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J. H. LaVail, G. Huang, D. A. Cortez, A. Sucher, J. M. Draper; Differential Targeting of HSV Structural Proteins to Axons Requires Association of Viral Us9 Protein to Lipid Rafts. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3812.
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© ARVO (1962-2015); The Authors (2016-present)
The Herpes simplex virus type 1 (HSV) envelope contains at least 10 glycoproteins, several of which are essential for viral spread leading to recurrent herpetic keratitis or viral encephalitis. How these glycoproteins are targeted within mature axons after synthesis is unclear.
Our goal is to examine the axonal transport of the HSV envelope glycoproteins and to determine whether targeting of newly synthesized glycoproteins requires an association with the lipid rafts in membranes of host neurons. Further, we tested whether the viral protein, Us9, facilitates axonal transport of viral structural proteins, as well as that of viral capsids.
Murine retinas were pulse infected with Us9-null mutant or wild type (wt) HSV. After 5 days the optic pathways were dissected and prepared in an Optiprep® flotation assay to separate raft (detergent-resistant, DRM) and non-raft (detergent-soluble, DSM) membranes. The proteins were separated by PAGE and processed for Western blotting using antibodies to gB, gD, Us9, VP5 and synaptophysin (Syn). We used antisera to caveolin and transferrin and biotinolylated cholera toxin B subunit to GM1 as controls.
By 5 days after infection with wt HSV, all proteins were transported to the optic tract. Two envelope glycoproteins (gB, gD), one capsid protein, VP5, and one membrane protein, Us9, were present in DRM fractions. In addition, gB, gD, Us9 and Syn, were found in DSM fractions. After infection with Us9-null HSV, the concentration of gB in both fractions was significantly reduced.
Lipid rafts play a role in the axonal transport of some, but not all of the HSV glycoproteins in axons of mature animals. Some glycoproteins are targeted independently of others. Specifically, the axonal transport of gB is impaired after Us9-null infection, but the transport of gD (and possibly gE and gC) is not impaired. Significantly, this impairment may account for the fact that cell-cell spread of new virus depends on gB expression. This suggests that axonal transport of HSV requires targeting of three subassemblies: membranes associated with gD, membranes associated with gB and the nucleocapsid.
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