3 4 BCOR 011 Lecture 19 Oct 12, 2005. Cell Communication Signal Transduction Chapter 11 Lecture Outline 1. Types of intercellular communication 2. The primary receiver Receptors 3. the concept of AMPLIFICATION 4. Types of receptors 5. Ion Channels Membrane depolarization 6. Trimeric GProtein coupled receptors the camp signal pathway the phophatidyl inositol pathway, Ca release 7. Tyrosine Kinase MAP Kinase Cascade 8. Internal cytosolic receptor systems External signal is received and converted to another form to elicit a response 1 2 xternal 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 General principles: 1. Signals act over different ranges. 2. Signals have different chemical natures. 3. The same signal can induce a different response in different cells. 4. Cells respond to sets of signals. 5. Receptors relay signals via intracellular signaling cascades.
7 8 Signals act over different ranges 1º messenger ndocrine ng distance. estrogen, inephrine Like Fig 11.4 Paracrine local ex. nitric oxide, histamines, prostaglandins Effector Enzymes Target Enzymes Cells detect signal & respond 2º messengers Neuronal/Synaptic ex. neurotransmitters direct contact Cellcell recognition ex. delta/notch 5 Signal transduction: ability of cell to translate receptorligand interaction into a change in behavior or gene expression 6 Primary essenger Secondary Messengers Target Enzymes Each protein in a signaling pathway Amplifies the signal by activating multiple copies of the next component in the pathway EXTRACELLULAR FLUID Plasma membrane CYTOPLASM 1 primary signal activates an enzyme activity, processes 100 substrates per second 1 Reception 2 Transduction 3 Response Primary enzyme activates 100 target enzymes Receptor Activation of cellular response Each of the 100 enzymes activates an additional 100 dowstream target enzymes Signal molecule Figure 11.5 Relay molecules in a signal transduction pathway Cascade Effect Each of the 10,000 downstream targets activates 100 control factors so rapidly have
eceptors relay signals via intracellular SIGNALING CASCADES Push doorbell Cellsurface receptors large &/or hydrophilic ligands ionchannellinked Ring bell Enzymatic activation of more ENZYMES Trimeric Gproteinlinked enzymelinked (tyrosine kinase) 9 10 Ion channel receptors xamples: Signal molecule (ligand) Gate closed Ligandgated ion channel receptor Ions Plasma Membrane Review: Remember the Na /K ATPase (Na /K pump)? [Na ] inside ~10mM; outside ~150mM [K ] inside ~100mM; outside ~5mM cell has membrane potential ~ 60mV uscle Contraction Gate open Na Cl erve Cell communication Gate close Cellular response 60mV K A 11 12
15 nerve impulse (action potential) 16 specifically let ions through membrane keys : small molecules (ligandgated) or change in membrane potential (voltagegated) Acetylcholine: common neurotransmitter 60 mv inside 13 opens ligandgated Na channels on muscle cell and some nerve cells 14 ated ion channels specifically let ions through membrane keys : small molecules (ligandgated) Gated ion channels specifically let ions through membrane keys : small molecules (ligandgated) 60 mv inside 10 mv inside Influx of Na ions causes local, transient depolarization of membrane potential
specifically let ions through membrane keys : small molecules (ligandgated) or change in membrane potential (voltagegated) specifically let ions through membrane keys : small molecules (ligandgated) or change in membrane potential (voltagegated) 10 mv inside 10 mv inside flux of Na ions causes local, transient depolarization of embrane potential erve impulse (action potential) 17 Influx of Na ions causes local, transient depolarization of membrane potential nerve impulse (action potential) 18 ated ion channels specifically let ions through membrane keys : small molecules (ligandgated) or change in membrane potential (voltagegated) 10 mv inside flux of Na ions causes local, transient depolarization of embrane potential erve impulse (action potential) 19 a. polarized b. Action potential Initiated by Ligandgated gated Na channels opening Local depolarization Na Depolarization opens Voltagegated gated Na channels K repolarization Na channels close K channels open Action potential Propagates to as more Transmission of action potential Na K Na 20
ction potential: erve impulse; rapid, elfpropagating electrical signal Signal transmitted to muscle cell across a synapse a. Depolarization opens voltagegated Ca 2 channels Muscle cell a. b. Ca 2 rushes in; Vesicles fuse with membrane Muscle cell b Muscle cell c. Neurotransmitter released; opens ligandgated Na channels on muscle cell 21 Depolarizes muscle cell Signal: electrical to chemical to electrical 22 c. epolarization of Muscle Cell Results in release of [Ca ]: ypically in cytosol Ca is 10 7 M, aintained ultralow by active transport umps Ca /ATPases vacuums a Stored in mooth ndoplasmic eticulum Turning off the synapse.. Acetylcholine degraded by acetylcholinesterase or removed by reuptake & endocytosis a. b. if not removed a,b Pesticides c Nerve gases Potent enzyme inhibitors a from SER Cytosol riggers Activation of Myosin ATPase c. Postsynaptic membrane can t repolarize Paralysis, Tetany 23 24
ellsurface receptors large &/or hydrophilic ligands nchannellinked Trimeric G proteinlinked receptors: largest family of cellsurface receptors 7pass membrane receptor ligand rimeric Gproteinlinked Ligand binding nzymelinked (tyrosine kinase) activates Gprotein by GTP exchange GproteinGTP 25 26 Segment that interacts with G proteins Gproteinlinked Receptor CYTOPLASM Signalbinding site GDP Plasma Membrane Gprotein (inactive) Trimeric Gproteinlinked receptors Enzyme Activated Receptor GDP Signal molecule GTP Inctivate enzyme Gprotein activation molecular switch (b) Ligand binds Gprotein associates (c) GDPGTP exchange αsubunit dissociates inactive GTP Activated Effector enzyme GDP Active GProteinGTP > allosteric modulator of target effector enzyme active P i 27 28
Like Fig 119 31 32 All Gproteins similar structure/activation There are TWO broad subclasses of trimeric Gproteinactivated signal transduction pathways: An activated G α proteingtp Can trigger the formation of camp, which then acts as a second messenger in cellular pathways First messenger (signal molecule such as epinephrine) G protein Adenylyl cyclase depends on their target effector enzymes A. adenylyl cyclase B. phospholipase C Gproteinlinked receptor GTP ATP camp Protein kinase A 29 Figure 11.10 Cellular responses 30 proteingtp activation of ffector Enzyme adenylyl cyclase roduces the 2 nd messenger camp Activated Gprotein camp activates target enzyme Protein Kinase A (PKA) Inactive PKA phosphorylates target proteins Active PKA
35 36 rotein Kinase A hosphorylates downstream target enzymes inactive Phosphorylase kinase P active Breaks down Starch A Signal Cascade amplification Binding of epinephrine to Gproteinlinked receptor (1 molecule) Transduction Inactive G protein Active G protein (10 2 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (10 2 ) ATP Cyclic AMP (10 4 ) Inactive protein kinase A Active protein kinase A (10 4 ) Inactive phosphorylase kinase Active phosphorylase kinase (10 5 ) Inactive glycogen phosphorylase Active glycogen phosphorylase (10 6 ) Response Glycogen Into Glucose 33 Figure 11.13 34 Glucose1phosphate (10 8 molecules) 1 10 2 10 4 10 5 10 6 10 8 What are targets for Protein Kinase A?? camp regulated pathways How to shut it off? No ligand Gprotein αsubunit is on a timer Function target tissue signal Glycogen breakdown muscle,liver epinephrine Heart rate cardiovascular epinephrine Water reabsorption kidney antidiuretic hormone Auto Shutoff Inherent GTPase activity
ow to shut it off? 39 How do you turn it off? 40 kinases phosphatases Diametrically Opposed camphosphodiesterase rapidly cleaves camp Remember: whether you active or inactivate by adding P depends on the specific protein (so short lived) 37 38 What if you can t turn off cascade? Vibrio cholera causes cholera 7 great pandemics, Ganges Valley, Bangladesh Normal gut: H 2 0, NaCl, NaHCO 3 secretion controlled by hormones via Gs/cAMP signal pathways V. cholera secretes enterotoxin, chemically modifies αgs no GTPase activity stays ON TWO subclasses of trimeric Gproteinactivated signal transduction pathways: A. target protein adenylate cyclase camp> PKA B. target protein phospholipase C Severe watery diarrhea dehydration, death
target effector enzyme is Phospholipase C PIP 2 PLC cleaves a membrane phospholipid (Phoshatidyl inositol) to two 2nd Messengers: DAG Lipid Soluble Inositol1,4,5Trisphosphate (InsP3) & InsP 3 Water Soluble Diacylglycerol (DAG) 41 42 DAG Activates Protein Kinase C (Starts Cascade) InsP 3 Ligand for ER ligandgated Ca channels Response: Protein Kinase C phosphorylates target proteins (ser & thr) cell growth regulation of ion channels cytoskeleton increases cell ph Protein secretion Ca Binds & activates calmodulin Calmodulinbinding proteins activated (kinases & phosphatases) levels 43 44
Figure 11.12 to a receptor, leading to activation of phospholipase C. EXTRA CELLULAR FLUID Endoplasmic reticulum (ER) 4 IP 3 quickly diffuses through the cytosol and binds to an IP 3 gated calcium channel in the ER membrane, causing it to open. Signal molecule (first messenger) Gproteinlinked receptor IP 3 gated calcium channel Ca 2 plasma membrane phospholipid called PIP 2 into DAG and IP 3. G protein GTP Ca 2 (second messenger) Phospholipase C 5 Calcium ions flow out of the ER (down their concentration gradient), raising the Ca 2 level in the cytosol. Various proteins activated a second messenger in other pathways. PIP 2 DAG IP 3 (second messenger) Cellular response 6 The calcium ions activate the next protein in one or more signaling pathways. 45 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 7pass membrane receptor catalyzes GTP exchange to G a subunit of trimeric Gprotein active G a subunitgtp is allosteric activator of effector enzymes: ADENYLATE CYCLASE: makes cyclic AMP PHOSPHOLIPASE C: makes DAG and IP 3 these second messengers activate target enzymes Trigger cascades Must shut off cascade: removal of ligand, hydrolysis of GTP, phosphodiesterase, protein phosphatases, Ca ion pumps 46