Cell-Cell Communication - Cell Biology MED102 PDF

Cell-Cell Communication Cell Biology MED102 Prof A. Stephanou  Objectives To be familiar with the following concepts: 1. Types of intercellular communication & receptors 2. The primary receiver – Receptors 3. - the concept of LIF...

Cell-Cell Communication Cell Biology MED102 Prof A. Stephanou  Objectives To be familiar with the following concepts: 1. Types of intercellular communication & receptors 2. The primary receiver – Receptors 3. - the concept of LIF AMP TIO ICA N 4. Ion Channels – Membrane depolarization 5. Trimeric G-Protein coupled receptors - the cAMP signal pathway - the phophatidyl inositol pathway, Ca++ release 7. Tyrosine Kinase – MAP Kinase Cascade 8. Receptor defects and diseases 3 Communication and Cell Signalling Cells must communicate in order to proliferate, differentiate, migrate and maintain a functional state cell-cell signalling permits coordinated function of cells within and between tissues, up to the organism level Signalling informs cells what they are, where they are, and what they should be doing.  External signals are converted to Internal Responses Cells sense and respond to the environment Prokaryotes: chemicals Humans: light - rods & cones of the eye sound – hair cells of inner ear chemicals in food – nose & tongue Cells communicate with each other Direct contact Chemical signals Local and Long-Distance Signaling Cells in a multicellular organisms communicate by chemical messengers Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells In local signaling, animal cells may communicate by direct contact In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances In long-distance signaling, plants and animals use chemicals called hormones  Signals act over different ranges Endocrine Paracrine local ex. nitric oxide, histamines prostaglandins Long distance ex. estrogen, epinephrine direct contact Neuronal/Synaptic Cell-cell recognition ex. neurotransmitters ex. delta/notch  Local and Long-Distance Signaling EXTRACELLULAR CYTOPLASM FLUID Plasma membrane Reception Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Signal Receptor (sensor) Transduction Cascade Targets Response  What can be the Signal? External message to the cell Signal = LIGAND Ligand- A molecule that binds to a specific site on another molecule, usually a protein, ie receptor Peptides / Proteins- Growth Factors Amino acid derivatives - epinephrine, histamine Other small biomolecules - ATP (adenosine tri-phosphate) Steroids, prostaglandins Gases - Nitric Oxide (NO) Photons- such as g-irradiation Damaged DNA  What are Receptors? Senses and initiates Signal Transduction (ST) Extracellular receptor / Cell surface Cell Surface Receptor Types: Most common Enzyme-linked Receptor eg Growth Factor Receptors Intracellular (steroid receptors)  Signal Transduction Pathway Signal Receptor (sensor) Transduction Cascade Targets Metabolic Gene Regulator Cytoskeletal Protein Enzyme Altered Altered Altered Metabolism Gene Cell Shape Response Expression or Motility Adapted from Molecular Biology of the Cell,(2002),, Alberts et al.  Intracellular Receptors Some receptor proteins are intracellular, found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the steroid and thyroid hormones of animals An activated hormone-receptor complex can act as a transcription factor, turning on specific genes Hormone EXTRACELLULAR (testosterone) The steroid FLUID hormone testosterone passes through the plasma membrane. Plasma membrane Receptor Testosterone binds protein to a receptor protein Hormone- in the cytoplasm, receptor activating it. complex The hormone- receptor complex enters the nucleus and binds to specific genes. DNA mRNA The bound protein stimulates the transcription of the gene into mRNA. NUCLEUS New protein The mRNA is translated into a specific protein. CYTOPLASM  3 Types of Extracellular Cell-surface receptors: Large &/ bound by hydrophilic ligands ⚫ Ion-channel- linked Trimeric G-protein-linked ⚫ Enzyme-linked (tyrosine kinase) 1. Trimeric G-protein-linked receptors A G-protein-linked receptor is a plasma Signal-binding site membrane receptor that works with the help of a G protein Segment that interacts with The G-protein acts as an on/off switch: If GDP is G proteins bound to the G protein, the G protein is inactive G-protein-linked Activated Inctivate Plasma Membrane Signal molecule Receptor Receptor enzyme GDP G-protein GDP GTP CYTOPLASM (inactive) Enzyme Activated Effector enzyme GTP GDP Pi Cellular response G-protein activation “molecular switch” inactive (b) Ligand binds G-protein associates (c) GDP-GTP exchange -Subunit dissociates Active G-Protein-GTP -> allosteric modulator active of target effector enzyme  All G-proteins – similar structure/activation There are TWO broad subclasses of trimeric G-protein-activated signal transduction pathways: depends on their target effector enzymes A. adenylyl cyclase B. phospholipase C An activated Ga-protein-GTP – Can trigger the formation of cAMP, which then acts as a second messenger in cellular pathways First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein GTP G-protein-linked receptor ATP cAMP Protein kinase A Cellular responses Protein Kinase A Phosphorylates downstream target enzymes Phosphorylase kinase inactive + P active Breaks down Starch Into Glucose  Reception Binding of epinephrine to G-protein-linked receptor 1 A Signal (1 molecule) Cascade Transduction Inactive G protein Active G protein (102 molecules) 102 amplification Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A 104 Active protein kinase A (104) 105 Inactive phosphorylase kinase Active phosphorylase kinase (105) 106 Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response 108 Glycogen 20 Glucose-1-phosphate 8 (10 molecules) Protein Phosphorylation and Dephosphorylation Receptor Signal molecule Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase ATP 2 ADP Active P protein PP kinase Pi 2 Inactive protein kinase ATP ADP Active P 3 protein PP kinase Pi 3 Inactive protein ATP ADP P Active Cellular PP protein response Pi How to shut it off? cAMP-phosphodiesterase rapidly cleaves cAMP (so short lived) 22  Protein Phosphorylation and Dephosphorylation In many pathways, the signal is transmitted by a cascade of protein phosphorylations Phosphatase enzymes remove the phosphates This phosphorylation (kinases) and dephosphorylation (phosphotases) system acts as a molecular switch, turning activities on and off  What are targets for Protein Kinase A?? cAMP regulated pathways Function target tissue signal Glycogen breakdown muscle, liver epinephrine Heart rate cardiovascular epinephrine Water reabsorption kidney antidiuretic- hormone B. target protein phospholipase C target effector enzyme is Phospholipase C PLC cleaves a membrane phospholipid (Phoshatidyl inositol) to two 2nd Messengers: Inositol-1,4,5-Trisphosphate (InsP3) & Diacylglycerol (DAG) Calcium Signaling DAG Activates Protein Kinase C (Starts Cascade) InsP3 Ligand for ER ligand- gated Ca++ channels  Ca++ levels Signal 2. Receptor tyrosine kinases Signal-binding site molecule  Helix in the Signal membrane molecule Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins Dimer CYTOPLASM (inactive monomers) Activated relay proteins Cellular Tyr Tyr P Tyr Tyr P P Tyr Tyr P response 1 Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Cellular 6 ATP 6 ADP response 2 Activated tyrosine- Fully activated receptor kinase regions tyrosine-kinase (unphosphorylated (phosphorylated Inactive dimer) dimer) relay proteins Receptor tyrosine kinases-Insulin Receptor Growth Factor Receptors 3 Ion channel receptor An ion channel receptor acts as a gate when the receptor changes shape When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor Ion channel receptors Signal molecule (ligand) Gate closed Ions Ligand-gated Plasma ion channel receptor Membrane Examples: Gate open Muscle Contraction Nerve Cell communication Cellular response Gate close 31 Review: Na+ Cl- Remember the Na+/K+ ATPase (Na+/K+ pump)? [Na+] inside ~10mM; outside ~150mM -60mV [K+] inside ~100mM; outside - K+ A- ~5mM + - - cell has membrane potential ~ + - - + - -60mV + + +  Acetylcholine: common neurotransmitter opens ligand-gated Na+ channels on muscle cell and some nerve cells Action potential: nerve impulse; rapid, self-propagating electrical signal Muscle cell Signal transmitted to muscle Muscle cell across a synapse cell a. a. Depolarization opens voltage-gated Ca+2 channels Muscle cell b. Ca+2 rushes in; Vesicles b. fuse with membrane c. Neurotransmitter released; opens ligand-gated Na+ channels on muscle cell Depolarizes muscle cell c. Signal: electrical to chemical to electrical  The Specificity of Cell Signaling Different kinds of cells have different collections of proteins These differences in proteins give each kind of cell specificity in detecting and responding to signals The response of a cell to a signal depends on the cell’s particular collection of proteins Pathway branching and “cross-talk” further help the cell coordinate incoming signals The Specificity of Cell Signaling Signal molecule Receptor Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads Cell B. Pathway branches, to a single response leading to two responses Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs Cell D. Different receptor between two pathways leads to a different response  Termination of the Signal Inactivation mechanisms are an essential aspect of cell signaling When signal molecules leave the receptor, the receptor reverts to its inactive state  Intracellular Signalling & Diseases What if you can’t turn off cascade? Vibrio cholera - causes cholera Normal gut: H20, NaCl, NaHCO3 secretion controlled by hormones via Gs/cAMP signal pathways V. cholera – secretes enterotoxin, chemically modifies Gs – no GTPase activity - stays ON Severe watery diarrhea – dehydration, death  Beta blockers The drug has the same shape as the shape of neurotransmitter combining with the receptor molecule… Receptors for everything (!!!) that fits into the shape (lock and Key model) Proto-oncogenes - Signalling Proteins Proto-oncogenes- protiens/enzymatic kinases capable of promoting cellular transformation Many Oncogenes are Viral protein kinases that are constitutively active Serine/Threonine Kinases c-raf family-downstream activator ERK akt Non-receptor Tyrosine Kinases src abl Receptor associated binding proteins c-ras family These are commonly amplified and overexpressed in most forms of human breast cancer Cancer Drug-targeting therapy herceptin gefitinib AZD4309 AZD6244 Summary - signaling is endocrine, paracrine, synaptic, or direct cell contact - signal transduction is mediated by receptor proteins - Receptors bind primary signal (ligand) - Some amplification event occurs - Example: ligand gated ion channel opens influx of ions triggers change in activity (vesicle fusion in nerve end, contraction in muscle) - Example: ligand binds to 7-pass membrane receptor catalyzes GTP exchange to Ga-subunit of trimeric G-protein active Ga-subunit-GTP is allosteric activator of effector enzymes: - ADENYLATE CYCLASE: makes cyclic AMP - PHOSPHOLIPASE C: makes DAG and IP3 these second messengers activate target enzymes Trigger cascades - Must shut off cascade: removal of ligand, hydrolysis of GTP, phosphodiesterase, protein phosphatases, Ca++ ion pumps  On-Line Resources Mechanisms of Signal Transduction http://www-isu.indstate.edu/thcme/mwking/signal-transduction.html Clear, illustrated summaries of the various mechanisms of signal transduction Pathways http://www.biocarta.com/genes/PathwayGeneSearch.asp?geneValue=g Comprehensive illustrations of signaling pathways Extracellular Signal Molecules http://www.grt.kyushu-u.ac.jp/spad/menu.html Signals and the pathways stimulated by each Mammalian MAPK signalling pathways http://kinase.oci.utoronto.ca/signallingmap.html MAPK signaling pathway, with information on each component Small Molecule Platform http://www.onyx-pharm.com/onyxtech/small_molecule_platform.html The development of anti-cancer drugs that act on the ras signaling pathway Signal Transduction http://www.kumc.edu/biochemistry/bioc800/siglofra.htm Signal transduction from a medical viewpoint Viruses and Cancer http://www.geocities.com/tumorbio/vir/vir.htm History and current summary of viruses and human cancer Science Maagazine Signal Tansduction Knowledge Environment-Pathways http://stke.sciencemag.org/cm/index.dtl