Molecular mechanism of neoplasia

1. MOLECULAR MECHANISM
OF NEOPLASIA

2. Cellular Basis of Cancer
• Cancer is characterized by
abnormal and uncontrolled
growth of cells.
• Cancer arises from a loss of
normal growth control.
• In normal tissues, the rates of new
cell growth and old cell death are
kept in balance.
• In cancer, this balance is disrupted.
• This disruption can result from
1) uncontrolled cell growth or
2) loss of a cell's ability to undergo
apoptosis.

3. Cancer Cell Do Not Grow Faster Than
Normal Cells
Rather, Their Growth is Just
Uncontrolled

4. What causes Cancer?
• Cancer is caused by
alterations or mutations in
the genetic code.
• Can be induced in somatic
cells by:
-Carcinogenic chemicals
-Radiation
-Viruses
-Heredity

5. Hanahan and Weinberg, Cell 100: 57, 2000
Apoptosis
Oncogenes
Tumor Suppressor
Inv. and MetsAngiogenesis
Cell cycle

6. • What isthe molecularbasisof cancer?
• Cancerisagenetic disease.
• Mutations in genesresult in alteredproteins
–During cell division
–External agents
–Randomevent
• Most cancers result from mutations in somatic
cells
• Some cancers are caused by mutations in
germline cells

7. THEORIESOFCANCERGENESIS
Standard Dogma
• Proto-oncogenes(Ras– melanoma)
• Tumor suppressor genes (p53 – various
cancers)
Modified Dogma
• Mutation in a DNA repair gene leads to the
accumulation of unrepaired mutations
(xeroderma pigmentosum)
Early-InstabilityTheory
• Master genes required for adequate cell
reproduction are disabled, resulting in
aneuploidy (Philadelphiachromosome)

9. • Approximately 90-95% of all cancers
are sporadic.
• 5-10% are inherited.
CANCER AND
GENETICS

10. • Oncogenes
• Tumor suppressor genes
• DNA repair genes
GENES PLAYING ROLE IN
CANCER DEVELOPMENT

11. What are the genes responsible for tumorigenic
cell growth?
Normal
Cancer
Mutated or “activated”
oncogenes
Loss or mutation of
Tumor suppressor genes
Proto-oncogenes Cell growth
and
proliferationTumor suppressor genes
+
-
Malignant
transformation
++

12. ONCOGENES
• Oncogenesaremutated formsof cellular proto-
oncogenes.
• Proto-oncogenescodefor cellularproteins which
regulatenormalcellgrowthand differentiation.

13. 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
Five types of proteins encoded by proto-
oncogenes participate in control of cell growth:

14. 4. Nuclear
Proteins:
Transcription
Factors
5. Cell Growth
Genes
3. Cytoplasmic
Signal Transduction
Proteins
1. Secreted Growth Factors
2. Growth Factor Receptors
Functions of Cellular Proto-Oncogenes

15. 18
A generic signalling
pathway

16. ONCOGENES
• proto-oncogene =ras
• Oncogene =mutated ras
• Always activated
• Always stimulating
• proliferation

17. amino acid position
Ras gene 12 59 61 Tumor
c-ras (H, K, N) Gly Ala Gln normal cells
H-ras
K-ras
N-ras
Gly
Val
Cys
Arg
Val
Gly
Gly
Ala
Ala
Ala
Ala
Ala
Ala
Ala
Leu
Gln
Gln
Gln
Gln
Lys
Arg
lung carcinoma
bladder carcinoma
lung carcinoma
lung carcinoma
colon carcinoma
neuroblastoma
lung carcinoma
Murine sarcoma virus
H-ras Arg Thr Gln Harvey strain
K-ras Ser Thr Gln Kirsten strain
Amino acid substitutions in Ras family proteins
(inactivates GTPase)

18. Activation mechanisms of proto-oncogenes
proto-oncogene -->oncogene

19. CHROMOSOMAL REARRANGEMENTS OR TRANSLOCATIONS
Neoplasm
Burkitt lymphoma
Translocation
t(8;14) 80% of cases
Proto-oncogene
c-myc1
t(8;22) 15% of cases
t(2;8) 5% of cases
Chronic myelogenous
leukemia
t(9;22) 90-95% of cases bcr-abl2
Acute lymphocytic
Leukemia
t(9;22) 10-15% of cases bcr-abl2
1c-myc is translocated to the IgG locus, which results in its activated expression
2bcr-abl fusion protein is produced, which results in a constitutively active abl kinase

20. GENE AMPLIFICATION
Oncogene Amplification Source of tumor
c-myc ~20-fold leukemia and lung carcinoma
N-myc 5-1,000-fold neuroblastoma
retinoblastoma
L-myc 10-20-fold small-cell lung cancer
c-abl ~5-fold chronic myoloid leukemia
c-myb 5-10-fold acute myeloid leukemia
colon carcinoma
c-erbB ~30-fold epidermoid carcinoma
K-ras 4-20-fold
30-60-fold
colon carcinoma
adrenocortical carcinoma

21. Oncogenes are usually dominant
(gain of function)
•cellular proto-oncogenes that have been mutated
(and “activated”)
•cellular proto-oncogenes that have been captured by
retroviruses and have been mutated in the process (and
“activated”)
•virus-specific genes that behave like cellular proto-
oncogenes that have been mutated to oncogenes (i.e.,
“activated”)

22. Theresult:
•
•
•
Overproductionof growthfactors.
Floodingof the cellwith replicationsignals
Uncontrolled stimulation in the intermediary
pathways
Cell growth by elevated levels of transcription
factors
•

23. TUMORSUPPRESSORGENES
•
•
•
•
Lossoffunction
Normal function - inhibit cell proliferation
Absence/inactivation of inhibitor --> cancer
Both genecopiesmust bedefective

24. Rb gene
•
•
•
•
•
•
•
Rbprotein controls cell cycle moving past G1checkpoint
Rbprotein binds regulatory transcription factor E2F
E2Frequired for synthesisof replication enzymes
E2F- Rbbound =no transcription/replication
Growth factor -->Raspathway --> G1Cdk-cyclin synthesized
Active G1Cdk-cyclin kinase phosphorylates Rb
Phosphorylated Rb cannotbind E2F --> Sphase
–
–
Disruption/deletion of Rbgene
Inactivation of Rbprotein
--> uncontrolled cell proliferation -->cancer

25. p53
• Phosphyorylated p53activates
transcription of p21gene
p21 Cdkinhibitor (bindsCdk-
cyclin complex --> inhibits
kinase activity)
Cell cycle arrested to allow
DNAto berepaired
If damagecannot berepaired
--> cell death (apoptosis)
•
•
•
•
•
Disruption/deletion of p53gene
Inactivation of p53protein
--> uncorrected DNAdamage
--> uncontrolled cellproliferation
--> cancer

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

29. These are genes that ensure each strand of genetic
information is accurately copied during cell division of
the cell cycle.
Mutations in DNA repair genes lead to an increase in
the frequency of mutations in other genes, such as
proto- oncogenes and tumor suppressor genes.
i.e. Breast cancer susceptibility genes (BRCA1 and
BRCA2) Hereditary non-polyposis colon cancer
susceptibility genes
(MSH2, MLH1, PMS1, PMS2) have DNA repair
functions. Their mutation will cause tumorigenesis.
DNA REPAIR GENES

30. Van Gent et al,
2001
Molecular
mechanisms of
DNA double
strand break
repair
BRCA1/2

31. IMPORTANCE OF DNA REPAIR

32. 35
Hanahan & Weinberg 2000
Summary of 30 years of research (1971-2001)

33. Translocation and Bcr-Abl fusion in CML

34. Smart bullet STI-571 lockes itself to the target molecule
STI-571

35. STI-571 against Bcr-Abl

36. Molecular Basisof Multistep
Carcinogenesis

37. Post mitotic
Stem cell
Differentiated Normal
senescent
differentiated
cell
Benign
tumor
Grade 2
malignancy
Grade 3 or 4
malignancy
Stem cells as the target of carcinogens

38. Invasion and Metastasis
• Abnormal cells proliferate
and spread (metastasize) to
other parts of the body
• Invasion - direct
migration and
penetration into
neighboring tissues
• Metastasis - cancer cells
penetrate into lymphatic
system and blood vessels

39. • Benign tumors
generally do not
spread by
invasion or
metastasis
• Malignant
tumors are
capable of
spreading by
invasion and
metastasis
Malignant versus Benign Tumors

40. RB RB
RB
LOH
RB
Mutation
Normal
Cells
Tumor cells
KNUDSON TWO HIT HYPOTHESIS IN SPORADIC CASES
RB RB
Inactivation of a tumor
suppressor gene
requires two somatic
mutations.

41. KNUDSON TWO HIT HYPOTHESIS IN FAMILIAL
CASES
RB rbNormal cells
rb RB rb
Familial RB (%30)
Tumor cells Normal cells
Inactivation of a tumor suppressor
gene requires two mutations, inherited
mutation and somatic mutation.
RB
LOH

42. Tumor Progression
aMrultiple mutations lead to coloncancer
Genetic changes--> tumor changes

43. THANKYOU