Ethanol Decreases the Efficiency of Phosphorylation of Thymidine Kinase in a Human T‐Lymphocytic Cell Line

Abstract

Thymidine kinase (TK) and thymidylate kinase (TMPK) are the two rate-limiting enzymes in the cascade of activation of the anti-human immunodeficiency virus (HIV) drug 3'-azido-3'-deoxythymidine (AZT) to its active triphosphate form. We examined the effect of ethanol and a combination of ethanol and AZT on TK and TMPK activities in human Jurkat T cells. Jurkat T cells were exposed to 0.2 and 0.5% (v/v) ethanol concentrations alone or in combination with 5 or 10 microM AZT for 48 hr in growth medium. TK and TMPK activities were determined by measuring the conversion of [3H] substrates (thymidine or AZT for TK and thymidine monophosphate for TMPK) to their respective monophosphate or diphosphate forms. The effect of ethanol on the transcriptional activity of TK was determined by reverse transcription-polymerase chain reaction and on the growth of Jurkat cells by [3H]-thymidine incorporation and cell-cycle analysis. Treatment of Jurkat cells with 0.2 and 0.5% ethanol concentrations resulted in 25 and 50% decreases (p < or = 0.05) in TK activity, respectively. No significant changes were observed in the TMPK activities. However, ethanol decreased the formation of thymidine diphosphate from thymidine in coupled TK/TMPK reactions, suggesting that decreases in TK activity could result in an overall decrease in the phosphorylation of AZT. The effect of ethanol on TK was independent of its transcript level. AZT in combination with ethanol decreased the inhibitory effect of ethanol on TK activity. However, it did not block the ethanol effect even at higher concentrations. Ethanol significantly decreased the proliferative capacity and cell cycle progression of the Jurkat cells. Our in vitro study in human Jurkat T cells indicates that at physiologically achievable concentrations in humans, ethanol can decrease TK activity through decreases in cell proliferation, and it suggests that ethanol ingestion in HIV-1-infected individuals could compromise activation of AZT and related drugs through decreased TK activity.