Lecture 9 - Retroviruses and HIV

Question 1

The reason retroviruses mutate so frequently is because the _____ _____ enzyme they use for replication is highly error prone. In order for their genes to be transcribed, they have to integrate into the host genome, which may cause gene ______ (incorporation of host genes into replicated virus.)

Answer 1

Reverse Transcriptase

Transduction

Question 2

Of the oncogenic retroviruses only _____retroviruses (Human T-lymphotrophic viruses) cause cancer in humans.

Answer 2

Deltaretroviruses

Question 3

Retrovirus virion structure contains a _____ protein and surface _____ in its envelope. It also contains a _____ layer, which lies just below and is attached to the envelope. Within the virion, there is a protease, ____ transcriptase, and an _____.

Answer 3

Transmembrane protein

Surface Glycoprotein

Matrix

Reverse transcriptase

Integrase

Question 4

Retrovirus genomes consist of ____ copies of _____ sense RNA. The RNA consists of at least 3 open reading frames that produce polyproteins: ____ (encodes structural proteins), ____ (encodes enzymatic proteins), _____ (encodes envelope/glycoproteins proteins.) The virus also brings with it host ____ that anneal to the 5’ end of its genome to prime the reverse transcriptase reaction.

Answer 4

2 copies

Positive

Gag

Pol

Env

t-RNA

Question 5

Note: viral protease has 2 functions:

1. cleave ______ in the cytosol of host cells to make individual protein products.
2. Aid in ______ of the virus once it buds off from host cell. Until this occurs, the newly budded virus is NOT infectious.

Answer 5

Polyproteins

Maturation

Question 6

While HIV uses CD4 and a co-receptor for cell adhesion, MLV uses a more ubiquitous basic ______ transporter, and GALV uses a ______ transporter.

Answer 6

Amino Acid

Phosphate

Question 7

The reverse transcriptase enzyme retroviruses bring with them can be found in the capsid. It has 3 distinct functions:

1. RNA-dependent ____ polymerase activity
2. DNA-dependent _____ polymerase activity
3. _____ H (destroys the original RNA genome.)

The reverse transcriptase enzyme adds long terminal _____ to the dsDNA it makes, which are necessary for _____ into host genome.

Answer 7

RNA-dependent DNA polymerase

DNA-dependent DNA polymerase

RNAse H

Repeats

Integration

Question 8

Retroviral genome transcription once integrated into the host genome is dependent on the formation of a transcription complex at the 5’ end. The complex consists of a host RNA ____ II, host _____ factors, and viral ____ factors.

Answer 8

RNA Pol II

Transcription

Transcription

Question 9

While retroviruses regulate gene expression via protease activity on polyproteins, they also regulate gene expression via alternative _____ of _____.

Answer 9

Splicing

RNA

Question 10

Keep in mind that ____ polyproteins are cleaved by ____ proteases (Furin) in the golgi rather than viral proteases, whereas gag and pol polyproteins are the opposite.

Answer 10

Env

Host proteases

Question 11

Viral oncogenes (v-Onc) are oncogenes that have become incorporated into _____ genomes (transduction.)

Answer 11

Retroviral genomes

Question 12

Overexpression of viral oncogenes is characteristic of Acute ______ Retroviruses (i.e. RSV-alpharetrovirus.) They are considered Acute because tumors form very rapidly from this mechanism.

Answer 12

Acute Transforming Retroviruses

Question 13

Chronic Transforming Retroviruses promote oncogenesis via KO of host _____ _____ genes or via activation of host ___-oncogenes (by integrating such that the ____-oncogene is under control of viral promoter.) Chronic transforming Retroviruses do NOT bring oncogenes with them.

Answer 13

Tumor Suppressor

Proto-oncogene

Proto-oncogene

Question 14

HTLV-1 is the only retrovirus linked to _____ in humans. It is associated with a rare type of ____ T-cell leukemia, but can sometimes give rise to lymphoma. It’s endemic to parts of Japan, Caribbean, and West Africa. Transmission is through _____, sexual intercourse, and ____ ____. Keep in mind the incubation period is around 25-35 years.

Answer 14

Cancer

Cutaneous T-cell leukemia

Blood, sexual intercourse, Breast Milk

Question 15

Microscopic presentation of HTLV-1 induced cancer shows characteristic ____+/____+ “flower cells” (nucleus appears to have petals.) Macroscopic presentation includes skin lesions, hyper_____, lytic bone lesions, and immunosuppression.

Answer 15

CD4+/CD25+

Hypercalcemia

Question 16

HTLV-1 encodes a transcription factor _____ which can trans-activate proto-oncogenes or bind ___ and/or ____ (sequestering and inactivating them.)

Answer 16

Tax

p53

Rb

Question 17

HIV is considered a _______virus. These viruses can actually infect post-mitotic cells because they bring with them a _____ protein that complexes with the Integrase and carries the dsDNA into the nucleus. It’s life cycle is characteristic of retroviruses, except that it activates ______ in T-cells (causes their death via this mech, NOT through replicative lysis.)

Answer 17

Lentivirus

VPR protein

Apoptosis

Question 18

Unique to HIV is the large number (6) of ______ proteins it encodes.

1. ____ is an early gene product that promotes more rapid/efficient elongation via RNA Pol II.
2. ____ binds RPE-intron and activates nuclear export of unspliced or incompletely spliced viral RNAs (ensures availability of new genomes for packaging.)
3. ____ binds CD4 and ____ class I molecules, causing their internalization, thus allowing the cell to evade Cytotoxic T-cells.
4. ____ binds to ____ as it’s being made to replace what was internalized/degraded from the cell surface, and marks it for degradation.
5. ____ targets APOBEC (prevents it from being packaged into virions), which normally interferes with Reverse Transcriptase activity.
6. ____ promotes entry pf pre-integration complex into nucleus and can cause G2 ccell cycle arrest (which is good for viral replication because promoter is more active in this phase.)

Answer 18

TAT (binds CDK9)

Rev

Nef

MHC class I

Vpu

CD4

Vif

Vpr

Question 19

______ interacts with CD4 and and co-receptors on target cells (CXCR4 on naive, activated, and memory T-cells OR CCR5 on activated T-cells, Memory cells, macrophages, and dendritic cells.)

Answer 19

GP120

Question 20

HIV can be transmitted sexually from male to female through free ____ or through infected cells passed in the semen. The virus invades the _____ or _____ epithelium in the female.

Answer 20

Virus

Cervical or Vaginal epithelium

Question 21

_____ delta 32 is a plymorphism in HIV co-receptors present in about 1% of caucasians that confers resistance to ____ strains of HIV.

Answer 21

CCR5 delta 32

R5

Question 22

HAART is a combination therapy for HIV that uses ____ antiviral drugs. 2 are usually _____ RT inhibitors, and the third can be any one of the following:
Protease inhibitor
Integrase inhibitor
Non-nucleoside RT inhibitor.

Answer 22

3

Nucleoside RT inhibitors

Question 23

PrEP and PEP are two methods for prevention of HIV infection. PrEP (Truvada) uses 2 ____ RT inhibitors and is given prophylactically to high risk groups. PEP is just 28 day HAART treatment using 2 ____ RT inhibitors and an _____ inhibitor within ____ hrs of exposure.

Answer 23

Nucleoside RT inhibitors (NRTIs)

NRTIs

Integrase inhibitor

72hrs