Lecture I: Growth Factors and Receptors What is Signal Transduction? Signal Transduction is the process by which a cell converts an extracellular signal into a response. Involved in: Cell-cell communication Cell’s response to environment Intracellular homeostatsis- internal communication
Generic Signalling Pathway Signal Receptor (sensor) Transduction Cascade Targets Response Altered Metabolism Metabolic Enzyme Gene Regulator Cytoskeletal Protein Altered Gene Expression Altered Cell Shape or Motility Adapted from Molecular Biology of the Cell,(2002), 4th edition, Alberts et al.
Components of Signalling What can be the Signal? External message to the cell
Peptides / Proteins- Growth Factors
Amino acid derivatives - epinephrine, histamine
Other small biomolecules - ATP
Gases - Nitric Oxide (NO)
Signal = LIGAND Ligand- A molecule that binds to a specific site on another molecule, usually a protein, ie receptor
Components of Signalling What are Receptors? Sensors, what the signal/ligand binds to initiate ST
Hydrophillic Ligand Cell-Surface Receptor Plasma membrane Hydrophobic Ligand Carrier Protein Intracellular Receptor Nucleus Adapted from Molecular Biology of the Cell,(2002), 4th edition, Alberts et al.
Growth Factors Ligands which bind enzyme linked receptors Signal diverse cellular responses including: Proliferation Differentiation Growth Survival Angiogenesis Can signal to multiple cell types or be specific
Growth Factors Factor Principal Source Primary Activity Comments PDGF platelets, endothelial cells, placenta promotes proliferation of connective tissue, glial and smooth muscle cells two different protein chains form 3 distinct dimer forms; AA, AB and BB EGF submaxillary gland, Brunners gland promotes proliferation of mesenchymal, glial and epithelial cells TGF- common in transformed cells may be important for normal wound healing related to EGF FGF wide range of cells; protein is associated with the ECM promotes proliferation of many cells; inhibits some stem cells; induces mesoderm to form in early embryos at least 19 family members, 4 distinct receptors NGF promotes neurite outgrowth and neural cell survival several related proteins first identified as proto-oncogenes; trkA ( trackA ), trkB, trkC Erythropoietin kidney promotes proliferation and differentiation of erythrocytes TGF- activated TH 1 cells (T-helper) and natural killer (NK) cells anti-inflammatory (suppresses cytokine production and class II MHC expression), promotes wound healing, inhibits macrophage and lymphocyte proliferation at least 100 different family members IGF-I primarily liver promotes proliferation of many cell types related to IGF-II and proinsulin, also called Somatomedin C IGF-II variety of cells promotes proliferation of many cell types primarily of fetal origin related to IGF-I and proinsulin
Growth Factor Receptors
Most growth factors bind Receptor Tyrosine Kinases
Growth Factor Receptor Activation I RTK RS/TK
Growth Factor Receptor Activation II
Growth signal autonomy, Insensitivity to anti-growth signals, Resistance to apoptosis: Uncouple cell’s growth program from signals in the environment. Growth factors in normal cells serve as environmental signals. Growth Factor ST and Cancer Growth factors regulate growth, proliferation, and survival. These are all deregulated in cancer. Hanahan and Weinberg, (2000) Hallmarks of Cancer, Cell (100) 57
Growth factors with Oncogenic Potential PDGF, originally shown to regulate proliferation, was also shown to have homology to v-sis , the simian sarcoma virus. Other viral oncogenes encoded protein products that were growth factors that often overexpressed in cancer such as TGF-a. Autocrine signalling leads to deregulated growth. PDGF family Neurotrophins A chain NGF B chain (c-sis) BDNF FGF Family NT3 acidic FGF Cytokines (Hematopoietic) basic FGF IL-2 EGF Family IL-3 EGF M-CSF TGF-a GM-CSF
GF Receptors with Oncogenic Potential EGFR , kinase activity stimulated by EGF-1 and TGF-a involved in cell growth and differentiation, was linked via sequence homology to a known avian erythroblastosis virus onocgene, v- erbB . Since then, many oncogenes have been shown to encode for GFRs. EGFR family Insulin Receptor family erbB1 ( c-erbB ) IGF-1 (c- ros ) erbB2 ( neu ) Neurotrophins FGF Family NGFR ( trk ) FGFR-1( fig) BDNFR ( trk -B) FGFR-2(K- sam) NT3 R ( trk -C) PDGFR Family CSF-1R (c- fms ) SLF R (c- kit )
Induction of cancer by alternations in several types of proteins involved in cell growth control
Signal Transduction and Cancer
Lecture II: Intracellular Signalling
What are some signalling pathways?
What are their cell biological outputs?
How do these result in the cancer phenotype?
How can we exploit signalling pathways for therapy?
Generic Signal Transduction
RTK Signal Transduction
Signal Transduction Downstream effectors Protein Signaling Modules (Domains) SH2 and PTB bind to tyrosine phosphorylated sites SH3 and WW bind to proline-rich sequences PDZ domains bind to hydrophobic residues at the C-termini of target proteins PH domains bind to different phosphoinositides FYVE domains specifically bind to Pdtlns(3)P (phosphatidylinositol 3-phosphate)
Mechanisms for Activation of Signaling Proteins by RTKs Activation by membrane translocation Activation by a conformational change Activation by tyrosine phosphorylation
Mechanisms for Attenuation & Termination of RTK Activation 1) Ligand antagonists 2) Receptor antagonists 3) Phosphorylation and dephosphorylation 4) Receptor endocytosis 5) Receptor degradation by the ubiquitin-proteosome pathway
Activation of MAPK Pathways by Multiple Signals Growth, differentiation, inflammation, apoptosis -> tumorigenesis
Overview of MAPK Signaling Pathways
The MAPK Pathway Activated by RTK
P RTK ST- PI3K pathway
Proto-oncogenes that Encode for Signalling Proteins Serine/Threonine Kinases c- raf family akt Non-receptor Tyrosine Kinases src abl Receptor associated binding proteins c-ras family
Ras recruits Raf to the membrane
C-abl: Tyrosine Kinase activation by Translocation
ST intermediates can be targets for anti-cancer drugs Kinases: Raf
ST intermediates can be targets for anti-cancer drugs Kinases: Bcr-Abl