Mechanism by which phosphonoformic acid resistance mutations restore 3'-azido-3'-deoxythymidine (AZT) sensitivity to AZT-resistant HIV-1 reverse transcriptase.
The development of phosphonoformic acid (PFA) resistance against a background of 3'-azido-3'-deoxythymidine (AZT) resistance in human immunodeficiency virus type 1 (HIV-1) restores viral sensitivity to AZT. High level AZT resistance requires multiple mutations (D67N/K70R/T215F/K219Q). In order to characterize the mechanism of PFA resistance-mediated resensitization to AZT, the A114S mutation associated with PFA resistance was introduced into the reverse transcriptase (RT) of both wild type and drug-resistant virus. We previously showed that pyrophosphorolytic removal of chain-terminating AZT is the primary mechanism of the AZT resistance phenotype (Arion, D., Kaushik, N., McCormick, S., Borkow, G., and Parniak, M. A. (1998) Biochemistry 37, 15908-15917). Introduction of A114S into the AZT resistance background significantly diminishes both the enhanced pyrophosphorolytic activity and the DNA synthesis processivity associated with the AZT-resistant RT. The A114S mutation also alters the nucleotide-dependent phosphorolysis activity associated with AZT resistance. The presence of the A114S mutation therefore severely impairs the mutant enzyme's ability to excise chain-terminating AZT. The decrease in phosphorolytic activity of RT conferred by the PFA resistance A114S mutation resensitizes AZT-resistant HIV-1 to AZT by allowing the latter to again function as a chain terminator of viral DNA synthesis. These data further underscore the importance of phosphorolytic removal of chain-terminating AZT as the primary mechanism of HIV-1 AZT resistance.
Arion
D
D
Lady Davis Institute for Medical Research and McGill University AIDS Centre, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Sluis-Cremer
N
N
Parniak
M A
MA
D019380:Anti-HIV Agents / Q000494:pharmacology; D001483:Base Sequence; D017931:DNA Primers; D004261:DNA Replication; D004352:Drug Resistance, Microbial / Q000235:genetics; D017245:Foscarnet / Q000494:pharmacology*; D054303:HIV Reverse Transcriptase / Q000187:drug effects*; D015497:HIV-1 / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D009154:Mutation; D011994:Recombinant Proteins / Q000187:drug effects; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*; D015215:Zidovudine / Q000494:pharmacology*
D019380:Anti-HIV Agents; D017931:DNA Primers; D011994:Recombinant Proteins; D018894:Reverse Transcriptase Inhibitors; D017245:Foscarnet; D015215:Zidovudine; D054303:HIV Reverse Transcriptase