Adenosine A2B Receptors Behave as an Alternative Anchoring Protein for Cell Surface Adenosine Deaminase in Lymphocytes and Cultured Cells
- 1Department of Biochemistry and Molecular Biology, Faculty of Chemistry, University of Barcelona, Barcelona, Spain (C.H., V.C., F.C., J.M., C.L., R.F.); and the 2Neurobiology Division, Garvan Institute, Darlinghurst, Australia (P.S.)
Abstract
Adenosine deaminase (ADA) is an enzyme of the purine metabolism that has been largely considered to be cytosolic. Recently, it has been demonstrated that the enzyme appears on the surface of lymphocytes where it interacts with the T-cell activation antigen CD26. ADA also appears on the surface of nonlymphoid cells anchored to adenosine A1 receptors. Here it is demonstrated that cell surface ADA in ADA+/CD26− T lymphocytes anchors to adenosine receptors of the A2B subtype (A2BR). An interaction between A2BR and cell surface ADA has been demonstrated in transfected Chinese hamster ovary cells and Jurkat J32 T lymphocytes. This has been proved by coimmunoprecipitation, binding of exogenous ADA to A2BR+ cells, and coimmunolocalization. The specificity of the interaction has also been demonstrated by the lack of interaction with other members of the G protein-coupled receptor superfamily. Binding of ADA to A2BR increases the affinity of the agonist 5′-N-ethylcarboxamidoadenosine and cAMP production. This effect occurs even when ADA devoid of enzyme activity is used. Therefore, in lymphocytes, cell surface ADA, apart from degrading extracellular adenosine, regulates those actions of adenosine that are mediated via adenosine receptors of the A2B subtype.
Footnotes
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Send reprint requests to: Prof. Rafael Franco, Dept. Bioquı́mica i Biologia Molecular, Universitat de Barcelona, Martı́ i Franquès 1, 08028 Barcelona, Spain. E-mail:r.franco{at}sun.bq.ub.es
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This research was supported by Spanish Comisión Interministerial de Ciencia y Tecnologia's Investigation and Development programs Salud y Farmacia (SAF97/0066) and Biotechnology (BIO1999/0601/C02).
- Abbreviations:
- SCID
- severe combined immunodeficiency syndrome
- ADA
- adenosine deaminase
- A2BR
- adenosine A2B receptor
- CHO
- Chinese hamster ovary
- NECA
- 5′-N-ethylcarboxamidoadenosine
- mAb
- monoclonal antibody
- FITC
- fluorescein isothiocyanate
- TRITC
- tetramethylrhodamine isothiocyanate
- DMEM
- Dulbecco's modified Eagle's medium
- HEK
- human embryonic kidney
- PHA
- phytohemagglutinin
- mAb
- monoclonal antibody
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- Received January 5, 2000.
- Accepted August 11, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
