Signal Transduction 2024 Current PDF

Cell Signalling and Signal Transduction pathways Dr. Wilhelmina Annie Mensah UGMS 1 11/24/2024...

Cell Signalling and Signal Transduction pathways Dr. Wilhelmina Annie Mensah UGMS 1 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS After the lesson, students should be able to: Explain the importance of cellular communication in multi-cellular organisms Differentiate between paracrine, endocrine and autocrine signaling. Understand the basic principles of signal transduction mechanisms, the concepts of receptor, second messenger, amplification, cellular effector proteins, signaling pathway. Know the different receptor categories Using examples, identify the various types of cellular receptors (ion- channel-linked, G-protein-linked, and enzyme-linked). Using examples, explain the mode of action of steroid hormones on nuclear receptors 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 2 After the lesson, students should be able to: Understand the importance and examples of second messengers Trace the pathway for cell communication beginning at the receptor and ending with the cellular response, and explain why the process is often referred to as signal transduction, noting the major components of signal transduction pathways Understand the importance of cellular effector proteins and know the role of Adenylyl/guanylyl cyclases (e,g, cAMP pathway, PLC pathway, cGMP pathway) Describe G-protein mediated signaling and explain how heterotrimeric GTP-binding proteins function in signaling pathways 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 3 After the lesson, students should be able to: Give examples of non-G protein mediated signal transduction pathways Describe RTK signaling Insulin signaling and the role of relevant kinases and signaling proteins Discuss signaling defects/signal transduction dysfunction and disease 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 4 Teaching outline CELL COMMUNICATION PLAYERS IN SIGNAL TRANSDUCTION PATHWAYS SIGNAL TRANSDUCTION MECHANISMS CELL SURFACE RECEPTORS. MAJOR SIGNAL TRANSDUCTION PATHWAYS A. the cAMP signal pathway and B. the phosphatidylinositol signal pathway. HEALTH IMPLICATIONS 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 5 1.INTRODUCTION In human body, numerous processes are required for coordinating individual cells to support the body as a whole. At the cellular level, cell communication for coordination relies on signal transduction Many disease processes, such as diabetes and heart disease arise from defects or dysregulations in these pathways, highlighting the importance of these processes in human biology and medicine 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 6  Cell Communication/Signaling Cell communication is the process by which a cell detects and responds to signals in its environment. Occurs through chemical signals and cellular receptors by either the 1) direct contact of molecules on two cells surfaces or the 2) release of a "chemical signal" recognized by another cell (near or far). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 7 Some signals to which cells respond Mechanical touch Antigens Growth factors Light Nutrients Odorant Neurotransmitters Pheromones 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 8 Importance of cell Signaling/communication 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 9 Types of Signals: Cell-Cell Communication/Signaling types 1) Endocrine 2) Paracrine 3) Autocrine 4) Juxtacrine (contact dependent ) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 10 In animals, specialized endocrine cells release hormones into the circulatory system, by which they travel to target cells in other parts of the body. E.g. Growth hormone Paracrine signaling occurs when a nearby cell receives and respond to growth factors produced by a single cell in their vicinity. Synaptic Signalling In autocrine signaling, a cell signals to itself, releasing a ligand that binds to receptors on its own surface (or, depending on the type of signal, to receptors inside of the cell). This type of signaling is particularly common in tumor cells, many of which overproduce and release growth factors that stimulate inappropriate, unregulated proliferation of themselves as well as adjacent non tumor cells; this process may lead to formation of tumor mass. Direct contact or contact dependent (Juxtacrine) Cells may also communicate via direct contact between substances on their surfaces. This kind of signaling is especially important in the immune system, where immune cells use cell-surface markers to recognize “self” cells (the body's own cells) and cells infected by pathogens 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 14 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 15 Cell Cell Communication Summary  The major players in every 1. Ligand (First messenger) signalling pathway 2. The 1. The ligand / Stimulus receptor (The first messenger) 2. The Receptor 3. Primary effector 4. Second messenger 3. The primary effector 5. Secondary 4. The second messenger effector 6. Responds 5. Secondary effector 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 17 Ligand(1st Messenger) A small molecule that binds specifically to a larger one; for example, a hormone is the ligand for its specific protein receptor. Hormones are the major signaling molecules of the endocrine system Neurotransmitters are signaling molecules of the nervous system Cytokines are signaling molecules of the immune system 1. Stimulus/ ligands Type Examples Ligands These include growth factors, cytokines and neurotransmitters, odorants Mechanical forces Mechanosensation: hearing, touch, osmotic pressure , air pressure ( Mechanotransductio n) Temperature Many other thermosensory mechanisms exist in Thermoception both prokaryotes and eukaryotes Light Rhodopsin in rod and cone cells. In the case of the circadian clock, a Visual different photopigment, melanopsin, is responsible for detecting light phototransduction in intrinsically photosensitive retinal ganglion cells. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 19 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 20 2. Receptor ( Signal transducers)-Primary Effector Receptors are specific membrane proteins, which are able to recognize and bind to corresponding ligand molecules, become activated, and transduce signal to next signaling molecules. it can be a Glycoprotein or Lipoprotein The binding of a signaling molecule with a receptor causes a change in the conformation of the receptor, known as receptor activation. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 22  Messenger molecules ( Second Messengers) These can be amino acids, peptides, proteins, fatty acids, lipids, nucleosides or nucleotides. Hydrophilic messengers bind to cell membrane receptors (extracellular)===mostly first messengers (ligands) Hydrophobic messengers bind to intracellular receptors which regulate expression of specific genes (mostly secondary messengers) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 23 Differences btn 1st and 2nd messengers 1st Messenger 2nd Messenger Location Outside of the cell/ Inside of the cell/ intracellular small Extracellular molecules Substances Operation Through binding Through activation of respective with their protein kinases respective receptors Example Hormones , cAMP, phosphoinositol system , neurotransmitters, cGMP system , tyrosine kinase local mediators system, arachidonic acid system 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 24 Second messenger: They are small molecules and ions synthesized in cells in response to an external signal They relay signals received by cell- surface receptors to effector proteins. Such as Ca2+, cAMP, cGMP Types of secondary messengers Hydrophobic Hydrophilic Gases 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 26 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 27 Second Messengers and Responses  1. On the left, binding of growth factors to -a receptor tyrosine kinase (RTK; the receptor) can 1 activate -PI3K (the effector) to generate - PIP3 (the second messenger), which activates -Akt (the target). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 29 1 1. In the center, binding of 3 ligands to a GPCR (receptor) activates phospholipase C (PLC; the effector), 2 to generate two second messengers, DAG and IP3, which activate protein kinase C (PKC; the target) and release calcium from intracellular stores, respectively. 2. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 30  3 1. On the right, binding of agonists to a GPCR (the 1 2 receptor) can activate adenylyl cyclase (the effector) 2. to produce cAMP (the second messenger) to activate protein kinase A (PKA; the target). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 31 1. Ligand (First Effectors messenger) An effectors in signaling are 2. The proteins that are activated by receptor the receptor or the secondary messenger A molecule selectively binds 3. Primary effector to it and regulates its biological activity. 4. Second messenger Effectors can increase or decrease enzyme activity, gene expression, or cell 5. Secondary effector signaling. 6. Responds 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 32  SIGNAL TRANSDUCTION Any process occurring within cells that convert one kind of signal/stimulus into another type. It also known as cell signaling in which the transmission of molecular signals from a cell's exterior to its interior. It is also defined as the ability of a cell to change behavior in response to a receptor- ligand interaction.(signal) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 33 Signal transduction stages 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 34 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 35 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 36  11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 37 The ligand is the primary messenger. second messengers : these are produced as the result of binding the receptor, Second messengers relay the signal from one location to another (such as from plasma membrane to nucleus) leading to cascade of events/changes within a cell 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 38  The stages of chemical cell signaling 1. Reception The target cell must be able to detect that a signal is "arriving". This requires a chemical binding to a receptor molecule (protein), specialized for different functions. Most receptor molecules are found on the cell surface, but there area also intracellular receptors. 2. Transduction - Initiating the Intracellular Signal The receptor molecule binds to the signal molecule resulting often in a conformational change This change effectively translates (or transduces) the signal into a form that the target cell can respond to. Responder – Intracellular Secondary Transduction A responder will often serve to amplify the signal for a greater response. Secondary messengers are important in the signal transduction.. Response 3 The cell makes an appropriate response to the signal. A signal can activate enzymatic activity, genetic transcription, movement of cytoskeletal components, or other cell activities. Characteristics of signal transduction pathways  With prolonged exposure to a ligand (and occupation of the receptor) cells often become desensitized. Desensitization of the cell to a ligand depends upon receptor down- regulation. Desensitization may lead to tolerance, a phenomenon that results in the loss of medicinal effectiveness of some medicines that are over prescribed. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 46 Teaching Objectives PLAYERS IN SIGNAL TRANSDUCTION PATHWAYS CELL-CELL COMMUNICATION SIGNAL TRANSDUCTION MECHANISMS CELL SURFACE RECEPTORS. MAJOR SIGNAL TRANSDUCTION PATHWAYS A. the cAMP signal pathway and B. the phosphatidylinositol signal pathway. HEALTH IMPLICATIONS 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 47 RECEPTORS Receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems Receptor proteins can be classified by their location. Transmembrane( Cell Surface) receptors and Intracellular receptors are those found inside the cell, 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 48 RECEPTORS Transmembrane or cell surface receptors (Extracellular) include G protein-coupled receptors. Receptors with Kinase activity. Ligand-gated ion channel receptors. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 49 RECEPTORS Intracellular receptors are those found inside the cell, include Cytoplasmic receptors and nuclear receptors 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 50  Ligand binding domain Transduction of signal into response Receptor Functions : Two essential functions 1. Recognition of specific ligand molecule (Ligand binding domain) 2. Transduction of signal into response (Effector domain) Receptors of interest 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 52 Receptor families Four types of receptors families 1. Ligand-gated ion channels 2. G-protein coupled receptors 3. Enzymatic receptors (tyrosine kinase) 4. Receptor regulating gene expression (Nuclear hormone receptor ) Major transduction signalling pathways 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 54  Gated ion channels Receptors of the plasma membrane that open and close (hence the term “gating”) in response to the binding of chemical ligands or changes in transmembrane potential. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 55 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 56  Ligand Gated ion channels The acetylcholine receptor ion channel is an example of this mechanism They respond to neurotransmitters such as 5-hydroxytryptamine (serotonin), glutamate, and glycine 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 57 The acetylcholine receptor ion channel is an example of this mechanism The arrival of an action potential triggers neurotransmitter release from the presynaptic cell. The neurotransmitter (acetylcholine, for example) diffuses to the postsynaptic cell, Binds to specific receptors in the plasma membrane, and triggers a change in Vm. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 58 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 59 Acetylcholine is the chief neurotransmitter of the nervous system, that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows heart rate Neurotransmitters are chemical substances made by the neuron specifically to transmit a message. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 60 Acetyl choline ligand gated channels 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 61 Voltage-gated ion channels (VGICs) The activity of VGICs is regulated by the membrane potential of a cell, and open channels allow the movement of ions along an electrochemical gradient across cellular membranes. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 62 Voltage gated ion channels 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 63 Mechanically gated channels - open and close in response to mechanical vibration or pressure, such as sound waves or the pressure of touch (found in sensory receptors in the skin, ear, etc.); involved in generating graded potentials. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 64  Mechanical gated ion channel 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 65 Ion channel related diseases Genetic and autoimmune disorders of ion channels and are known as channelopathies. Eg. Generalized epilepsy with febrile seizures plus (GEFS+)- voltage gated ion channel disease Cystic fibrosis is caused by mutations in the CFTR gene, which is a ligand gated ion channel disease Congenital lymphatic dysplasia in deficiency in PIEZO1 a large mechanosensitive ion channel protein. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 66 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 67 Cystic fibrosis and ion channels 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 68 CRISPA-CAS and CF gene editing 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 69 Epilepsy voltage ion channels 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 70  Anesthesia and ion channels 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 71 G PROTEIN–COUPLED RECEPTORS (GPCRs) Also known as Seven-transmembrane domain receptors, 7TM receptors, Heptahelical receptors, and G protein–linked receptors (GPLR). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 72  G PROTEIN–COUPLED RECEPTORS (GPCRs G-protein of complexes is made up of alpha (α), beta (β) and gamma (γ) subunits. The beta and gamma subunits can form a stable dimeric complex referred to as the beta-gamma complex while alpha subunit dissociates on activation. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 73 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 74 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 75 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 76  G PROTEIN–COUPLED RECEPTORS (GPCRs The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein–coupled receptors are involved in many diseases, and are also the target of approximately 40% of all modern medicinal drugs. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 77 Classification 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 78 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 79 G PROTEIN–COUPLED RECEPTORS (GPCRs GPCRs—some 1,000 types are encoded by the human genome alone Examples of GPCRs include Beta-adrenergic receptors, which bind epinephrine; Prostaglandin receptors, which bind inflammatory substances called prostaglandins Rhodopsin which contains a photoreactive chemical called retinal that responds to light signals received by rodcells in the eye. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 80 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 81 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 82  11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 83 cAMP pathway and GPCR Adrenergic Receptors B- adrenergic 11/24/2024 cAMP SIGNAL TRANSDUCTION MECHANISMS 84 pathway  GPCR and cAMP-dependent pathway Activated GPCRs cause a conformational change in the attached G protein complex, which results in the Gs alpha subunit's exchanging GDP for GTP and separation from the beta and gamma subunits. The Gs alpha subunit, in turn, activates adenylyl cyclase, which quickly converts ATP into cAMP. This leads to the activation of the cAMP-dependent pathway. This pathway can also be activated downstream by directly activating adenylyl cyclase or PKA. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 85 cAMP The stimulation of glycogen breakdown by PKA epinephrine involves a G-protein-linked PK receptor, a G Protein, adenylyl cyclase and cAMP, and several PA protein kinases before glycogen phosphorylase Glycogen Glycogen1P is activated. Fig. 11.16  Phosphorylase kinase and phosphorylase a Glycogen breakdown 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 87 The Protein kinase A (PKA) enzyme is also known as cAMP-dependent enzyme because it gets activated only if cAMP is present. Once PKA is activated, it phosphorylates a number of other proteins including: Phosphorylase kinase Phosphorylase b enzymes that convert glycogen into glucose ( glycogen phosphorylase) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 88 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 89 Molecules that activate and inactivate cAMP pathway include: Gai Protein Activates Epinephrine Inactivates Caffeine Gai Theophylline cAMP PDE theophylline 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 90  DEACTIVATION The pathway may also be deactivated downstream by directly inhibiting adenylyl cyclase or dephosphorylating the proteins phosphorylated by PKA. Molecules that inhibit the cAMP pathway include: Gi protein, which is a G protein that inhibits adenylyl cAMP cyclase phosphodiesterase which degrades cAMP reducingthe cAMP levels Gai protein, which is a G protein that inhibits adenylyl cyclase, reducing cAMP levels. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 91 Molecules that activate cAMP pathway include: Caffeine inhibit cAMP phosphodiesterase, which degrades cAMP - thus enabling higher levels of cAMP than would otherwise be had. Theophylline is a drug used in therapy for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma under a variety of brand names. relaxing bronchial smooth muscle increasing heart muscle contractility and efficiency; as a positive inotropic increasing heart rate: (positive chronotropic-)[ increasing blood pressure 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 92 Phosphatidylinositol , Phospholipase C (PLC) and a-adrenergic GPCR pathway a- adrenergic 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 93 phospholipase C 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 94  In the phosphatidylinositol signaling pathway, activated phospholipase C (PLC) by the binding extracellular signal molecule to the receptor on the cell surface catalyzes the hydrolysis of phosphatidylinositol-(4,5)-bisphosphate (PIP2) into two secondary messengers IP3 (inositol triphosphate) and (diacylglycerol) DAG, IP3 binds with the IP3 receptor in the membrane of the smooth endoplasmic reticulum and mitochondria to open Ca2+ channels. DAG helps activate protein kinase C (PKC), which phosphorylates many other proteins, changing their catalytic activities, leading to cellular responses. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 95 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 96  The effects of Ca2+ are also remarkable: It can activate the CaM kinase pathway, in which calcium-modulated protein calmodulin (CaM) binds Ca2+, undergoes a change in conformation, and activates CaM kinase. Which causes muscle contraction, glycogen metabolism and neurotransmitter secretion 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 97 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 98 Rho Pathway Rho Kinase this kinase is activated by GPCRs that are coupled to G12/G13 G-proteins. G12/G13 G-proteins regulate cell processes using guanine nucleotide exchange factors (GEFs). The free G-protein alpha subunit interacts with a guanosine nucleotide exchange factor(GEF) that facilitates the GDP-GTP exchange at another GTPase known as Rho. Rho-GDP (resting form) is activated when the GDP-GTP exchange occurs. The activated GTPase Rho goes on to activated Rho kinase. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 99 Rho Kinase (ROCK) (GEFs)--guanine nucleotide exchange factors GDI ---Rho guanine nucleotide dissociation inhibitor). GTPase-activating proteins (GAPs) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 100  11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 101 Rho kinase phosphorylates a number of substrate proteins. This phosphorylation controls a number of cellular functions such as: Smooth muscle contraction and proliferation Angiogenesis and synaptic remodeling Hypothesized to be important in the pathogenesis of pulmonary hypotension Rho kinase inhibitors are an up-and-coming area of drug development with a wide range of clinical indications Example Fasudil a selective Rho-Kinase inhibitor indicated for the management of cerebrovascular disorders such as vasospasm post-surgery for subarachnoid hemorrhage. It is currently under investigation for angina, acute cerebral thrombosis and pulmonary hypertension. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 102 Rho-associated kinase (Rho- kinase/ROCK/ROK) in health 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 103 RHO Protein Pathway 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 104  WHEN G PROTEIN SIGNALING IS DISRUPTED G protein-related diseases are characterized by either deficient or excessive G protein signal transmission, which arises through abnormal signal initiation, defective termination, or reduced levels of G proteins Deficient G protein signaling can arise through either reduced levels of G proteins, or through decrease signal initiation. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 105 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 106  RECEPTORS WITH KINASE ACTIVITY; A kinase is a type of enzyme that transfers phosphate groups from high- energy donor molecules, such as ATP to specific target molecules (substrates); the process is termed phosphorylation. For every phosphorylation event, there is a phosphatase, an enzyme that can remove phosphate residue and thus modulate signaling Kinase enzymes that specifically phosphorylate tyrosine amino acids are termed tyrosine kinases. SIGNAL TRANSDUCTION MECHANISMS 11/24/2024 107 RECEPTOR TYROSINE KINASE (RTKs) It is a cell surface receptor that also has a tyrosine kinase activity. The signal binding domain of the receptor tyrosine kinase is on the cell surface, while the tyrosine kinase enzymatic activity resides in the cytoplasmic part of the protein. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 108 How do the enzyme linked receptors work 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 109 Binding of signal molecules to the extracellular domains of receptor tyrosine kinase molecules causes two receptor molecules to dimerize. This brings the cytoplasmic tails of the receptors close to each other and causes the tyrosine kinase activity of these tails to be turned on. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 110  The activated tails then phosphorylate each other on several tyrosine residues. This is called autophosphorylation. The phosphorylation of tyrosines on the receptor tails triggers the assembly of an intracellular signaling complex on the tails. The newly phosphorylated tyrosines serve as binding sites for a variety of signaling proteins that then pass the message on to yet other proteins. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 111 The most important groups of signals that bind to receptor tyrosine kinases are: Peptide growth factors like nerve growth factor (NGF) and epidermal growth factor (EGF) Peptide hormones, like insulin. Insulin-like growth factor(IGF) 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 112 Example: the action of insulin 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 113 PIP3/ Atk Pathway (responds to insulin) PD I PI3 Kinase RAB GDP---RAB GTP GRB2 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 114 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 115 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 116 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 117 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 118 The MAPK/ERK pathway (also known as the Ras-Raf-MEK-ERK pathway) The signal ends when the DNA in the nucleus expresses a protein and produces some change in the cell, such as cell division. The pathway includes many proteins, including MAPK (mitogen- activated protein kinases, originally called ERK,extracellular signal- regulated kinases), which communicate by adding phosphate groups to a neighboring protein, which acts as an "on" or "off" switch. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 119 GERB2 & SOS 11/24/2024 SIGNAL TRANSDUCTION 120 MECHANISMS  The RAS protein has the following important features: 1. It is associated with the cytosolic face of the plasma membrane 2. It is a monomeric GTP-binding protein 3. Ras is active when GTP is bound to it and inactive when GDP is bound to it. Like the a subunit, Ras can hydrolyze the GTP to GDP 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 121 Ras-Raf-MEK-ERK pathway 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 122 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 123 The MAPK/ERK pathway (also known as the Ras-Raf-MEK-ERK pathway) When one of the proteins in the pathway is mutated, it can become stuck in the "on" or "off" position, which is a necessary step in the development of many cancers. Components of the MAPK/ERK pathway were discovered when they were found in cancer cells. Drugs that reverse the "on" or "off" switch are being investigated as cancer treatments 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 124 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 125 NON RECPETOR TYROSINE KINASE (nRTKs) Non-receptor tyrosine kinases are a subgroup of protein family tyrosine kinases, enzymes that can transfer the phosphate group from ATP to a tyrosine residue of a protein (phosphorylation). nRTKs regulate cell's growth, proliferation, differentiation, adhesion, migration and apoptosis and they are critical components in the regulation of the immune system. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 126  11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 127 The JAK-STAT system is a major signaling alternative to the second messenger system and is an example of nRTK. The JAK-STAT system consists of three main components: 1. a receptor 2. Janus kinase (JAK) Family proteins JAK1 JAK2 JAK3 TYK2 3. Signal Transducer and Activator of Transcription (STAT). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 128 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 129 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 130 JAK-STAT signaling pathway The pathway transmits information from extracellular chemical signals to the nucleus resulting in DNA transcription and expression of genes involved in immunity, proliferation,differentiation, apoptosis and oncogenesis. Disrupted or dysregulated JAK-STAT functionality can result in immune deficiency syndromes and cancers. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 131 The main function of nRTKs is their involvement in signal transduction in activated T- and B-cells in the immune system. CD4 and CD8 receptors on T lymphocytes require for their signaling 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 132  Role of JAK/STAT Rheumatoid arthritis Rheumatoid arthritis, or RA, is an autoimmune and inflammatory disease , which means that your immune system attacks healthy cells in your body by mistake, causing inflammation (painful swelling) in the affected parts of the body. RA mainly attacks the joints, usually many joints at once. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 133 Role of JAK/STAT Crohn's disease Inflammatory bowel disease (IBD) is a term for two conditions (Crohn's disease and ulcerative colitis) that are characterized by chronic inflammation of the gastrointestinal (GI) tract. 1 Prolonged inflammation results in damage to the GI tract. https://www.youtube.com/watch?v=dnnsqiDjAgM 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 134  JAK-STAT pathway mutations are associated with many hematological malignancies caused by gaining constitutive functions e.g. MYELOPROLIFERATIVE NEOPLASMS; Myeloproliferative Neoplasms (MPNs) are blood cancers that occur when the body makes too many white or red blood cells, or platelets. This overproduction of blood cells in the bone marrow can create problems for blood flow and lead to various symptoms. MULTIPLE MYELOMA Multiple myeloma is a cancer that forms in a type of white blood cell called a plasma cell. Healthy plasma cells help you fight infections by making antibodies that recognize and attack germs. In multiple myeloma, cancerous plasma cells accumulate in the bone marrow and crowd out healthy blood cells. Rather than produce helpful antibodies, the cancer cells produce abnormal proteins that can cause complications. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 135 INTRACELLULAR RECEPTORS Intracellular receptors are receptors located inside the cell rather than on its cell membrane. Classic hormones that use intracellular receptors include thyroid and steroid hormones. Examples are: Class of nuclear receptors located in the cell nucleus and cytoplasm IP3 receptor located on the endoplasmic reticulum. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 136  The ligands that bind to them are usually: Intracellular second messengers like inositol trisphosphate (IP3) Extracellular lipophilic hormones like steroid hormones. Activated nuclear receptors attach to the DNA at receptor-specific hormone-responsive element (HRE) sequences, located in the promoter region of the genes activated by the hormone-receptor complex. Due to their enabling gene transcription, they are alternatively called inductors of gene expression. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 137 All hormones that act by regulation of gene expression have two consequences in their mechanism of action; 1. their effects are produced after a characteristically long period of time 2. their effects persist for another long period of time, even after their concentration has been reduced to zero, due to a relatively slow turnover of most enzymes and proteins that would either deactivate or terminate ligand binding onto the receptor. E.g. Thyroid Hormone 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 138 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 139 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 140 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 141 CONCLUSION The entire signal transduction system normally works astonishingly well, but serious problems can occur. Cancer is unregulated cell growth and occurs when the machinery tightly regulating cell growth breaks down. Mutations in growth factor receptors, G proteins, MAP kinases, and other molecules frequently contribute to cancer, and generally result in these molecules losing their normal switching function, staying in the activated form and therefore inappropriately stimulating these important enzyme cascades. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 142  The complexity of the signaling system makes for challenging research, but once understood it holds the promise for better treatments for cancer and other diseases. This is because each step in each pathway provides one or more targets for drugs. Designing a drug that could quiet the excess signaling caused by defective MAP kinase, for example, might provide a promising cancer treatment. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 143 The examples given thus far provide only an outline of how signal transduction cascades work and an overview of a few of the most important pathways. The actual process is much more complex, and there is much about the process that remains mysterious. Perhaps the biggest mystery is how the cell makes sense of all of the input from different growth factors, hormones, extracellular substrates, and so on to produce an appropriate response. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 144  The solution to this problem will result from a complete understanding and computer modeling of the biochemical and kinetic properties of the components of all these signaling cascades. _______________________.____________________________ 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 145 THANK YOU 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 146  The CFTR gene codes for an ABC transporter-class ion channel protein that conducts chloride and thiocyanate ions across epithelial cell membranes 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 147 4c. INTEGRINS Integrins are produced by a wide variety of cells; they play a role in: 1. Cell attachment to other cells and the extracellular matrix and 2. In the transduction of signals from extracellular matrix components such as fibronectin and collagen. Ligand binding to the extracellular domain of integrins changes the protein's conformation, clustering it at the cell membrane to initiate signal transduction. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 148  Integrins lack kinase activity; hence, integrin-mediated signal transduction is achieved through a variety of intracellular protein kinases and adaptor molecules, the main coordinator being integrin-linked kinase. Integrin signaling exist in two places mainly; Integrin-signaling in circulating blood cells and non-circulating cells such as epithelial cells. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 149 Important differences exist between two is that integrins of circulating cells are normally inactive. For example, cell membrane integrins on circulating leukocytes are maintained in an inactive state to avoid epithelial cell attachment; they are activated only in response to stimuli such as those received at the site of an inflammatory response. In a similar manner, integrins at the cell membrane of circulating platelets are normally kept inactive to avoid thrombosis. Epithelial cells (which are non-circulating) normally have active integrins at their cell membrane, helping maintain their stable adhesion to underlying stromal cells that provide signals to maintain normal functioning 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 150  4c. TOLL GATE RECEPTORS Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. TLRs are a type of pattern recognition receptor (PRR) and recognize molecules that are broadly shared by pathogens but distinguishable from host molecules, collectively referred to as pathogen-associated molecular patterns (PAMPs). 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 151 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 152  Proteins and peptides: Effect by Hormones, cytokines membrane Amino acid derivatives: receptors Catecholamines Extracellular Fatty acid derivatives: molecules Prostaglandins Effect by Signal intracellular Steroid hormones, molecule receptors Thyroxine, VD3 s Intracellular cAMP, cGMP, IP3, DG, Ca2+ molecules REFRENCES 1. KUMAR, ABBAS AND COTRAN, ROBBINS BASIC PATHOLOGY OF DISEASES, NINTH EDITION 2. GUYTON AND HALL, TEXT BOOK OF MEDICAL PHYSIOLOGY, ELEVENTH EDITION. 3. KIM E BARRET, SUSAN M BARMAN, SCOT BIOTANO,GANONG’S MDEICAL PHYSIOLOGY, TWENTY THIRD EDITION. 4. INTERNET SOURCES. 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 154 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 155 GPC Receptors G Receptors Signaling Pathway Protein GS Beta adrenergic receptors, Increase CAMP glucagon, histamine, serotonin Excitatory effects Gi Alpha2 adrenergic receptors, Decrease CAMP opioid, serotonin Cardiac K+ channel open- decrease heart rate Gq Vasopressin type 1, PLC- IP3 , DAG Increase Cytoplasmic Ca Gt Rhodopsin and colour opsins in Increase cGMP retinal rod and cone cells phosphodiesterase. 156 Decrease cGMP 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 158 11/24/2024 SIGNAL TRANSDUCTION MECHANISMS 159