2. P Wheater, G Burkitt, A Stevens, J Lowe. Basic Histopathology,
Second Edition, ELBS with Churchill Livinstone. 1991:2
(Acute
cell injury)
(Sublethal damage)
3.
4. P Wheater, G Burkitt, A Stevens, J Lowe. Basic Histopathology,
Second Edition, ELBS with Churchill Livinstone. 1991:2
(Acute
cell injury)
(Sublethal damage)
Metaplasia
5. 5
Fundamental principles of the
molecular basis of cancer
•Nonlethal genetic damage determines carcinogenesis
•A tumor is formed by the clonal expansion of a single
genetically damaged precursor cell (monoclonality)
•Four classes of normal regulatory genes are the
principal targets of genetic damage
the growth-promoting protooncogenes
the growth-inhibiting tumor suppressor genes
the genes regulating apoptosis
the genes involved in DNA repair
TRANSFORMATION
7. 7
...molecular basis of cancer
• Carcinogenesis is a multistep process at
both the genetic and phenotypic levels
•A malignant neoplasm has
several phenotypic attributes:
- excessive growth
- local invasiveness
- the ability to form metastases
•These features are acquired in a
stepwise fashion, a phenomenon
called tumor progression
8. 8
•GF binding to specific receptor
•signal-transducing proteins on the inner leaflet
of the membrane are activated
• transmission of the signal to the nucleus
• DNA transcription is initiated
• the cell enters into cell cycle, resulting in
cell division
Steps in cell proliferation
9. 9
How do cells acquire uncontrolled
proliferation potential?
TNF
IL-6...
10. 10
How do cells acquire uncontrolled
proliferation potential? +intra-S phase
checkpoint
11. 11
The progression of cells through the cell
cycle is regulated by cyclins and
cyclin-dependent kinases (CDKs)
•CDKs drive the cell cycle by phosphorylating
critical target proteins
• expressed constitutively in an inactive form
•activated by phosphorylation after binding to
proteins called CYCLINS
How do cells acquire uncontrolled
proliferation potential?
12. 12
•synthesized during the cell cycle
•they activate the CDKs
•cyclin levels decline rapidly on task completion
•more than 15 cyclins have been identified -
cyclins D, E, A, and B appear sequentially during
the cell cycle and bind to one or more CDKs
CYCLINS
13. 13
•Cyclin D appears first in mid G1
•cyclin D binds to CDK4, forming
a cyclin D-CDK4 complex
•This complex phosphorylates the
retinoblastoma susceptibility protein (RB)
•The phosphorylation of RB is a molecular
ON-OFF switch for the cell cycle
Cyclin D and RB Phosphorylation
*
•Cyclins D genes are overexpressed in breast, liver,
and esophagus Ca, and mantle-zone lymphoma
•amplification of CDK4 gene - sarcoma, glioblastoma
14. 14
•In its hypophosphorylated state, RB prevents
cells from replicating by forming a tight,
inactive complex with the transcription factor
E2F (a family of transcription factors)
•Phosphorylation of RB dissociates the complex
and releases the inhibition on E2F transcriptional
activity
Thus phosphorylation of RB eliminates
the main barrier to cell-cycle progression
and promotes cell replication
Cyclin D and RB Phosphorylation
17. 17
Expression of cyclin-CDK complexes in cell cycle
Further progression through the
S phase and the initiation of
DNA replication needs an active
complex between cyclin E and
CDK2
19. 19
The activity of cyclin-CDK complexes
is regulated CDK inhibitors
There are two main classes of CDK inhibitors:
the Cip/Kip and the INK4/ARF families
These inhibitors function as tumor suppressors
and are frequently altered in tumors
*
INK4a/ARF locus =
("inhibitor of k inase 4/alternative reading frame")
20. 20
Role of cyclins, CDKs
and CDK-inhibitors
in regulating the G1/S
cell-cycle transition
SUMMARY
21. 21
Main Function
• CDK4 - Forms a complex with cyclin D
- phosphorylates RB, allowing pass
through G1 restriction point
• CDK2 - Forms a complex with cyclin E
in late G1, for the G1/S transition
- Forms a complex with cyclin A
at the S phase for G2/M transition
• CDK1 - Forms a complex with cyclin B,
which acts on the G2/M transition
SUMMARY
22. 22
•Cell-cycle arrest in response to DNA damage and
other cellular stresses is mediated through p53
Defect in cell-cycle checkpoint components is
a major cause of genetic instability in cancer cells
23. 23
Seven fundamental changes
determine malignant phenotype
•Self-sufficiency in growth signals
•Insensitivity to growth-inhibitory signals
•Evasion of apoptosis
•Defects in DNA repair
•Limitless replicative potential
•Sustained angiogenesis
•Ability to invade and metastasize
7
24. 24
Oncogenes = promote autonomous cell growth in
cancer cells
Protooncogenes = physiologic regulators of cell
proliferation and differentiation
Oncogenes are characterized by:
- the ability to promote cell growth in the absence
of normal mitogenic signals
- oncoproteins, resemble the normal oncoproteins
but are devoid of important regulatory elements and
are produced in transformed cells constitutively
Self-sufficiency in growth signals
1
26. 26
• Growth factors (PDGF, TGF-, EGF, FGF)
- synthesis of GF for autocrine activation
+ targeted therapy - HER2 (Ab), c-KIT (TRK)
• GF receptors - constitutive dimerization and
activation without binding of ligand
- mutations
- gene rearrangement
- overexpression
Self-sufficiency in growth signals
1
Point mutation of RAS family genes is the single
most common abnormality of dominant oncogenes
in human tumors
27. 27
Insensitivity to growth-inhibitory signals
The proteins that apply brakes to cell proliferation
are the products of tumor suppressor genes
The mutations required to produce retinoblastoma
involve the RB gene, located on chromosome 13q14
2
•Cancer develops when the cell becomes
homozygous for the mutant allele or when
the cell loses heterozygosity for the normal
RB gene (loss of heterozygosity - LOH)
•Also referred to as a recessive cancer gene
28. 28
Insensitivity to
growth-inhibitory signals
The "two-hit" hypothesis of oncogenesis (Knudson)
•in hereditary cases- one genetic change ("first hit")
is inherited from an affected parent and present in all
somatic cells
•the second mutation ("second hit") occurs in one of
the retinal cells (already has the first mutation)
In sporadic cases, however, both mutations
(hits) occur somatically within a single retinal
cell, whose progeny then form the tumor
RB
2
30. 30
in majority of human cancers dysregulated is at
least one of the four key regulators of the cell cycle:
- p16INK4a
- cyclin D
- CDK4
- RB
In cells that harbor mutations in any one of
these other genes, the function of RB is disrupted
even if the RB gene itself is not mutated
Tu suppressor genes in human neoplasms
Insensitivity to growth-inhibitory signals
2
31. 31
Other pathways of cell growth regulation,
also converging on RB
•TGF-β inhibits cell proliferation by up-regulation
of the CDK inhibitor p27
•human DNA viruses seem to act by neutralizing
the growth inhibitory activities of RB
Insensitivity to
growth-inhibitory signals
2
32. 32
APC/β-Catenin Pathway
•Down-regulation of growth-promoting signals is
another potential area in which products of tumor
suppressor genes may be operative
•APC and NF-1 gene products fall into this category
•Germ line mutations at the APC (5q21)
and NF-1 (17q11.2) loci are associated with benign
tumors that are precursors of Ca that develop later
2
34. 34
p53: Guardian of the Genome
•p53 gene is located on chromosome 17p13.1
•most common target for genetic alteration in tumor
•p53 acts as a "molecular policeman" that prevents
the propagation of genetically damaged cells
•p53 protein is a DNA-binding protein in nucleus
•controls transcription of several other genes
the growth-inhibiting effects of p53 are produced by
up-regulating the synthesis of the CDK inhibitor p21
Evasion of apoptosis
3
36. 36
Subcellular localization and functions of
major classes of cancer-associated genes
protooncogenes - red
cancer suppressor genes - blue
DNA repair genes - green
genes that regulate apoptosis - purple
4
37. 37
LIMITLESS REPLICATIVE POTENTIAL:
TELOMERASE
•After a fixed number of divisions, normal cells
become arrested in a terminally nondividing state
known as replicative senescence
•With each division telomeres, at the ends of
chromosomes shorten
•In germ cells, telomere shortening is prevented
by the enzyme telomerase
•This enzyme is absent from most somatic cells, and
hence they suffer progressive loss of telomeres
5
39. 39
“And of course... telomerase is required to allow
cancer cells to remain immortal
And so the successful clones in a cancer mutate
so as to express telomerase
It's a target for anti-cancer therapy today:
•Nat Med 5: 1164, 1999
•Anticancer Res 20: 4419, 2000
Only cancer cells stain positive for telomerase
•Cancer 90: 117, 2000
Is this the dream of a pathologist's
"stain for malignancy"?
*
40. 40
ANGIOGENESIS
•Tumors stimulate the growth of host blood vessels
•Tumors exist in situ without developing a blood
supply for months to years
•but some cells change to an angiogenic phenotype
•this change is known as the angiogenic switch
6
41. 41
Seven fundamental changes
determine malignant phenotype cont’d
I. Self-sufficiency in growth signals: proliferation
without external stimuli due to oncogene activation
II. Insensitivity to growth-inhibitory signals: no
response to proliferation inhibitors (TGF-β, direct
inhibitors of cyclin-dependent kinases
III. Evasion of apoptosis: due to inactivation of p53
IV. Defects in DNA repair: failure to repair DNA
after carcinogens or unregulated cellular proliferation
(genomic instability)
42. 42
Seven fundamental changes
determine malignant phenotype cont’d
V. Limitless replicative potential:
maintenance of telomere length and function
VI. Sustained angiogenesis: Tu are able to provide
vascular supply, induced by various factors (VEGF)
VII.Ability to invade and metastasize:
depend on processes intrinsic to
the cell and initiated from environment
44. 44
A paraneoplastic syndrome - when a neoplasm
elaborates a substance that results in an effect
that is not directly related to growth, invasion,
or metastasis
•most paraneoplastic syndromes result from
production of hormone-like substances, but a
variety of effects are possible
•paraneoplastic syndrome may precede diagnosis
46. 46
Oncogenesis
Mechanism Action Example
Overexpression of growth factor receptors (such as epidermal
growth factor, or EGF) making cells more sensitive to growth
stimuli
c-erb-B2
Increased growth factor signal transduction by an oncogene that
lacks the GTPase activity that limits GTP induction of cytoplasmic
kinases that drive cell growth
ras
Overexpression of a gene product by stimulation from an oncogene
(such as ras)
c-sis
Lack of normal gene regulation through translocation of a gene
where it is controlled by surrounding genes to a place where it is no
longer inhibited
c-abl
Growth
Promotion
Binding of oncogene product to the nucleus with DNA
transcriptional activation to promote entry into the cell cycle
c-myc
Loss of normal growth inhibition BRCA-1
Lack of regulation of cell adhesion with loss of growth control
through cell interaction
APC
Loss of down-regulation of growth promoting signal transduction NF-1
Loss of regulation of cell cycle activation through sequestation of
transcriptional factors
Rb
Loss of
Tumor
Suppressor
Gene
Function
Loss of regulation of cell cycle activation through lack of inhibition
of cell proliferation that allows DNA repair
p53
Limitation
of
Apoptosis
Overexpression of gene, activated by translocation, prevents
apoptosis
bcl-2
