2013 Scientific Report

VARI | 2013
The death of one hypothesis, however, gives life to new ideas. After the initial infection of a cold sore subsides, herpes simplex
virus establishes a life-long latent infection in sensory neurons. In the latent state, the viral genome is essentially quiet; very
few viral genes are expressed. Moreover, the viral genome becomes packaged in chromatin much like the silent genes of
the host cell. So our new hypothesis is that the coactivators recruited by VP16 are required to reactivate the viral genes from
the latent or quiescent state. We now have evidence that VP16 is likely the very first viral gene to be expressed during the
reactivation process. We want to test whether the ability of VP16 to recruit coactivators is essential for subsequent events
of reactivation. We will test this hypothesis both in quiescent infections in cultured cells and in animal models with genuinely
latent herpesvirus infections.
Regulating the regulatory proteins: posttranslational modifications of VP16
The activity of a given protein is not only dependent on being expressed at the right time, but also on chemical modifications
of its amino acids and on its interactions with other proteins. Proteins can be posttranslationally modified by adding chemical
groups including phosphates, sugars, methyl or acetyl groups, lipids, or small proteins such as ubiquitin. Each of these
modifications might affect the protein in different ways, including how the protein folds, how it interacts with other proteins,
and how stable it remains in the cell.
We know that VP16 can be phosphorylated, and we have already defined several sites within the VP16 protein where
this happens. We are now testing whether these modifications matter for how VP16 functions, either as a transcriptional
activator protein or as a structural protein of the HSV-1 virion. In some experiments, we create mutations that either prevent
phosphorylation or that introduce an amino acid that mimics phosphorylation, and then we test the effects of these mutations
on VP16 functions. In other experiments, we inhibit the enzymes that apply the modifications (for phosphorylation, these
enzymes are known as protein kinases). We expect that this work will lead to new ideas about ways that we can selectively
inhibit modification of VP16 using small-molecule drugs, and thereby prevent or shorten the infection process by HSV.
Recent Publications
Danaher, Robert J., Ross K. Cook, Chunmei Wang, Steven J. Triezenberg, Robert J. Jacob, and Craig S. Miller. In press.
C-terminal trans-activation sub-region of VP-16 is uniquely required for forskolin-induced herpes simplex virus type 1
reactivation from quiescently infected-PC12 cells but not for replication in neuronally differentiated-PC12 cells. Journal of
Neurovirology.
Silva, Lindsey, Hyung Suk Oh, Lynne Chang, Zhipeng Yan, Steven J. Triezenberg, and David M. Knipe. 2012. Roles of the
nuclear lamina in stable nuclear association and assembly of a herpesviral transactivator complex on viral immediate-early
genes. mBio 3(1): e00300–11.
Sawtell, Nancy M., Steven J. Triezenberg, and Richard L. Thompson. 2011. VP16 serine 375 is a critical determinant of
herpes simplex virus exit from latency in vivo. Journal of Neurovirology 17(6): 546–551.
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