The cellular APOBEC3F and -3G proteins restrict the ability of retroviruses, including HIV-1, to successfully infect human cells. This novel innate immune defense occurs by APOBEC-catalyzed deamination of nascent cytosine residues in the cDNA strand of a replicating retrovirus. At least four mechanistic steps are required for APOBEC-dependent retroviral restriction. First, these APOBEC proteins must avoid the HIV-1 counterdefense protein Vif, which can mediate their destruction. Second, the APOBECs must incorporate into viral particles. Third, upon retroviral reverse transcription the APOBECs deaminate nascent cDNA cytosines. This produces uracil residues within the retroviral DNA, which are regarded as lesions by cellular DNA repair pathways. Thus, the fourth step may involve both the replication and fixation of minus strand uracils as plus strand adenines (hypermutation) and also the recognition and processing of uracils by other unidentified cellular enzymes. The latter event is likely to block the retrovirus from integrating. This proposal will better define these steps by delineating the key APOBEC protein domains and amino acid residues required for the first three steps. A powerful combination of model microbial, biochemical and retroviral systems will be used and complemented with somatic cell genetic techniques. These systems will be further applied to identify cellular DNA repair enzymes, likely base excision repair proteins, responsible for the fourth step. Finally, the identity and relative contributions of the APOBEC proteins that inhibit HIV-1 infection in the primary human viral reservoirs will be defined. Together the proposed studies will result in a fundamental understanding of the mechanism of APOBEC-dependent retroviral restriction. This will assist the rational design of therapies that could potentially attenuate HIV-1 by modulating the cellular APOBEC defense and the retroviral Vif counterdefense. The consequences of failing to appreciate these fundamental steps could be catastrophic as mis-regulation/expression of APOBEC family members has been associated with carcinogenesis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI064046-04
Application #
7384477
Study Section
AIDS Molecular and Cellular Biology Study Section (AMCB)
Program Officer
Embry, Alan C
Project Start
2005-07-01
Project End
2010-03-31
Budget Start
2008-04-01
Budget End
2009-03-31
Support Year
4
Fiscal Year
2008
Total Cost
$304,585
Indirect Cost
Name
University of Minnesota Twin Cities
Department
Biochemistry
Type
Schools of Medicine
DUNS #
555917996
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
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Shi, Ke; Carpenter, Michael A; Kurahashi, Kayo et al. (2015) Crystal Structure of the DNA Deaminase APOBEC3B Catalytic Domain. J Biol Chem 290:28120-30

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