cell signaling bruno sopko. signal transduction pathways organization signals receptors – soluble...
TRANSCRIPT
Cell Signaling
Bruno Sopko
• Signal Transduction Pathways• Organization• Signals• Receptors– Soluble Receptors– Transmembrane Receptors
• Enzyme Coupled Receptors• G-Protein Coupled Receptors• Ion-Channel Coupled Receptors
• Second Messengers, Amplifiers, Integrators• Response Changes to Signals• Inhibitors
Content
Signal Transduction Pathways
Signal Transduction Pathways
Signals
Receptors
• Soluble Receptors• Transmembrane Receptors– Enzyme Coupled Receptors– G-Protein Coupled Receptors– Ion-Channel Coupled Receptors
Soluble Receptors - The steroid/Thyroid Hormone Superfamily of receptors
Cortisol (glucocortikoid) Androsteron (steroid)
All-trans retinol acid (retinoid)Vitamin D2
3,3',5-trijodo-L-thyronine (thyroid)
Soluble Receptors - The steroid/Thyroid Hormone Superfamily of receptors
Soluble Receptors - The steroid/Thyroid Hormone Superfamily of receptors
Transmembrane Receptors - Enzyme Coupled Receptors
• Tyrosine kinases phosphorylate protein tyrosine residues using ATP.
• Phospholipase C cleaves PIP2 into IP3 and DAG.
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / RAS MAP kinases
Tyrosine kinases / Insuline receptor
Tyrosine kinases / JAK-STAT receptors
JAK – Janus KinaseSTAT – Signal Transducer and Activator of Transcription
Tyrosin kinases / Receptors of Serin-Threonin Kinases
Cytokins mostly
Transmembrane Receptors / G-Protein Coupled Receptors
Charakteristic receptor structure
Heptahelical receptors (7 transmembrane α-helixes)
Transmembrane Receptors / G-Protein Coupled Receptors
Transmembrane Receptors / Ion Channel Coupled Receptors
Second messengers
• cAMP• cGMP• Phospholipids and Ca2+
• PI3 kinase/AKT and mTOR• MAP kinase pathway
cAMP
cAMP
cAMP
cGMP
Phosholipids and Ca2+
Phospholipids and Ca2+
Phospholipase C
Phosholipids and Ca2+
PI3 kinase/AKT and mTOR
MAP kinase pathway
Signalling molecules – vesicle stored and releasedSNAP-SNARE proteins
Signalling molecules – directly synthesized (Eicosanoids ...)
• compounds containing a 20-carbon core
• Members of this group:– prostaglandins– prostacyclines– tromboxanes– leukotrienes– lipoxins– hydroxyeicosatetraenoic acids (HETE)– hepoxilins
Eicosanoids biosynthesis
• A path in metabolism of polyunsaturated fatty acids (PUFAs), mainly linoleic and arachidonic acid arachidonic acid is (in humans) synthesized from linoleic acid:
• !!! it is not possible to synthesise de novo
• Most animals cannot form double bonds behind position ∆9linoleic and linolenic acids are essential: must be taken from food (plant oils, peanuts, soya beans, maize)
Eicosanoids biosynthesis - overview
Main eicosanoid production sites
• Endothelial cells • Leukocytes• Platelets• Kidneys
• Unlike e.g. histamin, eicosanoids are not synthesized in advance and stored in granules
• In case of an emergent need, these are rapidly produced from a released arachidonate
• Eicosanoids biosynthesis takes place in every cell type except red blood cells
Main steps of eicosanoids production
1) Activation of phospholipase A2 (PLA2)
2) Release of arachidonate into cytosol from membrane phospholipids by PLA2
3) Eicosanoids synthesis from arachidonate COX or LO pathway + further modifications by synthases/isomerases (PGH2
conversion to other prostanoids, LTA4 conversion..) depending on cell type
• PLA2 expression / activity stimulate:– interleukin-1– angiotensin II– bradykinin– thrombin– epinephrine…
1) Activation of phospholipase A2• Ca2+ dependent
• PLA2 expression / activity block:– dexamethasone (synthetic
corticoid)– annexin 1 (lipocortin) –
protein inducible by glucocorticoids
– caspase-3
dexamethasone
2) Arachidonate mobilization for eicosanoid synthesis
• From membrane phospholipids mostly by the action of phospholipase A2:
Release of arachidonate from phospholipids is blockedby anti-inflammatory steroids!
Eicosanoids biosynthesis
• 3 pathways:– A) cyclooxygenase – produces prostaglandins and
thromboxanes– B) lipoxygenase – produces leukotrienes, lipoxins,
hepoxilins and 12- and 15-HETE (hydroxyeicosatetraenoic acids)
– C) cytochrome P450 enzymes (monooxygenases) – produces HETE, e.g. 20-HETE; it is a main pathway in kidney proximal tubules
Products of COX pathway
• (thromboxane)
• (thromboxane)
• (prostacyclin)
Inhibition of COX pathway
Aspirin inhibits cyclooxygenase activity of PGHS-1 i PGHS-2 (by acetylation of enzyme serine)
Other non-steroidal anti-inflammatory drugs inhibit cyclooxygenase activity (ibuprofen – competes with arachidonate)
Anti-inflammatory corticosteroids block PGHS-2 transcription
Corticosteroids
Lipooxygenase pathway
• 3 different lipoxygenases indroduce oxygen to position 5, 12 or 15 in arachidonate; a primary product is hydroperoxy-eicosatetraenoic acid (HPETE)
• Only 5-lipoxygenase produces leuko-trienes; it requires protein FLAP
15-lipoxygenase
-GluLeukotriene D4 Leukotriene E4-Gly
peptidoleukotrienesGly–Cys–Glu
Hepoxilins(HXA3)
15-lipoxygenase12-lipoxygenase
5-lipoxygenase
15-lipoxygenase
5-lipoxygenase
Synthesis of eicosanoids by enzymes CYP450
• cytochrome P450 enzymes – monooxygenases: RH + O2 + NADPH + H+ ROH + H2O + NADP+
• Two types of compounds are produced:– epoxygenases - catalyse production of epoxyeicosatrienoic acids
(EETs) which are metabolized by epoxid-hydrolases into almost inactive dihydroxyeicosatrienoic acids (DiHETEs)
– hydroxylases - catalyse production of HETEs (20-HETE, 13-HETE etc.)
Eicosanoids - list
• arachidonic acid • CYP450
• DiHETEs
• 19-, 20-, 8-, • 9-, 10-, 11-, • 12-, 13-, 15-, • 16-, 17-,• 18-HETE
• cyklooxygenases
• prostacyklins
• prostaglandins
• tromboxanes
• lipoxygenases
• 5-, 8-, 12-, • 15-HETE
• lipoxins
• hepoxilins
• leukotrienes
EETs (epoxides)
Cytokines
• Group of proteins and peptides (glycopeptides) • Influence cell growth (growth factors) • Signal transmission from a cell to another cell
• Important group - lymphokines (also interleukins), proteins released from activated cells of immune system which coordinate immune response of the organism
Cytokine nomenclature• Lymphokines - produced by activated T-
lymphocytes, they control the response of immune system by signalization between immunocompetent cells
• Interleukins (IL) - target cells for IL are leukocytes • Chemokines - specific class, mediating chemotaxis
between cells; stimulate leukocyte movement and regulate their migration from blood into tissues
• Monokines - produced mainly by mononuclear cells, such as macrophages
Main function of cytokines
• Hematopoiesis (e.g. CSF - colony stimulating factor)
• Inflammatory reactions (e.g. IL1 - interleukin, TNF - tumor necrosis factor)
• Chemotaxis (e.g. IL8, MIP1- macrophage inflammatory protein 1, BLC – B-lymphocyte chemoatractant)
• Imunostimulation (e.g. IL12, IFNg - interferon)
• Imunosupression (e.g. IL10)
• Angiogenesis (e.g. VEGF- vascular endothelial growth factor)
• Embryogenesis (e.g. TGF-b, LT – lymphotoxin)
Signal termination
• The chemical messenger itself (acetylcholine esterase, insulin degradation in liver)
• The reaction itself (when GTP in G-protein is used, G-protein GDP complex forms the original structure)
• Degradation of second messenger (phosphodiesterase cleavage of cAMP)
• Phosphatases
Response Changes to Signals
• Intracellular Phosphorylation sites• Receptor number – downregulation• Hormone-receptor complex taken into cell by
endocytis• Degradation and recyclation of receptors• Number of available receptors can be altered
by other hormones
Response Changes to Signals
Literature
• R.K. Murray et al.: Harper's Illustrated Biochemistry, twenty-sixth edition, McGraw-Hill Companies, 2003
• Allan D. Marks, MD: Basic Medical Biochemistry a Clinical Approach, Lippincott Williams & Wilkins, 2009
• Ernst J. M. Helmreich, The Biochemistry of Cell Signalling, Oxford University Press, USA, 2001
• Geoffrey M. Cooper, Robert E. Hausman, The Cell: A Molecular Approach, Fourth Edition, Sinauer Associates, Inc., 2006
• Michael J. Berridge, Peter Lipp and Martin D. Bootman, The versatility and universality of calcium signalling, Nature Reviews | Molecular Cell Biology (1), 2000