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CMD Block 2 > Oncogenic Viruses > Flashcards

Oncogenic Viruses Flashcards

1
Q

What percentage of human cancers are caused by viruses?

A

15-20%

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2
Q

Viruses are the leading cause of what 2 types of cancer?

A

liver

cervical

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3
Q

How do viruses cause cancer?

A

Altering the control of cell proliferation:

  1. Activate signaling pathways to stimulate constitutive growth
  2. Release cell cycle control, which allows uncontrolled growth
  3. Infected cell destruction/clearance leads to unplanned regeneration
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4
Q

Who is most likely to be affected by a virus-caused cancer?

A

immunocompromised patients

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5
Q

T/F: In order for a virus to replicate in a host, cancer cells must be produced.

A

F: cancer is simply a side effect of the viral infection

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6
Q

What cancer-related process is an alternative to viral lytic replication?

A

cell transformation (cancer induction)

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7
Q

Malignant tumors are (more/less) likely to yield viruses.

A

less

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8
Q

Why is the presence of viral genome in a tumor cell not sufficient evidence that it was the causative agent?

A
  1. it may be coincidentally located in a typical site of replication
  2. assay could have been contaminated
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9
Q

Epidemiologic criteria to be considered a cancer-causing virus:

A

a. Coincident geographic distribution of infection and cancer
b. Higher incidence of viral markers in cancer cases vs control references
c. Viral markers should precede cancer
d. Reduction in infection rates should reduce cancer

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10
Q

Virologic criteria to be considered a cancer-causing virus:

A

a. Virus should transform cells in vitro
b. Virus genome present in tumor but not normal cells
c. Tumor induction in experimental animals

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11
Q

6 known human cancer viruses

A
  1. Human T-lymphotropic virus type 1
  2. Human Herpesvirus 8
  3. Epsterin-Barr
  4. HPV
  5. Hep B virus
  6. Hep C virus
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12
Q

3 Viruses known to transform cells or cause tumors in animals.

A
  1. adenovirus
  2. polyomavirus
  3. poxvirus
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13
Q

What are properties of immortalized cells in culture?

A

Retain original properties but grow indefinitely

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14
Q

What are properties of transformed cells in culture?

A

Immortalized but lose many growth properties, such as:

  1. Reduced need for serum growth factors
  2. Loss of contact inhibition
  3. Do not need to be anchored
  4. Round morphology
  5. May cause tumors when introduced to appropriate animal
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15
Q

What makes it possible for RNA tumor viruses to cause cancer without killing hosts?

A

V-oncogene

derived from cellular oncogenes or protooncogenes

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16
Q

From where are v-oncogenes derived?

A

likely, ancestor picked up from host during replication

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17
Q

3 classifications of retroviruses

A

transducing
nontransducing
nontransducing, long latency

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18
Q

What type of retrovirus?

Contain v-oncogene, related to c-oncogene

A

Transducing

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19
Q

What type of retrovirus?

Low (<5%) rate of tumor formation

A

Nontransducing, long latency

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20
Q

What type of retrovirus?

No v-oncogene, but can activate c-oncogene via integration

A

Nontransducing

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21
Q

What type of retrovirus?

100% rate of tumor formation

A

Transducing

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22
Q

What type of retrovirus?

High rate of tumor formation, but not 100%

A

Nontransducing

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23
Q

What type of retrovirus?

Rapid tumor formation (days)

A

Transducing

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24
Q

What type of retrovirus?

Months or years to tumor formation

A

Nontransducing, long latency

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25
Q

What type of retrovirus?

Intermediate time to tumor (weeks to months)

A

Nontransducing

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26
Q

What type of retrovirus?

Rous sarcoma virus

A

Transducing

27
Q

What type of retrovirus?

Contains a v-oncogene unrelated to c-oncogenes

A

Nontransducing, long latency

28
Q

What types of viruses can induce transformation by activation of signaling pathways?

A

both DNA and RNA tumor viruses

29
Q

2 possible results of transformation by activation of signaling pathways

A
  1. increase/dysregulation in kinase
    (phosphorylation) cascades which increase gene expression related to cell division
  2. upregulation of gene expression by the introduction of new transcription factors
30
Q

How do transducing retroviruses affect host cell processes?

A

Carry v-oncogenes that control signal

transduction related to cell growth/regulation

31
Q

What host proteins are affected by transducing retroviruses?

A 
tyrosine kinases
tyrosine kinase growth factor receptors
Ser/Thr kinases
transcription factors 
hormone receptors 
G proteins
32
Q

How do v-oncogenes differ from c-oncogenes, and what is the result of this?

A

v-oncogenes are always active (constitutive)

results in loss of signaling control and inappropriate growth

33
Q

T/F: All transducing retroviruses cause cancer in humans.

A

F: no examples exist

34
Q

How do nontransducing retroviruses operate?

A

insertional activation

  1. part/whole genome randomly inserts into host chromosome
  2. Strong promoters or transcriptional enhancers in virus genome lead to unregulated overexpression of nearby concogenes
35
Q

Nontransducing tumors are _____-clonal

A

mono

36
Q

Why is there an intermediate-to-long lag time for tumor induction in nontransducing tumors?

A

integration events next to c-oncogenes and the subsequent alterations resulting in increased expression are rare

37
Q

T/F: HTLV-1 is the only human example of a long latency retrovirus leading to cancer.

A

T

Causes adult T cell leukemia and lymphoma (ATL), an aggressive/fatal non-Hodgkin’s lymphoma

38
Q

How HTLV-1 induce cancer?

A

Once it infects, it transforms CD4+ T cells:
a. Expresses an oncogene, Tax

b. Tax stimulates Ikk complex to cause IkB
degradation

c. IkB degradation frees NF-kB to direct transcription in the nucleus of T cells
d. Dysregulation of NF-kB function leads to immortalization and subsequent transformation of the T cells

39
Q

Where does latent Epstein-Barr virus reside?

A

in B cells

causes Burkitt’s lymphoma, Hodgkin’s, post-transplantion lymphoma, nasopharyngeal carcinoma

40
Q

Epstein Barr virus is a (DNA/RNA) virus

A

DNA

41
Q

How does Epstein Barr virus infection lead to cell immortilization?

A

Virally encoded Latency membrane protein-1 (LMP-1) activates a kinase cascade that localizes NF-kB to the nucleus in B-cells, leading to immortalization

42
Q

What does Epstein Barr virus encode?

A

multispanning transmembrane protein
that is similar to normal plasma membrane proteins, except it functions independent of ligand
THUS is it ALWAYS active

43
Q

What 3 conditions are caused by Human herpesvirus 8 (KSHV)?

A
  1. Kaposi’s sarcoma (lymphatic endothelial cancer)
  2. Pleural effusion lymphoma (non-Hodgkin’s body cavity lymphoma)
  3. Castleman’s disease (lymph node tumors, not strictly a cancer)
44
Q

KSHV encodes several potential oncogenes involved in signaling, including:

A
  1. Cytokine and chemokine homologues (stimulate transformation)
  2. vGPCR (constitutively active due to amino acid substitutions; induces growth and transformation)
45
Q

What type of virus is Simian virus 40 (SV40)?

A

[DNA] polyomavirus

46
Q

SV40 encodes:

A

2 versions of a “T” (transforming) antigen:

  1. Large (LT) antigen
  2. Small (sT) antigen
47
Q

How does sT cause uncontrolled cell division?

A
  1. Antigen binds/inactivates 2A phosphatase (a Ser/Thr phosphatase) that is abundant in cells
  2. This increases the halflife of phosphorylation events, which results in longer kinase cascades

(Longer kinase cascades = uncontrolled cell division)

48
Q

How does SV40 ultimately cause uncontrolled cell division?

A

SV40 sustains kinase cascades longer

49
Q

How does LT cause uncontrolled cell division?

A

LT inhibits the negative regulation of the cell cycle by:
1. Binds/inactivates Rb protein
–This induces E2f-dependent transcription
and cell division
2. Binds/inactivates p53
–Prevents apoptosis

50
Q

DNA tumor viruses inactivate:

A

tumor suppressor genes

Note: this is a side effect–not something needed for viral replication

51
Q

How does HPV affect permissive cells?

A

undergoes lytic replication in them

52
Q

How does HPV affect non-permissive cells?

A

transforms them, no replication in them

53
Q

Low risk forms of HPV cause:

A

warts (benign tumors)

54
Q

High risk forms of HPV cause:

A

cervical cancer
penile cancer
oral cavity/throat cancers

55
Q

HPV is closely related to:

A

SV40

56
Q

Explain how HPV drives formation of metastatic tumors.

A

In metastatic tumors, HPV is integrated into the genome.

  1. Integration disrupts expression of E2 (viral regulatory gene, dampens E6/E7 expression)
  2. No E2 = high level expression of E6/E7
  3. E6 binds and degrades p53
  4. E7 binds and inactivates Rb
57
Q

What is E2?

A

a vira; regulatory gene that functions in decreasing E6/E7 expression

58
Q

What does E6 do?

A

bind/degrade p53

59
Q

What does E7 do?

A

bind/inactivate Rb

60
Q

What does KSHV alter?

A

Cell signaling

Cell cycle control

61
Q

What is v-cyclin?

A

KSHV-produced cyclin homologue, that binds/activates cyclin-dependent kinase 6

  1. This complex is not inhibited by Cdk inhibitors
  2. Cell cycle progresses rather than being regulated
62
Q

What causes hepatocellular carcinoma?

A

chronic infection of the liver by hep B or C

theory:
1. Constant elimination of infected hepatocytes
2. Replication of hepatocytes (replacement?)
3. mutations accumulate, leading to uncontrolled proliferation/cancer

63
Q

What is protein X?

A

produced by Hep B virus

liver-specific transcription factors that may play a role on dysregulation of cell division

64
Q

Although EBV encodes proteins that lead to immortalization, Burkitt’s lymphoma asrises from:

A

chromosomal translocations
(after infection and immortalization of B cells, errors are made during cell division which causes c-myc over-expression)

CMD Block 2 (38 decks)

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