Download Oncology - Biomedic Generation

Sir Percival Pott (1775) related the increased
incidence of scrotal cancer in chimney sweeps.
On his findings, Danish Chimney Sweeps Guild
ruled that it’s members must bathe daily. No
public health measure since that time, has so
successfully controlled a form of cancer……!!!
O ye who believe! when ye prepare for prayer, wash your
faces, and your hands (and arms) to the elbows; rub your
heads (with water); and (wash) your feet to the ankles. If
ye are in a state of ceremonial impurity, bathe your whole
body…
The Qura’n 5:6
Prophet Mohammed said: When anyone among you
wakes up from sleep, he must not put his hand in the
utensil till he has washed it three times, for he does not
know where his hand was during the night.
Sahih Muslim
OPTIONS OPEN TO A CELL
In response to internal and external
signals, a cell may choose
STASIS
MITOSIS
APOPTOSIS
DIFFERENTIATION
(proliferation)
Growth: Increase in size, tissue component synthesis
Proliferation: Cell division
Differentiation: functional and structural maturity of cells
Tumor: Swelling/new growth/mass
FACTORS CONTRIBUTING TO THE
CONTROL OF GROWTH
Cytokines: Cyclins, CDK
Growth factors: PDGF, FGF
Growth Inhibitors
Cancer suppressor genes: p53
Oncogenes: c-onc, p-onc, v-onc etc.
SIGNALS FEED INTO A COMPLEX
NETWORK OF PARTIALLY
REDUNDANT INTERACTIONS,
THE OUTCOME OF WHICH IS NOT
EASY TO PREDICT.
STIMULATION () OR INHIBITION (-|)
CANCER IS A GROUP OF NEOPLASTIC DISEASES
IN WHICH THERE IS A TRANSFORMATION OF NORMAL
BODY CELLS INTO MALIGNANT ONES.
NEOPLASIA:
PROGRESSIVE PURPOSELESS PATHOLOGIC PROLIFERATION of
cells characterized by LOSS OF CONTROL over cell division.
DNA DAMAGE at growth control genes is central to neoplasm
development
NEOPLASM is an ABNORMAL MASS of tissue the GROWTH
OF WHICH EXCEEDS and is UNCOORDINATED with that of
normal tissue and PERSISTS IN THE SAME EXCESSIVE
manner after cessation of the stimuli which evoked the change
NEOPLASTIC TRANSFORMATION is a process of
conversion of normal cells into a malignant cells
CARCINOGENESIS is a multi step process of
tumor development
process of accumulation of mutations (genetic
changes)
process of genetic & cellular changes leading to
tumor development
is dependent on the cooperation between multiple
genetic changes within a single cell
Carcinogens (Chemical, physical & genetic)  DNA damage  Neoplasm
NEOPLASTIC PROLIFERATION:
UNCONTROLLED AND IRREVERSIBLE
Benign: localized, non-invasive.
Malignant (Cancer): spreading, Invasive
Hypertrophy – Size
Hyperplasia – Number
Metaplasia – Change
Dysplasia – Disordered
Cancer Progression:
Dysplasia to Neoplasia
BENIGN
slow growing,
capsulated,
non-invasive
do not metastasize,
well differentiated,
suffix “oma” e.g. Fibroma.
MALIGNANT
fast growing,
non capsulated,
Invasive & Infiltrate
metastasize.
poorly differentiated,
suffix ‘Carcinoma’ or ‘Sarcoma’
Related with birth defects
CARCINOGEN - agent causing cancer
ONCOGEN - agent causing neoplasm
MUTAGEN - agent causing mutation
ONCOGENES - genes responsible in cancer development
p-onc, v-onc, c-onc: proto/viral/cell oncogenes
PATHWAYS OF SPREAD:
Direct Spread
Body cavities
Blood vessels
Lymphatic vessels
Lungs – Systemic Venous blood
Liver – GIT venous return, nutrition
Brain – End arteries
CANCER CACHEXIA (wasting)
Progressive weakness, loss of appetite, anemia and
profound weight loss (>20%)
Often correlates with tumor mass & spread
Etiology includes a generalized increase in metabolism
and central effects of tumor on hypothalamus
Probably related to macrophage production of TNF-a
HALLMARK OF METASTATIC CELLS
Loss of contact inhibition
Changes in cytoskelton
Changes in the ECM
Novel angiogenesis factors secreted
Defense Mechnisms
What else?
THE BARRIERS TO METASTASIS
THE ABILITY TO ESCAPE FROM THE PARENT TISSUE,
AND AN ABILITY TO SURVIVE AND GROW IN THE
FOREIGN TISSUE, ARE KEY PROPERTIES THAT CELLS
MUST ACQUIRE TO BECOME METASTATIC.
(A.F. Chambers et al., Breast Cancer Res. 2:400 407, 2000.)
IN VITRO ALTERATIONS OF TRANSFORMED CANCER CELLS
1. Cytologic changes includes: increased cytoplasmic basophilia, increased
number and size of nuclei, increased nucleus-cytoplasmic ratio, and
formation of clusters and cords of cells.
2. Alteration in growth characteristics:
 become ‘immortal’ and can be passaged in culture indefinitely
 loss of ‘contact inhibition’ i.e., density-dependent inhibition of growth
 increased uptake of amino acids, hexoses, nucleosides
 require lower concentrations of serum or growth factors in culture
 may lose requirement to grow attached to surfaces and can grow as free
colonies in semisolid media
 fail to stop at cell-cycle checkpoints
 resistance to apoptosis (programmed cell death).
3. Changes in cell membrane structure and function includes: increased
agglutinability by plant lectins; alteration in composition of cell surface
glycoproteins, proteoglycans, glycolipids, and mucins; appearance of tumorassociated Ags.
4. Loss of cell-cell and cell-extracellular matrix interactions that foster cell
differentiation.
Loss of contact inhibition in cell culture. Most normal
cells stop proliferating once they have carpeted the dish
with a single layer of cells: proliferation seems to depend
on contact with the dish, and to be inhibited by contacts
with other cells. Cancer cells, in contrast, usually
disregard these restraints and continue to grow, so that
they pile up on top of one another.
OUR FINGERS, EARS GROW UPTO A CERTAIN SIZE
IS IT ONLY THE CONTACT INHIBITION?
BONUS assignment
TOTAL MRKS: 5
WILL BE ADDED TO YOUR FINAL RESULT AS BONUS
Submit Online
(email: [email protected])
Deadline: 28th February, 2008
Maximum number of words: 300
IN VIVO ALTERATIONS OF TRANSFORMED CANCER CELLS
1. Increased expression of oncogene proteins as a consequence of
2.
3.
4.
5.
6.
7.
8.
9.
chromosomal translocation, amplification, or mutation.
Loss of tumor-suppressor gene protein because of deletion or mutation
Alterations in DNA methylation patterns
Genetic imprinting errors that lead to overproduction of growth-processing
substances (eg, IGF-2).
Increased or unregulated production of growth factors tumor angiogenesis
factors, PDGF, hematopoietic growth factors (e.g., CSF, IL).
Genetic instability and/or activation of telomerase leading to progressive loss
of regulated cell proliferation, increased invasiveness, and increased
metastatic potential
increased levels of enzymes involved in DNA synthesis and higher levels of
lytic enzymes (eg, proteases, collagenases, glycosidases).
increased amounts of oncofetal Ags (eg, carcinoembryonic Ag), placental
hormones (eg, chorionic gonadotropin), or placental-fetal type isoenzymes
(eg, placental alkaline phosphatase).
Ability to avoid the host's antitumor immune response.
CSF = colony stimulating factor
PDGF = platelet-derived growth factor
IGF = insulin-like growth factor
IL= Interleukin
Ag=Antigen.
ANGIOGENESIS
Process of vascularization of a tissue involving development of
new capillary blood vessels; branching and extension of
existing capillaries
Angiogenesis occurs normally in:
 Repair of damaged tissues
 Formation of placenta
 Building up lining of uterus before menstruation
Naturally occurring proangiogenic and antiangiogenic factors
regulate development of blood vessels
Angiogenesis also occurs in tumor development
 Tumors release compounds inducing existing blood vessels
to grow within
 Increased blood supply provides nutrients, carries away
waste
CELL DIVISION AND CELL CYCLE
The continuity of life from one cell to another is based on the
reproduction of cells via cell division. The division of a
unicellular organism reproduces an entire organism,
increasing the population. Cell division on a larger scale can
produce progeny for some multicellular organisms. Cell
division is also central to the development of a multicellular
organism that begins as a fertilized egg or zygote. They also
use cell division to repair and renew cells that die from
normal wear and tear or accidents.
This division process occurs as part of the cell cycle, the life of
a cell from its origin in the division of a parent cell until its
own division into two.
CELL DIVISION DISTRIBUTES IDENTICAL SETS
OF CHROMOSOMES TO DAUGHTER CELLS
Cell division requires the distribution of identical genetic material to
two daughter cells.
 What is remarkable is the fidelity with which DNA is passed
along, without dilution, from one generation to the next.
A dividing cell duplicates its DNA, allocates the two copies to
opposite ends of the cell, and then splits into two daughter cells.
A cell’s genetic information, packaged as DNA, is called its genome.
 In prokaryotes, the genome is often a single long DNA molecule.
 In eukaryotes, the genome consists of several DNA molecules.
DNA molecules are packaged into chromosomes.
 Every eukaryotic species has a characteristic number of
chromosomes in the nucleus.
 Human somatic cells (body cells) have 46 chromosomes
 Human gametes (sperm or eggs) have 23 chromosomes
Each eukaryotic chromosome consists of a long, linear CHROMOSOMES
DNA molecule.
AND DNA
Each chromosome has thousands of genes, the units
that specify an organism’s inherited traits.
Associated with DNA are proteins that maintain its
structure and help control gene activity. This DNAprotein complex, CHROMATIN, is organized into a long
thin fiber.
Each duplicated chromosome consists of two SISTER
CHROMATIDS which contain identical copies of the
chromosome’s DNA.
As they condense, the region where the strands connect
shrinks to a narrow area, is the CENTROMERE.
Each of us inherited 23 chromosomes from each parent:
one set in an egg and one set in sperm
The fertilized egg or zygote undergo trillions of cycles of
mitosis and cytokinesis to produce a fully developed
multicellular human. These processes continue every
day to replace dead and damaged cell.
Gametes (eggs or sperm) are produced only in gonads (ovaries or testes). In the
gonads, cells undergo a variation of cell division, meiosis, which yields 4 daughter cells,
each with half the chromosomes of the parent.
THE CELL
CYCLE
All the events that occur when a cell divides
Time required can vary from minutes to days, depending
on the cell. e.g., Salmonella = 29 min; RBC 120 days
The mitotic (M) phase of the cell cycle alternates with the much
longer interphase.
 The M phase includes mitosis and cytokinesis.
 Interphase accounts for 90% of the cell cycle. During
interphase the cell grows by producing proteins and
cytoplasmic organelles, copies its chromosomes, and prepares
for cell division.
Interphase has three subphases:
 the G1 phase (first gap) centered on growth,
 the S phase (synthesis),
the chromosomes are copied,
 the G2 phase (second gap),
cell completes preparations for cell division,
 and divides (M)
The daughter cells may then repeat the cycle.
Mitosis is a continuum of changes, usually broken into 5 phases
Late INTERPHASE,
the chromosomes
have been duplicated
but are loosely
packed. The
centrosomes have
been duplicated and
begin to organize
microtubules into an
aster (star).
In PROPHASE, the chromosomes During PROMETAPHASE, the nuclear
are tightly coiled, with sister
envelope fragments and microtubules
chromatids joined together. The
from the spindle interact with the
nucleoli disappear. The mitotic
chromosomes. Microtubules from one pole
spindle begins to form and
attach to one of two kinetochores, special
appears
to push the centrosomes regions of the centromere, while
Fig. 12.5 left
away from each other toward
microtubules from the other pole attach to
opposite
(poles)
of Inc.,
thepublishing
cell. as Benjamin
the other
kinetochore.
Copyright ©ends
2002 Pearson
Education,
Cummings
at ANAPHASE, the
centromeres divide,
separating the
sister chromatids.
Each is now pulled
toward the pole to
which it is attached
by spindle fibers.
By the end, the two
poles have
equivalent
collections of
chromosomes.
The spindle fibers push the
sister chromatids until they
are all arranged at the
METAPHASE plate, an
imaginary plane equidistant
Fig. 12.5 right
between
the poles, defining
metaphase.
at TELOPHASE, the cell continues to
elongate as free spindle fibers from each
centrosome push off each other. Two nuclei
begin for form, surrounded by the fragments
of the parent’s nuclear envelope. Chromatin
becomes less tightly coiled. Cytokinesis,
division of the cytoplasm, begins.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Cytokinesis divides the cytoplasm
Cytokinesis, division of the cytoplasm, typically
follows mitosis.
In animals, the first sign of cytokinesis (cleavage)
is the appearance of a cleavage furrow in the
cell surface near the old metaphase plate.
On the cytoplasmic side of the cleavage furrow
a contractile ring of actin microfilaments and
the motor protein myosin form.
Contraction of the ring pinches the cell in two.
GENETIC ANALYSIS of cancer suggests that neoplastic
cells arise through accumulation of mutations
RANDOM MUTATIONS IN
NORMAL CELLS
GENERATE SEVERAL
DISTINCT MUTANTS
The GENETIC
CLONALITY in most
cancers suggests that
a single neoplastic cell
that has undergone
multiple rounds of
mutation, proliferation
& selection and finally
give rise the cancer.
SELECTION
MULTISTAGE EVOLUTION OF CANCER
NEOPLASTIC
CELL
SURVIVING VARIANTS (MUTANTS) UNDERGO NEXT
ROUNDS OF MUTATION & SELECTION.
SUBVARIANTS ESCAPING NORMAL GROWTH
CONTROLS EXPAND TO FORM PRENEOPLASTIC
LESIONS.
ADDITIONAL MUTATIONS WITHIN THE POPULATION
OF PRENEOPLASTIC CELLS GIVE RISE TO CLONAL
VARIANTS THAT PROLIFERATE INTO CANCER.
Each successive mutation gives the cell a growth
advantage, so that it forms an expanded clone, thus
presenting a larger target for the next mutation
Molecular Basis of Neoplasia
CAUSES OF NEOPLASIA
Environmental causes
Chemicals
Viruses
Radiation
Hereditary (Genetic) defects
Combination
Obscure defects !
How do we know if a Compound is
Carcinogenic?
Epidemiology: do the study
of correlation, incidence of
cancer and exposure to the
compound
Animal testing: does the
same compound give similar
cancer?
Ames test
 Short-term assay for
mutagenicity
 Test compound for ability
to induce reversion in
Salmonella typhimurium
strains
 his-  his+; base
substitution or frameshift
 Liver microsomal extracts
used for activation
 Senstive, fast,
inexpensive
Prof. Dr. Bruce Ames
DoB 16th Dec, 1928
Biochem Mol Biol
UC Berkeley, USA
CHEMICAL
CARCINOGENESIS
Initiation
 DNA damage eg.Benzpyrene
Promotion
 Histologic change: eg. Turpentine (co-carcinogens)
Malignant transformation:
 Visible tumor formation: further DNA damage.
Direct Acting Chemical Carcinogens:
 Alkylating Agents: Cyclophosphamide
Procarcinogenes (needs activation)
 Polycyclinc hydrocarbons – Benzpyrene
 Aromatic amines, dyes - Benzidine
 Natural products: Aflotoxin
 Others: Vinyl chloride, turpentine etc.
Arsenic as a Carcinogen
Arsenic has both cancer and noncancer effects
 Noncancer effects
Acute toxicity – relatively high levels
 High blood pressure (?)
 Diabetes (?)


Cancer effects

Skin, bladder, and lung cancer
Radiation as carcinogen
Ultraviolet radiation
UV = 200-400 nm
UV-A: 320-400 nm
UV-B: 280-320 nm
UV-C: 200-280 nm
Cosmic radiation
Ionizing radiation: Ionizing
radiation is produced when the
nucleus of an unstable atom
decays, releasing energy as
ionizing radiation
Radon
Medical exposure (X-ray)
Occupational exposure
EXAMPLE:
X Ray workers – Leukemia
Radio-isotopes – Thyroid carcinoma
Atomic explosion – Skin cancer, Leukemia
Particles from radioactive decay
alpha particles: Particles emitted from the
nucleus of an atom, containing two
protons and two neutrons, identical to
the nucleus (without the electrons) of a
helium atom
beta particles: High-speed particles,
identical to an electron, emitted from
an atomic nucleus
e  h
 
c

UV Damage of DNA
A common type of DNA damage is associated with exposure to
Ultraviolet Light:
can produce thymine dimers (260 nm light)
---GCTATTCACGA-----CGATAAGTGCT---
Blocks replication & transcription because helix distortion
blocks polymerization past this site
Formed from two adjacent thymine residues joined by
either cyclobutane rings involving carbons 5 and 6 or
6-4 carbon linkages
Ability of an organism to survive UV irradiation directly
correlated with its ability to remove thymine dimers
from its DNA
Thymine dimers: major
cause of UV-induced
mutations
These can be corrected by a
process termed ‘photo-reactivation’
Another dimer called a 6-4 dimer is
now know to be the major cause of
UV induced mutations
• Biological effects with UV-B
• dead skin absorb UV-C
• Ozone hole – increased UV
exposure in Australia, other
areas
• Laboratory exposure to short
wavelength UV hazardous
EFFECTS OF IONIZING RADIATION ON
NORMAL AND CANCER CELLS
CANCER CELLS
TEND TO BE MORE
SUSCEPTIBLE
THAN NORMAL
CELLS TO THE
DAMAGING
EFFECTS OF
IONIZING
RADIATION
BECAUSE THEY
LACK AN ABILITY
TO ARREST THE
CELL CYCLE AND
MAKE THE
NECESSARY
REPAIRS
UNFORTUNATELY, THE SAME GENETIC DEFECTS MAY RENDER
SOME CANCER CELLS RESISTANT TO RADIATION TREATMENT,
AS THEY MAY ALSO BE LESS ADEPT AT ACTIVATING APOPTOSIS
IN THE FACE OF DNA DAMAGE.
MEDICINES AND CANCER
Diethylstilbesterol (DES)
 Daughters of women treated with DES had increased risk
of vaginal, cervical cancer
 Affected embryonic or fetal development - long lag time
before cancer appeared
Estrogen replacement therapy
 Increased risk of endometrial cancer - stimulation of cell
proliferation
 Reduced by treatment in combination with progesterone
 Benefit of treatment may be greater than risk of cancer
Anticancer drugs, immunosuppressive drugs may increase
cancer risk
Diethylstilbesterol (or diethylstilbetrol; DES) was a drug prescribed to women from
1938 through 1971 to prevent miscarriages in high-risk pregnancies. However, acting
as a potent estrogen, exposed female fetuses had an increased risk to developing
abnormal reproductive tracts and cancer.
Asbestosis
Most common disease due to asbestos
can lead to lung cancer
Appear in 20 years time after exposure
Reduce lungs function
Asbestos is really a danger to human’s life
Despite of it’s danger, it is still used
considering no alternative substances has
been found
BE CAREFUL OF ASBESTOS!
VIRAL ONCOGENESIS:
insertion of viral nucleic acids  mutation
alterations in oncogenes, tumor suppressor genes and
genes regulating DNA repair resulting in increased cell
division  arcinogenesis.
EXAMPLES:
Human Papilloma Virus
 Cervical neoplasia – warts, papilloma, ca cx
Epstein-Barr virus –
 Burkitts Lymphoma, Nasopharyngeal ca.
Hepatitis B & C virus
 Hepatocellular carcinoma.
Hereditary Causes:
FAP (Familial adenomatous polyposis)– gene C5,
Adenocarcinoma colon
Retinoblastoma – Rb gene – (C13)
Neuroblastoma – (C17)
Trisomy 21 – Down’s syndrome – Leukemias in infants.
Malaysian women have a 1 in 20 chance of developing
breast cancer in their lifetime.
Asian Pac J Cancer Prev. 2007 Oct-Dec;8(4):525-9
LATENCY: IT TAKES 10-50 YEARS
TO DEVELOP CANCER
Age vs. cancer incidence
1.0
3
0.8
0.6
2
background lung
cancer incidence
0.4
1880
1900
1920
1940
1960
1980
Year
Lung cancer is the most frequent site of
cancer in UK men
cancer per 10
60
40
20
0
90
Agein females
Colon cancer
80
IS70CANCER INCREASING ?
60 Colon cancer vs age
50
East
40
West
30
North
20
10
0
1st 2nd 3rd 4th
Qtr Qtr Log
Qtr Qtr
age
0
Log10 incidence per 10
Lung cancer mortality
80
10
20
30
40
50
60
70
80
5
Log10 tobacco consumption
(lb)
60-00
cigarette smoking an “accepted habit”
rise in male lung cancer- alarm
smoking is shown tobe the cause of
lung cancer
People who started smoking before
1960 die of lung cancer
Log10 cancer incidence
1900
1940
1960
5
100
2
1
0
-1
0
1
10
2
TUMOR DIAGNOSIS
History and Clinical examination
Imaging - X-Ray, US, CT, MRI
Tumor markers Laboratory analysis
Cytology –Pap smear, FNAB
Biopsy - Histopathology, markers.
Molecular Tech – Gene detection.
BILATERAL CYSTADENOMA OVARY
OSTEO - SARCOMA
LIPOMA INTESTINE
MENINGIOMA
MOLECULAR BASIS OF CARCINOGENESIS
Genes controlling cell div, cytokines etc. GENETIC DAMAGES: CENTER
OF CARCINOGENESIS
Regulatory genes (4 classes)
Loss/damage to suppressor genes
Promoters: proto-oncogenes
Duplication of promoter genes
Inhibitors: tumor suppressor genes
Loss/damage to Apoptosis genes
Genes regulating Apoptosis
Loss/damage of DNA repair genes
DNA repair genes
IN NORMAL CELLS:
PROTO-ONCOGENES ARE ONLY TRANSIENTLY ACTIVATED
TUMOR SUPPRESSOR GENES ARE ONLY TRANSIENTLY INACTIVATED
WHEN THE PROTO-ONCOGENES ARE ACTIVATED IN NORMAL CELLS BY
MITOGENS, THEY OVERCOME THE SUPPRESSIVE EFFECTS OF THE TUMOR
SUPPRESSOR GENES IN A TRANSIENT FASHION
ONCOGENES
Stimulate Proliferation
Inhibit Differentiation
Inhibit Apoptosis
TUMOR SUPP. GENES
Inhibit Proliferation
Promote Differentiation
Stimulate Apoptosis
WHILE ONCOGENES ACT AS THE ‘GAS PEDAL’ IN A
CAR (THEY ARE NEEDED FOR CELLS TO
PROLIFERATE), THE TUMOR SUPPRESSOR GENES
ACT AS THE ‘BRAKE PEDAL’ OF THE CAR (THEY
NEED TO PREVENT UNCONTROLLED CELL
PROLIFERATION).
PROTO-ONCOGENES
mutations cause permanent
(constitutive) activation
(ONCOGENES); mutant
allele act in a DOMINANT
manner, a GAIN OF
FUNCTION mutation in a
single copy of the cancercritical gene can drive a cell
toward cancer
BOTH UNCONTROLLED
ACTIVATION OF
ONCOGENES and
PERMANENT
INACTIVATION OF TUMOR
SUPPRESSOR GENES
OCCUR IN CANCER CELL
TUMOR SUPPRESSOR GENES code for
proteins that control proliferation or cell
cycle; mutations lead to permanent
inactivation! mutant alleles are
RECESSIVE, means the function of both
alleles of the cancer-critical gene must be
lost to drive a cell toward cancer
WAYS IN WHICH A PROTO-ONCOGENE BECOME
OVERACTIVE TO CONVERT
IT INTO AN ONCOGENE
SINGLE NUCLEOTIDE CHANGE → rasH ONCOGENE
SIX WAYS OF LOSING
THE REMAINING GOOD
COPY OF A TUMOR
SUPPRESSOR GENE
A cell that is defective in only one of its two copies of a tumor suppressor
gene for example, the Rb gene usually behaves as a normal, healthy cell. A
seventh possibility, encountered with some tumor suppressors, is that the
gene may be silenced by an epigenetic change, without alteration of the DNA
sequence. (Nature 305:779, 1983).
CHROMOSOMAL CHANGES IN CANCER
CELLS REFLECTING GENE AMPLIFICATION
AMPLIFICATION of ONCOGENES, may result in formation of
ADDITIONAL PAIRS OF MINIATURE CHROMOSOMES socalled DOUBLE MINUTE CHROMOSOMES or to have a
HOMOGENEOUSLY STAINING REGION interpolated in the
normal banding pattern of one of its regular chromosomes.
Both these aberrations consist of
MASSIVELY AMPLIFIED NUMBERS
OF COPIES OF A SMALL SEGMENT
OF THE GENOME.
MULTIPLE myc GENE COPIES
APPEAR AS A HOMOGENEOUSLY
STAINING REGION (YELLOW)
INTERPOLATED IN ONE OF THE
REGULAR CHROMOSOMES.
THE myc GENE COPIES ARE
PRESENT AS DOUBLE MINUTE
CHROMOSOMES
(PAIRED YELLOW).
BIOCHEMICAL CLASSIFICATION OF
PROTO-ONCOGENES
Growth factors and its receptors
Nonreceptor tyrosine kinases
GTP-binding proteins & regulators
 ras and related proteins
 GTPase activating proteins
Cytoplasmic Ser/Thr kinases
Nuclear signaling
Transcription factors and Nuclear
receptors
GROWTH FACTOR
LIGAND (EPO, IL)
EXTRACELLULAR DOMAIN
TRANSMEMBRANE DOMAIN
PPP-
INTRACELLULAR DOMAIN
PROTEIN KINASE
A
A
-P
signaling pathways
Phosphorylation
cascades
TRANSCRIPTION
FACTORS
DNA
GENE
EXPRESSION
SIGNALING
PATHWAYS,
RELEVANT TO
HUMAN CANCER
CELLS, INDICATING
THE CELLULAR
LOCATIONS OF
SOME OF THE
PROTEINS
MODIFIED BY
MUTATION
Products of both oncogenes and tumor suppressor genes often
occur within the same pathways. Individual signaling proteins are
indicated by red circles, with the cancer-critical components and
control mechanisms in green (Cell 100:57-70, 2000)
Chromosomal translocation
joins the Bcr gene
(chromosome 22) to the Abl
gene (chromosome 9), and
generates a Philadelphia
chromosome.
conversion of Abl proto-oncogene into an oncogene in
patients with CHRONIC MYELOGENOUS LEUKEMIA.
fusion protein has N-terminus of Bcr protein joined to C-terminus of Abl
tyrosine kinase
the Abl kinase domain becomes inappropriately active, driving
excessive proliferation of a clone of hemopoietic cell in bone marrow
abl proto-oncogene contains 2 alternative first exons (1A &1B)
1A can join to the middle of the bcr gene (chromosome 22).
Exon-1B is deleted as a result of the translocation
In the fused gene transcription starts at the bcr promoter and
continues through abl.
Splicing generates a fused Bcr/Abl mRNA, deleting abl exon 1A
Fusion protein contains bcr sequences abl exons from exon 2
normal individual
has 2 Rb+ alleles
loss of allele in somatic
cell has no effect, loss
of one allele in germ
cells create carrier with
wild phenotype
loss of 2nd allele in
somatic cell induces
tumor formation
Loss of both alleles of Rb leads to
RETINOBLASTOMA development
In Humans Rb is seldom mutated
in sporadic human cancers.
Rb inhibits both proliferation and
apoptosis; promotes
differentiation – TUMOR
SUPPRESSOR GENE
Retinoblastoma is caused by loss of both copies of the RB
genes in chromosome 13q14. In the inherited form, one
chromosome has a deletion in and the 2nd copy is lost by
somatic mutation. In the sporadic form, both copies are lost by
individual somatic events (LOSS OF HETEROZYGOSITY).
PATHWAY THAT
CONTROLS
CELL CYCLING
VIA Rb PROTEIN
GREEN: PRODUCTS OF
PROTO-ONCOGENES
RED: PRODUCTS OF
TUMOR SUPPRESSOR
GENES
p16 inhibits the formation of an
E2F (blue) has active Cdk4/cyclin D1 complex,
preventing proliferation. Inactivation
both inhibitory
and stimulatory (mutation) of Rb or p16 encourages
actions,
cell division (thus each acts as
depending on
tumor suppressor) while over
the other
activity of Cdk4 or cyclin D1
proteins that are
encourages cell division thus can be
bound to it.
regarded as proto-oncogene).
The Rb protein inhibits
entry into the cell-division
cycle when it is
unphosphorylated. The
Cdk4-cyclinD1 complex
phosphorylates Rb,
thereby encouraging cell
proliferation.
Tumor Suppressor Rb
Controls the Cell Cycle
G0/G1 phase: nonphosphorylated
S phase: phosphorylated by cyclin/cdk
Target of Rb: E2F group of TF, which activate
genes essential for the S phase
Rb prevents cells from entering S phase;
released E2F prompts the cell to enter S
phase
Viral tumor antigens (SV40’s T Ag, Adenovirus
E1A and HPV E6) bind specifically to Rb
Inactivation of Rb is needed for the cell to cycle,
which can be done by cyclic phosphorylation
or by sequestering by tumor antigens
OVER-EXPRESSION OF RB IMPEDED CELL GROWTH
A BLOCK TO THE CELL CYCLE IS RELEASED WHEN RB IS
PHOSPHORYLATED (IN THE NORMAL CYCLE) OR WHEN
IT IS SEQUESTERED BY A TUMOR ANTIGEN (IN A
TRANSFORMED CELL)
p53 IS A TUMOR SUPPRESSOR GENE
P53 SUPPRESSES GROWTH OR TRIGGERS APOPTOSIS ?
p53- mice develop a variety of tumors
p53 protein level is increased in many tumor cells
Mutant protein acted as dominant negative mutants
Cell growth advantage; not tissue-specific (many cancers)
p53 inhibits normal cells’ capacity of unrestrained growth
p53 ACTS AS A SENSOR THAT INTEGRATES INFORMATION FROM
MANY PATHWAYS THAT AFFECT THE CELL’S ABILITY TO DIVIDE
p53 family of TFs contains 3 members:
p53, p63 & p73
p73 stimulates apoptosis but, it also inhibits differentiation
p63 and p73 may function to maintain the stem cell fate
p53
DNA
damage
p53
DNA DAMAGE
ACTIVATES
p53
Progression in cell cycle
APOPTOSIS
eliminate cells with damaged DNA
Stop cell cycle in
G1 phase
REPAIR DNA
DAMAGE
p53 PROTECTS CELLS FROM
CONSEQUENCES OF DNA DAMAGES
p53  ACTIVATES DNA REPAIR OR
DESTRUCTION OF THE CELL IF IT IS UNABLE
TO REPAIR!
ACTIVATION OF P53  GROWTH ARREST OR
APOPTOSIS, DEPENDING ON CELL CYCLE
WILD TYPE p53 RESTRAINS CELL GROWTH
DELETION OF BOTH WT ALLELES
OR BY A DOMINANT MUTAION IN
ONE ALLELE
P53 functions as tetramer or higher oligomer
mutation of even one p53 allele can abrogate almost
all p53 activity, since virtually all of the oligomers will
contain at least one defective subunit
SEVERAL COMPONENTS CONCERENED WITH G0/G1 OR G1/S
CYCLE CONTROL ARE FOUND AS TUMOR SUPPRESSORS
Cdc-Cell division cycle
DNA DAMAGE INDUCES P21
DNA damage results in the
elevation of intracellular levels
of p53
p53 activates transcription of
the Cdk inhibitor p21
p21 inhibits cell cycle
progression by binding to
Cdk/cyclin complexes
or p21 may directly inhibit DNA
synthesis by interacting with
PCNA (a subunit of DNA pol).
DNA damage arrests the cell cycle in G1
DNA damage activates protein
kinases that phosphorylate p53
Mdm2 normally binds to p53 and
promotes its ubiquitylation and
destruction in proteasomes
In some cases, DNA
damage also induces
either the
phosphorylation of
Mdm2 or a decrease in
Mdm2 production,
which causes an
increase in p53.
The murine double minute (mdm2)
Phosphorylation of p53
blocks its binding to Mdm2
p53 accumulation
stimulates transcription of
p21 (a Cyclin Dependent
Kinase Inhibitor)
p21 binds and
inactivates G1/S-Cdk
and S-Cdk complexes
and arrest the cell in G1
G1 phase checkpoints
mediated by p53 and Rb
The genes regulated by Rb/TF complexes
include cyclin-dependent kinases (CDKs),
following a positive feedback loop
This feedback is damped by the presence of CDK inhibitors
(CKIs) such as p16INK4a and p21CIP1.
CKI expression can be modulated by the p53 DNA damage
response pathway as indicated. Phosphorylation status of
proteins is indicated by ‘P’ where relevant.
DIFFERENT DOMAINS ARE
RESPONSIBLE FOR EACH OF
THE ACTIVITIES OF P53
P53 ACTIVITY IS
ANTAGONIZED BY
Mdm2, Which Is
Neutralized By p19ARF
Two products of CDKN2A
gene (also known as MTS
and INK4A)
CDKN2A, or p16INK4A:
transcribed from 1, 2 and 3
CONTROLS ON CELL CYCLE
PROGRESSION AND
GENOMIC INTEGRITY
MEDIATED BY THE RB1, p53
AND CDKN2A GENE
PRODUCTS
p19ARF : transcribed from
1, 2 and 3
For exons 2 and 3 reading
frames are different for thse
proteins.
Both the gene products are
active in the RB1 and p53
arms of cell cycle control,
respectively.
REGULATION OF
CYCLIN-DEPENDENT KINASES (CDKs)
1. SYNTHESIS OF CYCLINS
OCCURS AT SPECIFIC
TIMES DURING THE CELL
CYCLE OR IN RESPONSE
TO CERTAIN GROWTH
FACTORS.
3. THE CYCLIN SUBUNIT
MUST COMPLEX WITH THE
CATALYTIC CDK SUBUNIT.
2. DEGRADATION OF
CYCLINS OCCURS AT
SPECIFIC TIMES
DURING THE CELL
CYCLE AND IS
MEDIATED BY
5. THE ASSEMBLED
UBIQUITINCOMPLEX IS INACTIVATED
DEPENDENT
BY PHOSPHORYLATION ON
PROTEOLYSIS.
SPECIFIC RESIDUES IN THE
ADENOSINE
TRIPHOSPHATE BINDING
SIGHT OF THE ENZYME (5B)
AND CAN BE REACTIVATED
BY DEPHOSPHORYLATION
OF THESE RESIDUES BY
CDC25 (5A).
THE ACTIVITY OF
CYCLIN-DEPENDENT
KINASES (CDKS) IS
CONTROLLED AT
SEVERAL LEVELS
4. THE ASSEMBLED
COMPLEX REQUIRES
PHOSPHORYLATION BY
CDK-ACTIVATING KINASE
(CAK) TO REACH MAXIMUM
SPECIFIC ACTIVITY.
6. CDK INHIBITORS
(CKIS) CAN INHIBIT
ASSEMBLY OF THE
CYCLIN/CDK COMPLEX
(6A) OR THE
ACTIVATION OF THE
ASSEMBLED COMPLEX
(6B).
Mechanisms of Cdk regulation
The activities of Cdk's are regulated by four molecular
mechanisms
CONTROL OF THE
G2 CHECKPOINT
MPF: Mitosis Promoting Factor
A COMPLEX OF CHECKPOINT
PROTEINS RECOGNIZES
UNREPLICATED OR
DAMAGED DNA AND
ACTIVATES THE PROTEIN
KINASE CHK1, WHICH
PHOSPHORYLATES AND
INHIBITS THE CDC25 PROTEIN
PHOSPHATASE. INHIBITION
OF CDC25 PREVENTS
DEPHOSPHORYLATION AND
ACTIVATION OF CDC2.
ACTIVATION of M-Cdk
Cdk1 associates with M-cyclin as the levels of M-cyclin gradually rise. The
resulting M-Cdk complex is phosphorylated on an activating site by the Cdkactivating kinase (CAK) and on a pair of inhibitory sites by the Wee1 kinase.
The resulting inactive M-Cdk complex is then activated at the end of G2 by the
phosphatase Cdc25. Cdc25 is stimulated in part by Polo kinase, which is not
shown for simplicity. Cdc25 is further stimulated by active M-Cdk, resulting in
positive feedback. This feedback is enhanced by the ability of M-Cdk to inhibit
Wee1.
Cdk
Inhibitors
Cdk/Cyclin
Complex
p21, p27, p57
Cdk4/CyclinD
G1
Cdk6/CyclinD
G1
Cdk2/CyclinE
G1/S
Cdk2/CyclinA
S
Cdk4/CyclinD
G1
Cdk6/CyclinD
G1
p15, p16, p18, p19
Effected
Cell Cycle
Human
creatine
transporter
overview of the cell-cycle control system. The core of the cellcycle control system consists of a series of cyclin-Cdk complexes
(yellow). The activity of each complex is also influenced by
various inhibitory checkpoint mechanisms, which provide
information about the extracellular environment, cell damage, and
incomplete cell-cycle events (top). These mechanisms are not
present in all cell types; many are missing in early embryonic cell
cycles, for example.
Proteins
selectively
expressed in
human tumors
are candidate
tumor rejection
antigens. The
molecules listed
here have all
been shown to be
recognized by
cytotoxic T
lymphocytes
raised from
patients with the
tumor type listed.
Tumor rejection antigens are
specific to individual tumors.
Mice immunized with an
irradiated tumor and challenged
with viable cells of the same
tumor can, in some cases,
reject a lethal dose of that
tumor (left panels). This is the
result of an immune response
to tumor rejection antigens. If
the immunized mice are
challenged with viable cells of a
different tumor, there is no
protection and the mice die
(right panels).
Tumor Surveillance
Macrophage/Dendritic cell
attack or Ag presentation
CD8 mediated cytotoxicity
ADCC
NK cells
the balance in activation and
suppression of immunity determines
the fate of cancer development
Tumors can activate the
immune response e.g.
expression of foreign
antigen with MHC-I
or suppress the immune
response e.g. activation
of T regulatory cells that
release IL-10 and TGF
TGF 1 inhibits proliferation
and apoptosis of B cells
IL-10 inhibits synthesis of proinflammatory cytokines like IFN-γ, IL-2,
IL-3, TNFα and GM-CSF
Nature Immunology. 2002; 3, 999 - 1005
IL-10 suppress Ag- presentation
capacity of antigen presenting cells.
Basic Tumor
Immunosurveillance
1) The presence of tumor
cells and tumor
antigens initiates the
release of “danger”
cytokines such as
IFN and heat shock
proteins (HSP).
2) These cause the
activation and
maturation of dendritic
cells such that the
present tumor antigens
to CD8 and CD4 cells
3) subsequent T cytotoxic
destruction of the
tumor cells the occurs
Nature Immunology. 2001; 2, 293 - 299
Tumor surveillance
by NK Cells
Tumor cells produce reactive
oxygen species and stress
induced ligands that can be
recognized by NK cells
Do not recognize tumor cell via
antigen specific cell surface
receptor, but rather through
receptors that recognize loss of
expression of MHC I molecules,
therefore detect “missing self”
common in cancer.
Immunoediting of cancer cells
Elimination refers to
effective immune
surveillance for clones
that express TSA
Equilibrium refers
to the selection for
resistant clones
(red)
Escape refers to the
rapid proliferation of
resistant clones in the
immunocompetent host
Tumor Escape Mechanisms
Low immunogenicity
Antigen modulation
Immune suppression by tumor cells
or T regulatory cells
Induction of lymphocyte apoptosis
Lack of MHC-I as a tumor escape mechanism
Defects in
mechanisms
of MHC-I
production
can render
cancer cells
invisible to
CD8 cells
Tumors can escape immunity (and immunotherapy) by
selecting for resistant clones that have occurred due to
genetic instability
1
Tumor cells induce
apoptosis in T cells
via FAS activation
2
Tumor cell
production of
immune
suppressants
such as TGF-
T regulatory cell
stimulation with
production of
immune
suppressants
such as TGF- 
J Clin Oncol. 22:1136-51, 2004
a) Cancer cells express FAS ligand
b) Bind to FAS receptor on T
lymphocytes leading to apoptosis