Basis for resistance to 3-deazaaristeromycin, an inhibitor of S-adenosylhomocysteine hydrolase, in human B-lymphoblasts.
Clones resistant to 3-deazaaristeromycin, a potent inhibitor of S-adenosylhomocysteine hydrolase, were selected from a nucleoside kinase-deficient derivative of the WIL-2 human B-lymphoblastoid cell line. The resistant clones took up 3-deazaaristeromycin and showed no alteration in the level of S-adenosylhomocysteine hydrolase activity or in the sensitivity of the enzyme to inhibition by 3-deazaaristeromycin. However, they displayed markedly elevated S-adenosylmethionine content during growth in 3-deazaaristeromycin and, following prolonged selection, enhanced export of S-adenosylhomocysteine. As a result they maintained a high ratio of S-adenosylmethionine to S-adenosylhomocysteine and thus were resistant to the inhibition of S-adenosylmethionine turnover and transmethylation caused by 3-deazaaristeromycin. Expanded S-adenosylmethionine pools declined over several weeks of nonselective growth, suggesting a metabolic adaptation rather than a mutational mechanism. No alterations in S-adenosylmethionine synthetase activity were found in the 3-deazaaristeromycin-resistant clones. S-Adenosylhomocysteine export appeared to be carrier-mediated and largely unidirectional. The resistant clones showed a 5-fold increased rate of S-adenosylhomocysteine export compared with parental cells, but a similar Km for intracellular S-adenosylhomocysteine, estimated to be approximately 1 mM. Our results highlight the opposing effects of S-adenosylmethionine and S-adenosylhomocysteine on transmethylation and suggest that the ability to elevate S-adenosylmethionine pools and to export S-adenosylhomocysteine may provide for homeostatic control of transmethylation in lymphoid cells when S-adenosylhomocysteine hydrolase activity is limited.
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27707.
M L
ML
Greenberg
S
S
Chaffee
M S
MS
Hershfield
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D043383:Adenosylhomocysteinase; D001402:B-Lymphocytes / Q000187:drug effects / Q000201:enzymology; D002460:Cell Line; D002999:Clone Cells; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D006867:Hydrolases / Q000037:antagonists & inhibitors*; D007536:Isomerism; D007700:Kinetics; D014372:Tubercidin / Q000494:pharmacology
D004791:Enzyme Inhibitors; C018258:3-deazaadenosine; C030034:aristeromycin; C034583:3-deazaaristeromycin; D006867:Hydrolases; D043383:Adenosylhomocysteinase; D000241:Adenosine; D014372:Tubercidin