Basic Mutagenic signal Transduction or the cancer signal transduction that control cell cycle are important pathways to understand cancer in molecular level and to invent targeted treatment.

1. Molecular Pharmacology course
lecture No.5
Mutagenic Signal Transduction
and apoptosis
Dr.Omer Yahia Elhussein
B.sc. Pharmacy.
M.sc. Molecular Medicine.

3. Normal Cell Signal
Transduction Associated with tumor
• Wnt-B catenin path way.
• Cell Cycle Arrest.
• Growth Factor Tyrosine Kinase.
• DNA Damage and repair.
• Apoptosis.
• Telomere Maintenance.

4. 1. Wnt-B catenin path way.
(Drosophila mutants :Nobel Prize 1995)
(the term Wnt is an amalgam of Wg and Int1)
• In resting cell cytoplasmic beta catenin
turns over rapidly , with little entering
the nucleus.
• Degradation is controlled by
acytoplasmic complex that include
the product of apc gene (tumor
suppressor) and GSK , a kinase protein
that phosphorylates beta catenin.

5. Wnt-B catenin path way

6. Continue…
• Mutation in APC phosphorylation site or
loss of APC result in excess free beta
catenin that enter the nucleus .
• eg: defect in APC in patient with familial
Adenomatous Polyposis Coli, giving rise
to multible pre cancerous polyps in the
large intestine.

8. The gene rearrangements resulting from
chromosome translocations frequently
lead to the generation of oncogenes.
The first characterized example of
oncogene activation by chromosome
translocation was the involvement of the
c-myc oncogene in human Burkitt's
lymphomas and mouse plasmacytomas,
which are malignancies of antibody-
producing B lymphocytes
(immunoglobulins).
For example, virtually all Burkitt's
lymphomas have translocations of a
fragment of chromosome 8 to one of the
immunoglobulin gene loci, which reside
on chromosomes 2, (k light chain), 14
(heavy chain), and 22 (g light chain).
Chromosomal abnormalities and cancer
The c-myc proto-oncogene is translocated from chromosome 8 to the
immunoglobulin heavy-chain locus (IgH) on chromosome 14 in Burkitt's
lymphomas, resulting in abnormal c-myc expression.

9. Cancer therapeutics that target
components of
the canonical Wnt pathway
APC, adenomatous polyposis coli ; TCF, T-cell factor
BCL9, B-cell lymphoma 9. P, phosphorylation
CBP, CREB-binding protein; PS1, presenilin 1
CK1α, casein kinase;1α; Pygo, Pygopus
DKK, Dickkopf; RTKs, receptor tyrosine kinases
DVL, Dishevelled; WIF,Wnt inhibitory factor 1
GSK3β, glycogen synthase kinase 3β LEF, lymphoid enhancer factor;
LRP5, LDL-receptor related protein 5MAPK,mitogen-activated protein kinase;
NRTKs, non-receptor tyrosine kinases; SFRP, secreted Frizzled-related protein

10. Cancer therapeutics that target
components of
the canonical Wnt pathway

11. Continue …..
• The non-steroidal anti-inflammatory drug (NSAID) celecoxib,
which targets the Wnt target gene COX2 (cyclooxygenase 2), is
already approved for the treatment of patients with familial
adenomatous polyposis (FAP)
• Therapeutic proteins, antibodies and low-molecular-weight
products that interfere with aberrant activity of the canonical Wnt
pathway are currently being developed or might be future
candidates.
• Imatinib mesylate (Gleevec), a tyrosine kinase inhibitor and an
approved therapeutic for chronic myeloid leukaemia (CML),
shows promise for the treatment of Wnt-induced gastrointestinal
tumours.

12. • Interference with members of other signalling
pathways, which directly or indirectly control
β-catenin stability (such as γ-secretase or ADAM, a
disintegrin and metalloproteinase ) might also provide
therapeutics against disease
Note :
• ADAM and γ-secretase are
• These metalloproteinase activities result in the
enhancement of migratory and invasive properties of
endothelial cells, which are required for tumour
angiogenesis.

14. 2-Cell cycle Arrest

15. • Transforming growth factor-β (TGFβ) signalling is transduced
through Smad and non-Smad pathways.
• TGFβ ligand binds to TGFBR2 and TGFBR1.
• TGFBR2 phosphorylates (P) TGFBR1, which subsequently
phosphorylates and activates SMAD2 and SMAD3.
• Activated SMAD2 and SMAD3 form a Smad complex with
SMAD4 and translocate into the nucleus.
• In the nucleus, the Smad complex interacts with other
DNA-binding transcription factors, and co-activators and
co-repressors, binds to the promoter regions of TGFβ target
genes and regulates the transcription of target genes.

16. • TGFβ also regulates non-Smad pathways.
• TGFβ receptors activate p38, JNK, Ras–Erk, PI3K–Akt, and
small GTPases such as RHOA and CDC42.
• TGFβ stimulation inhibits cancer cell proliferation in some
cellular contexts and promotes it in others.
• Numerous factors are involved in TGFβ-regulated
cell proliferation and keep its signalling pathways balanced
1. It inhibit the proliferation of most adult cells (eg: TGF-beta null
mutation in mice causing death of inflammation in multiple
organs caused by excessive proliferation of lymphocytes )
2. TGF-beta stimulate production extra cellular matrix, including
collagen,proteoglycans and adhesion glycoprotein

17. • In addition to perturbation of TGFβ signalling, disruption or
mutation of regulators of TGFβ signalling can lead to a loss of
balanced TGFβ signalling, resulting in the generation and
progression of tumours.
• TGFβ signalling in cancer cells has dual roles in the regulation
of cell death and proliferation.
• TGFβ signalling has crucial roles in the maintenance of
self-renewal and tumorigenic activity of glioma-initiating cells
and leukaemia-initiating cells , whereas the function of TGFβ
signalling in breast cancer-initiating cells is controversial.

19. • TGFβ signalling is involved in several cell responses during
cancer cell metastasis, and cell type-dependent and
context-dependent factors contribute to the regulation of tumour
metastasis.
• Mutation in gene of TGF-beta or SMADS appear in up to 50% of
some types of eg: heridetary hemorrhagic telangiecta
• The TGFβ pathway has been targeted for cancer therapy using
multiple strategies. Some of them are currently in clinical trials
• Reserverotral (a potent antitumor factor) inhibit invasiveness of
human SCC cell at least in part , through Down regulation of
TGF-beta2 (Kopelovich L et al 2011)

21. 3- FGFr signalling network.

22. Continue…
• Following ligand binding and receptor dimerization, the kinase domains
transphosphorylate each other, leading to the docking of adaptor proteins and
the activation of four key downstream pathways:
o RAS–RAF–MAPK signal transducer .
o PI3K(inositol triphosphate kinase)–AKT signal transducer.
o activator of transcription (STAT).
o phospholipase Cγ (PLCγ) .
• FGFRs have also been shown to bind and directly phosphorylate ribosomal S6
kinase17 .
• Signalling can be negatively regulated at several levels by receptor
internalization or the induction of negative regulators, including
o FGFR-like 1 (FGFRL1),
o SEF, Sprouty (SPRY),
o CBL,
o MAPK phosphatase 1 (MKP1) and MKP3 (brown).

23. Continue…
• These regulators may modulate ligand binding
(FGFRL1 and SEF) or interfere with intracellular
signalling, principally through modulation of the
MAPK pathway.
o DAG, diacylglycerol;
o FRS2α, FGFR substrate 2α;
o GRB2, growth factor receptor-bound 2;
o IP3, inositol triphosphate;
o P, phosphorylation;
o PIP2, phosphatidylinositol-4,5 biphosphate;
o PKC, protein kinase C;
o Sos, son of sevenless.

25. The epidermal growth factor receptor
signalling network

26. Continue…
• On activation (by ligand binding), the epidermal growth factor receptor
(EGFR, also known as ERBB1) autophosphorylates tyrosine residues
in its cytoplasmic domain, which serve as docking sites for the
assembly of protein complexes that transduce EGF signals to generate
specific biological responses.
• Scaffold protein : A protein that can simultaneously bind two or more
other proteins, and thereby facilitate physical and functional interactions
between the client proteins that bind to it.
o Kinases are light blue,
o scaffolds are dark blue,
o adaptor proteins are yellow,
o G proteins are green and
o transcription factors are orange.

27. Factor Principal
Source
Primary Activity Comments
PDGF platelets,
endothelial
cells, placenta
promotes proliferation of connective
tissue, glial and smooth muscle cells
two different protein chains form 3 distinct
dimer forms; AA, AB and BB
EGF submaxillary
gland, Brunners
gland
promotes proliferation of
mesenchymal, glial and epithelial
cells
TGF- common in
transformed
cells
may be important for normal wound
healing
related to EGF
FGF wide range of
cells; protein is
associated with
the ECM
promotes proliferation of many cells;
inhibits some stem cells; induces
mesoderm to form in early embryos
at least 19 family members, 4 distinct
receptors
NGF promotes neurite outgrowth and
neural cell survival
several related proteins first identified as
proto-oncogenes; trkA (trackA), trkB, trkC
Erythropoietin kidney promotes proliferation and
differentiation of erythrocytes
TGF- activated TH1
cells (T-helper)
and natural killer
(NK) cells
anti-inflammatory (suppresses
cytokine production and class II
MHC expression), promotes wound
healing, inhibits macrophage and
lymphocyte proliferation
at least 100 different family members
IGF-I primarily liver promotes proliferation of many cell
types
related to IGF-II and proinsulin, also called
Somatomedin C
IGF-II variety of cells promotes proliferation of many cell
types primarily of fetal origin
related to IGF-I and proinsulin
Growth Factors

29. 4- DNA damage and repair
(Retinoblastoma , P53 , Mdm, E2F , Waf-1 , Bax)
• pRB primary function is to block cell cycle
progression and it is in activated in response
to mitogenic stimulation .
• So,loss of Prb can lead to in appropriate cycle
progression and cancer
• Rare individuals who inherit one inactivated
rb gene are predisposed to develop
Retinoblastoma as children and
Osteosarcomas as adult

30. • Homozygous loss of p RB is lethal during
embryogenesis, as the protein is essential for
promoting differentiation in various organs
and tissues.
• E2F is a tumor suppressor because it
opposes the cell cycle progression prior to
the restriction point when partnered with p RB
; However it can act also as an Oncogene as
it promotes the cell cycle when p RB in
activated

34. Retroviral Oncogenes
• Viral oncogenes were first
defined in Rous Sarcoma
Virus (RSV), which transforms
chicken embryo fibroblasts in
culture and induces large
sarcomas within 1-2 weeks
after inoculation into chickens.
• In contrast, the closely related
avian leukosis virus (ALV)
replicates in the same cells as
RSV without inducing
transformation.
Both RSV and ALV infect and replicate in
chicken embryo fibroblasts, but only RSV
induces cell transformation.

36. 5- Apoptosis and cancer
• Cell dies because of :
Old and defective - incur some damage - surplus to the requirement of
tissues ( like finger formation )
• Cell dies in different ways:
1. Necrosis.
2. Apoptosis.
3. Autophagy.
Apoptosis :
controlled process leading to cell death that is triggered by intracellular
damage (e.g., DNA lesions) or by external signals from neighboring
cells. Also called programmed cell death.

37. Continue …..
Extrinsic path way
T cell induced death
Intrinsic path way

39. 5-Telomer Maintenance
• Telomerase is the enzyme for maintaining the
end of the chromosome
• While the Telomerase enzyme is not active
in most normal human cells , the enzyme is
active in all types of cancer , but enables
cancer cells that have telomerase too short
for chromosome replication to divide
indefinitely by lengthening the telomeres and
stabilizing the chromosomes

41. • During successive cell cycles the telomeres shorten
because the primer needed by DNA Polymerase for
new DNA synthesis is removed.
• This action is counteracted by the action of
telomerase, which adds new telomere repeat
sequences to the ends of chromosomes.
• Eventually ,the telomeres become so short that the
complex between sequences and the proteins that
bind to them disrupted , and DNA damage occur.

43. Thanks