Oncogenic Viruses- An Overview

  • Viruses are intracellular pathogens that reproduce only in the living cell and manipulate the cellular machinery to produce more viruses.
  • Viral replications can affect the cellular genes of the host in multiple cancerous ways.
  • Anย oncovirusย is aย virusย that can causeย cancer.
  • Viruses account for about 20% of total human cancer cases.
  • Although many viruses can cause various tumors in animals, only seven of them are associated with human cancers and are currently considered oncogenic viruses.

Oncogenic Viruses

Image Source: Massachusetts Institute of Technology

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Introduction

  • These viruses include hepatitis B virus (HBV), hepatitis C virus (HCV), human papillomavirus (HPV), Epstein Barr virus (EBV), human herpes virus 8 (HHV8),ย Merkel cell polyomavirus (MCPyV), and HTLV-1.
  • HBV and HCV cause approximately 80% of hepatocellular carcinoma (HCC), the most common cancer of the liver.
  • High-risk HPV strains are the major causes of cervical cancer and other ano-genital neoplasms as well as a significant proportion of head and neck tumors.
  • EBV is associated with nasopharyngeal carcinoma, Hodgkinโ€™s lymphoma, and Burkittโ€™s lymphoma.
  • HHV8 (also called Kaposiโ€™s sarcoma-associated herpesvirus, KSHV) is responsible for Kaposiโ€™s sarcoma often found in patients with acquired immunodeficiency syndrome (AIDS).
  • MCPyV causes Merkel cell carcinoma and HTLV-1 is the causative agent of adult T-cell lymphoma.

Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV)

  • HBV and HCV can cause aย liver infection that can sometimes lead toย liver cancer.
  • You pick up these viruses if you share needles used to inject drugs, have unprotected sex, or get a transfusion with contaminatedย blood.
  • Doctors treat HBV and HCV infections with medicine.
  • You can often get rid of HCV after a few months of treatment.ย 
  • Medicationย doesn’t cure HBV, but it can lower the chance ofย liverย damage andย liver cancer.
  • There’s a vaccine to prevent HBV, but not HCV. Those with higher chances of getting HBV should get vaccinated. That includes people who haveย HIV, inject illicit drugs, or areย health careย workers.

Kaposi Sarcoma-Associated Herpesvirus (KSHV)

  • KSHV is aย herpesย virus that can causeย Kaposi sarcoma, aย cancerย of the blood vessels, as well as two types ofย lymphoma.
  • You’re more likely to get cancer from KSHV if you have a weakenedย immune system because you had anย organ transplant, getย chemotherapy, or have AIDS.
  • The virus can be spread during sex, and also throughย bloodย andย saliva.

Merkel Cell Polyomavirus (MCV)

  • MCV is a common virus that infects theย skin.
  • It usually doesn’t cause symptoms or lead to cancer. But in some people, MCV causes a rareย skin cancerย called Merkel cellย carcinoma.

Human Papillomavirus (HPV)

  • HPVย is a group of more than 200 viruses, and at least a dozen of them can cause cancer.
  • HPV spreads during vaginal or anal sex.
  • HPV often goes away on its own and doesn’t cause any health problems. Some people stay infected, though.
  • If they have theย HPVย that causes cancer, it can lead to cancers of theย cervix, vulva,ย vagina,ย penis,ย anus,ย tonsils, orย tongue.
  • HPVย vaccinesย can keep you from getting infected with the virus. Health officials recommend them for young women through age 26 and young men through age 21.

Human T-Cell Lymphotropic Virus Type 1 (HTLV-1)

  • HTLV-1 infects T cells, which are a type of white blood cell. It can causeย leukemia and lymphoma.
  • HTLV-1 spreads several ways, including: From mother to child during birth or throughย breastfeeding, sharing needles with infected people, organ transplant, unsafe sex, etc.
  • About 2% to 5% of people who have the virus get adult T-cell leukemia or other health conditions. It’s not clear why some people get leukemia and others don’t. Symptoms and how it develops are different for each person.
  • There isn’t a cure or treatment for HTLV-1. It’s a lifelong condition. But regular checkups can lower your chances of cancer.

Epstein-Barr Virus (EBV)

  • EBVย is a common virus. Most people get infected with it at some point in their lives. Most of the time, people with EBV stay healthy and don’t have symptoms.
  • For others, EBV can cause mononucleosis and other more serious conditions, fromย viral meningitisย to pneumonia.

Several cancers are linked with EBV as well:

  • Burkitt’s lymphoma
  • Nasopharyngeal carcinoma (cancer of the upper throat)
  • Hodgkin’s and non-Hodgkin’s lymphoma
  • T-cell lymphomas
  • Post-transplant lymphoproliferative disorder (too many white blood cells)
  • Leiomyosarcomaย (cancer in the soft tissue)
  • There’s no vaccine for EBV, but you can help protect yourself by notย kissingย or sharing drinks, food, or personal items with someone who has the virus.
  • There’s no specific treatment if you have EVB, but you can ease symptoms if you drink plenty of fluids, get rest, and take medicines forย painย andย fever.

Mechanisms of Viral Oncogenesis

The molecular mechanisms of viral oncogenesis are complex and may involve:

  1. Induction of chronic inflammation
  2. Disruption of host genetic and epigenetic integrity and homeostasis
  3. Interference with cellular DNA repair mechanisms resulting in genome instability
  4. Cell cycle dysregulation.
  5. Oncogenic DNA viruses can also insert their genomic DNA into cellular chromosomes, resulting in genetic abnormity.
  6. Viral โ€˜oncoproteinsโ€™ can activate cellular signaling pathways, alter the expression of cellular genes and microRNAs either transcriptionally or post-transcriptionally, and destabilize or inactivate tumor suppressor proteins and proteins that regulate cell polarity, signal transduction, immune response, and apoptosis.
  7. Genetic and epigenetic alterations induced by infection and replication of oncogenic viruses may lead to the appearance and proliferation of cancer stem cells, which are important for the initiation, progression, metastasis, relapse, and chemotherapy resistance of cancers.

The importance and underlying molecular mechanisms of specific cellular genes and signaling pathways in viral oncogenesis are subjects of intense research efforts.

References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4731227
  2. https://www.ncbi.nlm.nih.gov/pubmed/27830995
  3. https://www.asm.org/Articles/2019/January/The-Seven-Viruses-that-Cause-Human-Cancers
  4. https://www.nature.com/articles/onc2009351
  5. https://www.nature.com/articles/nrc3400
  6. https://www.webmd.com/cancer/viruses-that-can-lead-to-cancer#3
  7. https://www.microrao.com/micronotes/oncogenic_viruses.htm
  8. https://www.onlinebiologynotes.com/oncogenic-viruses

About Author

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Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He is doing his Ph.D. at the Central Department of Microbiology, Tribhuvan University, Kathmandu, Nepal. He was awarded the DAAD Research Grant to conduct part of his Ph.D. research work for two years (2019-2021) at Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. Sagar is interested in research on actinobacteria, myxobacteria, and natural products. He is the Research Head of the Department of Natural Products, Kathmandu Research Institute for Biological Sciences (KRIBS), Lalitpur, Nepal. Sagar has more than ten years of experience in blogging, content writing, and SEO. Sagar was awarded the SfAM Communications Award 2015: Professional Communicator Category from the Society for Applied Microbiology (Now: Applied Microbiology International), Cambridge, United Kingdom (UK). Sagar is also the ASM Young Ambassador to Nepal for the American Society for Microbiology since 2023 onwards.

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