Transcript Polyomaviridae

Polyomaviridae
Molecular Virology
Introduction
• Group I：ds DNA virus
• Family: Polyomaviridae
• Genus: Polyomavirus
– Diameter: 40-50nm(small)
– Cubic symmetry (icosahedral)
– no envelope
– Genome size:5kbs
– eg. SV40, may cause tumors
Introduction
• potentially oncogenic (tumor-causing)
• persist as latent infections without causing
disease
• They may produce tumors in a host of a
different species, or a host with an
ineffective immune system
• The name polyoma refers to the viruses'
ability to produce multiple (poly-) tumors (oma)
Introduction
• Polyomaviruses have been extensively studied as
tumor viruses in humans and animals, leading to
fundamental insights into carcinogenesis, DNA
replication and protein processing.
• The tumor suppressor molecule p53 was discovered,
for example, as a cellular protein bound by the major
oncoprotein (cancer-causing protein)
• T antigen made by Simian vacuolating virus 40
(SV40).
Taxonomy
• Simian virus 40 (SV-40)
（ REFERENCE STRAIN ）
• Common Type
BK polyomavirus (BKPyV)
JC polyomavirus (JCPyV)
Bovine polyomavirus (BPyV)
Murine polyomavirus (MPyV)
Taxonomy
• Murine polyomviruswas
the first polyomavirus
discovered by Ludwik
Gross in 1953.
• Mammals and birds
GROSS L (June 1953). Society for Experimental
Biology and Medicine 83 (2): 414–21.
Classification
JCV則可能會在免疫低下或缺陷的病人引發進
行性多灶性白質腦病(progressive multifocal
leukoencephalopathy，PML)
是一種神經髓鞘剝落的病症，有很高的死亡率
皮膚的神經內分泌癌症—一般稱為默克細胞癌(Merkel
cell carcinoma)
BKV引起的病變--移植腎臟的間質性腎炎，可能導致腎功能受損或喪
失，稱為BKV nephropathy
默克細胞癌是罕見但侵犯快速的癌症
BKV nephropathy臨床上並不常見，盛行率約1.5-5.0%，通常發生在
這種皮膚癌的發生率在過去20年增加3倍，每年約有1,500案例
腎移植後第一年（因此時的免疫抑制最強）
BKV nephropathy也常合併輸尿管阻塞、淋巴積液、細菌性泌尿道感
常見於年長者和免疫功能不佳者，如AIDS或者服用免疫抑制藥物者
染、血尿及全身性CMV感染。
發生惡性默克細胞癌的病患，約有半數活不到9個月
默克細胞多瘤病毒是另外一種可以增加對癌症的了解的模式
Classification
Human Polyomaviruses
JCV and BKV
first isolated in 1971 (JCV-brain tissue of patient with progressive
multifocal leukoencephalopathy (PML)
BKV from urine of renal transplant patient
Epidemiology:
BKV first acquired by age 3-4
JCV by age 10-14
60-80% of adults are seropositive for both
in pre-HIV era PML was seen in older adults
with hematologic malignancies
now seen in ~5% of HIV/AIDS patients
Classification
•
Polyomaviruses are divided into three major
genetically-related groups
Pérez-Losada M, Christensen RG, McClellan DA, et al. (June 2006). "Comparing phylogenetic
codivergence between polyomaviruses and their hosts". Journal of Virology 80 (12): 5663–9.
Molecular biology
• VIRION
成熟的病毒外殼是由72個五倍體病毒殼粒(pentameric capsomeres)所組成
每一個病毒殼體由360個 VP1(monomer) 所組成，每5個VP1分子形成一個次殼體 (五聚體)
(capsomere/pentamer) 的構造，在 BK 病毒中共有72個 pentamer，為主要的外殼蛋白(major
capsid protein) ，大小為45 kD，約佔成熟病毒外殼的80%
VP2及VP3為次要蛋白(minor capsid protein)，會與病毒的基因纏繞包裹於病毒顆粒之中，大小
分別為35kD及25kD，約各佔成熟病毒外殼的10%
Cell Receptor
• SV-40: Gangliosides
JCPyV: terminal alpha(2,6)-linked sialic
acids
• BFPyV and MPyV: alpha(2,3)-linked sialic
acids
Polyomavirus的receptor為sialic acid醣類而非proteins
Polyomavirus需要蛋白質coreceptor才能順利感染
coreceptor包括MHC-1 (SV40)、α4β1 integrin (mPyV)或血清素receptor (JCV)
polyomavirus感染細胞的方式：
連結帶有sialic acid的coreceptor (或未知的真正receptor?)之後
virus被帶引到coreceptor而結合
這樣的結合強化了細胞的內吞作用而進入到細胞質內，反向地經過內質網而進入到
細胞核
CELL RECEPTOR (S)
Genome
• Circular dsDNA about 5 kb in size
• associated with cellular histones in a chromatin-like
complex
• genomes divided into two regions, early and late
• Early proteins
LT, MT and sT antigens expressed
from differentially spliced mRNAs
• Late, capsid proteins
VP1, VP2 and VP3 (viral capsid)
• BKV and JCV : 75%
(nucleotide sequence Homology)
• 70% with SV40
Replication of DNA Viruses
1
Virus replication
1. Cellular receptors for polyomaviruses
are sialic acid residues of gangliosides.
The attachment is mediated by viral
protein 1 (VP1) via the sialic acid
attachment region.
2. Virus is endocytosed into vesicles in the
host cell
3. Virion transits through endoplasmic
reticulum where host protein disulfide
isomerases rearrange its capsid
structure
3.1 Export of misfolded virion to the
cytoplasm
3.2 Loss of VP1 in the low-calcium
conditions of the cytosol
4- 5. Import of genomic DNA into host
nucleus. Then by an unknown mechanism
the virus is exported to the nucleus
Virus replication
6-9. Transcription of early genes (LT and sT
genes)
•
Early gene expression is responsible for
the synthesis of non-structural proteins.
•
The role of the non-structural proteins
is to regulate the cellular mechanisms
and gene expression.
•
Close to the N terminal end of
polyomavirus genome are enhancer
elements which induce activation and
transcription of a molecule known as the
T-antigen.
•
Early mRNA’s, encoding T-antigen are
produced by host RNA polymerase II.
•
T-antigen autoregulates early mRNA’s,
subsequently leading to elevated levels
of T-antigen.
•
At high concentrations of LT-antigen,
triggering the late phase of viral
infection to begin.
6. & 10. Replication of the DNA genome in the nucleus
Virus replication
10. Genome replication acts to separate
the early and late phase gene
expression.
• The duplicated viral genome is
synthesised and processed as if it were
cellular DNA
• As the daughter viral DNA are
synthesised they associate with cellular
nucleosomes to form structures that
are often referred to as
"minichromosomes“
• In this manner the DNA is packaged
more efficiently.
Virus replication
10-14. Transcription of late genes
encoding for structural proteins
(VP1, VP2 and VP3)
• Late gene expression synthesises the
structural proteins, responsible for
the viral particle composition.
• This occurs during and after genome
replication.
• late gene expression generates an
array of proteins as a result of
alternative splicing.
Virus replication
15. Assembly of new virions in the
nucleus
• Within each viral protein are 'nuclear
localization signals' which cause the
viral proteins to amass in the nucleus.
• Assembly of new virus particles
consequently occurs within the
nucleus of the host cell
Virus replication
16. Virions are released by lysis of the cell.
• Release of newly synthesized
polyomavirus particles exit the infected
cell by one of two mechanisms.
• Firstly and less commonly, they are
transported in cytoplasmic vacuoles to the
plasma membrane, where budding occurs.
• More frequently, they are released when
the cell lyses due to the cytotoxicity of
virus particles present in the infected cell.
The large T-Antigen
• The large T-antigen plays a key role :
1. in regulating the viral life cycle by binding to the viral origin of DNA
replication where it promotes DNA synthesis.
2. replicate the host cell needs to be in s-phase for this to begin
3. modulates cellular signaling pathways
• This is achieved by a two prong attack of inhibiting tumor suppressing
genes p53 and members of the retinoblastoma (pRB) family
• Stimulating cell growth pathways by binding cellular DNA, ATPase-helicase,
DNA polymerase α association, and binding of transcription preinitiation
complex factors.
• This abnormal stimulation of the cell cycle is a powerful force for
oncogenic transformation.
•T-antigen also binds and inactivates tumor
suppressor proteins (p53, p105).
•This causes the cells to leave G1 phase and
enter into S phase, which promotes DNA
replication.
The large T-Antigen
SV40 effects in different cellular environments
Infection of permissive
cells results in cell death
and virion production.
SV40 infection of rodent
cells induces S-phase but
does not result in cell
death or virus production.
Integration of viral DNA occurs in a
very low percentage of nonpermissive
cells, which then become stably
transformed
The Middle T-Antigen
• The Polyoma Middle T-Antigen is used
in animal like the where it is coupled
to the MMTV promoter.
• There it functions as an oncogene,
while the tissue where the tumor
develops is determined by the MMTV
promoter.
The small T-Antigen
• The small T-antigen protein is also able
to activate several cellular pathways
which stimulate cell proliferation.
• Such as the mitogen-activated protein
kinase (MAPK) pathway, and the stressactivated protein kinase (SAPK)
pathway.
Polyomavirus Infection
1. Capable of causing tumors in animals and
humans
2. Can cause other diseases
3. BK and JC viruses are endemic worldwide
4. Infection outcome depends on the individual’s
immune system
•
•
Normal immune systems tend to prevent latent
infections
Compromised immune systems allow latent
infections to become established in the kidneys
Polyomavirus Infection
• All the polyomaviruses are highly common
childhood and young adult infections.
• Most of these infections appear to cause little or
no symptoms.
• These viruses are probably life-long persistent
among almost all adults.
• Diseases caused by human polyomavirus
infections are most common among persons
who become immunosuppressed by AIDS, old
age or after transplantation and include Merkel
cell carcinoma, PML and .
Polyomavirus Infection
Reactivation events are different between the
BK and JC viruses
•
BK virus
– Potentially severe urinary tract infections can develop
•
JC virus
– Can cause progressive multifocal
leukoencephalopathy
» Viruses infect and kill the white matter of the CNS
» Paralysis and death eventually result
PML
focal neurological defects due to
demyelination
parieto-occipital brain involvement associated
with muscle weakness, gait disturbance,
speech defect, or visual blind spot
H&E staining of PML brain biopsy; black
cerebellum involvement associated with
broadlegged gait and imbalance
Diagnosis:
CT or MRI
lumbar puncture for JCV PCR
Treatment:
none, except for highly active antiretroviral
therapy( HAART) in AIDS patients
arrows point out some of the reactive
astrocytes; blue arrow points toward an
oligodendrocyte nucleus which has been
markedly enlarged with viral particles, giving
it a magenta color
BK nephropathy:
no evidence that BKV causes
disease in the immune competent
population
possible route of infection through
contaminated food or water or
respiratory spread
remains latent in lymphocytes,
urogenital tract, and brain but may
be reactivated if the host becomes
immunocompromised.
viral inclusions and cellular changes
in BK nephropathy are seen in tubular
epithelium of a renal transplant case
especially associated with disease in renal transplant patients;
thought to cause graft failure in 2-5% of this population
treatment is to decrease immunosuppression as much as possible
without causing rejection
Cidofovir appears to reduce BKV-associated nephropathy
Polyomavirus Infection
• Two recently discovered (2007/2010)
polyomaviruses, KI (Karolinska Institute) and
WU (Washington University) viruses, are
closely related to each other and have been
isolated from respiratory secretions and skin
secretions.
• In January 2008, a new virus, Merkel cell
polyoma virus was described and shown to
cause most Merkel skin cancer.
Polyomavirus Infection
• In March, 2011, a ninth polyoma virus
HPyV9, related to a monkey lymphotropic
virus (LPV) was cultured from the blood of
immunosuppressed patients.
Diagnosis
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