Spencer Cell Signaling LN Flashcards
Juxtacrine
Direct physical contact between cells
- surface protein/receptor interactions
Endocrine on/off response speed, affinity, type of molecule
Hormones
- slow on/off
- very high affinity
Paracrine on/off response speed, affinity, type of molecule
Local mediators (growth factors, cytokines)
- rapid response
- low-high affinity
Synaptic on/off response speed, affinity, type of molecule
NTs
- very low affinity
- very rapid response
Autocrine on/off response speed, affinity, type of molecule
Large proteins (GFs, Cytokines)
- Low to high affinity
- Rapid response
Types of 1st messengers
NTs, Hormones, GFs, Cytokines
Are NTs hydrophilic or hydrophobic
Hydrophilic
Hydrophilic vs Hydrophobic hormones
Hydrophilic: usually charged, interact with cell-surface receptors
Hydrophobic: membrane permeable, interact with intracellular receptors
Growth Factors range
Long range
Cytokines range
local range, coordinate immune response
Agonist
Ligand that activates normal response
- inhibitor or excitatory
Antagonist
Ligand that induces no response
- blocks normal response
Effector
Intracellular receptor that responds to activated receptors and generates 2º messengers
Coupling
Transmits signal from activated receptor to effector
Adaptor
Intracellular protein that lacks enzymatic activity but contains several domains that mediate protein-protein interactions
What are the 2 molecular switches
1) Protein phosphorylation
2) Guanine NT binding (G protein cycle)
Activation of G protein cycle
GDP is exchanged for GTP
- assisted by receptor if trimeric
- GEF (Guanine NT EF) for monomeric
Inactivation of G protein cycle
GTP hydrolyzed to GDP using GTPase
- If monomeric, requires GAPs (GTPase activating proteins)
3 receptor criteria
1) Specificity
2) Appropriate binding affinity
3) Transmission of message via further modification of signaling cascade
2 receptor classes
1) Intracellular
- causes long-lasting changes
- displaces HSP
2) cell-surface receptors
- triggers an increase in 2º messenger concentration
GPCR mechanism
1) Ligand binds (activates up to 100)
2) conformational change exposes regulatory site, allowing G-protein to bind
3) GDP exchanged for GTP, causes G protein dissociation
4) alpha subunit binds to membrane-bound enzymes, activates 2º messengers
5) Intrinsic GTPase activated, hydrolyzing GTP causing release from enzyme
6) G protein alpha subunit reassembles with beta gamma complex
Affinity of ligands for GPCR?
Low to high affinity
How is GPCR terminated
Phosphorylation of Ser/Thr on C-terminal tail
What 1º messengers does the GPCR react to?
NTs, hormones, cytokines (especially chemokine)
GPCR structure
N-terminal outside, C-terminal inside, 7 transmembrane subunits
Structure of GPCR alpha subunit
Hydrophilic with a lipid membrane anchor
beta-gamma complex
- hydrophobic
- covalently attached lipid anchor
4LOKO example
EtOH
1) EtOH binds to allosteric site
2) prolonged opening of GABA channel
3) increased negative membrane potential
4) suppression of neural activity
Caffeine
1) Blockage of binding site (antagonist)
2) cancellation of Adenosine effect
3) increased neural activity
4) blood vessel construction, epi release, increased alertness
Both
5) increased dopamine release
2 types of enzyme-linked receptors
1) Tyrosine Kinase
2) Serine/Threonine Kinase
Tyrosine Kinase receptor mechanism
1) Ligand binds to RTK causing dimerization and activation of kinase domain
2) Active RTK autophosphorylates Tyrosine residues
3) Phosphorylation causes binding and activation of adaptor proteins (cascade)
MAP Kinase cascade
Example of Tyrosine Kinase Receptor triggered cascade
1) Adaptor protein binds RAS-activating protein
2) Activation of RAS via GDP to GTP
3) RAS attracts MAPKKK
4) MAPKKK activated by membrane
5) MAPKKK to MAPKK via ATP
6) MAPKK to MAPK by ATP
7) MAPK phosphorylates targets
Receptor Serine/Threonine Kinase
1) Autophosphorylation causes type II homodimer to become constitutively active
2) Ligand pulls Type I to combine with Type II
3) Ser/Thr becomes phosphorylated
4) SMAD binds to Type I and becomes phosphorylated
5) SMAD unfolds and activates
6) SMAD dimerizes with other SMAD, exposes NLS
7) Alters gene expression
Traits of enzyme-linked receptors
Binding activates cytoplasmic enzyme activity
- Endocrine, Paracrine
- Hormones, Growth Factors
- Very high affinity
How do enzyme-linked receptors terminate
Receptor-mediate endocytosis
- down-regulation
Traits of cytokine-linked receptors
Binding of ligand causes association and activation of cytoplasmic enzymes
- paracrine, autocrine
- cytokines, GFs
- low to high binding affinity
How are cytokine-linked receptors terminated
Via receptor-mediated endocytosis and protein phosphatases
JAK-STAT Pathway mechanism
type of cytokine receptor
1) JAK attracted to Pro-rich regions on transmembrane peptides
2) Cytokine binds causes association of subunits and JAK activation
3) JAK Tyr + subunit phosphorylation
4) STAT dimer binds to Tyr
5) STAT phosphorylated
6) STATS dissociate, dimerize, expose NLS
Ebola virus mechanism
Normally
1) STAT1 dimer binds to Importin a5/ß complex
2) ß brings Importin complex through nuclear pore
3) Ran-GTP dissociates Importin complex
4) STAT1 causes expression of antiviral immune response
Ebola effect
- VP24 ebola protein displaces STAT1 to form Importin complex
Types of 2º messengers
Ions: Ca2+
H2O-soluble molecules: cAMP, cGMP, IP3
Membrane-associated molecules: DAG, Arachidonic acid, PIP3
Ca2+ concentration which means the cell is quiet
10^-7 M or less
Ca2+ concentration which means the cell is active
10^-6 M or greater
Ca2+ removal mechanisms
1) NCX Na+/Ca2+ exchanger
2) PMCA Ca2+ ATPase
3) SERCA
NCX mechanism
Gets most Ca2+ out
- Ca2+ out, 3 Na+ in
- low affinity, high rate
PMCA
Gets rest of Ca2+ out
- ATP pushes Ca2+ into protein
- eversion, Ca2+ out
- high affinity, low rate
Ca2+ addition mechanisms
1) Ligand-gated ion channel
2) Voltaged-gated Ca2+ channel
3) RyR
4) IP3R
RyR
2 Ca2+ bind to cause more Ca2+ release
IP3R
IP3 and Ca2+ bind to release Ca2+ from ER
CICR
Ca2+-induced Ca2+ release
Creation of cAMP
ATP dephosphorylated by Adenylate Cyclase, creation of phosphodiester bond
Degradation of cAMP
cAMP phosphodiesterase uses H2O to create 5’-AMP
Regulation of cAMP
Regulated by balance of G proteins
- G proteins can be inhibitory or excitatory
Cholera
Binding of ADP-ribose causes constitutive activation of adenylate cyclase
- increase in cAMP, excessive loss of H2O, shock
Pertussis
Prevents activity of inhibitory G protein
- increased PKA, high insulin producing low glucose, high histamine sensitivty
cGMP creation
Guanylate cyclase creates phosphodiester bond in cGMP
cGMP degradation
cGMP phosphodiesterase uses H2O to degrade it to 5’-GMP
Effect of NO in cGMP
Increases cGMP production by binding to soluble guanylate cyclase
Effect of ANF (hormone)
Increases cGMP production by binding to membrane Guanylate cyclase
Effect of increase cGMP
Production of PKG, phosphorylation of target proteins
Phospholipid sources of 2º messengers
- Phosphatidylcholine
- Phosphoethanolamine
- Phosphatidylinositol
Enzyme that converts PI to PIP
PI-4 kinase
Enzyme that converts PIP to PIP2
PI-5 Kinase
What is special about PIP2
Contains 3 PO4- groups, major substrate for producing 2º messengers
Types of 2º messengers derived from phospholipids
IP3, DAG, Arachidonic acid, PIP3
What is the largest GPCR subunit?
Alpha subunit
Which subunit contains the GTP/GDP binding site?
Alpha subunit
Which subunit determines the G protein subtype?
Alpha subunit
Do RTKs and Ser/Thr Kinases have intrinsic enzymatic activity?
Yes, binding activates intrinsic enzymatic activity of cytoplasmic domain
Do cytokine receptors have intrinsic enzymatic activity?
No
