Cell Signaling (Chapter 16) PDF

Cell Signaling (Chapter 16) Minwook Kim, PhD Assistant Professor Department of Molecular Biology Rowan-Virtua School of Osteopathic Medicine and Translational Biomedical Engineering and Sciences Cell Biology (MBS00502)...

Cell Signaling (Chapter 16) Minwook Kim, PhD Assistant Professor Department of Molecular Biology Rowan-Virtua School of Osteopathic Medicine and Translational Biomedical Engineering and Sciences Cell Biology (MBS00502) 11.13.2024  Learning objectives Contrast the terms endocrine, paracrine, and autocrine based on the site of hormone release and the pathway to the target tissue List two advantages of using a multistep pathway in the transduction stage of cell signaling Describe how signal amplification is accomplished in target cells. Explain how different types of cells may respond differently to the same signal molecule Describe how phosphorylation propagates signal information and how protein phosphatases turn off signal-transduction pathways Define the term ‘second messenger’. Briefly describe the role of these molecules in signaling pathways Describe how the cytosolic concentration of Ca2+ can be altered and how the increased pool of Ca2+ is involved with signal transduction Compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand gated ion channels State how signals can be terminated  Signal transduction is the conversion of one type of signal into another When a mobile telephone receives a radio signal, it converts it into a sound signal (it does the reverse when transmitting a signal) A target (recipient) cell converts an extracellular signal molecule into an intracellular signal  General Principles of Cell Signaling Signals can act over a long or short range (distance) A limited set of extracellular signals can produce a huge variety of cell behaviors A cell’s response to a signal can be fast or slow Cell-surface receptors relay extracellular signals via intracellular signaling pathways Some intracellular signaling proteins act as molecular switches Cell-surface receptors fall into three main classes · Cascadesdon Channel Reapt · Switches : G-protein Coupled · Enzyme Coupled Recept  General Principles of Cell Signaling Signals can act over a long or short range (distance)  Animal cells use extracellular signal molecules to communicate with one another in various ways Hormones produced in endocrine glands are secreted into the bloodstream and are distributed widely through the body Travel long distances  Animal cells use extracellular signal molecules to communicate with one another in various ways Paracrine signals are released by cells into the extracellular fluid in their neighborhood and act locally · Close Proximity - but doesn't need Contact - "Locd" Signaliy  Animal cells use extracellular signal molecules to communicate with one another in various ways Neuronal signals are transmitted electrically along a nerve cell axon When this electrical signal reaches the nerve terminal, it causes of neurotransmitters onto adjacent target cells  Animal cells use extracellular signal molecules to communicate with one another in various ways In contact-dependent signaling, a cell-surface-bound signal molecule binds to a receptor protein on an adjacent cell Many of the same types of signal molecules are used for endocrine, paracrine, and neuronal signaling. The crucial differences lie in the speed and selectivity with which the signals are delivered to their targets Extracellular signal molecules bind either to cell-surface receptors or to intracellular receptors Most extracellular signal molecules are large and hydrophilic and thus unable to cross the plasma membrane directly  bind to cell-surface receptors, which generate one or more intracellular signaling molecules in the target cell Large hydrophilic signal · mole. bind to all-Surface Receptors ↳ = Insidecell ble too difficult 4 themto cross plasma membran directly Extracellular signal molecules bind either to cell-surface receptors or to intracellular receptors Some small, hydrophobic, extracellular signal molecules pass through the target cell’s plasma membrane and bind to intracellular receptors – in the cytosol or in the nucleus that then regulate gene transcription or other functions cytosol Same signal molecule can induce different responses in different target cells Different cell types are configured to respond to the neurotransmitter acetylcholine in different ways Acetylcholine: a neurotransmitter that plays a role in brain (e.g., memory) and body (e.g., muscle contraction to move your muscles) Acetylcholine binds to similar receptor proteins on different cells ((A) heart pacemaker cells, (B) salivary gland cells, and (C) muscle cells) may respond to the same signal in different ways signomy decreases Antylcholine Responds Causes muscles In This all contract to all to it causes to secrete G-protein coupled molec Receptor Same molecule Different cells Different responses  An animal cell depends on multiple extracellular signals Every cell type displays a set of receptor proteins that enables it to respond to a specific set of extracellular signal molecules produced by other cells These [signal molecules work in combinations to regulate the behavior of the cell2. As shown here, cells may require multiple signals (blue arrows) to - survive, additional signals (red arrows) to grow and divide, and still other signals (green arrows) to differentiate If deprived of the necessary survival signals, most cells undergo a form of cell death (apoptosis) A + b+ C = A + b C + f+ 6 + = cell survives Differentiate lie become nerve, skin bone , Cells A+b+ C + D+ E = Proliferate /divide It not enough signals dies/Apoptosis > -  Extracellular signals can act rapidly or slowly Changes in all Certain Types of all Respense like Movement, Secretiona Metabolism Differentiation Dall , growth d division - need not involve changes in gene Involves changes synthesis - in gene expressiona expression of New proteins > - Occurs relativelySlowly ↳ occur More quickly Intracellular signdly Cascade S b Transduced to nuc. · If they don't have to go des thre all An Intracellular signly Cascades the nucleus - Thy in > Can jo FAST Certain types of cell responses (e.g., cell differentiation or increased cell growth and division) involve changes in gene expression and the synthesis of new proteins  They occur relatively slowly Other responses (e.g., cell movement, secretion, or metabolism) need not involve changes in gene expression and therefore occur more quickly Extracellular signals activate intracellular signaling pathways to change the behavior of the target cell A cell-surface receptor protein activates one or more intracellular 1 signaling pathways, activates each mediated by a series of intracellular signaling molecules, which can be proteins or (e.g., proteins, small messenger small messenger molecules) molecules Signaling molecules Signaling molecules eventually interact with 2 specific effector altering effector proteins proteins, altering them to change cell behaviors to change the behavior of the cell in various (e.g., metabolism, ways cell shape/ movement, or gene expression) Intracellular signaling proteins can relay, amplify, integrate, distribute, and modulate via feedback an incoming signal Thru Looping System - 1 molecular signal (e.g., ligand and ions) receptor protein transduces signal into the cell 2 This signal transduction initiates one or more intracellular signaling pathways that relay the molecular signal into the cell interior Small intracellular molecules: - mediate the effect - are produced after a receptor is activated by a first messenger are called Second messenger molecules 3 Each pathway includes intracellular signaling proteins that can function in various ways -Integrate signals from other intracellular signaling pathways -Many of the steps can be modulated via feedback by other molecules 4 Sent to effector proteins  affect cell behaviors A receptor protein on the cell surface transduces an extracellular signal into an intracellular signal, initiating intracellular signaling pathways Many of the steps in the process can be modulated via feedback by other molecules Some proteins in the pathway may be held in close proximity by a scaffold protein, which allows them to be activated at a specific location in the cell and with greater speed, efficiency, and selectivity Feedback regulation within an intracellular signaling pathway can adjust the response to an extracellular signal Y-Amplifies T Inhibition Overexpression Protein Y increases Protein T (that Protein Y inhibits Protein T (that activated Protein Y) activated Protein Y) Positive loops can ignite an explosive Negative loops can generate response (e.g., the activation of oscillations proteins that trigger cell division) (A) A downstream protein in a signaling pathway, protein Y, acts to increase the activity of the protein that activated it - a form of positive feedback Positive feedback loops can ignite an explosive response, such as the activation of the proteins that trigger cell division (B) Protein Y inhibits the protein that activated it Negative feedback loops can generate oscillations, similar to the way that populations of predators and prey can seesaw: an increase in prey (here, protein T) would promote the expansion of predators (protein Y); as the number of predators increases, the availability of prey will fall (via negative feedback), which will ultimately cause the predator population to decline As the predators disappear, the prey populations will recover and multiply, providing food for more predators, and so on  Some intracellular signaling proteins act as molecular switches Adding Phosphate ON: Phosphate is added ON: GTP-binding protein is activated by protein kinase from when it exchanges its bound GDP ATP to the signaling for GTP (+ phosphate) protein Guanine nucleotide exchange factors (GEFs) promote the OFF: Phosphate is exchange of (GDP  GTP) removed by a protein phosphatase OFF: hydrolyzing its bound GTP to GDP (- phosphate) GTPase-activating proteins (GAPs) promote hydrolysis of (GTP  GDP) Remary These proteins can be activated or in some cases inhibited by the addition or removal of a phosphate group (A) In one class of switch protein, the phosphate is added covalently by a protein kinase, which transfers the terminal phosphate group from ATP to the signaling protein; the phosphate is then removed by a protein phosphatase (B) In the other class of switch protein, a GTP-binding protein is activated when it exchanges its bound GDP for GTP (which, in a sense, adds a phosphate to the protein); the protein then switches itself off by hydrolyzing its bound GTP to GDP The activity of monomeric GTPases is controlled by two types of regulatory protein Another molecular switch is guanosine triphosphate (GTP) When a G protein coupled receptor is activated, GDP is exchanged for GTP (now “on”) When GTP is hydrolyzed to GDP, pathway is turned off  Kinase Protein phosphorylation: add a phosphate group (from ATP) Phosphate groups attach to amino acid with -OH groups in their side chains Serine (86.4%), threonine (11.8%), tyrosine (1.8%) Transfer of the phosphate group is catalyzed by a kinase Cells contain different kinases that phosphorylate different targets Lipid-soluble ligand (signaling molecules) Water-soluble ligand (e.g., hormones) Can pass the membrane Can NOT enter the membrane but very slow  need cell surface receptor  binds to intracellular receptor ExT3, T4 Vitamm D Steroid Hormones ,. peripheral water-loving water-loving integral protein (e.g., GPCR) cytoplasm nucleus Intracellular Receptors: Cytoplasmic and Nuclear  Cell surface receptors fall into one of three main classes Signaling molecules bind Channel (closed  open) Ions pass the membrane Signaling molecules bind GPCR (inactive  active) signal G protein hunt gameSenot Separated turn (on/off) Enzyme (or ion channel) Signaling molecules bind ECR (inactive  active) extracel ulaactors r signal inside the cell Have own Need an enzyme activity associated Intracellularly enzyme enzymatee (A) An ion-channel-coupled receptor opens in response to binding an extracellular signal molecule. These channels are also called transmitter-gated ion channels. (B) When a G-protein-coupled receptor binds its extracellular signal molecule, the activated receptor signals to a trimeric G protein on the cytosolic side of the plasma membrane, which then turns on (or off) in the same membrane. (C) When an enzyme-coupled receptor binds its extracellular signal molecule, an enzyme activity is switched on at the other end of the receptor, inside the cell. Many enzyme-coupled receptors have their own enzyme activity (left), while others rely on an enzyme that becomes associated with the activated receptor (right).  G-Protein-Coupled Receptor 1 G-Protein-Coupled-Receptor 3 - Common structure: seven (7) transmembrane alpha helices 5 7 - Outer surface  binding site for ligand molecule 2 4 - Inner surface  binding site for G-protein 6 - When a ligand bounds to receptor, it undergoes conformational changes  activates a G-proteins that are inside surface of the plasma membrane GPCR -Integral protein receptor Signal molecule -The action of GPCR depends on: (1) Receptor jembentegral Protein (2) G-Protein mus stimulate a (3) Effector molecule (Gq, Gs, Gi) hi α β ϒ Effector (e.g., enzyme) GTP GDP active GTP G-protein Effector - Guanine nucleotide Binding Protein - Synthesizes GTPase hydrolysis (GDP or GTP can bind) cyclic Adenosine MonoPhsphotate GDP - Heterotrimeric: (α, β, γ subunit) (cAMP) p inactive - G-protein (α, β, γ) + GDP = inactive - G-protein (α) + GTP = active  G-Protein activation ① ② α α β ϒ ⑤ GTP GDP ③ GTP β ϒ ④ effector ↳ 3 Types active Inhibity cAMP GTP (1) Ligand binds to GPCR Cakumby Stimulating , GS O cAMP GTPase hydrolysis (2) GPCR undergoes conformational change GDP (3) G-protein binds to GPCR inactive p (4) Alpha subunit exchanges GDP for GTP (5) Alpha subunit dissociates with beta/gamma subunit complex  G-Proteins are molecular switches that activate Enzymes that generate Second messengers Stimulatory Inhibitory Stimulatory receptors receptors receptors Gg T Phospholipase C..  Cyclic AMP Cyclic AMP (cAMP) is one of the most widely used second messengers A small, hydrophilic molecule Facilitate or promote for signal transduction (mobilization) Adenylyl cyclase (enzyme that in the plasma membrane) converts ATP to cAMP in response to an extracellular signal 2P ATP cAMP AMP Adenylate cyclase Phosphodiesterase (PDE) + - - Gs Gi Phosphodiesterase (stimulate) (inhibit) inhibitors ↑ Gs  ↑ cAMP ↑ Gi  ↓ cAMP Kinase: + P ↓ PDE  ↑ cAMP Phosphatase: - P  cAMP α Adenylate cyclase (enzyme) β ϒ GTP ATP cAMP Second messenger Protein Kinase A (PKA) Cellular response Many signal molecules trigger formation of cAMP (EPI, glucagon) Other components of cAMP pathways are: G-protein-linked receptors G proteins Protein kinases cAMP usually activates protein kinase A, which phosphorylates other proteins There are also G-protein systems that inhibit adenylyl cyclase An activated GPCR activates G proteins by encouraging the alpha subunit to expel its GDP and pick up GTP In the unstimulated state, the receptor and the G protein are both inactive Binding of a signal molecule to the receptor changes the conformation of the receptor and alters the conformation of the bound G protein The alpha-subunit of the G protein allows it to exchange its GDP for GTP The α-subunit and β /γ -complex dissociate to interact with their preferred target proteins in the plasma membrane The receptor stays active as long as the external signal molecule is bound to it, and it can activate many molecules of G protein Both the α-subunit and β/γ-complex have covalently attached lipid molecules (red) that help anchor the subunits to the membrane The G-protein alpha subunit switches itself off by hydrolyzing its bound GTP to GDP When an activated α-subunit interacts with its target protein, it activates that target protein for as long as the two remain in contact The α-subunit then hydrolyzes its bound GTP to GDP—an event that takes place usually within seconds of G-protein activation The hydrolysis of GTP inactivates the α subunit, which dissociates from its target protein and—if the α subunit had separated from the β/γ complex — reassociates with a β/γ complex to re-form an inactive G protein The G protein is now ready to couple to another activated receptor Both the activated α subunit and the activated β/γ complex can interact with target proteins in the plasma membrane Some G-proteins regulate ion channels directly (K pump in the heart is controlled) Binding of the neurotransmitter acetylcholine to its GPCR on the heart cells results in the activation of the G protein. The activated β/γ complex directly opens a K+ channel, increasing its permeability to K+ Inactivation of the α- subunit by hydrolysis of its bound GTP returns the G protein to its inactive state, allowing the K+ channel to close.  Enzymes activated by G proteins directly increase the concentration of small intracellular signaling molecules Because each activated enzyme generates many molecules of these second messengers, the signal is greatly amplified at this step in the pathway The signal is relayed onward by the second messenger molecules, which bind to specific signaling proteins in the cell and influence their activity Epinephrine stimulates glycogen breakdown in skeletal muscle cells The hormone (i.e., Epinephrine) activates a GPCR, which turns on a G protein (Gs) that activates adenylyl cyclase (enzyme) to boost the production of cAMP. The increase in cAMP activates protein kinase A (PKA), which phosphorylates and activates phosphorylase kinase (enzyme) This kinase activates glycogen phosphorylase (the enzyme) that breaks down glycogen A rise in intracellular cAMP can activate gene transcription Protein Kinase A (PKA), activated by a rise in intracellular cyclic AMP (cAMP), can enter the nucleus and phosphorylate specific transcription regulators Once phosphorylated, these proteins stimulate the transcription of a whole set of target genes This type of signaling pathway controls many processes in cells, ranging from hormone synthesis in endocrine cells to the production of proteins involved in long-term memory in the brain  Phospholipase C Calcium ions and Inositol triphosphate (IP3) Activates A : hydrophilic Calcium ions (Ca2+) act as a second messenger in many pathways Calcium is an important second messenger because cells can regulate its concentration Two messenger molecules are produced when a membrane inositol phospholipid is hydrolyzed by activated phospholipase C (enzyme) hydrophobic there a Inositol 1,4,5-trisphosphate (IP3) diffuses through the cytosol and triggers -directly diffuse. b the release of Ca2+ from the ER by binding to and opening special Ca2+ channels in the ER membrane The large electrochemical gradient for Ca2+ across this membrane causes Ca2+ to rush out of the ER and into the cytosol  Calcium ions and Inositol triphosphate (IP3) Cellular response Second messenger Diacylglycerol (DAG bound to glycerol molecule) remains in the plasma membrane and, together with Ca2+, helps activate the enzyme protein kinase C (PKC), which is recruited from the cytosol to the cytosolic face of the plasma membrane PKC then phosphorylates its own set of intracellular proteins, further propagating the signal At the start of the pathway, both the α-subunit and the β/γ complex of the G protein Gq are involved in activating phospholipase C  Enzyme-coupled receptors: Receptor Tyrosine Kinase (RTK) When signaling molecules bind to RTKs, they cause neighboring RTKs to associate with each other, forming cross-linked dimers Cross-linking activates the tyrosine kinase activity in these RTKs through phosphorylation – specifically, each RTK in the dimer phosphorylates multiple tyrosines on the other RTK (cross-phosphorylation)  Comparing G Protein Coupled Receptors and Receptor Tyrosine Kinases Similarities Receptors involved in cell signaling pathways Cell surface receptors hydrophilic Transmembrane proteins Integral) Activated by binding a ligand to the receptor