Download Cancer Causing Viruses

CANCER CAUSING
VIRUSES
VIRUSES CAUSING CANCER?
 Can this really happen??
 Think about this for a moment. Viruses causing cancer??
 According to researchers, some of the more common viruses
that occur today have the potential to cause certain cancers
Cancer Cell
Specific Viruses
Cancers Caused
Mechanism that causes
cancer
Epstein-Barr Virus (EBV)
Burkitt’s Lymphoma,
Hodgkin’s Lymphoma
Cell proliferation,
inhibition of apoptosis,
cell migration
Hepatitis B Virus (HBV)
Hepatocellular Carcinoma
Inflammation
Hepatitis C Virus (HCV)
Hepatocellular Carcinoma
Inflammation
Human Immunodeficiency Kaposi's Sarcoma,
Virus (HIV)
Lymphoma
Indirect action of
immunosuppression
Human Papilloma Virus
(HPV)
Cervical Cancer
Inhibition of DNA damage
response, anti-apoptotic
activity
Human T-cell
Lymphotropic Virus
Adult T-cell Leukemia and
Lymphoma
Immortalization and
transformation of
T-cells
SO HOW DO THESE VIRUSES CAUSE CANCER?
 Researchers are not 100% sure of how a virus may cause
tumor formation, but there are a few methods that are being
proposed and studied
 The first theory is that a virus interrupts the natural cell cycle
in some way. Dr. Yuri Lazebnik at Cold Spring Harbor
Laboratory found that fusing normal cultured human cells and
Mason-Phizer Monkey Virus (MPMV) did NOT cause the cells to
proliferate (meaning grow) uncontrollably
 Wait, if fusing a virus and a normal cell DID NOT cause
uncontrollable growth, how can this cause cancer??
 The same researchers found that if one of the original cell
partners (human cell or monkey virus) carried a “pre disposing” mutation then a large percentage of the resulting
hybrid cells would grow uncontrollably and become potentially
cancerous
 When the cells that had the pre -disposing cells were fused,
mutations showed on the oncogenes (specifically E1A and
Myc) or to the tumor suppressor gene, p53.
 If oncogenes are activated, cancerous cells are encouraged to
grow. If the tumor suppressor gene p53 is deactivated, the
cells are not signaled to stop growing at any time and
continue to grow uncontrollably
HIT AND RUN THEORY
 Normally, when a virus inserts itself into a cells DNA
structure, it is able to “hide” from the body’s immune system
and it is not eliminated from the host
 Later, these host cells are found to have proof of a previous
infection. The virus left evidence of an infection -much like
fingerprints at a crime scene
 Cells with certain mutations normally will self -destruct so that
they do not turn cancerous, but the viruses interfere with this
defense mechanism
 The hit and run theory proposes that a virus can cause cancer
without inserting itself into the host cell’s DNA
 A cell develops a genetic mutation, but the virus present in
the cell overrides the defense mechanisms and allows the cell
to continue to live. Over time, more and more mutations
develop, and the cell turns cancerous
 However, by the time the cancer is discovered, the virus has
been eliminated by the immune system, leaving behind no
“fingerprints”
“QUOTE OF THE DAY”
 “Viruses don’t set out to cause cancer, but their replication
uses all the same functions. So they tend to inhibit the whole
set of these protective mechanisms,” Stevenson said, “so they
are kind of ideal agents for causing cancer”
TUMOR VIRUSES
 Transformation of a cell can cause
 Loss of growth control
 An ability to form tumors-viral genes interfere with control of cell
replication
 Transformed cells frequently exhibit chromosomal abnormalities
Viral Transformation
The changes in the biological functions of a cell that result from
Regulation
Of the cells metabolism by viral genes and that confer on the
infected cell certain properties characteristic of
Neoplasia
• These changes often result from the integration of the viral
genome into the host cell DNA
• Source:faculty.easnville.edu /md7/bact02/retro/ retro_file /retro .ppt
MAJOR CLASSES OF TUMOR VIRUSES
 DNA Tumor Viruses
 Uses host mechanisms to create new viral particles
 Examples: Papilloma viruses, Herpes Viruses, etc.
 RNA Tumor Viruses
 Carries its own RNA polymerase to create new viral particles
 Examples: Human T-cell Lymphoma, Human Immunodeficiency Virus,
etc.
DNA TUMOR VIRUSES
 Papilloma Viruses
 Cause natural cancers in animals
 Cause benign warts
 Ubiquitous
 Human Papilloma Virus (HPV)
 Persistent HPV infections are now recognized as the cause of
essentially all cervical cancers
 It was estimated that in 2010, 12000 women would be diagnosed
with cervical cancer with 4000 cases resulting in death
 HPV types 16 and 18 transform certain gene products in the cell that
bind to the cell cycle control agents, the Rb and p53
 Note: p53 is the cells tumor suppressor gene….
DNA TUMOR VIRUSES
 Herpes Virus
 Considerable evidence for role in human cancer
 Some are very tumorigenic in animals
 Viral DNA found in a small proportion of tumor cells “hit and run”
 Some cancers possible caused by herpes viruses (specifically
Epstein-Barr Virus)
 Burkitts Lymphoma
 Nasopharyngeal Cancer
 This virus transforms human B-lymphocytes in vitro (possible
mechanism)
DNA TUMOR VIRUSES
 Hepatitis B Virus (HBV)
 Can cause Hepatocellular Carcinoma
 The cancer MAY be caused by the chronic inflammation of the liver
 The mechanism that inflammation causes in the promotion of cancer
is not well understood, but there is evidence of a hit and run
mechanism
 There have been no viral oncogenes found in HBV particles as of yet
 There have been studies that suggest the deletion of the p53 gene
may play a role in the proliferation of mutated liver cells
 *note: Hepatitis C Virus (HCV) is believed to cause Hepatocellular
carcinoma as well, though it is RNA Tumor Virus
DNA TUMOR VIRUSES IN HUMAN CANCER
 Some DNA viruses…
 Can transform cells or have lytic life cycle
 Often integrate into the host genome
 In transformation only genes are transcribed
RNA TUMOR VIRUSES
 Retroviruses known to cause human cancer
 Human T-cell Lymphotropic Virus
 Causes Adult T-cell leukemia and hairy cell leukemia
 Human Immunodeficiency Virus
 Can lead to Kaposi’s Sarcoma
How do retroviruses transform Animal Cells??
The genetic information that leads to cellular transformation has no role in
the viral reproductive cycle and in some cases, is not even contained in the
genome of the virus
Some viruses contain another gene that is a tumor causing gene called an
oncogene. These retroviruses are called transducing viruses.
ONCOGENIC VIRUSES
 Oncogenesis 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
af fect cell growth and division
 Cancer arises from a combination of dominant gain of
function mutation in proto -oncogenes and recessive loss of
function mutations in tumor suppressor genes
Watch: Oncogenes
Source:http://www.youtube.com/watch?v=eoWRZbtqB_s&feature=related
NAMING CANCERS
 Dif ferent types of cancers are named according to the type of
tissue they inhabit.
 -oma=a benign tumor of any tissue group
 Carcinoma=cancer of the epithelial tissues (this does not just
mean the outside layer of skin. This includes ALL epithelial
layers of the body systems)
 This layer of tissue arises from the ectodermal region of embryonic
development
 Sarcoma=connective tissues
 This layer of tissue arises from the mesodermal region of embryonic
development
 Examples:
 A benign fatty mass
 =lipoma
 A malignant tumor that involves glandular tissues
 =adenocarcinoma
 A malignant tumor that involves the bone
 =osteosarcoma
 Also, the term in situ means pre-invasive. Cancers that have not
spread through their original basement membrane will have this
designation
 Ductal Carcinoma In Situ (DCIS) is a cancer of the milk ducts in a woman’s
breast. The cancer is confined to the ductal region and is considered an
early stage of breast cancer
SPECIAL THANKS TO….
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Wordpress.com
Sciencephoto.com
Cancer.gov
www,cancerhelp.org.uk
www.eurekalert.org
www.livescience.com
Faculty.clintoncc.suny.edu
Irapilgrim.mcn.org
www.your-cancer-prevention-wuide.com
Faculty.eansville.edu/md7/bact02/retro/ retro_files/retro.ppt