signalling secondmessengers 2019 · endocrine – paracrine - autocrine chemical synapsis electric...

2019.09.11.

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Cell siganlling – second messenger systems (introduction)

Learning objective: 7. 11.09.2019.

Regulation of the cellular functions

Types of the intercellular communications:

Endocrine – paracrine - autocrine

Chemical synapsis

Electric synapsis/gap junctions

Chemical signaling molecules („primary messengers”) :

Hormones

Neurotransmitters

Local chemical signals (paracrine substances):

Cytokines, inflammatory mediators, growth factors, antigenes etc.

Membrane receptors:

Specific binding of mediator substances – activation (conformation change)

– signalisation process

Consequence of the receptor activation I.:

Changes in the membrane potential:

• Ligand-gated ion channels (ionotropic receptors)

• functional coupling with ion channels (metabotropic receptors)

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Types of the intercellular communication processes(primary messengers and their receptors)

Consequence of the receptor activation II:

Activation of second messenger systems - intracellular signal transduction

Functions:

Functional connection between the activated receptor and effector (enzymes,

ion channels, transporters, motor elements, regulator proteins etc.) molecules

Second messenger systems:

Intracellular Ca2+ transients

cAMP (cGMP): adenylate-(guanylate-) cyclase – protein kinase A system

Phosphoinositol: PIP2 - phospholipase C – protein kinase C system

Tyrosine kinases: growth factors, insulin

Nitric oxide (NO): NO receptors - guanylate cyclase

Arachidonic acid – phopholipase A

Cytoplasmic/nuclear receptors: steroid hormones, T3/T4, eicosanoids, NO

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What are the common traits of these systems?

Specificity: selective ligand binding to the receptors

selective phosphorylation by protein kinases

(Specific binding sites, phosphorylation sites: Ser, Thr or Tyr)

but: protein kinases can activate or inactivate different proteins (divergence)

one protein can be regulated by different protein kinases or other second

messenger systems (convergence)

Overlaps and bidirectional interactions between different messenger systems

(inhibition or stimulation, feed-back/feed-forward; regulatory networks)

Amplification: Cascade systems – adenylate cyclase, protein kinases can activate

large number of downstream elements – auto-amplification

„chain reaction”

Safety factors: The signal must be limited both spatially and temporally

– intrinsic regulatory mechanisms („breaks”)

e.g.:

Adenylate cyclase – G-Protein: GTP hydrolysis limits G-prot. activity

cAMP – Phosphodiesterase inactivates cAMP

Ca2+ - pumps maintain resting plasma Ca2+ concentration at low level

Plasma concentrations of the hormones are in a very low pmol/nmol/ low micromolar range

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Signal amplification – cascade mechanism

Intracellular calcium as a second messenger (ion)

www.cellsignallingbiology.org

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www.cellsignallingbiology.org

„Modular” composition of the calcium-signalling

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Functional model of calmodulin and other intracellular Ca-binding proteins

VOC: Voltage Operated Calcium Channel; CCE: Capacitive Calcium Entry; CaM: Calmodulin; MLCK Myosin

Light Chain Kinase

Example I: Calcium – calmodulin system (smooth muscle cells)

[Ca2+]ic ~10-7

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Measurement of the Ca-transients – Ca-sensitive fluorescent dyes (e.g.: FURA-2)

G-proteins and G-protein coupled receptors (GPCRs)

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Connections of heterotrimer G-proteins to different intracellular signal pathways

www.cellsignallingbiology.org

G-protein coupled receptors (GPCRs) – adenylyl cyclase / protein kinase A

pathway

www.cellsignallingbiology.org

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Adenylyl cyclase- cAMP – proteinkinase-A system II.

www.cellsignallingbiology.org

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GPCRs – phospholypase C – DAG/InsP3 – Protein Kinase C pathway

www.cellsignallingbiology.org

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(cAMP) - System