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CMBM exam 5 > Viral Oncogenesis > Flashcards

Viral Oncogenesis Flashcards

1
Q

What is cancer characterized by?

A

An accumulation of mutations due to uncontrolled cell growth which ultimately deregulate the cell cycle, DNA repair machine and cell differentiation

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2
Q

Proto-oncogenes

A

Promote progression of the cell cycle

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3
Q

Oncogene

A

Mutated to promote unchecked cell growth (cancer)

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4
Q

What are the DNA virus families which are capable of oncogenesis?

A 
Papilloma
Polyoma
Adeno
Herpes
Hepandna 
Pox
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5
Q

What are the RNA virus families which are capable of oncogenesis?

A

Adult T-cell leukemia (HTVL)

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6
Q

What is a direct acting oncogenic virus?

A

The virus introduced a new transforming gene into the cell

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7
Q

What is an indirect acting oncogenic virus?

A

The virus alters the expression of pre-existing cellular genes

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8
Q

What is an onco-protein?

A

Proteins with the ability to become oncogenic and interact and inactive cellular tumor suppressors

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9
Q

Will all people infected with oncogenic viruses get cancer and why?

A

No because transformation is a rare process

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10
Q

What type of infections does a transforming virus set up?

A

Long term/persistent

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11
Q

If someone is infected with an oncogenic virus, what is the key factor to being forming tumors?

A

Viral infection in sufficient amount

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12
Q

How does a virus act as cofactor for tumor formation?

A

Provide certain steps in process of transformation (but not all)

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13
Q

If there are viral genetic material expressed in every cell what does that indicate?

A

Indicates viral genes are necessary for maintaining a transformed state

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14
Q

If the viral infection is only necessary to begin the transformation process what does that mean?

A

Viral genes drive tumor initiation but does need to stay for the transformation to continue

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15
Q

What are the two ways that tumor causing retroviruses cause tumors?

A

Carry transduced cellular oncogenes that play no role in replication
Act through indirect mechanism (location of viral gene insertion)

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16
Q

Are the transforming genes from tumor-causing DNA match the homologs to the host genome?

A

No

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17
Q

Which type of virus will cause the majority of human cancers?

A

DNA

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18
Q

What are some of the mechanisms involved in tumorogenesis?

A

Expression of viral oncoproteins can alter different cellular proteins
Indirect mechanism of tumor formation where viral proteins interact with other cellular processes

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19
Q

Episome

A

When a DNA virus maintains their genome outside of the host genome

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20
Q

How many different genera exist in the Human Papillomavirus (HPV)?

A

16

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21
Q

What tissues are HPV likely to infect?

A

Epithelial cells in skin and mucous membranes

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22
Q

Which HPV types are considered “low-risk”?

A

6 and 11 (ano-genital warts)

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23
Q

Which HPV types are considered “high-risk”?

A

16 and 18 (genital and oral cancer)

24
Q

What is the prognosis for most HPV infections?

A

Cleared in 2-3 years

25
Q

Where does the primary infection of HPV occur and how?

A

Basal cells by micro-cuts in the skin

26
Q

When does the HPV viral load increase?

A

When the basal cells proliferate into prickle cells (early viral genes expressed)

27
Q

What is it referred to as when infected ells differentiate into later stages?

A

Terminal sequence

28
Q

Which are the transformative onco-proteins that are high-risk HPV types?

A

E6 and E7

29
Q

What are the most important proteins in cell cycle checkpoints and that E6 and E7 bind to in producing tumors?

A

p53 and retinoblastoma protein (Rb)

30
Q

What are the normal functions for p53?

A

Tumor suppressor
Induces growth arrest and G1/S phase of cell cycle upon detection of DNA damage
Becomes phosphorylated to be active

31
Q

What is p53’s inhibitor?

A

MDM2

32
Q

What occurs if DNA damage appears in the cell cycle?

A

MDM2 and p53 are phosphorylated to induce DNA repair

33
Q

What shape must multiple p53 take to form an active state?

A

4 - a tetramer

34
Q

Which protein does E6 bind to?

A

p53

35
Q

When bound to E6 what happens to p53?

A

It cannot function as a transcriptional activator causing the cell cycle to progress regardless of DNA damage

36
Q

What is the normal function of Rb?

A

When hypophosphorylated it binds to E2F transcription factors and blocks them from binding to DNA
Halts the cell cycle at G1/S
When phosphorylated will release E2F which then bind to DNA and begins transcript of cell cycle genes

37
Q

Which protein does E7 bind to?

A

Rb

38
Q

How does E7 induce tumors in the cell cycle?

A

The E7 sequesters Rb which does not allow E2F to block transcription

39
Q

What are some other factors that can induce tumors in HPV?

A

Prolonged chronic infection
Integration of viral DNA into host genome
Modulation of cyclins and CDK inhibitors
Reactivation of telomerase
Genomic instability
Blocking apoptosis

40
Q

What is Kapsoi’s sarcoma?

A

Mutlifocal neoplasm characterized by dark purple lesions

Caused by Kaposi’s sarcoma associated herpes virus (KSHV)

41
Q

Classic Kaposi’s s sarcoma

A

Mostly found in the elderly male patients of Mediterranean decent with very slow progression

42
Q

Endemic Kaposi’s sarcoma

A

Commonly found in HIV-negative children in Africa

Expressed a very aggressive lymphadenopathy

43
Q

Iatrogenic Kaposi’s sarcoma

A

Post-transplant pts undergoing immunosuprressive therapies

44
Q

AIDS-associated Kaposi’s sarcoma

A

Most common cancer found in AIDS pts in the US and Europe

Most aggressive

45
Q

KSHV is _____ but not _____ to cause cancer.

A

Necessary, sufficient

46
Q

What is the major viral protein and mechanism for KSHV transformation?

A

Latency-associated nuclear antigen 1 (LANA 1)

Binds well to p53 blocking transcription and pro-apoptosis activities

47
Q

What are the mechanisms of KSHV to cause cancer?

A

Supressing function of p53 and Rb
Induction of chromosome instability
Dysregulation cellular apoptotic pathways
Inducing secretion of growth factors

48
Q

What are the ways KSHV plays a systemic role in promoting tumor growth?

A

Immune evasion - interferes with complement system, interferon signaling and antigen presentation
Angiogenesis - stimulating cytokine release from infected cells

49
Q

What are the cancers associated with EBV?

A 
Burkitt's lymphoma
Hodgkin's disease
T-cell lymphoma
Nasopharyngeal carcinoma 
Gastric carcinomas 
Lymphoproliferative disorders
50
Q

What is the key factor in EBV transformation?

A

Expression of latent genes EBNA2 and LMP2

51
Q

EBNA2

A

Acts as a transcriptional activator fir many downstream genes
Upregulates other late genes and promoters in viral genes
Upregulates B cell antigens CD21 and CD23 in host genes
Can alter cell expression of host cell oncogene c-MTC

52
Q

LMP1

A

Thought to act as a constitutively active member of the TNF receptor superfamily
Looks like CD40 so can active B cells causing proliferation without a stop signal
Activates anti-apoptotic and cytokine genes and cell surface proteins are altered

53
Q

What are the general hallmarks of a retroviral infection?

A

Non-lytic (except lenti)
Genetic material inserted at random within host genome (except lenti)
Viral genetic material remains within the cellular DNA for the life of the cell
Implicated in certain types of cancers like lymphomas and sarcomas

54
Q

Acute transforming retrovirus

A

Virus carries an oncogene which is incorporated into the host genome under the viral promoter
Oncogene does not play a direct role in viral replication

55
Q

Slow transforming retrovirus

A

Does not carry and oncogene

Tumor formation through variety of mechanisms depending on where the viral genome is inserted into host genome

CMBM exam 5 (19 decks)

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