Exley cell signalling lecture 3 Flashcards
How is Ins(1,4,5)P3 formed?
Receptor-activated hydrolysis of
phosphatidylinsitol (4,5) bisphosphate / PIP2
What is the function of Ins(1,4,5)P3 in cells?
Acts as a receptor for release of Ca2+ from specialized intracellular stores
And regulates the flow, through a high conductance channel
What do IP3 induced sparks and puffs represent?
Highly localized Ca2+ release from the ER through ryanodine receptors and inositol trisphosphate receptors
Variability in the sensitivity of individual receptors to Ins(1,4,5)P3 is an important factor in determining…….?
If the quanta of Ca2+ release are fated to remain localized or to produce regenerative waves which sweep across the whole cell.
What are the 3 ways in which sensitivity to stimulation via Ins(1,4,5)P3 is achieved?
1) Receptor clustering
2) at least 3 different classes of Ins(1,4,5)P3, with different sensitivities to the agonist
3) Rate of metabolism of InsP3
What happens to the behaviours of the inositol trisphosphate receptor channels in the presence of
a) Low agonist stimulaion
b) Higher agonist stimulation
c) Very high agonist stimulaton
a) Few receptors bind InsP3. High localized Ca2+ ‘blips’ signals are generated from cytoplasmic Ca2+
b) Coordinated openings of several InsP3 channels within a cluster, stimulating gating of nearby channels - Ca2+ induced Ca2+ release
c) Propogation of Ca2+ waves, due to release at adjacent clusters, diffusion and CICR.
What structural change occurs within IP3 when Ca2+ is bound and why?
Large-scale relocations of IP3 binding domains.
IP3 binding cores ligand with IP3 -> Lys-C digestion
= Windmill structure
Give some cellular processes what the IP3/Ca2+ signalling pathway is involved in
Metabolism, Fertilization, Exocytosis, Proliferation, Differentiation, Aldosterone secretion, Ion channel opening, Aggregation, Neuronal synaptic pasticity, Fluid secretion, Muscle contraction…
What are the stages of mammalian fertilization in relation to IP3/Ca2+?
1) Sperm chemotaxis and acrosome reaction
2) PLC injected into the occyte
3) PLC binds to PIP2
4) PIP2 ligand binds to IP3
5) Cytosolic calcium oscillator -> Ca2+ oscillations
6) Oocyte activation and cell proliferation
What is the role of the IP3/Ca2+ signalling pathway in regulating gene transcription and proliferation in T cells?
1) Antigen binds to TCR
2) PLC-1 binds to PIP2
3) PIP2 binds to IP3
4) IP3 binds to IP3 receptor on endoplasmic reticulum
5) Direct release of Ca2+ and stimulation of CRAC Orai 1 channel -> Calcineurin
6) Release of NFAT
7) Gene transcription and proliferation
What Ca2+ activated channels are responsible for pacemaker depolarization, which trigger the action potentials that control breathing?
TRPM4 channels
Ins(1,4,5)P3 is metabolised into Ins(1,3,4,5)P4 - by what enzyme?
Ins(1,4,5)P3 3-kinase.
How many isoforms of the Ins(1,4,5)P3 3-kinase enzyme are there? What 2 regulated by?
3
Ca2+/calmodulin-dependent protein kinase II (CAMKII).
What is the definition of a kinase?
an enzyme involved in the transfer of a phosphate group (phosphotransferase) without regeneration of the donor molecule
In vivo, what does a pool of Ins(1,3,4,5)P4 protect against and why?
protects against the hydrolysis of Ins(1,4,5)P3
because it has a ten-fold higher affinity for the enzyme (inositol phosphate 5 phosphatase) whose major activity is the hydrolysis of inositol phosphates.
