Crosstalk and specificity

Question 1

Helper T cells and IL-2

Answer 1

Antigen binds to TCR
Activation of PLC-gamma
Activation of IP3R and Ca2+ release from ER
Activation of calcineurin (PP2B)
Calcineurin dephosphorylates NFAT (nuclear factor of activated T-cells)
NFAT binds to promoter of IL-2 gene transcription

Question 2

Calcineurin

Answer 2

Ca2+/calmodulin-sensitive serine-threonine protein phosphatase
Calcineurin A (protein phosphatase 2B)
Calcineurin B (calcium sensor)
Ca2+ binding to EF hand in CB allows binding to CA
Ca/CAM activation leads to binding to CA and full calcineurin A activation

Question 3

cAMP

Answer 3

Signal perception by GPCR leading to activation and interaction with G protein

GDP to GTP exchange. Alpha subunit activates adenylate cyclase which converts ATP to cAMP

Question 4

cAMP signalling

Answer 4

Increase in cAMP activates PKA
PKA phosphorylates TF CREB and inhibits SIK2 kinase allowing dephosphorylation of TORC (TF)

CREB and TORC2 bind to promoters of CRE gene (cAMP response element) and promote transcription

Question 5

Helper T cells and cAMP signalling

Answer 5

Cross-talk between Ca2+ and cAMP pathway

Antigen binding and PLC-gamma activation. Increase in Ca2+
Activation of CaMKIV (Ca/calmodulin activated PK IV) which activates CREB
Ca2+ activates calcineurin which dephosphorylates TORC
Both CREB and TORC promote CRE-containing genes

Question 6

Calcium signalling specificity

Answer 6

Involvement of events occurring parallel to changes in calcium (crosstalk)
Expression of Ca2+ and decoders required for signal (cell can only respond if present)

Expression of IP3R differs by location (different responses to IP3 and Ca2+). Stimulus specific changes (calcium signature)

Question 7

Decoding Ca2+ oscillations

Answer 7

Response oscillates at a frequency which mimics oscillations (digital tracking). Ca2+ and CBF oscillations in airway epithelial cells

Ca2+ oscillations result in steady state responses (integrative tracking). Oscillations and NFAT nuclear translocation in T cells

Question 8

Ca2+ signalling mutations in stroma

Answer 8

Stimulation of wild type stromatal guard cells leads to Ca2+ influx/release and stromatal closure

Arabidopsis det3 mutant (enzyme involved in Ca2+ loading to ER).
Stimulation leads to no oscillations and no guard cell closure

Question 9

Ca2+ and ROS crosstalk

Answer 9

Ca2+ signalling influences generation of ROS from NADPH oxidases and mitochondria.
Surges of Ca2+/ROS promote apoptosis

In cancer, localised sub-lethal increases in ROS/Ca2+ may be involved in proliferation and metastasis