Download The nucleolus and herpesviral usurpation

Journal of Medical Microbiology (2012), 61, 1637–1643
DOI 10.1099/jmm.0.045963-0
The nucleolus and herpesviral usurpation
Review
Liwen Ni, Shuai Wang and Chunfu Zheng
Correspondence
Molecular Virology and Viral Immunology Research Group, State Key Laboratory of Virology,
Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, PR China
Chunfu Zheng
[email protected]
The nucleolus is a distinct subnuclear compartment known as the site for ribosome biogenesis in
eukaryotes. Consequently, the nucleolus is also proposed to function in cell-cycle control, stress
sensing and senescence, as well as in viral infection. An increasing number of viral proteins have
been found to localize to the nucleolus. In this article, we review the current understanding of the
functions of the nucleolus, the molecular mechanism of cellular and viral protein targeting to the
nucleolus and the functional roles of the nucleolus during viral infection with a specific focus on
the herpesvirus family.
Overview
The nucleolus is a large, dynamic subnuclear structure
present in eukaryotes and its primary function is rRNA
synthesis and ribosome biogenesis. Nucleoli disassemble
during cell division and reform at the end of mitosis
around tandemly repeated clusters of rRNA genes, which
are known as nucleolar organizing regions. rRNA is
synthesized and processed in the nucleolus with the help
of RNA polymerase I (RNA pol I) (Caburet et al., 2005;
Dimario, 2004; Leung et al., 2004; Olson & Dundr, 2005).
Electron microscopy analysis has shown that the nucleolus
can be divided into at least three different regions: a
fibrillar centre (FC), a dense fibrillar component (DFC)
and a granular component (GC) (Boisvert et al., 2007;
Hernandez-Verdun, 2006). The FC contains the transcription factor upstream binding factor (UBF) and RNA pol I.
The rDNA is transcribed at the border between the FC and
the DFC (Cmarko et al., 2008; Raska et al., 2006). The DFC
is usually associated with and surrounds the FC, within
which pre-rRNA and small nucleolar ribonucleoproteins
(snoRNPs) are accumulated and the post-transcriptional
processing and modification takes place. Maturation of
pre-rRNA in the DFC leads to formation of 18S, 5.8S and
28S rRNA (Bártova et al., 2010). The DFC contains
fibrillarin, an RNA methyl-transferase, and nucleolin, a
protein that has multiple roles in nucleolar and cellular
biology (Mongelard & Bouvet, 2007). The GC, surrounding both the FC and the DFC, is the region where the late
RNA processing takes place, such as pre-ribosomal particle
maturation and ribosomal subunit synthesis and transportation (Hernandez-Verdun, 2006; Olson & Dundr,
2005).
Well-documented studies have established that nucleoli
participate in gene silencing, senescence, cell-cycle regulation,
stress responses and innate immune responses. In addition,
numerous viral components have been demonstrated to
target the nucleolus, manipulating the cell cycle and triggering
045963 G 2012
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apoptosis and the innate immunity of host cell. The discovery
of this phenomenon provides a possible link between viral
components and viral evasion from host innate immune
responses, providing an impetus for further investigation
(Boulon et al., 2010; Hernandez-Verdun, 2011; Pederson,
2011).
The multifunctional nucleolus
The nucleolus contains a number of nucleolar proteins,
leading to a high degree of functional complexity that is
restricted to the biosynthesis of ribosomes (Andersen et al.,
2005; Andersen et al., 2002; Scherl et al., 2002). Recently,
proteomic studies have shown that the nucleolus contains
over 4500 identified proteins (Ahmad et al., 2009;
Andersen et al., 2005; Boisvert et al., 2010; Leung et al.,
2006). These proteins were found to be involved in cellcycle regulation, stress-specific responses, DNA processing
and DNA damage response and repair, regulation of
tumour suppressor and oncogene activities, signal recognition particle assembly, modification of small RNAs,
control of ageing, senescence and modulation of telomerase function (Boisvert et al., 2007; Grisendi et al., 2006; Kar
et al., 2011; Olson & Dundr, 2005; Ruggero & Pandolfi,
2003), as well as ribosome subunit production (Moore
et al., 2011).
Small ubiquitin-like modifier (SUMO) modification is
reported to affect recruitment of transcription factors and
chromatin-modifying enzymes, often leading to transcriptional repression (Gill, 2004). Recently, a quantitative
proteomics screen, using stable isotope labelling of amino
acids in cell culture (SILAC) and mass spectrometry,
revealed that the nucleoli contained some snoRNP
proteins, specifically Nop58, Nhp2 and DKC1 as the
substrates of SUMO1 or SUMO2 (Westman & Lamond,
2011). Together with the nucleolar targeting of SUMOspecific proteases SENP3 and SENP5 (Gong & Yeh, 2006;
Nishida et al., 2000) and the co-localization of SUMO-1
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L. Ni, S. Wang and C. Zheng
and UBF in the GFC of neuronal cells (Casafont et al.,
2007), this suggests a potential role of SUMOylation in the
regulation of rDNA transcription, ribosome assembly and,
thus, cellular translation, growth and proliferation; however, the molecular mechanisms require further investigation (Sirri et al., 2008; Westman & Lamond, 2011).
Nucleolin, fibrillarin and B23 are three of the most abundant,
well-understood and multifunctional proteins in the nucleolus. Nucleolin (first known as C23) represents ~10 % of
the total nucleolar protein content and is a ubiquitous,
multifunctional and mobile protein. Nucleolin shuttles
between the nucleolus, nucleoplasm, cytoplasm and cell
surface, plays roles in interaction with viruses at the cellular
membrane and regulates gene expression, chromatin remodelling, DNA recombination and replication, RNA synthesis
by RNA pol I and II, rRNA processing, mRNA stabilization,
cytokinesis and apoptosis (Callé et al., 2008; Mongelard &
Bouvet, 2007; Storck et al., 2007). Nucleolin is modified by
phosphorylation, methylation and ADP-ribosylation, which
may enable it to target various compartments to exert
different functions (Lo et al., 2006). Fibrillarin, a small
nuclear RNP component with a highly conserved sequence,
structure and function in eukaryotes, is a potential RNAbinding protein (Nicol et al., 2000). Fibrillarin is involved in
many post-transcriptional processes including pre-rRNA
processing, pre-rRNA methylation and ribosome assembly
(Tollervey et al., 1993).
B23 (also called NPM, nucleophosmin, NO38 or numatrin) is a highly conserved protein, which plays several
important roles in ribosomal biogenesis in the nucleolus.
Previous publications have proven that B23 has multiple
functions, including ribosome assembly, binding to other
nucleolar proteins, nucleocytoplasmic shuttling and possibly regulating transcription of rDNA by mediating
structural changes in chromatin (Hiscox, 2002). Recent
studies have indicated that B23 is implicated in the p53
network by its interaction with the ARF tumour suppressor
protein, a major upstream activator of p53 (Boulon et al.,
2010; Lindström & Zhang, 2006). The subcellular localization of B23 is also regulated by SUMOylation, which
occurs in close proximity to its nucleolar localization signal
(NoLS) motif (Liu et al., 2007) and can affect the role of
B23 in 28S rRNA maturation (Emmott & Hiscox, 2009;
Haindl et al., 2008).
Proteins that are present in the nucleolus also have functions
involved in cell growth control, telomere maintenance and
protein degradation, tumour suppression, and apoptosis. For
example, cyclin phosphatase Cdc14 and nucleostemin, a
nucleolar protein highly expressed in stem cells and cancer
cells, are involved in cell-cycle progression and cell division.
Nucleostemin regulates the cell cycle perhaps as a consequence of its interaction with a multitude of proteins,
including p53, the murine double minute 2 protein (MDM2),
telomeric repeat-binding factor 1 (TRF1), alternative reading
frame (ARF), ribosomal L1-domain-containing protein 1
(RSL1D1, also known as cellular senescence-inhibited gene or
1638
CSIG), and B23 (Pederson & Tsai, 2009). N-acetyltransferase
10 (NAT10), which has been shown to play a role in
maintaining or enhancing the stability of a-tubulin, also
influences the cell cycle. The depletion of NAT10 induces
defects in nucleolar assembly and cytokinesis and decreases
acetylated a-tubulin, leading to G2/M cell-cycle arrest or
delay of mitotic exit (Shen et al., 2009).
PICT1 (also known as GLTSCR2) is a nucleolar protein
that is essential for embryogenesis and ES cell survival; it
is a potent regulator of the MDM2-P53 pathway and
promotes tumour progression by retaining RPL11 in the
nucleolus (Sasaki et al., 2011). This apoptosis repressor,
which contains a caspase-recruitment domain (ARC, also
known as NOL3), is also an anti-apoptotic protein
originally found to be involved in apoptosis of cardiac
cells (Carter et al., 2011). NOL-6 and some other nucleolar
proteins were reported to be involved in innate immunity.
Mutation or silencing of NOL-6 could increase the
transcriptional levels of genes regulated by CEP-1, a p53
homologue in Caenorhabditis elegans. It has been reported
that activation of innate immunity by the inhibition of
nucleolar proteins requires p53/CEP-1 and its transcriptional target SYM-1 (Fuhrman et al., 2009).
Nucleolus targeting of cellular and viral proteins
The nuclear localization signal (NLS) is crucial for proteins
to be transported across the nuclear membrane into the
nucleus. The NLS motifs, which are well-characterized and
moderately conserved, are usually abundant in basic amino
acids or can be predicted by suitable algorithms (Cokol et al.,
2000; la Cour et al., 2004). Dedicated transport systems
interact with the NLS and carry the protein into the nucleus
(Boulikas, 1993; Emmott & Hiscox, 2009). Unlike the
nucleus, the nucleolus is a non-membranous subnuclear
region where any soluble molecule can spread into and out
of. Even so, many researchers have reported that nucleolar
localized proteins contain some distinct short sequences,
which have been identified as functional NoLSs (Emmott &
Hiscox, 2009; Scott et al., 2010). For example, the amino
acid sequence RSRKYTSWYVALKR of fibroblast growth
factor 2 (Sheng et al., 2004), the amino acid sequence
KKLKKRNK at (position 466–473) of MDM2 (Lohrum
et al., 2000) and the RKKRKKK residues in nuclear factorkB-inducing kinase (Birbach et al., 2004) have been
identified as functional NoLSs. It has been reported that in
human immunodeficiency virus-1 (HIV-1)-infected HeLa
cells, the expression of the viral regulatory protein Rev,
which governs viral gene expression, induces nucleoporins
Nup98 and Nup214 and a significant fraction of the nuclear
export factor chromosome region maintenance protein 1
(CRM1) to relocalize into the nucleolus (Michienzi et al.,
2000; Zolotukhin & Felber, 1999). Some nucleolus proteomics experiments have indicated that some host proteins
enter into and accumulate in the nucleolus. For example,
nuclear pore complex component (NUP210), rPIK3-p87
(also known as PIK3R6) and ribosomal protein S15a were
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Journal of Medical Microbiology 61
Viral and host proteins localize into the nucleolus
more than twofold enriched in adenovirus-infected cell
nucleoli compared with uninfected cell nucleoli (Lam et al.,
2010).
During infection, many viral proteins also target to the
nucleolus. For example, the HIV-1 transactivator of
transcription protein TAT contains a NoLS amino acid
sequence of RKKRRQRRRAHQ, which targets the nucleolus (Siomi et al., 1990). Herpes simplex virus type-1
(HSV-1) infected cell protein 27 (ICP27) is suggested to be
a nucleolar targeting protein and contains a relatively short
sequence, mapping to residues 110–152, which functions as
an NoLS and plays important roles in efficient viral RNA
export and regulation of HSV-1 replication (Mears et al.,
1995). Analysis carried out in our lab identified an argininerich domain (RPRRPRRRPRRR) as a functional NoLS in
bovine herpesvirus-1 infected cell protein 27 (BICP27),
which localizes predominantly in the nucleolus (Guo et al.,
2009). Recently, a genuine NoLS of the pseudorabies
virus early protein UL54, with the amino acid sequence
RRRRGGRGGRAAR, was identified in our lab and its
nucleolar localization was found to regulate viral gene
expression and DNA synthesis. Recombinant viruses with
mutations of the NoLS in UL54 displayed a defect in viral
gene expression and DNA synthesis (Li et al., 2011). It was
previously established that the US11 protein of HSV-1
contains unique XPR repeats, which are responsible for its
retention within the nucleolus (Catez et al., 2002), and in our
lab, Xing et al. (2010) identified that, for what is believed to
be for the first time, amino acids 84–125, 126–152 and 89–
146 of the US11 XPR repeats are able to target reporter
proteins at the nucleolus. Post-translational modifications
might also influence the activity of an NoLS. A notable
example of this can be found in the NoLS of the HSV-1 US11
protein, in which a single proline-rich motif, mediating
nucleolar localization of US11 protein, is regulated by
phosphorylation (Catez et al., 2002).
HSV-1 ICP34.5, a viral neurovirulence-associated protein,
mediates eukaryotic translation initiation factor 2 subunit
a (eIF-2a) dephosphorylation and prevents the shut-off of
protein synthesis mediated by dsRNA-dependent protein
kinase PKR. The ICP34.5 protein distributes throughout
the nucleus, the nucleolus and the cytoplasm in transfected
or infected cells, functioning by blocking the cellular
antiviral response, viral egress, glycoprotein processing,
DNA replication and cell-cycle regulation. A NoLS of the
ICP34.5 protein was identified and mapped to amino acids
1–16, consisting of a cluster of arginine residues (MARRRRHRGPRRPRPP). The function of the nucleolar-targeting protein ICP34.5 needs further investigation (Cheng
et al., 2002).
The herpesvirus saimiri ORF57 protein is a nucleolar
targeting protein, which redistributes the host-cell human
transcription/export (TREX) proteins leading to ORF57mediated viral mRNA nuclear export. Its NoLS consists of
two distinct NLSs, which function in tandem to localize
ORF57 to the nucleolus (Boyne & Whitehouse, 2006). A
http://jmm.sgmjournals.org
homologous ORF57 protein from Kaposi’s sarcomaassociated herpesvirus (KSHV) has been described as
presenting a similar characteristic. NLS1, in combination
with either NLS2 or NLS3 are able to function as NoLSs,
which target the ORF57 protein to the nucleolus.
Disruption of the nucleolus by actinomycin D or 5,6dichloro-1-b-D-ribofuranosylbenzimidazole leads to a
reduction of KSHV ORF57-mediated intronless mRNA
export, revealing that the intact nucleolus is essential for
KSHV ORF57 to efficiently export the intronless mRNA
(Hiscox et al., 2010; Boyne & Whitehouse, 2009).
NoLSs are, thus, emerging as a predominant mechanism in
the targeting of proteins to the nucleolus. Determination of
NoLSs is one way to identify potential nucleolar localization proteins from the large number of host and viral
proteins (Scott et al., 2011; Simpson et al., 2001). Although
NoLSs commonly vary in context and in length and
sometimes overlap with each other (Emmott & Hiscox,
2009), Scott et al. (2011) collated and statistically analysed
46 human nucleolar localization sequences and developed a
web server, the Nucleolar Localization Sequence Detector
(NoD), and a command line program that predicts the
presence of NoLSs in eukaryotic and viral proteins (Scott
et al., 2011) based on that database. Further investigation is
required to clarify whether NoLS predictions using this
method are practical.
Many factors can determine the nucleolar localization of a
protein. For instance, soluble proteins smaller than 40–
60 kDa can passively diffuse through the nuclear pore
complex and into, or out of, the nuclear compartment.
Some RNA binding-domain-containing proteins can be
found in nucleoli where the rRNA is present. Many proteins,
including host proteins and viral proteins, diffuse through
the nuclear pore into the nucleoplasm and localize in the
nucleolus, associating with nucleolar factors (Hiscox, 2002).
Mutagenesis studies have demonstrated that the nucleocapsid (N) protein of infectious bronchitis virus presents a
motif eight amino acids long, which functions as an NoLS
and is necessary and sufficient for nucleolar retention of the
N protein and colocalization with nucleolin and fibrillarin,
i.e. the NoLS is required for interaction with cell factors
(Reed et al., 2006; Sirri et al., 2008).
Viral proteins interact with the nucleolus
Many viral proteins interact with and/or alter the
nucleolus. These are produced by RNA viruses, retroviruses
and DNA viruses (Hiscox, 2002, 2007; Hiscox et al., 2010)
and function as part of their infection strategy. It is
believed that localization of the viral proteins to the
nucleolus results from one of three different direct or
indirect types of interactions with rDNA, nucleolar RNA
(consisting mainly of rRNA) or nucleolar protein components (Carmo-Fonseca et al., 2000; Scott et al., 2011; Wang
et al., 2010). Thus, the viruses take over host-cell functions
and recruit nucleolar proteins to help with viral replication.
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L. Ni, S. Wang and C. Zheng
The HIV-1 Rev protein also contains an NoLS and
predominantly localizes to the nucleolus (Kubota et al.,
1999); meanwhile, B23 stimulates nuclear import of the
HIV-1 Rev protein and interacts with Rev (Fankhauser
et al., 1991; Szebeni et al., 1997). It has been wellestablished that a complex assembled within the nucleolus,
composed of Rev, two nucleoporin proteins and nuclear
export factor CRM1, helps HIV traffic its mRNA from the
nucleolus to the cytoplasm (Daelemans et al., 2004).
Previous experiments demonstrated that HSV-1 induced
modification of the nucleoli and ribosomes. Soon after
HSV-1 infection, the nucleoli localize close to the nuclear
membrane and finally fragment into small pieces. In
addition, the non-reversible phosphorylation of ribosomal
protein S6 is stimulated by infection (Diaz et al., 2002).
In prior studies, several HSV-1 proteins (ICP0, ICP4, ICP27,
ICP34.5, UL12, UL24 and US11) were reported to associate with the nucleolus, in some cases causing nucleolar
reorganization or redistribution of nucleolar components
(Burch & Weller, 2004; Callé et al., 2008; Cheng et al., 2002;
Lymberopoulos & Pearson, 2007; MacLean et al., 1987;
Mears et al., 1995; Morency et al., 2005).
The ICP0 protein, which plays a crucial role during HSV-1
lytic cycle and reactivation, accumulates within the nucleoli
of infected or transfected cells, presenting a particular
spotted phenotype. The RING finger domain of ICP0 is
essential for its nucleolar localization. It is described that
ICP0 and the heat-shock protein 70 co-localize with each
other in the nucleoli of infected cells during heat-shock
stress (Burch & Weller, 2004). Although the nucleolar
distribution of ICP0 partially overlaps with mRPA43, an
essential subunit of Pol I that localizes in FC, ICP0 does not
enhance Pol I activity compared to its activity on Pol II
promoters, which suggests that the function of ICP0 in the
nucleolus is still to be unravelled (Morency et al., 2005).
In addition to enhancing viral replication, nucleolar proteins
are redistributed to alter cellular pathways during infection.
For example, the redistribution of nucleolin from the
nucleolus requires HSV-1 protein ICP4 or a factor(s) whose
expression involves ICP4 (Callé et al., 2008). Apart from
ICP4, several other HSV-1 proteins have also been shown to
delocalize nucleolin. VP22 targets the nucleolus and disperses
nucleolin and chromatin (López et al., 2008). UL24 has been
reported to induce redistribution of nucleolin and B23 from
the nucleolus during HSV-1 infection, promoting nuclear
egress of nucleocapsids, possibly through its effect on the
nucleolus (Pearson et al., 2011; Lymberopoulos et al., 2011).
It has been reported that UL12 protein forms a complex with
nucleolin in HSV-1-infected cells (Balasubramanian et al.,
2010; Sagou et al., 2010). The amount of nucleolin increased
progressively during HSV-1 infection, and co-localization
between nucleolin and ICP8 was found to occur in the viral
replication compartments, suggesting that nucleolin may
take part in the HSV-1 replication process (Fig. 1). Knocking
down nucleolin by using small interfering RNA inhibited the
proliferation of HSV-1, demonstrating that viral replication
1640
Transactivate HSV-1
genes
ICP0
ICP4
ICP27
HSV-1 replication
Delocalize nucleolin
compartment
ICP4
ICP8
VP22
UL12
UL24
Unknown function
US11
ICP34.5
UL3
U58.5
Fig. 1. HSV-1 proteins target or associate with the nucleolus.
HSV-1 IE proteins ICP0, ICP4 and ICP27 targeting the nucleolus
maybe related to transactivating the expression of HSV-1 genes.
ICP4, VP22 and UL24 delocalize nucleolin from the nucleolus to
the HSV-1 replication compartment. UL12 forms complex with
nucleolin and colocalizes with ICP8 for viral replication. Other
HSV-1 proteins, for example US11, ICP34.5, UL3 and US8.5,
target to the nucleolus for as yet unknown functions.
requires a high level of nucleolin expression and nucleolar
protein plays a direct role in HSV biology (Callé et al., 2008),
contributing to efficient nuclear egress of HSV-1 nucleocapsids in infected cells.
UL12 protein is also proven to interact with the viral
single-stranded DNA-binding protein ICP8, forming a
two-subunit recombinase. UL12 protein is able to promote
strand exchange in vitro in conjunction with ICP8, contributing to viral genome replication through a homologous recombination-dependent DNA replication mechanism (Balasubramanian et al., 2010).
Recent studies demonstrated a major tegument protein of
human cytomegalovirus (HCMV), ppUL83 (pp65), located
in the nucleolus, leading to cell-cycle arrest in G1-G1/S by
HCMV and the promotion of viral infection. Simultaneously,
nucleolin has been found to interact with pp65, revealing that
pp65 might be involved in regulatory/signalling pathways
related to nucleolar functions, such as cell-cycle control
(Arcangeletti et al., 2011). In addition, nucleolin is also
involved in viral DNA synthesis in HCMV-infected cells.
During infection, the viral DNA polymerase processivity
factor UL44 could co-localize with nucleolin. Treating
HCMV-infected cells with small interfering RNA targeting
nucleolin mRNA could impair viral DNA synthesis and there
is a correlation between the efficacy of knock-down and effect
on viral replication (Strang et al., 2010). Furthermore, Kuo
et al. (2011) found that the Rta protein of Epstein–Barr virus
(EBV), a transcription factor that activates the EBV lytic
genes, interacts with MCRS2, a nucleolar protein promoting
the transcription of the rRNA gene.
Perspectives
The nucleolar proteome in humans, cows and plants has
shed light on the evolution and new function of the
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Journal of Medical Microbiology 61
Viral and host proteins localize into the nucleolus
nucleolus. Microarrays, combined with high-throughput
techniques and advanced bioinformatics tools, could be
applied to study new functions of nucleolar proteins.
Simultaneously, studies of the nucleolar proteome in
uninfected cells are relatively well advanced but the
application of these approaches to examine the role of
the nucleolus in infection is just in its infancy and could, in
turn, prove highly informative for the understanding of the
entire role of the nucleolus in the eukaryotic cell.
in comparison with non-nucleolar compartments. J Histochem
Cytochem 58, 391–403.
It has been well-recognized that, in addition to lytic
infection, herpesvirus, especially HSV-1, can establish an
infection with life-long latency and may periodically
reactivate from latency under certain conditions. As shown
in Fig. 1, the nucleolus is involved in HSV-1 replication
during lytic infection. Whether the nucleolus participates
in the establishment of latent herpesvirus infection and its
reactivation from latency still need further investigation.
Furthermore, it has been well established that the repressor
complex REST/CoREST/LSD1/HDAC plays a critical role
during the initiation of HSV-1 IE gene expression. It is
worth investigating whether the nucleolus functions in this
process during the establishment of latent infection. This
might open new avenues of research for investigation of
HSV-1 infection and its latency.
quantitative proteomics analysis of subcellular proteome localization
and changes induced by DNA damage. Mol Cell Proteomics 9, 457–470.
Birbach, A., Bailey, S. T., Ghosh, S. & Schmid, J. A. (2004). Cytosolic,
nuclear and nucleolar localization signals determine subcellular
distribution and activity of the NF-kB inducing kinase NIK. J Cell
Sci 117, 3615–3624.
Boisvert, F. M., van Koningsbruggen, S., Navascués, J. & Lamond,
A. I. (2007). The multifunctional nucleolus. Nat Rev Mol Cell Biol 8,
574–585.
Boisvert, F. M., Lam, Y. W., Lamont, D. & Lamond, A. I. (2010). A
Boulikas, T. (1993). Nuclear localization signals (NLS). Crit Rev
Eukaryot Gene Expr 3, 193–227.
Boulon, S., Westman, B. J., Hutten, S., Boisvert, F. M. & Lamond, A. I.
(2010). The nucleolus under stress. Mol Cell 40, 216–227.
Boyne, J. R. & Whitehouse, A. (2006). Nucleolar trafficking is
essential for nuclear export of intronless herpesvirus mRNA. Proc Natl
Acad Sci USA 103, 15190–15195.
Boyne, J. R. & Whitehouse, A. (2009). Nucleolar disruption impairs
Kaposi’s sarcoma-associated herpesvirus ORF57-mediated nuclear
export of intronless viral mRNAs. FEBS Lett 583, 3549–3556.
Burch, A. D. & Weller, S. K. (2004). Nuclear sequestration of cellular
chaperone and proteasomal machinery during herpes simplex virus
type 1 infection. J Virol 78, 7175–7185.
Caburet, S., Conti, C., Schurra, C., Lebofsky, R., Edelstein, S. J. &
Bensimon, A. (2005). Human ribosomal RNA gene arrays display a
broad range of palindromic structures. Genome Res 15, 1079–1085.
Acknowledgements
We apologize that the excellent studies of many other investigators
could not be included due to space constraint. I would also like to
thank members of my laboratory for helpful discussions and
comments on this manuscript. We thank the anonymous reviewers
for critical review of the manuscript.
Callé, A., Ugrinova, I., Epstein, A. L., Bouvet, P., Diaz, J. J. & Greco, A.
(2008). Nucleolin is required for an efficient herpes simplex virus type
1 infection. J Virol 82, 4762–4773.
Carmo-Fonseca, M., Mendes-Soares, L. & Campos, I. (2000). To be
or not to be in the nucleolus. Nat Cell Biol 2, E107–E112.
Carter, B. Z., Qiu, Y. H., Zhang, N., Coombes, K. R., Mak, D. H.,
Thomas, D. A., Ravandi, F., Kantarjian, H. M., Koller, E. & other
authors (2011). Expression of ARC (apoptosis repressor with caspase
References
Ahmad, Y., Boisvert, F. M., Gregor, P., Cobley, A. & Lamond, A. I.
(2009). NOPdb: Nucleolar Proteome Database – 2008 update. Nucleic
Acids Res 37 (Database issue), D181–D184.
recruitment domain), an antiapoptotic protein, is strongly prognostic
in AML. Blood 117, 780–787.
Casafont, I., Bengoechea, R., Navascués, J., Pena, E., Berciano, M. T.
& Lafarga, M. (2007). The giant fibrillar center: a nucleolar structure
analysis of the human nucleolus. Curr Biol 12, 1–11.
enriched in upstream binding factor (UBF) that appears in
transcriptionally more active sensory ganglia neurons. J Struct Biol
159, 451–461.
Andersen, J. S., Lam, Y. W., Leung, A. K., Ong, S. E., Lyon, C. E.,
Lamond, A. I. & Mann, M. (2005). Nucleolar proteome dynamics.
Catez, F., Erard, M., Schaerer-Uthurralt, N., Kindbeiter, K., Madjar,
J. J. & Diaz, J. J. (2002). Unique motif for nucleolar retention and
Andersen, J. S., Lyon, C. E., Fox, A. H., Leung, A. K., Lam, Y. W.,
Steen, H., Mann, M. & Lamond, A. I. (2002). Directed proteomic
Nature 433, 77–83.
Pearson, A., Bourget, A., Abdeljelil, N. B. & Lymberopoulos,
M. H. (2011). Role of the viral protein UL24 in nucleolar modifications
nuclear export regulated by phosphorylation. Mol Cell Biol 22, 1126–
1139.
induced by herpes simplex virus 1. BMC Proceedings 5, 102.
Cheng, G., Brett, M. E. & He, B. (2002). Signals that dictate nuclear,
nucleolar, and cytoplasmic shuttling of the c134.5 protein of herpes
Arcangeletti, M. C., Rodighiero, I., Mirandola, P., De Conto, F.,
Covan, S., Germini, D., Razin, S., Dettori, G. & Chezzi, C. (2011). Cell-
Cmarko, D., Smigova, J., Minichova, L. & Popov, A. (2008).
cycle-dependent localization of human cytomegalovirus UL83
phosphoprotein in the nucleolus and modulation of viral gene
expression in human embryo fibroblasts in vitro. J Cell Biochem 112,
307–317.
Balasubramanian, N., Bai, P., Buchek, G., Korza, G. & Weller, S. K.
(2010). Physical interaction between the herpes simplex virus type 1
exonuclease, UL12, and the DNA double-strand break-sensing MRN
complex. J Virol 84, 12504–12514.
Bártová, E., Horáková, A. H., Uhlı́rová, R., Raska, I., Galiová, G.,
Orlova, D. & Kozubek, S. (2010). Structure and epigenetics of nucleoli
http://jmm.sgmjournals.org
simplex virus type 1. J Virol 76, 9434–9445.
Nucleolus: the ribosome factory. Histol Histopathol 23, 1291–1298.
Cokol, M., Nair, R. & Rost, B. (2000). Finding nuclear localization
signals. EMBO Rep 1, 411–415.
Daelemans, D., Costes, S. V., Cho, E. H., Erwin-Cohen, R. A., Lockett, S.
& Pavlakis, G. N. (2004). In vivo HIV-1 Rev multimerization in the
nucleolus and cytoplasm identified by fluorescence resonance energy
transfer. J Biol Chem 279, 50167–50175.
Diaz, J. J., Giraud, S. & Greco, A. (2002). Alteration of ribosomal
protein maps in herpes simplex virus type 1 infection. J Chromatogr B
Analyt Technol Biomed Life Sci 771, 237–249.
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 05:11:55
1641
L. Ni, S. Wang and C. Zheng
Dimario, P. J. (2004). Cell and molecular biology of nucleolar
assembly and disassembly. Int Rev Cytol 239, 99–178.
protein UL54 reveals that its nuclear targeting is required for efficient
production of PRV. J Virol 85, 10239–10251.
Emmott, E. & Hiscox, J. A. (2009). Nucleolar targeting: the hub of the
Lindström, M. S. & Zhang, Y. (2006). B23 and ARF: friends or foes?
matter. EMBO Rep 10, 231–238.
Cell Biochem Biophys 46, 79–90.
Fankhauser, C., Izaurralde, E., Adachi, Y., Wingfield, P. & Laemmli,
U. K. (1991). Specific complex of human immunodeficiency virus
Liu, X., Liu, Z., Jang, S. W., Ma, Z., Shinmura, K., Kang, S., Dong, S.,
Chen, J., Fukasawa, K. & Ye, K. (2007). SUMOylation of
type 1 rev and nucleolar B23 proteins: dissociation by the Rev
response element. Mol Cell Biol 11, 2567–2575.
nucleophosmin/B23 regulates its subcellular localization, mediating
cell proliferation and survival. Proc Natl Acad Sci U S A 104, 9679–
9684.
Fuhrman, L. E., Goel, A. K., Smith, J., Shianna, K. V. & Aballay, A.
(2009). Nucleolar proteins suppress Caenorhabditis elegans innate
immunity by inhibiting p53/CEP-1. PLoS Genet 5, e1000657.
Gill, G. (2004). SUMO and ubiquitin in the nucleus: different
functions, similar mechanisms? Genes Dev 18, 2046–2059.
Lo, S. J., Lee, C. C. & Lai, H. J. (2006). The nucleolus: reviewing oldies
to have new understandings. Cell Res 16, 530–538.
Lohrum, M. A., Ashcroft, M., Kubbutat, M. H. & Vousden, K. H.
(2000). Identification of a cryptic nucleolar-localization signal in
Gong, L. & Yeh, E. T. (2006). Characterization of a family of nucleolar
MDM2. Nat Cell Biol 2, 179–181.
SUMO-specific proteases with preference for SUMO-2 or SUMO-3.
J Biol Chem 281, 15869–15877.
López, M. R., Schlegel, E. F., Wintersteller, S. & Blaho, J. A. (2008).
Nucleophosmin and cancer. Nat Rev Cancer 6, 493–505.
The major tegument structural protein VP22 targets areas of
dispersed nucleolin and marginalized chromatin during productive
herpes simplex virus 1 infection. Virus Res 136, 175–188.
Guo, H., Ding, Q., Lin, F., Pan, W., Lin, J. & Zheng, A. C. (2009).
Lymberopoulos, M. H. & Pearson, A. (2007). Involvement of UL24 in
Characterization of the nuclear and nucleolar localization signals of
bovine herpesvirus-1 infected cell protein 27. Virus Res 145, 312–320.
herpes-simplex-virus-1-induced dispersal of nucleolin. Virology 363,
397–409.
Haindl, M., Harasim, T., Eick, D. & Muller, S. (2008). The nucleolar
Lymberopoulos, M. H., Bourget, A., Ben Abdeljelil, N. & Pearson, A.
(2011). Involvement of the UL24 protein in herpes simplex virus 1-
Grisendi, S., Mecucci, C., Falini, B. & Pandolfi, P. P. (2006).
SUMO-specific protease SENP3 reverses SUMO modification of
nucleophosmin and is required for rRNA processing. EMBO Rep 9,
273–279.
induced dispersal of B23 and in nuclear egress. Virology 412, 341–348.
Hernandez-Verdun, D. (2006). Nucleolus: from structure to
dynamics. Histochem Cell Biol 125, 127–137.
gene US11 of herpes simplex virus type 1 are DNA-binding and
localize to the nucleoli of infected cells. J Gen Virol 68, 1921–1937.
Hernandez-Verdun, D. (2011). Assembly and disassembly of the
Mears, W. E., Lam, V. & Rice, S. A. (1995). Identification of nuclear
nucleolus during the cell cycle. Nucleus 2, 189–194.
and nucleolar localization signals in the herpes simplex virus
regulatory protein ICP27. J Virol 69, 935–947.
Hiscox, J. A. (2002). The nucleolus – a gateway to viral infection? Arch
MacLean, C. A., Rixon, F. J. & Marsden, H. S. (1987). The products of
Virol 147, 1077–1089.
Michienzi, A., Cagnon, L., Bahner, I. & Rossi, J. J. (2000). Ribozyme-
Hiscox, J. A. (2007). RNA viruses: hijacking the dynamic nucleolus.
mediated inhibition of HIV 1 suggests nucleolar trafficking of HIV-1
RNA. Proc Natl Acad Sci U S A 97, 8955–8960.
Nat Rev Microbiol 5, 119–127.
Hiscox, J. A., Whitehouse, A. & Matthews, D. A. (2010). Nucleolar
proteomics and viral infection. Proteomics 10, 4077–4086.
Kar, B., Liu, B., Zhou, Z. & Lam, Y. W. (2011). Quantitative nucleolar
proteomics reveals nuclear re-organization during stress-induced
senescence in mouse fibroblast. BMC Cell Biol 12, 33.
Kubota, S., Copeland, T. D. & Pomerantz, R. J. (1999). Nuclear and
nucleolar targeting of human ribosomal protein S25: common
features shared with HIV-1 regulatory proteins. Oncogene 18, 1503–
1514.
Kuo, C. W., Wang, W. H. & Liu, S. T. (2011). Mapping signals that are
important for nuclear and nucleolar localization in MCRS2. Mol Cells
31, 547–552.
la Cour, T., Kiemer, L., Mølgaard, A., Gupta, R., Skriver, K. & Brunak, S.
(2004). Analysis and prediction of leucine-rich nuclear export signals.
Protein Eng Des Sel 17, 527–536.
Lam, Y. W., Evans, V. C., Heesom, K. J., Lamond, A. I. & Matthews,
D. A. (2010). Proteomics analysis of the nucleolus in adenovirus-
Mongelard, F. & Bouvet, P. (2007). Nucleolin: a multiFACeTed
protein. Trends Cell Biol 17, 80–86.
Moore, H. M., Bai, B., Boisvert, F. M., Latonen, L., Rantanen, V.,
Simpson, J. C., Pepperkok, R., Lamond, A. I. & Laiho, M. (2011).
Quantitative proteomics and dynamic imaging of the nucleolus reveal
distinct responses to UV and ionizing radiation. Mol Cell Proteomics
10, (Suppl. 10) (available online).
Morency, E., Couté, Y., Thomas, J., Texier, P. & Lomonte, P. (2005).
The protein ICP0 of herpes simplex virus type 1 is targeted to nucleoli
of infected cells. Brief report. Arch Virol 150, 2387–2395.
Nicol, S. M., Causevic, M., Prescott, A. R. & Fuller-Pace, F. V. (2000).
The nuclear DEAD box RNA helicase p68 interacts with the nucleolar
protein fibrillarin and colocalizes specifically in nascent nucleoli
during telophase. Exp Cell Res 257, 272–280.
Nishida, T., Tanaka, H. & Yasuda, H. (2000). A novel mammalian
Smt3-specific isopeptidase 1 (SMT3IP1) localized in the nucleolus at
interphase. Eur J Biochem 267, 6423–6427.
infected cells. Mol Cell Proteomics 9, 117–130.
Olson, M. O. & Dundr, M. (2005). The moving parts of the nucleolus.
Leung, A. K., Gerlich, D., Miller, G., Lyon, C., Lam, Y. W., Lleres, D.,
Daigle, N., Zomerdijk, J., Ellenberg, J. & Lamond, A. I. (2004).
Pederson, T. (2011). The nucleolus. Cold Spring Harb Perspect Biol 3,
Quantitative kinetic analysis of nucleolar breakdown and reassembly
during mitosis in live human cells. J Cell Biol 166, 787–800.
Pederson, T. & Tsai, R. Y. (2009). In search of nonribosomal
Histochem Cell Biol 123, 203–216.
(part 3) (available online).
Leung, A. K., Trinkle-Mulcahy, L., Lam, Y. W., Andersen, J. S., Mann, M.
& Lamond, A. I. (2006). NOPdb: Nucleolar Proteome Database. Nucleic
Acids Res 34 (Database issue), D218–D220.
nucleolar protein function and regulation. J Cell Biol 184, 771–776.
Li, M., Wang, S., Cai, M. & Zheng, C. (2011). Identification of nuclear
Reed, M. L., Dove, B. K., Jackson, R. M., Collins, R., Brooks, G. &
Hiscox, J. A. (2006). Delineation and modelling of a nucleolar
and nucleolar localization signals of pseudorabies virus (PRV) early
1642
Raska, I., Shaw, P. J. & Cmarko, D. (2006). New insights into
nucleolar architecture and activity. Int Rev Cytol 255, 177–235.
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 05:11:55
Journal of Medical Microbiology 61
Viral and host proteins localize into the nucleolus
retention signal in the coronavirus nucleocapsid protein. Traffic 7,
833–848.
Ruggero, D. & Pandolfi, P. P. (2003). Does the ribosome translate
cancer? Nat Rev Cancer 3, 179–192.
Sagou, K., Uema, M. & Kawaguchi, Y. (2010). Nucleolin is required for
efficient nuclear egress of herpes simplex virus type 1 nucleocapsids.
J Virol 84, 2110–2121.
Siomi, H., Shida, H., Maki, M. & Hatanaka, M. (1990). Effects of a
highly basic region of human immunodeficiency virus Tat protein on
nucleolar localization. J Virol 64, 1803–1807.
Sirri, V., Urcuqui-Inchima, S., Roussel, P. & Hernandez-Verdun, D.
(2008). Nucleolus: the fascinating nuclear body. Histochem Cell Biol
129, 13–31.
Storck, S., Shukla, M., Dimitrov, S. & Bouvet, P. (2007). Functions of the
histone chaperone nucleolin in diseases. Subcell Biochem 41, 125–144.
Sasaki, M., Kawahara, K., Nishio, M., Mimori, K., Kogo, R., Hamada, K.,
Itoh, B., Wang, J., Komatsu, Y. & other authors (2011). Regulation of
Strang, B. L., Boulant, S. & Coen, D. M. (2010). Nucleolin associates with
the MDM2-P53 pathway and tumor growth by PICT1 via nucleolar
RPL11. Nat Med 17, 944–951.
the human cytomegalovirus DNA polymerase accessory subunit UL44
and is necessary for efficient viral replication. J Virol 84, 1771–1784.
Scherl, A., Couté, Y., Déon, C., Callé, A., Kindbeiter, K., Sanchez,
J. C., Greco, A., Hochstrasser, D. & Diaz, J. J. (2002). Functional
Szebeni, A., Mehrotra, B., Baumann, A., Adam, S. A., Wingfield, P. T.
& Olson, M. O. (1997). Nucleolar protein B23 stimulates nuclear
proteomic analysis of human nucleolus. Mol Biol Cell 13, 4100–4109.
import of the HIV-1 Rev protein and NLS-conjugated albumin.
Biochemistry 36, 3941–3949.
Scott, M. S., Boisvert, F. M., McDowall, M. D., Lamond, A. I. & Barton,
G. J. (2010). Characterization and prediction of protein nucleolar
localization sequences. Nucleic Acids Res 38, 7388–7399.
Scott, M. S., Troshin, P. V. & Barton, G. J. (2011). NoD: a nucleolar
localization sequence detector for eukaryotic and viral proteins. BMC
Bioinformatics 12, 317.
Tollervey, D., Lehtonen, H., Jansen, R., Kern, H. & Hurt, E. C. (1993).
Temperature-sensitive mutations demonstrate roles for yeast fibrillarin in pre-rRNA processing, pre-rRNA methylation, and ribosome
assembly. Cell 72, 443–457.
Wang, L., Ren, X. M., Xing, J. J. & Zheng, A. C. (2010). The nucleolus
and viral infection. Virol Sin 25, 151–157.
Shen, Q., Zheng, X., McNutt, M. A., Guang, L., Sun, Y., Wang, J.,
Gong, Y., Hou, L. & Zhang, B. (2009). NAT10, a nucleolar protein,
Westman, B. J. & Lamond, A. I. (2011). A role for SUMOylation in
localizes to the midbody and regulates cytokinesis and acetylation of
microtubules. Exp Cell Res 315, 1653–1667.
snoRNP biogenesis revealed by quantitative proteomics. Nucleus 2,
30–37.
Sheng, Z., Lewis, J. A. & Chirico, W. J. (2004). Nuclear and nucleolar
Xing, J., Wu, F., Pan, W. & Zheng, C. (2010). Molecular anatomy of
localization of 18-kDa fibroblast growth factor-2 is controlled by Cterminal signals. J Biol Chem 279, 40153–40160.
subcellular localization of HSV-1 tegument protein US11 in living
cells. Virus Res 153, 71–81.
Simpson, J. C., Neubrand, V. E., Wiemann, S. & Pepperkok, R.
(2001). Illuminating the human genome. Histochem Cell Biol 115, 23–
Zolotukhin, A. S. & Felber, B. K. (1999). Nucleoporins nup98 and
29.
http://jmm.sgmjournals.org
nup214 participate in nuclear export of human immunodeficiency
virus type 1 Rev. J Virol 73, 120–127.
Downloaded from www.microbiologyresearch.org by
IP: 88.99.165.207
On: Fri, 16 Jun 2017 05:11:55
1643