定时油炸弹乙型肝炎病毒的技巧

StephenW

Tricks of Ticking time bomb Hepatitis B Virus7 hours 42 minutes ago

Hepatitis B virus (HBV) causes hepatitis B, an infectious disease that afflicts 230 million people worldwide, thereof 440 000 in Germany. Persistence of the virus in liver cells leads to progressive organ damage in the patient and contributes to a high risk of cirrhosis and liver cancer development. Providing a new paradigm to hepatitis B understanding, researchers at the German Cancer Research Center (DKFZ) in Heidelberg, Germany, and Department of Infectious Diseases, Molecular Virology, Heidelberg University Hospital have now uncovered a novel maturation mechanism employed by HBV to improve its infection success. Their findings are reported in the newest issue of Cell Host & Microbe.

HBV (green) in liver cells (red) Only virions of the N-Type (left) are able to infect liver cells, HBV of the B-type (right) are not. | © Universitätsklinikum Heidelberg/S. Seitz
To infect cells, viruses need to first attach to specific cellular receptors, i.e. molecules on the cell’s surface. In the case of HBV, a portion of the large surface protein (L protein) in the viral envelope binds to heparan sulfate proteoglycans (HSPG) on the liver cell, and subsequently mediates uptake of the virus particle into the cell where progeny viruses are produced.

‘The effectiveness of HBV in establishing an infection is several orders of magnitude above that of most other animal viruses,’ describes Dr. Stefan Seitz, the lead author of the study. Indeed, it has been demonstrated that HBV is remarkably specific in infecting liver cells even after transmission of virus particles at extremely low number. Yet this presents a paradox, since HSPG are ubiquitously expressed across virtually all cell types in the human body. ‘For a virus which has to reach a target organ in far distance from the transmission site, HSPG seemed to be the most disadvantageous attachment receptors one could imagine,’ Seitz continues. So what might explain this discrepancy?

In tackling this question, the researchers were inspired by two past findings. First, cryo-electron microscope images of HBV showed that the virus appears in two morphologically distinct forms. Second, the L protein in the viral envelope can adopt two structural states. In one state, the receptor-binding determinant is oriented to the virus particle interior, in the other state it is exposed on the outer particle surface. The latter is required for the HBV infection process.

Seitz and colleagues believed that these two observations are linked, and hypothesized that HBV particles undergo a dynamic switch of their morphology during which they change the structural state of the L protein.

To investigate this, they established a biochemical method to differentiate the two groups of HBV particles, based on their binding abilities to HSPG: an ‘immature’, non-binding (N) type, and a ‘mature’, binding (B) type. Subsequent characterization showed that nearly all virus particles are released from the cells in the immature (N) state and spontaneously convert into mature (B) viruses over time by turning the receptor-binding determinant inside out across the viral membrane.

The maturation from N-type into B-type particles was determined to be a slow process rendering HBV infectious. Crucially, after injecting low numbers of virus particles into mice, the researchers found that N-types were superior over B-types in establishing infections in the liver, while B-type particles were prone to associate to multiple tissues outside the liver.

This slow maturation mechanism is believed to increase the effectiveness of HBV infection, and explains why liver cells are still targeted specifically even at low doses despite the widespread presence of HSPG on other organs. ‘In the immature N-type state the viral particles are inert and hence can cycle in the bloodstream continuously until they once reach the liver where they finally will be trapped. Conversion into mature particles afterwards will lead to a productive infection,’ Prof. Ralf Bartenschlager, Head of Division and second corresponding and last author of the study summarizes. ‘It is a novel and highly elegant paradigm for a viral maturation mechanism that differs fundamentally from all previously described viral maturation mechanisms. Our study also shows that HBV particles are not stiff and static objects, but highly dynamic nanomachines with a precisely running stochastic clockwork. Literally, they are little ticking time bombs which suddenly shoot out molecular grappling hooks.’

From a clinical point of view, Seitz and Bartenschlager believe this finding could provide another perspective to develop HBV combating drugs. ‘It offers the possibility to develop inhibitors of the maturation mechanism that lead to a “lock-in” or “freezing” of HBV particles in the immature, non-infectious state. Such inhibitors could be used to support therapy of chronic hepatitis B which is still incurable and represents a leading cause of cancer in mankind’ states Stefan Seitz.

With this discovery, the lab is now aiming to discover the exact molecular mechanisms and stimulus of the HBV maturation process, and also to identify inhibitors against it. ‘Obviously, breaking chronicity of HBV infection and eradicating the virus would reduce the risk of infected individuals to develop hepatocellular carcinoma’, Bartenschlager adds.


Stefan Seitz, Caroline Iancu, Tassilo Volz, Walter Mier, Maura Dandri, Stephan Urban, Ralf Bartenschlager: „A Slow Maturation Process Renders Hepatitis B Virus Infectious“ in: Cell Host & Microbe, 16.6.2016. DOI: http://dx.doi.org/10.1016/j.chom.2016.05.013

Pictures are available at:

http://www.dkfz.de/de/presse/pressemitteilungen/2016/bilder/SmilingHBV.jpg
Caption: Electron micrograph of HBV virions released from infected cells. (large ovals with dark, center)

http://www.dkfz.de/de/presse/pressemitteilungen/2016/bilder/Immunhisto-HBV.jpg
Caption: HBV (green) in liver cells (red) Only virions of the N-Type (left) are able to infect liver cells, HBV of the B-type (right) are not.

Source: Universitätsklinikum Heidelberg/S. Seitz


The German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) with its more than 3,000 employees is the largest biomedical research institute in Germany. At DKFZ, more than 1,000 scientists investigate how cancer develops, identify cancer risk factors and endeavor to find new strategies to prevent people from getting cancer. They develop novel approaches to make tumor diagnosis more precise and treatment of cancer patients more successful. The staff of the Cancer Information Service (KID) offers information about the widespread disease of cancer for patients, their families, and the general public. Jointly with Heidelberg University Hospital, DKFZ has established the National Center for Tumor Diseases (NCT) Heidelberg, where promising approaches from cancer research are translated into the clinic. In the German Consortium for Translational Cancer Research (DKTK), one of six German Centers for Health Research, DKFZ maintains translational centers at seven university partnering sites. Combining excellent university hospitals with high-profile research at a Helmholtz Center is an important contribution to improving the chances of cancer patients. DKFZ is a member of the Helmholtz Association of National Research Centers, with ninety percent of its funding coming from the German Federal Ministry of Education and Research and the remaining ten percent from the State of Baden-Württemberg.

StephenW

定时油炸弹乙型肝炎病毒的技巧
7小时41分钟前

乙型肝炎病毒（HBV）引起乙肝，全球折磨2.3亿人的传染病，在德国其440 000。在肝细胞中的病毒的持久性导致在患者渐进器官损伤并有助于肝硬化和肝癌发展的危险性高。提供了一种新的模式对乙肝的认识，研究人员在德国癌症研究中心（DKFZ）在德国海德堡和传染病系，分子病毒学，海德堡大学医院目前已发现有HBV采用了一种新的成熟机制，以提高其感染成功。他们的研究结果报道在细胞宿主与微生物的最新问题。
乙肝病毒（绿色）中的肝细胞（红色）只有N型（左）的病毒粒子能感染的肝细胞，B型（右）的HBV的则不是。 | ©Universitätsklinikum海德堡/ S。塞茨

感染细胞，病毒需要先附加到特定的细胞受体结合，即，分子的细胞的表面上。乙型肝炎病毒的情况下，在病毒包膜的大表面蛋白（L蛋白）的一部分结合到肝细胞的硫酸乙酰肝素蛋白多糖（HSPG），并且随后介导的病毒颗粒的摄取到哪里子代病毒产生细胞。

“乙肝病毒在建立感染的效力高于大多数其它动物病毒几个数量级，”描述斯特凡博士塞茨，该研究的主要作者。事实上，已经证明HBV是即使在极低数目的病毒颗粒的发送之后感染的肝细胞显着地特定。然而，这提供了一个矛盾，因为HSPG横跨几乎所有类型的细胞在人体内广泛表达。 “对于具有到达在从发送站点远距离的靶器官中的病毒，HSPG似乎是最不利附着受体人们可以想象，'Seitz的继续。那么，什么可以解释这种差异？

在解决这个问题，研究人员进行了两个以往的研究结果的启发。首先，乙肝病毒的低温电子显微镜图像显示，该病毒出现在两个形态不同的形式。第二，在病毒包膜蛋白L可以采取两种结构状态。在一种状态下，受体结合决定是面向病毒颗粒内，在其他状态下它暴露在外颗粒表面上。后者是必需的HBV感染的过程。


的Seitz及其同事认为，这两个观测被连接，并且推测HBV颗粒经受其形态的动态开关期间，他们改变的L蛋白的结构状态。

为了研究这一点，他们建立了生物化学方法来区分这两种基团的HBV颗粒，根据它们的结合能力HSPG：一个“不成熟的”，非约束性（N）型，和一个“成熟”，结合（B）的类型。随后表征表明，几乎所有的病毒颗粒从细胞中释放的未成熟（N）的状态，并自发地转动受体结合跨病毒膜行列式而外转换成成熟（B）中的病毒随时间。

从N型的成熟为B型颗粒被确定为是一个缓慢的过程，呈现HBV感染。重要的是，病毒颗粒的数量低注入到老鼠后，研究人员发现，N-二型均超过B-类型在肝脏建立感染出众，而B型颗粒容易联想到肝外的多个组织。

这种缓慢的成熟机制被认为是增加HBV感染的效力，并解释了为什么肝细胞以低剂量尽管HSPG的对其他器官的广泛存在仍然专门针对偶数。 “在不成熟的N型状态的病毒颗粒是惰性的，因此可以循环不断，直到他们到达后，他们终于将被困肝脏血液。转化为成熟的颗粒后会导致生产性感染，“教授拉尔夫Bartenschlager，研究部主管及相应的第二和最后笔者总结。 “这是来自所有先前描述的病毒的成熟机制有着根本的不同病毒的成熟机制，一个新的高度和优雅的典范。我们的研究还表明，HBV颗粒是不僵硬和静态对象的，但有一个精确的运行随机发条高度动态纳米机器。从字面上看，它们是突然拍出来的分子抓钩小定时油炸弹“。

从临床上看，赛兹和Bartenschlager认为，这一发现可能提供了另一种视角来发展HBV打击毒品。 “它提供了开发导致”锁定“或不成熟，非感染状态HBV颗粒的”冻结“的机制，成熟的抑制剂的可能性。这样的抑制剂可以用来支持慢性乙型肝炎这仍然是无法治愈的，并且表示的癌症在人类的主要原因的疗法“规定的Stefan Seitz的。

与此发现，实验​​室现在旨在发现确切的分子机制和乙肝病毒成熟过程的刺激物，并且还识别人反对抑制剂。 “很显然，打破乙肝病毒感染的慢性化和消除病毒会降低感染者的风险制定肝癌”，Bartenschlager补充道。


斯特凡·塞茨，卡罗琳扬库，塔西洛Volz的，沃尔特·米尔，莫拉Dandri，斯蒂芬城市，拉尔夫Bartenschlager：“一个缓慢的成熟过程呈现乙型肝炎病毒感染”中有：细胞宿主与微生物，2016年6月16日。 DOI：http://dx.doi.org/10.1016/j.chom.2016.05.013

图片可在：

http://www.dkfz.de/de/presse/p​​ressemitteilungen/2016/bilder/SmilingHBV.jpg
说明：从感染细胞释放的HBV病毒粒子的电子显微镜照片。 （暗，中心大椭圆）

http://www.dkfz.de/de/presse/p​​ressemitteilungen/2016/bilder/Immunhisto-HBV.jpg
字幕：HBV（绿色）中的肝细胞（红色）只有N型的病毒粒子（左）能够感染的肝细胞，B型（右）的HBV的则不是。

来源：Universitätsklinikum海德堡/ S。塞茨

德国癌症研究中心（德意志Krebsforschungszentrum，DKFZ），其3000多名员工是最大的生物医学研究所在德国。在DKFZ，1000多名科学家研究癌症如何发展，找出癌症的危险因素，并努力寻找新的战略，以防止人们患癌症。他们开发的新方法，使肿瘤的诊断更精确，治疗癌症患者更成功。癌症信息服务（KID）的工作人员提供了有关癌症的普遍的疾病的患者，他们的家庭，和一般公众的信息。会同海德堡大学医院，DKFZ建立了肿瘤疾病（NCT）海德堡，来自癌症研究有前途的方法转化为临床国家中心。在德国的联合会转化癌症研究（DKTK），六德中心健康研究之一，DKFZ七所大学建立伙伴关系的网站翻译维护中心。在亥姆霍兹中心结合高调研究优秀大学医院是提高癌症患者的机会做出了重要贡献。 DKFZ是国家研究中心的亥姆霍兹联合会的成员，其资金的百分之九十，从教育的德国联邦研究和巴登 - 符腾堡州，其余百分之十的到来。