title: Induction of apoptosis by cordycepin in ADA-inhibited TdT-positive leukemia cells.
abstract: The nucleoside analogue cordycepin (3'-deoxyadenosine), when protected against ADA deamination, is specifically cytotoxic for TdT-positive leukemia cells. Cordycepin-treated, ADA-inhibited, TdT-positive cells undergo the classic changes associated with drug-induced apoptosis: reduction in cell volume, chromatin clumping, membrane blebbing, and 180-bp multimer DNA laddering on agarose gels. In common with the apoptosis seen in normal TdT-positive thymocytes, following exposure to various agents, apoptosis induced by cordycepin in TdT-positive leukemia cells was associated with increased protein kinase A (PK-A) activity. Unlike thymocyte apoptosis however, no elevation in cAMP levels was seen preceding the rise in PK-A activity. Ex vivo we show that cordycepin monophosphate can activate PK-A as efficiently as cAMP. On this basis we speculate that cordycepin monophosphate in TdT-positive cells may be able to activate PK-A in place of cAMP, and that PK-A may phosphorylate TdT, augmenting its activity as an endonuclease. In cell-free experiments, the activity of recombinant TdT as an endonuclease digesting supercoiled plasmid DNA into linear fragments was dramatically increased following phosphorylation of TdT by PK-A. A role for TdT as an apoptotic endonuclease in TdT-positive leukemia cells following cordycepin exposure is now the subject of on-going work.
authors.affiliation: Martin H Semler Laboratory, Section of Medical Oncology, Evans Memorial Department of Clinical Research, Boston University Medical Center, MA 02118, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Koç
authors.forename: A G
authors.initials: AG
authors.lastname: Urbano
authors.forename: E B
authors.initials: EB
authors.lastname: Sweeney
authors.forename: R
authors.initials: R
authors.lastname: McCaffrey
mesh_terms: D058892:Adenosine Deaminase Inhibitors; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D003070:Coformycin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism*; D003839:Deoxyadenosines / Q000494:pharmacology*; D004720:Endonucleases / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007938:Leukemia / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
chemical_list: D058892:Adenosine Deaminase Inhibitors; D000970:Antineoplastic Agents; D003839:Deoxyadenosines; D004791:Enzyme Inhibitors; D003070:Coformycin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D004253:DNA Nucleotidylexotransferase; D004720:Endonucleases; C058120:cordycepin