14. Adenovirus 1 Flashcards
what happens when adenovirus is injected in rodents?
causes cancer
does adenovirus cause cancer in humans? why?
no –> virus kills cells and we have immune response against it
is adenovirus enveloped?
no
describe the shape and size of adenovirus
icosahedral with fibres sticking out –> 90nm in diameter
3 characteristics of the genome
- dsDNA
- 35-45 kb
- linear
what is the family name of adenoviruses?
adenoviridae
what genus of adenoviridae infect humans?
Mastadenovirus
who are most at risk for adenovirus?
military recruits, boarding schools, infants
how many adenovirus types are there? how many infect humans?
> 100 adenovirus types identified, 50 infect humans
what are 3 types of diseases caused by adenovirus?
- Respiratory infection
- Conjunctivitis
- Gastrointestinal infection
which 2 types of adenovirus cause the most severe cases of respiratory illness
4 and 7
where does adenovirus replicate in the cell? how do we know?
in nucleus
can detect inclusion bodies in nucleus
how does the virus life cycle progress in 16h?
once the virus enters, can make 10,000 copies in 16h
what does adenovirus induce in human kidney tissue culture cells?
cytopathic effects (CPE)
How can we purify adenovirus?
with CsCl density gradient
gives us specific band
what is the biggest and most abundant viral protein?
hexon protein
describe the placement of hexon
in the capsid, has 6 other copies around it
besides hexon, what is the other major capsid protein?
penton
describe the placement of penton
associated with fibre protein
what is within the capsid?
a core that holds the genome
what is the role of VII protein?
acts as histones, surrounding DNA
what is the role of VI protein?
associates the outer hexon/penton structure with the core
discovery of what part of the genome won a nobel prize?
splicing! –> mRNAs look different than genome
why does the adenovirus life cycle cause cancer?
infects upper respiratory tract where cells aren’t dividing and forces cells to replicate so it can replicate its genome –> forces them to become cancer
how did scientists find that adenovirus uses splicing?
annealed the genome with mRNA –> pieces of genomic DNA were looped out –> these are introns that are spliced out
what are the 2 unique features on the end of the adenovirus genome?
- terminal protein
- nucleotide repeat
describe the terminal protein
covalently linked to 5’ end via phosphodiester link
describe the nucleotide repeats
they are complementary, can fold back on itself
how does adenovirus enter cells?
virus enters epithelium via microlesions and binds Coxsackie B virus and Adenovirus Receptor (CAR) and breaks epithelial layer
what are CAR receptors used for normally?
used in cell-cell adhesion in tight junctions
describe the 6 stages of the virus from cell entry to nuclear entry
- fibres bind CAR
- penton binds integron
- enters as coated vesicle
- enters endosome and capsid is broken down
- travels thru cytoplasmic via microtubules
- imports DNA into nucleus via nuclear pore complex
what happens to the virus in the endosome?
endosome acidifies and activates protease to break protein VI and release the core
what is the first gene transcribed? what is its role?
E1A –> transcription factor
what genes does E1A turn on?
E1B, E2, E3, E4
what are the 2 types of E1A protein?
- 289R
- 243R
what is the difference btwn 289R and 243R?
289R has conserved region 3 (CR3)
describe CR3
- 2 functions
- binds DNA so E1A can increase activity TATA box binding protein
- binds DNA so E1A can increase activity of cell cycle promoters
what is the similarity and difference in function between 289R and 243R?
similarity: both very oncogenic
difference: without CR3, E1A cannot turn on E1B, E2, E3, E4
what is E2F?
activates S phase genes
3 examples of S phase genes:
- DNA pol
- nucleotide synthesis enzymes
- cyclins required for progression thru cell cycle
how does E1A affect E2F?
ACTIVATES transcription
describe how E1A activates E2F transcription
normally Rb binds E2F to repress S phase genes when cells not dividing
but E1A binds and sequesters Rb so E2F can be active to activate S phase and E2 genes
how is E2F transcription normally activated when the cell wants to divide?
Cdk cell cycle protein phosphorylates Rb so E2F is free
why is Rb such an important molecule?
it is the decision point between G1 and S phase –> past this point, the cell must commit to replication
what are the 3 functional domains of E1A in both 289R and 243R?
- N
- CR1
- CR2
what 2 proteins interact with N and CR1 domain?
- p300
- CBP
what type of protein are p300 and CBP? and their 2 roles
Histone acetyltransferases (HAT)
stimulate transcription for:
1. stimulating viral gene expression
2. allow cells to stay in differentiated state
what happens with E1A binds p300 and CBP?
E1A inhibits cell differentiation thru binding p300/CBP
How does E1A inhibit cell differentiation by binding p300/CBP?
p300 and CBP acetylate histones which relaxes the histone/DNA complex formation –> this allows increased gene expression for cell differentiation and allows cell cycle arrest
but when E1A binds p300 and CBP, cell differentiation is inhibited and cell can continue proliferating
