Oncogenic viruses

Shirin Shahana.N
3-BSc.Biotechnology
SIAS

1. O N C O G E N I C V I R U S E S S h i r i n S h a h a n a . N 6 - B B T R . N o : 2 8

2. O n c o g e n i c V i r u s e s V i r u s e s t h a t p r o d u c e tumors i n t h e i r n a t u r a l h o s t s o r i n e x p e r i m en t a l a n i m a l s , o r i n d u c e m a l i g n a n t t r a n s f o r m ation o f cells i n c u l t u r e a r e k n o w n a s o n c o g e n i c v i r u s e s . I t 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 . O ncogenic viruses cause cancer by inducing changes that affect cell growth and division .

3. P r o p e r t i e s o f Transformed c e l l s A l t e r e d c e l l m o r p h o l o g y . A l t e r e d c e l l m e t a b o l i s m . A l t e r e d g r o w t h c h a r a c t e r i s t i c s . A n t i g e n i c a l t e r a t i o n s . C a p a c i t y t o i n d u c e tumours i n s u s c e p tible a n i m a l s .

4. R N A V I R U S E S R e t r o v i r u s e s 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).

5. R e v e rse transcriptase enzyme prepares a DNA copy of the retroviral RNA genome initially an RNA:DNA hybrid and then its double-stranded DNA form. The provirus is integrated into the DNA of the infected host cell. It is from the provirus that all retrovirus proteins are translated. Infection with oncogenic retroviruses does not lead to cytolysis or death of infected cells but the provirus remains integrated with the host cell DNA for the rest of the life of the cell . While all oncogenic RNA viruses belong to the family Retroviridae, all retroviruses are not oncogenic.

6. D N A V I R U S E S P a p o v a v i r u s 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.

7. Poxviru s Three members of the poxvirus group induce benign tumours, rabbit fibroma, molluscum contagiosum and Yaba virus. The last causes naturally occurring benign histiocytomas in monkeys. It is apparently transmitted by insects. Similar tumours can be induced experimentally in many species of primates, including human beings. The tumours regress spontaneously in a few weeks. Nonprimates are unsusceptible.

8. 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.

9. M e c h a n i s m o f v i r a l o n c o g e n e s i s

10. 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.

11. T h a n k y o u . . . . . ! ! ! !