Signal Transduction Lecture Notes PDF

BASIC PRINCIPLES OF MEDICINE 1: FOUNDATIONS TO MEDICINE LECTURE 20 Signal Transduction Dr. Robert Finn ([email protected]) Acknowledgements: Sharmila Upadhya, MBBS, MD, Shellon Thomas, MD Andrew Sobering, PhD Copyright All year 1 courses materials, whether in print or online, are protected by copyri...

BASIC PRINCIPLES OF MEDICINE 1: FOUNDATIONS TO MEDICINE LECTURE 20 Signal Transduction Dr. Robert Finn ([email protected]) Acknowledgements: Sharmila Upadhya, MBBS, MD, Shellon Thomas, MD Andrew Sobering, PhD Copyright All year 1 courses materials, whether in print or online, are protected by copyright. The work, or parts of it, may not be copied, distributed or published in any form, printed, electronic or otherwise. As an exception, students enrolled in year 1 of St. George’s University School of Medicine and their faculty are permitted to make electronic or print copies of all downloadable files for personal and classroom use only, provided that no alterations to the documents are made and that the copyright statement is maintained in all copies. View only files, such as lecture recordings, are explicitly excluded from download and creating copies of these recordings by students and other users are strictly illegal. The author of this document has made the best effort to observe current copyright law and the copyright policy of St George's University. Users of this document identifying potential violations of these regulations are asked to bring their concern to the attention of the author. Recommended Reading • Lippincott's Illustrated Reviews: Cell and Molecular Biology, 2e: Chapters 17, 18, 19. https://meded-lwwhealthlibrarycom.sgu.idm.oclc.org/content.aspx?sectionid=181789294&bookid=2335 • Lippincott Illustrated Reviews: Biochemistry, 8: Chapter 8 (Introduction to Metabolism and Glycolysis) - Metabolism Regulation: Introduction to Metabolism and Glycolysis | Lippincott® Illustrated Reviews: Biochemistry, 8e | Medical Education | Health Library (lwwhealthlibrary.com) • Practice Questions: 8.6 • Reference: Marks’ Basic Medical Biochemistry: A Clinical Approach, 5e: Chapter 11. https://meded-lwwhealthlibrarycom.sgu.idm.oclc.org/content.aspx?sectionid=249263758&bookid=2170 Signal Transduction SOM.MK.I.BPM1.1.FTM.3.BCHM.0120 SOM.MK.I.BPM1.1.FTM.3.BCHM.0121 SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 SOM.MK.I.BPM1.1.FTM.3.BCHM.0124 SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 SOM.MK.I.BPM1.1.FTM.3.BCHM.0126 Describe different types of cell signalling: endocrine, autocrine, paracrine, neuronal & contact-dependent. Indicate four different classes of receptors (steroid receptors, ion-channel receptor, receptor enzyme, receptors that form second messengers including G-protein-coupled receptors) with specific examples for each class. Discuss events involved in signal transduction Identify the location of the receptors for steroid hormones. Describe intracellular signal transduction by steroid hormones. Describe the molecular changes when insulin binds to its receptor. Describe the different target (effector) enzymes of G proteins. Describe the two major second messenger systems (adenylate cyclase and phosphoinositide systems) associated with G-proteins and signal termination. Cell-Cell Signaling and Communication • Key role in cellular processes such as proliferation, growth, differentiation, cellular maintenance and results in a variety of cellular responses • Regulation of – Gene expression – Metabolism – Cell shape and cellular migration – Neuronal signaling • Mis-regulation of signal transduction pathways • Cellular transformation (carcinogenesis) • Endocrine disorders like diabetes mellitus, thyroid disorders…. SOM.MK.I.BPM1.1.FTM.3.BCHM.012 Regulation of Metabolism Metabolic pathways coordinated to produce energy or synthesize products to meet needs of cell and organism Efficient communication system necessary to coordinate various functions Regulation depends on: • Intercellular signals • Intracellular signals SOM.MK.I.BPM1.1.FTM.3.BCHM.012 Chemical (Intercellular) messengers SOM.MK.I.BPM1.1.FTM.3.BCHM.012 Compare: Intracellular vs cell-surface (plasma membrane) receptors • Plasma membrane receptors have extracellular binding domains for ligand binding • Intracellular receptors bind lipophilic/hydrophobic (steroid hormones or other messengers) that diffuse through plasma membrane • Intracellular receptors present in: • Cytoplasm and translocate to the nucleus on binding to hormone, or • Nucleus and Hormone-receptor complex binds to DNA SOM.MK.I.BPM1.1.FTM.3.BCHM.012 Intracellular vs cell-surface (plasma membrane) receptors Cell surface receptors Intracellular receptors • Hormone hydrophilic • Extracellular domain for binding hormone/ signal • Intracellular domain for signal transduction • Many produce second messengers within cells • Rapid response; slower response effect on gene • Examples: Peptide hormones – Insulin, glucagon, epinephrine; Acetylcholine; GABA; Eicosanoids • Lipophilic/ hydrophobic signals diffuse through plasma membrane • Located in nucleus or cytosol • Conformational change on binding hormone • H-R complex enter nucleus • Bind to specific regions of DNA • Influence transcription and translation (gene expression) • Function like transcription factors • Response is slower • Steroid hormones, thyroxine, retinoic acid(Vitamin A) and vitamin D SOM.MK.I.BPM1.1.FTM.3.BCHM.012 Intercellular signals are converted to an intracellular signal in the adjacent cell Many extracellular signals (hormones) exert their effects by producing intracellular second messengers Intracellular signals cAMP Enzyme-P SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Endocrine Types of intercellular signals Paracrine • Some growth factors • Eicosanoids Autocrine Hormones: • Insulin • Glucagon • Epinephrine • Steroid hormones • Peptide hormones Marks’ Basic Medical Biochemistry: A Clinical Approach, 5e, 2018 • • • • Neurotransmitters Some Growth factors Eicosanoids Nitric oxide (gas) SOM.MK.I.BPM1.1.FTM.3.BCHM.0120 Synaptic cleft Other types of signaling Axon Neuronal Signaling Contact Signaling SOM.MK.I.BPM1.1.FTM.3.BCHM.0120 SOM.MK.I.BPM1.1.FTM.3.BCHM.0120 Features of intracellular signal-transduction (receptor-mediated) systems Each hormone has specific receptors A hormone may have more than one type of receptor: Epinephrine and Norepinephrine have alpha1, alpha2 and beta receptors (different tissues) Acetylcholine has nicotinic and muscarinic receptors SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Features of intracellular signal-transduction (receptor-mediated) systems Rapid biological response SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Features of intracellular signal-transduction (receptor-mediated) systems SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Features of intracellular signal-transduction (receptor-mediated) systems “Outcome” is additive SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Features of intracellular signal-transduction (receptormediated) systems A. Specificity • Specific signals (i.e. hormone) activate a specific receptor B. Amplification of signal • One hormone molecule outside the cell can result in many thousands of activated molecules inside the cell C. Desensitization/Adaptation • Must have a way to turn off the stuff that was activated, or to reduce responses to excessive signals D. Integration • Many pathways feed into each other, output depends on network of all pathways SOM.MK.I.BPM1.1.FTM.3.BCHM.0122 Receptor-mediated Signal Transduction (Extracellular signals producing intracellular signals) 4 basic types of signal transduction pathways mediated by 4 different types of receptors: 1. Intracellular receptor (steroid receptor) 2. Gated-ion channel (neurotransmitters) Imp 3. Receptor enzyme (Catalytic receptor) 4. Receptors that form intracellular second messengers SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 GPCR 2 4 3 Four general types of signal transducers SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 1 4 basic types of signal transduction pathways mediated by 4 different types of receptors: 1. Intracellular (steroid) receptor 2. Gated-ion channel 3. Receptor enzyme (Catalytic receptor) 4. Receptors that form intracellular second messengers SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 1. Steroid and thyroid receptor family (Intracellular) Lipophilic hormones cross cell membrane to bind specific intracellular receptors Examples include: • Testosterone, estrogen, cortisol, aldosterone (steroid hormones) • Vitamin D and retinoic acid (Vitamin A) • Thyroid hormone (thyroid receptors) Hydrophobic/ lipophilic hormones induce (up-regulate) or repress (down-regulate) gene expression at level of transcription SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Steroid-thyroid receptor family Bind intracellular receptors Change in expression of target genes Increased production of protein (Induction) or Repression SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Steroid receptor signal transduction • Hormone diffuses into cell (lipophilic/ hydrophobic) • Binds specific receptor (cytosol or nucleus) • Forms hormone-receptor complex; Conformational change in receptor • H-R complex enters nucleus • H-R complex binds specific regions of DNA (Hormone Response Elements; HRE) • H-R complex binds enhancer regions, activates promoter, increases transcription (INDUCTION of gene expression) and translation to form protein → Cellular response • If H-R complex binds repressor regions → decreased transcription (REPRESSION of gene expression) SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Steroid receptor signal transduction • Binding of Hormone-Receptor complex to HRE regulates expression of adjacent genes • Increase or decrease rates of mRNA synthesis (Transcription) • Cause INDUCTION or REPRESSION of gene expression • Works through modulating gene expression • Hormone-Receptor complex works like a transcription factor • Comparatively slow: response may take hours to days to be effective SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Steroid receptor signal transduction Works through gene expression Comparatively slow; Response may take hours or days SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 4 types of signal transduction pathways mediated by 4 different types of receptors: 1. Intracellular (steroid) receptor 2. Gated-ion channel 3. Receptor enzyme (Catalytic receptor) 4. Receptors that form intracellular second messengers SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Fors 2. Gated ion channel: Ligand or Voltage-gated ion channel Manstrate • Binding of neurotransmitter causes channel to open • Results in influx of ions through ion channel • Alters membrane potential → Promotes or inhibits nerve impulse transmission • Ligand gated • Some Examples: • Nicotinic ACh receptors in parasympathetic ganglia and Neuromuscular junction (muscle) • Glutamate receptors (Ionotropic) in CNS • GABA-A (-aminobutyric acid) receptors in CNS • Glycine receptors in CNS SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 2. Gated ion channel • Parasympathetic ganglia (Autonomic nervous system) • Neuromuscular junction (muscle) Nicotinic Acetyl Choline receptors SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 2. Gated ion channel Nicotinic ACh receptors Conformational change on binding to Acetyl Choline SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 Termination of Acetylcholine signal Enters synaptic cleft or neuromuscular junction Signal is given! Cleaved by Acetylcholine esterase (an enzyme) Acetate and choline may be recycled SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 + 2. Voltage Gated ion channels respond to change in voltage Nicotinic Acetyl Choline receptors SOM.MK.I.BPM1.1.FTM.3.BCHM.0123 4 types of signal transduction pathways mediated by 4 different types of receptors: 1. Steroid receptor 2. Gated-ion channel 3. Receptor enzyme (Catalytic receptor) 4. Receptors that form intracellular second messengers SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ 3. Receptor enzyme (Catalytic receptor) Insulin Receptor Tyrosine Kinase as an example SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ 3. Receptor enzyme (Catalytic receptor) • Transmembrane catalytic receptors have intrinsic enzymatic activity • Enzyme is tyrosine-specific protein kinase (adds P to Tyrosine) • Insulin receptor • Extracellular domain for binding insulin and • Intracellular domain with tyrosine kinase activity • Binding of ligand (Insulin) → ATP cleavage and autophosphorylation of tyrosine residues Insulin receptor tyrosine kinase (IR) → and then phosphorylation of specific tyrosine side chains in target proteins SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ Extracellular 1 Insulin binds 2 Insulin receptor activated IR phosphorylated/ activated 3 = insulin P P P P P P ADP = tyrosine kinase domain (inactive) IR phosphorylated P Cytoplasm ATP 4 P ATP P ADP = IR active as a tyrosine kinase Activation of tyrosine kinase domains of IR by insulin binding, followed by autophosphorylation SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ Insulin Receptor: Intracellular effects • Intracellular effectors: • Insulin receptor substrates: IRS 1-4 • Enzyme effectors: Activation of PI3-Kinase • Multiple signaling pathways • Cellular responses: • Increased glucose uptake • Regulation of transcription • Activation of enzymes and regulation of metabolism • Covalent modification • Upregulation (increased synthesis of enzymes) SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ Insulin stimulated glucose transport (GLUT-4) in adipose or muscle cells 5. Insulin dissociates from receptor; Inactivation Glucose transporter (GLUT-4) 6. Vesicle containing GLUT4 translocated back to Golgi 4. Glucose transport allowed in response to insulin Glucose Golgi 2. GLUT4 translocation from Golgi to plasma membrane (signal) 3. Vesicle containing GLUT4 binds and fuses to plasma membrane SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ P- -P 1. Insulin binds to its Receptor Insulin Receptor: Intracellular effects Type 2 Diabetes mellitus SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ Pay attention to the outcome of insulin signaling GLUT4 for glucose uptake Oh my gosh, that is a lot of detail Transcription SOM.MK.I.BPM1.1.FTM.3.BCHM.0124​ Glycolysis Protein synthesis 4 types of signal transduction pathways mediated by 4 different types of receptors: 1. Steroid receptor 2. Gated-ion channel 3. Receptor enzyme (Catalytic receptor) 4. Receptors that form intracellular second messengers • G-protein coupled receptor (GPCR) • Guanylate cyclase SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 4. Receptors that form second messengers • Receptors pass signal (message) from outside cell by producing second messenger inside the cell • Types of receptors • G-protein coupled receptors • Guanylate cyclase (cGMP) • Rapid and immediate effects • Phosphorylation of enzymes (activation or inactivation of key regulated enzymes) • Changes in ion levels (calcium) • Slower effects on gene expression SOM.MK.I.BPM1.1.FTM.3.BCHM.0126 Covalent modification of enzymes Gene Induction/ Repression 4. G-protein coupled receptors and intracellular second messenger • Hormone (first messenger) changes concentration of some other molecule (second messenger) inside the cell • Generally small, non-protein molecules • Produced intracellularly when hormone binds to its receptor • Initiate cascade of intracellular events (enzyme activation/inhibition, altered gene regulation) resulting in specific cellular responses • Examples: • Adenylate cyclase system produces cAMP • Calcium - Phosphatidylinositol system produces inositol triphosphate (IP3), diacyl glycerol (DAG), Ca2+ SOM.MK.I.BPM1.1.FTM.3.BCHM.0126 4. Heptahelical receptors, G-protein coupled receptors (GPCR’s) and second messengers 1 2 3 4 5 6 7 GTP-binding protein SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 4. Heptahelical receptors (GPCR’s) and second messengers • Hormone (or cytokine or neurotransmitter) is first messenger • Binds plasma membrane heptahelical receptors • Hormone–receptor complex activates G-protein that activates membranebound enzyme (effector enzyme) • Activation of different GPCRs lead to generation of different intracellular second messengers, such as cAMP or DAG/IP3. GPCR SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 [ ] [ ] Heterotrimeric G proteins • Binding of hormone to receptor activates G protein • The G alpha-subunit dissociates from GFP; binds GTP (G-GTP) • G-GTP activates enzymes to produce intracellular second messengers • G subunit has intrinsic GTPase activity (intrinsic timer) – termination of signal dime Finite SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 4. Heptahelical receptors (GPCR’s) and second messengers: Types of G • Alpha1 adrenergic receptor: Gq • Activates phospholipase C (enzyme) • Increases IP3, DAG and Ca2+ (second messengers) • Alpha2 adrenergic receptor (inhibitory): Gi • Inhibits adenylate cyclase • Decreases cAMP levels • Beta-adrenergic receptor; Glucagon (stimulatory): Gs • Activates adenylate cyclase • Increases cAMP levels SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 Adrenergic receptors generate different second messengers -1 adrenergic receptor Epinephrine or Norepinephrine -adrenergic receptor -2 adrenergic receptor Gq Gi Gs Phospholipase C Adenylate cyclase Phosphatidylinositol bisphosphate (PIP2) IP3 Ca2+ Adenylate cyclase DAG ATP ATP cAMP SOM.MK.I.BPM1.1.FTM.3.BCHM.0125 cAMP