Overexpression of the herpes simplex virus type 1 immediate-early regulatory protein, ICP27, is responsible for the aberrant localization of ICP0 and mutant forms of ICP4 in ICP4 mutant virus-infected cells

Abstract

ICP0 and ICP4 are immediate-early regulatory proteins of herpes simplex virus type 1. Previous studies by Knipe and Smith demonstrated that these two proteins are characteristically observed in the nuclei of wild-type virus-infected cells but predominantly in the cytoplasms of cells infected with several ICP4 temperaturesensitive (ts) mutant viruses at the nonpermissive temperature (NPT) (D. M. Knipe and J. L. Smith, Mol. Cell. Biol. 6:2371-2381, 1986). Consistent with this observation, it has been shown previously that ICP0 is present predominantly in the cytoplasms of cells infected with an ICP4 null mutant virus (n12) at high multiplicities of infection and that the level of ICP27, a third viral regulatory protein, plays an important role in determining the intracellular localization of ICP0 (Z. Zhu, W. Cai, and P. A. Schaffer, J. Virol. 68:3027-3040, 1994). To address whether the cytoplasmic localization of ICP0 is a common feature of cells infected with all ICP4 mutant viruses or whether mutant ICP4 polypeptides, together with ICP27, determine the intracellular localization of ICP0, we used double-staining immunofluorescence tests to examine the intracellular staining patterns of ICP0 and ICP4 in cells infected with an extensive series of ICP4 mutant viruses. In these tests, compared with the localization pattern of ICP0 in wild-type virus-infected cells, more ICP0 was detected in the cytoplasms of cells infected with all ICP4 mutants tested at high multiplicities of infection. Each of the mutant forms of ICP4 exhibiting predominantly cytoplasmic staining contains both the nuclear localization signal and the previously mapped ICP27-responsive region (Z. Zhu and P. A. Schaffer, J. Virol. 69: [49][50][51][52][53][54][55][56][57][58][59] 1995). No correlation between the intracellular staining patterns of ICP0 and mutant forms of ICP4 was demonstrated, suggesting that mutant ICP4 polypeptides per se are not responsible for retention of ICP0 in the cytoplasm. This observation was confirmed in studies of cells cotransfected with plasmids expressing ICP0 and mutant forms of ICP4, in which the staining pattern of ICP0 was not changed in the presence of mutant ICP4 proteins. Studies of cells infected at low multiplicities with a variety of ICP4 ts mutant viruses at the NPT showed that both ICP0 and ts forms of ICP4 were localized predominantly within the nucleus. These observations are a further indication that the aberrant localization of the ts forms of ICP4 at the NPT is not a direct result of specific mutations in the ICP4 gene. In the final series of tests, the localization of ICP0 in cells infected with a double-mutant virus unable to express either ICP4 or ICP27 was examined. In these tests, ICP0 was detected exclusively in the nuclei of Vero cells but in both the nuclei and the cytoplasms of ICP27-expressing cells infected with the double mutant. These results demonstrate that ICP27, rather than the absence of functional ICP4, is responsible for the cytoplasmic localization of ICP0 in ICP4 mutant virus-infec...

Prolonged gene expression and cell survival after infection by a herpes simplex virus mutant defective in the immediate-early genes encoding ICP4, ICP27, and ICP22

“…The insets show an enlargement of a nucleus from the larger field. As previously observed (31,81,82), ICP0 accumulated in fine punctate structures at early times (6 h) postinfection (Fig. 8A).…”

“…The formation of large nuclear inclusions correlated with the absence of ICP27. This finding may reflect previous observations that the expression of ICP27 in the absence of ICP4 results in the cytoplasmic localization of ICP0 (81,82). Also of note is the observation that the expression of ICP22 results in the formation of fine granular structures in the nucleus.…”

“…ICP0 clearly alters the nuclear ultrastructure and potentially the compartmentalization of nuclear proteins involved in cell cycle regulation. In cells infected with wild-type virus (31) or an ICP4 Ϫ ICP27 Ϫ mutant (d92 [82]), ICP0 accumulates in many small punctate intranuclear structures. Everett and Maul have shown that these structures are coincident with PML-containing structures (17,38), also known as ND10, PODs, or Kr bodies (2,15,32,75,78).…”

Interaction of herpes simplex virus 1 alpha regulatory protein ICP0 with elongation factor 1delta: ICP0 affects translational machinery

“…In continuous cell lines, ICP0 accumulated in the cytoplasm later than in primary human fibroblasts. Recently, it has been reported that in Vero cells infected with mutants overproducing ICP27, ICP0 accumulated at 5 h after infection in both nuclei and cytoplasm, whereas in cells infected with the wild-type virus, ICP0 was detected by immunofluorescence in nuclei only (38). It is conceivable that in these studies, overexpression of ICP27 resulted in accelerated accumulation of ICP0 in the cytoplasm of Vero cells.…”

Herpes Simplex Virus ICP27 Activation of Stress Kinases JNK and p38

“…Normally, ICP4 and ICP0 are found in both the nucleus and the cytoplasm. Infection with ICP27 mutants, however, results in accumulation of ICP0 and ICP4 exclusively in the nucleus (100)(101)(102). Finally, ICP27 is implicated in the posttranslational modifications of ICP0 and ICP4, and it has been suggested that, in the absence of ICP27, ICP4 may not be phosphorylated (65,73).…”