The C-terminal repressor region of herpes simplex virus type 1 ICP27 is required for the redistribution of small nuclear ribonucleoprotein particles and splicing factor SC35; however, these alterations are not sufficient to inhibit host cell splicing

Abstract

Herpes simplex virus type 1 infection results in a reorganization of antigens associated with the small nuclear ribonucleoprotein particles (snRNPs), resulting in the formation of prominent clusters near the nuclear periphery. In this study, we show that the immediate-early protein ICP27, which is involved in the impairment of host cell splicing and in the changes in the distribution of snRNPs, is also required for reassorting the SR domain splicing factor SC35. Other viral processes, such as adsorption and penetration, shutoff of host protein synthesis, early and late gene expression, and DNA replication, do not appear to play a role in changing the staining pattern of splicing antigens. Furthermore, the C-terminal repressor region of ICP27, which is required for the inhibitory effects on splicing, also is involved in redistributing the snRNPs and SC35. During infection or transfection with five different repressor mutants, the speckled staining pattern characteristic of uninfected cells was seen and the level of a spliced target mRNA was not reduced. Infections in the presence of activator mutants showed a redistributed snRNP pattern and a decreased accumulation of spliced target mRNA. Moreover, two arginine-rich regions in the N-terminal half of ICP27 were not required for the redistribution of snRNPs or SC35. Substitution of these regions with a lysine-rich sequence from simian virus 40 large-T antigen resulted in a redistribution of splicing antigens. Unexpectedly, a repressor mutant with a ts phenotype showed a redistributed staining pattern like that seen with wild-type infected cells. During infections with this ts mutant, splicing was not inhibited, as shown in this and previous studies, confirming its repressor phenotype. Furthermore, both the mutant and the wild-type protein colocalized with snRNPs. Therefore, the redistribution of snRNPs and SC35 correlates with ICP27-mediated impairment of host cell splicing, but these alterations are not sufficient to fully inhibit splicing. This indicates that active splicing complexes are still present even after dramatic changes in the organization of the snRNPs.

Herpes Simplex Virus ICP27 Activation of Stress Kinases JNK and p38

“…ICP27 has many roles during the course of the HSV-1 replication cycle. In addition to being necessary for transcription of ␥1 and ␥2 viral genes (79), ICP27 regulates polyadenylation site selection (22,31,55), regulates the intranuclear distribution of splicing factors (52,82), interacts with the export factor Aly/Ref (13), shuttles between the nucleus and cytoplasm (60,69,87), and demonstrates RNA binding activity (59). These functions are consistent with a role of ICP27 in suppressing cellular posttranscriptional processing and transport while promoting viral transcription.…”

Nucleolar disruption impairs Kaposi's sarcoma‐associated herpesvirus ORF57‐mediated nuclear export of intronless viral mRNAs

“…Kaposi's sarcoma-associated herpesvirus (KSHV) ORF57 is an essential protein conserved amongst all herpesviruses [1][2][3][4][5][6][7][8][9][10][11]. It is a multi-functional regulator of gene expression assuming many roles during the course of infection, including transcriptional activation, enhancing viral splicing and viral mRNA accumulation [12][13][14].…”

The herpes simplex virus type 1 regulatory protein ICP27 coimmunoprecipitates with anti-Sm antiserum, and the C terminus appears to be required for this interaction

“…It is believed that the nuclear speckles serve as storage sites for splicing factors, while splicing occurs on nascent transcripts (18,63,81). Splicing factors have been found to redistribute in response to transcription inhibition (9), splicing inhibition (19,46), and viral infection (5,8,13,28,37,49,53). During infection with herpes simplex virus type 1 (HSV-1), a dramatic redistribution of snRNPs and the SR protein SC35 from their normal speckled staining pattern occurs with the formation of prominent clusters, which appear to condense throughout the nucleus and then migrate to the nuclear periphery as infection proceeds (37,49,53).…”

“…Splicing factors have been found to redistribute in response to transcription inhibition (9), splicing inhibition (19,46), and viral infection (5,8,13,28,37,49,53). During infection with herpes simplex virus type 1 (HSV-1), a dramatic redistribution of snRNPs and the SR protein SC35 from their normal speckled staining pattern occurs with the formation of prominent clusters, which appear to condense throughout the nucleus and then migrate to the nuclear periphery as infection proceeds (37,49,53). Furthermore, studies by Phelan et al (49) and in our laboratory (53) demonstrated that an HSV-1 immediate-early regulatory protein, ICP27 (IE63), was essential for the relocalization of the snRNPs and that ICP27 colocalized with the snRNPs.…”

“…During infection with herpes simplex virus type 1 (HSV-1), a dramatic redistribution of snRNPs and the SR protein SC35 from their normal speckled staining pattern occurs with the formation of prominent clusters, which appear to condense throughout the nucleus and then migrate to the nuclear periphery as infection proceeds (37,49,53). Furthermore, studies by Phelan et al (49) and in our laboratory (53) demonstrated that an HSV-1 immediate-early regulatory protein, ICP27 (IE63), was essential for the relocalization of the snRNPs and that ICP27 colocalized with the snRNPs. We (23,25,54) and others (55) have presented evidence that HSV-1 inhibits host cell splicing and that ICP27 is required for this effect (25).…”