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The herpes simplex virus regulatory protein ICP27 contributes to the decrease in cellular mRNA levels during
M A Hardwicke1, R M Sandri-Goldin
1Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine 92717-4025.
Abstract:
We have previously shown that the herpes simplex virus immediate-early regulatory protein ICP27 acts posttranscriptionally to affect mRNA processing (R. M. Sandri-Goldin and G. E. Mendoza, Genes Dev. 6:848-863, 1992). Specifically, in the presence of ICP27, spliced target mRNAs were decreased 5- to 10-fold in transfections with target genes containing a 5' or 3' intron. Here, we have investigated the effect of ICP27 during herpes simplex virus type 1 (HSV-1) infection on accumulation of spliced cellular mRNAs. ICP27 viral mutants have been shown to be defective in host shutoff (W. R. Sacks, C. C. Greene, D. P. Aschman, and P. A. Schaffer, J. Virol. 55:796-805, 1985). Therefore, we examined whether ICP27 could contribute to this complex process by decreasing cellular mRNA levels through its effects on host cell splicing. It was found that in infections with viral mutants defective in ICP27, the accumulated levels of three spliced host mRNAs were higher than those seen with wild-type HSV-1. The differences occurred posttranscriptionally as shown by nuclear runoff transcription assays. The stabilities of the spliced products during infection with wild-type or ICP27 mutant viruses were similar, and unspliced precursor mRNA for a viral spliced gene was detected in infections with wild-type HSV-1 but not in infections in which ICP27 was not expressed. These results suggest that the reduction in cellular mRNA levels and the accumulation of pre-mRNA are related and may be caused by an impairment in host cell splicing. These data further show that ICP27 is required for these effects to occur.
Insights
Herpes simplex virus protein ICP27 impairs host cell splicing, reducing cellular mRNA levels during infection. ICP27 is essential for this effect, impacting viral replication and host gene expression.
Area of Science:
- Virology
- Molecular Biology
- Gene Expression
Background:
- Herpes simplex virus (HSV) immediate-early protein ICP27 is known to regulate gene expression posttranscriptionally.
- Previous studies indicated ICP27 affects mRNA processing, decreasing spliced target mRNAs in transfection assays.
- ICP27 is also implicated in the "host shutoff" phenomenon observed during HSV infection.
Purpose of the Study:
- To investigate the role of ICP27 in modulating the accumulation of spliced cellular mRNAs during herpes simplex virus type 1 (HSV-1) infection.
- To determine if ICP27 contributes to the reduction of cellular mRNA levels by affecting host cell splicing.
- To elucidate the mechanism by which ICP27 influences host mRNA processing during viral infection.
Main Methods:
- Utilized HSV-1 viral mutants defective in ICP27 expression.
- Performed infections with wild-type HSV-1 and ICP27 mutant viruses.
- Conducted nuclear runoff transcription assays to differentiate transcriptional and posttranscriptional effects.
- Analyzed the accumulation levels of spliced host mRNAs and precursor mRNAs.
Main Results:
- Infections with ICP27-defective viral mutants showed higher accumulated levels of spliced host mRNAs compared to wild-type HSV-1 infections.
- Nuclear runoff assays confirmed that the observed differences in mRNA levels occurred posttranscriptionally.
- The stability of spliced mRNA products was similar between wild-type and ICP27 mutant infections.
- Unspliced precursor mRNA for a viral gene was detected during wild-type HSV-1 infection but not when ICP27 was absent.
Conclusions:
- ICP27 plays a critical role in reducing cellular mRNA levels during HSV-1 infection.
- The reduction in cellular mRNA and accumulation of pre-mRNA are linked and likely caused by ICP27-mediated impairment of host cell splicing.
- ICP27 is required for the observed effects on host cell mRNA processing and accumulation.