title: 2-Chloro-2'-deoxyadenosine-induced apoptosis in T leukemia cells is mediated via a caspase-3-dependent mitochondrial feedback amplification loop.
abstract: 2-Chloro-2'-deoxyadenosine (CdA; cladribine) is a chemotherapeutic agent used in the treatment of certain leukemias. However, the signalling events that govern CdA-mediated cytotoxicity in leukemia cells remain unclear. We show here that CdA treatment caused Jurkat human T leukemia cells to die via apoptosis in a dose- and time-dependent fashion. Bcl-2 overexpression protected Jurkat T leukemia cells from CdA-induced apoptosis and loss of mitochondrial transmembrane potential (Delta Psi m). Furthermore, mitochondria that were isolated from Jurkat T leukemia cells and then exposed to CdA showed a loss of Delta Psi m, indicating that CdA directly compromised outer mitochondrial membrane integrity. CdA treatment of Jurkat T leukemia cells resulted in the activation of caspase-3, -8, and -9, while inhibition of these caspases prevented the CdA-induced loss of Delta Psi m, as well as DNA fragmentation. In addition, caspase-3 inhibition prevented caspase-8 activation while caspase-8 inhibition prevented caspase-9 activation. Death receptor signalling was not involved in CdA-induced apoptosis since cytotoxicity was not affected by FADD-deficiency or antibody neutralization of either Fas ligand or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Taken together, these data suggested that CdA-induced apoptosis in Jurkat T leukemia cells was mediated via a caspase-3-dependent mitochondrial feedback amplification loop. CdA treatment also increased p38 mitogen-activated protein (MAPK) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation in Jurkat T leukemia cells. Although ERK1/2 inhibition did not affect CdA-mediated cytotoxicity, inhibition of p38 MAPK had an enhancing effect, which suggested a cytoprotective function for p38 MAPK. Agents that inhibit p38 MAPK might therefore increase the effectiveness of CdA-based chemotherapy.
authors.affiliation: Department of Microbiology & Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, B3H 1X5, Canada.
authors.forename: David M
authors.initials: DM
authors.lastname: Conrad
authors.forename: Matthew R J
authors.initials: MR
authors.lastname: Robichaud
authors.forename: Jamie S
authors.initials: JS
authors.lastname: Mader
authors.forename: Robert T M
authors.initials: RT
authors.lastname: Boudreau
authors.forename: Angela M
authors.initials: AM
authors.lastname: Richardson
authors.forename: Carman A
authors.initials: CA
authors.lastname: Giacomantonio
authors.forename: David W
authors.initials: DW
authors.lastname: Hoskin
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism*; D017338:Cladribine / Q000494:pharmacology*; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D025461:Feedback, Physiological; D006801:Humans; D019169:Jurkat Cells / Q000378:metabolism / Q000473:pathology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D000970:Antineoplastic Agents; D053200:Fas-Associated Death Domain Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D017338:Cladribine; D020928:Mitogen-Activated Protein Kinases; D053148:Caspase 3