Cell Signaling PDF

Cell Signaling  Contact Karron J. James, Ph.D. Professor, Dept. Biochemistry, Cell Biology & Genetics Office: GB6, Block B Email: [email protected] Phone 484-8900 ext 1041 Office hours (in-person or on MS Teams ): Mon- Fri, by appointment – Teams message @kjames@au...

Cell Signaling  Contact Karron J. James, Ph.D. Professor, Dept. Biochemistry, Cell Biology & Genetics Office: GB6, Block B Email: [email protected] Phone 484-8900 ext 1041 Office hours (in-person or on MS Teams ): Mon- Fri, by appointment – Teams message @[email protected]  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  Readings Alberts et al., Molecular Biology of the Cell, 4ed. Ch 15: Extracellular Signal Molecules Bind to Specific Receptors Extracellular Signal Molecules Can Act Over Either Short or Long Distances (1st, 2nd, 3rd, 4th paragraphs) Autocrine Signalling Can Coordinate Decisions by Groups of Identical Cells (1st paragraph) Different Cells Can Respond Differently to the Same Extracellular Signal Molecule Nuclear Receptors Are Ligand-activated Gene Regulatory Proteins The Three Largest Classes of Cell-Surface Receptor Proteins Are Ion-Channel-linked, G-Protein-linked, and Enzyme-linked Receptors Most Activated Cell-Surface Receptors Relay Signals Via Small Molecules and a Network of Intracellular Signalling Proteins (1st, 2nd, 3rd paragraphs) Cells Can Respond Abruptly to a Gradually Increasing Concentration of an Extracellular Signal (Figure 15-24) Cells Can Adjust Their Sensitivity to a Signal Trimeric G Proteins Disassemble to Relay Signals from G-Protein-linked Receptors (1st, 2nd paragraphs) Some G Proteins Signal By Regulating the Production of Cyclic AMP (1st, 2nd paragraphs) Cyclic-AMP-dependent Protein Kinase (PKA) Mediates Most of the Effects of Cyclic AMP (1st, 2nd paragraphs) Some G Proteins Activate the Inositol Phospholipid Signalling Pathway by Activating Phospholipase C-β Ca2+ Functions as a Ubiquitous Intracellular Messenger (1st paragraph) Phosphorylated Tyrosines Serve as Docking Sites For Proteins With SH2 Domains (1st, 2nd paragraphs) PI 3-Kinase Produces Inositol Phospholipid Docking Sites in the Plasma Membrane (1st, 2nd paragraphs) Signal Proteins of the TGF-β Superfamily Act Through Receptor Serine/Threonine Kinases and Smads (1st, 2nd paragraphs)  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  Signaling and basic requirements for signal transduction Transduction of message(s) from one cell to another cell resulting in altered behaviour of target cell Lodish, et al. ‘Molecular Cell Biology’. 6ed. Basic requirements: – Signaling cell – Extracellular ligand (signaling molecule) – Target (responding) cell – Receptor (plasma membrane or intracellular) Signal transduction Fig 15-1. Alberts.  Types of Signaling Signaling by secreted molecules 1. Endocrine: signaling molecules travel through bloodstream and interact with distant target cells 2. Paracrine: signaling molecules act on nearby cells i. Juxtacrine (contact-dependent): signaling molecules stay attached to synthesizing cell while interacting with target cell ii. Synaptic: action potentials used to transmit signals mediated by neurotransmitters 3. Autocrine: synthesizing cell is also target cell Fig 15-4. Alberts. All signaling molecules only active on target cells that express an appropriate receptor  See Figure legend in textbook Fig 15-8. Alberts.  Individual signaling molecule can have different effects on different target cells Fig 15-9. Alberts.  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  Hormones “Chemical messengers” Hormones released mainly from specialized cells in gonads, thyroid, pituitary, pancreas,… Regulate physiologic processes, eg. reproduction, growth, metabolism Classified as lipophilic or hydrophilic  Nomenclature—FYI Lipophilic hormones – These are generally alcohols or ketones so many of their names end in –ol (eg. cortisol) or –one (eg. progesterone) Hydrophilic hormones—include amino acid and peptide hormones – Many of their names end in –ine or –in, eg. insulin – Note that there are exceptions: thyroxine (a thyroid hormone), is lipophilic Note: this is just for your information and is not covered by a learning objective here.  Lipophilic Hormones or Signaling Molecules Include: 1. Steroid hormones es_hormones_homeostasis/index.htm http://www.tokresource.org/tok_classes/biobiobio/biomenu/nerv 2. Thyroid hormones 3. Retinoic acid Small, cross plasma membrane, and interact with receptor inside cell Can alter gene expression  1. Steroid hormones Derived from cholesterol Synthesized and quickly released → bloodstream, bound by carrier proteins → hormone, only, taken up by target cell Eg. Adrenal hormones (eg. cortisol), sex hormones (testosterone, estradiol, progesterone) What type of carrier protein? Vitamin D3—synthesized in skin  2. Thyroid hormones daltonsurgical.com Precursor = Thyroglobulin (Tg) large glycoprotein Thyroid hormones (T3, T4) made by and secreted from thyroid gland Bound by carrier proteins for transport through circulation  3. Retinoic acid Retinoic acid—synthesized from retinol, not cholesterol Retinol transported into cytosol and is converted to retinoic acid – Tc factor, important for embryonic development  Lipophilic hormones bind nuclear receptor superfamily Located primarily in cytosol*, nucleus (T3, RA) Ligand binding → binding of DNA regulatory sequence by receptor → activation of transcription studyblue.com Pause for Retrieval Practice https://www.bookw idgets.com/play/SV uuDo-U- iQAFKwW22gAAA/3 E9BX3W/lipophilic- horm  Hydrophilic Hormones Amino acids, peptides, proteins Synthesized and secreted by cells of hypothalamus, pituitary, pancreas, … Inactive precursor stored in secretory vesicles, released through exocytosis Bind plasma membrane receptors  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  Three major classes of cell surface receptors R1. R2. R3. Fig 15-15. Alberts.  R1. Ligand-gated Ion Channel Ionotropic receptor Membrane protein complex that includes ligand binding sites forms a pore https://www.nature.com/scitable/topicpage/ion-channel-14047658  Ligand-gated ion channel The neurotransmitter is the ligand. Examples: Nicotinic acetylcholine receptor GABA receptor Fig. 2. Diagram for ligand-gated ion channels Siegelbaum et al (2000).  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  R2. G-protein-coupled Receptor A.k.a. seven-transmembrane receptor Gs, Gi, Gq proteins – αβγ subunits Relies on second messengers to relay intracellular signals https://www.nature.com/scitable/topicpage/gpcr-14047471  G-proteins a. Gs Activates adenylyl cyclase b. Gi Inhibits adenylyl cyclase c. Gq Activates phospholipase C  R2a. GPCR—Gs signalling What is the role of phosphodiesterase? PKA From: 1 Cell and Membrane Physiology Lippincott® Illustrated Reviews: Physiology, 2e, 2019 R2a. GPCR—Gs signalling Pause for Retrieval Practice https://www.bookw idgets.com/play/FP B5jK2C- iQAEtO3EOgAAA/TE 83ET8/gs R2b. GPCR—Gi signalling X Adapted from: Wettschureck, N. and Offermanns, S. Mammalian G Proteins and Their Cell Type Specific Functions. Physiology Reviews, 85, 4, 2005, 1159-1204. R2c. GPCR—Gq signalling From: 1 Cell and Membrane Physiology Lippincott® Illustrated Reviews: Physiology, 2e, 2019 R2c. GPCR—Gq signalling Pause for Retrieval Practice https://www.bookwidgets.co m/play/OQu8uXIZ-iQAFC5o- 2gAAA/BE87XBK/gq- signaling?teacher_id=48370122 12285440  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors. R3. Some cell surface receptors have enzymatic activity—Enzyme-coupled Receptors A. Receptor tyrosine kinase B. Receptor serine-threonine kinase  R3. Enzyme-linked Receptors A. Receptor tyrosine kinase B. Class I cytokine receptor C. Receptor serine-threonine kinase R3A. Receptor Tyrosine Kinase– Activation Overview Change in protein activity or change in gene expression See Fig 15-52. Alberts.  RTK Signaling can occur via 3 pathways Signal transduction pathways: 1. PI3-K 2. Ras/MAPK 3. PLC Signaling molecules include insulin, some growth factors Some signaling molecules bind >1 member of the RTK family  A 44-year-old female performs a finger-stick test to check her blood glucose 2 hours after eating a meal and sees a reading of 140 mg/dL (normal: 70-100 mg.dL). Three hours later, she does another test and the result is 99mg/dL.  A1. PI3-K Pathway Ligand binding→ receptor dimerization→ RTKs activate kinase activity in each other Activated RTKs recruit intracellular signal transducers near membrane. Eg. IRS1 – Phosphorylate Y’s→formation of binding sites for substrates w/ SH2 domains, eg. PI3K Activated PI3-K: PIP2→ PIP3 PIP3→→ phosphorylates, activates Akt (PKB) → phosphorylation cascade downstream→→→ →GLUT4 translocates to https://employees.csbsju.edu/hjakubowski/classes/ch331/signaltrans/ST_9 C9_Insulin_Sig_PI3K_Ak.html membrane  A2. RAS/MAPK Pathway Examples: insulin, EGF Activated RTKs recruit intracellular signal transducers Insulin near membrane. – Phosphorylate Y’s→formation of (Insulin receptor) binding sites for substrates w/ SH2 domains Ras converted of from inactive to active (GTP-bound) form Ras-GTP interacts with and stimulates downstream effectors, leading to activation of the MAP kinases ERK1 and 2 ERK enters nucleus, phosphorylates and activates Tc factors for growth, proliferation; affects differentiation of genes  A3. PLC Pathway Example: EGF Activated RTKs recruit intracellular signal transducers near membrane – Bind and phosphorylate substrates w/ SH2 domains, eg. PLCγ→ stimulation of phospholipase activity PLC: PIP2→ IP3, DAG IP3→ Ca2+ release from ER http://publication.letstalkacademy.com/ip3-dag-pathway-of-receptor-tyrosine- Ca2+, DAG activate kinase-in-cell-signalling PKC→→→ activate Tc of genes involved in proliferation, survival, etc. Pause for Retrieval Practice https://www.bookw idgets.com/play/zBr dMYRn- iQAFUTH82gAAA/U E9CEUU  R3B. Class I Cytokine Receptors No intrinsic TK activity Associate with ‘non- receptor tyrosine kinase’— Jak (in cytosol) Jak/STAT pathway STAT regulates transcription Fig 1-6  R3B. Receptor Serine Threonine Kinases Cell surface receptors that are activated to phosphorylate S or T on substrate proteins Bind TGF-β family of signalling molecules – TGF-β involved in proliferation of various cell types, cell differentiation Activated receptor complex binds Smad proteins— Fig. 15-65. Alberts. transcription regulators Smads enter nucleus to regulate transcription of target genes  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.  Positive feedback amplifies a response Output stimulates its continued production May be stopped by a definitive event Example? Fig 15-17. Alberts. Describe the occurrence of positive feedback in generation of an action potential See Fig 15-24.  Negative feedback can terminate signaling event Output inhibits its continued production or activation Limits cellular response to maintain stability Example? Fig 15-17. Alberts. 6ed. Feed-forward Fig 7-40. Alberts. 6ed.  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors. Ligand binding can serve to activate the receptor  Response to ligand-binding is regulated Receptors may be up-regulated – May be in response to activation of receptor – May be in response to reduced level of ligand – Increase transcription, translation – Decrease degradation of receptors Receptors may be down-regulated – Reduce transcription, translation – Increase degradation of receptors  “Opioids are the most potent drugs used for pain relief. However, their therapeutic potential could be limited as a protracted use will lead to tolerance to analgesic effects requiring escalating doses that is associated with side effects such as respiratory depression.” – Allouche, S., Noble, F., and Marie, N. (2014). Opioid receptor desensitization: mechanisms and its link to tolerance. Frontiers in Pharmacology, 5(280), 1-20. doi: 10.3389/fphar.2014.00280.  Cell can become de-sensitized to ligand Desensitization (adaptation) can occur after prolonged exposure of receptor to ligand Reduced response to future stimulation by same ligand or same concentration of ligand – Over time, no response to same ligand concentration – Need greater ligand concentration to produce response Fig 15-48. Alberts. Can occur by receptor endocytosis, receptor down- regulation, receptor inactivation (eg. by phosphorylation) Can lead to cessation of signaling Regulation mechanisms: See Fig 15-25. Alberts. A bit more about cell signaling… A ligand can activate more than one signaling pathway Note that there are other signaling routes that do not involve GPCR, receptor enzymes, ion channels – Many target gene expression – Regulate variety of cell functions Use a medical dictionary to define these two terms: Agonist Antagonist  Goal MCB.12. Understand the general principles of cell signaling and its clinical significance Learning Objectives Given a clinical or research vignette, scenario, table, graph, or diagram, students should be able to: MCB.12.1. Distinguish the basic components of a reaction: releasing cell, signaling molecule (ligand), target cell, receptor. MCB.12.2. Classify signaling molecules as lipophilic and peptide ligands. MCB.12.3. Distinguish membrane-bound and intracellular receptors based on their location, structure, and function. MCB.12.4. Contrast the pathways involved in use of G protein-coupled receptors, enzyme-linked receptors, and ligand-gated ion channels. MCB.12.5. Recognize negative and positive feedback and their downstream effects. MCB.12.6. Recognize activation, deactivation, up-regulation, down- regulation, sensitization, and de-sensitization of receptors.