U S 3 Protein Kinase of Herpes Simplex Virus 1 Blocks Caspase 3 Activation Induced by the Products of U S 1.5 and U L 13 Genes and Modulates Expression of Transduced U S 1.5 Open Reading Frame in a Cell Type-Specific Manner

Abstract

ABSTRACT The coding domain of the herpes simplex virus type 1 (HSV-1) α22 gene encodes two proteins, the 420-amino-acid infected-cell protein 22 (ICP22) and U S 1.5, a protein colinear with the carboxyl-terminal domain of ICP22. In HSV-1-infected cells, ICP22 and U S 1.5 are extensively modified by the U L 13 and U S 3 viral protein kinases. In this report, we show that in contrast to other viral proteins defined by their properties as α proteins, U S 1.5 becomes detectable and accumulated only at late times after infection. Moreover, significantly more U S 1.5 protein accumulated in cells infected with a mutant lacking the U L 13 gene than in cells infected with wild-type virus. To define the role of viral protein kinases on the accumulation of U S 1.5 protein, rabbit skin cells or Vero cells were exposed to recombinant baculoviruses that expressed U S 1.5, U L 13, or U S 3 proteins under a human cytomegalovirus immediate-early promoter. The results were as follows. (i) Accumulation of the U S 1.5 protein was reduced by concurrent expression of the U L 13 protein kinase and augmented by concurrent expression of the U S 3 protein kinase. The magnitude of the reduction or increase in the accumulation of the U S 1.5 protein was cell type dependent. The effect of U L 13 kinase appears to be specific inasmuch as it did not affect the accumulation of glycoprotein D in cells doubly infected by recombinant baculoviruses expressing these genes. (ii) The reduction in accumulation of the U S 1.5 protein was partially due to proteasome-dependent degradation. (iii) Both U S 1.5 and U L 13 proteins activated caspase 3, indicative of programmed cell death. (iv) Concurrent expression of the U S 3 protein kinase blocked activation of caspase 3. The results are concordant with those published elsewhere (J. Munger and B. Roizman, Proc. Natl. Acad. Sci. USA 98:10410–10415, 2001) that the U S 3 protein kinase can block apoptosis by degradation or posttranslational modification of BAD.