Copyright (c) by W. H. Freeman and Company 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  (1) synthesis of the signaling molecule by the signaling cell  (2) release of the signaling molecule by the signaling cell  (3) transport of the signal to the target cell  (4) detection of the signal by a specific receptor protein  (5) a change in cellular metabolism, function, or development triggered by the receptor-signal complex  (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 Figure 20-1 Receptor proteins exhibit ligand-binding and effector specificity

Copyright (c) by W. H. Freeman and Company 20.1 Hormones can be classed based on their solubility and receptor location Water soluble Lipophilic (prostaglandins) Lipophilic Steroids (cortisol,progesterone,estradiol,testosterone) Thyroxine retinoic acid

Copyright (c) by W. H. Freeman and Company 20.1 Cell-surface receptors belong to four major classes Figure 20-3a,b

Copyright (c) by W. H. Freeman and Company 20.1 Cell-surface receptors belong to four major classes Figure 20-3c,d

Copyright (c) by W. H. Freeman and Company 20.1 The effects of many hormones are mediated by second messengers Figure 20-4 Inositol phospholipids (phosphoinositides) Ca 2+

Copyright (c) by W. H. Freeman and Company 20.1 Other conserved proteins function in signal transduction: GTPase switch proteins Figure 20-5a

Copyright (c) by W. H. Freeman and Company 20.1 Other conserved proteins function in signal transduction: protein kinases Figure 20-5b Protein Kinases tyrosine serine/threonine

Copyright (c) by W. H. Freeman and Company 20.1 Other conserved proteins function in signal transduction: adapter proteins Figure 20-5c

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  Many different mammalian cell-surface receptors are coupled to a trimeric signal-transducing G protein  Ligand binding activates the receptor, which activates the G protein, which activates an effector enzyme to generate an intracellular second messenger  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  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 Figure 20-10

Copyright (c) by W. H. Freeman and Company 20.3 Example: G-Protein coupled  -adrenergic recept. mediate the induction of cAMP synthesis Figure 20-12

Copyright (c) by W. H. Freeman and Company 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 Figure 20-13

Copyright (c) by W. H. Freeman and Company 20.3 The structure of adenylyl cyclase Figure 20-15

Copyright (c) by W. H. Freeman and Company 20.3 Trimeric G s protein links  -adrenergic receptors and adenylyl cyclase animação

Copyright (c) by W. H. Freeman and Company 20.3 Some bacterial toxins irreversibly modify G proteins Figure 20-17

Copyright (c) by W. H. Freeman and Company 20.3 Adenylyl cyclase is stimulated and inhibited by different receptor-ligand complexes Figure 20-18

Copyright (c) by W. H. Freeman and Company 20.3 GTP-induced changes in G s  favor its dissociation from G  and association with adenylyl cyclase Figure  -subunit  -subunit  -subunit Switch regions of  -subunit

Copyright (c) by W. H. Freeman and Company 20.3 The structure of G s  ·GTP complexed with two fragments from the adenylyl cyclase catalytic domain Figure 20-20

Copyright (c) by W. H. Freeman and Company 20.4 Receptor tyrosine kinases and Ras  Receptor tyrosine kinases recognize soluble or membrane bound peptide/protein hormones that act as growth factors  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  RTK pathways are involved in regulation of cell proliferation and differentiation, promotion of cell survival, and modulation of cellular metabolism  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 Figure 20-21

Copyright (c) by W. H. Freeman and Company 20.4 Ras cycles between active and inactive forms Figure GEF=guanine nucleotide exchange factor GAP=GTPase activating protein

Copyright (c) by W. H. Freeman and Company 20.4 An adapter protein and GEF link most activated RTKs to Ras Figure 20-23

Copyright (c) by W. H. Freeman and Company 20.4 Analysis of eye development in Drosophila has provided insight into RTK signaling pathways Figure Wild-typesevenless mutant

Copyright (c) by W. H. Freeman and Company 20.4 Genetic analysis of induction of R7 photoreceptor in the Drosophila eye Figure 20-25

Copyright (c) by W. H. Freeman and Company 20.4 Models of SH2 and SH3 domains bound to short target peptides (SH2/SH3=Src homology domain 2/3) a) SH2 domain in GRB2 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 SH3 domains in GRB2 (SH3 domains have similar 3D, but different a.a. sequences) P-Tyr pocket hydrophobic pocket Non pro residues determine specificity

Copyright (c) by W. H. Freeman and Company 20.4 Structures of Ras·GDP-Sos complex and Ras·GTP Figure 20-27

Copyright (c) by W. H. Freeman and Company 20.5 MAP kinase pathways  Activated Ras induces a kinase signal cascade that culminates in activation of MAP kinase  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 Figure 20-28

Copyright (c) by W. H. Freeman and Company 20.5 Phosphorylation of a tyrosine and a threonine activates MAP kinase Figure Liga ATP Dimeriza Activada 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 20.5 Multiple MAP kinase pathways are found in eukaryotic cells Figure 20-32

Copyright (c) by W. H. Freeman and Company 20.6 Second messengers  Hormone stimulation of G s protein-coupled receptors leads to activation of adenylyl cyclase and synthesis of the second messenger cAMP  cAMP does not function in signal pathways initiated by RTKs, but other second messengers may be initiated by both GPCRs and RTKs  cAMP and other second messengers activate specific protein kinases  cAMP specifically activates cAMP-dependent protein kinases (cAPKs)

Copyright (c) by W. H. Freeman and Company 20.6 Kinase cascades permit multienzyme regulation and amplify hormone signals Figure 20-37

Copyright (c) by W. H. Freeman and Company 20.6 Cellular responses to cAMP 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 20-38a

Copyright (c) by W. H. Freeman and Company 20.6 Hormone-induced release of Ca 2+ from the ER is mediated by IP 3 Animação

Copyright (c) by W. H. Freeman and Company 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 Figure 20-41

Copyright (c) by W. H. Freeman and Company 20.6 cGMP mediates local signaling by NO Figure Guanilate cyclase

Copyright (c) by W. H. Freeman and Company 20.7 Interaction and regulation of signaling pathways  The effects of activation of GPCRs and RTKs is more complicated than a simple step-by-step cascade  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  The same cellular response may be induced by multiple signaling pathways  Interaction of different signaling pathways permits fine-tuning of cellular activities