Cancer and Infectious Agents

Question 1

Bladder cancer is associated with what infectious agent?

Answer 1

Schistosoma haematobium (parasitic infection).

Question 2

Epstein-Barr virus is associated with causing which cancers?

Answer 2

Stomach cancers
Hodgkin’s and Non-Hodgkin’s lymphoma
Nasopharyngeal cancer

Question 3

Hepatitis B / C viruses are associated with what cancer?

HBV / HCV

Answer 3

Hepatocellular carcinoma

Question 4

What is meant by HBV and HCV are indirect carcinogens?

Answer 4

HBV and HCV are indirect carcinogens through chronic inflammation; HIV-1 is an indirect carcinogen through immune suppression.

Question 5

An organism that possesses its own genetic information in the form of nucleic acid packaged into a protein coat or capsid and which is entirely dependent upon a host
cell to supply essential replicative functions.

Answer 5

Virus

Question 6

What distinguishes retroviruses from other viruses?

Answer 6

Retroviruses are distinguished from other viruses by the presence of reverse transcriptase, an enzyme that transcribes RNA into DNA.

Question 7

What is viral transformation?

Answer 7

Viral transformation is the change in growth,
phenotype, or indefinite reproduction of cells caused
by the introduction of inheritable material.

Question 8

Oncogenic viruses

Answer 8

Oncogenic viruses promote cancer directly, typically by harbouring oncogenes. These viruses typically can transform cells.

Question 9

Non-oncogenic viruses

Answer 9

Non-oncogenic viruses promote cancer indirectly, e.g. both HBV and HCV cause chronic liver damage and the proliferative response to this promotes cancer.

Question 10

Explain the difference between transforming and non-transforming viruses.

Answer 10

Oncogenic viruses (also called transforming) = directly promote cancer.
Non-oncogenic viruses (also called non-transforming) = indirectly promotes cancer.

Question 11

In relation to cancer what type of virus is HPV?

Answer 11

Oncogenic virus.

Question 12

Explain the pathogenesis of HPV in causing cancer.

Answer 12

HPV encodes EARLY proteins that inactivate p53 and RB and in so doing, promote cell cycle progression and in some cases protect the cell from p53 mediated apoptosis.

Question 13

In relation to cancer what type of viruses are HBV and HCV?

- how do they cause cancer?

Answer 13

Non-oncogenic viruses - HBV and HCV induce cancer through inflammation.
- increase the risk of cancer but lack oncogenicity.

Question 14

What is aflatoxin?

Answer 14

Aflatoxin is a byproduct of mold that can cause DNA mutations.

Question 15

How does aflatoxin cause cancer?

Answer 15

Aflatoxin causes DNA damage and with prolonged exposure to aflatoxin, cells accumulate DNA mutations and thus are at increased risk of developing into cancer cells.

Question 16

What may occur in cells that do not permit virus replication?

Answer 16

In cells that do NOT permit virus replication (non permissive cells), this can lead to transformation and ultimately to tumour formation.

Question 17

HCC

Answer 17

Hepatocellular carcinoma

Question 18

What are the three basic mechanisms of retroviral oncogenicity?

Answer 18

1. Insertional mutagenesis
2. Proto-oncogene transduction
3. Transformation by and endogenous viral oncogene.

Question 19

How do Transforming DNA viruses cause cancer?

Answer 19

Inactivate tumour suppressor genes.

- for example HPV

Question 20

How do Transforming RNA viruses (retroviruses) cause cancer?

Answer 20

Activate oncogenes.

Question 21

How do Transforming DNA viruses cause cancer?

Answer 21

Inactivate tumour suppressor genes.

- for example HPV

Question 22

How do Transforming RNA viruses (retroviruses) cause cancer?

Answer 22

Activate oncogenes.

Question 23

In oncogenic viruses genetic information is almost always found in what form at some point in their life cycle?

Answer 23

Almost all oncogenic viruses that promote cancer exist in a double stranded DNA form at some point in their life cycle.

Question 24

Why do most oncogenic viruses have dsDNA as an intermediate in a part of their life cycle?

Answer 24

The virus needs to have double stranded DNA in order to insert into human DNA.

Question 25

How do most dsDNA viruses cause cancer?

Answer 25

Most of the dsDNA viruses that cause cancer inactivate p53 as part of the viral life cycle, they need to push the cell into S phase so inactivating p53 and RB is part of that process.