Alternative Entry Mechanism for Pathogenic Retroviruses

描述(由申请人提供)：在小鼠中与生态型逆转录病毒感染相关的白血病发病机制中的一个关键步骤是改变对myc或其他原癌基因的调节，这是由MCF前病毒的相邻整合引起的(12，30，57)。MCF病毒是具有煽动性的生态型病毒基因组与缺陷内源性前病毒(27-29，79)的宿主序列重组的产物。在对人类293细胞中病毒受体功能的研究中，我们观察到，暴露于MCF247病毒的细胞获得的前病毒/细胞比暴露于密切相关的非致病逆转录病毒的细胞多20-40倍(85)。我们的研究发现了两种可能的解释：1)MCF247 env gp的受体结合亲和力显著低于其他病毒(KA&GT；100 nM)，因此在通过受体下调抑制额外感染之前，需要更高水平的env gp表达。2)MCF247病毒特别适合通过一种不依赖于与细胞受体直接结合的替代机制进入某些细胞。通过这种途径，通过将MCF247病毒包膜糖蛋白结合到位于目标细胞(85)表面膜上的具有其受体的复合体中的生态病毒的包膜糖蛋白上而触发感染。这种称为“反式激活”的机制不受MCF247病毒env gp表达的下调，因此其活性与先前感染(和前病毒插入)的数量无关。我们认为，结合使用受体和反式激活依赖机制为MCF247病毒提供了比正在进行的生态型病毒复制过程中产生的其他重组病毒更具选择性的优势，这可能在一定程度上解释了为什么MCF247病毒具有高度的白血病致病性。此外，我们观察到反式激活是感染FeLV-T(8)的唯一机制，FeLV-T(8)是一种重组猫科逆转录病毒，与大量前病毒聚集和T细胞凋亡导致的严重免疫缺陷有关(25，66)。FeLV-T和MCF247病毒的行为表明，重组病毒和激发病毒之间的协同作用可能有助于感染宿主中准物种的含量和性质。到目前为止，我们对反式激活的研究主要局限于FeLV-T和MCF247病毒的体外。我们的具体目标是： 1.确定对反式激活的易感性是否是致病性MCF病毒的共同特征。 2.建立反式激活机制的体外研究体系。 3.探讨反式激活在逆转录病毒诱导的小鼠白血病发病机制中的作用。

DESCRIPTION (provided by applicant): A key step in the pathogenesis of leukemia associated with ecotropic retrovirus infection in mice is altered regulation of myc or other proto-oncogenes caused by adjacent integration of an MCF provirus (12, 30, 57). MCF viruses are the product of recombination between the genome of the inciting ecotropic virus and host sequences derived from defective endogenous proviruses (27-29, 79). In studies of virus receptor function in human 293 cells, we observed that cells exposed to MCF247 virus acquired 20-40-fold more proviruses/cell than cells exposed to closely related retroviruses that are not pathogenic (85). Our studies have identified two possible explanations for this observation: 1) The receptor binding affinity of the MCF247 env gp is significantly lower than other viruses (Ka >100 nM) and therefore a substantially higher level of env gp expression is required before additional infection is blocked by receptor down regulation. 2) MCF247 viruses are uniquely suited to gain entry into certain cells through an alternative mechanism that is not dependent on direct binding to a cellular receptor. By this route, infection is triggered by binding of the MCF247 virus env gp to the env gp of an ecotropic virus located in a complex with its receptor on the surface membrane of the target cell (85). This mechanism, termed "trans-activation" is not down regulated by expression of the MCF247 virus env gp and therefore its activity is independent of the number of prior infections (and provirus insertions). We propose the combined use of both receptor and trans-activation-dependent mechanisms provides the MCF247 virus with a selective advantage over other recombinant viruses that are created during ongoing ecotropic virus replication and may explain, in part, why MCF247 virus is highly leukemogenic. In addition, we observe that trans-activation is the sole mechanism of infection by FeLV-T (8), a recombinant feline retrovirus associated with profound immunodeficiency caused by massive provirus accumulation and apoptosis in T cells (25, 66). The behavior of FeLV-T and MCF247 viruses suggests that cooperative interactions between recombinant and inciting viruses may contribute to the content and properties of the quasi-species in an infected host. To date, our studies of trans-activation have been largely limited to FeLV-T and MCF247 viruses in vitro. Our specific aims are to: 1. Determine if susceptibility to trans-activation is a common property of pathogenic MCF viruses. 2. Develop an in vitro system to investigate the mechanism of trans-activation. 3. Assess the contribution of trans-activation to the pathogenesis of retrovirus-induced leukemia in mice.