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ICP27 interacts with SRPK1 to mediate HSV splicing inhibition by altering SR protein phosphorylation
Kathryn S Sciabica1, Qian J Dai, Rozanne M Sandri-Goldin
1Department of Microbiology and Molecular Genetics, University of California, Irvine, CA 92697, USA.
Abstract:
Infection with some viruses can alter cellular mRNA processing to favor viral gene expression. We present evidence that herpes simplex virus 1 (HSV-1) protein ICP27, which contributes to host shut-off by inhibiting pre-mRNA splicing, interacts with essential splicing factors termed SR proteins and affects their phosphorylation. During HSV-1 infection, phosphorylation of several SR proteins was reduced and this correlated with a subnuclear redistribution. Exogenous SR proteins restored splicing in ICP27-inhibited nuclear extracts and SR proteins isolated from HSV-1-infected cells activated splicing in uninfected S100 extracts, indicating that inhibition occurs by a reversible mechanism. Spliceosome assembly was blocked at the pre-spliceosomal complex A stage. Furthermore, we show that ICP27 interacts with SRPK1 and relocalizes it to the nucleus; moreover, SRPK1 activity was altered in the presence of ICP27 in vitro. We propose that ICP27 modifies SRPK1 activity resulting in hypophosphorylation of SR proteins impairing their ability to function in spliceosome assembly.
Insights
Herpes simplex virus 1 (HSV-1) protein ICP27 inhibits pre-mRNA splicing by altering SR protein phosphorylation. This mechanism disrupts spliceosome assembly, favoring viral gene expression during infection.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Viral infections can manipulate host cell mRNA processing to promote viral gene expression.
- Herpes simplex virus 1 (HSV-1) protein ICP27 is known to inhibit pre-mRNA splicing, contributing to host cell shut-off.
Purpose of the Study:
- To investigate the mechanism by which HSV-1 protein ICP27 inhibits pre-mRNA splicing.
- To elucidate the interaction between ICP27 and SR proteins and its effect on splicing factor phosphorylation.
Main Methods:
- Analysis of SR protein phosphorylation and subnuclear localization during HSV-1 infection.
- In vitro splicing assays using nuclear extracts and purified proteins.
- Investigation of ICP27 interaction with SRPK1 and its enzymatic activity.
Main Results:
- HSV-1 infection leads to reduced phosphorylation and altered subnuclear localization of SR proteins.
- ICP27 inhibits splicing by blocking spliceosome assembly at the pre-spliceosomal complex A stage.
- ICP27 interacts with and relocalizes SRPK1, altering its activity and causing SR protein hypophosphorylation.
Conclusions:
- HSV-1 ICP27 inhibits pre-mRNA splicing through a reversible mechanism involving SRPK1-mediated hypophosphorylation of SR proteins.
- This modification of SR proteins impairs their function in spliceosome assembly, thereby favoring viral gene expression.
- The findings provide insight into viral strategies for manipulating host cell machinery.