Impact of Rac1 and Cdc42 signaling during early herpes simplex virus type 1 infection of keratinocytes.

Keratinocytes of the skin or mucosa are the primary entry portals for herpes simplex virus type 1 (HSV-1) in vivo. We hypothesized that dynamics of cell motility and adhesion contribute to the initial steps of HSV-1 infection of epithelial cells, and thus, we investigated the impact of Rac1 and Cdc42, which serve as key regulators of actin dynamics. Measurement of endogenous Rac1 and Cdc42 in the human keratinocyte cell line HaCaT indicated temporary changes in activity levels of Rac1/Cdc42 upon HSV-1 infection. Overexpression of Rac1/Cdc42 mutants in HaCaT cells demonstrated a decrease of infection efficiency with constitutively active Rac1 or Cdc42, while dominant-negative Rac1 had no effect. Accordingly, we addressed whether the absence of Rac1 and/or Cdc42 influenced infection, and we performed RNA interference studies. Both in HaCaT cells and in primary human keratinocytes, reduction of Rac1 and/or Cdc42 did not suppress infection. When mouse epidermis was infected ex vivo, we observed early HSV-1 infection in basal keratinocytes. Similar results were obtained upon infection of mouse epidermis with a keratinocyte-restricted deletion of the rac1 gene, indicating no inhibitory effect on HSV-1 infection in the absence of Rac1. Our results suggest that HSV-1 infection of keratinocytes does not depend on pathways involving Rac1 and Cdc42 and that constitutively active Rac1 and Cdc42 have the potential to interfere with HSV-1 infectivity.