Genome stability function of APOBEC3 retroviral restriction factors

描述（由申请人提供）：与一般人群相比，HIV-1艾滋病的特点是肿瘤发展的发生率明显更高。虽然这些恶性肿瘤中的一些，被描述为艾滋病定义，其病因是已知的，但艾滋病非定义恶性肿瘤的病因仍然不确定。尽管抗逆转录病毒治疗非常有效，但非艾滋病恶性肿瘤仍然是艾滋病毒-1感染者死亡的主要原因之一。在这里，我们提出验证HIV-1感染导致基因组不稳定和恶性肿瘤的假设，因为它解除了对内源性逆转录病毒生产性复制的自然抑制。人类内源性逆转录病毒（herv）占据了人类基因组的显著部分。在人类进化过程中，基因组不断受到逆转录病毒的入侵，逆转录病毒的复制策略包括在生殖系细胞中整合。这种现象被称为内源性，允许逆转录病毒在纵向和纵向上延续自身。虽然有几种宿主机制保证了大多数herv的失活，但有令人信服的证据表明，内源性逆转录病毒与恶性肿瘤有关。事实上，在几种类型的肿瘤以及HIV-1感染患者中已经报道了HERV的产生。APOBEC3家族的胞苷脱氨酶（A3）是逆转录病毒的有效抑制剂。通过使输出病毒体无传染性，A3分子可能阻止herv扩散和诱导致癌转化。我们假设，7种A3蛋白与HERV之间现有平衡的改变导致了HERV高效复制导致基因组不稳定。这种保护机制可以被不同的原因所抑制，包括a) HIV Vif，它有效地介导了几种A3分子的降解，b) A3位点的基因组结构变异。基因组结构变异是指个体间存在拷贝数变异的基因组DNA片段。据报道，A3位点包含至少三个CNVs，其中一个移除了整个APOBEC3B开放阅读框。我们的实验策略将测试A3家族成员的抑制（由A3B基因缺失多态性介导的HIV蛋白Vif）在多大程度上去抑制内源性逆转录病毒，从而为通过插入突变进行致癌转化铺平道路。在我们的第一个特异性目标中，我们将确定hiv -1依赖性HERV感染的分子基础。我们将测试vif介导的A3限制性释放对PBMC中HERV复制的影响。在第二个特定目标中，我们将确定A3基因组变异如何影响herv复制。本实验将确定在HIV/AIDS疾病存在和不存在的情况下，A3功能调控如何影响基因组稳定性。这些研究可能有助于开发恶性肿瘤的新标志物，并为开发旨在稳定内在免疫防御的新治疗方案打开大门。

DESCRIPTION (provided by applicant): HIV-1 AIDS is marked by a significantly higher incidence of tumor development, compared to the general population. Although for some of these malignancies, described as AIDS-defining, the cause is known, the etiology of the AIDS non-defining malignancies remains uncertain. Despite highly active antiretroviral treatments, non-AIDS defining malignancies remain among the leading causes of death in HIV-1 infected individuals. Here we propose to test the hypothesis that HIV-1 infection leads to genomic instability and malignancies because it lifts the natural inhibition on productive replication of endogenous retroviruses. Human endogenous retroviruses (HERVs) occupy a remarkable portion of the human genome. During human evolution the genome has been under constant invasion by retroviruses whose replicative strategy includes integration in the germ-line cells. This phenomenon, known as endogenization, permits the retrovirus to perpetuate itself both vertically and longitudinally. While several host mechanisms have guaranteed the inactivation of most HERVs, there is compelling, albeit circumstantial, evidence implicating endogenous retroviruses in malignancies. HERV production has, indeed, been reported in several types of tumors as well as in HIV-1 infected patients. Cytidine deaminases of the APOBEC3 family (A3) are potent inhibitors of retroviruses. By rendering egressing virions non infectious, A3 molecules potentially prevent HERVs from spreading and inducing oncogenic transformation. We hypothesize that alteration of the existing equilibrium between the seven A3 proteins and HERVs leads to genomic instability due to productive HERV replication. This protective mechanism can be suppressed by different causes, including a) HIV Vif, which efficiently mediates the degradation of several of the A3 molecules, b) genomic structural variation of the A3 locus. Structural genomic variation refers to genomic DNA segments that show copy number variation (CNV) among individuals. The A3 locus has been reported to encompass at least three CNVs, one of which removes the whole APOBEC3B open reading frame. Our experimental strategy will test to what extent suppression of A3 family members (mediated by HIV protein Vif or by A3B genetic deletion polymorphism) de-represses endogenous retroviruses, paving the way to oncogenic transformation via insertional mutagenesis. In our first Specific Aim, we will determine the molecular basis of HIV-1-dependent HERV infectivity. We will test the impact of Vif-mediated release of the A3 restriction on HERV replication in PBMC. In the second Specific Aim we will determine how A3 genomic variation influences HERVs replication. The proposed experiments will establish how (dys)regulation of A3 function affects genome stability in the absence and presence of HIV/AIDS disease. These studies may help develop new markers for malignancies and open doors for the development of new treatment options aimed at stabilizing intrinsic immune defenses.