Oncogenic viruses are viruses that can cause cancer. They do this by inducing genetic changes that alter the expression or function of proteins involved in controlling cell growth and division. There are RNA viruses and DNA viruses that are oncogenic. Retroviruses are a type of RNA virus that contain the enzyme reverse transcriptase and can integrate near proto-oncogenes, activating their expression. DNA viruses like papillomavirus and polyomavirus can contain oncogenes that encode transforming proteins to stimulate tumor formation. Many viruses are associated with specific types of cancer in animals and humans.

1. ONCOGENIC VIRUSES
Shirin Shahana.N
6-BBT
R.No:28

2. Oncogenic Viruses
• Viruses that produce tumors in their natural hosts
or in experimental animals,or induce malignant
transformation of cells in culture are known as
oncogenic viruses.
• It is the result of genetic changes that alter the
expression or function of proteins that play critical
roles in the control of cell growth and division.
• Oncogenic viruses cause cancer by inducing
changes that affect cell growth and division.

3. Properties of Transformed cells
1. Altered cell morphology.
2. Altered cell metabolism.
3. Altered growth characteristics.
4. Antigenic alterations.
5. Capacity to induce tumours in susceptible
animals.

6. RNA VIRUSES
• Retroviruses
• Retroviruses are enveloped, spherical viruses that are
released by budding through the host cell membrane.
• They are approximately 100 nm in size.
• The genome consists of two identical, linear, single-
stranded RNA molecules.
• The characteristic feature of retroviruses is the
presence of the enzyme Reverse transcriptase (hence
the name retro, meaning reverse).

8. DNA VIRUSES
• Papovavirus
• The Papovaviridae family is comprised of two
genera: papillomaviruses and polyomaviruses.
• The family name is derived from the names of
three prototypical members: rabbit papilloma
virus, mouse polyoma virus, and simian virus
40 (SV40), originally called vacuolating virus.

10. • Adenovirus
• Though some types (12, 19, 21) of human
adenovirus may produce sarcomas in newborn
rodents after experimental inoculation, they do not
appear to have any association with human cancer.
• Herpesvirus
• Many herpesviruses have been associated with
natural cancers in animals and humans.
• Hepatitis B and C Virus
• HBV and HCV has been directly or indirectly
involved in the causation of hepatocellular
carcinoma.

11. Mechanism of viral
oncogenesis

12. • The oncogenic DNA and RNA viruses that are
carrying oncogenes encode transforming proteins
to stimulate tumor formation
• Many retroviruses do not have viral oncogenes.
• They integrate near some of the protooncogenes,
activate their expression by proviral insertional
mutagenesis, and modulate growth and di
fferentiation of the host cells.
• Retroviruses that carry v-onc genes induce a wide
range of malignancies, including sarcomas and
hematopoietic cell tumors, in a short period of
time.

13. Thank you.....!!!!