title: Adenosine-induced apoptosis in EL-4 thymoma cells is caspase-independent and mediated through a non-classical adenosine receptor.
abstract: Cell death caused by the accumulation of extracellular adenosine is believed to contribute to the profound loss of T lymphocytes in patients with severe combined immunodeficiency disease due to adenosine deaminase deficiency. Although adenosine is known to trigger apoptosis in thymocytes and peripheral T cells, the molecular basis of this effect is not understood. In this study, we show that adenosine-induced apoptosis in mouse EL-4 thymoma cells was associated with the generation of reactive oxygen species and a reduction in mitochondrial transmembrane potential. In addition, cell death was by a caspase-independent mechanism because caspase inhibitors did not protect EL-4 cells from adenosine-induced cytotoxicity. Although reverse transcriptase polymerase chain reaction revealed that EL-4 cells expressed A2b and A3 adenosine receptor subtypes, blockade of A2b and A3 adenosine receptors with receptor-selective antagonists did not attenuate adenosine-induced cell death. Nevertheless, the failure of nucleoside transport inhibitors to prevent adenosine cytotoxicity suggested that adenosine was acting through a cell-surface receptor. In addition, adenosine-induced apoptosis was not due to an accumulation of intracellular cyclic adenosine monophosphate (cAMP) since neither forskolin nor 8-Br-cAMP was cytotoxic for EL-4 cells. Adenosine therefore acts through a non-classical receptor at the cell surface to trigger caspase-independent apoptosis in mouse thymoma cells.
authors.affiliation: Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Asile
authors.initials: A
authors.lastname: El-Darahali
authors.forename: Helen
authors.initials: H
authors.lastname: Fawcett
authors.forename: Jamie S
authors.initials: JS
authors.lastname: Mader
authors.forename: David M
authors.initials: DM
authors.lastname: Conrad
authors.forename: David W
authors.initials: DW
authors.lastname: Hoskin
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000241:Adenosine / Q000502:physiology*; D058917:Adenosine A2 Receptor Antagonists; D058918:Adenosine A3 Receptor Antagonists; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000819:agonists / Q000378:metabolism; D004789:Enzyme Activation; D008564:Membrane Potentials; D051379:Mice; D051336:Mitochondrial Membranes / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D043704:Receptor, Adenosine A2B / Q000378:metabolism*; D043684:Receptor, Adenosine A3 / Q000378:metabolism*; D013601:T-Lymphocytes / Q000166:cytology* / Q000378:metabolism; D013945:Thymoma; D013953:Thymus Neoplasms
chemical_list: D058917:Adenosine A2 Receptor Antagonists; D058918:Adenosine A3 Receptor Antagonists; D061945:Caspase Inhibitors; D017382:Reactive Oxygen Species; D043704:Receptor, Adenosine A2B; D043684:Receptor, Adenosine A3; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D020169:Caspases; D000241:Adenosine