SR proteins SRp20 and 9G8 contribute to efficient export of herpes simplex virus 1 mRNAs

Abstract

Herpes simplex virus 1 (HSV-1) mRNAs are exported to the cytoplasm through the export receptor TAP/NFX1. HSV-1 multifunctional protein ICP27 interacts with TAP/NXF1, binds viral RNAs, and is required for efficient viral RNA export. In ICP27 mutant infections, viral RNA export is reduced but not ablated, indicating that other export adaptors can aid in viral RNA export. Export adaptor protein Aly/REF is recruited to viral replication compartments, however, Aly/REF knockdown has little effect on viral RNA export. SR proteins SRp20 and 9G8 interact with TAP/NXF1 and mediate export of some cellular RNAs. We report that siRNA knockdown of SRp20 or 9G8 resulted in about a 10 fold decrease in virus yields and in nuclear accumulation of poly(A+) RNA. In infected cells depleted of SRp20, newly transcribed Bromouridine-labelled RNA also accumulated in the nucleus. We conclude that SRp20 and 9G8 contribute to HSV-1 RNA export.

Herpes simplex virus ICP27 regulates alternative pre-mRNA polyadenylation and splicing in a sequence-dependent manner

“…ICP27 has a role in transcriptional regulation through association with the C-terminal domain of RNA polymerase II (2,3), forms homodimers (4,5), interacts with U1 small nuclear ribonucleoprotein (snRNP) through its C-terminal domain, and colocalizes with U1 and U2 snRNPs (6,7). It also interacts with splicing factors such as SRSF3, SRSF1, SRSF7, and SRSF2 (8)(9)(10)(11), and is involved in nuclear export of some viral transcripts (12,13). The role of ICP27 in regulating pre-mRNA splicing remains controversial.…”

Three Arginine Residues within the RGG Box Are Crucial for ICP27 Binding to Herpes Simplex Virus 1 GC-Rich Sequences and for Efficient Viral RNA Export

“…Aly/REF does not appear to bind viral RNA directly (3), and it is not essential for HSV-1 RNA export based upon small interfering RNA (siRNA) knockdown studies (20), but it contributes to the efficiency of viral RNA export (3,23). ICP27 also interacts with the SR splicing proteins SRp20 and 9G8 (11,36), which have been shown to shuttle between the nucleus and the cytoplasm (1). SRp20 and 9G8 have also been shown to facilitate the export of some cellular RNAs (16,17,27) by binding RNA and interacting with TAP/ NXF1 (14,16,18).…”

“…SRp20 and 9G8 have also been shown to facilitate the export of some cellular RNAs (16,17,27) by binding RNA and interacting with TAP/ NXF1 (14,16,18). The knockdown of SRp20 or 9G8 adversely affects HSV-1 replication and specifically results in a nuclear accumulation of newly transcribed RNA during infection (11). Thus, these SR proteins also contribute to the efficiency of viral RNA export.…”

“…Thus, these SR proteins also contribute to the efficiency of viral RNA export. However, the overexpression of SRp20 was unable to rescue the defect in RNA export during infection with an ICP27 mutant that cannot bind RNA (11), suggesting that ICP27 is the major HSV-1 RNA export protein that links viral RNA to TAP/NXF1. ICP27 was shown previously to bind RNA through an RGG box motif located at amino acids 138 to 152 within the 512-amino-acid protein (28,34).…”

The Varicella-Zoster virus IE4 protein: A conserved member of the herpesviral mRNA export factors family and a potential alternative target in antiherpetic therapies

“…Furthermore, the knockdown of TAP/ NXF1 was shown to result in barely detectable level of two late proteins gB and gC, and in greatly reduced HSV-1 viral titers [34]. Very recently, the knockdown of SRp20 and 9G8 was also shown to reduce the virus growth, suggesting that these factors could play a role as HSV-1 mRNAs export adaptors and contribute to the overall export efficiency during HSV-1 infection [43].…”