target effector enzyme is Phospholipase C A. target protein adenylate cyclase camp-> PKA B. target protein phospholipase C two 2nd Messengers:

Transcription

1 COR 011 Cell Communication II Lect 19 Lecture Outline Signal molecule Activated Ras-GT A G-rotein And they tell friends And they tell friends And they tell friends 1. Finish Trimeric G-rotein: hospholipase C -DAG, I second messengers rotein C, Ca ++ release hapt 11 MAKKK 1 MAKKK 1. Nitric Oxide, cgm activation - consequences of failing to inactivate 0/17/05 rotein hosphatases MAKK i AT MAK AD i AT MAKK AD i AT MAK AD hosphorylation cascade 1response. osine - RAS G-, MA Cascade - Cell Cycle Control, Gene Control 4. Internal s Steroid - Gene Regulation WO subclasses of trimeric G--activated ignal transduction pathways: target effector enzyme is hospholipase C A. target adenylate cyclase cam-> KA B. target phospholipase C LC cleaves a membrane phospholipid (hoshatidyl inositol) to two nd Messengers: Inositol-1,4,5-Trisphosphate (Ins) & Diacylglycerol (DAG) 4

2 DAG Lipid Soluble I Ins Water Soluble 5 DAG Activates rotein C (Starts Cascade) Ins Ligand for ER ligandgated Ca ++ channels Ca ++ levels 6 1 A signal molecule binds to a receptor, leading to activation of phospholipase C. EXTRA- CELLULAR FLUID Signal molecule (first messenger) G--linked receptor I -gated calcium channel hospholipase C cleaves a plasma membrane phospholipid called I into DAG and I. G GT hospholipase C DAG functions as a second messenger in other pathways. I DAG I (second messenger) Response: rotein C phosphorylates target s (ser & thr) cell growth regulation of ion channels cytoskeleton increases cell ph rotein secretion Figure 11.1 Endoplasmic reticulum (ER) Ca + 4 I quickly diffuses through the cytosol and binds to an I Ca + (second messenger) 5 Calcium ions flow out of the ER (down their con- Various s activated response 6 The calcium ions activate the next 7 Ca++ Binds & activates calmodulin Calmodulin-binding s activated (kinases & phosphatases) 8

3 11 1 hut Off remember, signal needs to be transient Must shut off cascade: removal of ligand, (self)-hydrolysis of GT, remove I, phosphatases, Ca ++ ion pumps Direct activation - signal: nitric oxide (NO) It s a gas! lipid soluble, binds directly to activate enzyme made by: endothelial cells (line blood vessels) target: guanylyl cyclase GT->cGM NO synthase response: relaxes smooth muscle vessels dilate, blood flow +NO arginine citrulline 9 10 Nitroglycerine taken to relieve angina target Shut off by cgm phosphodiesterase 1977 Ferid Murad Nitroglycerine acts to elict release of NO, relaxes cardiac muscle 1998 Nobel rize Murad, Furchgott, Ignarro

4 Sildenafil citrate (VIAGRA) Nitro glycerine Shut off By cgm phosphodiesterase VIAGRA 1 14 cell-surface receptors a. ion-channel-linked b. G--linked c. rotein-kinase associated (enzyme-linked) 15 Mitogen Activated rotein- associated receptors receptor has enzymatic activity - only when ligand binds ligand: allosteric effector -> conformational change receptor tyrosine kinases Growth & differentiation control of cell cycle control of gene expression 16

5 rowth Factor itogen-activated ignaling Cascade CYTOLASM hosphorylation cascade Transduction EGFR epidermal growth factor receptor Monomer receptor 1 transmembrane segment Ligand binds receptors dimerize Activates kinase autophosphorylate DNA transcription factor transcription factor Response Scaffold to Bind/activate Target s Figure NUCLEUS mrna Gene 17 GD/GT exchange Activate Ras G- EGF growth facto or mitogen 18 Mitosis-generator Signal molecule αhelix in the Membrane tyrosine kinases Signal-binding site Signal molecule tyrosine kinases can activate ras ras is a monomeric G- molecular switch osines Figure 11.7 CYTOLASM tyrosine kinase s (inactive monomers) Dimer Activated relay s 6 AT 6 AD response 1 response Activated tyrosinekinase regions (unphosphorylated Fully activated receptor tyrosine-kinase (phosphorylated relay s 19 0

6 phosphorylation cascade Figure 11.8 MA kinase 1 MA kinase Signal molecule Ras-GT Activated relay molecule i MA kinase 1 AT MA AD 1 A relay molecule activates kinase 1. kinase 1 transfers a phosphate from AT to an inactive molecule of kinase, thus activating this second kinase. MA kinase kinase AT AD 5 Enzymes called MA phosphatases () catalyze the removal of kinase the phosphate groups i from the s, making them inactive and available for reuse. AT AD i kinase then catalyzes the phosphorylation (and activation) of kinase. hosphorylation cascade 4 Finally, active kinase phosphorylates a (pink) that brings about the cell s response to the signal. 1response Ras activation sets off a phosphorylation cascade MAKK MAK 1, ,000 MAKKK Mitogen Activated rotein s MAKs Controls: -Transcription Factors -Translation Factors -Cell Division ow do you turn it off? phosphatases GTase (GT->GD + ) ROBLEMS IN CANCER: - broken ras won t shut off - Broken receptor thinks ligand there even when it isn t -broken MAK on all the time, even when not phosphorylated RESULT: continuous signal for cell to divide molecular switch on internal timer 4

7 Specific signal transduction cascades: 1. receptor-mediated cell-surface.receptor receptor-mediated intracellular Lipid soluble things: steroid hormones 5 Steroid Hormone Lipid soluble Crosses membranes Binds intracellular receptor In cytosol steroid receptor Complex Changes shape Releases from tether Travels to Nucleus steroid receptor Binds DNA Turns genes ON Figure 11.6 (testosterone) mrna NUCLEUS lasma membrane The mrna is translated into a specific. The steroid hormone testosterone passes through the plasma membrane. Testosterone binds to a receptor in the cytoplasm, activating it. Hormonereceptor complex The hormonereceptor complex enters the nucleus and binds to specific genes. The bound stimulates the DNA transcription of the gene into mrna. New 6 CYTOLAS The Specificity of Cell Signaling athway cross-talk Signal molecule The different combinations of s in a cell Give the cell great specificity in both the signals it detects and the responses it carries out Cell A. athway leads to a single response Response 1 Relay molecules Response Response Cell B. athway branches, leading to two responses Same hormone can give different responses in different cells Figure Activation or inhibition 7 Cell C. Cross-talk occurs Response 4 Response 5 Cell D. Different receptor 8

8 pecific pathways 1. Cell-surface receptor mediated a. ion-channel-linked b. trimeric G--linked (i) adenylyl cyclase cam -> kinase A (ii) phospholipase C Ins, DAG, Ca ++, kinase C Direct activation - NO c. kinase-associated (enzyme-linked) tyrosine kinase monomeric G- (ras), MAKs. Intracellular receptors steroid hormones, dioxin 9