Herpesvirus saimiri ORF57: a post-transcriptional regulatory protein

Boyne, James R.; Kj, Colgan; Whitehouse, Adrian

doi:10.2741/2898

Cited by 37 publications

(44 citation statements)

References 56 publications

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“…This is caused by a conserved group of viral posttranscriptional regulator proteins comprising the herpes simplex virus type 1 ICP27, the herpesvirus saimiri open reading frame 57, the Kaposi's sarcoma-associated herpesvirus open reading frame 57, and the Epstein-Barr virus EB2 proteins that promote nuclear export of intronless viral mRNA. These viral regulators bind to viral mRNA transcripts and interact directly or indirectly with the speckle-associated nuclear export factor Aly/REF and thereby access the TAP-dependent major mRNA export pathway (5,10,33,37,45). In addition, they associate with RNA-processing factors and regulate pre-mRNA splicing (5,31,34,44,64).…”

Section: Vol 83 2009 Influenza B Virus Ns1 Protein Interacts With Smentioning

confidence: 99%

Analysis of Influenza B Virus NS1 Protein Trafficking Reveals a Novel Interaction with Nuclear Speckle Domains

Schneider

Dauber

Melén

et al. 2009

J Virol

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Many proteins that function in the transcription, maturation, and export of metazoan mRNAs are concentrated in nuclear speckle domains, indicating that the compartment is important for gene expression. Here, we show that the NS1 protein of influenza B virus (B/NS1) accumulates in nuclear speckles and causes rounding and morphological changes of the domains, indicating a disturbance in their normal functions. This property was located within the N-terminal 90 amino acids of the B/NS1 protein and was shown to be independent of any other viral gene product. Within this protein domain, we identified a monopartite importin ␣ binding nuclear localization signal. Reverse-genetic analysis of this motif indicated that nuclear import and speckle association of the B/NS1 protein are required for the full replication capacity of the virus. In the late phase of virus infection, the B/NS1 protein relocated to the cytoplasm, which occurred in a CRM1-independent manner. The interaction of the B/NS1 protein with nuclear speckles may reflect a recruitment function to promote viral-gene expression. To our knowledge, this is the first functional description of a speckle-associated protein that is encoded by a negative-strand RNA virus.The nucleus of a vertebrate cell is highly organized in nonmembranous domains that exert distinct biochemical activities involved in gene expression (39). This partition gives rise to discrete structures, such as nuclear speckles, nucleoli, Cajal bodies, and promyelocytic leukemia protein (PML) bodies, which can be visualized by staining for antigens accumulating in these nuclear domains (4, 30). The concentration of proteins with functions in the same process in one nuclear compartment supports the spatial and temporal integration of tightly coupled nuclear processes, such as the transcription, splicing, and export of mRNA (46,47).Recent studies have shed light on the components and functions of several nuclear domains. Cajal bodies and nuclear speckles are enriched in spliceosomal small nuclear ribonucleoproteins (snRNPs) and have a specific role(s) in the biogenesis of cellular RNAs (9, 66). Nuclear speckles are defined by the irregular and punctate immunofluorescent staining patterns of RNA-processing factors, such as the serine/ arginine-rich (SR) splicing factor SC35, and correspond largely to the interchromatin granule clusters (66). The current concept is that the enrichment of a given protein in speckles is mediated by its function and interactions with other factors residing in interchromatin granule clusters, although the existence of specific targeting or retention signals cannot be ruled out (61). Originally, it was proposed that nuclear speckles are mainly storage sites for RNA-processing factors from which they were recruited to sites of active transcription (36,54,77). However, more recent findings also suggest an active role of the compartment in mRNA biogenesis (7,51,59). The structural organization of nuclear speckles and their morphological appearance are tightly associated with th...

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Section: Vol 83 2009 Influenza B Virus Ns1 Protein Interacts With Smentioning

confidence: 99%

Analysis of Influenza B Virus NS1 Protein Trafficking Reveals a Novel Interaction with Nuclear Speckle Domains

Schneider

Dauber

Melén

et al. 2009

J Virol

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“…These include well-characterized HSV-1 ICP27 (28), human cytomegalovirus virus (HCMV) UL69 (29), Epstein-Barr virus (EBV) EB2 (or EB-SM) (30), and herpesvirus saimiri (HVS) ORF57 (31). While all homologues in the family share many common activities, they diverge with regard to specific functions and target specificities.…”

mentioning

confidence: 99%

Stability of Structured Kaposi's Sarcoma-Associated Herpesvirus ORF57 Protein Is Regulated by Protein Phosphorylation and Homodimerization

Majerčiak

Pripuzova

Chan

et al. 2015

J Virol

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Kaposi's sarcoma-associated herpesvirus (KSHV) ORF57 plays an essential role in KSHV lytic infection by promoting viral gene expression at the posttranscriptional level. Using bioinformatic and biochemical approaches, we determined that ORF57 contains two structurally and functionally distinct domains: a disordered nonstructural N-terminal domain (amino acids [aa] 1 to 152) and a structured ␣-helix-rich C-terminal domain (aa 153 to 455). The N-terminal domain mediates ORF57 interaction with several RNA-protein complexes essential for ORF57 to function. The N-terminal phosphorylation by cellular casein kinase II (CKII) at S21, T32, and S43, and other cellular kinases at S95 and S97 residues in proximity of the caspase-7 cleavage site, 30-DETD-33, inhibits caspase-7 digestion of ORF57. The structured C-terminal domain mediates homodimerization of ORF57, and the critical region for this function was mapped carefully to ␣-helices 7 to 9. Introduction of point mutations into ␣-helix 7 at ORF57 aa 280 to 299, a region highly conserved among ORF57 homologues from other herpesviruses, inhibited ORF57 homodimerization and led to proteasome-mediated degradation of ORF57 protein. Thus, homodimerization of ORF57 via its C terminus prevents ORF57 from degrading and allows two structure-free N termini of the dimerized ORF57 to work coordinately for host factor interactions, leading to productive KSHV lytic infection and pathogenesis. IMPORTANCEKSHV is a human oncogenic virus linked to the development of several malignancies. KSHV-mediated oncogenesis requires both latent and lytic infection. The KSHV ORF57 protein is essential for KSHV lytic replication, as it regulates the expression of viral lytic genes at the posttranscriptional level. This report provides evidence that the structural conformation of the ORF57 protein plays a critical role in regulation of ORF57 stability. Phosphorylation by CKII on the identified serine/threonine residues at the N-terminal unstructured domain of ORF57 prevents its digestion by caspase-7. The C-terminal domain of ORF57, which is rich in ␣-helices, contributes to homodimerization of ORF57 to prevent proteasome-mediated protein degradation. Elucidation of the ORF57 structure not only enables us to better understand ORF57 stability and functions but also provides an important tool for us to modulate ORF57's activity with the aim to inhibit KSHV lytic replication. K aposi's sarcoma-associated herpesvirus (KSHV) ORF57 (also known as Mta) is expressed early in the KSHV lytic cycle and is required for the efficient expression of a subset of viral genes, including KSHV PAN, ORF59, K8, viral interleukin-6 (vIL-6), ORF47, and others (1-7). A KSHV genome lacking ORF57 expression is associated with a defective lytic cycle incapable of producing infectious virions (8, 9).KSHV ORF57 functions as a posttranscriptional regulator of viral gene expression by affecting RNA stability (PAN, ORF59, and ORF47), splicing (ORF50 and K8), polyadenylation (ORF59), and translation (vIL-6) (1, 2, 4-7, 10) but ...

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“…To facilitate this function, ORF57 shuttles between the nucleus and the cytoplasm, trafficks through the nucleolus, binds viral RNA and interacts with various cellular nuclear import/export proteins (Boyne & Whitehouse, 2006b;Goodwin et al, 1999;Williams et al, 2005). HVS ORF57 comprises several functional domains, which are conserved between its viral homologues (Boyne et al, 2008a), including two nuclear localization signals (Boyne & Whitehouse, 2006b), a leucine-rich nuclear export signal (Goodwin & Whitehouse, 2001) and carboxy-terminal zinc finger-like and hydrophobic GLFF domains (Goodwin et al, 2000). Furthermore, the RNA-binding domain has been mapped to an amino terminus arginine-rich region (Goodwin et al, 1999).…”

mentioning

confidence: 99%

“…ORF57 is a multifunctional protein that regulates viral gene expression at the post-transcriptional level (Boyne et al, 2008a;Boyne & Whitehouse, 2006a;Cooper et al, 1999;Goodwin et al, 1999;Goodwin & Whitehouse, 2001;Whitehouse et al, 1998). The primary role of ORF57 is to mediate the nuclear export of HVS intronless transcripts.…”

mentioning

confidence: 99%

Identification of a response element in a herpesvirus saimiri mRNA recognized by the ORF57 protein

Colgan

Boyne

Whitehouse

2009

Journal of General Virology

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The herpesvirus saimiri (HVS) ORF57 protein binds viral RNA, enabling the efficient nuclear export of intronless viral mRNAs. However, it is not known how ORF57 recognizes these viral mRNAs. In this study, a systematic evolution of ligands by exponential enrichment (SELEX) approach was used to select RNA sequences that are preferentially bound by the ORF57 protein.Results identified a recurring motif, GAAGRG, within the majority of selected RNAs, which is also present in many late HVS mRNAs. RNA immunopreciptations demonstrated that disruption of this motif within a viral intronless RNA ablates ORF57 binding. These data suggest that the GAAGRG motif may be required within a HVS intronless mRNA for recognition by the ORF57 protein.The herpesvirus saimiri (HVS) ORF57 protein is homologous to gene products identified in all classes of herpesviruses (Bello et al., 1999;Perera et al., 1994;Sacks et al., 1985;Winkler et al., 1994). ORF57 is a multifunctional protein that regulates viral gene expression at the post-transcriptional level (Boyne et al., 2008a;Boyne & Whitehouse, 2006a;Cooper et al., 1999;Goodwin et al., 1999;Goodwin & Whitehouse, 2001;Whitehouse et al., 1998). The primary role of ORF57 is to mediate the nuclear export of HVS intronless transcripts. This event is essential for viral replication, as intronless transcripts are retained in the nucleus following transcription due to the splicingdependent nature of cellular mRNA export. To facilitate this function, ORF57 shuttles between the nucleus and the cytoplasm, trafficks through the nucleolus, binds viral RNA and interacts with various cellular nuclear import/export proteins (Boyne & Whitehouse, 2006b;Goodwin et al., 1999;Williams et al., 2005). HVS ORF57 comprises several functional domains, which are conserved between its viral homologues (Boyne et al., 2008a), including two nuclear localization signals (Boyne & Whitehouse, 2006b), a leucine-rich nuclear export signal (Goodwin & Whitehouse, 2001) and carboxy-terminal zinc finger-like and hydrophobic GLFF domains (Goodwin et al., 2000). Furthermore, the RNA-binding domain has been mapped to an amino terminus arginine-rich region (Goodwin et al., 1999). However, how ORF57 specifically recognizes and binds viral intronless mRNAs is yet to be elucidated. At present, no specific response element has been identified in any HVS mRNAs; therefore, in this study, we have utilized a systematic evolution of ligands by exponential enrichment (SELEX) approach (Joyce, 1994;Stoltenburg et al., 2007) to identify RNA sequences that ORF57 specifically binds from a random pool. Results identified a core response element, GAAGRG (where R is a purine). Moreover, mutation of this element within the intronless ORF47 mRNA ablated ORF57 binding.To identify RNA sequences recognized by ORF57, a SELEX screen was performed. SELEX utilizes the ability to create different aptamers quickly by generating a random pool and selecting those species that have an increased affinity towards a target (Stoltenburg et al., 2007). Selected RNAs...

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Herpesvirus saimiri ORF57: a post-transcriptional regulatory protein

Cited by 37 publications

References 56 publications

Analysis of Influenza B Virus NS1 Protein Trafficking Reveals a Novel Interaction with Nuclear Speckle Domains

Analysis of Influenza B Virus NS1 Protein Trafficking Reveals a Novel Interaction with Nuclear Speckle Domains

Stability of Structured Kaposi's Sarcoma-Associated Herpesvirus ORF57 Protein Is Regulated by Protein Phosphorylation and Homodimerization

Identification of a response element in a herpesvirus saimiri mRNA recognized by the ORF57 protein

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