Transcript Genes-and-the-environment

Genes and the
Environment
Viruses and Cancer.
Environmental Exposure and
Cancer.
Carcinogenesis
What Causes Cancer?
Carcinogens
 Age
 genetic make up
 immune system
 diet
 day-to-day environment
 Viruses
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Age
Diet
Factors in Carcinogenesis
Chromosomes/DNA
In addition to chemicals and radiation, a few viruses also can trigger the
development of cancer. In general, viruses are small infectious agents that cannot
reproduce on their own, but instead enter into living cells and cause the infected cell
to produce more copies of the virus. Like cells, viruses store their genetic
instructions in large molecules called nucleic acids. In the case of cancer viruses,
some of the viral genetic information carried in these nucleic acids is inserted into
the chromosomes of the infected cell, and this causes the cell to become malignant.
Viruses
Viruses contribute to development of some
cancers. Typically, the virus can cause genetic changes
in cells that make them more likely to become
transformed.
These cancers and viruses are linked
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Cervical cancer and the genital wart virus, HPV
Primary liver cancer and the Hepatitis B virus
T cell leukaemia in adults and the Human T cell
leukaemia virus
HTLV-1
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naturally infects CD4+ T lymphocytes and can be
transmitted between close contacts through blood
transfer or from mother to infant through cells in breast
milk.
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In most cases the infection is harmless. However, as many as
1 in 20 infected individuals eventually develop a type of adult
T cell leukaemia in which every tumour cell carries a clonally
integrated HTLV1 provirus.
HTLV1 differs from the standard 'chronically
oncogenic' and 'acutely oncogenic' retroviruses in its
mechanism of action;
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it appears to drive cell growth through expression of a
particular viral protein, Tax, in latently-infected cells
HTLV retrovirus and adult T-cell leukaemia
Mode of action
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Tax can transactivate expression of a
number of key cellular genes that enhance
cell growth.
 The
best examples are the genes encoding
interleukin 2 (a T cell growth factor) and
 the interleukin 2 receptor (a molecule that allows
cells to respond to the growth factor).
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 As
a consequence, the infected cells not only
make their own growth signals, but also
respond to them
Mode of action
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HTLV1 induces a weak growth transformation of T cells in the
laboratory but, in the body, is probably never sufficiently strong to
induce T cell leukaemia on its own.
BUT, a virally infected cell in which growth controls have even partly
broken down, is more susceptible to further genetic accidents.
During persistent infection a gradual build-up of HTLV1-positive T
cells which have accumulated additional genetic changes may
occur.
Eventually this can lead to selection and outgrowth of a fully
malignant, HTLV1-positive clone
At this stage malignant cell growth can occur in the absence of tax
gene expression.
Epstein Barr Virus
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Epstein-Barr virus (EBV), also called Human
herpesvirus 4 (HHV-4), is a virus of the herpes family
(which includes Herpes simplex virus and
Cytomegalovirus),
one of the most common viruses in humans.
Most people become infected with EBV,
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often asymptomatic
but commonly causes infectious mononucleosis.
It is named after Michael Epstein and Yvonne Barr, who
together with Bert Achong discovered the virus in 1964.
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On infecting the B-lymphocyte, the linear virus genome
circularises and the virus subsequently persists within
the cell as an episome.
The virus can execute several distinct programmes of
virally-encoded gene expression
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broadly categorised as being lytic cycle or latent cycle.
The lytic cycle or productive infection results in staged
expression of a host of viral proteins with the ultimate objective
of producing infectious virions. Formally, this phase of infection
does not inevitably lead to lysis of the host cell as EBV virions
are produced by budding from the infected cell.
The latent cycle programmes are those that do not result in
production of virions.
EBV-associated malignancies
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The strongest evidence linking EBV and
cancer formation is found in Burkitt's
lymphoma and Nasopharyngeal
carcinoma
Burkitts Lymphoma
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a type of Non-Hodgkin's lymphoma
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most common in equatorial Africa
 co-existent with the presence of malaria.
 Malaria infection causes reduced immune surveillance of EBV
immortalised B cells, so allowing their proliferation. This proliferation
increases the chance of a mutation to occur. Repeated mutations can
lead to the B cells escaping the body's cell-cycle control, allowing the
cells to proliferate unchecked, resulting in the formation of Burkitt's
lymphoma. Burkitt's lymphoma commonly affects the jaw bone, forming
a huge tumour mass. It responds quickly to chemotherapy treatment,
namely cyclophosphamide, but recurrence is common.
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Other B cell lymphomas arise in immunocompromised patients such
as those with AIDS or who have undergone organ transplantation
with associated immunosuppression.
Smooth muscle tumours are also associated with the virus.
Nasopharyngeal carcinoma
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found in the upper respiratory tract, most
commonly in the nasopharynx, and is linked to
the EBV virus.
It is found predominantly in Southern China and
Africa, due to both genetic and environmental
factors. It is much more common in people of
Chinese ancestry (genetic), but is also linked to
the Chinese diet of a high amount of smoked
fish, which contain nitrosamines, well known
carcinogens (environmental).
Kaposi's sarcoma
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form of skin cancer that can involve
internal organs. It most often is found in
patients with acquired immunodeficiency
syndrome (AIDS), and can be fatal.
K.S.
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Kaposi's sarcoma (KS) was once a very rare form of
cancer, primarily affecting elderly men of Mediterranean
and eastern European background (tumours on lower
legs), until the 1980s, when it began to appear among
AIDS patients.
AIDS-related KS, emerged as one of the first illnesses
observed among those with AIDS. Unlike classic KS,
AIDS-related KS tumours generally appear on the upper
body, including the head, neck, and back. The tumours
also can appear on the soft palate and gum areas of the
mouth, and in more advanced cases, they can be found
in the stomach and intestines, the lymph nodes, and the
lungs.
Kaposi Sarcoma and HHV8
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Studies in 2000 showed that HHV-8 was the culprit
behind KS.
It does not work alone.
In combination with a patient's altered response to
cytokines (regulatory proteins produced by the immune
system) and the HIV-1 transactivating protein Tat which
promotes the growth of endothelial cells, HHV-8 can then
encode interleukin 6 viral proteins, specific cytokines that
stimulate cell growth in the skin.
This becomes KS.
HHV-8
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HHV-8 destroys the immune system further by
directing a cell to remove the major
histocompatibility complex (MHC-1) proteins that
protect it from invasion.
These proteins are then transferred to the
interior of the cell and are destroyed.
This leaves the cell unguarded and vulnerable to
invaders which would normally be targeted for
attack by the immune system.
The natural history of HPV infection and cervical cancer
Cervical Screening
Genomic Map of HPV
(von Knebel Doberitz/European Journal of Cancer 2002; 38: 2229-2242).
The interacting worlds of HPV and p16
The Hepatitis B Virus (HBV)
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HBV is a mostly double-stranded DNA virus in the
Hepadnaviridae family.
HBV causes hepatitis in human.
The HBV genome has four genes: pol, env, pre-core and
X that respectively encode the viral DNA-polymerase,
envelope protein, pre-core protein (which is processed to
viral capsid) and protein X.
The function of protein X is not clear but it may be
involved in the activation of host cell genes and the
development of cancer.
Consequences of HBV Infection
HBV causes acute and chronic hepatitis.
 The chances of becoming chronically
infected depends upon age.
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 About
90% of infected neonates and 50% of
infected young children will become
chronically infected.
 In contrast, only about 5% to 10% of
immunocompetent adults infected with HBV
develop chronic hepatitis B.
Hepatocellular carcinoma
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cancer that arises from hepatocytes, the major
cell type of the liver.
Hepatocellular carcinoma is one of the major
cancer killers.
It affects patients with chronic liver disease who
have established cirrhosis, and currently is the
most frequent cause of death in these patients.
The main risk factors for its development are
hepatitis B and C virus infection, alcoholism and
aflatoxin intake.
integrated HBV can generate
chromosomal instability
 it has been suggested that viral DNA
sequences encompassing the
encapsidation signal may exhibit intrinsic
recombinogenic activity via binding to a
putative ‘recombinogenic’ cellular protein
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Genes and the
Environment –
Thyroid Disease
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The thyroid gland is a small
gland located at the front and
sides of the neck.
It is made up of right and left
lobes connected by a bridge
called the isthmus and weighs
between 20 and 30 grams.
It is slightly heavier in females
and becomes enlarged during
menstruation and pregnancy.
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The thyroid gland produces three
hormones called thyroxine (T4), triiodothronine (T3) and calcitonin. These
hormones help to regulate the body's
metabolism.
Iodine is essential for the production of the
thyroid hormones.
 Good sources of iodine include fish such
as cod, sea bass and haddock.
 Dairy products and plants grown in soil
that is rich in iodine are also good sources.
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The thyroid participates in these processes by producing
thyroid hormones, principally thyroxine (T4) and
triiodothyronine (T3).
These hormones regulate the rate of metabolism and
affect the growth and rate of function of many other
systems in the body.
Iodine is an essential component of both T3 and T4.
The thyroid also produces the hormone calcitonin, which
plays a role in calcium homeostasis.
Physiology
The primary function of the thyroid is
production of the hormones thyroxine (T4),
triiodothyronine (T3), and calcitonin.
 Up to 80% of the T4 is converted to T3 by
peripheral organs such as the liver, kidney
and spleen.
 T3 is about ten times more active than T4.
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The function of the thyroid
gland is to take iodine,
found in many foods, and
convert it into thyroid
hormones: thyroxine (T4)
and triiodothyronine (T3).
Thyroid cells are the only
cells in the body which can
absorb iodine.
These cells combine iodine
and the amino acid tyrosine
to make T3 and T4.
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T3 and T4 are then released into the blood
stream and are transported throughout the body
where they control metabolism (conversion of
oxygen and calories to energy).
Every cell in the body depends upon thyroid
hormones for regulation of their metabolism.
The normal thyroid gland produces about 80%
T4 and about 20% T3, however, T3 possesses
about four times the hormone "strength" as T4.
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The thyroid gland is under the
control of the pituitary gland, a
small gland at the base of the
brain.
When the level of thyroid hormones
(T3 & T4) drops too low, the
pituitary gland produces Thyroid
Stimulating Hormone (TSH)
which stimulates the thyroid gland
to produce more hormones.
Under the influence of TSH, the
thyroid will manufacture and
secrete T3 and T4 thereby raising
their blood levels.
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The thyroid gland is invested
by a thin capsule of
connective tissue, which
projects into its substance
and imperfectly divides it into
masses of irregular form and
size.
Cut surface reveals a
number of closed vesicles,
containing a yellow fluid, and
separated from each other
by intermediate connective
tissue
Significance of iodine
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In areas of the world where iodine
(essential for the production of thyroxine,
which contains four iodine atoms) is
lacking in the diet, the thyroid gland can be
considerably enlarged, resulting in the
swollen necks of endemic goitre.
Significance of iodine
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Because of the thyroid's selective uptake and
concentration of what is a fairly rare element, it
is sensitive to the effects of various radioactive
isotopes of iodine produced by nuclear fission.
In the event of large accidental releases of such
material into the environment, the uptake of
radioactive iodine isotopes by the thyroid can, in
theory, be blocked by saturating the uptake
mechanism with a large surplus of nonradioactive iodine, taken in the form of
potassium iodide tablets.
Significance of iodine
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While biological researchers making compounds
labelled with iodine isotopes do this, in the wider
world such preventive measures are usually not
stockpiled before an accident, nor are they
distributed adequately afterward.
One consequence of the Chernobyl disaster was
an increase in thyroid cancers in children in the
years following the accident.
Chernobyl
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On April 26, 1986, the
fourth reactor of the
Chernobyl Nuclear Power
Plant, exploded at 01:23
AM local time. All
permanent residents of
Chernobyl and Zone of
alienation were
evacuated because
radiation levels in the
area had become unsafe.
Chernobyl
Chernobyl
Chernobyl
Identifying molecular mechanisms that
reveal underlying pathobiology in
Thyroid Neoplasia
Background
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Thyroid Cancer
 most
frequently occurring endocrine malignancy,
 sub-divided into a number of diagnostic
/morphological categories.
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Papillary thyroid carcinoma (PTC)
 Most
common thyroid malignancy
 Ireland<100 cases/yr, U.S.~24,000 cases/yr
 Incidence on the rise - global estimate 0.5 million
new cases this year
 Fastest growing cancer in women worldwide
Pathological Pathways
Papillary Thyroid Carcinoma
Follicular Epithelial Cell
Follicular Carcinoma
Molecular markers in PTC
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ret/PTC
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To date 15 chimeric mRNAs involving
10 different genes have been
described
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Ret/PTC-1 and ret/PTC-3 are the most
common types, accounting for 90%.
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Morphological variants are likely to
reflect variations in tumour biology
which have yet to be fully defined.
ret/PTC-1 expression and associated thryoiditis.
20
18
16
14
12
10
8
6
4
2
0
Hashimoto
thyroiditis ret
pos
Hashimoto
thyroiditis ret
neg
Lymphocytic
thyroiditis ret
pos
Lymphocytic
thyroiditis ret
neg
Graves disease
ret pos
Graves disease
ret neg
E-cadherin expression and radiation dose
0.5
0.45
E-cadherin expression index
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
10
20
30
40
50
Radiation Dose (Gy)
Ret/PTC-1 activation
60
70
80
90
100
ret/PTC-3 activation
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commonly seen in children
exposed to ionizing radiation.
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? Radiation signature
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Literature demonstrates
correlation with solid/follicular
variant morphology, poorer
prognosis and aggressive tumor
behavior.
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Correlation between tumor
morphology and specific ret
rearrangements
Ret/PTC-3 activation
 commonly seen in children exposed to ionising
radiation.
 Literature demonstrates correlation with solid/follicular variant
morphology, poorer prognosis and aggressive tumour
behavior.
 ? prevalence of the common ret chimeric
transcripts (ret/PTC-1 and ret/PTC-3) in a group of
“sporadic” PTC.
 Correlation between tumour morphology and specific ret
rearrangements
Ret/PTC-3 analysis in sporadic cases
 Ret/PTC-1 and ret/PTC-3 transcripts were detected in
43% and 18 % of PTCs respectively.
 Ret/PTC-3 correlated strongly with the solid/follicular
variant [55%] and was not detected in conventional
PTC.
Ret/PTC chimeric transcripts in an Irish Cohort of Sporadic Papillary Thyroid Carcinoma.
SP Finn, P Smyth, O’ Leary JJ, Sweeney EC, Sheils O.
J Clin Endocrinol Metab 2003 Feb; 88(2):938-41.PMID: 12574236 [PubMed - in process]
Real time analysis of beta and gamma catenin mRNA expression in ret/PTC-1 activated and non-activated thyroid
tissues. Smyth P, Finn S, O’Leary J, Sheils O.
Diagn Mol Pathol 2003 Mar;12(1):44-9 PMID: 12605035 [PubMed - in process]
Conclusion of ret/PTC 3 analysis in
sporadic cases
 Significant prevalence of ret/PTC transcripts
in this sporadic group of PTC.
 Higher incidence than previously reported in
areas not affected by ionising radiation
?
More sensitive technique
 ? Effect of exposure to ionising radiation…..
Ret activation and morphology

In the setting of radiation induced PTC it is
apparent that specific ret/PTC
rearrangements are associated with specific
tumour morphology
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ret/PTC-1 associated with classic morphology
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?low dose/long latency
ret/PTC-3 associated with solid/follicular morphology and
adverse prognosis.
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?higher dose/short latency
BRAF
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Raf kinases
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Serine/threonine kinases
Function in Ras/Raf/MEK/ERK
pathway
3 isoforms: A-Braf, B-Raf, CRaf/Raf-1
BRAF implicated in many
cancers
Temporal trends?
9
8
7
6
5
4
3
2
1
0
ret/PTC
Year
-0
2
20
00
19
82
-8
4
19
85
-8
7
19
88
-9
0
19
91
-9
3
19
94
-9
6
19
97
-9
9
T1799A mutation
Microarray analysis
Effect of BRAF mutation on transcriptome
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
‘Normal’ thyroid cell line (left)
PTC Cell Lines with BRAF mutation
(right)
BRAF (mut) transfection experiment
• Left cluster = wt braf–normal cell line
•Right Cluster = (mut) braf–Normal cell line
transfected with braf (mut).
Effect of ret/PTC-1 activation on transcriptome
ret/PTC-1 transfection
experiment
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Left cluster = wt ret
 normal cell line
Right Cluster = ret/PTC-1 Normal cell line
transfected with ret/PTC-1
Genes differentially expressed (upregulated) in
PTC vs benign
Name
Panther Function
Galectin 3
Signalling molecule, cell adhesion
molecule
Calcium Calmodulin-dependant protein
kinase 1
Non-receptor serine/threonine protein
kinase
TGFB1
Angiogenesis
Syndecan 3
Cell adhesion, proliferation,
differentiation
TGFb1
Receptor protein serine/threonine kinase
signalling. Cell cycle control
Calgizzarin (S100A11)
Tumour suppressor, calmodulin related
protein
CD44
Cell adhesion, inhibition of apoptosis
TIMP1
Metalloprotease and its inhibitor
MMP14
Metalloprotease and its inhibitor
Data derived from array analysis of surgically resected lesions
Genes differentially expressed
(downregulated) in PTC vs benign
Name
Panther Function
TIMP4
Metalloprotease Inhibitor
RAB23
Small GTPase – Member RAS oncogene family
FGFR2
Tyrosine Protein Kinase receptor, MAPKKK
cascade, JAK-STAT cascade
Metallothionein
Homeostasis activities
Syndecan 2
Cytoskeletal protein, defence and immunity protein,
extracellular matrix glycoprotein
MAPK4
TSHr
G-protein receptor
Lectin, mannose-binding1
(LMAN1)
Immunity and Defence
Data derived from array analysis of surgically resected lesions
Archival ffpe Tissues
TSHr index
TSHr Expression
30
25
20
15
10
5
0
1=FTC/well diff
2=FTC/poorly diff
3=PTC/well diff
4=PTC/poorly diff
5=FA/norm
6=ATC
7=MTC
0
1
2
3
4
5
6
7
Archival FFPE Tissues
PTC
PTC
ret-ve
PTC
ret+ve
HT
FTC
ATC
FA/NORM