Herpes simplex virus type-1 infection and ND10 characteristics in cultured fibroblast and neuronal-like cells
Nuclear domain 10 (ND10) are punctate subnuclear structures that exist in most cell types. It has been suggested that ND10 structures serve as the site for initial viral genome deposition and some viral proteins, such as the ICP0 protein of HSV-1, have been shown to colocalise to, and subsequently induce the degradation of, proteins present in ND10. However the exact function of ND10 during HSV-1 infection is still unknown. In this study, the potential role of ND10 in HSV-1 infection was investigated by assessing the efficiency of viral IE and E gene expression or viral replication in cultured cells in which the expression of ND10 proteins was increased by IFN treatment or transient transfection methods. Furthermore, this study objective was also approached by using a human neuron precursor cell line (NT2) that naturally lacks one ND10 component, Sp100, and was found to have abnormal ND10 characteristics. The infectivity of HSV-1 in NT2 and differentiated hNT neuronal-like cells was investigated and the function of ICP0 in these cells was studied in more detail. Treatment with IFN- increased the number and size of ND10, whereas heat-stress caused dispersal of ND10 proteins, although this did not appear to affect HSV-1 infection. Pre-treatment with IFN- slightly inhibited HSV-1 gene expression, however it was not clear whether this effect was mediated by the ND10 proteins that are up-regulated by IFN. Examination of cells transiently transfected with plasmids expressing ND10 proteins (either PML, Sp100, SUMO-1 or Ubc9) demonstrated that the expression of viral IE and L genes was not affected by high expression levels of ND10 proteins. However, decreased viral gene expression was observed at an early time of infection in cells co-transfected with three plasmids expressing PML, Sp100, and Ubc9 or with four plasmids expressing PML, Sp100, Ubc9, and SUMO-1. Notably, in cells transfected with multiple plasmids, the exogenous ND10 proteins were sequestered in ND10 to a greater extent than in cells singly transfected. These observations suggested that over-expression of ND10 proteins, properly located in ND10, confers a marginal resistance to HSV-1 infection at an early time of infection, but this effect was less clear at later times of infection.