| Herpes Simplex Virus 1 is a large DNA virus that can cause a variety of diseases ranging from mild cold sores to life threatening encephalitis. One of the key virulence factors of HSV-1 is the gamma134.5 protein, which contains 263 amino acids, with a N-terminal domain, linker region, and a C-terminal domain.;In this study we uncovered that gamma134.5 is required to prevent the induction of antiviral genes early in HSV infection. We found that the gamma134.5 protein interacts with and inhibits TBK 1, a key component of antiviral signaling pathways. This function maps to the amino terminal domain of the protein. These results occurred at early time points post infection, before the appearance of phosphorylated eIF2alpha. Therefore, inhibition of TBK 1 by gamma134.5 is independent of the PKR response.;The second part of our work focuses on the carboxyl terminus of gamma 134.5. An HSV-1 virus with two point mutations in the PP1 signature binding motif of gamma134.5 was unable to dephosphorylate eIF2alpha, correlating with impaired viral growth in vitro. Also, this mutant failed to replicate in the eye, trigeminal ganglia, and brain of infected mice. Next, we used a recombinant virus in which the C-terminus of gamma134.5 is replaced with its cellular homologue, GADD34. This virus replicated similar to wild type virus in vitro. However, this virus was severely attenuated in vivo. Kinetic analysis of infection showed impaired neuroinvasion, and rapid clearance of the virus when compared to wild type HSV-1.;This study suggests both the amino and carboxyl termini have distinct roles in viral infection. This underscores the importance of gamma 134.5 in antagonizing TBK 1 mediated antiviral immunity during early infection, and later inhibiting the PKR response. We also provide evidence for a previously unrecognized role for the C-terminus in viral replication and neuroinvasion in vivo. Collectively, this study indicates that efficient HSV-1 replication and pathogenesis requires the coordinated action of both the amino and carboxyl termini of gamma134.5. |
