Crosstalk + Specificity Flashcards
What is an example of coupling an extracellular stimulus to gene expression with cytoplasmic calcium concentration?
e.g. Helper T cells (stimulate responses in other cells) and IL-2
- Binding of antigen to T-cell receptor
- Activation of PLCγ
- Generation of increases in cytoplasmic calcium conentration
- Activation of calcineurin (PP2B)
- Dephosphorylation of NFAT
(Nuclear Factor of Activated T-cells) - Promotion of IL-2 gene transcription by NFAT
(encoding a growth factor)
What is Calciuneurin?
= a Ca2+/calmodulin-sensitive serine/threonine protein phosphatase
Calcineurin B (CaNB)
= Ca2+ binding to CaNB binding domain
= CaNB-BD
Calmodulin (CaM)
= Ca2+ binding to CaM binding domain
= CaM-BD
Removal of autoinhibitory domain (AID) from catalytic site
What is cAMP signalling?
= second messenger
(increases in response to many stimuli)
- Activation of GPCR
- Activation of adenylate cyclase
- Generation of increases in cAMP conc
- Activation of Protein Kinase A (PKA)
- Phosphorylation of CREB / dephosphorylation of TORC
- Promotion of transcription of CRE-containing genes by CREB/TORC
How do Helper-T cells and IL-2 experience cross-talk?
- Binding of antigen to T-Cell Receptor
- Activation of PLCγ
- Generation of increases in calcium conc.
- Activation of CAMKIV and CaN
- Phosphorylation of CREB / dephosphorylation of TORC
- Promotion of transcription of CRE-containing genes by CREB / TORC
= crosstalk
(calicum dependent and involves cAMP)
EXTRA READING
= crosstalk between Helper T cells and IL-2 occurs through positive feedback loop
= Helper-T cells release IL-2 which activates IL-2 receptors on other T cells
= which leads to activation and proliferation of these T cells = which then release more IL-2
What type of crosstalk between signalling systems is there?
Exponential
= nodes are joined by similar numbers of connectors
Scale-free
= contain hubs
(nodes with a high degree of connectivity)
Signalling Networks can be:
Linear
= 1 stimulus, 1 response
Divergent
= 1 stimulus, multiple responses
Network
= 1 stimulus, multiple responses with multiple interactions
= crosstalk
What are scale-free networks?
= characterised by a power law degree distribution
= requires a relatively large network map (typically 1000+ nodes) to test degree distribution
Emergent properties of scale free networks:
Robustness
= tolerate error
Flexibility
= process multiple signals
Fragility
= against major node (hub) removal
e.g. serotonin-induced calcium signalling pathway
(Hubs = IP3R, canonical TRP channel 3 (TRPC3)
e.g. ABA signalling network in stomatal guard cells
EXTRA READING (more examples)
= AKT signalling (cell growth, survival and metabolism)
= MAPK signalling (cell proliferation, differentiation and survival)
= Wnt signalling (embryonic development)
= Notch signalling (cell fate determination, differentiation and development)
= few hubs have many connections to downstream effectors and many other proteins have only a few connections
Where is there specificity in calcium signalling systems?
- Involvement of additional signalling events occurring in parallel to changes in Ca2+ conc.
= (crosstalk with Ca2+ independent signalling)
- The expression of the appropriate signalling machinery (Ca2+ sensors and decoders) required for the transduction of a given signal
= (the cell context)
- Stimulus-specific changes in Ca2+ conc
= including spatial and heterogeneities
(such as localised elevations, oscillations and transients)
= (the Ca2+ signature)
How do IP3Rs differ? (e.g. of specificity)
= in their response to IP3 and where they are expressed
IP3R-1
= expressed mainly in the CNS
IP3R-2
= predominantly expressed in hepatocytes and lymphocytes
IP3R-3
= expression in cardiomyocytes
(binding affinity dependent on Ca2+ release)
How do VGCC isoforms differ? (e.g. of specificity)
L-type / CaV1
= skeletal and cardiac muscle, brain, other non-muscles
= EC-coupling, sensitive to DHP
= 25pS
N-type / CaV2
= neurons, endocrine cells
= neurotransmitter release at synaptic gaps
= sensitive to conotoxin
= 13 pS
P-type / CaV2
= purkinje cells
= sensitive to FTX
= 10-20 pS
T-type / CaV3
= heart cells
= single channel conductance is tiny = <8 pS
= sensitive to mibefradil
What is an example of spatial heterogeneities in Ca2+ conc.?
= sperm-triggered Ca2+ waves in sea squirt
(Ascidiella aspersa)
What is an example temporal hetergoneities in Ca2+ conc.?
= Transients and Oscillations
EXTRA READING
= variations in frequency duration and magnitude of calcium signals over time
= can be due to variations in the expression or activity of calcium channels, pumps, transports / changes in external or environment of cell
e.g. in neurons
= calcium signalling temporal heterogeneities inflence strength and timing of synaptic transmission
(role in synaptic plasticity and neurons)
e.g. in cardiac muscle
= affects strength and timing of contractions
How is signalling information encoded in Ca2+ conc. oscillations?
Oscillation frequency
= controls ciliary beat frequency in airway epithelial cells
(decoded through digital tracking)
= affects Ca2+ dependent NFAT nuclear translocation
(decoded through integrative tracking)
Do oscillations in Ca2+ conc. encode information? (+evidence)
WT
= Ca2+ influx across plasma membrane
= Ca2+ and release from internal stores
= reductions in stomatal aperture
Arabidopsis det3 mutant
= lesion in enzyme involved in loading Ca2+ into ER
= NO oscillations in Ca2+ conc,
= NO reduction in stomatal aperture
A defined range of parameters encode stomatal movements
Encoding signalling information in Ca2+ conc. oscillations
= frequency modulation
= amplitude modulation
= shape modulation
