Role of the endosomal compartment in Nipah virus replication
Prof. Dr. Andrea Maisner
Institute of Virology
Nipah virus (NiV) is a highly pathogenic, biosafety level 4 (BSL-4) classified paramyxovirus, which encodes for two viral surface glycoproteins: the receptor-binding protein G and the fusion protein F. As for all paramyxoviruses, proteolytic activation of the NiV F protein is an indispensable prerequisite for viral infectivity and thus an important pathogenicity factor. Interestingly, the activation mechanism completely differs from the well-studied viral cleavage pathways involving furin- or trypsin-like proteases in the Golgi or at the plasma membrane. Namely, activation of the NiV F protein takes place within the endosomal-recycling compartment and is mediated by endosomal cathepsins. Activation of F therefore depends on a functional YxxΦ internalization signal in the cytoplasmic tail of the protein. We have recently found that after clathrin-mediated endocytosis, pH-dependent cleavage is mediated by cathepsin L or B in early or recycling endosomes before F is incorporated into budding virions. Neither endocytosis nor cathepsin cleavage steps are required during virus entry into new target cells (Fig. 1). We now want to extend our studies on trafficking of internalized F within the endosomal-recycling compartment focusing on the role of F tail sequences for sorting in the recycling pathway, for efficient transport back to the cell surface and subsequent incorporation into infectious virions.
Fig. 1: Current model of Nipah virus F protein activation
Polarized epithelial cells are important target cells in early and late stages of NiV infection in vivo. Recently, we found that the YxxΦ endocytosis motif in cytoplasmic tail of the F and a di-tyrosine motif in the G cytoplasmic tail mediate basolateral targeting and are required for efficient spread of infection in polarized cells via cell-to-cell fusion. Based on this result, we want to analyze the trafficking of wildtype and mutant F and G proteins in this specialized cell type. Epithelia differ from non-polarized cells not only in the polarized sorting of membrane proteins but also in their distinct populations of apical and basolateral early or recycling endosomes. Thus, we want to reveal which endosomal compartments are traversed by the NiV glycoproteins before reaching the basolateral cell surface compartment. In addition, it is planned to identify cellular adaptor or sorting proteins which interact with peptide motifs in the F or G cytoplasmic tails and thus mediate glycoprotein sorting to specific endosomal compartments or to the surface of polarized and non-polarized cells.
Dr. Stephanie Erbar (Postdoc)
Boris Lamp (PhD student)
Anja Heiner (Technician)
Publications since 2007
Erbar, S., and A. Maisner (2010). Nipah virus infection and glycoprotein targeting in endothelial cells. Virol. J. 7: 305
Weise, C., Erbar, S., Lamp, B., Vogt, C., Diederich, S., and A. Maisner (2010). Tyrosine residues in the cytoplasmic domains affect sorting and fusion activity of the Nipah virus glycoproteins in polarized epithelial cells. J. Virol. 84: 7634–7641.
Maisner, A., Neufeld, J., and H. Weingartl (2009). Organ- and endotheliotropism of Nipah virus infections in vivo and in vitro. Thromb Haemost 102:1014-1023.
Diederich, S., Dietzel, E., and A. Maisner (2009). Nipah virus fusion protein: Influence of cleavage site mutations on the cleavability by cathepsin L, trypsin and furin. Virus Res. 145: 300-306.
Niedermeier, S., Singethan, K., Rohrer, S.G., Matz, M., Kossner, M., Diederich, S., Maisner, A., Schmitz, J., Baumann, K., Holzgrabe, U., and J. Schneider-Schaulies (2009). A small molecule inhibitor of Nipah virus envelope protein-mediated membrane fusion. J. Med. Chem. 52: 4257-4265.
Thiel, L., Diederich, S., Erbar, S., Pfaff, D., Augustin, H. G., and A. Maisner (2008). Ephrin-B2 expression critically influences Nipah virus infection independent of its cytoplasmic tail. Virol. J. 5:165.
Erbar, S., Diederich, S., and A. Maisner (2008). Selective receptor expression restricts Nipah virus infection of endothelial cells. Virol. J. 5:142.
Diederich, S., Thiel, L., and A. Maisner (2008). Role of endocytosis and cathepsin-mediated activation in Nipah virus entry. Virology 275: 391-400.
Diederich, S., and A. Maisner (2007). Molecular characteristics of the Nipah virus glycoproteins. Ann. N.Y. Acad. Sci. 1102:39-50.