The roles of HSV-1 VP16 and ICP0 in modulating cellular innate antiviral responses

• Author / Creator

  Hancock, Meaghan

• Infection of most cell types with herpes simplex virus (HSV) mutants lacking the activation functions of VP16 and/or ICP0 results in repression of viral gene expression. However, the human osteosarcoma cell line U2OS supports the replication of VP16 and ICP0 mutants to nearly wild type levels. Prior to the studies presented in this thesis, the basis for the permissivity of U2OS cells to VP16 and ICP0 mutants had not been explored. Here, somatic cell fusion assays were used to determine that U2OS cells support the replication of VP16 and ICP0 mutants due to a defect in an innate gene silencing mechanism. The artificial induction of interferon stimulated genes that occurs during the somatic cell fusion assays is not the basis for the observed repression of viral gene expression. As one means of identifying components of the antiviral pathway defective in U2OS cells, restrictive cell types were treated with kinase inhibitors and infected with VP16 and/or ICP0 mutants. Although several compounds were identified which compensate for the defect in gene expression of VP16 mutants, these drugs also stimulate mutant virus gene expression in U2OS. Thus, U2OS are most likely not defective in the cellular signalling pathway(s) targeted by these compound(s). Finally, the importance of VP16 and ICP0 in modulating chromatin structure on the viral genome in both restrictive and permissive cells was examined, uncovering an essential role for both proteins in altering histone occupancy and acetylation levels. Importantly, U2OS cells have a defect in the chromatin-based pathway targeted by ICP0. However, evidence suggests that the ability of VP16 and ICP0 to affect histone occupancy and acetylation levels is not required for viral gene expression. Taken together, the results of this thesis demonstrate that U2OS cells support the replication of VP16 and ICP0 mutants due to a defect in an innate antiviral mechanism which does not involve the targets of several well characterized kinase inhibitors. The significance of the defect in a chromatin-based pathway targeted by ICP0 in U2OS cells remains to be elucidated.

• Subjects / Keywords

  • HSV-1
  • U2OS
  • VP16
  • ICP0
  • P14

• Graduation date

  Spring 2010

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R33S8R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.