An oncovirus is a virus that can induce malignant transformation of infected cells, leading to tumour formation.
Explanation
Oncoviruses contribute to cancer development by altering host cell regulation. These viruses include DNA and RNA viruses that establish persistent infections and interfere with cell cycle checkpoints. DNA oncoviruses such as human papillomavirus (HPV), Epstein-Barr virus (EBV) and hepatitis B virus integrate their genomes into the host or maintain episomal DNA. They express viral proteins that inactivate tumour suppressors and promote cell division. For example, HPV E6 and E7 proteins degrade p53 and retinoblastoma protein, allowing unchecked proliferation. EBV latent membrane proteins mimic signalling receptors and drive B cell growth. Hepatitis B virus contributes to hepatocellular carcinoma through chronic inflammation and integration-induced genetic instability. Retroviruses like human T-cell leukaemia virus type 1 (HTLV-1) and some animal sarcoma viruses use reverse transcription to integrate into the host genome, sometimes adjacent to proto-oncogenes. Their long terminal repeats and regulatory proteins activate host genes or provide viral oncogenes, leading to uncontrolled division.
Notable oncoviruses and cancers
High-risk HPV types 16 and 18 are linked to cervical, anal and oropharyngeal cancers. EBV is associated with Burkitt lymphoma, Hodgkin lymphoma and nasopharyngeal carcinoma. Kaposi’s sarcoma-associated herpesvirus causes Kaposi’s sarcoma and certain lymphomas, especially in immunocompromised patients. HTLV-1 leads to adult T-cell leukaemia/lymphoma, particularly in endemic regions. Chronic infection with hepatitis B virus and hepatitis C virus predisposes to hepatocellular carcinoma due to inflammatory damage and insertional events. Animal oncoviruses include Rous sarcoma virus and feline leukaemia virus, which provided early models for understanding viral oncogenesis.
The ability of oncoviruses to persist in host cells and manipulate gene expression provides insights into cancer biology and antiviral strategies. Understanding their mechanisms has led to vaccines for HPV and hepatitis B virus that reduce the incidence of associated cancers.
Related Terms: Oncogene, Proto-oncogene, Retrovirus, Tumour suppressor, Carcinogenesis