L8, Crosstalk and specificity Flashcards
1
Q
How does helper T-cell activation come about, and what is the effect?
A
- Binding of antigen to T-cell receptor (TCR)
- Activation of PLC-gamma
- PLCy hydrolyses PIP2 to release IP3 -> Generates increase in Ca2+ by stimulating release from ER (IIP3R)
- Activation of Calcineurin (PP2B)
- Dephosphorylation of NFAT -> shuttled to nucleus -> binds to promoter regions of IL-2 by NFAT
2
Q
Structure and function of CaNA:
A
- CaNB -Ca2+ is able to bind to CaNB Binding domain on CaNA (1)
- CaM binding domain (2)
- Autoinhibitory domain blocks catalytic domain until both CaNB-Ca2+ and CaM-Ca2+ have bound -> sufficient for conformational change -> activation and subsequent phosphorylation of substrates (e.g. NFAT, PP1)
3
Q
cAMP signalling pathway:
A
- Activation of GPCR
- Activation of adenylate cyclase
- Generation of increases in [cAMP]
- Activation of PKA
- Phosphorylation of CREB/ dephosphorylation of TORC
- TORC2 and pCREb bind to CRE containing genes -> gene expression
4
Q
Calcium dependent regulation of TORC (analogous to cAMP):
A
- Binding of antigen to TCR
- Activation of PLCy
- Generation of increases in Calcium
- Activation of CAMKIV and CaN
- Dephosphorylation of TORC and phosphorylation of CREB
- Promotion of transcription of CRE-containing genes by CREB/TORC
* Prime example of crosstalk in Calcium signalling
5
Q
Types of networks:
A
- Exponential (nodes are joined by similar numbers of connectors)
- Scale-free (contain hubs, which are nodes with a high degree of connectivity)
6
Q
Issues with characterisation of calcium signalling:
A
- Scale-free networks are characterised by power law degree distribution
- This requires quite a large network map to test, which biological examples typically would not satisfy
- Must use emergent properties instead (can be experimentally tested e.g. knockouts for fragility etc)
7
Q
Emergent properties of scale-free networks:
A
- Robustness (tolerate error)
- Flexibility (process multiple signals)
- Fragility (against major node removal)
8
Q
How is specificity conferred in calcium signalling systems?
A
- Involvement of additional signalling events occurring in parallel to changes in [Ca2+]cyt (Crosstalk with Ca2+-independent signal)
- Expression of appropriate signalling machinery required for transduction of a given signal (the cell context)
- Stimulus-specific changes in [Ca2+]cyt including spatial and temporal heterogeneities such as localised elevations, oscillations and transients (the calcium signature)
9
Q
Expression of different IP3R isoforms -> application?
A
- IP3R-1 is expressed mainly in the CNS
- IP3R-2 is predominantly expressed in hepatocytes and lymphocytes
- IP3R-3 is expressed in cardiocytes
- -> differing sensitivities to Calcium allows tissue appropriate response
10
Q
Define EC50:
A
- Half maximal Calcium release (reflects binding affinity)
11
Q
Example: Spatial heterogeneities in cytosolic free calcium
A
- Sperm-triggered Calcium-waves in sea squirt eggs
12
Q
Temporal heterogeneities in cytosolic free calcium:
A
- Membrane oscillators (FAST! milliseconds)
- Cytosolic calcium oscillators
- GnRH neurons
- Circadian clock (SLOW! - 24hrs)
13
Q
What ways may calcium oscillations be programmed?
A
- Frequency modulation
- Amplitude modulation
- Magnitude modulation
- Shape modulation (Properties)
14
Q
Example: Frequency modulation
A
- Oscillation frequency controls ciliary beat frequency in airway epithelial cells
- The frequency of oscillations affects calcium-dependent NFAT nuclear translocation
15
Q
Types of tracking:
A
- Digital tracking: physiological response directly related to digital info (pulses)
- Integrative tracking: steady state responses depending on pattern (staircase)
