Nucleoside reverse transcriptase (RT) inhibitors continue to be an important component of therapy against human immunodeficiency virus type 1 (HIV-1). These compounds are phosphorylated by cellular enzymes and are incorporated into DNA by HIV-1 RT leading to chain termination during viral DNA synthesis. The ability of mutants of HIV-1 RT to remove chain-terminating nucleotides from nascent DNA chains (excision activity) is an important mechanism of drug resistance, and mutants with elevated excision activity are often selected during therapy. We propose to develop an analytical approach to determine what influences excision activity in infected cells that will help us understand what drives mutant selection in vivo.
Aim 1 is to use purified wild type and mutant HIV-1 recombinant proteins to evaluate the roles of RNA cleavage by the ribonuclease H activity of RT and template fragment dissociation in regulating excision rescue of blocked DNA chains.
Aim 2 is to determine the effect of HIV nucleocapsid proteins on the release of secondary ribonuclease H cleavage fragments and excision of chain terminators.
Aim 3 is to develop methods to measure intracellular excision activity and to use lentivirus vectors packaged with wild type or mutant RTs to evaluate factors that regulate excision in infected cells. The use of the excision reaction of HIV RT as a therapeutic target is limited by our lack of understanding of the intracellular reaction, including factors that influence timing and rate of the reaction, stability of the enzyme-substrate complexes that carry out secondary ribonuclease H cleavage and chain terminator excision, contribution of viral and cellular factors to these reactions, and accessibility of the viral replication machinery to acceptor substrates and inhibitory molecules. These questions will be addressed by the proposed studies.

Public Health Relevance

Developoment of new therapies against HIV will continue to be necessary because of the rapid mutation rate of this virus that facilitates selection of drug resistance and because of the need to continue therapy in each patient over many years. Research is proposed to characterize intracellular processes that influence the ability of HIV to escape from a class of drugs that blocks viral DNA synthesis, which will provide insight into the potency of these drugs in different tissues and metabolic conditions, the tissue sites where selection of resistance mutants takes place, and how therapeutic strategies can be changed to optimize drug efficacy and avoid selection of resistant mutants.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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AIDS Molecular and Cellular Biology Study Section (AMCB)
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Livnat, Daniella
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University of Miami School of Medicine
Schools of Medicine
Coral Gables
United States
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Acosta-Hoyos, Antonio J; Matsuura, Suzanne E; Meyer, Peter R et al. (2012) A role of template cleavage in reduced excision of chain-terminating nucleotides by human immunodeficiency virus type 1 reverse transcriptase containing the M184V mutation. J Virol 86:5122-33
Scott, Walter A (2011) Structures of reverse transcriptase pre- and post-excision complexes shed new light on HIV-1 AZT resistance. Viruses 3:20-5
Acosta-Hoyos, Antonio J; Scott, Walter A (2010) The Role of Nucleotide Excision by Reverse Transcriptase in HIV Drug Resistance. Viruses 2:372-394
Rutvisuttinunt, Wiriya; Meyer, Peter R; Scott, Walter A (2008) Interactions between HIV-1 reverse transcriptase and the downstream template strand in stable complexes with primer-template. PLoS One 3:e3561
Meyer, Peter R; Rutvisuttinunt, Wiriya; Matsuura, Suzanne E et al. (2007) Stable complexes formed by HIV-1 reverse transcriptase at distinct positions on the primer-template controlled by binding deoxynucleoside triphosphates or foscarnet. J Mol Biol 369:41-54
Meyer, Peter R; Smith, Anthony J; Matsuura, Suzanne E et al. (2006) Chain-terminating dinucleoside tetraphosphates are substrates for DNA polymerization by human immunodeficiency virus type 1 reverse transcriptase with increased activity against thymidine analogue-resistant mutants. Antimicrob Agents Chemother 50:3607-14
Smith, Anthony James; Scott, Walter Alvin (2006) The influence of natural substrates and inhibitors on the nucleotide-dependent excision activity of HIV-1 reverse transcriptase in the infected cell. Curr Pharm Des 12:1827-41
Smith, Anthony J; Meyer, Peter R; Asthana, Deshratn et al. (2005) Intracellular substrates for the primer-unblocking reaction by human immunodeficiency virus type 1 reverse transcriptase: detection and quantitation in extracts from quiescent- and activated-lymphocyte subpopulations. Antimicrob Agents Chemother 49:1761-9
Meyer, Peter R; Smith, Anthony J; Matsuura, Suzanne E et al. (2004) Effects of primer-template sequence on ATP-dependent removal of chain-terminating nucleotide analogues by HIV-1 reverse transcriptase. J Biol Chem 279:45389-98
Meyer, Peter R; Matsuura, Suzanne E; Zonarich, Dianna et al. (2003) Relationship between 3'-azido-3'-deoxythymidine resistance and primer unblocking activity in foscarnet-resistant mutants of human immunodeficiency virus type 1 reverse transcriptase. J Virol 77:6127-37

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