Adenovirus (Dr. Frappier) Flashcards
Discoveries from adenovirus
i) 1st human virus shown to induce cancer
ii) alternative RNA splicing
Types of adenovirus
one for mammals, one for birds
components of capsid
hexon, penton
what is found in penton
a base + projecting fibre
feature of genetic material
linear ds DNA
+ terminal protein attached to 5’ ends
+ inverted terminal repeats
What is VII in virion core similar to?
histone
What is the function of VII?
protect genome from being recognized by host DNA damage response
What is found in virion core?
linear dsDNA
4 proteins (V, VII, X, terminal protein)
where does terminal protein attach to?
5’ end of each viral DNA strand
What cell receptor is responsible for entry of adenovirus?
CAR (coxsackievirus and adenovirus receptor)
How does virion enter nucleus?
using hexons to interact with microtubules
(too big to get in thru pores)
Describe the steps for adenovirus entry
i) knob at end of fibre on penton bind CAR
ii) penton base bind integrin on surface
–> endocytosis
iii) virion released from endosome into cytoplasm (acidification)
iv) virion move to nucleus thru interactions between hexon and microtubules
v) virion disassembled at nuclear pore
–> DNA enter nucleus
Components of genes expressed by adenovirus
i) 6 early transcription units
ii) 2 intermediate transcription units
iii) 1 late transcription unit
iv) VA genes
After RNA splicing, how much mRNA is formed from late transcription unit?
5 (L1 to L5)
Features of L1 to L5
all have tripartite leader sequence added to them
What is VA gene transcribed by?
RNA pol III
Function of VA genes
act as microRNA
Function of early gene expression
i) induce host cells to enter S phase
ii) Defense against antiviral defense of host
iii) make viral proteins needed for DNA replication
Which gene is first expressed in adenovirus?
E1A
Which early genes help induce host cell to enter S phase?
E1A, E1B, E4
Which early genes help protect infected cells from antiviral defense of host?
E1A,B, E3,E4, VA RNA
which early genes make viral proteins needed for DNA replication?
E2 transcript
what cellular proteins do E1A interact with?
i) pRb
ii) p300, CBP histone acetyltransferase (add acetyl grp to histone tails)
iii) TBP (TATA binding protein)
What happens when E1A binds to pRb?
i) pRb dissociate from E2F
—> E2F activate expression of viral and cellular genes (e.g. viral E2) that move to S phase
ii) recruit pRb to promoter of antiviral genes –> turn them off
What happens if acetyl group is added to histone tail?
allow TFs to access the DNA
enzymes that add acetyl group to histone tail
histone acetyltransferase (HAT)
What happens after E1A binds to p300, CBP?
i) E1A associate with promoters of cell cycle
ii) recruit p300/CBP to them
–> promote transcription
–> lower histone acetylation in promoters unrelated to E1A
What happens after E1A bind TBP?
E1A stimulate transcription by binding of TBP
–> increased expression of early viral genes
Target of E1B
one form: p53
another form: pretends to be Bcl2
What happens after E1B bind p53?
i) block transcriptional activation of cell cycle inhibitors
–> induce cell cycle
ii) form complex with E4 (ubiquitin ligase)
–> degrade p53
–> lower p53 level –> prevent apoptosis
What happens after E1B mimics Bcl2
it inhibits apoptosis by associating with mitochondrial membranes
Function of E3
- affect expression of cell surface receptor
- inhibit secretion of proinflammatory stuff
–> help infected cell acoid destruction by immune system
Function of E4
i) form ubiqutin ligase with E1B –> degrade p53
ii) promote chromatin change at p53 controlled promoters (prevent p53 binding)
iii) prevent DNA repair pathways from ligating adenovirus genomes
iv) reorganize PML bodies into track like structures
What is the function of PML bodies?
apoptosis, p53 activation, DNA repair
viral proteins needed for DNA replication
i) pTP (preterminal protein)
ii) DNA pol
iii) ssDNA binding protein (DBP)
cellular proteins needed for DNA replication of adenovirus
NFI, NFII, NFIII
What is the origin of replication in adenovirus?
inverted terminal repeats at either end of genome
What can u find in the origin of replication?
i) binding site for pTP, DNA pol complex
ii) binding site for NFI, II
What is the primer for DNA replication in adenovirus?
dCMP (3’OH help extend DNA)
Describe steps in DNA replication of adenovirus
i) pTP/Pol complex, NFI, III bind to origin
ii) dCMP covalently link to pTP
iii) dCMP hybridize to DNA template (3’OH as primer)
iv） after NFI, III leave + 2 more nts made
–> pTP shift back to end of DNA
v) nucleotide chain extends until one strand is copied
vi) displaced ssDNA used as template to make dsDNA
proteins needed to extend one entire nucleotide chain
DNA pol,, DBP, NFII
What happens to the displaced ssDNA?
able to form panhandle with inverted terminal repeats
–> can repeat the same replication stepsW
When is pTP cleaved?
packaging of DNA into virions and converted into TP
What recognizes tripartite leader sequence?
complex from E4, E1B
How are cellular gene expression inhibited by adenovirus?
i) blocking the export of cellular mRNA to cytoplasm
ii) prefer translating viral mRNA over cellular ones
How does adenovirus block the export of cellular mRNA?
using E1B/E4 complex
–> bind tripartite leader sequence on viral mRNA + transport out of nucleus
–> relocalize cellular proteins needed for transport to adenovirus replication (not available for cellular mRNA)
What is targeted in cells to give preference to viral mRNA translation for adenovirus?
i) cellular protein kinase R (PKR)
ii) cellular translation factor EIF4F (helicase)
How is PKR inhibited?
adeno VA RNA bind to PKR (prevent activation)
–> protect only translation of viral mRNA
What is the function of cellular PKR
after activated in adenovirus infection
–> phosphorylate translation factor
–> inactivate translation of viral mRNA
What inhibits eIF4F?
L4 inactivates it
What happens after eIF4F is inhibited?
i) stop cellular mRNA translation
ii) viral one continue with presence of tripartite leader sequence
Why can viral translation continue after eIF4F is inhibited?
hv tripartite leader sequence
–> ribosome can find AUG without scanning
What is ribosome shunting?
finding AUG on mRNA without scanning
what is viral precursor cleaved to form mature proteins?
L3
where are hexon and pentons assembled?
cytoplasm
Describe steps in virus assembly of adenovirus
i) hexon, pentons assembled in cytoplasm
ii) hexon, penton transported to nucleus + assembled into capsid
iii) viral DNA insert in capsid starting from packaging sequence
iv) viral precursors cleaved by L3
v) virions released from cells
where does viral DNA start inserting into capsid?
packaging sequence
what is involved in virion release of adenovirus?
i) cleave cytoskeleton components
– promote cell lysis
ii) accumulate E3 late in infection –> cause cell lysis
iii) apoptosis induced by E4 accumulated
How long can adenovirus stay in host after initial infection?
for years
Where does most adenovirus replicate in?
respiratory epithelium
Vaccines for adenovirus?
type 4,7 (only for military)
antiviral specific to adenovirus?
nope
symptoms for adenovirus
i) pneumonia
ii) conjunctivitis
iii) kidney infection
