The document discusses oncogenes, their activation mechanisms, classifications, and clinical implications, detailing how proto-oncogenes, when uncontrolled, become oncogenes leading to cancer. Key topics include the history of oncogenes, types of oncogenes such as growth factors and transduction molecules, and notable examples like EGFR and RAS mutations. It also covers oncogenic microbes, detection methods for oncogenic alterations, and targeted therapies for various cancers.

1. ONCOGENE
By SOUMYADIP ROY
Moderator: Dr. SHYAMA PREM
Additional Professor,
RADIATION ONCOLOGY, JIPMER

2. HEADINGS
• INTRODUCTION
• HISTORY
• MECHANISMS OF ACTIVATION
• CLASSIFICATION OF ONCOGENE
• LIST OF ONCOGENES
• ONCOGENIC MICROBES
• DETECTION OF ONCOGENES
• CLINICAL IMPLICATIONS

3. INTRODUCTION
CELL
CYTOPLASM NUCLEUS
NUCLEAR
MEMBRANE
NUCLEOPLASM
NUCLEOLUS
CHROMOSOME

4. PARTS of
CHROMOSOME
Metaphase arrest (by
colchicine)chromosom
e=,if treated with
trypsin and stained
with Giemsa shows 2
sister chromatids
joined together at the
centromere and
having light and dark
regions called bands
which itself have
several subbands.
Sister chromatids

5. ORGANIZATION
OF A
CHROMOSOME
Chromosome is
highly coiled
structure made of
DNA and histone
proteins.

6. ORGANIZATION
OF DNA
DNA is a double
helix made of 2
antiparallel
strands.

7. ORGANIZATION
OF GENE
Gene is part a part
of DNA which
codes for a
protein.It has
expressing
sequences(exons)
interspersed by
intervening
sequences(introns)

8. LOCATION OF
GENE
Each chromosome
has two
sets,likewise each
gene also has two
sets.The location of
the gene in
chromosome is
called a locus
where one allele of
the gene resides

9. ALTERATION IN
DNA SEQUENCE
Mutation if
happens in coding
part of gene it
hampers gene
function

10. INTRODUCTION
• Normally chromosome contains genes which
promote growth of the cell and cell survival.
These are called proto-oncogene.
• Proto-oncogenes are under strict control and
are activated for a short period of time on a
particular part of cell cycle.
• If this control over them is lost, the proto-
oncogene is converted to an oncogene.
• Product of the oncogene is oncoprotein.

11. HISTORY
• In 1911,Peyton
Rous prepared cell-
free filtrate from
sarcoma of chicken
• Injection of this cell
free filtrate to
healthy chicken
caused sarcoma
Nobel Prize in
1966

12. Cont.
• In 1958 Hary Rubin and
Howard Temin showed
morphological changes
in chicken embryo
fibroblast by infection
with RSV

13. Cont.
• C-src was found to
be the normal
counterpart of v-src
• Conversion of
normal
protooncogene c-
src to oncogene v-
src causes sarcoma.
• Transmission of v-
src from one host
to another is by the
process of
transduction

14. MECHANISMS OF ONCOGENE
ACTIVATIONS
• 3 mechanisms
1. Mutation:
a) It is insertion or deletion or missence
b) Affect only one allele; i.e.,heterozygous
c) Affects only one codon or clustered in
neighbouring codons

15. Cont.
2)Gene amplification:
a) Here the number of the copies of the gene
gets amplified
b) Oncoprotein is normal but present in
excessive amount.
c) Example is Her2/neu amplification in breast
cancer.

16. Cont.
• 3)Translocation OR
REARRANGEMENT:
a) They cause the
gene to be
expressed
continuously
b) Oncoprotein is
normal
c) Example:
formation of BCR-
ABL fusion gene
in CML

18. CLASSIFICATION
OF ONCOGENES
1.Growth factors
2.Growth factor
receptors
3.Cytoplasmic signal
transduction
molecules
4.Nuclear
transcription
activators
5.Cell cycle
regulators

19. Growth factors
Growth
Factors
Source Function
EGF Platelets,macro
phages
Mitogenic for
keratinocytes and
fibroblast
TGF-a Macrophages,Tl
ymphocytes
Similar to EGF;stimulates
hepatocyte growth
HGF/scatter
factor
Mesenchymal
cells
Proliferation of
hepatocytes,epithelial,e
ndothelial cells
VEGF-
A,B,C,D
Many cell types Mitogenic for
endothelial cells
PDGF-
A,B,C,D
Platelets,kerati
nocytes,endoth
elial cells
MMP
production,angiogenesis
,fibroblast growth
FGF-1,2 Fibroblasts,mas
t
cells,keratinocy
tes
Keratinocytes and
fibroblast
growth,angiogenesis
KGF(FGF-7) fibroblasts Keratinocyte
migration,proliferation
They have
paracrine action.
They are
expressed only
in small part of
cell cycle. But in
cancers there is
continuous
expression.

20. Cont.
• Growth factor
receptors:
a) They have
extracellular ligand-
binding,
transmembrane and
intracellular domains
b) Intracellular domain
has intrinsic tyrosine
kinase activitity

21. Cont.
d) Dimerization causes autophosphorylation
of intrinsic domain and recruitment of
other signalling proteins
e) Growth factor receptor oncoproteins are in
constitutively dimerized condition without
binding to ligand

22. Cont.
• Cytoplasmic signal transduction molecules:
a) These are serine/threonine or tyrosine
kinases
b) examples:RAS,RAF,MEK,PI3K,AKT

23. Cont.
• Nuclear transcription factors:
a)Growth factors ultimately induce synthesis or activity
of transcription factors
b)C-fos,N-myc

24. Cont.
•Cell cycle regulators:
•They are cyclins and
cyclin dependent
kinases regulating
transition from one
phase of cell cycle to
another
•Ink family cyclin
inhibitors:p15,p16,p18
,p19
•CIP/WAF family cyclin
inhibitors:p21.p27,p57

25. PROTOTYPE ONCOGENES
• EGFR:
a) Also called erbB or HER
b) 4 types:1,2,3,4
c) HER2 does not bind to a known ligand but
acts as co-factors for other members of the
family
d) HER3 does not have tyrosine kinase domain

26. Cont.
e)Ligand binding to extracellular domain causes
conformal changes and 2 receptors come in
close alignment-this is called dimerization.
F) ERBB1 is overexpressed in 80% of squamous
cell carcinomas of lung,80-100% of head and
neck malignancies and 50% glioblastomas
G) ERBB2 is overexpressed in 25% breast cancers

27. EGFR
SIGNALLING
Binding of growth
factor to the
extracellular
domain of EGFR
causes conformal
changes in
extracellular
domain so that 2
receptors come in
close alignment-
dimerization.

28. Cont
Dimerization
causes
phosphorylation of
intracellular
tyrosine kinase
residue which
leads to multiple
downstream
signalling molecule
recruitment.

29. EGFR SIGNALLING PATHWAY

30. RAS ONCOGENE
• Point mutation of RAS is single most common
abnormality of human tumours.
• Multiple growth factor(EGF,PDGF) signal
transduction pathways depend on RAS
• Mutated in 15-20% cancers
• 90% cholangiocarcinima,pancreatic
adenocarcinoma;50%colon,endometrial and
thyroid cancers and 30% lung and myeloid
leukemias have RAS mutation

31. Cont.
• 3 RAS proteins are: K-RAS,H-RAS and N-RAS
• K-RAS: colon and pancreas cancer
• H-RAS: bladder and kidney cancer
• N-RAS: melanoma and haematologic
malignancies
• Inactivated RAS in GDP bound state is anchored
to inner cell membrane by farnesyl group.

32. RAS –RAF-MAP KINASE PATHWAY
Growth factor binds to its tyrosine kinase receptor
Cross phosphorylation of intracellular domain of each monomers
Activation of bridging protein (GRB2,SOS)
GDP bound RAS exchanges GDP with GTP and gets activated

33. Recruitment of RAF
Stimulation of mitogen-activated protein(MAP) kinase
Transcription signal to nucleus

34. Cont.
• Active RAS gets
inactivated by its
intrinsic GTP ase
activity which itself
is stimulated by
GTP ase-activating
proteins(GAPs)
• This step is blocked
in mutant RAS

35. MAP KINASES
• They are serine/threonine kinases
• 3 parallel MAP kinase pathways are
there:MAPK,JNK,p38 pathways
• MAPK is activated by growth factors
• JNK and p38 are activated by environmental
stress signals,like ionizing radiations and UV
rays
• MAP enters nucleus to activate transcription
factors

36. BRAF
• Serine/threonine kinase
• Mutation present in 100% hairy cell leukemia's,>60%
melanomas,80% of benign nevi, small percentage of
colon and dendritic tumours

37. LIST OF ONCOGENES

38. ONCOGENIC MICROBES
• VIRUSES
1. HTLV-1:
a)Causes human T cell leukaemia in 3-5% of infected
persons after a latency of 4-5 decades
b)Do not contain any oncogene
c)But one gene called TAX causes increase expression
of FOS gene, genes encoding IL-2,its receptor activates
NF-Kb, inhibits ATM mediated cell cycle checkpoints
activated by DNA damage and inactivates cell cycle
inhibitor p16/INK4a

39. Cont.
• DNA viruses:
1. HPV:

40. Cont.
2)EBV:
a)African Burkitt lymphoma,nasopharyngeal
carcinoma,subset of Hodgkin lymphoma
b)LMP-1(latent membrane protein) acts as an
oncogene and behaves like constitutively active CD40
receptor which helper cell uses to activate B cells.
c)EBNA-2 activates NOTCH receptor, cyclin D and src
protooncogene

41. 3)Hepatitis B and C :
a)Cause 70-85% of HCC
b)Chronic inflammation is the predominant etiology of
HCC which causes DNA damage.
c)NF-Kb pathway plays role
d)HBx gene of HBV activates several transcription
factors

42. Cont.
3)Hepatitis B and C :
a)Cause 70-85% of
HCC
b)Chronic
inflammation is the
predominant etiology
of HCC which causes
DNA damage.
c)NF-Kb pathway plays
role
d)HBx gene of HBV
activates several
transcription factors
Genome and transcribed component of HBV

43. Cont.
Bacteria
H.pylori:
3% of Chronically
infected patients
develop
adenocarcinoma after
decades
Pathogenic strains of
H.pylori contain
cytotoxin associated A
A(CagA) gene acting as
a growth promoting
gene

44. DETECTION OF
ONCOGENIC
ALTERATION
FISH:DNA probes
specific for a gene or
particular chromosome
region are labeled and
hybridized to denatured
metaphase
chromosomes or on
interphase nuclei on
paraffin embedded
tissue.After washing
fluorescent labeled
antibodies are added
and cells or tissues are
examined under
fluorescent microscopy

45. MICROARRAY
•Alteration of multiple genes
can be studied at one time.
• Steps:
1. Isolation and purification
of mRNA from the sample
2. Reverse transcribe the
mRNA to cDNA and
fluroscent labelling
3. Hybridization of the
labelled cDNA to
microarray chips.
4. Wash
5. Fluorescent labelled
hybridized DNA will be
excited by laser and the
signal will be expressed
digitally.

46. DRUGS TARGETTING ONCOPROTEINS
oncoproteins drugs
EGFR Trastuzumab(breast cancer), gefitinib, erlotinib, afatinib,
osimertinib(lung cancer), cetuximab(head and neck and colon
cancer), panitimumab(colon cancer)
BRAF Vemurafenib, dabrafenib(melanoma)
MET Tivantinib (advanced HCC)
PI3K Alpelisib (breast cancer)
mTOR Everolimus