05_Cell_Signal_Transduction_2024.07.18_Student.pptx

Cell Signal Transduction Steven J. Ontiveros, MBA, PhD  Objectives Describe the principal modes of cell signaling. Explain the role of cAMP and the regulation of cAMP-dependent protein kinases. Explain the role of PLC and the regulation of IP3/DAG second me...

Cell Signal Transduction Steven J. Ontiveros, MBA, PhD  Objectives Describe the principal modes of cell signaling. Explain the role of cAMP and the regulation of cAMP-dependent protein kinases. Explain the role of PLC and the regulation of IP3/DAG second messenger systems. Explain the structure of G-protein coupled receptors (GPCRs) and how they carry signals to their target enzymes. Explain the various receptor types and signaling molecules used in intracellular signaling and transduction.  Overview of Intercellular Communication Cell Communication: Transmission of messages between cells Signaling Cell Make sense of environment Mechanism: Signaling cell (communicates) Signal (ligand) Produce ligands (message) Target cell (listens to communication) Receptors (ears) specific for ligand Ligand (message): Extracellular signal (proteins, peptides, steroids, Recept fatty acids, or gases) or Carry messages long distance or locally Act on target receptors (cell membrane/cytosol) Response Signal Transduction: Conversion of extracellular signal peptide to a Target Cell biological response  Mechanisms of Cell-to-Cell Signaling Endocrine Long distance targets Hormone Signaling molecule carried through blood circulation Ex: Sex hormones, Thyroid hormone Neuroendocrine Long distance targets Cells with neuronal input Release hormone into blood circulation Ex: Adrenal medulla and adrenalin Paracrine Short distance Acts on neighboring cells Gradient factor can determine outcome Ex: Somatostatin Histology and Cell Biology 5 th Edition, 2020  Mechanisms of Cell-to-Cell Signaling Neurotransmitter (synapse) Action potential Long/short distance Ex: Muscle stimulation Juxtacrine (Direct/Contact-dependent) Ligand and receptor are on cell membrane Ex: Intestinal crypts (absorptive/secretive cells) Ex: Fas signaling (apoptosis) Autocrine Cells respond to their own signaling molecule Ex: T-Lymphocytes – drive their own proliferation Histology and Cell Biology 5 th Edition, 2020  Signaling Molecules Steroid Hormones: Neurotransmitters: Synthesized from cholesterol Released by neurons via action potentials Hydrophobic Hydrophilic Bind internal receptors Bind cell surface receptors Ex: Sex hormones and corticosteroids Ex: Acetylcholine Peptide Hormones, Neuropeptides, and Growth Nitric Oxide: factors: Synthesized from arginine by nitric oxide synthase Few to several hundred amino acids Diffuse across cell membrane Bind cell surface receptors Acts as a paracrine molecule within nervous, immune, and Ex: Insulin, Glucagon, FSH circulatory system Does not bind receptors - Directly regulates target enzymes Receptors Composed of protein Receptors Receive a signal (chemical messenger) Transduce the signal into a cellular response 2 Types of Receptors Intracellular (nuclear) receptors: Used by steroid hormones Signal diffuses across membrane bind internal receptor Example: Nuclear receptors Cell surface (membrane) receptors: Used by soluble signals Signal binds cell surface receptor Leads to signal transduction Example: G protein-coupled receptors  Intracellular Receptors (aka Nuclear Receptors) Used by steroid hormones Estrogen, testosterone, progesterone, cortisol… Hormones diffuse through the cell membrane Internal receptor Found in cytosol or nucleus Transcriptional regulator Receptor functions as a transcription regulator once activated Promote or inhibit cell activity Histology and Cell Biology 5th Edition, 2020 Regulate many biological processes Cell proliferation Metabolism Reproduction  Plasma Membrane Receptors Receptors located on cell membrane Spans length of plasma membrane Contains extracellular & cytosolic domains Types: G-protein coupled receptor (GPCR) Membrane receptor that activates downstream effectors Enzymatic (catalytic) receptors Histology and Cell Biology 5 th Edition, 2020 Membrane receptor that mimics enzymes Ionotropic receptors (Aka ligand-gated ion channels, channel receptors) Membrane receptor Opens to allow conduction of ions Receptors that undergo cleavage Fragments upon activation  Intracellular Signaling through Membrane Receptors 1. Reception of first messenger Extracellular signal molecules 2. Transduction and activation of second messenger: Intracellular molecules Transmit and amplify the strength of the first message Can activate or inhibit targets Types of second messengers: cAMP cGMP Ca2+ Phosphatidylinositols (PIP2 and PIP3) Diacylglycerol (DAG) 3. Cell Response  Signal Amplification Amplification of primary signal Second messengers activate other proteins and amplify the signal Advantages Regulation Cascade is regulated by a single molecule Amplification One molecule  many molecules  Speed of Signaling Signaling targets Cytosolic targets (cause altered protein function) Nuclear targets (regulate gene expression) Cytosolic targets: fast cell response Some responses take milliseconds Signaling alters the activity of proteins present in the cytoplasm Ex: Muscle contractions Nuclear targets: slow cell response Minutes to hours Signals affect gene expression Ex: Signals for cell division G-Protein Coupled Receptors (GPCRs)  GPCRs and Heterotrimeric G-proteins G-Protein Coupled Recetpors (GPCRs) Used by many biological processes Largest family of cell surface receptors Activate G proteins on inner face of cell membrane Initiate intracellular signaling cascades G-proteins Composed of three subunits α, β, and ɣ Types Gs – stimulates cAMP pathways Gi – inhibits cAMP pathways Golf – stimulates Adenylyl cyclase  cAMP Gq – activates Phospholipase C pathway  GPCR activates the G protein G protein (trimeric G protein) G Protein Activation Three protein subunits: α, β, and ɣ Subunits are inactive when complexed together α subunit Activated by GPCR Exchanges GDP with a GTP When bound to GTP (active) Dissociates from β/ɣ subunit GTPase activity (Hydrolyzes GTP  GDP) When bound to GDP (inactive) β/ɣ subunit Active when not in complex with the α subunit Both α and β/ɣ subunits interact with membrane-bound enzymes Ex: Adenylyl cyclase (α) and phospholipase C (β/ɣ)  Adenylyl Cyclase & cAMP Pathway Gα Activates adenylyl cyclase Adenylyl Cyclase Enzyme: ATP -> cAMP (cyclization reaction) Histology and Cell Biology 5th Edition, 2020 Activated by the α subunit of “stimulatory” G proteins (Gs) Note: Also inhibited by the α subunit of “inhibitory” G proteins (Gi) cAMP PKA Secondary messenger Activates Protein Kinase A (PKA) Regulation of Protein Kinase A (PKA) PKA Activated by cAMP AKA cAMP-dependent protein kinase PKA regulation Inactive: Large complex of two regulatory (blue) and 2 catalytic subunits (purple) Active: cAMP binds regulatory subunits Releases the catalytic subunits (active)  Full AC & cAMP Pathway PKA Histology and Cell Biology 5th Edition, 2020 ***PKA can affect cytosolic and/or nuclear targets Adenylyl Cyclase & cAMP Pathway  G Protein Mutation Pseudohypoparathyroidism (PHP) Resistance to parathyroid hormone (parathormone, parathyrin) Normal levels of PTH are produced by parathyroid gland PTH Target bone cells Regulates levels of calcium and phosphorus in blood Pathogenesis Mutations in G Protein (Gα subunit) Elevated phosphorus Reduced calcium Clinical Presentation Hypocalcemia (low blood calcium) Short stature Shortening of the limbs 4th Metacarpal Shortening of the 4th metacarpal Generalized obesity Springer Link - Hypoparathyroidism p. 365-362, 2015 Developmentally delayed Phospholipase C Pathway  PLC Pathway: Activates the release of intracellular Ca2+ Phospholipase C Pathway Very important for glycogen breakdown and muscle contraction Phospholipase C (PLC): Generally activated by Gq Can also be activated by Gβ/ɣ Characteristics of PLC: Membrane-associated enzyme Catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) PIP2: Phospholipid with sugar moiety Hydrolysis of PIP2 creates 2-second messengers Inositol 1,4,5-trisphosphate (IP3) - cytosolic Diacylglycerol (DAG) – membrane bound  Second Messengers of PLC and Calmodulin Second Messengers of PLC IP3: Cytosolic Hydrophilic sugar phosphate Binds and opens calcium channels on ER Causes cytosolic Ca2+ levels increase DAG: Membrane-bound Recruits protein kinase C (PKC) PKC: Protein kinase (similar to PKA) Activated by Ca2+ and DAG PLC & Inositol Phospholipid Pathway  Other Major Pathways Receptor Tyrosine Kinases (Enzyme coupled receptors) Can use Monomeric GTPases Insulin signaling Cell survival, proliferation, cell growth JAK STAT Cytokine signaling Macrophage activation, milk production, erythropoiesis WNT Pathway Cell growth, proliferation Delta-Notch Signaling Cell-to-cell communication Proliferation, differentiation