This presentation discusses the etiology of cancer, focusing on viruses, radiation, environmental and industrial carcinogens, diet, nutrition, tobacco, alcohol consumption, and genetic susceptibility as causes of cancer. Dr. Manash K. Paul from the Department of Biology at the Indian Institute of Science Education and Research will provide the presentation for teaching purposes only. The document contains no other information.

1. This presentation is for teaching purpose only
Cancer and Therapeutics
The Etiology of Cancer
Dr. Manash K. Paul
Department of Biology
Indian Institute of Science Education and Research
Mohali; www.iisermohali.ac.in

2. The Etiology of Cancer
Viruses (papilloma. Epstein-Barr, hepatitis B, retrovirus)
Radiation exposure
Environmental/ industrial carcinogens
* Asbestos
* Aromatic amines Textbook & Readings:
As a general background source Alberts B. et al., The
* Bischloromethyl ethers Molecular Biology of the Cell 4th Edition (2002)
* Beta-naphthalene and benzedrine Garland Science Press, ISBN 0-8153-3218-1 is
recommended. As a detailed source Robert A. Weinberg,
* Polycyclic hydrocarbons The Biology of Cancer Garland Science Press, ISBN
0-8153-4078-8 (2007). Lauren Pecorino, Molecular
* Drug-induced cancers (alkylators: Biology of Cancer, Oxford University Press. ISBN
978-0-19-921148-7 (2008). M. Molls, P. Vaupel, C.
melphalan and cyclophosphamide) Nieder, M.S. Anscher. The impact of tumor biology on
cancer treatment and multidisciplinary strategies,
* Nickel Springer. ISBN 978-3-540-74385-9 (2009). Yi Lu, R. I.
* Vinyl chloride Mahato, Pharmaceutical perspectives of cancer
therapeutics, Springer. ISBN 978-1-4419-0130-9 (2009).
* Isopropyl alcohol Robert Gallo, Virus Hunting: Aids, Cancer, And The
Human Retrovirus, Basic Books. ISBN13:9780465098156
* Diet and nutrition
Tobacco and alcohol consumption
Immunodeficiency syndromes: HIV is associated with Kaposi's sarcoma,
non-Hodgkin's lymphoma
Genetic susceptibility syndromes

3. VIRUSES
Pic ref: http://cathylwood.files.wordpress.com
/2009/04/computer-virus-bugs
Viruses are infectious agents that can
replicate only within the cells of other living
organisms. Humans are affected by a variety
of viruses. Some cause minor illnesses like
the common cold; others can lead to more
serious conditions like influenza and AIDs.
Pic ref: betterhealthnaturally.wordpress.com/.../viruses/ Pic ref: www.bleepingcomputer.com/blogs/flex-it/index....

4. Structure of Viruses
Structure of viruses
Virion
Capsid
Capsomere
Genome
Nucleocapsid
www.nsf.gov/od/lpa/news/03/pr0328_images.htm
Envelope DNA containing Viruses
Hepatitis B virus HBV Human Papiloma virus HPV Adenovirus Parvovirus
RNA containing Viruses
Rota virus Paramyxo virus Entero virus Influenza virus
Source: Viruses; http://virology-online.com/viruses

5. History of study for
Tumor Viruses
As early as 1876, a researcher in Russia reported the
transmission of a tumor from one dog to another.
In 1908, Wilhelm Ellerman and Olaf Bang in Copenhagen
reported the extract from chicken leukemia cells could
cause tumor.
In 1909, Rous found that the extract from sarcoma of
chicken could induce tumor.
Harry Rubin discovered that RSV-infected chicken embryo
fibroblasts could survive for several months to produce
viral particles.

6. Early Cancer Research on Rous Sarcoma Virus (RSV)
Redrawn as per The Biology of Cancer (© Garland Science 2007)

7. Major human Oncogenic Viruses
At least 6 viruses are thought to contribute to cancers (15 – 20%):
DNA Viruses
Small DNA tumor viruses
- Human Papilloma virus (HPV)
- SV40
- Adenovirus
Herpesviruses (large)
Hepatitis B virus HBV Human Papillomavirus
- Epstein Barr virus (EBV) www.hivandhepatitis.com/.../hbv_virus4..jpg www.hyscience.com/hpv_380.jpg
- Kaposi’s Sarcoma Herpesvirus (KSHV)
Other
- Hepatitis virus B
RNA Viruses
Human T-cell Leukemia Virus 1 (HTLV1)
Hepatitis virus C
80% of viral-associated cancers Adeno virus Hepatitis virus C
commons.wikimedia.org/wiki/File:Adenovirus.jpg kenoath.wordpress.com/2009/04/
Cervical cancer (HPV)
Liver cancer (HBV and HCV)

8. How do Viruses
Enter and Exit the
body
Attachment/Adsorption Penetration
Uncoating Biosynthesis
Assembly Release
Maturation
False colored transmission electron micrograph images
showing virus budding off from cell surface
www.abovetopsecret.com/forum/thread476457/pg1
science.nationalgeographic.co.in/science/wall

9. DNA tumor Viruses
Life cycle of DNA tumor Viruses
DNA
Virus
Coat Protein
Needs Entry into cell and
Cell in uncoating of DNA
S-Phase
Uses host
enzymes Viral DNA
Transcription Uses host
enzymes
Replication
RNA Translation
DNA
Coat Protein
Assembly of progeny
virus partcile followed
by exit from the cell
9
Redrawn as per The Biology of Cancer
(© Garland Science 2007) Paul Graphics

10. RNA tumor Viruses
Life cycle of RNA tumor Viruses
Integration of viral DNA into host chromosome
DNA Provirus
Reverse transcriptase RNA Assembly of many
makes DNA/RNA and virus particle
DNA
then DNA/DNA
Capsid RNA Transcription
Envelope
Reverse transcriptase*
RNA copies
Translation
RNA
Entry into cell and + +
shedding of envelope Envelope Capsid Reverse
Paul Graphics * virus encoded protein protein transcriptase
Redrawn as per The Biology of Cancer (© Garland Science 2007)

11. Oncogenesis & Oncogenes
Oncogene
– A gene that has the potential to convert a normal cell to a
cancerous or transformed cell
Viral oncogene (v-onc)
– A viral gene responsible for the oncogenicity of the virus
● Retroviruses may carry altered cellular genes that are tumor
promoters
Proto-oncogene
– Cellular genes that promote the normal growth and division of cells.

12. How do Viruses contribute to cancer?
Integrations that cause activation or
inactivation of oncogenes or tumor
suppressors (e.g. RNA viruses)
Expression of genes that alter key
signal transduction pathways - this is our
focus
Chronic activation of inflammatory
responses
www.bayloraids.org/atlas/images/22.jpg www.hivandhepatitis.com/recent/2009/060909_d.html
Can You Guess What are these?
examiner.com healingrosacea.com

13. Human Papilloma Virus (HPV)
DNA TUMOR VIRUS
Small (52-55 nm in diameter)
Non-enveloped
Icosahedral-shaped
Circular dsDNA genome (~8000 bp in length) www.dkfz.de/en/f020/index.html
100 types identified - most common are types 6 and 11
HPV infections most common among sexually active adults and adolescents.
There are over 100 different types of HPV’s (low, medium and high-risk).
Low-risk types cause warts or papillomas (e.g. genital warts).
High-risk types cause cervical, vulva, vagina, anus and penis cancers (e.g.
types 16 and 18).
10% of human cancers may be HPV-linked
16% of all female cancers linked to HPV
Papilloma viruses are found in 91% of women with cervical cancer 13
www.eurocytology.eu/.../LP1ContentMcontA1.html

14. Discoverers of Cancer Viruses Win Nobel
Human Papilloma virus (HPV)
• HPV causes cancer of the cervix, anal,
perianal, vulvar, penile cancers and close
to 20% of oropharyngeal cancers. Recent
evidence also points to a possible role of
other HPV infections in squamous cell
carcinomas of the skin.
Dr. Harald zur Hausen

15. The Human Papilloma virus story
• Rigoni-Stern in the mid 19th century correlated uterine cancer with marraige
• Kennaway, Dorn and Cutler, Levin etc, 1940-60 had the similar inferences
• Rotkin, 1962-72, onset of sexuality and multiple sexual consorts
• Search for a carcinogenic principle, Hausen HZ, postulates the presence
of a DNA virus. Curr. Top. Microbiol. Immunol., 1977, 78: 1-30
• Existance of human papilloma virus type 6 (HPV 6) was obtained from
human genital warts. Int J. Cancer, 1980, 25: 605-9
• DNA homologue HPV 6 was found in majority of the genital worts but not
associated with tumorigenicity. Int J. Cancer, 1982, 29: 143-6
• Viral DNA from a laryngeal papilloma was cloned. J. Virol. 1982, 44: 393-400
• This DNA had 25 % similarity with that of HPV 6, labelled it as HPV 11
15

16. The Human Papilloma virus story
• Presence of HPV 11 DNA was reported in genital, laryngeal papillomas
and in some cervical cancers. PNAS. 1983, 80: 560-3; PNAS. 1983, 80:
3812-5
• HPV types 6, 10, and 11 were preferentially found in benign lesions
whereas HPV 16 prevails in malignant and in pre-malignant
proliferations. P.Takamatsu Symp, 1983; 14: 147-52
• Papillomavirus DNA in human tongue and oral carcinomas. Int. J.
Cancer, 1985, 36: 575-8; Med. Microbiol. Immunol., 1986, 174: 287-94
• The complete nucleotide sequence of HPV11 DNA (7931 bp) was
determined. Virology, 1986, 151: 124-30
• The etiology of cancer of the cervix has been linked to HPV16. Laryngol.
Rhinol. Otol., 1986; 65: 177-9
• Discovered HPV 18
16

17. Human Papilloma Virus and cancer
The important transforming
genes in papilloma viruses are
the non-structural regulatory
genes, E6 and E7
HPV is normally episomal but
is always integrated in tumors
Schematic representation of the genomic organization of HPV 16
17
Ref: Clinical Science (2006) 110, (543–552) Human papillomavirus in cervical screening and vaccination,
Emma J. CROSBIE and Henry C. KITCHENER

18. HPV gene expression and cancer
Changes in viral gene expression
accompanying the progression from
cervical intraepithelial neoplasia to
squamous cell carcinoma. Expression of
E6/E7 oncogenes increases with the
severity of the lesion. In cervical
carcinoma the virus is integrated into the
host cell chromosomes, this leads to
further deregulation of E6/E7 expression.
CIN: Cervical intraepithelial neoplasia.
18
Source: Human papillomavirus E6/E7 mRNA testing as a predictive marker for cervical carcinoma. A Kathrine Lie,
Gunnar Kristensen, Expert Review of Molecular Diagnostics, July 2008, Vol. 8, No. 4, Pages 405-415.

19. Schematic representation of HPV entry and growth
Source: http://nobelprize.org/nobel_prizes/medicine/laureates/2008/press.html

20. Human Papilloma virus – mechanism
Composed of eight genes - E1, E2, E4, E5, E6, E7, L1 and L2, expressed at
different times during the HPV life cycle - categorized as early or late
HPV virion infects epithelial tissues through micro-abrasions and enters the
basal epithelial cells, genome exists as 20-100 copy episome
Viral genome then enters the cell nucleus and now the early E1 and E2 genes
replicate the virus genome. E1 and E2 then build messenger RNA molecules
As the host epithelial cells divide and differentiate, a transcription cascade
takes place
E4 and E5 genes, respectively, assist in the virus genome production
E7 interfere with the work of the human genes Rb gene that regulate normal
cell division
The function of Rb is to accumulate important proteins like the E2F protein that
are essential for cell division; if enough proteins are not accumulated, Rb
prevents cell division from taking place
E6 binds & stops p53 from repairing cell damage or causing the damaged cell
to die
Leading to continued cell division of damaged cells, and can end up causing
cancer or tumors.
The L1 and L2 genes help create viral capsid proteins required to build new
viruses.
The entire HPV life cycle depends strictly on the process of epithelial cell
differentiation.

21. The p53 Tumor Suppressor Gene
Most cancers result from mutations in P53 mediated G1 arrest
several genes. A gene mutated in about 1⁄2 of Induction of
DNA lesions
human cancers is p53. Tumors arise when
the second p53 allele is mutated, so the trait
is inherited as an autosomal dominant. The P53 protein
p53 tumor suppressor protein (393 amino
Stabilization of P53
acids) is involved in many processes,
by unknown means
including: a). Transcription b). Cell cycle Gene activation
control c). DNA repair and d). Apoptosis WAF1
(programmed cell death). Promoter
Damage to cellular DNA causes p53 to initiate Cdk2 p21
Cyclin E
the cascade of events leading to G1 arrest.
Kinase No Kinase activity
At least 17 cellular and viral proteins interact activity blocks transition to S
with p53. Virus proteins typically inactivate
G1 S
p53, allowing products needed for replication
Paul Graphics Arrest in G1
to be expressed. 21
Cascade of events by which DNA lesions
cause a p53 dependent arrest in G1
Redrawn as per Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

22. HPV E6 oncoproteins and cancer
The HPV E6 and E7 oncoproteins
inactivate the p53 and pRB tumor
suppressors.
HPV E7 proteins interact with
pRB and the related “pocket
proteins” p107 and p130.
Together regulate the activities of
the E2F family of transcription
factors that control multiple cell
cycle transitions.
E6 do not directly associate with
p53 but form a complex with the
cellular E6-AP protein, which is
essential for p53 interaction. E6
Schematic outline of critical steps of high-risk HPV- retarget E6-AP to induce
induced carcinogenesis. Inactivation of the pRB and p53 ubiquitination and rapid
tumor suppressor pathways and expression of the catalytic proteasomal degradation of p53
telomerase subunit hTERT constitute a subset of the steps
that have been shown to be necessary for the generation of
fully transformed human epithelial cells in vitro. HPV E6 can activate telomerase
Mechanisms of Human Papillomavirus-Induced Oncogenesis, Munger et al; hTERT transcription.
Journal of Virology, November 2004, p. 11451-11460, Vol. 78, No. 21

23. RNA Tumor Viruses (RETROVIRUSES)
A normal retrovirus has: 3 genes;
Structure of RNA Virus
GAG : internal proteins Transmembrane
Glycoprotein
ENV: Envelope glycoproteins Membrane
associated
protein
POL: Enzymes Capsid
Reverse transcriptase
RNA
Integrase Lipid membrane
Reverse
Protease transcriptase
•Retroviruses causes cancers Surface
Glycoprotein
•Hepatitis C Virus Paul Graphics
Hepatocellular carcinoma
•Human T cell lymphotropic virus -1 (HTLV-1)
Adult T cell leukemia and Sezary T-cell leukemia
•Human T cell lymphotropic virus -2 (HTLV-2)
Hairy cell leukemia

24. Hepatitis virus C
Hepatitis C virus is an enveloped RNA virus of the flavivirus family, a blood
borne virus. The world health organization estimates that approximately 170
million people worldwide are infected with hepatitis C.
It is capable of causing both acute and chronic hepatitis in humans by
infecting liver cells. Chronic infection with hepatitis C virus results in cirrhosis,
which in turn can lead to primary hepatocellular carcinoma (HCC).
HC is an aggressive tumor that can occur in the setting of liver disease
resulting from infections with hepatitis B and/or hepatitis C virus, although the
exact mechanism of oncogenesis by these viruses is unclear.
Long latency period to development of
HCC is 20-30 years. Mechanism is
probably due to chronic inflammatory
response.
HOW IT INDUCES CANCER? Hepatitis virus C
kenoath.wordpress.com/2009/04/
http://en.wikipedia.org/wiki/Hepatitis_C

25. The structure of the
HCV genome.
Envelope glycoproteins E1 and E2 are integral for cell recognition and viral fusion
NS2 and NS3 autocatalytically cleaves to release a serine proteinase situated at
the N region of the NS3. NS3 then cleaves the rest of the non-structural proteins
when complexed with its co-factor NS4A to release NS4B, NS5A and NS5B.
NS4B is involved in the replication complex of HCV. NS5A is thought to interact
with the cell pathways and NS5B acts as RNA-dependent RNA polymerase.
HCV core interact with RNA-activated protein kinase, PKR. PKR is activated by
IFN and phosphorylates the eukaryotic initiation factor, eIF2a, limiting protein
synthesis and inhibiting cell and viral growth. Core may mediate G2/M phase
arrest via a p53-independent manner.
Core phosphorylates PKR at threonine 446, which alters PKR activity on different
substrates and prevent apoptosis. Mutations of PKR at residue 446 in mice have
been shown to cause tumours.
Core protein is able to bind to p53 and p21WAF1/CIP leading to G1 arrest.
Bioscience Horizons, Volume 1, No. 2, 2008, 167-175.

26. FOR DISCUSSION
- in the next class
Gui Tran, The role of hepatitis C virus in the pathogenesis of hepatocellular carcinoma. Bioscience Horizons,
Volume 1, No. 2, 2008, 167-175.