Einfluss des Nipahvirus-Matrixproteins auf die Lokalisation von viralen Nukleokapsiden und inclusion bodies

Summary Nipah virus (NiV) is a biosafety level 4 (BSL-4) classified paramyxovirus. The NiV matrix protein (NiV-M) plays a major role in virus assembly and is indispensable for the production of infectious viral particles because it mediates the contact between cytosolic viral nucleocapsids (RNPs) and the NiV surface glycoproteins. To fulfil its important functions, NiV-M must be transported to the plasma membrane. In some cell types, NiV-M surface trafficking is known to be preceded by a transport through the nucleus. In the first part of this thesis, nuclear import and export NiV-M mutants were characterized by immunofluorescence analyses in fixed and living cells. This study revealed that a nuclear transit of NiV-M is principally required for a successful plasma membrane transport, even in cell types in which nuclear NiV-M cannot be detected in steady state analyses. The second part of this thesis addressed the question, where and how NiV-M interacts with viral RNPs. First studies in infected cells had shown that viral RNPs accumulated in large cytoplasmic inclusion bodies (IB). These were either located perinuclearly or were closely associated with the plasma membrane, where the virus assembly occurs. To determine, if NiV-M plays a role in RNP transport to the plasma membrane and in the formation of the two differently located IB, the influence of NiV-M on the localization of IB was analyzed. Both, infection and cotransfection studies showed that correct nuclear trafficking and subsequent surface targeting of NiV-M was essentially needed for the formation of IB at the plasma membrane and for virus assembly. Transport-defect NiV-M mutants and matrix proteins of other viruses such as measles or Ebola viruses, could not support the formation of plasma membrane associated IB. However, these non-functional M proteins colocalized with perinuclear IB suggesting that perinuclear IB represent a separate cellular compartment that recruits abundantly expressed cytosolic proteins. IB at the plasma membrane are formed independently if functional NiV-M is present. This idea of two separate IB types was also supported by electron-microscopic studies revealing that perinuclear and peripheral IB differed ultrastructurally. In the last part of this thesis, studies with different cytoskeleton inhibitors revealed that actin disruption by Cytochalasin D efficiently prevented M transport and IB accumulation at the plasma membrane. This indicates that actin filaments rather than mircotubuli play an essential role in the NiV-M mediated virus assembly. Altogether, this thesis provides new fundamental knowledge about the intracellular transport of NiV-M and the formation of plasma membrane associated inclusion bodies, both essential prerequisites for efficient assembly and release of infectious Nipah viruses.