Herpes simplex virus type IICP27-Dependent activation of NF-κB

The ability of herpes simplex virus type 1 (HSV-1) to activate NF-kappa B has been well documented. Beginning at 3 to 5 h postinfection, HSV-1 induces a robust and persistent nuclear translocation of an NF-kappa B-dependent (p50/p65 heterodimer) DNA binding activity, as measured by electrophoretic mobility shift assay. Activation requires virus binding and entry, as well as de novo infected-cell protein synthesis, and is accompanied by loss of both I kappa B alpha and I kappa B beta. In this study, we identified loss of I kappa B alpha as a marker of NF-kappa B activation, and infection with mutants with individual immediate-early (IE) regulatory proteins deleted indicated that ICP27 was necessary for I kappa B alpha loss. Analysis of both N-terminal and C-terminal mutants of ICP27 identified the region from amino acids 21 to 63 as being necessary for I kappa B alpha loss. Additional experiments with mutant viruses with combinations of IE genes deleted revealed that the ICP27-dependent mechanism of NF-kappa B activation may be augmented by functional ICP4. We also analyzed two additional markers for NF-kappa B activation, phosphorylation of the p65 subunit on Ser276 and Ser536. Phosphorylation of both serines was induced upon HSV infection and required functional ICP4 and ICP27. Pharmacological inhibitor studies revealed that both I kappa B alpha and Ser276 phosphorylation were dependent on Jun N-terminal protein kinase activity, while Ser536 phosphorylation was not affected during inhibitor treatment. These results demonstrate that there are several layers of regulation of NF-kappa B activation during HSV infection, highlighting the important role that NF-kappa B may play in infection.