Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
162 Cards in this Set
- Front
- Back
|
Who discovered the first retrovirus?
|
Peyton Rous
Rous sarcoma virus |
|
|
Who discovered reverse transcriptase?
|
Temin & Baltimore
|
|
|
Who developed the Rous-sarcoma virus oncogene hypothesis?
|
Bishop & Varmus
|
|
|
Who discovered HTLV-1?
|
Robert Gallo
|
|
|
Who discovered HIV-1?
|
Montagnier & Gallo
1983 |
|
|
What is the name of a recent retrovirus discovered in 2007? What can it cause?
|
XMRV
prostate cancer potentially chronic fatigue syndrome |
|
|
What are the old classifications of retroviruses?
|
Oncoviruses (cancer)
Lentiviruses (HIV) Spumaviruses (foamy, human endogenous retroviruses) |
|
|
What are the new classifications of retroviruses?
|
alpha
beta gamma delta epsilon lenti spuma |
|
|
How big are retroviruses?
|
100nm
|
|
|
What are the two Env proteins?
|
SU (gp120)
TM (gp41) |
|
|
What are the 3 Gag proteins?
|
MA (p17)
CA (p24) NC |
|
|
What are the 3 Pol proteins?
|
PR (p9)
RT (p66) IN (p32) |
|
|
What form is the genome of retroviruses in?
|
(+) ssRNA
5' cap poly(A) tail 2 copies (diploid) bound at 5' end (U5) in kissing loop tRNA bound to PBS |
|
|
How big is the genome of retroviruses?
|
7-10kb
|
|
|
What do the 5' and 3' untranslated regions do?
|
reverse transcrition
integration modified to become a transcriptinal enhancer |
|
|
Describe the 5' and 3' regions:
|
R----U5----PBS
ppt----U3----R |
|
|
What are the steps of a retrovirus life cycle (early phase)?
|
1. binding
2. fusion 3. penetration/entry 4. reverse transcription 5. transport 6. integration |
|
|
What are the steop of a retrovirus life cycle (late phase)?
|
1. transcription
2. assembly 3. budding 4. maturation |
|
|
Which retroviruses enter by pH-independent binding?
|
HIV-1
HTLV-1 |
|
|
Which retroviruses are pH-dependent?
|
MLV
FV |
|
|
Describe entry of HIV-1:
|
-gp120 binds CD4 (conformational change)
-gp41 binds CCR5/CXCR4 (conformational change) -gp41, expose, inserts into PM and forms a hairpin structure -membranes fuse |
|
|
How does the retrovirus core transform following entry?
|
-CORE
-RTC (reverse transcriptase complex) -PIC (pre-integration complex) |
|
|
What two main events occur during reverse transcription?
|
-generation of dsDNA from ssRNA
-LTRs are generated |
|
|
What kind of activity does RT have?
|
-RNA-dep.-DNA-pol.
-DNA-dep.-DNA-pol. -RNAse H activity |
|
|
Which way does RT transcribe?
|
5'--->3'
|
|
|
Where is the tRNA bound to (+) ssRNA of the retrovirus?
|
PBS
|
|
|
Where does RT first bind?
|
to 3' OH end of tRNA
|
|
|
What does RT synthesize first?
|
(-) strand strong stop
|
|
|
Before the first template exchange, what does RNAse H remove?
|
R and U5 at 5' end of (+) ssRNA
|
|
|
In the first template exchange what jumps, to where?
|
New R'---U5' DNA jumps to R at 3' end of RNA
|
|
|
After the synthesis of the first full strand of (-) DNA, RNAse H digests all the remaining (+) ssRNA except...:
|
ppt region
|
|
|
What makes up the (+) strong stop DNA?
|
U3--R--U5--PBS
|
|
|
What jumps where in the second template exchange?
|
U3-R-U5-PBS jumps to PBS of 3' end of (-) ssDNA
|
|
|
Describe the two LTRs of the RTC:
|
U3--R---U5
U3--R--U5 |
|
|
Which 2 subunits make up RT?
|
p66 (catalytic)
p51 (non-catalytic) |
|
|
Which of the subunits has RNAse H activity?
|
p66
|
|
|
Why are so many mutations generated from reverse transcription?
|
RT has no exonuclease activity (no proofreading)
|
|
|
Which retrovirses can enter terminally differentiated cells?
|
HIV-1
HTLV-1 |
|
|
How is the RTC converted to a PIC?
|
breakdown of outer core complex
trafficking to nucleus |
|
|
Does intergration of the PIC occur at random?
|
No!!
preferentially in actively expressed genes or CpG islands |
|
|
What 2 elements does integration require?
|
1. integrase
2. cellular DNA repair machinery |
|
|
Characterize the HIV-1 integrase:
|
32kDA protein
acts as a dimer or tetramer |
|
|
What end of the the PIC complex are cleaved?
|
3' ends (LTRs)
|
|
|
What kind of overhands are generated in the host-chromosome?
|
5'
|
|
|
Besides integrates, which enzymes are required for integration?
|
host repair enzymes
|
|
|
What happens to cellular material during integration?
|
duplication of 4-6NTs
|
|
|
What are 2 ways in which cells can be infected by retroviruses?
|
-replication of rv genome during cell division so daughter cells are infected
-beginning of rv late phase to produce infectious virions |
|
|
What part of the integrated rv genome serves as the promoter(s)?
|
LTR
|
|
|
What part of the LTR do transcription factors bind?
|
U3 region
|
|
|
What transcription factors are there in HTLV-1?
|
Tax (viral)
CREB/ATF (cellular) |
|
|
What transcription factors are there in MMTV?
|
GRE (glucocorticoid response element)
|
|
|
What transcription factors are there in HIV-1?
|
NFAT
NF-kB Sp1 ---->T-cell specific transcription factors |
|
|
Which enzyme transcribes the integrated viral DNA?
|
cellular DNA pol. II
|
|
|
What is "promoter interference"?
|
When the pol. II dislodges TFs bound to the 3' LTR
|
|
|
What allows termination of transcription?
|
3' poly(A) tail
termination sequence |
|
|
Are transcribed + processed mRNA and the RNA genome distinguishable?
|
no!!
|
|
|
How does the viral genome generate more than one protein product?
|
alternative splicing
frameshift |
|
|
What two main mRNA products are produced in all retroviruses?
|
Gag-Pol (full genome)
Env (1 splice site) |
|
|
How is fully spliced mRNA exported?
|
by cellular exportin proteins
|
|
|
How is full-length mRNA exported in simple retroviruses?
|
CTE (constitutive transport elemen) embedded in mRNA
|
|
|
How is full-length mRNA exported in complex retroviruses?
|
auxiliary proteins
e.g. HIV-1 (Rev), HTLV-1 (Rex) |
|
|
If HIV-1 did not have any Rev, what would happen?
|
full-length mRNA could not be exported from the nucleus
|
|
|
What is the expression method of the Gag-Pol polypeptide used by complex retroviruses?
|
ribosomal frameshift
|
|
|
What are the requirements for ribosomal frameshift?
|
-slippery heptamer sequence (oligo-U/oligo-A)
-hairpin structure (ribosome stalk) |
|
|
Which retroviruses perform a single frameshift?
|
-alpha
-lenti |
|
|
Which retroviruses perform two frameshifts?
|
-beta
-delta |
|
|
How often is Gag-Pol produced (from slip-back)?
|
10%
|
|
|
What is the expression method of the Gag-Pol polypeptide used by simple retroviruses?
|
translational readthrough
|
|
|
What are the requirements for translational readthrough?
|
-purine-rich sequences
-pseudo-knot structure |
|
|
How often does translational readthrough to produce Gag-Pol occur?
|
5-10%
|
|
|
Why do retroviruses need less Gag-Pol than Gag?
|
Pol = enzymatic
Gag = structural |
|
|
What part of the Env polypeptide is the signal peptide?
|
first few aas
|
|
|
How is the Env polyprotein processed in the ER?
|
-heavily glycosylated
-folded -oligemirized |
|
|
How is the Env polypeptide processed in the Golgi?
|
cleaved to SU and TM
|
|
|
How is TM inserted into the membrane?
|
after cleavage, it's NH3-terminus is hydrophobic
|
|
|
What binds to the RNA genome?
|
NC region of Gag (psi sequence)
|
|
|
Why is the full-genome the only RNA to contain the psi sequence?
|
so only full-length RNA is packaged
|
|
|
Which tRNA is incorporated into HIV-1?
|
lysine
|
|
|
Are auxiliary proteins packaged?
|
sometimes
|
|
|
When and how does maturation occur?
|
after budding
PR cleaves polyproteins to individual proteins |
|
|
Why is PR a good anti-viral target?
|
no cleavage ---> non-functional virus
|
|
|
What are 3 ways a cell can be transformed by a retrovirus?
|
1. acquire a mutated cellular gene
2. code for a viral oncogene 3. insertion near a proto-oncogene |
|
|
Name 4 retroviruses that 'steal' cellular oncogenes?
|
RSV
Rev-T AMV E26 |
|
|
Which gene is stolen by RSV?
|
mutated Src (inserted in Env)
it is always activated |
|
|
What pathways are turned on by Src?
|
-growth-factor-induced mitogenesis
-promotion of G1/S phase -survival -migration (metastasis...) |
|
|
What kind of transformation does RSV acquire?
|
acute (very rapidly transformed)
|
|
|
Which gene is stolen by Rev-T?
|
mutated Rel (member of NF-kB family)
|
|
|
What kind of cells are transformed by Rev-T?
|
those of hematopoietic lineage
|
|
|
Where is Rel inserted in Rev-T?
|
Pol-Env regions (virus is replication-defective)
|
|
|
Which gene is stolen by both AMV and E26?
|
Myb
|
|
|
What does AMV cause?
|
acute leukemia in chickens
|
|
|
What does E26 cause?
|
acute erythroblastosis
|
|
|
What happens to Myb in AMV?
|
constitutively active (loses part of regulatory region)
|
|
|
What happens to Myb in E26?
|
fusion protein with Ets to create a cellular oncogene
|
|
|
What are the three types of transforming retroviruses?
|
-Non-defective
-Replcation defective -Replication non-defective |
|
|
Name a retrovirus that is non-defective:
|
RSV
|
|
|
What is a helper virus?
|
helps a relication-defective transforming retrovirus replicate
|
|
|
What is a helper virus of RSV?
|
RAV
|
|
|
What is a helper virus of AMV?
|
MAV-1, MAV-2
|
|
|
Give an example of a virus that produces a viral oncogene:
|
HTLV-1 produces Tax
|
|
|
How does Tax transform T-lymphocytes?
|
Tax promotes constutive activation of NF-kB and AP-1
|
|
|
Is transformation by Tax fast or slow?
|
very slow...only 2-5% get cancer after 30-40 years
|
|
|
Give an example of a retrovirus that transforms a cell through insertion near a proto-oncogene:
|
MMTV
|
|
|
What are the 3 ways MMTV can transform cells?
|
1. loss of 5' LTR leads to transcription from 3' LTR (new promoter)
2. 3' LTR acts as an enhancer for expression of oncogene 3. Provirus integration disrupts expression of a tumor-suppressor gene |
|
|
What are some advantages of using retroviruses for gene therapy?
|
-permanent insertion of new gene
-easy to modify genome in vitro -simple |
|
|
What are some disadvantages of using retroviruses for gene therapy?
|
-random integration site
-recombination with other viruses |
|
|
What must retroviruses for gene therapy be?
|
replication-defective!!
|
|
|
Did retrovirus gene therapy succeed in correcting SCID?
|
yes
|
|
|
What went wrong?
|
leukemia -- non-radom integration in promoter element...
|
|
|
What percentage of the human genome consists of endogenous retroviruses?
|
8%
|
|
|
What are some positive functions of retroviruses?
|
-placenta formation
-immunosuppression in pregnancy |
|
|
What are some potential negative functions of endogenous retroviruses?
|
multiple sclerosis
schizophrenia certain types of cancer... |
|
|
Who discovered the Human T-cell leukemia virus?
|
Robert Gallo, 1980
|
|
|
What two diseases are caused by HTLV-1?
|
Adult T cell Leukemia
Tropical Spastic Paraparesis (HAM) |
|
|
What gene of the virus is an oncogene?
|
Tax
|
|
|
What part of the world is there a large presence of Human T-cell leukemia?
|
Southern Japan
|
|
|
What part of the world is tropical spastic paraparesis present in?
|
South America
South Africa |
|
|
How can HTLV-1 be transmitted?
|
-breast milk
-pregnancy -blood -sexual contact |
|
|
How many people in the world are estimated to be infected with HTLV-1?
|
15-20 million
|
|
|
What accessory proteins are made by HTLV-1?
|
Rex
Tax |
|
|
What purpose does Tax serve for the virus, and where does it bind?
|
-upregulates transcription
-binds to TREs in U3 in 5' LTR |
|
|
What are the 3 mRNAs transcribed of the HTLV-1 genome?
|
-gag/prt/pol full genome
-env singly-spliced -tax/rex doubly-spliced |
|
|
How many frameshifts are required to transcribe the full RNA genome?
|
2
|
|
|
What does Rex do?
|
Binds to full and singly-spliced RNA for export to nucleus
|
|
|
Are Tax and Rex coded in the same ORF?
|
no!
|
|
|
Name some ways in which Tax causes cellular transformation:
|
-activates cellular TFs
-IL-2 actocrine loop -induction of G1/S transition -inhibit DNA repair mechanisms |
|
|
What occurs after HTLV-1 infection that leads to ATL?
|
IL-2 dependent growth phase
(polyclonal T cell proliferation) IL-2 independent growth phase (monoclonal leukemic T cells) |
|
|
How can leukemic T-cells be distinguished under a microscope?
|
hyper-lobulated (flower-cell)
|
|
|
Name some cellular TFs to which Tax binds:
|
-CREB
-CBP -NF-kB dimerization domain |
|
|
What does activation of gene expression by Tax involve?
|
-activating Txn factor/cAMP response/element binding proteins (ATF/CREB)
-CREB binding proteins -NF-kB -Serum Response Factor |
|
|
How does Tax affect TXN factors?
|
-increase interaction with one another
-increase affinity with DNA to turn on transcription -increase amouth of transcription and nuclear translation |
|
|
What gene expression is controlled by NF-kB?
|
-immune cell activation
-control of apoptosis -anti-viral/anti-microbial responses -viral gene expression |
|
|
What virus has encorporated NF-kB binding sites into its genome?
|
HIV-1 (binding sites in LTR)
|
|
|
What are 2 ways Tax can activate NF-kB?
|
-associate with NF-kB DBD directly
-associate with IKK complex, phosphorylate IkB so it is degraded |
|
|
What genes are regulated by Tax?
|
cytokines
receptors surface proteins oncogene products growth factors |
|
|
What viral element interacts with Tax?
|
ATF/CREB (LTR transcription)
|
|
|
What percentage of people infected with HTLV-1 will develop leukemia?
|
2.5%
|
|
|
How long does is take for ATL do develop?
|
decades
|
|
|
What is the main manifestation of ATL?
|
abnormal and elevated lymphocytes
|
|
|
What are the 4 phases of ATL?
|
1. Smoldering
2. Chronic 3. Lymphoma 4. Acute |
|
|
When is ATL usually diagnosed?
|
Lymphoma/Acute
|
|
|
How long does the acute stage last?
|
6 months
|
|
|
What is an experimental treatment for ATL?
|
AZT + interferon
|
|
|
What is the main manifestation of HAM?
|
infiltration of HTLV-1 infected cells into the spinal cord
|
|
|
What are the 3 mechanisms of HAM pathogenesis?
|
1. autoimmune
2. direct infection 3. bystander damage |
|
|
Is HAM chronic or acute?
|
chronic
|
|
|
Is ATL chronic or acute?
|
acute
|
|
|
What is the goal of gene therapy?
|
To replace a defective gene by stably introducing a correct copy
|
|
|
Name 5 gene therapy strategies:
|
1. apoptosis-related gene
2. p53 tumor suppressor gene 3. dominant negative protein 4. immunomodulatory protein 5. toxin (drug delivery system) |
|
|
What is a virus commonly used for gene theray?
|
VSV (vesicular stomatitis virus)
|
|
|
What is retroviral pseudotyping?
|
substituting the retroviral Env glycoprotein for a one with a broader range of cellular receptors
|
|
|
What is the receptor for VSV?
|
G protein (sialic acid)...common
|
|
|
What are 3 ways to deliver a gene via gene therapy?
|
1. ex vivo
2. in situ 3. in vivo |
|
|
What are 4 limitations of gene therapy?
|
1. efficient delivery
2. transduction of non-dividing cells 3. long term gene expression 4. cost effective manufacturing |
|
|
What is an oncolytic virus?
|
a virus designed to kill tumour cells, but not normal cells
|
|
|
What is the TI of oncolytic viruses?
|
10 000:1!!!
|
|
|
What are some requirements of an oncolytic virus?
|
-not pathogenic
-no neutralizing Abs -sensitive to anti-viral response (IFN) -strictly cytoplasmic replication -no integration step -genetically stable -easily modified by recombinant technique -grows to high titer in culture |
|
|
In which types of tumours does oncolytic therapy work well?
|
solid tumours
|
|
|
Why do malignant cancer cells respond to VSV oncolytic therapy?
|
actively dividing
less IFN/anti-viral response |
|
|
What are 4 mechanisms of oncolysis?
|
1. direct viral-induced apoptosis
2. indirect apoptosis caused by cytokine release 3. shutdown of tumour vasculature 4. adaptive response against tumour antigens... |
|
|
What therapy is effective when combined with oncolytic viral methods?
|
HDIs (histone deacetylase inhibitors)
|
|
|
What is it hypothesized that HDIs do to aid oncolytic therapy?
|
inhibition of innate immune response in tumour cells (IFN, etc...)
|
