Transcript 19 Cell Signaling 10 17 05

BCOR 011
Cell Communication II
Lect 19
Signal molecule
Activated
Ras-GTP
A G-Protein
Receptor
Chapt 11
Inactive
MAPKKK
1
Active
MAPKKK
1
Inactive
MAPKK
2
ATP
Protein
Phosphatases
P
ADP
Pi
10/17/05
And they tell 2 friends
And they tell 2 friends
And they tell 2 friends…
Active
MAPKK
2
PP
Inactive
MAPK
3
ATP
P
ADP
Pi
Active
MAPK
3
PP
Inactive
protein
ATP
P
ADP
Pi
PP
Active
protein
Cellular
1response
Lecture Outline
1. Finish Trimeric G-Protein: Phospholipase C
-DAG, IP3 second messengers
Protein Kinase C, Ca++ release
2. Nitric Oxide, cGMP activation
- consequences of failing to inactivate
3. Tyrosine Kinase Receptor
- RAS G-protein, MAP Kinase Cascade
- Cell Cycle Control, Gene Control
4. Internal Receptors – Steroid Receptor
- Gene Regulation
2
TWO subclasses of trimeric G-protein-activated
signal transduction pathways:
A. target protein adenylate cyclase
cAMP-> PKA
B. target protein phospholipase C
3
target effector enzyme
is Phospholipase C
PLC cleaves a membrane
phospholipid (Phoshatidyl inositol) to
two 2nd Messengers:
Inositol-1,4,5-Trisphosphate
(InsP3) &
Diacylglycerol (DAG)4
PIP2
DAG
Lipid
Soluble
InsP3
Water
Soluble
5
DAG
Activates
Protein
Kinase C
(Starts
Cascade)
InsP3
Ligand
for ER
ligandgated
Ca++
channels
6
 Ca++ levels
1 A signal molecule binds
to a receptor, leading to
activation of phospholipase C.
EXTRACELLULAR
FLUID
2 Phospholipase C cleaves a
3 DAG functions as
a second messenger
in other pathways.
plasma membrane phospholipid
called PIP2 into DAG and IP3.
Signal molecule
(first messenger)
G protein
DAG
GTP
PIP2
G-protein-linked
receptor
Phospholipase C
IP3
(second messenger)
IP3-gated
calcium channel
Endoplasmic
reticulum (ER)
Various
proteins
activated
Ca2+
Figure 11.12
Cellular
response
Ca2+
(second
messenger)
4 IP quickly diffuses through
3
the cytosol and binds to an IP3–
gated calcium channel in the ER
membrane, causing it to open.
5 Calcium ions flow out of
6 The calcium ions
the ER (down their concentration gradient), raising
the Ca2+ level in the cytosol.
activate the next
protein in one or more
signaling pathways.
7
Response:
Protein Kinase C phosphorylates
target proteins (ser & thr)
cell growth
regulation of ion channels
cytoskeleton
increases cell pH
Protein secretion
Ca++
Binds & activates calmodulin
Calmodulin-binding proteins activated
(kinases & phosphatases)
8
Shut Off
-
remember, signal needs to be transient
-
Must shut off cascade:
removal of ligand,
(self)-hydrolysis of GTP,
remove IP3, protein phosphatases, Ca++ ion pumps
9
Direct activation signal: nitric oxide (NO) It’s a gas!
lipid soluble, binds directly to activate enzyme
made by: endothelial cells (line blood vessels)
target: guanylyl cyclase GTP->cGMP
NO synthase
response: relaxes smooth muscle
vessels dilate, blood flow
+NO
arginine
citrulline
10
target
Shut off
by cGMP
phosphodiesterase
11
Nitroglycerine – taken to relieve angina
1977 –Ferid Murad
Nitroglycerine acts to elict release of NO,
relaxes cardiac muscle
1998 Nobel Prize – Murad, Furchgott, Ignarro
12
Nitro
glycerine
Shut off
By cGMP
phosphodiesterase
13
Sildenafil citrate (VIAGRA)
14
cell-surface receptors
a.
ion-channel-linked
b. G-protein-linked
c. Protein-kinase associated
(enzyme-linked)
15
Mitogen Activated
Protein-Kinase associated receptors
receptor has enzymatic activity
- only when ligand binds
ligand:
allosteric effector -> conformational change
receptor tyrosine kinases
Growth & differentiation
control of cell cycle
control of gene expression
bad news when messed up - cancer
16
Growth factor
Reception
Receptor
Growth Factor
“Mitogen-activated”
Phosphorylation
cascade
Transduction
Signaling Cascade
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
Response
P
DNA
Gene
NUCLEUS
Figure 11.14
mRNA
17
EGFR – epidermal growth factor receptor
•Monomer receptor
1 transmembrane
segment
•Ligand binds –
receptors dimerize
•Activates Tyr kinase
•autophosphorylate
•Scaffold to Bind/activate
Target proteins
•GDP/GTP exchange
•Activate Ras G-protein
EGF – growth factor
or mitogen
18
“Mitosis-generator”
Receptor tyrosine kinases
Signal-binding site
Signal
molecule
Signal
molecule
Helix in the
Membrane
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
CYTOPLASM
Dimer
Figure 11.7
Activated
relay proteins
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
Tyr
Tyr
P Tyr
Tyr P
P Tyr
Tyr P
6
Activated tyrosinekinase regions
(unphosphorylated
dimer)
ATP
6 ADP
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
19
Receptor tyrosine kinases can activate ras
ras is a monomeric G-protein
“molecular switch”
20
A phosphorylation
cascade
Signal molecule
Ras-GTP
Receptor
MAP
Kinase
Inactive
protein kinase
Kinase
1
Kinase
Activated relay
molecule
MAP
Kinase
Active
protein
Kinase
kinase
1
Kinase
MAP
Inactive
Kinase
protein kinase
2
Kinase
phosphatases (PP)
catalyze the removal of
the phosphate groups
from the proteins,
making them inactive
and available for reuse.
2 Active protein kinase 1
transfers a phosphate from ATP
to an inactive molecule of
protein kinase 2, thus activating
this second kinase.
P
MAP
Active
protein
Kinase
kinase
2
Kinase
ATP
ADP
Pi
5 Enzymes called protein
1 A relay molecule
activates protein kinase 1.
PP
MAP
Kinase
Inactive
protein kinase
3
ATP
Active
MAP
protein
kinase
Kinase
3
ADP
Pi
3 Active protein kinase 2
then catalyzes the phosphorylation (and activation) of
protein kinase 3.
PP
Inactive
protein
P
4 Finally, active protein
kinase 3 phosphorylates a
protein (pink) that brings
about the cell’s response to
the signal.
ATP
P
ADP
Figure 11.8
Pi
PP
Active
protein
Cellular
21response
Ras activation sets off a phosphorylation cascade
10
100
MAPKK
1,000
MAPK
100,000
MAPKKK
Mitogen
Activated
Protein
Kinases
MAPKs
Controls:
-Transcription
Factors
-Translation
Factors
22
-Cell Division
How do you turn it off?
phosphatases
GTPase
(GTP->GDP + P)
molecular switch on internal timer
If timer broken – on all the time
23
PROBLEMS IN CANCER:
- broken ras – won’t shut off
- Broken receptor – thinks ligand there
even when it isn’t
-broken MAPK – on all the time, even when
not phosphorylated
RESULT: continuous signal for cell to divide
24
Specific signal transduction cascades:
1. receptor-mediated
cell-surface
2.receptor-mediated
intracellular
Lipid soluble things:
steroid hormones
25
Steroid Hormone
Plasma
membrane
Lipid soluble
Crosses membranes
Receptor
protein
Binds intracellular receptor
In cytosol
steroid receptor Complex
Changes shape
Releases from tether protein
Travels to Nucleus
steroid receptor
Binds DNA
Turns genes ON
EXTRACELLULAR
FLUID
Hormone
(testosterone)
Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
The hormonereceptor complex
enters the nucleus
and binds to specific
genes.
Hormonereceptor
complex
The bound protein
stimulates the
DNA transcription of
the gene into mRNA.
mRNA
NUCLEUS
Figure 11.6
The steroid
hormone testosterone
passes through the
plasma membrane.
The mRNA is
translated into a
specific protein.
New protein
26
CYTOPLASM
The Specificity of Cell Signaling
• The different combinations of proteins
in a cell
– Give the cell great specificity in both the
signals it detects and the responses it
carries out
Same hormone can give different responses
in different cells
27
Pathway
“cross-talk”
Signal
molecule
Receptor
Relay
molecules
Response 1
Cell A. Pathway leads
to a single response
Response
Response
2
3
Cell B. Pathway branches,
leading to two responses
Figure 11.15
Activation
or inhibition
Response 4
Cell C. Cross-talk occurs
between two pathways
Response 5
28
Cell D. Different receptor
leads to a different response
Specific pathways
1. Cell-surface receptor mediated
a. ion-channel-linked
b. trimeric G-protein-linked
(i) adenylyl cyclase cAMP ->protein kinase A
(ii) phospholipase C
InsP3, DAG, Ca++, protein kinase C
Direct activation - NO
c. protein kinase-associated (enzyme-linked)
Receptor tyrosine kinase
monomeric G-protein (ras), MAPKs
29
2. Intracellular receptors – steroid hormones, dioxin