Basic of Cellular Signaling Network

1. Cell Division
Nucleus

2. Genetics: Studies of genes, heredity, and variations in organisms
Gene: a unit of heredity
Major Points
• Genes reside within chromosomes like beads on a string.
• Genes on the same chromosome are linked, but genes on
different chromosomes assorted independently.
• New genes can be identified using linkage analysis based on
recombination frequencies between known genes.
• Genes can become mutated to produce different phenotypes.
• Genes determine the activities of enzymes responsible for
producing phenotypic traits (the “one gene-one enzyme” hypothesis).
• The study of genes therefore is not just the study of inherited
traits, but also the study of cellular functions.

3. The “One gene-one enzyme”
hypothesis
Nobel Prize, 1958
George Beadle Edward Tatum

4. The Cell
Nucleus
Nuclear membrane
Cytoplasm
Cell membrane

6. Cell-Cell Communication

7. Communication by direct contact
between cells

8. Signal receiving cell
Overview of Cell Signaling

9. Transduction
Signal transduction converts the change in the receptor to a form that can
bring about a cellular response. This might involve a series of steps that
alters and amplifies the change.
Reception
The cell targeted by a signal has a receptor molecule complementary to
the signal molecule or ligand. The ligand fits like a key in a lock and
triggers a change in the receptor molecule.
Three stages of
signaling process:
• Reception
• Transduction
• Response
• Activation of certain enzyme
• Rearrangement of the cytoskeleton
• Activation of specific genes
Response
This can be any of many
cellular activities, such as:

12. • When the signal molecule binds to the receptor,
the receptor becomes activated.

13. Ligand-gated ion channels

14. Intracellular
Receptors

15. Amplification of signals
Protein kinases are important links in
Many signal-transduction pathways.
One kinase may activate many molecules
of the next type of kinases in the chain,
thus amplifying the signal, until the last
kinase activates many protein molecules
that carries out the final cellular response.

16. Non-protein molecules that act as intermediates e.g., cyclic AMP, calcium ions etc.
Second messengers
Calcium ion also acts as second messengers
cAMP-mediated
Signal Transduction

17. Cytoplasmic response to a signal
Ultimate effect:
Cellular response, such as-
• Alteration of metabolism
• Modulation of gene activity
• Rearrangement of cytoskeleton

18. • Signaling pathways with a multiplicity of steps have two important benefits
Protein kinase might activate a gene and
trigger the synthesis of a new protein
B. Specificity of response
A. Signal amplification

20. Hypothesis
Autocrine
Growth
Factor(s)
Constitutive
Stat3
Activation
Anti-apoptotic
Gene
Expression
Enhanced
Cell
Survival

21. Oligomerization
Domain
DNA-binding
Domain
SH2
Domain
Activation
Domain
Dimerization
Domain
Y S
N C
N C
JH1
JH2
JH3
JH4
JH5
JH6
JH7
Receptor-binding Region
Pseudo-kinase
Domain
Kinase
Domain
Janus Kinase (JAK)
Signal Transducer and Activator of Transcription (STAT)

22. Stat3 Activation Pathway
IL-6Ra
Stat3
Stat3
TTNNNNNAA
Transcription
IL-6
Membrane
Cytoplasm
Nucleus
Stat3
Stat3
Stat3
Stat3
gp130
gp130
Jak
Jak

23. • Small protein molecules produced
by mammalian cells
• Involved in cell-to-cell
communication network
• Control division, differentiation and
death of mammalian cells
• Essential for the development and
function of the immune system
• Function in redundant and/or
pleiotropic fashion
Cytokines
A
B C
D

24. Stat3 Signaling in Oncogenesis
EGF, TGF-a, PDGF Src-family Kinase
IL-6-family Cytokines
Stat3
(Activated)
BclXL
Mcl1
Survival
Bcl2
Pim Myc
Cdc25A
Division
p16 p21
Differentiation

25. Stat Stat
P
PTK
PTP
Stat-Tyrosine Phosphorylation Is
a Reversible Reaction

26. Question
Why is Stat3 constitutively activated
in certain human tumors?

27. Stat Recognition Sequences in
Cytokine Responsive Genes
N3-GAS
AAG NNN CTT
TTC NNN GAA
AAN NNN NTT
TTN NNN NAA
N5-GAS
Homodimers and
Heterodimers of
All Stats
N4-GAS
AAG NNNN CTT
TTC NNNN GAA
AAN NNNN NTT
TTN NNNN NAA
N6-GAS
Homodimer of Stat6

28.  Receptor Inactivation
- Receptor Antagonist
- Decoy Receptor
- Protein-tyrosine Phosphatase (PTP)
- Suppressor of Cytokine Signaling (SOCS)
- Proteolytic Degradation
Negative Regulation of Jak-Stat Signaling
 Jak Inactivation
- Protein-tyrosine Phosphatase
 Stat Inactivation
- Protein Inhibitor of Activated Stat (PIAS)
- Suppressor of Cytokine Signaling
- Proteolytic Degradation
- Protein-tyrosine Phosphatase
- Proteolytic Degradation

29. Mission-critical Cellular and Molecular Events
Underlying Cancer Progression
• Increased cell division
• Decreased cell death
• Gain-of-function status of Oncogenes/Oncoproteins
• Loss-of-function mutations of Tumor Suppressor Genes

30. Cellular and Molecular Biology of Gliomas
Glioblastoma
Multiforme
Anaplastic
Astrocytoma
Astrocytoma
Proliferation +/- ++ +++
Invasion ++ ++ +++
Angiogenesis - - +++
Rx Response - ++ -
Survival 5-10 Years 2-3 Years 9-12 Months
• Mutation of p53
• Over-expression of
PDGF/PDGFR
• Mutation of Rb
• Amplification of CDK4
• Loss of INK4A/ARF
• Loss of PTEN
• Amplification of EGFR
• Mutation of EGFR
• Loss of INK4A/ARF
• Loss of PTEN
• Mutation of Rb
• Amplification of IL-6

31. Oligomerization
Domain
DNA-binding
Domain
SH2
Domain
Activation
Domain
Dimerization
Domain
F S
Dominant Negative Mutant Stat3
N C

32. Common properties of most cancer cell lines
for enhanced proliferation and survival
• Constitutive Stat3/other Stat activation.
• Constitutive Akt activation.
• Activation of Ras-MAPK pathway.
• Decreased p27 expression.
• Mutation in pRb family genes.
• Mutation /deletion of PTEN gene.

33. The Hallmarks of Cancer
• Self-sufficiency in growth signals
Hanahan D and Weinberg RA
Cell 100: 57-70, 2000
• Insensitivity to anti-growth signals
• Evasion of programmed cell death
• Unlimited doubling potential
• Sustained angiogenesis
• Tissue invasion and metastasis

34. Mission-critical Cellular and Molecular Events
Underlying Cancer Progression
• Increased cell division
• Gain-of-function status of Oncogenes/Oncoproteins
• Decreased cell death
• Loss-of-function mutations of Tumor Suppressor Genes

35. EGFR Signaling Pathways
Stat3
PTEN
MEK1
Erk1/Erk2
Proliferation
PI3K
AKT
LY294002
Wortmannin
U0126
mTOR
S6 kinase
Other S/T kinases
Survival
Transcription
factors
PD153035
AG1478

36. CNS tumors
Retinoblastoma
[pRb]
Glioblastoma
[EGFR; PTEN; p53]
Medulloblastoma
De novo
[Primary]
Progressive
[Secondary]
P53 mutations and
accumulation
PTEN alteration and
EGFR amplification

37. • Malignant gliomas are the most common subtype of primary brain tumors
• Glioma cells are migrating away from the main tumor mass through the
brain parenchyma
• Clinically, gliomas are divided into four grades:
Grade-I : Pilocytic astrocytoma
Grade-II : Astrocytoma
Grade-III : Anaplastic astrocytoma
Grade-IV : Glioblastoma Multiforme (GBM)
• GBM(s) are multiforme in microscopically and genetically with various
deletions, amplifications and point mutations
• GBM(s) are highly proliferative and resistant to apoptosis
• GBM (s) are resistant to radiation therapy and chemotherapy
The Gliomas

38. Stat Family Members
• Stat1 : is crucial for interferon (IFN)-induced viral resistance
• Stat2 : is critical for IFN-a and IL-10 signaling
• Stat3 : deficiency results in very early embryonic lethality,
for unknown reasons
• Stat4 : is critical for interleukin-12 signaling
• Stat5 : are activated in the response to a variety of
(5A & 5B) cytokines including IL-13, EPO, OSM, GH,
prolactin and IL-2
• Stat6 : specifically mediates the effects of IL-4 and IL-13 on
B or T cells

39. { Ras
C-Myc
Raf
E2F
Apoptosis
and
proliferation
Survival
and
proliferation
Net Loss
of cells
Net expansion
of cells
Survival signals
Invasion
Angiogenesis
Metastasis
Immune evasion