Presentation on theme: "Lecture #9. July 13,2001 Cell signaling: Receptor tyrosine kinases NO and NYC. Chapter 15. Axiom #9: Multitasking is essential for success."— Presentation transcript:
1Lecture #9. July 13,2001 Cell signaling: Receptor tyrosine kinases NO and NYC. Chapter 15. Axiom #9: Multitasking is essential for success
2The importance of G-proteins The Nobel Prize in Physiology or Medicine 1994"for their discovery of G-proteins and the role of these proteins in signal transduction in cells"Alfred G. GilmanMartin RodbellUSAUniversity of Texas, Southwestern Medical Center Dallas, TX, USANational Institute of Environmental Health Sciences Research Triangle Park, NC, USA1941 -
3The significance of “signal transduction in the nervous system" The Nobel Prize in Physiology or Medicine 2000"signal transduction in the nervous system"Arvid CarlssonPaul GreengardEric R KandelSwedenUSAGöteborg University Göteborg, SwedenRockefeller University New York, NY, USAColumbia University New York, NY, USA1923 -1925 -1929 -
4Peptide signaling The Nobel Prize in Physiology or Medicine 1999 The Nobel Prize in Physiology or Medicine 1999"for the discovery that proteins have intrinsic signals that govern their transport and localization in the cell"Günter BlobelUSARockefeller University New York, NY, USA and National Institute of Environmental Health Sciences Research Triangle Park, NC, USA1936 -
5How do cells regulate [Ca2+]? Sequester in ER, bind to proteins! Calmodulin binds 4 Ca2+ ionsIn most cases, CM +Ca2+ binds to an effectorAccordingly, CM –Ca2+ dissociates from targetCM/kinase
7Protein Tyrosine Kinases (PTK) 5 classes in the superfamilyAGC group: PKA, PKG, PKC, Rac, G-protein kinasesCaMK group: kinases regulated by Ca2+/CaMCMGC group: cyclin-dependent kinases ERK, MAP, Casein kinasePTK group: conventional protein tyrosine kinases Src, Abl, Fak, PDGF, IR5. OPK: Other Protein Kinases
8Tyrosine kinases can be cytosolic or integral membrane receptors .SubstrateSingle Membrane spanningHydrophobic domain.How many does the GPCR have?No membrane-spanning domain
9Src, is the product of the first proto-oncogene to be characterized. What are the substrates for TKs? Src, is a non-receptor tyrosine kinaseSrc, is the product of the first proto-oncogene to be characterized.Fariba Fana
10Even though Src is a cytoplasmic Tyrosine Kinase, Src and other proteins that have Src-homology domains can bind to RTKs!Src homology domains: (SH)
11Other proteins have homologies to Src domains SH Src-homology regions SH1 domain: Catalytic domain of the protein: kinase activitySH2 and SH3 domains: mediate protein-protein interactions in cellular signaling cascades: very common in proteins outside the Src family.SH2: binds peptides with consensus: (PTyr-Met/Val-X-Met)SH3: b-barrel. Interacts with proline-rich peptide targetsSH4 domain: myristylation and membrane-localization signal
12The Src homology 2 (SH2) domain has been found in a number of signal transduction pathways. Its primary function is to bind phosphotyrosines and in doing so localizing different proteins necessary to transmitt the proper function Pawson, 1997.Elegant experiments using a combinatorial approach showed that specificity for a particular protein is encoded in the amino acids following the phosphotyrosine Songyang, Monday, April :26SH2 Domains
13SH3 b-barrel of 5-6 anti-parallel b-strands. Binds a polyproline helix The loss of binding can lead to a constitutively active Src molecule and cancerWilliams, 1998
14Receptor tyrosine kinases All are single membrane-spanning proteins General RelevanceTyrosine phosphorylation is frequently an EARLY event in signaling.Amplification by downstream signaling elements greatly amplifies the effects of low levels of tyrosine phosphorylation that are most directly induced by extracellular triggers. Example: PLC and PI3KActivation of multiple kinases (kinase cascades) including ser/thr as well as tyrosine kinases, is a frequent consequence of these early events. Example: MAP KinaseThere is often cross-talk between tyrosine kinase-induced pathways and other, e.g. G protein, signaling pathways.
15Cell-cell recognition Cell cycle control Immune responses Development You know that I’m going to ask you why you should care about receptor tyrosine kinases!Activation of receptor tyrosine kinases ultimately leads to cell division or differentiation, for example, during embryonic development.Other functionsGrowth controlCell-cell recognitionCell cycle controlImmune responsesDevelopmentDifferentiationAre these processes important?What happens if a checkpoint looses function?
16Tyrosine Kinases and associated genes and proteins are implicated in developmental defects and cancer.Excessive activation of receptor tyrosine kinases can lead to uncontrolled growth and malignant transformation.Many defective or viral forms of tyrosine kinases and associated proteins are oncogenic:v-srcablerbB
17Classes of Receptor Tyrosine kinases EGFreceptor, NEU/HER2,HER3Insulin receptorPDGFFGFVEGFEph
18What makes a RTK active? a) Conformational change: b) Dimerization: Insulin Receptor Kinase (IRK) Binds insulinAutophosphorylatesActivates substrates including IRS-1 (insulin receptor substrate 1) by tyrosine phosphorylationb) Dimerization:PDGF Receptor: Binds platelet derived growth factor (PDGF)Monomeric integral membrane proteinActivates enzymes including PI3 kinase, Phospholipase Cg and GAP (GTPase activating protein) by tyrosine phosphorylation2. EGF Receptor3. Eph Receptor family: Erythropoietin producing hepatocellular carcinoma cell lineBinds to Ephrins (ligand)Role in neurogenesis (neuronal pathfinding)
19Response of the insulin receptor kinase (IRK) to ligand binding Fig. 15.20 Heterotetramer (2a, 2b)Insulin binding leads to change in structure (different from other RTKs)Conformation change activates b-subunit TK activityb subunit phosphorylates Tyr residues on cytoplasmic domains as well as downstream substrates (IRS)
20Three-dimensional structures of the insulin receptor tyrosine kinase (IRK) IRK conformational change upon activation loop phosphorylation. The N-terminal lobe of IRK is colored white and the C-terminal lobe is colored dark grey. The activation loop (green) contains autophosphorylation sites Y1158, Y1162 and Y1163, and the catalytic loop (orange) contains the putative catalytic base, D1132. Also shown are the unbound/bound ATP analog and tyrosine-containing substrate peptide (pink). [Hubbard, EMBO J. 16, 5572 (1997)]
21Once Tyr-Phosphorylated, the IRK activity trigerrs a number of signaling pathways. Phosphatidylinositol 3-hydroxy kinase, makes PIP2,PIP3Grb2, Sos, activates RasActivation of PI-PLC
22Unlike IRK, most RTKs are present as a monomer in the resting cell membrane
23Receptor Tyrosine Kinases Receptor protein-tyrosine kinases transmit signals across the plasma membrane, from the cell exterior to the cytoplasm.
24Receptor tyrosine kinases The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, up-regulates the enzymatic activity of the intracellular catalytic domain, which causes tyrosine phosphorylation of cytoplasmic signaling molecules.Fig
25Fibroblast Growth Factor Receptor Tyrosine Kinase During the metastasis of tumor cells, the adhesion between normal cells and cancerous cells must be broken. Many molecules involved in this process have been identified, and most are implicated in either heritable human diseases or cancer. For instance, members of the fibroblast growth factor receptor (FGFR) family have been linked widely to the development of cancer and disease.Dimeric assembly of 2 FGF2:FGFR1 complexes. FGF2 is colored orange, Ig-like domain 2 of FGFR1 is colored green, and Ig-like domain 3 of FGFR1 is colored cyan. [Plotnikov et al., Cell 98, 641 (1999)]
26N-CAM modulates tumor-cell adhesion to matrix by inducing FGF-receptor signaling UGO CAVALLARO, JOACHIM NIEDERMEYER, MARTIN FUXA, Nature Cell Biology 3, (July 2001)
27Eph receptor kinase Putative signaling effectors are in light shading. Erythropoietin producing hepatocellular carcinoma cell linePutative signaling effectors are in light shading.Proteins with known SH2 domains are depicted as oval shapes
28RTKs can activate the Ras pathway of cellular signaling Ras is a small G-protein (monomeric 21-kD)Mutant Ras proteins are unable to dissociate GTP, so they are stuck in the ON or proliferative state: ras (gene) mutations found in 30% of human cancers.Do you think mutations in Ras-GAPs can lead to disease? Oui!
29Steps in the activation of Ras by RTKs. Fig. 15.24 Raf is a PK that triggers MAP-K pathwayRafSH2 binds RTK, SH3 binds SOSc-fos, c-junCell proliferationRas-GEF
30NO signaling The Nobel Prize in Physiology or Medicine 1998 The Nobel Prize in Physiology or Medicine 1998"for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system"Robert F. FurchgottLouis J. IgnarroFerid MuradUSASUNY Health Science Center Brooklyn, NY, USAUCLA School of Medicine Los Angeles, CA, USAUniversity of Texas, Health Science Center Dallas, TX, USA1916 -1941 -1936 -
31Nitric oxide is a free radical It contains an unpaired electron.N=ORole in macrophage killing of pathogensNO also acts as a second messenger that causes relaxation of smooth muscle
32Signal transduction pathway mediated by NO and cGMP. PDE5136252
33Nitric oxide (NO) is a small membrane-permeating free radical Nitric oxide (NO) is a small membrane-permeating free radical. It is synthesized as needed, since it cannot be stored in vesicles. Consequently, regulation of its synthesis is crucial.Nitric oxide synthase (NOS) converts arginine to NO and citrullineNOS is activated by Ca2+/calmodulinNOS is inactivated by phosphorylationNOS is located only in neurons in CNS (2% of all cells)
34NOS is a dystrophin-binding protein Nitric Oxide Synthase Complexed with Dystrophin and Absent from Skeletal Muscle Sarcolemma In Duchenne Muscular DystrophyJ. E. Brenman , D. S. Chao , H. Xia , K. Aldape , and D. S. Bredt 11 Department of Physiology, University of California, San Francisco School of Medicine , USANOS is a dystrophin-binding protein
35Pfizer web siteVIAGRA enables many men with erectile dysfunction to respond to sexual stimulation. When a man is sexually excited, VIAGRA helps the penis fill with enough blood to cause an erection. After sex is over, the erection goes away.
36How does Viagra work?Enlivens the male “wunder horn” with fresh sound?Sildenafil inhibits PDE5 (phosphodiesterase 5)cGMP build up in the cellEnhances the effects of NONot for patients using nitrates (nitroglycerine)
37Summary Be able to outline pathways for: GPCR (Fig. 15.13) IRK activation and downstream effectorsRTK and activation of RasCompare and contrast activation events mediated by Ca2+, cAMP and NO.
38FinitoFor MondayRead Chapter 16, the Biology of Cancer