Cancer and Infectious Agents Flashcards
Bladder cancer is associated with what infectious agent?
Schistosoma haematobium (parasitic infection).
Epstein-Barr virus is associated with causing which cancers?
Stomach cancers
Hodgkin’s and Non-Hodgkin’s lymphoma
Nasopharyngeal cancer
Hepatitis B / C viruses are associated with what cancer?
HBV / HCV
Hepatocellular carcinoma
What is meant by HBV and HCV are indirect carcinogens?
HBV and HCV are indirect carcinogens through chronic inflammation; HIV-1 is an indirect carcinogen through immune suppression.
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.
Virus
What distinguishes retroviruses from other viruses?
Retroviruses are distinguished from other viruses by the presence of reverse transcriptase, an enzyme that transcribes RNA into DNA.
What is viral transformation?
Viral transformation is the change in growth,
phenotype, or indefinite reproduction of cells caused
by the introduction of inheritable material.
Oncogenic viruses
Oncogenic viruses promote cancer directly, typically by harbouring oncogenes. These viruses typically can transform cells.
Non-oncogenic viruses
Non-oncogenic viruses promote cancer indirectly, e.g. both HBV and HCV cause chronic liver damage and the proliferative response to this promotes cancer.
Explain the difference between transforming and non-transforming viruses.
Oncogenic viruses (also called transforming) = directly promote cancer. Non-oncogenic viruses (also called non-transforming) = indirectly promotes cancer.
In relation to cancer what type of virus is HPV?
Oncogenic virus.
Explain the pathogenesis of HPV in causing cancer.
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.
In relation to cancer what type of viruses are HBV and HCV?
- how do they cause cancer?
Non-oncogenic viruses - HBV and HCV induce cancer through inflammation.
- increase the risk of cancer but lack oncogenicity.
What is aflatoxin?
Aflatoxin is a byproduct of mold that can cause DNA mutations.
How does aflatoxin cause cancer?
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.
What may occur in cells that do not permit virus replication?
In cells that do NOT permit virus replication (non permissive cells), this can lead to transformation and ultimately to tumour formation.
HCC
Hepatocellular carcinoma
What are the three basic mechanisms of retroviral oncogenicity?
- Insertional mutagenesis
- Proto-oncogene transduction
- Transformation by and endogenous viral oncogene.
How do Transforming DNA viruses cause cancer?
Inactivate tumour suppressor genes.
- for example HPV
How do Transforming RNA viruses (retroviruses) cause cancer?
Activate oncogenes.
How do Transforming DNA viruses cause cancer?
Inactivate tumour suppressor genes.
- for example HPV
How do Transforming RNA viruses (retroviruses) cause cancer?
Activate oncogenes.
In oncogenic viruses genetic information is almost always found in what form at some point in their life cycle?
Almost all oncogenic viruses that promote cancer exist in a double stranded DNA form at some point in their life cycle.
Why do most oncogenic viruses have dsDNA as an intermediate in a part of their life cycle?
The virus needs to have double stranded DNA in order to insert into human DNA.
