title: Role of S-adenosylhomocysteine hydrolase in adenosine-induced apoptosis in HepG2 cells.
abstract: Adenosine has been shown to initiate apoptosis through different mechanisms: (i) activation of adenosine receptors, (ii) intracellular conversion to AMP and stimulation of AMP-activated kinase, (iii) conversion to S-adenosylhomocysteine (AdoHcy), which is an inhibitor of S-adenosylmethionine (AdoMet)-dependent methyltransferases. Since the pathways involved are still not completely understood, we further investigated the role of AdoHcy hydrolase in adenosine-induced apoptosis. In HepG2 cells, adenosine induced caspase-like activity and DNA fragmentation, a marker of apoptosis. These effects were potentiated by co-incubation with homocysteine or adenosine deaminase inhibitor, pentostatin, and were mimicked by inhibition of AdoHcy hydrolase by adenosine-2',3'-dialdehyde (Adox). Adenosine-induced effects were significantly inhibited by dipyridamole, an inhibitor of adenosine transporter, whereas inhibitors of adenosine kinase did not affect adenosine-induced changes. Various adenosine receptor agonists and AICAR, an activator of AMP-activated kinase, did not mimic the effect of adenosine. Thus, adenosine-induced apoptosis is likely due to intracellular action of AdoHcy and independent of AMP-activated kinase and adenosine receptors. Because elevated AdoHcy levels are associated with reduced mRNA methylation, we studied mRNA expression in Adox-treated cells by microarray analysis. Since several p53-target genes and other apoptosis-related genes were up-regulated by Adox, we conclude that AdoHcy is involved in adenosine-induced apoptosis by altering gene expression.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Medicine, University of Tuebingen, Wilhelmstrasse 56, D-72074 Tuebingen, Germany.
authors.forename: Marina
authors.initials: M
authors.lastname: Hermes
authors.forename: Hartmut
authors.initials: H
authors.lastname: Osswald
authors.forename: Doris
authors.initials: D
authors.lastname: Kloor
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D058892:Adenosine Deaminase Inhibitors; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D043383:Adenosylhomocysteinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D017209:Apoptosis / Q000235:genetics*; D061945:Caspase Inhibitors; D020169:Caspases / Q000032:analysis / Q000378:metabolism*; D053938:DNA Fragmentation; D004176:Dipyridamole / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D006710:Homocysteine / Q000494:pharmacology; D006801:Humans; D008745:Methylation; D033703:Nucleoside Transport Proteins / Q000037:antagonists & inhibitors; D020411:Oligonucleotide Array Sequence Analysis; D015649:Pentostatin / Q000494:pharmacology; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism
chemical_list: D058892:Adenosine Deaminase Inhibitors; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D033703:Nucleoside Transport Proteins; D012333:RNA, Messenger; C444719:adenosine transporter; D006710:Homocysteine; D015649:Pentostatin; D004176:Dipyridamole; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D051736:Proto-Oncogene Proteins c-mdm2; D000248:Adenosine Kinase; D043383:Adenosylhomocysteinase; D020169:Caspases; D000241:Adenosine