Infection of herpes simplex virus type 1 (HSV-1) begins at the epidermis, a stratified layer
composed primarily of keratinocytes. The physiologically relevant cell type for the study of
HSV-1 assembly is therefore the human keratinocyte. Nonetheless, relatively little is known
about the replication of HSV-1 in this natural host cell.
Comparison of virus growth in monolayers of keratinocyte cells and Vero cells, a routinely
used cell line for HSV-1 studies, revealed that these keratinocytes support a more productive
virus replication than Vero cells. Furthermore, newly assembled virus is produced more
rapidly in keratinocytes and this enhancement occurs prior to, or upon the initiation of
immediate early gene transcription. This augmented replication in keratinocytes can be at
least partially attributed to the method of entry of the virus. We have found by penetration
assays and electron microscopy that the virus is able to penetrate keratinocyte cells much
more rapidly than Vero cells. We have also shown that the virus entry mechanism is more
efficient at lower temperatures in nTERT cells, with virus entering cells at temperatures as
low as 7°C. Additionally preliminary work implies that depletion of one of the herpes virus
entry receptors, Nectin-1, does not affect entry into nTERT cells, whereas entry is reduced
up to 65% in HeLa cells. Taken together, these results imply a role for other entry receptors,
possibly as yet unidentified, in the entry of human keratinocyte cells.
This work also identifies a role for cellular Rab proteins, GTPases essential for the regulation
of vesicle trafficking, in HSV-1 infection of keratinocytes. In particular Rab6, which was also
found to play a role in infected HeLa cells (Elliott Group), appears to have a similar function
in both these cells and together support a model for HSV-1 morphogenesis involving Rab-regulated
vesicle trafficking of viral glycoproteins to the cell surface. Several other Rabs
identified by this screen now provide interesting opportunities to elucidate further roles of
Rab proteins in HSV-1 infection of keratinocyte cells.
This project has broadly characterised the replication of HSV-1 in keratinocyte cells and
explored the role of Rab GTPases in virus trafficking within keratinocytes - a cell type that is
physiologically relevant to infection.