Entry mechanisms used by a model retrovirus

描述(申请人提供)：被包裹的病毒通过将其膜与细胞膜合并而将其核衣壳释放到细胞质中。这些病毒中的大多数被细胞内化，并与内小体融合。病毒-内小体融合及其调控的分子机制的阐明一直受到内小体高度动态的性质和无法进入这些间隔室的阻碍。我们已经开发了非侵入性成像技术，可以对病毒进入的关键步骤进行时间分辨可视化，从半融合(脂质转移)到小孔形成(释放小含量标志物)和孔扩大(释放衣壳)。最近实施的成像分析方法可以(I)测量携带病毒的内小体的pH值，以及(Ii)检测所产生的融合事件。我们建议应用这些成像和其他方法来确定禽肉瘤和白血病病毒(ASLV)的进入机制，这是阐明不同病毒所使用的进入途径的一个很好的模型。ASLV的两步触发--内小体融合--与同源受体结合并暴露在低pH环境下--允许对病毒进入过程进行前所未有的控制。我们的试验数据表明，引人注目的是，ASLV与早期酸性内体的融合在某些细胞类型中受到限制，并发生在晚期的内体隔室。这些发现表明，ASLV的融合受细胞因素的调控，这种病毒可能经历半融合或在早期的内体中形成一个小的融合孔，同时依赖宿主因素来驱动能量上不利的孔扩张步骤。为了验证这一假设，我们将：(1)研究ASLV融合的时空调节；(2)检查ASLV孔扩大的决定因素；(3)确定内体脂质在ASLV融合中的作用。这些研究将为ASLV的融合及其宿主因素的调控提供重要的见解。对ASLV融合机制的了解将为人类病毒(如HIV-1、丙型肝炎病毒和埃博拉病毒)的研究提供一个概念性框架，这些病毒通过内吞途径进入宿主细胞，并依赖于多种宿主因子。

DESCRIPTION (provided by applicant): Enveloped viruses release their nucleocapsids into the cytoplasm by merging their membrane with the cell membrane. The majority of these viruses is internalized by cells and fuses with endosomes. The elucidation of the molecular mechanisms of virus-endosome fusion and its regulation has been hampered by the highly dynamic nature of endosomes and the lack of access to these compartments. We have developed non- invasive imaging techniques that permit the time-resolved visualization of the critical steps of virus entry, from hemifusion (lipid transfer), to small pore formation (release o small content markers) and pore enlargement (release of the capsid). The recently implemented imaging assay enables (i) measurements of the pH in virus- carrying endosomes and (ii) detection of the resulting fusion events. We propose to apply these imaging and other approaches to define the mechanism of entry of the Avian Sarcoma and Leukosis Virus (ASLV), which is an excellent model for elucidating the entry pathways used by disparate viruses. The two-step triggering of ASLV-endosome fusion - binding to a cognate receptor and exposure to low pH - permit an unprecedented control over the virus entry process. Our pilot data suggest that, strikingly, the ASLV fusion with early acidic endosomes is restricted in some cell types and occurs in late endosomal compartments. These findings imply that ASLV fusion is regulated by cellular factors and that this virus may undergo hemifusion or form a small fusion pore in early endosomes, while relying on host factors to drive the energetically unfavorable step of pore enlargement. To test this hypothesis, we will: (1) investigate the spatio-temporal regulation of ASLV fusion; (2) examine the determinants of ASLV pore enlargement; and (3) define the role of endosomal lipids in ASLV fusion. These studies will provide critical insights into the ASLV fusion and its regulation by host factors. Knowledge of the mechanisms of ASLV fusion will offer a conceptual framework for studies of human viruses, such as HIV-1, Hepatitis C virus and Ebola virus, which enter host cells via the endocytic pathway and rely on a multitude of host factors.