Human oncogenic viruses and cancer

Genes that are involved in the control of normal cell proliferation can be classified as:

  1. Proliferative genes: Proto-oncogenes; mutated proto-oncogenes may become oncogenes.
  2. Antiproliferative or tumour-suppressor genes: act to suppress cell proliferation.

Tumour cells also can arise by non-genetic means through the actions of specific tumour viruses called oncogenic virus or oncovirus.

There are two classes of tumor viruses:

  1. Oncogenic DNA viruses
  2. Oncogenic RNA viruses (retroviruses)

Oncogenic DNA viruses:

Virus Disease Cancer
Papovaviridae 

Papillomavirus

Warts, including genital warts Cervical, penile, vulvar cancer 

Oropharyngeal, laryngeal carcinoma

Herpesviridae 

Epstein-Barr virus

(EBV)

Infectious mononucleosis Burkitt’s lymphoma 

Nasopharyngeal carcinoma

??Hodgkin’s disease

Hepadnavirus 

Hepatitis B virus (HBV)

Hepatitis B Liver cancer (hepatocellular carcinoma)
Adenoviridae Acute respiratory disease; Common cold Adenocarcinomas (cancer of glandular epithelial tissues)
HHV 8 

(Kaposi’s Sarcoma

Herpes virus)

Multicentric Castleman’s Disease Kaposi’s sarcoma

Mechanism:

Cellular transformation by DNA tumour viruses in most cases has been shown to be the result of protein protein interaction. Proteins encoded by the DNA tumour viruses, termed tumour antigens (T antigens), can interact with cellular proteins. This interaction effectively sequesters the cellular proteins away from their normal functional locations within the cell. The predominant types of protein sequestered by viral T antigens have been shown to be of the tumour-suppressor type. It is the loss of their normal suppressor functions that results in cellular transformation.

Oncogenic RNA viruses:

Human T-lymphotropic virus (HTLV)

  • HTLV-1
  • HTLV-2

Disease: Tropical spastic paraparesis

Cancer: Adult T-cell leukemia, Lymphoma

Mechanism:

In the retroviruses, the viral RNA genome is first converted into DNA. During this processpart of the host genome may be incorporated into the viral genome (transduction). Should thathost genome include a proliferative gene, the transduced gene will confer a growth advantage tothe infected cell. Alternatively, the integration of a retrovirus genome into the host genome (arandom process) may place the powerful viral promoter region close to a host gene that encodesa growth-regulating protein. If the protein is expressed at an abnormally elevated level it canresult in cellular transformation. This is termed retroviral integration-induced transformation. It has been shown that HIV also induces certain forms of cancer in infected individuals by thisintegration induced-transformation process.

Leave a Reply

Your email address will not be published. Required fields are marked *

banner