Polyomaviruses Flashcards
What family is polyomaviruses part of?
Polyomaviridae
Do polyomaviruses have envelopes?
No
Describe the virion of polyomaviruses?
Non-enveloped, 40-45nm, icosahedral
Polyomaviruses: What direction in DNA replication?
Bidirectional from a. Unique origin of replication
How many proteins are encoded in polyomaviruses?
5-9 viral proteins
What is the host range for polyomaviruses?
Mammals, birds, fish
PyV: Early and late transcripts are encoded on ___ DNA strands
Opposite
What is the link between SV40 and the vaccine?
Early batches of polyomyelitis vaccine were contaminated with SV40
Does SV40 cause cancer in rodents, monkeys, and humans?
Monkeys: replicates in kidneys without disease
Rodents: cancer in laboratory conditions
Humans: SV40 found in some cancers but no clear evidence of causal relationship
True or false: SV40 can be lytic and lysogenic
True
Infection in permissive cells: new virions and cell lysis
Abortive infection in non-permissive cells: result in transformation of cells
SV40: What is needed for cells to transform?
Expression of LTAg and STAg
What are the two PyVs identified?
BKPyV and JcPyV
How do BKPyV and JCPyV affect healthy children?
Primary infection
Causing mild illness
Through oral route
Describe latent infection of BKPyV and JCPyV and location
Establish life-long latency in immune privileged sites like the proximal renal tubes. 80-90% of people persistently infected
No disease during latency
When do JCPyV and BKPyV reactivate
Upon immunosuppression
Leads to productive lytic replication
BKPyV reactivating in common in …
Kidney transplant patients
BKPyV: lytic viral replication can result in …
Acute kidney injury, PVAN, and allograft loss
Haemorrhagic cystitis in bone marrow transplant patients
What is PVAN?
Polyomavirus-associated nephropathy
What are early symptoms of BKPyV?
Appearance of virus in urine (viruria) and blood (viremia)
What is the only treatment for PVAN?
Reduction of immunosuppression
What is a clear sign of BKPyV?
Immunohistochemical detection of LTAg
What is PML?
Progressive multi focal leukoencephalopathy
PML is caused by …
JCPyV
What is PML?
Demyelination disease of the CNS
Leads to progressive destruction of the white matter of the brain
PML is seen in…
AIDS patients, and multiple sclerosis patients treated with natalizumab (anti-integrin mAb drug)
How does JCPyV reach the brain?
Infecting B cells (leukocytes)
Productive replication of JCPyV in ____, the myelinated cells of the CNS, leads to their ____ and to _____
Oligodendrocytes
Lysis
PML
The JCPyV ___ is rearranged in PML, by deletions/duplication of DNA sequence blocks. The non-rearranged JCPyV is known as ____ and the rearranged ones as ____
NCRR
Archetype
Prototype
What are the four PyVs associated with cancer?
BKPyV, JCPyV, MCPyV, TSPyV
What is the only PyV identified as a human carcinogen?
MCPyV
What is MCC?
Merkel cell carcinoma
Rare and aggressive skin cancer
80% cases caused by MCPyV
What are Merkel cells?
Neuroendocrine cells at the base of the epidermis
Close to nerve endings and sense light touch
What are the two aberrant events that contribute to MCC?
Integration of viral genome into host DNA
Truncation/mutations in LTAg that impairs its DNA replication activity but keeps its transforming activity
What does LTAg do in MCPyV?
Inhibits pRb
Cooperates with STAg to transform Merkel cells into MCC cells
___ transcribes polyomavirus genome?
Host RNA pol II
What does the early region of the polyomavirus encode?
Alternatively spliced LTAg and STAg
What does the late region of the polyomavirus genome encode for?
Capsid proteins VP1, VP2, and VP3
The non-coding regulatory/control region (NCRR or NCCR) in a polyomavirus contains…
Early and late promoters
The origin of viral DNA replication (ori)
How do we determine a new species of polyomavirus?
LTAg sequence differs by more than 15% to known species
How many genera and species are there in polyomaviruses?
More than 100 species
6 genera (alpha, beta, delta, gamma, zeta)
SV40 is part of which genus and species?
Beta
Macaca mulatta polyomavirus 1
What genus is species does MPyV belong to?
Alpha
Mus musculus polyomavirus 1
BKPyV is part of which genus and species?
Beta
Human polyomavirus 1
What is LTAg in polyomavirus?
Oncogene
Involved in cellular proliferation (entry in S phase) and transformation
Hexamer is DNA helicase needed for viral DNA replication
Transcription factor that regulates the switch from early to late gene transcription
How does LTAg promote cellular proliferation and transformation?
Interacting with host proteins
- Hsc70 chaperone via the J-domain
-pRb and related family members p107 and p130, via the LxCxE motif. These interactions release active E2F to promote S-phase entry
-p53, via the helicase/p53-binding domain. Prevents apoptosis
What is the domain structure of SV40 LTAg?
JD: J-domain: binds to host HSc70 chaperone and stimulates its activity
LxCxE/pRb: Rb-binding motif. Binds host pRb, p107 and p130
NLS: Nuclear localization signal: interacts with host importing
OBD: Origin-binding domain. Binds to sites in the origin of DNA replication
Helicase/p53: Domain with DNA helicase activity and domain that binds to host p53
HR: Host range region
What is needed for the transformation activity of LTAg?
N-terminal region: JD, LxCxE/Rb-binding motif
Sometimes p-53 binding domain needed
The only viral protein required for genome replication in PyV is…
LTAg
Describe the structure and function of STAg.
Shares an N-terminal J-domain with LTAg (overlapping coding sequence)
Helps LTAg, can’t transform cells by itself except for in MCPyV
Activates expression of genes needed for S phase entry and progression.
Activity of STAg depends on its interaction with host phosphatase PP2A.
Active form of PP2A consists of a heterotrimer
STAg replaces the substrate-targeting B subunit, inactivating the enzyme
Describe icosahedral symmetry of PyV
T=7 icosahedral symmetry
72 pentamers of VP1 (12 pentamers with 5 neighbours, 60 pentamers with 6 neighbours)
Important: PyV: Pentamers interact via the C-terminal portion of VP1 and are further stabilized by ….
Pentamers interact via the C-terminal portion of VP1 and are further stabilized by calcium ions and disulfide bonds between them
SV40 entry: SV40 binds to ____ which triggers _____. SV40 moves to ____ and is targeted to the _____. Then enters into the _____ and then moves to _____. Genome is released for transcription and translation
GM1 gangliosides
Caveolae-dependent endocytosis
Endosomes
ER
Cytosol
Nucleus
What are the attachment factors commonly used by polyomaviruses?
All PyV use sialic acid-containing receptors for attachment
Glycosaminoglycans
Integrity
Gangliosides
What are sialic acid-containing receptors?
Glycoproteins or glycolipids with attached mono or oligosaccharides and terminal sialic residues
What are glycosaminoglycans?
Contain repeating disaccharides and are attached to the polysaccharide sugar core by link proteins
What are integrins?
Heterodimeric proteins comprised of alpha and beta chains
Contain beta propeller domain, thigh and calf domain, and epidermal growth factor binding domains
What are gangliosides?
Glycosphingolipids with ceramide embedded in the membrane and an oligosaccharide chain with one or more sialic acids
May also contain a terminal sialic acid
____ is the only PyV that uses clathrin-mediated endocytosis
JCPyV
SV40, MPyV, and MCPyV use ____ endocytosis and or ____ to enter the cell. JCPyV and BKPyV may also use ____ to enter cells.
Caveolin-mediated endocytosis
Non-clathrin/non-caveolin lipid raft uptake mechanisms
Extracellular vesicles
What attaches to the ganglioside receptor for PyV?
VP1
PyV vesicle translocates to the ER through…
Microtubules
In the ER, the PyV virion’s capsid structure is destabilized by…
Host disulfide isomerases
In the cytoplasm, the PyV virion loses VP1 due to…
Low calcium conditions of the cytosol
