MOLECULAR BASIS
of CANCER
• NON-lethal genetic damage
• A tumor is formed by the clonal expansion
of a single precursor cell (monoclonal)
• Four classes of normal regulatory genes
– PROTO-oncogenes
– Oncogenes Oncoproteins
– DNA repair genes
– Apoptosis genes
• Carcinogenesis is a multistep process
TRANSFORMATION &
PROGRESSION
•
•
•
•
•
•
•
•
Self-sufficiency in growth signals
Insensitivity to growth-inhibiting signals
Evasion of apoptosis
Defects in DNA repair: “Spell checker”
Limitless replicative potential: Telomerase
Angiogenesis
Invasive ability
Metastatic ability
Oncogenes
Cell cycle
Apoptosis
Angiogenesis
Tumor Suppressor
Inv. and Mets
3
Hanahan and Weinberg, Cell 100: 57, 2000
ONCOGENES
• Oncogenes are mutated forms of cellular
proto-oncogenes.
• Proto-oncogenes code for cellular proteins
which regulate normal cell growth and
differentiation.
4
Five types of proteins encoded by proto-oncogenes participate in
control of cell growth:
Class I: Growth Factors
Class II: Receptors for Growth Factors and Hormones
Class III: Intracellular Signal Transducers
Class IV: Nuclear Transcription Factors
Class V: Cell-Cycle Control Proteins
5
Functions of Cellular Proto-Oncogenes
1. Secreted Growth Factors
2. Growth Factor Receptors
3. Cytoplasmic
Signal Transduction
Proteins
4. Nuclear
Proteins:
Transcription
Factors
5. Cell Growth
Genes
6
ONCOGENES
• Are MUTATIONS of NORMAL genes
(PROTO-oncogenes)
– Growth Factors
– Growth Factor Receptors
– Signal Transduction Proteins (RAS)
– Nuclear Regulatory Proteins
– Cell Cycle Regulators
• Oncogenes code for  Oncoproteins
Mutations that confer these properties
fall into two categories
• Oncogene
• : a cancer-causing gene that has been mutated to cause
an increase in
• activity, or the activity becomes constitutive, or a new
activity is acquired.
• -a mutation in a single allele is sufficient to transform
cells (dominant).
• -originally identified as viral proteins that resembled
normal human proteins.
• -the term "proto-oncogene" refers to the normal
protein that has not been mutated
• tumor Suppressor gene
• : cancer-causing gene that has been mutated
to cause a loss of activity.
• -mutations are required in both alleles to
transform cells (recessive)
4 types of genetic
mutations that
contribute to cancer
1
2
4
3
• Categories of oncogenes
• A. Growth factors
• -generally not directly involved
transformation, but increased expression seen
as part of
• an autocrine loop due to changes in other
steps in the same pathway
growth factor receptors
• -They are transmembrane proteins with an
external ligand binding domain and an
• internal tyrsosine kinase domain.
• -oncogenic mutations can result in
dimerization and activation in the absence of
• ligand
• -more commonly, increased activity is a result
of overexpression of receptors
Growth factor receptors
• They are transmembrane proteins with an
external ligand binding domain and an
• internal tyrsosine kinase domain.
• -Oncogenic mutations can result in
dimerization and activation in the absence of
• ligand
• -More commonly, increased activity is a result
of overexpression of receptors.
signal transducers
• -Activated directly or indirectly by growth factor
receptors
• -Activation of signal transducers triggers a
phosporylation cascade that ultimately
• results in changes in gene expression at the
transcriptional level.
• -mutations in RAS
• , a GTPase, are the most common oncogenic
abnormality in tumors
• -failure to hydrolyze GTP locks RAS in its active form.
Transcription factors
• -Transcription factors contain DNA binding
domains.
• Sequences
• Regulate expression of genes essential for
passage through the cell cycle, or
• regulation of apoptosis.
• -
Normal CELL CYCLE Phases
INHIBITORS: Cip/Kip, INK4/ARF
Tumor (really growth) suppressor genes:
p53
cyclins and cyclin-dependent kinases
• -cyclins are only expressed at specific stages of
the cell cycle
• -cyclin-dependent kinases are expressed
constitutively, but must bind cyclins for
• activation; phosphorylation of target proteins
essential for progression through
• cell cycle
Regulation of G1/S
cell cycle transition
Cell cycle arrest at G1/S (in
response to DNA damage or
other stressors) is medicated
through which gene?
p53 (levels of p53 under
negative regulation by
MDM2 and p14 ARF)
• a second level of control is achieved by CDK
inhibitors
• -p21 family (broad specificity) and the INK4 (p16)
family (CDK4/6
• specific)
• -overexpression of cyclin D and CDK4 common.
• -phosphorylate and inactivate
• Rb
Category
PROTOOncogene
Mode of
Activation
Associated Human
Tumor
GFs
PDGF-β chain SIS
Fibroblast
HST-1
growth factors
INT-2
TGFα
HGF
Overexpression Astrocytoma
Osteosarcoma
Overexpression Stomach cancer
Amplification
Bladder cancer
TGFα
Breast cancer
Melanoma
Overexpression Astrocytomas
HGF
Hepatocellular
carcinomas
Overexpression Thyroid cancer
Category
PROTOOncogene
Mode of
Activation
Associated Human
Tumor
GF
Receptors
EGF-receptor
family
ERB-B1
(ECFR)
ERB-B2
Overexpression
Amplification
Squamous cell carcinomas of
lung, gliomas
Breast and ovarian cancers
CSF-1 receptor
FMS
Point mutation
Leukemia
Receptor for
neurotrophic
factors
PDGF receptor
RET
Point mutation
PDGF-R
Overexpression
Multiple endocrine neoplasia 2A
and B, familial medullary thyroid
carcinomas
Gliomas
Receptor for stem
cell (steel) factor
KIT
Point mutation
Gastrointestinal stromal tumors
and other soft tissue tumors
Category
PROTOOncogene
Mode of
Activation
Associated Human
Tumor
Signal
Transduction
Proteins
GTP-binding
Nonreceptor
tyrosine kinase
K-RAS
Point mutation
Colon, lung, and pancreatic
tumors
H-RAS
Point mutation
Bladder and kidney tumors
N-RAS
Point mutation
Melanomas, hematologic
malignancies
ABL
Translocation
Chronic myeloid leukemia
Acute lymphoblastic leukemia
RAS signal
transduction
BRAF
Point mutation
Melanomas
WNT signal
transduction
β-catenin
Point mutation
Hepatoblastomas,
hepatocellular carcinoma
PROTOOncogene
Category
Nuclear
Regulatory
Proteins
Transcrip. C-MYC
activators
N-MYC
L-MYC
Mode of
Activation
Associated Human
Tumor
Translocation Burkitt lymphoma
Amplification Neuroblastoma,
small cell
carcinoma of lung
Amplification Small cell
carcinoma of lung
2) Activation Growth-Promoting Oncogenes
Which signal
transduction
pathway is
continuously
activated by mutant
RAS?
MAP kinase
pathway
Point mutations of ras are seen
in what % of all human
malignancies?
15-20%
Tumor supressor gene
• . Tumor suppressor were originally identified
as inherited mutations that confer a
• predisposition to cancer (familial form).
• -inheritance is dominant, meaning a single
defective allele is sufficient to confer
• the predisposition
•
•
•
•
•
•
•
•
•
•
Inactivation of tumor suppressors can occur
Sporadically
-sequential inactivation of both alleles in somatic cells
You may hear the term
haploinsufficiency
, which refers to inactivation of a single
allele contributing to malignancy.
-usually not the initiating event, but exacerbating.
Viral inactivation
-HPV expresses proteins that inhibit Rb and p53
function.
P53 and RAS
p53
• Activates DNA repair
proteins
• Sentinel of G1/S
transition
• Initiates apoptosis
• Mutated in more than
50% of all human
cancers
RAS
• H, N, K, etc., varieties
• Single most common
abnormality of
dominant oncogenes in
human tumors
• Present in about 1/3 of
all human cancers
RB gene
• a.Loss of RB function confers a predisposition
to retinoblastoma.
• occurs in both the familial form (early onset)
and sporadic fromthe basis for tissue
specificity of some tumor suppressors is
unknown, but
• presumably is due to the transcriptional
profile of the tissue, determined by tissue
• function
P53
• p53 is the most commonly mutated gene in
tumors
• -over 50% of all tumors lack functional p53
• • Li-Fraumeni syndrome
• : inheritance of a single defective copy of p53
results in a
• predisposition to a wide spectrum of cancers.
• -p53 is a transcription factor.
1: Failure of
DNA Repair
(acquired)
Normal function of
p53 is to upregulate
activity of which 2
genes to allow repair
of DNA?
p21
GADD45
• Unlike Rb, p53 inhibits G1 progression only in response to
DNA damage
• -normally p53 is very unstable, due to proteolytic
degradation triggered by
• mdm2
• .
• -p53 is phosphorylated in response to DNA damage; mdm2
no longer binds p53
• -p53 upregulates expression of p21, which in turn inhibits
G1/S CDKs.
• c. In response to excessive DNA damage, p53 can trigger
apoptosis
• Some other tumor suppressors found to be inactivated in tumors
inhibit proliferation by
• various mechanisms:
• -APC: degradation of
• b
• -catenin, a transcriptional activator anchored to E-cadherins
• -NF-1: activates GTPase activity of ras
• -TGF• b
• receptor: a tyrosine kinase that upregulates expression of CDK
inhibitors
• -
• -PTEN: dephosphorylates inositol
phospholipids, which act as docking sites for
• intracellular signaling proteins
• VHL: transcriptional elongation
• -WT-1: transcriptional regulator
MYC
• Encodes for transcription factors
• Also involved with apoptosis
Tumor (really “GROWTH”)
suppressor genes
•
•
•
•
•
•
•
•
•
•
•
TGF-β  COLON
E-cadherin  STOMACH
NF-1,2  NEURAL TUMORS
APC/β-cadherin  GI, MELANOMA
SMADs  GI
RB  RETINOBLASTOMA
P53  EVERYTHING!!
WT-1  WILMS TUMOR
p16 (INK4a)  GI, BREAST
BRCA-1,2  BREAST
KLF6  PROSTATE
Evasion of APOPTOSIS
•BCL-2
•p53
•MYC
DNA REPAIR GENE DEFECTS
• DNA repair is like a spell checker
• HNPCC (Hereditary Non-Polyposis Colon
•
•
•
•
Cancer [Lynch]): TGF-β, β-catenin, BAX
Xeroderma Pigmentosum: UV fixing gene
Ataxia Telangiectasia: ATM gene
Bloom Syndrome: defective helicase
Fanconi anemia
LIMITLESS REPLICATIVE POTENTIAL
• TELOMERES determine the limited
number of duplications a cell will
have, like a cat with nine lives.
• TELOMERASE, present in >90% of
human cancers, changes telomeres so
they will have UNLIMITED replicative
potential
TUMOR ANGIOGENESIS
• Q: How close to a blood vessel must a cell be?
• A: 1-2 mm
• Activation of VEGF and FGF-b
• Tumor size is regulated (allowed) by
angiogenesis/anti-angiogenesis balance
TRANSFORMATION
GROWTH
BM INVASION
ANGIOGENESIS
INTRAVASATION
EMBOLIZATION
ADHESION
EXTRAVASATION
METASTATIC GROWTH
etc.
Invasion Factors
• Detachment ("loosening up") of the
tumor cells from each other
• Attachment to matrix components
• Degradation of ECM, e.g.,
collagenase, etc.
• Migration of tumor cells
METASTATIC GENES?
• NM23
• KAI-1
• KiSS
CHROMOSOME CHANGES
in CANCER
• TRANSLOCATIONS and INVERSIONS
• Occur in MOST Lymphomas/Leukemias
• Occur in MANY (and growing numbers) of NONhematologic malignancies also
Malignancy
Chronic myeloid leukemia
Translocation
(9;22)(q34;q11)
Affected Genes
Ab1 9q34
bcr 22q11
Acute leukemias (AML and ALL)
(4;11)(q21;q23)
AF4 4q21
MLL 11q23
(6;11)(q27;q23)
AF6 6q27
MLL 11q23
Burkitt lymphoma
(8;14)(q24;q32)
c-myc 8q24
IgH 14q32
Mantle cell lymphoma
(11;14)(q13;q32)
Cyclin D 11q13
IgH 14q32
Follicular lymphoma
(14;18)(q32;q21)
IgH 14q32
bcl-2 18q21
T-cell acute lymphoblastic leukemia
(8;14)(q24;q11)
c-myc 8q24
TCR-α 14q11
(10;14)(q24;q11)
Hox 11 10q24
TCR-α 14q11
Ewing sarcoma
(11;22)(q24;q12)
Fl-1 11q24
Carcinogenesis is “MULTISTEP”
• NO single oncogene causes cancer
• BOTH several oncogenes AND several
tumor suppressor genes must be involved
• Gatekeeper/Caretaker concept
–Gatekeepers: ONCOGENES and TUMOR
SUPPRESSOR GENES
–Caretakers: DNA REPAIR GENES
• Tumor “PROGRESSION”
– ANGIOGENESIS
– HETEROGENEITY from original single cell
Carcinogenesis:
The USUAL (3) Suspects
• Initiation/Promotion concept:
– BOTH initiators AND promotors are needed
– NEITHER can cause cancer by itself
–INITIATORS (carcinogens) cause MUTATIONS
– PROMOTORS are NOT carcinogenic by themselves,
and MUST take effect AFTER initiation, NOT before
–PROMOTORS enhance the proliferation of
initiated cells
Q: WHO are the usual suspects?
• Inflammation?
• Teratogenesis?
• Immune
Suppression?
• Neoplasia?
• Mutations?
A: The SAME 3 that are
ALWAYS blamed!
•1) Chemicals
•2) Radiation
•3) Infectious Pathogens
CHEMICAL CARCINOGENS:
INITIATORS
• DIRECT
• “PRO”CARCINOGENS
•
β-Propiolactone
Dimeth. sulfate
•
Diepoxybutane
Anticancer drugs
•
(cyclophosphamide,
chlorambucil, nitrosoureas,
and others)
• Acylating Agents
•
•
•
•
– 1-Acetyl-imidazole
– Dimethylcarbamyl chloride
Polycyclic and Heterocyclic
Aromatic Hydrocarbons
Aromatic Amines, Amides,
Azo Dyes
Natural Plant and Microbial
Products
–
–
–
–
–
Aflatoxin B1 Hepatomas
Griseofulvin Antifungal
Cycasin from cycads
Safrole from sassafras
Betel nuts Oral SCC
CHEMICAL CARCINOGENS:
INITIATORS
• OTHERS
•
•
•
•
•
•
•
Nitrosamine and amides (tar, nitrites)
Vinyl chloride angiosarcoma in Kentucky
Nickel
Chromium
Insecticides
Fungicides
PolyChlorinated Biphenyls (PCBs)
CHEMICAL CARCINOGENS:
PROMOTORS
•
•
•
•
HORMONES
PHORBOL ESTERS (TPA), activate kinase C
PHENOLS
DRUGS, many
“Initiated” cells respond and proliferate
FASTER to promotors than normal cells
RADIATION CARCINOGENS
• UV: BCC, SCC, MM (i.e., all 3)
• IONIZING: photons and particulate
– Hematopoetic and Thyroid (90%/15yrs) tumors in
fallout victims
– Solid tumors either less susceptible or require a
longer latency period than LEUK/LYMPH
– BCCs in Therapeutic Radiation
VIRAL CARCINOGENESIS
•
•
•
•
•
HPV SCC
EBV Burkitt Lymphoma
HBV HepatoCellular Carcinoma (Hepatoma)
HTLV1 T-Cell Malignancies
KSHV Kaposi Sarcoma
H. pylori CARCINOGENESIS
• 100% of gastric lymphomas (i.e., M.A.L.T.-omas)
• Gastric CARCINOMAS also!
HOST DEFENSES
• IMMUNE SURVEILLENCE CONCEPT
•
•
•
•
CD8+ T-Cells
NK cells
MACROPHAGES
ANTIBODIES
CYTOTOXIC CD8+ T-CELLS are the main eliminators of tumor cells
How do tumor cells
escape immune surveillance?
• Mutation, like microbes
• ↓ MHC molecules on tumor cell surface
• Lack of CO-stimulation molecules, e.g.,
(CD28, ICOS), not just Ag-Ab recognition
• Immunosuppressive agents
• Antigen masking
• Apoptosis of cytotoxic T-Cells (CD8), i.e., the
damn tumor cell KILLS the T-cell!
Effects of TUMOR on the HOST
•
•
•
•
•
Location anatomic ENCROACHMENT
HORMONE production
Bleeding, Infection
ACUTE symptoms, e.g., rupture, infarction
METASTASES
CACHEXIA
•
•
•
•
•
Reduced diet: Fat loss>Muscle loss
Cachexia: Fat loss AND Muscle loss
TNF (α by default)
IL-(6)
PIF (Proteolysis Inducing Factor)
PARA-Neoplastic Syndromes
•Endocrine (next)
• Nerve/Muscle, e.g., myasthenia w. lung ca.
• Skin: e.g., acanthosis nigricans,
dermatomyositis
• Bone/Joint/Soft tissue: HPOA (Hypertrophic
Pulmonary OsteoArthropathy)
• Vascular: Trousseau, Endocarditis
• Hematologic: Anemias
• Renal: e.g., Nephrotic Syndrome
ENDOCRINE
Cushing syndrome
Small cell carcinoma of lung
ACTH or ACTH-like substance
Pancreatic carcinoma
Neural tumors
Syndrome of inappropriate
antidiuretic hormone
secretion
Small cell carcinoma of lung;
intracranial neoplasms
Antidiuretic hormone or atrial
natriuretic hormones
Hypercalcemia
Squamous cell carcinoma of lung
Parathyroid hormone-related protein
(PTHRP), TGF-α, TNF, IL-1
Breast carcinoma
Renal carcinoma
Adult T-cell leukemia/lymphoma
Ovarian carcinoma
Hypoglycemia
Fibrosarcoma
Insulin or insulin-like substance
Other mesenchymal sarcomas
Hepatocellular carcinoma
Carcinoid syndrome
Bronchial adenoma (carcinoid)
Serotonin, bradykinin
Pancreatic carcinoma
Gastric carcinoma
Polycythemia
Renal carcinoma
Cerebellar hemangioma
Hepatocellular carcinoma
Erythropoietin
GRADING/STAGING
• GRADING: HOW “DIFFERENTIATED”
ARE THE CELLS?
• STAGING: HOW MUCH ANATOMIC
EXTENSION? TNM
• Which one of the above do you
think is more important?
WELL?
(pearls)
MODERATE?
(intercellular bridges)
POOR?
(WTF!?!)
GRADING for Squamous Cell Carcinoma
ADENOCARCINOMA GRADING
Let’s have some FUN!
LAB DIAGNOSIS
• BIOPSY
• CYTOLOGY: (exfoliative)
• CYTOLOGY: (FNA, Fine Needle
Aspirate)
IMMUNOHISTOCHEMISTRY
• Categorization of
undifferentiated tumors
• Leukemias/Lymphomas
• Site of origin
• Receptors, e.g., ERA, PRA