Scientific Publications by FDA Staff

J Virol 2013 May;87(10):5820-30

Herpes Simplex Virus 2 expresses a novel form of ICP34.5, a major viral neurovirulence factor, through regulated alternative splicing.

Tang S, Guo N, Patel A, Krause PR

HSV-1 and HSV-2, two closely related neurotropic human herpesviruses, achieve neurotropism through ICP34.5, a major viral neurovirulence factor. In this report, in addition to the full-length 38 kD protein (ICP34.5alpha), we identified a 28 kD novel form of ICP34.5 (ICP34.5beta) in HSV-2-infected cells. ICP34.5beta is translated from unspliced ICP34.5 mRNA, with the retained intron introducing a premature stop codon. Thus, ICP34.5beta lacks the C-terminal conserved GADD34 domain, but includes 19 additional amino acids encoded by the intron. While a fraction of both HSV-2 ICP34.5 proteins are detected in the nucleolus, ICP34.5alpha is predominantly located in cytoplasm and ICP34.5beta is mainly detected more diffusely in the nucleus. ICP34.5beta is unable to counteract PKR-mediated eIF2 phosphorylation, but does not interfere with ICP34.5alpha's function in this process. Efficient expression of ICP34.5beta in cell-culture assays is dependent on viral infection or expression of ICP27, a multifunctional immediate-early gene. The effect of ICP27 on the ICP34.5beta protein level is attributed to its selective inhibition of ICP34.5 splicing, which results in increased expression of ICP34.5beta but a reduced level of ICP34.5alpha. The C- terminal KH3 domain but not the RNA binding domain of ICP27 is required for its specific inhibition of ICP34.5 splicing and promotion of ICP34.5beta expression. Our results suggest that expression of ICP34.5alpha and ICP34.5beta is tightly regulated in HSV-2, and likely contributes to viral pathogenesis.