Studies on Oxidative Damage of the Wobble 5-methylcarboxymethyl-2-thiouridine in tRNA of Eukaryotic Cells with Disturbed Homeostasis of the Antioxidant System

We have previously shown that 2-thiouridine (S2U), either as a single nucleoside or as an element of RNA chain, is effectively desulfurized under applied in vitro oxidative conditions. Chemically induced desulfuration of S2U resulted in two products: 4-pyrimidinone nucleoside (H2U) and uridine (U). Recently, we investigated whether desulfuration of S2U is a natural process that also occurs in cells exposed to oxidative stress or whether it only occurs in the test tube during chemical reaction with oxidants at high concentrations. Using different types of eukaryotic cells, such as baker's yeast, human cancer cells or modified HEK293 cells with impaired antioxidant system, we confirmed that 5-substituted 2-thiouridines are oxidatively desulfurized in the wobble position of the anticodon of some tRNAs. Quantitative LC-MS/MS-MRMhr analysis of nucleoside mixtures obtained from hydrolyzed tRNA revealed the presence of desulfuration products of mcm5S2U: mcm5H2U and mcm5U modifications. We also observed some amounts of immature cm5S2U, cm5H2U and cm5U products, which may indicate a disruption of an enzymatic modification pathway at the C5 position of 2-thiouridine. The observed process, which is triggered by oxidative stress in living cells, could impair the function of 2-thiouridine-containing tRNAs and alter the translation of genetic information.