Cell Signaling Introduction PDF

Cell Signaling Introduction: Signaling Basics and Receptors BMS 531.12 SECTION 2 LECTURE  Objectives This lecture builds upon topics covered in previous courses. Much of the content is expected to be review though new applications of the material will be completed. Signaling in biochemistry is...

Cell Signaling Introduction: Signaling Basics and Receptors BMS 531.12 SECTION 2 LECTURE  Objectives This lecture builds upon topics covered in previous courses. Much of the content is expected to be review though new applications of the material will be completed. Signaling in biochemistry is about the biochemical activity and how changes in structure, binding, or regulation alter function. 1. Summarize the basics of cellular signaling and the difference between direct enzymatic activity and mediated enzymatic activity for receptors 2. Compare and contrast autocrine, juxtacrine, paracrine, and endocrine signaling 3. Compare and contrast protein-binding ligand models 4. Compare and contrast types of ligands with emphasis on the actions of lipid and water soluble hormones 5. Classify receptors based on type and identify corresponding catalytic activity and/or regulatory molecules involved with emphasis on G-coupled protein receptors, receptor tyrosine kinases, insulin receptors, and integrins 6. Summarize the steps of G-coupled protein receptor activation through reset 7. Assess the consequences for changes in the initiation, propagation, or termination/reset of a given pathway from the perspective of ligands, receptors, mediators, or transcription factors ◦ List the 3 major components to all signaling pathways and explain how alterations to each can lead to adverse consequences  MBG Callback Signaling Pathway Basics Post-translational modifications of proteins are critical to the function and activity of signaling pathways Termination Initiation Propagation and Reset Each step in a pathway can serve as a point for regulation of the pathway ◦ Enzymes represent a key means of controlling the rate and progression of the reactions 3  MBG Callback Signaling Basics Conversation in 2 parts ◦ Signal must be sent ◦ Signal must be received Structural, physical, and physiological consequences exist for both ◦ Failing to generate or send a signal ◦ Failing to receive/respond to a signal  MBG Callback Major Components to ALL Pathways… Receive Signal ◦ Could be from environment or produced internally then “received” ◦ Receptors Propagate Signal ◦ Mediators that trigger a stepwise reaction ◦ Can involve amplification of the signal Generate Cellular Response ◦ Activate cellular activities in response to the signal ◦ Activation of transcription factors that turn on genes in response to the signal 5 MBG Callback Signaling Basics Types: Endocrine ◦ Hormones produced away from site of action ◦ Signal must travel to responsive cells Paracrine ◦ Localized signaling to neighboring cells Juxtacrine ◦ Signaling the requires direct contact with the target cell Autocrine ◦ Generated by target cell (self-signaling) Signaling Basics: Normal Signaling Signal specificity is conferred by the receptor ◦ Differential expression ◦ Recognize only certain ligands ◦ Location is key ◦ Intracellular for molecules that readily enter cells vs. surface for molecules incapable of entering cells  Signaling Basics: Normal Signaling No Ligand = No Activity OR OFF OFF ON OFF ON ON ON OFF OFF OFF ON ON OFF OFF ON ON EX: Enzymatic EX: Direct Action of Mediator Enzymatic Action Ligands and Ligand-binding Ligands = Molecules that bind and form complexes with other molecules Basic protein-binding ligand models: ◦ Lock and Key ◦ Involves rigid binding interfaces (perfect match) ◦ Entropy-dominated process ◦ Induced Fit ◦ Assumes flexibility in binding site with the interaction inducing conformational changes ◦ Enthalpy-dominated process ◦ Conformational selection ◦ Takes into account the inherent dynamics of protein conformations ◦ Selective binding to the most suitable conformations ◦ Sequential entropy-enthalpy process All 3 models have been supported experimentally thus all 2 likely exist either simultaneously or sequentially for ligand-protein interactions Types of Ligands A wide range of small molecules fit the classification of ligand particularly situationally ◦ i.e. Heme prosthetic group acts as a ligand in cytochrome c553 Ligands can be ◦ Other proteins ◦ Hydrophobic molecules including steroids like cortisol ◦ Water soluble Hormones Each ligand has its own behavior and capabilities linked to the signaling that it will induce ◦ Intracellular – will likely readily pass through the membrane to trigger cytoplasmic receptors ◦ Extracellular – hydrophilic and likely to remain outside cell triggering surface receptors Lipid versus Water Soluble Hormones LIPID SOLUBLE WATER SOLUBLE Require a transport vehicle through blood Travel freely in blood Transporter into cell may be needed; serves as Typically do not enter cell and thus must be a false receptor recognized by cell using surface markers True receptor is intracellular and often Cell-surface receptor initiates second chromosomally associated messenger cascade once bound by hormone  MBG Callback Cell-Surface Receptors and Signaling Receptor can induce other molecules ◦ Activates Enzyme (i.e. adenylyl cyclase) ◦ Activates Channel (i.e. G-protein and epinephrine) ◦ Activates signaling cascade Receptor functions as an ion channel ◦ Acetylcholine Receptor is an enzyme ◦ Insulin Receptor is a signaling molecule ◦ EGFR 12 Receptor class Transmembrane-spanning Intrinsic Accessory Examples of receptor classes/ligands domains catalytic coupling/regulatory activity molecules G-protein–coupled Multipass (seven None G-proteins Glucagon, α-Adrenergic, β-adrenergic receptors (serpentine transmembrane α-helices) (epinephrine), Muscarinic (acetylcholine), receptors) rhodopsin (vision), Chemokines (IL-8) Ion-channel receptors Multipass; generally form Ion-channel None Neurotransmitters, Ions, Nucleotides, (ligand-gated channels) multimeric complexes activity Inositol trisphosphate (IP 3 ) Intrinsic tyrosine kinase Single-pass transmembrane Tyrosine kinase None Insulin receptors domain but may be Peptide growth factors (e.g., PDGF, FGF, multimeric (e.g., insulin NGF, EGF) receptor) Tyrosine kinase– Single-pass transmembrane None Some require ITAM/ITIM- Antigen receptors (ITAM-Src-related associated receptors domain but generally form containing proteins kinases) multimeric receptors FcγR (ITIM–Src-related kinases) Leptin, IL-6 (Janus kinases) Intrinsic tyrosine Single-pass transmembrane Tyrosine None CD45-phosphatase receptor phosphatase receptors domain phosphatase Intrinsic Single-pass transmembrane Serine/threonine None Transforming growth factor-β (TGF-β) serine/threonine kinase domain kinase receptors Intrinsic guanylate Single-pass transmembrane Guanylyl cyclase None Atrial natriuretic protein (ANP) cyclase receptors domain (generates cGMP) Death-domain Single-pass transmembrane None Death-domain accessory Tumor necrosis factor-α (TNF-α) receptors domain proteins (TRADD, FADD, RIP, Fas TRAFs)  MPP 2. G protein- coupled receptors (GPCR) Callback Largest (+1000) and most diverse form of membrane receptors Wide range of ligands target GPCR Effector Protein pathways ◦ Hormones ◦ Neurotransmitters ◦ Odors ◦ Pheromones Two main signal transduction pathways involving GPCR 1. cAMP 2. Phosphatidylinositol (IP3) LO1,2  G-protein Coupled Receptors Largest known family of receptor proteins Named for GTP/GDP binding site on alpha subunit Triggering receptors represents initiation steps for signaling G-protein Coupled Signaling Hydrolysis of GTP is a relatively slow process As long as the alpha subunit is bound to GTP it is active and can activate adenylate cyclase  Return of Inactive GDP Ligand bound Binding complex to receptor GTP displacement of GDP GTP (activation) hydrolysis to GDP G-protein Dissociation Activation of from effectors/mediators receptor  Partial Tyrosine Kinase Receptors/Receptor Tyrosine MBG Kinases Callback Includes critical growth stimulatory receptors such as Growth Factor Receptors Mechanism of activity is phosphorylation Ligand binding induces dimerization AUTOPHOSPHORYLATION ◦ Tyrosine residues within the receptors within or near the tyrosine kinase domains Binding of signaling mediators to the phosphotyrosines via SH2 domains within the mediator Tian et al 2020 18 Insulin Signaling Insulin receptor is a tyrosine kinase Like most receptors of this type, multiple mediators can be triggered based on specific phosphorylation patterns Insulin signaling can be growth stimulatory (mitogenic) in nature via Ras signaling Phosphatidylinositol3-kinase (PI3K) signaling leads to downstream activation of serine/threonine kinase activity via activation of AKT AKT mediates metabolic effects of insulin in muscle, liver, and adipose  MBG Callback Extracellular Matrix Signaling Communication also occurs between cells and the ECM Multiple means of signaling between ECM and cells exists Critical component of both morphogenesis and tissue repair Clause and Barker 2013 Integrins Signaling through integrins enables the ECM to influence multiple aspects of cellular behavior Downstream effects include cellular changes in major processes such as migration, proliferation, and differentiation Signaling can be self-promoting as in changing gene expression for more integrins to increase number of receptors Signaling mediation overlaps with other growth stimulatory signaling Vital role in wound healing