Aula Terica N 7 Sinalizao inter e intracelular

Aula Teórica Nº 7 Sinalização inter e intra-celular Copyright (c) by W. H. Freeman and Company

20. 1 Cell-to-cell communication by extracellular signaling usually involves six steps z (1) synthesis of the signaling molecule by the signaling cell z (2) release of the signaling molecule by the signaling cell z (3) transport of the signal to the target cell z (4) detection of the signal by a specific receptor protein z (5) a change in cellular metabolism, function, or development triggered by the receptor-signal complex z (6) removal of the signal, which usually terminates the cellular response Copyright (c) by W. H. Freeman and Company

20. 1 Signaling molecules operate over various distances in animals Receptor proteins exhibit ligand-binding and effector specificity Copyright (c) by W. H. Freeman and Company Figure 20 -1

20. 1 Hormones can be classed based on their solubility and receptor location Lipophilic • Steroids (cortisol, progesterone, estradiol, testosterone) • Thyroxine • retinoic acid Copyright (c) by W. H. Freeman and Company Water soluble Lipophilic (prostaglandins)

20. 1 Cell-surface receptors belong to four major classes Figure 20 -3 a, b Copyright (c) by W. H. Freeman and Company

20. 1 Cell-surface receptors belong to four major classes Figure 20 -3 c, d Copyright (c) by W. H. Freeman and Company

20. 1 The effects of many hormones are mediated by second messengers • Inositol phospholipids (phosphoinositides) • Ca 2+ Figure 20 -4 Copyright (c) by W. H. Freeman and Company

20. 1 Other conserved proteins function in signal transduction: GTPase switch proteins Figure 20 -5 a Copyright (c) by W. H. Freeman and Company

20. 1 Other conserved proteins function in signal transduction: protein kinases • Protein Kinases • tyrosine • serine/threonine Figure 20 -5 b Copyright (c) by W. H. Freeman and Company

20. 1 Other conserved proteins function in signal transduction: adapter proteins Figure 20 -5 c Copyright (c) by W. H. Freeman and Company

20. 1 Common signaling pathways are initiated by different receptors in a class Figure 20 -6 Copyright (c) by W. H. Freeman and Company

20. 1 The synthesis, release, and degradation of hormones are regulated Copyright (c) by W. H. Freeman and Company

20. 3 G protein-coupled receptors and their effectors z Many different mammalian cell-surface receptors are coupled to a trimeric signal-transducing G protein z Ligand binding activates the receptor, which activates the G protein, which activates an effector enzyme to generate an intracellular second messenger z All G protein-coupled receptors (GPCRs) contain 7 membrane-spanning regions with their N-terminus on the exoplasmic face and C-terminus on the cytosolic face z GPCRs are involved in a range of signaling pathways, including light detection, odorant detection, and detection of certain hormones and neurotransmitters Copyright (c) by W. H. Freeman and Company

20. 3 G protein-coupled receptors Copyright (c) by W. H. Freeman and Company Figure 20 -10

20. 3 Example: G-Protein coupled -adrenergic recept. mediate the induction of c. AMP synthesis Copyright (c) by W. H. Freeman and Company Figure 20 -12

20. 3 Critical features of catecholamines and their receptors have been identified Agonists antagonists Copyright (c) by W. H. Freeman and Company

20. 3 Model of complex formed between isoproterenol and the 2 -adrenergic receptor Copyright (c) by W. H. Freeman and Company Figure 20 -13

20. 3 The structure of adenylyl cyclase Copyright (c) by W. H. Freeman and Company Figure 20 -15

20. 3 Trimeric Gs protein links -adrenergic receptors and adenylyl cyclase Copyright (c) by W. H. Freeman and Company animação

20. 3 Some bacterial toxins irreversibly modify G proteins Copyright (c) by W. H. Freeman and Company Figure 20 -17

20. 3 Adenylyl cyclase is stimulated and inhibited by different receptor-ligand complexes Copyright (c) by W. H. Freeman and Company Figure 20 -18

20. 3 GTP-induced changes in Gs favor its dissociation from G and association with adenylyl cyclase -subunit Switch regions of -subunit Copyright (c) by W. H. Freeman and Company Figure 20 -19

20. 3 The structure of Gs ·GTP complexed with two fragments from the adenylyl cyclase catalytic domain Copyright (c) by W. H. Freeman and Company Figure 20 -20

20. 4 Receptor tyrosine kinases and Ras z Receptor tyrosine kinases recognize soluble or membrane bound peptide/protein hormones that act as growth factors z Binding of the ligand stimulates the receptor’s tyrosine kinase activity, which subsequently stimulates a signal-transduction cascade leading to changes in cell physiology and/or patterns of gene expression z RTK pathways are involved in regulation of cell proliferation and differentiation, promotion of cell survival, and modulation of cellular metabolism z RTKs transmit a hormone signal to Ras, a GTPase switch protein that passes the signal on to downstream components Copyright (c) by W. H. Freeman and Company

20. 4 Ligand binding leads to autophosphorylation of RTKs Copyright (c) by W. H. Freeman and Company Figure 20 -21

20. 4 Ras cycles between active and inactive forms GEF=guanine nucleotide exchange factor GAP=GTPase activating protein Copyright (c) by W. H. Freeman and Company Figure 20 -22

20. 4 An adapter protein and GEF link most activated RTKs to Ras Copyright (c) by W. H. Freeman and Company Figure 20 -23

20. 4 Analysis of eye development in Drosophila has provided insight into RTK signaling pathways Wild-type Copyright (c) by W. H. Freeman and Company sevenless mutant Figure 20 -24

20. 4 Genetic analysis of induction of R 7 photoreceptor in the Drosophila eye Copyright (c) by W. H. Freeman and Company Figure 20 -25

20. 4 Models of SH 2 and SH 3 domains bound to short target peptides (SH 2/SH 3=Src homology domain 2/3) Non pro residues determine specificity P-Tyr pocket hydrophobic pocket a) SH 2 domain in GRB 2 adapter protein binds to a specific phosphotyrosine in an activated RTK. The sequence surrounding the P-tyr is protein specific b) Proline rich domains in Sos(a GEF), binds to 2 SH 3 domains in GRB 2 (SH 3 domains have similar 3 D, but different a. a. sequences) Copyright (c) by W. H. Freeman and Company

20. 4 Structures of Ras·GDP-Sos complex and Ras·GTP Copyright (c) by W. H. Freeman and Company Figure 20 -27

20. 5 MAP kinase pathways z Activated Ras induces a kinase signal cascade that culminates in activation of MAP kinase z MAP kinase is a serine/threonine kinase that can translocate into the nucleus and phosphorylate many different proteins, including transcription factors that regulate gene expression Copyright (c) by W. H. Freeman and Company

20. 5 Signals pass from activated Ras to a cascade of protein kinases Copyright (c) by W. H. Freeman and Company Figure 20 -28

20. 5 Phosphorylation of a tyrosine and a threonine activates MAP kinase Ligação de MEK Induz alteração da conformação do Lip Expondo a Tyr Fosforilação da tyr E posteriormente da treonina Copyright (c) by W. H. Freeman and Company Liga ATP Dimeriza Activada Figure 20 -30

20. 5 Multiple MAP kinase pathways are found in eukaryotic cells Copyright (c) by W. H. Freeman and Company Figure 20 -32

20. 6 Second messengers z Hormone stimulation of Gs protein-coupled receptors leads to activation of adenylyl cyclase and synthesis of the second messenger c. AMP z c. AMP does not function in signal pathways initiated by RTKs, but other second messengers may be initiated by both GPCRs and RTKs z c. AMP and other second messengers activate specific protein kinases z c. AMP specifically activates c. AMP-dependent protein kinases (c. APKs) Copyright (c) by W. H. Freeman and Company

20. 6 Kinase cascades permit multienzyme regulation and amplify hormone signals Copyright (c) by W. H. Freeman and Company Figure 20 -37

20. 6 Cellular responses to c. AMP vary among different cell types Copyright (c) by W. H. Freeman and Company

20. 6 Modification of a common phospholipid precursor generates several second messengers: synthesis of DAG and IP 3 Figure 20 -38 a Copyright (c) by W. H. Freeman and Company

20. 6 Hormone-induced release of Ca 2+ from the ER is mediated by IP 3 Copyright (c) by W. H. Freeman and Company Animação

20. 6 IP 3 -induced Ca 2+ increases are used to trigger various responses in different cells Copyright (c) by W. H. Freeman and Company

20. 6 Ca 2+-calmodulin complex mediates many cellular responses Copyright (c) by W. H. Freeman and Company Figure 20 -41

20. 6 c. GMP mediates local signaling by NO Guanilate cyclase Copyright (c) by W. H. Freeman and Company Figure 20 -42

20. 7 Interaction and regulation of signaling pathways z The effects of activation of GPCRs and RTKs is more complicated than a simple step-by-step cascade z Stimulation of either GPCRs or RTKs often leads to production of multiple second messengers, and both types of receptors promote or inhibit production of many of the same second messengers z The same cellular response may be induced by multiple signaling pathways z Interaction of different signaling pathways permits fine-tuning of cellular activities Copyright (c) by W. H. Freeman and Company