Co-assembly of viral envelope glycoproteins regulates their polarized sorting in neurons.

Rafael Mattera,Juan S. Bonifacino,Ginny G. Farías,Gonzalo A. Mardones,Benhur Lee

doi:10.1371/journal.ppat.1004107

Abstract

Newly synthesized envelope glycoproteins of neuroinvasive viruses can be sorted in a polarized manner to the somatodendritic and/or axonal domains of neurons. Although critical for transneuronal spread of viruses, the molecular determinants and interregulation of this process are largely unknown. We studied the polarized sorting of the attachment (NiV-G) and fusion (NiV-F) glycoproteins of Nipah virus (NiV), a paramyxovirus that causes fatal human encephalitis, in rat hippocampal neurons. When expressed individually, NiV-G exhibited a non-polarized distribution, whereas NiV-F was specifically sorted to the somatodendritic domain. Polarized sorting of NiV-F was dependent on interaction of tyrosine-based signals in its cytosolic tail with the clathrin adaptor complex AP-1. Co-expression of NiV-G with NiV-F abolished somatodendritic sorting of NiV-F due to incorporation of NiV-G•NiV-F complexes into axonal transport carriers. We propose that faster biosynthetic transport of unassembled NiV-F allows for its proteolytic activation in the somatodendritic domain prior to association with NiV-G and axonal delivery of NiV-G•NiV-F complexes. Our study reveals how interactions of viral glycoproteins with the host's transport machinery and between themselves regulate their polarized sorting in neurons.

Highlights

Neurons are polarized cells comprising somatodendritic and axonal domains with unique structural and functional properties
To analyze the distribution of the Nipah virus glycoproteins NiV fusion (NiV-F) and NiV attachment or receptor-binding (NiV-G) (Figure 1A) in neurons, primary cultures of embryonic rat hippocampal neurons were transfected at day-invitro 4 (DIV4) with plasmids encoding NiV-F-GFP or NiV-G-HA and examined at day-in-vitro 10 (DIV10) by confocal microscopy
We found that whereas full-length Tac localized to both the somatodendritic and axonal domains (Figure 1D) (D/A: 1.160.2; Table 1), Tac-NiV-F was restricted to the somatodendritic domain (Figure 1E) (D/A: 6.761.8; Table 1)

Summary

Introduction

Neurons are polarized cells comprising somatodendritic and axonal domains with unique structural and functional properties (reviewed in [1]–[3]). Sorting of specific assortments of membrane proteins and lipids to these domains is essential for neuronal function. The axonal or somatodendritic distribution of viral membrane proteins must result from differences in their interaction with repurposed components of the neuronal sorting machinery. These primary interactions could be regulated by other proteins encoded in the viral genome. The analysis of these two layers of regulation is key to understanding the sorting of viral proteins in neurons

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Results

Conclusion