UW-M Cell Biology (Bio Sci 315)
Cell Signaling & Signal
Transduction
•Steroid hormones (also thyroid hormone)
enter cells to regulate gene expression.
•Signal molecules too big or polar to enter a
target cell transmit information by signal
transduction,
UW-M Cell Biology (Bio Sci 315)
Signal Transduction Themes:
•intracellular 2nd messengers
•Protein phosphorylation
•changes in
enzyme activity
1. large or very polar
extracellular ligand 4. protein •changes in
(e.g., hormone) phosphorylation cytoskeletal
organization
2. cell surface •changes in ion
receptor permeabilty
•activation of
3. intracellular 2nd
replication
messengers
•regulation
of transcription
•Membrane
depolarization
UW-M Cell Biology (Bio Sci 315)
Overview of the 3 Main Signal
Transduction Pathways:
e.g., neurotransmission
e.g., cAMP mediated flight
or fight response
(glycogen breakdown,
muscle contraction)
e.g., regulation
of many genes
UW-M Cell Biology (Bio Sci 315)
G-protein Mediated cAMP synthesis
a a g
GTP GDP b ATP
cAMP +PPi
GTP
When the [hormone] drops…
g a
b GTP
GDP ATP
Pi
cAMP +PPi
UW-M Cell Biology (Bio Sci 315)
c-AMP: a second messenger
UW-M Cell Biology (Bio Sci 315)
Index card assignment
Watch the animation. Collaborate with your
classmates to describe what’s happening, why it
might happen, and how these events are useful.
Write your response in your own words on an
index card.
g a
b GTP
GDP ATP
Pi
cAMP +PPi
UW-M Cell Biology (Bio Sci 315)
cAMP and the Fight-or-Flight Response;
adrenaline
activation of PKA
Liver cell
active
ATP inactive
cAMP adenylyl
cyclase
p
active
inactive
cAMP glycogen
inactive
active inactive
active p
phosphorylase phosphorylase
protein kinase
kinase A
glycogen glucose-1-phosphate
amplification cascade
UW-M Cell Biology (Bio Sci 315)
Caffeine keeps you awake because it
1. Prevents the synthesis of cAMP.
2. Prevents the breakdown of
cAMP.
3. Inactivates the enzyme protein
kinase A.
4. Inhibits the enzyme glycogen
phosphorylase
Caffeine inhibits the enzyme
phosphodiesterase, which
normally breaks down cAMP.
UW-M Cell Biology (Bio Sci 315)
Heart muscle
contraction mediated
by acetylcholine-
stimulated G-protein
signal transduction
pathway
UW-M Cell Biology (Bio Sci 315)
Which of the following is not a second
messenger resulting from G-protein-
mediated signal transduction?
20% 20% 20% 20% 20%
1. IP3
2. cGMP
3. diacyl glycerol
4. Ca++
5. protein kinase C
ol
P
C
+
3
a+
IP
M
er
se
cG
C
yc
na
gl
ki
yl
n
ac
ei
ot
di
pr
UW-M Cell Biology (Bio Sci 315)
G-protein mediated signal transduction is mediated
by several 2nd messengers:
Adenylate cyclase
cAMP
protein kinase A
SER
Phospholopase C IP3 Ca++ Ultimate
(inositol
triphosphate) effects
DAG
(diacyl glycerol)
protein kinase C
UW-M Cell Biology (Bio Sci 315)
Protein kinase C effects include:
• neurotransmitter release
• cell growth & division
• cell differentiation
• glycogen hydrolysis
• fat synthesis
Phospholipase C-mediated effects:
•Liver glycogen breakdown (vasopressin)
•Pancreatic amylase secretion (acetylcholine)
•Platelet aggregation (thrombin)
UW-M Cell Biology (Bio Sci 315)
Plant derived phorbol esters are
carcinogenic because they mimic DAG,
leading to...
• constant PKC activity
• constant cell growth & division
UW-M Cell Biology (Bio Sci 315)
PK-A and PK-C (activated by G-
protein mediated signal transduction)
are serine-threonine kinases because
they place phosphates on these amino
acids in target proteins.
UW-M Cell Biology (Bio Sci 315)
Receptor tyrosine kinase mediated
signal transduction
• does not involve G-proteins
• does involve phosphorylation of proteins
• … at tyrosines
UW-M Cell Biology (Bio Sci 315)
Receptor Tyrosine Kinase Activation
ligands
P- X -P
inactive
active …cross-phosphorylation of
tyr kinase
tyr kinase P- X -P tyrosines
monomer
dimer P- X -P
ATP
ADP
Phosphorylated tyrosines on
activated signaling proteins
cell response
UW-M Cell Biology (Bio Sci 315)
MAP (mitogen-activated protein) kinase activation:
ligands
inactive
active
Ras active
MAP kinase-kinase-kinase
inactive P- X -P
active GDP
tyr kinase P- X -P
MAP kinase-kinase
tyr kinase GTP
P-
monomer P- X -P
dimer
cross- ATP
ADP
phosphorylation
P-
of tyrosines adaptor protein
Ras-activatingprotein
translocation to nucleus…
nucleus
UW-M Cell Biology (Bio Sci 315)
P
| kinase
MAP
Transcription
P-
factors Other
P- nuclear
DNA proteins
binding Changes
in protein
changes in activity
gene
activity
Cell proliferation,
differentiation
UW-M Cell Biology (Bio Sci 315)
Many human cancers have mutations affecting
the Ras protein. Which of the following kinds of
mutations could account for this?
1. One resulting in less Ras gene
transcription
2. One resulting in tighter binding of
GDP to the Ras protein
3. One resulting in an inability to
hydrolyze GTP
4. One resulting in an inbility to
phosphorylate MAP kinase-kinase-
kinase
UW-M Cell Biology (Bio Sci 315)
Some final thoughts on signal transduction
•Signal Transduction is mediated by other kinds of
receptor-enzymes
•Signals include protein hormones, growth factors and
cytokines (the latter are signals between nearby cells).
•Signalling pathways can be direct, like those discussed
here, or…
•They can be complex, requiring the cooperation of twoi
or more signal molecules and the integration of
intracellular signalling pathways.
UW-M Cell Biology (Bio Sci 315)
PPT presentation ends here
UW-M Cell Biology (Bio Sci 315)
Signal transduction themes: 2nd messengers &
protein phosphorylation
extracellular signal
Signal Transduction
intracellular second messenger
…binds to inactive protein
kinase
activated protein kinase
ADP
ATP
Pi
phosphatase
UW-M Cell Biology (Bio Sci 315)
Plant derived phorbol esters are
carcinogenic because they mimic DAG,
leading to...
• constant PKC activity
• constant cell growth & division