on the cell surface has a role in lymphocyte-epithelial cell adhesion.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a hydrogen peroxide (H2O2) stimulus.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a stimulus indicating lowered oxygen tension. Hypoxia, defined as a decline in O2 levels below normoxic levels of 20.8 - 20.95%, results in metabolic adaptation at both the cellular and organismal level.
Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a morphine stimulus. Morphine is an opioid alkaloid, isolated from opium, with a complex ring structure.
The change in morphology and behavior of a mature or immature T cell resulting from exposure to a mitogen, cytokine, chemokine, cellular ligand, or an antigen for which it is specific.
The expression of surface adenosine deaminase (ADA) and CD26 in activated human T cells was studied by flow cytometry. PBLs and CD3+ or CD4+ cells, when subjected to a variety of stimuli (anti-CD3 Abs plus IL-2 or phorbol esters), presented two structurally different cell populations, which differed in size and cellular complexity (populations B1 and B2). In PBLs triggered by an anti-CD3 mAb there was no significant increase of expression of either surface ADA or CD26 in cells of population B1, whose structure is similar to that of nonstimulated cells. In contrast, there was a significant increase in the percentage of expression of ADA and CD26 in the population B2, which corresponds to structurally more complex and larger cells. In the case of activation via TCR-CD3 but in the presence of IL-2 or via phorbol esters, the increase was found in cells from both populations, but B2 cells always showed a higher percentage of expression than B1 cells. The results of increased expression of surface ADA and CD26 were similar in whole T cells or in purer preparations such as CD3+ or CD4+ lymphocytes. Polyclonal Abs against ADA were not able to induce an activation response in T cells even when cross-linked by a secondary Ab. Interestingly, these Abs produced anergy in CD4+ cells subjected to an anti-CD3 stimulus. In contrast, addition of ADA produced an enzyme-independent synergism in the response through the TCR-CD3 complex. In T cells, ADA and CD26 colocalized on the surface of T cells; thus, the effect of exogenous ADA seems to be mediated by CD26 molecules that are not interacting with endogenous ADA (spare CD26 molecules). The presence of spare CD26 molecules on the surface of CD4+ cells was demonstrated by flow cytometry in the presence of exogenous ADA and also by confocal microscopy. The set of results strongly indicates that ADA binding to CD26 produces a costimulatory response in T cell activation events.
The chemical reactions and pathways resulting in the formation of xanthine, 2,6-dihydroxypurine, a purine formed in the metabolic breakdown of guanine but not present in nucleic acids.
IEAOrtholog Compara
Enzymatic activity
This protein acts as an enzyme. It is known to catalyze the following reaction
Protein involved in the biochemical reactions of nucleotides. Nucleotides are phosphate esters of a nucleoside consisting of a purine or pyrimidine base linked to ribose or deoxyribose phosphates.
Enzyme which catalyzes hydrolysis reaction, i.e. the addition of the hydrogen and hydroxyl ions of water to a molecule with its consequent splitting into two or more simpler molecules.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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