Viruses and cancer

Question 1

1. What are the types of viruses that can cause cancer?

Answer 1

• EBV- Burkitt lymphoma, nasopharyngeal carcinoma
• HPV- cervical carcinoma
• Merckel virus- merckel cell cancer
• HTLV-1- adult t-cell lymphoma

Question 2

2. What evidence are there that links cancer with viruses?

Answer 2

• Epidemiological: Many different regions have a high coorelation with viral incidence and a specific cancer that isn’t found in other regions that doesn’t have this virus.
• Molecular evidence: If vaccinated against HBV since childhood, the risk of developing hepatocellular carcinoma drops significantly.

Question 3

3. Describe the mechanism of viral oncogenesis.

Answer 3

Modulation of cell cycle:
• Hijacks the cell’s transcription machinery at the s phase, transcribes it’s own genes and replicates it’s DNA. It can do this in many different ways, it can induce RB to not be inactive, it can act on E1 site and transcribe sphase genes, it can phosphorylate RB.
• Examples: HPV can inhibit RB and P53, which are both tumour suppressor genes needed to regulate cell cycle.
Modulation of apoptosis:
• BCL2-V-FLIP: They have this protein that is very similar to BCL-2 family, has the same sequence and structural homology, however even though it find to FAS recptor and binds to FADD it inhibits the recruitment of effector caspases, therefore inhibiting apoptosis.

Question 4

4. Give a specific example of the mechanism of viral oncogeneis.

Answer 4

So HPV infection causes cervical carcinoma, has two important onncoproteins E7 and E6. E7 will inhibit G1/ S phase, and E6 will inhibit p53 leading to excessive proliferation, and E6 also codes for HTRET which will extend telomeres, the cells are immortalized.