Regulation and Action of APOBEC3G

描述（由申请人提供）：载脂蛋白B mRNA编辑酶，催化多肽-1样3G（APOBEC 3G，A3 G）对应于显示有效抗逆转录病毒活性的宿主衍生胞苷脱氨酶。当A3 G酶被整合到萌芽的HIV病毒体中时，A3 G酶会使下一个靶细胞中逆转录过程中产生的新生HIV DNA发生大规模突变，从而阻止HIV生长。HIV通过其Vif基因产物对抗A3 G的这些作用，Vif基因产物促进加速蛋白酶体介导的降解和部分受损的A3 G从头合成。A3 G的细胞内消耗使得抗病毒酶不可用于并入子代病毒体中。我们最近的研究揭示了A3 G在静息CD 4 T细胞中的第二种抗病毒作用。在这些T淋巴细胞中，细胞A3 G作为高活性的进入后限制因子发挥作用，阻断野生型和deltaVif形式的HIV的生长。这种由A3 G介导的“抗Vif”抗HIV防御是否涉及胞苷脱氨基或不同的机制目前尚不清楚。此外，当T细胞被激活时，A3 G的这种进入后限制功能丧失的机制仍然不完全清楚。同样，关于宿主细胞如何保护自己的DNA免受A3 G的致突变作用，我们也知之甚少。最后，A3 G是否发挥这些抗病毒作用之外的其他关键功能仍然未知。在具体目标1中，将进行实验以破译A3 G和密切相关的A3 F和A3 B抗病毒酶如何在细胞中调节。在特定目标2中，将描述A3 G作为静息CD 4 T细胞中的进入后限制因子的作用机制、受此限制影响的病毒范围以及A3 F的潜在相似功能。最后，在具体目标3中，将进行研究以评估A3 G是否介导哺乳动物细胞中重要的非抗病毒功能。这些实验将涉及缺乏A3 G基因功能类似物的小鼠的制备和分析。总之，这个拟议的实验计划有望丰富我们对A3 G生物学以及相关A3 F和A3 B酶的理解。有了这样的理解，抑制艾滋病毒生长的新治疗策略可能会出现。

DESCRIPTION (provided by applicant): Apolipoprotein B mRNA editing enzyme, catalytic polypeptide-1 like 3G (APOBEC3G, A3G) corresponds to a host-derived cytidine deaminase that displays potent anti-retroviral activity. When incorporated into budding HIV virions, the A3G enzyme massively mutates nascent HIV DNA produced during reverse transcription in the next target cell thereby halting HIV growth. HIV counters these effects of A3G through its Vif gene product, which promotes accelerated proteasome-mediated degradation and partially impaired de novo synthesis of A3G. The intracellular depletion of A3G makes the antiviral enzyme unavailable for incorporation into progeny virions. Our recent studies have unveiled a second antiviral action of A3G operating in resting CD4 T-cells. In these T-lymphocytes, cellular A3G functions as a highly active post-entry restriction factor blocking the growth of both wild type and deltaVif forms of HIV. Whether this "Vif-resistant" anti-HIV defense mediated by A3G involves cytidine deamination or a different mechanism is currently unknown. Further, the mechanism by which this post-entry restricting function of A3G is forfeited when T-cells are activated remains incompletely understood. Similarly, little is known about how host cells safeguard their own DNA from the mutagenic effects of A3G. Finally, it remains unknown whether A3G exerts other key functions beyond these antiviral effects. In Specific Aim 1, experiments will be performed to decipher how A3G and the closely related A3F and A3B antiviral enzymes are regulated in cells. In Specific Aim 2, the mechanism of A3G action as a post-entry restriction factor in resting CD4 T-cells, the range of viruses affected by this restriction, and potential similar functions of A3F will be delineated. Finally, in Specific Aim 3, studies will be conducted to assess whether A3G mediates important non-antiviral functions in mammalian cells. These experiments will involve the preparation and analysis of mice lacking the functional analogue of the A3G gene. Together, this program of proposed experimentation promises to enrich our understanding of the biology of A3G as well as the related A3F and A3B enzymes. With such understanding, new therapeutic strategies for inhibiting HIV growth could emerge.