uw-m cell biology (bio sci 315) cell signaling & signal transduction steroid hormones (also...

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,


1. large or very polar extracellular ligand (e.g., hormone)

1. large or very polar extracellular ligand (e.g., hormone)

•changes in enzyme activity

Signal Transduction Themes:•intracellular 2nd messengers•Protein phosphorylation

3. intracellular 2nd messengers

4. protein phosphorylation

•changes in cytoskeletal organization

•changes in ion permeabilty

•activation of replication•regulation of transcription

2. cell surface receptor2. cell surface receptor

•Membrane depolarization


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


G-protein Mediated cAMP synthesis

GTP

GDP

GTP

ATP

cAMP +PPi

GTP

ATP

cAMP +PPi

GDPPi

When the [hormone] drops…


c-AMP: a second messenger


ATP

cAMP +PPi

GTPGDPPi

Index card assignmentWatch 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.


cAMP and the Fight-or-Flight Response; activation of PKA

cAMP

adrenaline

inactiveadenylylcyclase

inactiveactive protein kinase A

phosphorylase kinase

p

pglycogen

phosphorylase

glycogen glucose-1-phosphate

Liver cell

amplification cascade

cAMP

activeATP

inactiveinactive

activeactive


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.


Heart muscle contraction mediated by acetylcholine-stimulated G-protein signal transduction pathway


Which of the following is not a second messenger resulting from G-protein-

mediated signal transduction?

IP3

cG

MP

dia

cyl g

lyce

rol

Ca+

+

pro

tein

kin

ase

C

20% 20% 20%20%20%

1. IP3

2. cGMP

3. diacyl glycerol

4. Ca++

5. protein kinase C


SER

IP3 (inositol triphosphate)

Ca++

G-protein mediated signal transduction is mediated by several 2nd messengers:

DAG(diacyl glycerol)

OH

protein kinase C

Ultimateeffects

cAMPprotein kinase A

Adenylate cyclase

Phospholopase C


Phospholipase C-mediated effects:•Liver glycogen breakdown (vasopressin)•Pancreatic amylase secretion (acetylcholine)•Platelet aggregation (thrombin)

Protein kinase C effects include:• neurotransmitter release• cell growth & division• cell differentiation • glycogen hydrolysis• fat synthesis


Plant derived phorbol esters are carcinogenic because they mimic DAG,

leading to...

• constant PKC activity

• constant cell growth & division


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.


Receptor tyrosine kinase mediated signal transduction

• does not involve G-proteins• does involve phosphorylation of proteins• … at tyrosines


ligands

inactive tyr kinase monomer

…cross-phosphorylation of tyrosines

Receptor Tyrosine Kinase Activation

ATPADP

Phosphorylated tyrosines on activated signaling proteins cell response

P-P-P- -P

-P-Pactive

tyr kinase dimer

XXX


ligands

inactive tyr kinase monomer

cross-phosphorylation

of tyrosines

MAP (mitogen-activated protein) kinase activation:

ATPADP

P-P-P- -P

-P-Pactive

tyr kinase dimer

XXX

adaptor protein

Ras-activatingprotein

GDP

GTP

Rasinactiveactive

MAP kinase-kinase-kinaseactive

MA

P k

inase-k

inase

MA

P ki

nase

nucleus

P-

P-

translocation to nucleus…


P|MAP kinase

nucleus

Transcription factors Other

nuclear proteins

P-

P-

DNA binding Changes

in protein activitychanges in

gene activity

Cell proliferation, differentiation


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


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 two or more signal molecules and the integration of intracellular signalling pathways.


PPT presentation ends here


Signal transduction themes: 2nd messengers & protein phosphorylation

extracellular signal

intracellular second messenger

Signal Transduction

…binds to inactive protein kinase

activated protein kinase

phosphatase

ATP

Pi

ADP


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) cell signaling & signal transduction steroid hormones (also...

Documents

cell biology bio sci

target cell

protein kinase c slide

enzyme protein kinase

synthesis of camp

breakdown of camp

messenger slide

camp mediated flight