Herpes simplex virus type 1 (HSV-1)-induced apoptosis in human dendritic cells as a result of downregulation of cellular FLICE-inhibitory protein and reduced expression of HSV-1 antiapoptotic latency-associated transcript sequences

J Virol. 2010 Jan;84(2):1034-46. doi: 10.1128/JVI.01409-09. Epub 2009 Nov 11.

Abstract

Herpes simplex virus type 1 (HSV-1) is one of the most frequent and successful human pathogens. It targets immature dendritic cells (iDCs) to interfere with the antiviral immune response. The mechanisms underlying apoptosis of HSV-1-infected iDCs are not fully understood. Previously, we have shown that HSV-1-induced apoptosis of iDCs is associated with downregulation of the cellular FLICE-inhibitory protein (c-FLIP), a potent inhibitor of caspase-8-mediated apoptosis. In this study, we prove that HSV-1 induces degradation of c-FLIP in a proteasome-independent manner. In addition, by using c-FLIP-specific small interfering RNA (siRNA) we show for the first time that downregulation of c-FLIP expression is sufficient to drive uninfected iDCs into apoptosis, underlining the importance of this molecule for iDC survival. Surprisingly, we also observed virus-induced c-FLIP downregulation in epithelial cells and many other cell types that do not undergo apoptosis after HSV-1 infection. Microarray analyses revealed that HSV-1-encoded latency-associated transcript (LAT) sequences, which can substitute for c-FLIP as an inhibitor of caspase-8-mediated apoptosis, are much less abundant in iDCs as compared to epithelial cells. Finally, iDCs infected with an HSV-1 LAT knockout mutant showed increased apoptosis when compared to iDCs infected with the corresponding wild-type HSV-1. Taken together, our results demonstrate that apoptosis of HSV-1-infected iDCs requires both c-FLIP downregulation and diminished expression of viral LAT.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / physiology*
  • CASP8 and FADD-Like Apoptosis Regulating Protein / genetics
  • CASP8 and FADD-Like Apoptosis Regulating Protein / metabolism*
  • Cell Line
  • Dendritic Cells* / cytology
  • Dendritic Cells* / physiology
  • Dendritic Cells* / virology
  • Down-Regulation*
  • Herpesvirus 1, Human / genetics
  • Herpesvirus 1, Human / pathogenicity*
  • Herpesvirus 1, Human / physiology
  • Humans
  • MicroRNAs / metabolism*
  • Virus Latency

Substances

  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • MicroRNAs
  • latency associated transcript, herpes simplex virus-1