1. The Biology of Cancer Second Edition CHAPTER 3 Tumor Viruses
Robert A. Weinberg
The Biology of Cancer
Second Edition
CHAPTER 3
Tumor Viruses
Copyright © Garland Science 2014

2. Cancer is an infectious Disease ?
No.
Virus-induced cancers represent only a minority of human cancers
Study of tumor virus open many of the secrets of human cancer, even majority of cancer have no connection with tumor virus in human cancers.
Studying tumor virus, identification of oncogenes, changed the direction of cancer research .
1876, Russian research reported that the transmission of a tumor from one dog to another by xonografting. Questionable ?
1908, filtered extracts from Chicken leukemia cells induced tumors in other birds

3. 1910, Peyton Rous discovered that the Rous Sarcoma virus (RSV) is able to induce tumors in chicken
1913, Dane Johannes Grib Figiber reported that stomach cancers in rats could be traced to spirochete worms that they harbored. Thus, he received Nobel Prize, direct validation of the idea that cancer was an infectious disease
But Metastatic stomach epithelia in those rats were present in the normal stomach with Vitamin deficient. Misinterpretation? Fraud ? Things easily go wrong
Since then, Peyton Rous report had been disregarded for two decades
Figure 3.2 The Biology of Cancer (© Garland Science 2007)

4. Howard Temin showed the ability of RSV to transform cells in vitro.
In the Lab of Renato Dulbercco in CalTech, Harry Rubin and Howard Temin found that stocks of RSV infected in Chicken Embryonic Fibroblast and some of these cells survived indefinitely.
The RSV infected cells in cultures showed many traits of cancers.
Form a foci, round shape, loss of contact hibition, multilayer formation, highly metabolic stage etc
Cancer formation could be studied at the level of individual cells and these processes could be traced easily
Figure 3.6 The Biology of Cancer (© Garland Science 2007)

5. Transformation In vitro
Proposed the processes of transformation
Loss of contact inhibition, foci formation,
an anchorage independent growth
Tumorigenicity can be tested in a host nude mice
Figure 3.7b The Biology of Cancer (© Garland Science 2007)

6. Question is whether RSV is required for maintenance of transformation or simply initial infection is sufficient ?
The continued presence of RSV is needed to maintain transformation
How prove it ? Tem-sensitive mutant and the maintenance of transformation
Viral transforming gene is required to both initiate and maintain the transformed phenotype of virus-infected cells ?
This finding is also true In vivo ?
Figure 3.8 The Biology of Cancer (© Garland Science 2007)

7. Viruses have simple life cycles
ALV: avian leukosis virus
Figure 3.3 The Biology of Cancer (© Garland Science 2007)

8. Retroviral genome become integrated into the chromosome of infected cells
How did RSV RNA virus succeed in transmitting in genome through many generations within a cell lineage ?
Late 1960, Temin proposed a radical idea explaining that RSV made ds DNA from RNA and become a part of chromosomal DNA by integration
How was DNA made from RNA ? Central Dogma can not explain this phenomenon ?
Reverse transcriptase was found within a year
Retrovirus re-infection can explain the stable transformation ? No. RSV virus with no ability to replicate was still able to transform cells
Figure The Biology of Cancer (© Garland Science 2007)

9. Src gene from RSV is responsible for transformation
Retrovius has small number of genes (gag, poly, env genes.
Several mutant s of RSV
No replication with transformation activity
Replication without transformation activity
In 1974, Bishop and Varmus defined the transformation-associated sequences of RSV genome by making probes. How did they found ?
Src gene was found, but interestingly, this src was also clearly present in the uninfected chicken cells ? There are two copies of the src-related gene in normal cells
C-src play a role in cellular processes in normal cells, but v-src is able to transform normal cells to tumors
Figure The Biology of Cancer (© Garland Science 2007)

10. ALV (avian leukosis virus) may kidnap cellular Src gene during lysogenic life cycle and become RSV ?
Viral Oncogene would be changed, acquire the tranformation activity
What is the different action of Cellular oncogene and Viral Oncogene ?
How one Viral Oncogene can induce multiple change during tumorigenesis ?
C-oncogene might be modified in many non-viral induced tumors ?
How do other retrovirus without oncogene induce tumors ?
Figure The Biology of Cancer (© Garland Science 2007)

11. Retroviruses cause cancer by kidnapping
mutated versions of normal cellular genes

12. The structures of c-src and v-src and Deletion of the C-terminal region leads to activation of v-Src
Binds polyproline motifs
Binds peptides phosphorylated on Tyr

13. DNA viruses are able to induce cancer
1960, Shope found that papillomars can be induced a virus (papillomavirus). This Virus contain DNA molecule
Several tumor DNA tumor viruses were found.
Papillomavirus, the mouse polyomavirus and SV40 are grouped together as the Pavovavirus (papilloma, polyoma and Vacuoles); Circular ds DNA
Adenovirus and herpesvirus have long linear ds DNA
Figure 3.9a The Biology of Cancer (© Garland Science 2007)

14. SV40 tumor virus
SV40 virus (the 40th simian virus monkey virus) was discovered as a contaminant of the polyovirus vaccine stocks.
SV 40 induces cell lysis in permissive host cells, but can not replicate in Nonpermissive cells and instead transform these cells.
SV40 contaminant might trigger cancer (mesothelioma) in many people who were vaccinated, but no evidence ?
Figure 3.10a The Biology of Cancer (© Garland Science 2007)

15. Table 3.2 The Biology of Cancer (© Garland Science 2007)

16. Tumor Virus become part of host cell DNA in virus transformed cells
T Ag
in cancer
Discovery of tumor virus-associated proteins were found in cancers induced by DNA virus; indicating that the viral genome place in tumor cells encoded a protein (SV40 T Ag)
How could viral genomes be replicated and transmitted for many generations of cells ? The virus are replicated as extranchromosomal molecules in permissive cells.
In1968, it was found that the viral DNA in SV40-transforned cells was associated with chromosomal DNA, suggesting a integration of viral DNA into chromosome
Viral genome become a part of cell’s genome.
Figure The Biology of Cancer (© Garland Science 2007)

17. Integrated SV40 genomes How can you find this integrated SV40 genome in chromosomes ?

20. How do other retrovirus without any oncogene induce tumors ?
Slowly tranforming retrovirus activates proto-oncogene by inserting their genomes adjacent cellular genes
Avian Leukosis virus(AVL) or murine leukemia virus (MVL) with no concogen induce a malignancy ?
Map the site of integration of viral genome. Myc was a target site of viral integration of tumors induced by these viruses
Insertional mutagenesis
Is it possible to transform cells with random integration of DNA or Viral DNA in vitro ?
These insertional mutagenesis provided a powerful tool to find new oncogenes
Figure 3.23a The Biology of Cancer (© Garland Science 2007)

21. sites in different tumors
Retroviruses also cause cancer by randomly
inserting next to, thus activating the expression of proto-oncogenes
Retroviral insertion
sites in different tumors
Transcribe to mRNA
5 kilobases
exons

23. Some retroviruses naturally carry oncogene HTLV (human T cell leukemia virus) were transmitted via milk-borne from mother to infants. In Kyusu, 1 % infection in the population. Tax gene product from viral genome appears to activate the two cellular genes (IL-2, GM-CSF), which stimulates the proliferation of hematopoietic cells
Gene therapy can induce the tumors
Immune deficiency (AIDS) can induce the some types of viral-induced tomors ‘ Kaposi’s Sarcoma in endotherial lining of lymphduct. Related with human herpesvirus-8 (HHV-8).
How about the helicobacter ? HBV, HCV ?

24. Summary Retrovirus Retrovirus
The causative agents of transplantable tumors in chickens, mice, and rats RNA virus
The virus carries genetic information responsible for transforming a normal cell into tumor cell.
Retrovirus : RNA-containing animal virus that replicate through a DNA intermediate
Two classes based on the latent period of tumorogenesis
1) Acute transforming retrovirus rapidly produce tumors in newborn animals and carry genetic information capable of inducing tumors directly.
2) The slowly transforming retroviruses do not carry oncogenes and induce tumors by integrating themselves adjacent to a cellular gene and altering its transcriptional regulation.