HIV

Question 1

What would happen to the virus if tat was inhibited?

Answer 1

It would be unable to transcribe structural proteins

Question 2

What is the function of the LTR’s in viral RNA?

Answer 2

They serve as RNA pol II promoters once the viral nucleic acid is integrated into host DNA

Question 3

What has been associated with mutated nef?

Answer 3

Patients don’t develop full-blown AIDS

Question 4

I’m doing these quickly…

Answer 4

Sorry if they suck.

Question 5

What is targeted by drugs in order to prevent the “absolutely obligatory” step in viral replication?

Answer 5

Reverse transcriptase

Question 6

What is a provirus?

Answer 6

Virus that has integrated it’s DNA intermediate to the host DNA

*resembles a normal gene

Question 7

Name a cell (reservoir) in which HIV virus can integrate and “hide out” for decades.

Answer 7

Resting T cells

Question 8

Enzyme necessary for virus integration

Answer 8

Integrase

Question 9

What is notable about HIVs requirements for integration into the host DNA?

Answer 9

Cell does not need to be actively dividing (can be a terminally differentiated cell)

Question 10

Describe the early phase of HIV gene expression (3)

Answer 10

1. No transcription of the integrated provirus
2. Occurs during long, latency periods
3. Expresses low levels of proteins necessary for virus to persist

Question 11

Describe the late phase of HIV gene expression

Answer 11

1. Structural proteins synthesized (high levels)
2. tat turns weak promoter into strong promoter (binds TAR)
3. rev allows transport of unspliced mRNAs from nucleus (usually have to be spliced to leave nucleus)

Question 12

Where does HIV assembly occur?

Answer 12

Host plasma mem

Question 13

What is necessary for HIV budding?

Answer 13

Host cell’s ubiquitin ligases

Question 14

What enzyme is responsible for “maturation” cleavage of core proteins? What would happen if it was inhibited?

Answer 14

viral protease

inhibition = release of a non-infectious virus

Question 15

What is generated by the dimerization of gag-pol?

Answer 15

active protease

Question 16

Family and subfamily of HIV

Answer 16

Retroviridae

Lentivirus

Question 17

Which is more pathogenic: HIV1 or HIV2?

Answer 17

HIV1

Question 18

What are 2 ways in which HIV1 is subdivided, based on distribution?

Answer 18

1. M (major) vs O (outlier)
2. “clades” or genetic subtypes (determined by gag/envelope sequences)

(for example HIV1-M, Clade B)

Question 19

What are 2 ways in which HIV1 is subdivided, based on cellular features?

Answer 19

1. Chemokine co-receptor utilization
   CXCR4 + CCR5
2. Syncytium-inducing capability

Question 20

CXCR4 is __-tropic, while CCR5 is __-tropic

Answer 20

CXCR4 (T-tropic); CCR5 (M-tropic)

• M = on macrophages
• T = on Tcells (and other cells)

Question 21

How many copies of RNA are in the inner HIV capsid?

Answer 21

2 (survival advantage; RNA mutates a lot)

Question 22

Name 3 proteins (+function) that are involved in the HIV envelope.

Answer 22

p24 = capsid protein (forms cylindrical core of envelope)
gp120 = receptor binding
gp41 = membrane fusion activity

Question 23

3 enzymes that are common drug targets:

Answer 23

reverse transcriptase
protease
integrase
(these are all required for replication; they are originally one protein that is cleaved)

Question 24

Accessory protein that transports mRNA

Answer 24

rev

Question 25

What structures are involved in virus entry and replication?

Answer 25

1. CD4 and gp120 bind (gp120 undergoes a conf change to bring the cells closer) 2. gp120 binds to a chemokine receptor (CCR5, CXCR4, etc) 3. Eventually gp41 is activated, resulting in fusion

Question 26

RNA is converted into a _____, _sDNA molecule.

Answer 26

linear, double (this has to happen)

Question 27

(Review slide) Summary of Key Points:

Answer 27

1. Infections are characterized by lifelong persistence (can integrate and evade) 2. High mutation rate (changes in tropism; undergoes selection) 3. Variation is disease presentation (inf, development of cancers, wasting, etc) 4. Variation in time to disease onset 5. Stages: Acute, Latent (asymptomatic), Symptomatic (AIDS)

Question 28

3 Routes of Transmission

Answer 28

1. Direct sexual contact (50%M, 50%F) 2. Blood and blood products (mostly IV drug users these days) 3. Perinatal transmission (more HIV+ mothers taking AZT has improved the rates)

Question 29

Fluids that contain viruses (top 3):

Answer 29

Semen Cervical secretions Breast milk (less in Urine, Saliva, Tears, Cerebrospinal fluid--mostly because it needs to be in cells)

Question 30

What are the 3 stages of infection? (brief description included)

Answer 30

1. acute: flu-like symptoms occur ~3-6wks while the virus infects T cells and macrophages (big immune response) 2. asymptomatic: virus is latent, but stil replicating at high levels--CD4 cell #'s rebound 3. symptomatic: occurs when CD4 count drops dramatically, immune dysfunction = patient susceptible to opportunistic infections + AIDS-related cancers

Question 31

2 criteria used for predicting disease progression: | *high yield

Answer 31

1. CD4+ T cell count (lower = faster progression) 2. viral load (high = faster AIDS onset) *note: prior to drop in CD4, pts lose CD8 due to CD4-related immune dysfunction (less prolif of Tcells and IL2)

Question 32

3 determinants of HIV resistance:

Answer 32

1. Specific MHC-I allele 5-10% do not progress to clinical disease 2. CCR5 mutation (del = premature stop) homozygous = "resistant" heteozygous = slower disease progression 3. Nef-deletion mutation

Question 33

Once symptomatic HIV infection is diagnosed, survival is ~___ years

Answer 33

2

Question 34

WHat mutation increases HIV susceptibility?

Answer 34

loss of a cell-surface protein; same mutation makes Africans resistant to malaria

Question 35

6 Dx Tests: | this is probably not very high yield, according to objectives

Answer 35

1. Dipstick: saliva, blood, serum 2. ELISA: assay for p24 3. Western: confirms ELISA = antibody tests 4. PCR: detects viral DNA 5. RT-PCR: quantifies viral RNA in plasma 6. branched DNA: detects viral RNA and DNA = nucleic acid tests to determine the amount of virus

Question 36

What drug disrupts DNA chain elongation synthesis?

Answer 36

nuc analog reverse transcriptase inhibitors (bind to RT)

Question 37

WHat drug binds adjacent to the nucTP pocket and inhibits synthesis of provirus DNA?

Answer 37

Non-nucleoside reverse transcriptase inhibitors

Question 38

What drugs bind to active site on the protease and prevents gag-pol cleavage?

Answer 38

Protease Inhibitors

Question 39

What drugs bind to gp41 and prevents membrane fusion?

Answer 39

``` Entry Inhibitors (one new drug is a CCR5 antagonist) ```

Question 40

What drugs inhibit strand transfer of viral DNA to host cell DNA?

Answer 40

Integrase Inhibitor (final step in integration)

Question 41

T/F: A resistance mutant can arise in a week.

Answer 41

T (give a cocktail of drugs; if you have to change them, don't just change 1--change all and don't "just add" a drug)