Nuclear translocation of NF-kappaB precedes apoptotic poly(ADP-ribose) polymerase cleavage during productive HSV-1 replication in corneal epithelial cells

Abstract

Purpose: Herpes simplex virus (HSV)-1 infections of the human cornea range in severity from uncomplicated episodes that readily resolve to severe, recurring disease that invades the stroma, having a devastating permanent effect on vision. Recent published data implicate an apoptotic component to stromal HSV-1 infection. In a prior study, it was found that wild type (wt) HSV-1 infection induces, then blocks, apoptosis in epithelial cells derived from skin and that this block requires infected cell proteins (ICPs) synthesized between 3 and 6 hours post infection (hpi). This inhibition of apoptosis is in part dependent on the activation of inducible nuclear transcription factor kappaB (NF-kappaB).

Methods: HSV-1-dependent apoptosis in rabbit corneal epithelial (SIRC) cells was compared with that in infected human epithelial (HEp-2) cells.

Results: SIRC cells were sensitive to apoptotic cell death induced by environmental treatment with tumor necrosis factor (TNF)-alpha plus cycloheximide (CHX). HSV-1 stimulated the degradation of regulatory IkappaBalpha protein, resulting in nuclear translocation of NF-kappaB. This phenomenon was dependent on ICP synthesis. Neither wt nor apoptotic HSV-1 infection resulted in apoptosis in these cells. However, wt HSV-1-infected cells produced detectable levels of cleaved poly(ADP-ribose) (PARP). Inhibition of SIRC cell protein synthesis with CHX during wt HSV-1 infection led to a reduction in the amount of PARP cleavage. Whereas PARP cleavage defined cell death in most other cell types, its processing in SIRC cells was a reproducible characteristic of wt HSV-1 infection.

Conclusions: This is the first report of such an effect, and it suggests that in corneal epithelial cells, activation of apoptotic pathways may be necessary for productive viral replication. Thus, efficient replication of HSV-1 in the corneal milieu proceeds via a different mechanism than it does in skin. However, it appears that NF-kappaB participates in inhibiting apoptosis during HSV-1 infection in both systems.