Linking the HTLV-1 pre-integration complex to the chromatin

人类免疫缺陷病毒1型（HIV-1）和人类T细胞嗜淋巴细胞病毒1型（HTLV-1）是最臭名昭著的逆转录病毒，因为它们是严重的，致残的，有时是致命的疾病的原因。全世界有1000万到2000万人感染了HTLV-1。在这些人中，约有10%会生病。最严重的HTLV-1诱导的疾病是成人T细胞白血病（ATL）和神经系统疾病HTLV诱导的脊髓病/热带痉挛性下肢轻瘫（HAM/TSP）。到目前为止，HTLV-1感染患者的治疗被证明是非常低效的。被诊断为ATL的患者通常在出现后两年内死亡。HTLV-1与其他逆转录病毒一样，是将其RNA基因组逆转录为DNA的RNA病毒。逆转录病毒生命周期中的关键步骤是将该DNA拷贝整合（或插入）到宿主基因组中。该反应由病毒酶整合酶促进。病毒在宿主基因组中整合其DNA拷贝的位置不是随机的，我们知道基因组某些区域的整合可能使患者易于患病。我们的目标是了解整合机制如何选择将病毒DNA插入的位置。我们已经鉴定了一种重要的宿主蛋白复合物，蛋白磷酸酶2A（PP 2A），其特异性结合HTLV-1整合酶并强烈刺激整合酶活性。我们还表明，当我们使用突变的病毒失去与PP 2A的相互作用时，感染被严重抑制。PP 2A不结合DNA，但具有与人DNA相关的广泛的底物和结合伴侣。我们假设整合体使用PP 2A作为桥接因子将整合机制带到其整合位点，即基因组中富含PP 2A底物的位置。我们最近已经确定了一个复杂的染色质相关的蛋白质，调节染色质压实，影响基因表达和组织的细胞染色质（间接）与HTLV-1整合酶。我们已经表明，该复合物的结构完整性是必不可少的建立HTLV-1感染。在这里，我们的目标是剖析哪些组件是关键的HTLV-1感染和整合，并阐明了这种染色质相关的复合物影响HTLV-1感染的机制。我们的目标还在于解决与这些宿主蛋白质复合的整合机制的3D结构。了解这一过程不仅将增加我们对HTLV-1生物学的理解和疾病进展的可能性，而且还将推动癌症研究向前发展，因为PP 2A和这种染色质复合物都参与了广泛的人类疾病。最后，确定HTLV-1建立感染的机制，并从结构上表征参与这一过程的参与者，也将有助于设计和开发能够特异性阻止整合酶与其宿主之间相互作用的药物。

Human immunodeficiency virus type 1 (HIV-1) and human T-cell lymphotropic virus type 1 (HTLV-1) are the most notorious retroviruses since they are the cause of severe, disabling and sometimes fatal diseases. Ten to 20 million people worldwide are infected with HTLV-1. Of these individuals, about 10% will become ill. The most severe HTLV-1 induced diseases are adult T-cell leukaemia (ATL) and the neurological disorder HTLV-induced myelopathy/tropical spastic paraparesis (HAM/TSP). So far, treatment of HTLV-1 infected patients was proven to be very inefficient. Patients diagnosed with ATL, typically die within two years of presentation. HTLV-1, like other retroviruses, are RNA viruses that reverse transcribe their RNA genome into DNA. A critical step in the lifecycle of retroviruses is the integration (or insertion) of this DNA copy into the host genome. This reaction is facilitated by the viral enzyme integrase. Where in the host genome the virus will integrate its DNA copy is not random and we know that integration in certain areas of the genome likely predispose the patients to disease. Our aim is to understand the mechanism of how the integration machinery choses where it will insert the viral DNA. We have identified an important host protein complex, protein phosphatase 2A (PP2A), that specifically binds to HTLV-1 integrase and strongly stimulates integrase activity. We have also shown that when we use viruses mutated to lose its interaction with PP2A, infection is severely inhibited. PP2A does not bind DNA but has a wide range of substrates and binding partners that are associated with the human DNA. We hypothesize that the intasome uses PP2A as a bridging factor to bring the integration machinery to its site of integration, i.e. places in the genome that are enriched for substrates of PP2A. We have recently identified a complex of chromatin-associated proteins that modulate chromatin compaction, influence gene expression and organisation of the cellular chromatin which (indirectly) associates with HTLV-1 integrase. We have shown that the structural integrity of the complex is essential to establish HTLV-1 infection. Here we aim to dissect which components are critical for HTLV-1 infection and integration and characterise the mechanism by which this chromatin-associated complex influences HTLV-1 infection. We also aim to solve the 3D structure of the integration machinery in complex with these host proteins.Understanding this process will not only increase our understanding in HTLV-1 biology and possible chance of disease progression but will also propel cancer research forward since both PP2A and this chromatin complex are involved in a wide range of human diseases. Finally, identifying the mechanism by which HTLV-1 establishes infection, and structurally characterising the players involved in this process will also aid in the design and development of drugs that can specifically prevent the interaction between integrase and its host.