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The herpes simplex virus type 1 (HSV-1) virion protein VP22 exhibits the remarkable property of intercellular trafficking whereby the protein spreads from the cell in which it is synthesized to many surrounding cells. In addition to having implications for protein trafficking mechanisms, this function of VP22 might be exploited to overcome a major hurdle in gene therapy, i.e., efficient delivery of genes and gene products. We show that chimeric polypeptides, consisting of VP22 linked to the entire p53 protein, retain their ability to spread between cells and accumulate in recipient cell nuclei. Furthermore the p53-VP22 chimeric protein efficiently induces apoptosis in p53 negative human osteosarcoma cells resulting in a widespread cytotoxic effect. The intercellular delivery of functional p53-VP22 fusion protein is likely to prove beneficial in therapeutic strategies based on restoration of p53 function. These results, demonstrating intracellular transport of large functional proteins, indicate that VP22 delivery may have applications in gene therapy.

Herpes simplex virus 1 (HSV-1), a nudear replicating DNA virus, has 73 identified genes of which only 4 contain introns. For this reason the virus probably makes only minimal use of the cellular RNA-splicing machinery. Antigens associated with the small nuclear ribonucleoprotein particles (snRNPs) that are subunits of splicing complexes have been reported to redistribute in the nucleus and become concentrated into the intranuclear structures, the interchromatin granules, after HSV-1 infection [Martin, T. E., Barghusen, S. C., Leser, G. P. & Spear, P. G. (1987) J. Cel Biol. 105, 2069-2082. We observe this snRNP redistribution upon HSV-1 infection, in which the widespread snRNP staining pattern changes to a restricted punctate distribution with a concomitant loss of coiled bodies in HSV-1-infected cells. We show here that expression of the immediate-early (IE) subset of HSV-1 genes is necessary and sufficient for snRNP redistribution. Using a series of HSV-1 mutants in different IE genes, we have established that specifically the product of the viral IE63 (ICP27) gene is essential for this effect, and transfection experiments revealed that IE63 expression alone can cause the snRNP redistribution. Further, we show that the IE63 gene product colocalizes with the redistributed snRNP in the nucleus. The snRNP redistribution caused by HSV-1 infection resembles the effect seen after inhibition of transcription in uninfected cells. In HSV-1-infected cells, however, the snRNP redistribution is under the control of viral IE gene products and occurs during active virus gene transcription.In mammalian cells, the processes of splicing and polyadenylylation act on the primary transcript in the cell nucleus to generate mature mRNA. Nuclear pre-mRNA splicing requires a complex set of trans-acting splicing factors that bind to substrate RNAs in an ordered pathway to form an active splicing complex, or spliceosome. The major subunits of the spliceosome are the small nuclear ribonucleoprotein particles (snRNPs), specifically the Ul, U2, U4/6, and U5 snRNPs (1). In addition, a number of non-snRNP protein-splicing factors are also required for splicing in vitro (for review, see ref.2).Herpes simplex virus type 1 (HSV-1) is a nuclear replicating virus and upon infection reduces host-cell gene expression and promotes expression of the viral genome. As HSV-1 infection proceeds, the levels of cellular RNA polymerase I and polymerase III activity are dramatically reduced, and host ribosomal RNA synthesis is shut down; there is also a reduction in the level of host mRNA transcription (3). An unusual and interesting feature of HSV-1 gene organization from the viewpoint of posttranscriptional processing is that only 4 of the 73 genes contain introns. Of the spliced genes, 3 are expressed from immediate-early (IE) times after infection, whereas the fourth one, ULIS, is subsequently expressed at early-late times in infection. Transient expression of IE63 caused a reduction in the levels of spliced transcriptsThe publication costs of t...