Summary auto-generated
This study demonstrates that herpes simplex virus type 1 (HSV-1) immediate early protein IE63 (ICP27) is a nucleocytoplasmic shuttle protein capable of moving between the nucleus and cytoplasm. IE63 is an essential 63 kDa nuclear phosphoprotein with multiple regulatory functions, including inhibition of RNA splicing and interaction with cellular splicing machinery. Using indirect immunofluorescence and actinomycin D treatment to inhibit transcription, researchers showed that IE63 accumulates in the cytoplasm while remaining predominantly nuclear during normal infection. IE63 contains a putative nuclear export signal and shuttles in a manner similar to other known shuttle proteins like hnRNP A1. Notably, two other major HSV-1 nuclear proteins—IE110 and UL29—did not exhibit this shuttling ability under identical conditions. The snRNP components that IE63 associates with also failed to shuttle. These findings suggest IE63 facilitates nuclear export of HSV-1 transcripts, particularly unspliced RNAs which comprise the majority of viral transcripts, complementing its known role in retaining intron-containing RNAs in the nucleus.
Key findings
- HSV-1 IE63 protein exhibits nucleocytoplasmic shuttling ability, accumulating in the cytoplasm when transcription is inhibited with actinomycin D
- IE63 possesses a putative nuclear export signal (NES) homologous to the Rev protein export signal, enabling its shuttle activity
- Other nuclear HSV-1 proteins (IE110 and UL29) and snRNP components do not shuttle, indicating IE63's unique transport capability
- IE63 shuttling suggests a dual role: retaining intron-containing transcripts in the nucleus while facilitating export of unspliced viral transcripts to the cytoplasm
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Abstract
Herpes simplex virus type 1 (HSV-1) immediate early protein IE63, an essential nuclear protein, is pleiotropic in function and, at the post- transcriptional level, inhibits RNA splicing, interacts with cellular splicing small nuclear ribonucleoprotein particles (snRNPs), binds RNA and prevents the nucleocytoplasmic transport of intron-containing mRNAs. Here it is reported that IE63 is a nucleocytoplasmic shuttle protein able to travel from snRNP- and RNA-rich nuclear foci to the cytoplasm, where it accumulates during actinomycin D treatment. This newly identified property suggests that IE63 facilitates nuclear export of HSV-1 transcripts, in addition to retaining intron-containing transcripts in the nucleus. The mechanism by which IE63 controls RNA export has yet to be defined.