Effects of the S-adenosylhomocysteine hydrolase inhibitors 3-deazaadenosine and 3-deazaaristeromycin on RNA methylation and synthesis

The effects of 3-deazaaristeromycin and 3-deazaadenosine on RNA methylation and synthesis were examined in the mouse macrophage cell line, RAW264. S-Adenosylhomocysteine accumulated in cells incubated with 3-deazaaristeromycin while S-3-deazaadenosylhomocysteine was the major product in cells incubated with 3-deazaadenosine and homocysteine thiolactone. RNA methylation was inhibited to a similar extent by the accumulation of either S-adenosylhomocysteine or S-3-deazaadenosylhomocysteine, with S-adenosylhomocysteine being a slightly better inhibitor. In mRNA, the synthesis of N6-methyladenosine and N6-methyl-2′-O-methyladenosine were inhibited to the greatest extent, while the synthesis of 7-methylguanosine and 2′-O-methyl nucleosides were inhibited to a lesser extent. Incubation of cells with 100 μM 3-deazaaristeromycin or with 10 μM 3-deazaadenosine and 50 μM homocysteine thiolactone produced little inhibition of mRNA synthesis, even though mRNA methylation was inhibited. In contrast, mRNA synthesis was greatly inhibited by treatment of cells with 100 μM 3-deazaadenosine and the inhibition of synthesis was not correlated with an inhibition of methylation.