Institute of Molecular Virology and Cell Biology (IMVZ)

Pathogens

• highly pathogenic zoonotic viruses, in particular filo- and arenaviruses

Scientific Focus

The Laboratory for Integrative Cell and Infection Biology studies viral-host cell interactions of highly pathogenic zoonotic viruses in order to better understand how these interactions facilitate or impair viral infections, and how they influence the outcome of an infection. This work aims to understand pathogenicity determinants, and to characterize pro- and antiviral virus-host cell interactions that have the potential for exploitation as therapeutic targets. In the long term this enables the development of broadly effective drugs that are effective against both known and emerging viruses, and allows us to quickly assess the pathogenicity potential of emerging viruses.

Of particular interest to our laboratory are filoviruses (especially ebola-, marburg- and cuevaviruses) and highly pathogenic arenaviruses (especially Lassa and Junín viruses). These viruses are zoonotic agents that are transmitted from animal hosts to humans, and can then cause haemorrhagic fevers and neurological diseases with sometimes very high case fatality rates. Infectious work with these viruses takes place in the FLI’s biosafety level 4 laboratory for zoonotic agents. To complement this work we have developed a number of life-cycle modelling systems that allow to investigate the replication cycle of such highly pathogenic viruses safely outside of biosafety level 4 laboratories, and which are particularly suitable for use with high-throughput approaches such as siRNA screens. In addition to work on highly pathogenic zoonotic viruses we cooperate with other laboratories of the Institute of Molecular Virology and Cell Biology in order to study virus-host cell interactions also in the context of other zoonotic and animal pathogens.

A methodological focus of the laboratory is the production of recombinant viruses by means of reverse genetics, which we use together with life-cycle modelling systems to study individual virus-host cell interactions in more detail. In this context we apply a broad spectrum of virological, molecular biological and cell biological methods, such as Crispr/Cas9, confocal live cell microscopy, mutation analyses and CoIP methods. In addition, modern mass spectrometric approaches are pursued in cooperation with other laboratories of the Institute of Molecular Virology and Cell Biology.

Biology of viral inclusion bodies

In infected cells viral proteins often accumulate in structures called inclusion bodies. For filo- and arenaviruses these play important roles in the replication of viral genomes and their transcription into messenger RNAs, as well as in the assembly of viral nucleocapsids. However, the principles underlying the formation and organization of inclusion bodies for these viruses are unknown. However, for other negative-strand RNA viruses it could be shown that inclusion bodies often have properties of liquid organelles, i.e. intracellular structures that are not defined by enclosing membranes but are held together by liquid-liquid phase separation.

In a project partly funded by the German Research Foundation (DFG) we are investigating whether filoviral and arenaviral inclusion bodies also are liquid organelles, and which mechanisms contribute to their formation. Furthermore, we are investigating to what extent phase separation contributes to the export of nucleocapsids from inclusion bodies. For these studies we combine modern live cell microscopy techniques under S4 conditions with recombinant reporter-expressing filo- and arenaviruses. Ultimately, these studies aim to uncover commonalities between negative-strand RNA viruses, and to provide information on molecular targets for antiviral drugs directed against an essential aspect in the replication cycle of these viruses.

Characterization of the role of host cell factors in the replication cycle of RNA viruses

As intracellular parasites viruses depend on host cell proteins for successful replication. The interactions of viral factors with host cell proteins represent promising targets for therapeutics, as it is more difficult for viruses to develop resistances to such therapeutics than to those that are directly and exclusively directed against viral factors. In addition, interactions or certain host factors are often used by different viruses, so that therapeutics directed against them often have a broader spectrum of action than classical, directly acting antiviral therapies.

In addition to the identification of such virus-host interactions, which we pursue using high-throughput methods, we also strive for a more precise understanding of these interactions in order to be able to better define therapeutic targets. In a project partly funded by the German Research Foundation (DFG), we are focusing on host factors that play a role in viral genome replication and transcription. On the one hand interactions between these cellular proteins and viral factors are being characterized in more detail at the biochemical level, and on the other hand the exact role of the host proteins in the viral replication cycle is being investigated at the functional level. Both life-cycle modelling systems and recombinant viruses are used for this purpose. In the course of these studies we were able to show that the host protein NXF1 mediates an important role in the export of viral mRNAs from inclusion bodies (Figure 1), which we are currently investigating in more detail.

Figure 1: Model for the function of NXF1 in the replication cycle of filoviruses

Characterization of novel filoviruses

Although most outbreaks of filovirus diseases are caused by some long-known filoviruses such as the Ebola virus or the Marburg virus, novel filoviruses with unknown pathogenic potential have been repeatedly found in recent years. These include the Lloviu virus, which has been detected in bats in Spain and Hungary, and the Bombali virus, which was found in West Africa. Our lab is characterizing these novel viruses using life-cycle modelling systems, and trying to understand whether these novel filoviruses pose a health risk by comparing them to known pathogenic and apathogenic filoviruses. In addition, we are investigating which viral and host factors are responsible for some filoviruses (such as Ebola virus) being highly pathogenic to humans, while others (such as Reston virus) do not cause disease in humans. This work will help to provide rapid and fact-based risk assessments for emerging filoviruses in the future.