Biochemistry _ Cell Growth

biochemistry cell growth ppt

1. Lecture 27
Cell growth and carcinogenesis

2. Cell Growth•Limits to growth
–Stress on DNA
–Difficulty moving nutrients/wastes
across membrane
•Ratio of surface area to volume
•Volume increases at a faster rate than
surface area

3. Cell Division
•Before a cell becomes too large, it divides,
producing 2 daughter cells
–Each daughter cell is an exact replica of the
parent cell
•Before the cell divides, the DNA is
replicated, so each new cell will have the
same genetic information as the parent cell
•2 stages (eukaryotes)
–Mitosis- division of the cell nucleus
–Cytokinesis- division of the cytoplasm

4. The Cell Cycle
•2 major
phases
–Interphase
–Mitosis

5. Interphase
•3 phases
–G1 phase= cells do most
of their growing
•Increase in size and
synthesize new proteins
and organelles
–S phase= chromosomes are replicated and the synthesis
and DNA molecules takes place
•Usually if a cell enters S phase and begins replication, it completes
the rest of the cycle
–G2 phase= many of the organelles and molecules required
for cell division are produced
•Shortest of the 3 phases of interphase

6. Mitosis
•Divided into 4 phases
–Prophase
–Metaphase
–Anaphase
–Telophase
•Followed with Cytokinesis
•Depending on cell- may last a few
minutes to several days

8. Cell cycle regulation is necessary for
healthy growth.

9. Regulating Cell Growth
•Cyclins- proteins that regulate the
timing of the cell cycle in eukaryotic
cells
–Internal regulators: proteins that respond to
events inside the cell
•i.e. make sure all chromosomes have been
replicated; make sure all chromosomes are
attached to the spindle before entering
anaphase
–External regulators: proteins that respond
to events outside the cell
•i.e. embryonic development; wound healing

10. Cell cycle control
Animal cells have built-in “stop” signals that halt the cell
cycle at checkpoints until overridden by “go” signals
To function properly checkpoint signals have to percept
“reports” from crucial cellular processes:
have it been completed correctly and should the cell cycle
proceed.
Checkpoint also register signals from outside the cell

11. Cell cycle control
The most important decision to make is: to continue the cell
division after the exit from M phase or not.
Cells that do not receive the “go” signal at the G1
checkpoint, switch into a nondividing state called the G0
phase.

12. Cyclins and cyclin-dependent kinases (Cdks)
Regulatory molecules of the cycle transition are proteins
of two main types: protein kinases and cyclins.
Protein kinases are proteins that regulate the activity of
the others by phosphorylating them.

13. Cyclins and cyclin-dependent kinases (Cdks)
“Go” signal at the G1 and G2 checkpoints is regulated by
particular protein kinases.
To be active, such a kinase must be attached to a cyclin, a
protein that gets its name from its cyclically fluctuating
concentration in the cell
This kinases are called cyclin-dependent kinases – Cdks.

14. Control at the G2
checkpoint
The stepwise processes of
the cell cycle are timed by
rhythmic fluctuations in the
activity of protein kinases.
There is a direct
correlation between
cyclin accumulation
and the three major
cell cycle checkpoints.

15. Control at the G2
checkpoint
Cdk-cyclin complex called MPF
(maturation promotion factor),
acts at the G2 checkpoint to
trigger mitosis.
MPF activity fluctuates with the
level of cyclin in the cell.
The cyclin level rises
throughout interphase (G1, S,
and G2 phases), then falls
abruptly during mitosis (M
phase).
The Cdk itself is present at a
constant level.

16. Cdc2 (cdk1) is phosphorylated by Cyclin B at 3 regulatory positions
MPF promotes
mitosis by
phosphorylating
various proteins
One effect of MPF
is to the breakdown
of its own cyclin.
The Cdk component of
MPF is recycled.
Its kinase activity will be
restored by association
with new cyclin.

19. Internal regulation
Internal signals
Anaphase, the separation of sister chromatids, does not
begin until all the chromosomes are properly attached to
the spindle at the metaphase plate.
Certain associated proteins trigger a signalling pathway that
keeps an anaphase promoting complex (APC) in an
inactive state.
M-phase checkpoint is the gatekeeper.
Only when all the kinetochores are attached to the spindle
does the “wait” signal cease.

20. External regulation
External signals: growth factors.
Most of mammalian cells divide in culture only if the
growth medium includes specific growth factors.
PDGF – platelet-derived growth factor – is required for the
division of fibroblasts.

21. External regulation
Density-dependent inhibition of cell division, a
phenomenon in which crowded cells stop dividing.
Cultured cells normally divide until they form a single layer
of cells on the inner surface of the culture container.

22. Density-dependent
inhibition
•Effects of controlled cell
growth can be seen by placing
some cells in a petri dish
containing nutrient broth
•Cells grow until they form a
thin layer covering the bottom
of the dish
•Cells stop growing when they
come into contact with other
cells
•If cells are removed, the
remaining cells will begin
dividing again

23. Uncontrolled Cell Growth
•Cancer- disorder in which some of the body’s
own cells lose the ability to control growth
•Cancer cells do not respond to the signals that
regulate the growth of most cells
•P53 gene halts the cell cycle until all
chromosomes have been properly replicated
–A damaged or defective p53 gene causes the cells to
lose the information needed to respond to signals that
would normally control their growth

24. Cancer results from genetic changes that
affect cell cycle control
•The gene regulation systems that go wrong during
cancer are the very same systems involved in
embryonic development

25. Cancer is not a single disease but rather a name
applied to a great variety of malignant tumor that
are formed by the same basic process of
uncontrolled growth.
Cancer is one of the most common and severe
problem of clinical medicine.
Cancer has emerged as a major public health
problem in developing countries for the first time,
matching its effect in industrialized nations. This is
a global problem.
Cancer

26. Cancer may affect people at all ages, even fetuses
but risk for the more common varieties tends to
increase with age.
Early diagnosis and early treatment are vital, and
identification of persons at increased risk of
cancer before its development is an important
objective of cancer research.
Cancer

27. Self-limited in their growth.

Do not invade or metastasize (although
some benign tumor types are capable of
becoming malignant).
Benign Tumors

28. Excessive growth and division without
respect to normal limit,
Invasive, invade and destroy adjacent
tissues, and sometime,
Distant metastasis spread to other
locations in the body.
Malignant Neoplasm or Tumors (Cancer(

29. Old age
Unhealthy lifestyle (Western lifestyle), Poor diet,
lack of physical activity, or being overweight.
Environmental factors, defined broadly to include
tobacco use, diet, sunlight and infectious diseases.
Occupational carcinogens
Radiation
Family history of cancer (Genetic susceptibility)
Alcohol
Chemicals and other substance
Risk Factors

30. Cancer Type Risk Factor
Lung Cancer Tobacco smoke
Asbestos and other substances
Air pollution
Breast Radiation
Genetic changes (Inherited mutation)
Colorectal Genetic alteration
Diet
Cigarette smoking
Ulcerative colitis or chon's disease
Prostate Diet
Certain prostate changes
Race Africans Americans
Risk Factor/ Cancer Type

31. Cancer Type Risk Factor
Liver Hepatitis viruses (HCV.HBV)
Pancreas Smoking
Diabetes
Being male
Chronic pancreatitis
Kidney Tobacco smoking
High blood pressure
Von-Hippel-Lindau syndrome
(VHL)
Leukemia Radiation
Chemotherapy
Certain disease (Down syndrome)
Human T cell leukemia virus
Myelodysplatic syndrome
Risk Factor/ Cancer Type

32. Cancer Type Risk Factor
Bladder Occupation
Certain infection
Tobacco smoking
Race Twice as often as Africans Americans
Treatment with cyclophosphamide or arsenic
Uterine Endometrial hyperplasia
Race Africans Americans
Hormonal replacement therapy
Obesity
Melanoma Dysplastic nevi
Fair skin
Weakened immune system
Sever blistering/Sunburn
UV irradiation
Risk Factor/ Cancer Type

33. Microorganism Cancer
Human papilloma virus Cervical cancer
Helicobacter pylori Stomach cancer
Hepatitis B and hepatitis C viruses Liver cancer
Human T-cell leukemia/lymphoma
virus
Lymphoma and leukemia
Human immunodeficiency virus Lymphoma and a rare cancer
called Kaposi's sarcoma
Epstein-Barr virus Lymphoma
Human herpes virus 8 Kaposi's sarcoma
Certain viruses or bacteria may increase the risk of developing cancer

34. The etiology of cancer is multifactorial, with genetic,
environmental, medical, and lifestyle factors interacting
to produce a given malignancy.
Agents (molecules, radiation or viruses) that cause cancer
are called carcinogens. This causal process is called
carcinogenesis.
In humans, it is generally accepted that most epithelial
cancers are caused by environmental exposure to certain
kinds of chemicals. However, carcinogenesis is clearly
influenced by large numbers of genes and non-
carcinogenic environmental factors (notably diet, and
underlying inflammation).
Etiology

35. Etiology
Most cancer is caused by genetic mutations
often, by a series of mutations.
•New perceptions of previously known
carcinogens:
•Combined effects of multiple exposures

36.  Decreases time available for DNA repairDecreases time available for DNA repair
 Converts repairable DNA damage into non-repairable Converts repairable DNA damage into non-repairable
mutationsmutations
 Necessary for chromosomal aberrations, insertions, Necessary for chromosomal aberrations, insertions,
deletions and gene amplificationdeletions and gene amplification
 Clonally expands existing cell populationsClonally expands existing cell populations
Cell Replication is Essential for Multistage Cell Replication is Essential for Multistage
CarcinogenesisCarcinogenesis

37. THOUSANDS OF KNOWN CARCINOGENIC
AGENTS ARE IN THE ENVIRONMENT
•Organic molecules (aromatic amines)
•Inorganic molecules (vinyl chloride)
•Heavy metals (lead, arsenic, chromium[VI])
•Viruses (HBV, HCV, HPV, HIV)
•Radiation (gamma, X-ray, high energy beta)
•Inert substances (asbestos)

38. Proportion Percentage
Chemicals tested in both rats and mice 350/590 59%
Naturally occurring chemicals 79/139 57%
Synthetic chemicals 271/451 60%
Chemicals tested in rats and/or mice

Chem. in Carcinogen. Potency Database 702/1348 52%
Natural pesticides 37/71 52%
Mold toxins 14/23 61%
Chemicals in roasted coffee 21/30 70%
Physician’s desk reference

Drugs with reported cancer tests 117/241 49%
FDA database of drug submissions 125/282 44%
Proportion of chemicals evaluated as carcinogenicProportion of chemicals evaluated as carcinogenic
Ames and Gold Ames and Gold Mutat ResMutat Res 447:3-13, 2000 447:3-13, 2000

39. Classification of Carcinogens According to the Classification of Carcinogens According to the
Mode of ActionMode of Action
GENOTOXICGENOTOXIC::
DNA-reactive or DNA-reactive metabolitesDNA-reactive or DNA-reactive metabolites
Direct interaction to alter chromosomal Direct interaction to alter chromosomal
number/integritynumber/integrity
May be mutagenic or cytotoxicMay be mutagenic or cytotoxic
Usually cause mutations in simple systemsUsually cause mutations in simple systems
DNA AdductDNA Adduct MutationMutation CancerCancer
GENOTOXIC NON-GENOTOXIC NON-
GENOTOXICGENOTOXIC

40. Mechanism of Carcinogenesis:Mechanism of Carcinogenesis:
GenotoxicGenotoxic Carcinogens Carcinogens
1. Carcinogen activation1. Carcinogen activation2. DNA binding2. DNA binding 4. Gene4. Gene mutationmutation
Chemical "Activated“
carcinogen
3. Cell proliferation3. Cell proliferation
(fix mutation)(fix mutation)
“inactivated“
carcinogen
C
Y
P
450s
DNA Repair APOPTOSIS

41. the mechanism of causing cancer by exposure to polycyclic aromatic hydrocarbonsthe mechanism of causing cancer by exposure to polycyclic aromatic hydrocarbons

42. Classification of Carcinogens According to the Mode Classification of Carcinogens According to the Mode
of Actionof Action
NON-GENOTOXICNON-GENOTOXIC ::
Do not directly cause DNA mutation
Mechanism of action is not completely
understood
Difficult to detect - requires rodent
carcinogen bioassay
??
MutationMutationCancerCancer

43. Mechanisms of Non-Genotoxic Mechanisms of Non-Genotoxic
CarcinogenesisCarcinogenesis
““black box” black box”
Increased cell proliferationIncreased cell proliferation
Decreased apoptosisDecreased apoptosis
Changes in gene expression Changes in gene expression
Induction of metabolizing enzymesInduction of metabolizing enzymes
Activation of receptors (signaling)Activation of receptors (signaling)
Oxidative stressOxidative stress
??????

44. Oxidative StressOxidative Stress
Indirect DNA damageIndirect DNA damage
Induction of cell proliferation/apoptosis signaling Induction of cell proliferation/apoptosis signaling
cascadescascades

45. Non-Genotoxic CarcinogensNon-Genotoxic Carcinogens
1)1)Mitogens: Mitogens:
•stimulation of proliferationstimulation of proliferation
•mutations may occur secondarily to cell proliferationmutations may occur secondarily to cell proliferation
•may cause preferential growth of preneoplastic cellsmay cause preferential growth of preneoplastic cells
2) 2) Cytotoxicants: Cytotoxicants:
•cytolethalcytolethal
•induce regenerative growthinduce regenerative growth
•mutations maymutations may occur secondarily to cell proliferation occur secondarily to cell proliferation

46. Mechanism of Carcinogenesis:
Non-Genotoxic Carcinogens
Cell proliferation (to fix “spontaneous” mutation)Cell proliferation (to fix “spontaneous” mutation)
APOPTOSIS
CANCER
X

47. Apoptosis
•Apoptosis is a tightly regulated form of cell death, also called the
programmed cell death.
•Morphologically, it is characterized by chromatin condensation and cell
shrinkage in the early stage. Then the nucleus and cytoplasm
fragment, forming membrane-bound apoptotic bodies which can be
engulfed by phagocytes.
•In contrast, cells undergo another form of cell death, necrosis, swell
and rupture. The released intracellular contents can damage
surrounding cells and often cause inflammation.

49. Cancer: Pathogenesis
•General mechanisms:General mechanisms:
–Acquired capabilities (Self-maintained replication, Acquired capabilities (Self-maintained replication,
longer survival, genetic instability, longer survival, genetic instability,
neoangiogenesis, invasion and metastasis)neoangiogenesis, invasion and metastasis)
–Activation of oncogenes, inactivation of tumor-Activation of oncogenes, inactivation of tumor-
suppressor genes, non-effective DNA repairsuppressor genes, non-effective DNA repair
–Caretaker and gatekeeper pathwaysCaretaker and gatekeeper pathways

50. •Caretaker genes encode products that
stabilize the genome. Mutations in caretaker
genes lead to genomic instability.
•Gatekeeper genes encode gene products
that act to prevent growth of potential cancer
cells and prevent accumulation of mutations
that directly lead to increased cellular
proliferation.

52. Error in DNA replication (randomly acquired).
Effects of carcinogens, such as tobacco smoke,
radiation, chemicals, or infectious agents.
Inheritance, and thus present in all cells from
birth.
Abnormalities in the genetic material due to:

53. Series Mutation can Lead to Cancer

54. The Multistep Model of Cancer
Development
•Multiple mutations are generally needed for full-
fledged cancer; thus the incidence increases with
age
•At the DNA level, a cancerous cell is usually
characterized by at least one active oncogene and
the mutation of several tumor-suppressor genes

55. Colon
Normal colon
epithelial cells
Loss
of tumor-
suppressor
gene APC
(or other)
1
2
3
4
5
Colon wall
Small benign
growth
(polyp)
Activation
of ras
oncogene
Loss
of tumor-
suppressor
gene DCC
Loss
of tumor-
suppressor
gene p53
Additional
mutations
Malignant
tumor
(carcinoma)
Larger
benign growth
(adenoma)

56. Initiating
Event
Cell Proliferation
(clonal
expansion)
Progression
Cell Proliferation
Cell
Proliferation
Malignancy
Second M
utating
Event
"N" M
utating Event
Initiation
Promotion
Stages of CarcinogenesisStages of Carcinogenesis

57. Cellular and Molecular Mechanisms in Multistage
Carcinogenesis: INITIATION
Initiating event involves cellular genome – MUTATIONS
Target genes: - oncogenes/tumor suppressor genes
- signal transduction
- cell cycle/apoptosis regulators
“Simple”
genetic
changes

58. SOURCES OF MUTATIONSSOURCES OF MUTATIONS
ENDOGENOUS DNA DAMAGEENDOGENOUS DNA DAMAGE EXOGENOUS DNA DAMAGEEXOGENOUS DNA DAMAGE
DepurinationDepurination
DNA REPAIRDNA REPAIR
MUTATIONMUTATION
LifeLife
StylesStyles
EnvironmentalEnvironmental
AgentsAgents
FreeFree
RadicalsRadicals
PolymerasePolymerase
ErrorsErrors
CELL REPLICATIONCELL REPLICATION

59. Chemical ExposureChemical Exposure (air, water, food, etc.) (air, water, food, etc.)
Internal ExposureInternal Exposure
Metabolic ActivationMetabolic Activation
Macromolecular BindingMacromolecular Binding
DetoxicationDetoxication
DNADNA
RNARNA
ProteinProtein
Biologically Effective DoseBiologically Effective Dose
Efficiency of MispairingEfficiency of Mispairing
Cell ProliferationCell Proliferation
XX
XX
InitiationInitiation
(Biomarker)(Biomarker)

60. Epigenetic alterations – changes induced in cells that alter the
expression of the information on transcriptional, translational, or post-
translational levels without changes in DNA sequence
EPIGENETICS
SAMSAH
DNMT1
DNMT3a
DNMT3b
Methylation of
DNA
Modifications of
histones
RNA-mediated
modifications
•RNA-directed DNA
methylation
•RNA-mediated chromatin
remodeling
•RNAi, siRNA, miRNA …
A
Me
P
U
- acetylation
- methylation
- phosphorylation
- ubiquitination
P U
Me
A

61. GENETIC AND EPIGENETIC MODELS OF THE CANCER INITIATION
Epigenetically
reprogrammed cells
Mutator
phenotype cells
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ALTERATIONS IN
CELLULAR EPIGENOME
Normal cells
Cancer cells
Clonal selection and
expression of initiated cells
Mutator
phenotype cells
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ACQUISITION OF ADDITIONAL
RANDOM MUTATIONS
Normal cells
Cancer cells

62. Cellular and Molecular Mechanisms in Multistage
Carcinogenesis: PROMOTION
Reversible enhancement/repression of gene expression:
- increased cell proliferation
- inhibition of apoptosis
No direct structural alteration in DNA by agent or its metabolites

63. Cellular and Molecular Mechanisms in Multistage
Carcinogenesis: PROGRESSION
• Irreversible enhancement/repression of gene expression
• Complex genetic alterations (chromosomal translocations,
deletions, gene amplifications, recombinations, etc.)
• Selection of neoplastic cells for optimal growth genotype/
phenotype in response to the cellular environment
“Complex”
genetic
changes

64. •Immortalization
•Transformation
•Loss of contact growth inhibition
•Autonomy of proliferation
•Avoidance of apoptosis
•Aberrant differentiation
•Induction of angiogenesis
Phenotypic characteristics of cancer cells:

65. Tumor Cells and the Onset of Cancer

66. Hallmarks of Cancer Cells
•Self-maintained
replication
•Longer survival
•Genetic instability
•Capable of inducing
neoangiogenesis
•Capable of invasion
and metastasis
–Apoptosis down-
regulation
–Lack of response
to inhibitory
factors
–Self-sustained
proliferation

67. Hallmarks of Cancer Cells
•Self-maintained
replication
•Longer survival
•Genetic instability
•Capable of inducing
neoangiogenesis
•Capable of invasion
and metastasis
–Apoptosis
down-regulation
–Telomerase
reactivation

68. Hallmarks of Cancer Cells
•Self-maintained
replication
•Longer survival
•Genetic instability
•Capable of inducing
neoangiogenesis
•Capable of invasion
and metastasis
–Cooperative
genetic
damage
–Mutagenic
agents
–Defective repair
systems

69. Hallmarks of Cancer Cells
•Self-maintained
replication
•Longer survival
•Genetic instability
•Capable of inducing
neoangiogenesis
•Capable of invasion
and metastasis

70. Multistep Tumorigenesis

71. Stages of tumour development
Malignant cell
Dissemination
of other organs
Invasion
Proliferation Angiogenesis
Neovascular
endothelial
maintenance
Invasion
Cytotoxics
Endocrine
EGFR inhibitors
HER2 antibodies
Anti-
angiogenics
Vascular
targeting
agentsNovel
agents
Novel
agents
Metastatic
Cancer
of other
organs

72. Types of Genes Associated with Cancer
•Cancer can be caused by mutations to genes that
regulate cell growth and division
•Tumor viruses can cause cancer in animals
including humans

73. Alteration of Gene ExpressionAlteration of Gene Expression
Nuclear (hormone-like) receptors Nuclear (hormone-like) receptors
Kinase cascadesKinase cascades
Calcium-, nitric oxide-mediated signalingCalcium-, nitric oxide-mediated signaling
Transcription factorsTranscription factors
Gene methylation status (hypo -> enhanced gene Gene methylation status (hypo -> enhanced gene
expression; hyper -> gene silencing)expression; hyper -> gene silencing)

74. What types of genes get mutated in
cancer?
•Oncogenes are activated
–Normal function: cell growth, gene transcription
•Tumor suppressor genes are inactivated
–Normal function: DNA repair, cell cycle control,
cell death

75. •Oncogenes are cancer-causing genes
•Proto-oncogenes are the corresponding normal
cellular genes that are responsible for normal cell
growth and division
•Conversion of a proto-oncogene to an oncogene
can lead to abnormal stimulation of the cell cycle

76. •Proto-oncogenes can be converted to oncogenes
by
–Movement of DNA within the genome: if it ends up
near an active promoter, transcription may
increase
–Amplification of a proto-oncogene: increases the
number of copies of the gene
–Point mutations in the proto-oncogene or its
control elements: cause an increase in gene
expression

77. Proto-oncogene
DNA
Translocation or
transposition: gene
moved to new locus,
under new controls
Gene amplification:
multiple copies of
the gene
New
promoter
Normal growth-
stimulating
protein in excess
Normal growth-stimulating
protein in excess
Point mutation:
within a control
element
within
the gene
Oncogene Oncogene
Normal growth-
stimulating
protein in
excess
Hyperactive or
degradation-
resistant
protein

78. Tumor-Suppressor Genes
•Tumor-suppressor genes help prevent
uncontrolled cell growth
•Mutations that decrease protein products of tumor-
suppressor genes may contribute to cancer onset
•Tumor-suppressor proteins
–Repair damaged DNA
–Control cell adhesion
–Inhibit the cell cycle in the cell-signaling pathway

79. Interference with Normal Cell-Signaling
Pathways
•Mutations in the ras proto-oncogene and p53
tumor-suppressor gene are common in human
cancers
•Mutations in the ras gene can lead to production
of a hyperactive Ras protein and increased cell
division

80. Cancer Molecular Pathways

81. TUMOR SUPPRESSOR GENES
Disorders in which gene is affected
Gene (locus) Function Familial Sporadic
DCC (18q) cell surface unknown colorectal
interactions cancer
WT1 (11p) transcription Wilm’s tumor lung cancer
Rb1 (13q) transcription retinoblastoma small-cell lung
carcinoma
p53 (17p) transcription Li-Fraumeni breast, colon,
syndrome & lung cancer
BRCA1(17q) transcriptional breast cancer breast/ovarian
tumors
BRCA2 (13q) regulator/DNA repair

82. Inherited Predisposition and Other
Factors Contributing to Cancer
•Individuals can inherit oncogenes or mutant alleles
of tumor-suppressor genes
•Inherited mutations in the tumor-suppressor gene
adenomatous polyposis coli （APC）are
common in individuals with colorectal cancer
•Mutations in the BRCA1 or BRCA2 gene are found
in at least half of inherited breast cancers, and
tests using DNA sequencing can detect these
mutations

83. Multiple Stages of Human Colon Cancer
•It is estimated that by age 70, 50% of the population at large have acquired pre-
cancerous adenomas in the colon; 10% of this group will progress to malignancy in the
following 10 years.
•Familial Adenomatous Polyposis (FAP) is linked to the APC gene whose protein is
involved in ß-catenin signaling. The gene acts as a tumor suppressor, and the loss of
function mutation causes development of hundreds to thousands of adenomas, with a
consequent high risk of progression to malignancy.

84. Multiple Stages of Human Colon Cancer
APC protein (Adenomatous Polyposis Coli) is normally expressed
in colorectal epithelial cells, a site of relatively high natural
proliferation rates. The epithelium is convoluted into deep recesses
called crypts and projections called villi. Crypts contain stem cells
for tissue replacement, and the base of the crypt is a site of high
mitotic activity. As cells age, they progress up the villus to the tip.
Polyps Adenomas Progression to cancer
Germline APC+/–
FAP
>90% by age 20 >90% by age 30 50% by age 40
Germline APC+/+
normal
50% by age 70 5%
Cell accumulation
and dysplasia
hyperplasia,
aneuploidy
proliferating, anti-apoptotic,
metastatic, angiogenic

85. Growth
factor
1
2
3
4
5
1
2
Receptor
G protein
Protein kinases
(phosphorylation
cascade)
NUCLEUS
Transcription
factor (activator)
DNA
Gene expression
Protein that
stimulates
the cell cycle
Hyperactive Ras protein
(product of oncogene)
issues signals on its
own.
(a) Cell cycle–stimulating pathway
MUTATION
Ras
Ras
GTP
GTP
P
P
P
P
P
P
(b) Cell cycle–inhibiting pathway
Protein kinases
UV
light
DNA damage
in genome
Active
form
of p53
DNA
Protein that
inhibits
the cell cycle
Defective or missing
transcription factor,
such as
p53, cannot
activate
transcription.
MUTATION
EFFECTS OF MUTATIONS
(c) Effects of mutations
Protein
overexpressed
Cell cycle
overstimulated
Increased cell
division
Protein absent
Cell cycle not
inhibited
3

86. •Suppression of the cell cycle can be important in
the case of damage to a cell’s DNA; p53 prevents
a cell from passing on mutations due to DNA
damage
•Mutations in the p53 gene prevent suppression of
the cell cycle

87. p53 in apoptosis
Following DNA damage, e.g. by radiation, p53 levels rise, and
proliferating cells arrest in G1. This allows time for DNA repair
prior to the next round of replication. This arrest is mediated by
stimulation of expression of p21CIP1, the cyclin kinase inhibitor.
Very high p53 levels, or susceptible cell types, e.g. lymphocytes,
are triggered to undergo apoptosis. Bcl-2 acts between p53 and the
caspase.

88. P53 can bind to DNA
DNA
p53
P53 as a transcription factor which exerts
its effect by regulating other genes

89. Allow cells time
to repair the
damaged DNA
Induce DNA
repair enzymes
Li-Fraumeni Syndrome
(hereditary p53 mutation)
High risk of getting mutation
of the second copy of the
gene
DNA damaging
chemicals and
radiation
Tobacco---Lung cells
UVB --- Skin cells
p53 upregulated modulator
of apoptosis

90. P53 and the cell cycle
P53 arrests the cell cycle primarily by
upregulating p21 (Cip1/Waf-1), which
inactivates CDK/cyclin
P53 can also activate apoptosis
P21 is a kinase inhibitor

91. Inhibition of p53 functions

92. Genetic Instability in Tumors
•(+) Oncogenes
•(-) Tumor
suppressor genes
•Telomere shortening
•Mismatch repair
(MMR) genes
•Chromosomal
Instability
•Microsatellite
Instability

93. Aneuploidy in Human Hepatocellular Carcinoma Cell Line
Hsr = homogeneously staining region due to
endoreduplication of chromosomal segments
resulting in gene amplification

94. Figure 1.11b The Biology of Cancer (© Garland Science 2007)
Fluorescent in
situ
hybridization
(FISH) of
normal
metaphase
human
chromosomes
using
chromosome
specific DNA
probes with
different
fluorescent
dyes

95. Aneuploid
karyotype of
human breast
cancer cell.
Note
“scrambling” of
colors
demonstrating
chromosomal
reciprocal
translocations

96. Intra-
chromosonal
inversion by
M-band
fluorescent
in situ
hybridization
(mFISH)

97. Telomeres and Cell
Senescence

98. 1800
Human
Genes
mRNA’s From
142 different
human tumors
Red =
elevated
expression
Green =
diminished
expression
Gene Expression DNA
Array Analysis

99. Tumor Immunity
•General Principles
–Tumors not entirely self
•Express non-self proteins
–Immune-mediated recognition of tumor
cells may be “positive mechanism of
eliminating transformed cells
•Immune surveillance

100. Tumor Antigens
•Tumor Specific Antigens
–Present only on Tumor cells
–Recognized by cytotoxic T cells
•Bound by class I MHC
–Several antigens in humans found that are not
unique for tumor, however are generally not
expressed by normal tissue
•Melanoma-associated antigen-1 (MAGE-1):
–Embryonal protein normally expressed in testis
»Melanomas, breast ca, lung ca

101. Tumor Antigens
•Tumor Associated Antigens
–Not unique to tumors, shared by normal
cells
•Differentiation- specific antigens
–CALLA (CD10) in early B cells
–Prostate specific antigen PSA

102. Antitumor Effector Mechanisms
•Cytotoxic T-cells
–MHC restricted CD-8 cells (viruses)
•NK cells
–Destroying tumor cells without prior sensitization
•Macrophages
–Ifn-gamma
•Humoral Mechanisms
–Via complement and NK cells

103. Antitumor Effector Mechanisms
Cytotoxic T-cell
NK cell
MacrophageHumoral
Mechanisms

104. IMMUNOSURVAILLANCE
•Argument for:
–Increased cancer in immunodeficient hosts
•200x increase in immunodeficiencies (lymphoma)
–X-linked lymphoproliferative disorder (XLP
»EBV related
•Escape Mechanism Theories
–Selective outgrowth of antigen-negative variants
–Loss or reduction of HLA (escape T-cells)
–Immunosuppression (Tumors secrete factors
TGF-b)

105. IMMUNOTHERAPY
•Replace suppressed components of
immune system or stimulate
endogenous responses
–Adoptive Cellular Therapy
•Incubation of lymphocytes with IL-2 to generate
lymphokine activated killer (LAK) cells with
potent antitumor activity
–Enriched tumor specific cytotoxic T cells
»Tumor infiltrating lymphocytes (TIL)

106. Cytokine Therapy
–Activate specific and nonspecific
(inflammatory) host defenses.
•Interferon-a, TNF-a, Il-2, IFN-g
–IFN-a activates NK cells, increase MHC expression
on tumor cells
»Used for hairy cell leukemia

107. Antibody-Based Therapy
–Antibodies as targeting agents
–Direct use of antibodies to activate host
immune system
•Her-2/neu in advance breast cancer

110. Sample questions
•The event(s) which does not occur
during interphase, is/are
•A.Chromatin condenses
•B.Protein Synthesis
•C.Organelles replication
•D.DNA replication

111. •At the center of the cell cycle control
system is Cdk, a protein that
•A.is phosphorylated to become active
•B.binds to different cyclins
•C.is only active during mitosis
•D.manufactures growth factors

112. Sample questions
•An oncogene is
•A.a viral gene with no relation to the host
cell's genes.
•B.a mutated form of a proto-oncogene.
•C.a bacterial gene that causes cancer in the
host.
•D.a gene that turns off cellular reproduction.