Apoptosis and transmethylation metabolites in HL-60 cells

To investigate the role of transmethylation metabolites in initiation of apoptosis in human leukemia HL-60 cells exposed to 9-deazaadenosine (c(3)Ado) as single agent and c(3)Ado plus homocysteine thiolactone (Hcy), S-adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy) and 3-deazaadenosylhomocysteine (c(3)AdoHcy), were measured by HPLC in HL-60 cells exposed to 1-100 mu M c(3)Ado as single agent and 1 to 100 mu M c(3)Ado plus 1 mM Hcy. 3-deaza-(+/-)-aristeromycin (c(3)Ari), a more specific and potent S-adenosylhomocysteine hydrolase inhibitor compared with c(3)Ado, was used to inhibit synthesis of c(3)AdoHcy. AdoMet increased to maximum values 1.5- and 2.3-fold control in cultures treated with c(3)Ado as single agent and c(3)Ado plus Hcy, respectively. AdoHcy did not change in cultures treated with c(3)Ado as single agent, but increased to maximum values 2.0-fold control when Hcy was added. The synthesis of c(3)AdoHcy was favored by Hcy, and 35- to 70-fold higher levels of c(3)AdoHcy were found in cultures treated with c(3)Ado plus Hcy vs. c(3)Ado as single agent. The amounts of c(3)AdoHcy in cultures treated with c(3)Ado at concentrations initiating apoptosis did not exceed c(3)AdoHcy levels in cultures treated with c(3)Ado plus Hcy at concentrations not initiating apoptosis. Pretreatment of c(3)Ado plus Hcy cultures with c(3)Ari diminished c(3)AdoHcy and almost completely abrogated apoptosis. Exposure of cells to 100 mu M c(3)Ari as single agent resulted in an increase in AdoHcy to 8.4-fold control but no changes in AdoMet and no initiation of apoptosis. Our findings indicate that c(3)Ado as single agent exerts its apoptosis-initiating effect through a nontransmethylase-related biochemical action. c(3)AdoHcy seems to be related to biochemical events initiating apoptotic cell death of HL-60 cells when c(3)Ado and Hcy are combined.