A Novel Cellular Protein, p60, Interacting with both Herpes Simplex Virus 1 Regulatory Proteins ICP22 and ICP0 Is Modified in a Cell-Type-Specific Manner and Is Recruited to the Nucleus after Infection

Abstract

ABSTRACT Herpes simplex virus 1 encodes two multifunctional regulatory proteins, infected-cell proteins 22 and 0 (ICP22 and ICP0). ICP0 is a promiscuous transactivator, whereas ICP22 is required in vivo and for efficient replication and expression of a subset of late (γ 2 ) genes in rodent or rabbit cell lines and in primary human cell strains (restrictive cells) but not in HEp-2 or Vero (permissive) cells. We report the identification in the yeast two-hybrid system of a cellular protein designated p60 that interacts with ICP22. This protein (apparent M r of 60,000) has not been previously described and has no known motifs. Analyses of p60 revealed the following. (i) p60 bound fast-migrating, underprocessed wild-type ICP22 and ICP22 lacking the carboxyl-terminal 24 amino acids but not ICP22 lacking the carboxyl-terminal 40 amino acids, whereas the previously identified cellular protein p78 (R. Bruni and B. Roizman, J. Virol. 72:8525–8531, 1998) bound all forms of ICP22. The interaction of p60 with only one isoform of ICP22 supports that hypothesis that each isoform of herpes simplex virus proteins performs a specific function that may be different from that of other isoforms. (ii) p60 also bound ICP0; the binding of ICP0 was independent of that of ICP22. (iii) p60 localized in uninfected rabbit skin cells in both nuclei and cytoplasm. In rabbit skin cells infected with wild-type virus, p60 was posttranslationally processed to a higher apparent M r but was not redistributed. Posttranslational processing required the presence of the genes encoding ICP22 and U L 13 protein kinase. (iv) In uninfected HEp-2 cells, p60 localized primarily in nuclei. Soon after infection with wild-type virus, the p60 localized in discrete small nuclear structures with ICP0. Late in infection, both ICP0 and p60 tended to disperse but p60 did not change in apparent M r . The localization of p60 was independent of ICP22, but p60 tended to be more localized in small nuclear structures and less dispersed in cells infected with mutants lacking the genes encoding the U L 13 or U S 3 protein kinases. The results suggest that posttranslational modification of p60 is mediated either by ICP0 (permissive cells) or by ICP22 and U L 13 protein kinase (restrictive rabbit skin cells) and that the restrictive phenotype of rabbit skin cells may be related to the failure to process p60 by mutants lacking the genes encoding U L 13 or ICP22.