Regulation and Action of APOBEC3G

描述(申请人提供)：载脂蛋白B信使核糖核酸编辑酶，催化多肽-1样3G(APOBEC3G，A3G)对应于一种宿主衍生的胞苷脱氨酶，具有强大的抗逆转录病毒活性。当被整合到萌芽中的艾滋病毒病毒粒子中时，A3G酶在下一个目标细胞中大规模突变在逆转录过程中产生的新生艾滋病毒DNA，从而阻止艾滋病毒的生长。HIV通过其Vif基因产物对抗A3G的这些影响，Vif基因产物促进蛋白酶体介导的加速降解，并部分损害A3G的从头合成。A3G的细胞内耗尽使得抗病毒酶不能被整合到后代病毒粒子中。我们最近的研究揭示了A3G在静止的CD4T细胞上发挥的第二种抗病毒作用。在这些T淋巴细胞中，细胞A3G作为一种高度活跃的进入后限制因子，阻止了野生型和DeltaVif形式的艾滋病毒的生长。目前尚不清楚A3G介导的这种对Vif耐药的抗艾滋病毒防御是否涉及胞苷脱氨基或其他机制。此外，当T细胞被激活时，A3G的这种进入后限制功能丧失的机制仍不完全清楚。同样，宿主细胞如何保护自己的DNA免受A3G的突变效应也知之甚少。最后，目前尚不清楚A3G是否在这些抗病毒作用之外发挥了其他关键功能。在具体目标1中，将进行实验以破译A3G以及密切相关的A3F和A3B抗病毒酶在细胞中是如何调节的。在具体目标2中，将描述A3G作为进入后限制因子作用于静止的CD4T细胞的机制，受此限制影响的病毒范围，以及A3F潜在的类似功能。最后，在具体目标3中，将进行研究，以评估A3G是否在哺乳动物细胞中介导重要的非抗病毒功能。这些实验将涉及缺乏A3G基因功能类似物的小鼠的准备和分析。总之，这项拟议的实验计划有望丰富我们对A3G生物学以及相关A3F和A3B酶的理解。有了这样的理解，就可能出现抑制艾滋病毒增长的新的治疗策略。

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.