Article

Antiretroelement Activity of APOBEC3H Was Lost Twice in Recent Human Evolution

Molecular and Cellular Biology Program, University of Washington, Seattle, WA 98195, USA.
Cell host & microbe (Impact Factor: 12.19). 10/2008; 4(3):249-59. DOI: 10.1016/j.chom.2008.07.005
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ABSTRACT The primate APOBEC3 gene locus encodes a family of proteins (APOBEC3A-H) with various antiviral and antiretroelement activities. Here, we trace the evolution of APOBEC3H activity in hominoids to identify a human-specific loss of APOBEC3H antiviral activity. Reconstruction of the predicted ancestral human APOBEC3H protein shows that human ancestors encoded a stable form of this protein with potent antiviral activity. Subsequently, the antiviral activity of APOBEC3H was lost via two polymorphisms that are each independently sufficient to destabilize the protein. Nonetheless, an APOBEC3H allele that encodes a stably expressed protein is still maintained at high frequency, primarily in African populations. This stable APOBEC3H protein has potent activity against retroviruses and retrotransposons, including HIV and LINE-1 elements. The surprising finding that APOBEC3H antiviral activity has been lost in the majority of humans may have important consequences for our susceptibility to retroviral infections as well as ongoing retroelement proliferation in the human genome.

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Available from: Harmit Singh Malik, Aug 30, 2015
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    • "In humans, certain A3H haplotypes influence both the activity of the protein and their subcellular location (OhAinle et al., 2008; Li and Emerman, 2011; Harari et al., 2009). Some of these haplotypes encode a completely inactive A3H, thus promoting retroviral infections in the subjects that display such haplotypes (OhAinle et al., 2008; Li and Emerman, 2011; Harari et al., 2009). In the present study, the haplotype ''GGGGCC'' was significantly more frequently detected in the FIV-and FeLV-uninfected animals, suggesting a possible protective effect of this allelic combination in relation to infection by FIV and FeLV. "
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    ABSTRACT: Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are widely distributed retroviruses that infect domestic cats (Felis catus). Restriction factors are proteins that have the ability to hamper retroviruses' replication and are part of the conserved mechanisms of anti-viral immunity of mammals. The APOBEC3 protein family is the most studied class of restriction factors; they are cytidine deaminases that generate hypermutations in provirus DNA during reverse transcription, thus causing hypermutations in the viral genome, hindering virus replication. One of the feline APOBEC3 genes, named APOBEC3H, encodes two proteins (APOBEC3H and APOBEC3CH). In other mammals, APOBEC3H single-nucleotide polymorphisms (SNPs) can alter the stability and cellular localization of the encoded protein, thus influencing its subcellular localization and reducing its anti-viral effect. In cats, the association of APOBEC3H SNPs with susceptibility to retroviral infections was not yet demonstrated. Therefore, this study aimed the investigation on the variability of APOBEC3H and the possible association with FIV/FeLV infections. DNA obtained from whole blood of fifty FIV- and/or FeLV-infected cats and fifty-nine FIV- and/or FeLV-uninfected cats were used as templates to amplify two different regions of the APOBEC3H, with subsequent sequencing and analysis. The first region was highly conserved among all samples, while in the second, six single-nucleotide variation points were identified. One of the SNPs, A65S (A65I), was significantly correlated with the susceptibility to FIV and/or FeLV infections. On the other hand, the haplotype analysis showed that the combination "GGGGCC" was positively correlated with the lack of FIV and/or FeLV infections. Our results indicate that, as previously shown in other mammals, variability of restriction factors may contribute to susceptibility of domestic cats to retroviral infections; however, these results should be confirmed by more extensive analysis and in vitro experiments.
    Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 08/2014; 27. DOI:10.1016/j.meegid.2014.08.024 · 3.26 Impact Factor
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    • "A3H Hap I encodes GKE at these three positions and A3H Hap II encodes RDD at these positions. It was shown that at position 105, the Arg is required for stable expression in cells and that the 178 position had little effect on Vif-mediated degradation (OhAinle et al., 2008; Harari et al., 2009; Li et al., 2010). Therefore, a single amino acid homologous to A3G 128 D at position 121 in A3H Hap II was determined to control sensitivity to Vif-mediated degradation (Li et al., 2010; Zhen et al., 2010, Figure 3F). "
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    ABSTRACT: The APOBEC3 restriction factors are a family of deoxycytidine deaminases that are able to suppress replication of viruses with a single-stranded DNA intermediate by inducing mutagenesis and functional inactivation of the virus. Of the seven human APOBEC3 enzymes, only APOBEC3-D, -F, -G, and -H appear relevant to restriction of HIV-1 in CD4+ T cells and will be the focus of this review. The restriction of HIV-1 occurs most potently in the absence of HIV-1 Vif that induces polyubiquitination and degradation of APOBEC3 enzymes through the proteasome pathway. To restrict HIV-1, APOBEC3 enzymes must be encapsidated into budding virions. Upon infection of the target cell during reverse transcription of the HIV-1 RNA into (-)DNA, APOBEC3 enzymes deaminate cytosines to form uracils in single-stranded (-)DNA regions. Upon replication of the (-)DNA to (+)DNA, the HIV-1 reverse transcriptase incorporates adenines opposite to the uracils thereby inducing C/G to T/A mutations that can functionally inactivate HIV-1. APOBEC3G is the most studied APOBEC3 enzyme and it is known that Vif attempts to thwart APOBEC3 function not only by inducing its proteasomal degradation but also by several degradation-independent mechanisms, such as inhibiting APOBEC3G virion encapsidation, mRNA translation, and for those APOBEC3G molecules that still become virion encapsidated, Vif can inhibit APOBEC3G mutagenic activity. Although most Vif variants can induce efficient degradation of APOBEC3-D, -F, and -G, there appears to be differential sensitivity to Vif-mediated degradation for APOBEC3H. This review examines APOBEC3-mediated HIV restriction mechanisms, how Vif acts as a substrate receptor for a Cullin5 ubiquitin ligase complex to induce degradation of APOBEC3s, and the determinants and functional consequences of the APOBEC3 and Vif interaction from a biological and biochemical perspective.
    Frontiers in Microbiology 08/2014; 5:450. DOI:10.3389/fmicb.2014.00450 · 3.94 Impact Factor
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    • "Some of these haplotypes have a variable frequency. Haplotype 2 is present in high frequency in African populations [233]; haplotype V is more frequently detected in African-Americans, Caribbeans, and Chinese, while haplotype VII was rarer and found only in European Caucasians [157]. "
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    ABSTRACT: The APOBEC family of proteins comprises deaminase enzymes that edit DNA and/or RNA sequences. The APOBEC3 subgroup plays an important role on the innate immune system, acting on host defense against exogenous viruses and endogenous retroelements. The role of APOBEC3 proteins in the inhibition of viral infection was firstly described for HIV-1. However, in the past few years many studies have also shown evidence of APOBEC3 action on other viruses associated with human diseases, including HTLV, HCV, HBV, HPV, HSV-1, and EBV. APOBEC3 inhibits these viruses through a series of editing-dependent and independent mechanisms. Many viruses have evolved mechanisms to counteract APOBEC effects, and strategies that enhance APOBEC3 activity constitute a new approach for antiviral drug development. On the other hand, novel evidence that editing by APOBEC3 constitutes a source for viral genetic diversification and evolution has emerged. Furthermore, a possible role in cancer development has been shown for these host enzymes. Therefore, understanding the role of deaminases on the immune response against infectious agents, as well as their role in human disease, has become pivotal. This review summarizes the state-of-the-art knowledge of the impact of APOBEC enzymes on human viruses of distinct families and harboring disparate replication strategies.
    06/2013; 2013:683095. DOI:10.1155/2013/683095
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