APOBECs and virus restriction

Harris, Reuben S.; Dudley, Jaquelin P.

doi:10.1016/j.virol.2015.03.012

Cited by 465 publications

(532 citation statements)

References 242 publications

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“…3,4 APO-BEC3 enzymes play a role in innate immunity as viral restriction factors, in part by inducing mutations in viral genomes. [5][6][7] AID/APOBEC3 family members also inhibit retrotransposition of genetic elements including long terminal repeat (LTR) and non-LTR (LINE-1) elements. [8][9][10][11] Although these deaminases have important physiologic functions in innate defense, their DNA mutator activity also threatens host genome integrity.…”

Section: Introductionmentioning

confidence: 99%

APOBEC3A damages the cellular genome during DNA replication

et al. 2016

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The human APOBEC3 family of DNA-cytosine deaminases comprises 7 members (A3A-A3H) that act on single-stranded DNA (ssDNA). The APOBEC3 proteins function within the innate immune system by mutating DNA of viral genomes and retroelements to restrict infection and retrotransposition. Recent evidence suggests that APOBEC3 enzymes can also cause damage to the cellular genome. Mutational patterns consistent with APOBEC3 activity have been identified by bioinformatic analysis of tumor genome sequences. These mutational signatures include clusters of base substitutions that are proposed to occur due to APOBEC3 deamination. It has been suggested that transiently exposed ssDNA segments provide substrate for APOBEC3 deamination leading to mutation signatures within the genome. However, the mechanisms that produce single-stranded substrates for APOBEC3 deamination in mammalian cells have not been demonstrated. We investigated ssDNA at replication forks as a substrate for APOBEC3 deamination. We found that APOBEC3A (A3A) expression leads to DNA damage in replicating cells but this is reduced in quiescent cells. Upon A3A expression, cycling cells activate the DNA replication checkpoint and undergo cell cycle arrest. Additionally, we find that replication stress leaves cells vulnerable to A3A-induced DNA damage. We propose a model to explain A3A-induced damage to the cellular genome in which cytosine deamination at replication forks and other ssDNA substrates results in mutations and DNA breaks. This model highlights the risk of mutagenesis by A3A expression in replicating progenitor cells, and supports the emerging hypothesis that APOBEC3 enzymes contribute to genome instability in human tumors.

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Section: Introductionmentioning

confidence: 99%

APOBEC3A damages the cellular genome during DNA replication

et al. 2016

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“…During this time, single-stranded minus-strand DNA is vulnerable to A3 deaminations of cytosine that form uracil (2,3,5). The reverse transcriptase is forced to use uracil as a template during plus-strand DNA synthesis, which induces C/G¡T/A mutations and can functionally inactivate the virus or lead to its degradation through DNA repair pathways that excise uracil (6). The effect of A3 enzymes on HIV replication in infected individuals is severely dampened by the viral infectivity factor (Vif) that interacts with A3 enzymes, recruits an E3 ubiquitin ligase complex, and induces A3 ubiquitination and degradation in the proteasome (7)(8)(9)(10)(11)(12).…”

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confidence: 99%

Mechanism of Enhanced HIV Restriction by Virion Coencapsidated Cytidine Deaminases APOBEC3F and APOBEC3G

Ara

Love

Follack

et al. 2017

J Virol

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The APOBEC3 (A3) enzymes, A3G and A3F, are coordinately expressed in CD4 ϩ T cells and can become coencapsidated into HIV-1 virions, primarily in the absence of the viral infectivity factor (Vif). A3F and A3G are deoxycytidine deaminases that inhibit HIV-1 replication by inducing guanine-to-adenine hypermutation through deamination of cytosine to form uracil in minus-strand DNA. The effect of the simultaneous presence of both A3G and A3F on HIV-1 restriction ability is not clear. Here, we used a single-cycle infectivity assay and biochemical analyses to determine if coencapsidated A3G and A3F differ in their restriction capacity from A3G or A3F alone. Proviral DNA sequencing demonstrated that compared to each A3 enzyme alone, A3G and A3F, when combined, had a coordinate effect on hypermutation. Using size exclusion chromatography, rotational anisotropy, and in vitro deamination assays, we demonstrate that A3F promotes A3G deamination activity by forming an A3F/G hetero-oligomer in the absence of RNA which is more efficient at deaminating cytosines. Further, A3F caused the accumulation of shorter reverse transcripts due to decreasing reverse transcriptase efficiency, which would leave singlestranded minus-strand DNA exposed for longer periods of time, enabling more deamination events to occur. Although A3G and A3F are known to function alongside each other, these data provide evidence for an A3F/G hetero-oligomeric A3 with unique properties compared to each individual counterpart.IMPORTANCE The APOBEC3 enzymes APOBEC3F and APOBEC3G act as a barrier to HIV-1 replication in the absence of the HIV-1 Vif protein. After APOBEC3 enzymes are encapsidated into virions, they deaminate cytosines in minus-strand DNA, which forms promutagenic uracils that induce transition mutations or proviral DNA degradation. Even in the presence of Vif, footprints of APOBEC3-catalyzed deaminations are found, demonstrating that APOBEC3s still have discernible activity against HIV-1 in infected individuals. We undertook a study to better understand the activity of coexpressed APOBEC3F and APOBEC3G. The data demonstrate that an APOBEC3F/ APOBEC3G hetero-oligomer can form that has unique properties compared to each APOBEC3 alone. This hetero-oligomer has increased efficiency of virus hypermutation, raising the idea that we still may not fully realize the antiviral mechanisms of endogenous APOBEC3 enzymes. Hetero-oligomerization may be a mechanism to increase their antiviral activity in the presence of Vif.

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“…1,2 Previously, A3 proteins were studied in the context of their interactions with viruses and efforts were undertaken to discover small molecules that modulate the mutational activities of the virally restrictive APOBEC3G enzyme. 3,4 Recent studies have linked cancer progression and recurrence to A3 activity.…”

Section: Introductionmentioning

confidence: 99%

Determinants of Substrate Specificity in APOBEC3B

Wagner

Demir²,

Carpenter³

et al. 2018

Preprint

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APOBEC3B (A3B) is a newly discovered driver of mutation in many cancers. We use computational tools to revert a recent crystal structure of an A3B construct to its native sequence, and run molecular dynamics simulations to study its underlying dynamics and substrate recognition mechanisms. The A3B oligonucleotide substrate simulations show a series of dynamic substrate protein contacts that correlate with previous work on A3B substrate selectivity. A second series of simulations in which the target cytosine nucleotide was computationally mutated from a deoxyribose to a ribose showed a change in sugar ring pucker, leading to a rearrangement of the binding site and revealing a potential intermediate in the binding pathway. Finally, apo simulations of A3B beginning in the open state experience a rapid and consistent closure of the binding site, reaching a conformation incompatible with substrate binding. These simulations agree with previous experimental studies, and we report the atomistic details of these events to further therapeutic studies on A3B. IntroductionThe APOBEC3 (A3) family of cytidine deaminases is a recently discovered endogenous source of mutation in cancer. 1,2 Previously, A3 proteins were studied in the context of their interactions with viruses and efforts were undertaken to discover small molecules that modulate the mutational activities of the virally restrictive APOBEC3G enzyme. 3,4 Recent studies have linked cancer progression and recurrence to A3 activity. 5-9 A3 proteins have specific substrate sequence preferences, and analyses of some cancer genomes have shown an enrichment of A3 mutation signatures. [10][11][12][13][14][15] Recent evidence suggests that APOBEC3B (A3B) is an important driver of tumor progression in the A3 family. 16,17

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APOBECs and virus restriction

Cited by 465 publications

References 242 publications

APOBEC3A damages the cellular genome during DNA replication

APOBEC3A damages the cellular genome during DNA replication

Mechanism of Enhanced HIV Restriction by Virion Coencapsidated Cytidine Deaminases APOBEC3F and APOBEC3G

Determinants of Substrate Specificity in APOBEC3B

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