2010 Lecture 20

From CellBiology

Cell Signaling 2

This lecture is the second in a series of lectures on cell signaling. The first lecture was a general introduction to the different signaling mechanisms and steroid pathways. The following lecture looks in detail at two specific examples of signaling pathways: G Protein-Coupled Signal and Receptor Tyrosine Kinases. Note that you have already been introduced to signaling in many of your other lecture topics and the lectures on stem cells and development will further discuss cell signaling events.


2008: ANAT3231 Lecture 18-19 Cell Signaling

Signal transduction pathways.png

Signaling

Table 20-1. Characteristic Properties of Principal Types of Mammalian Hormones

Classes of Surface receptor

G Protein-Coupled Signal Pathways

Figure 20-6. Schematic overview of common signaling pathways downstream from G protein–coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs)

Activation of adenylyl cyclase following binding to a Gs protein – coupled receptor

G-protein-coupled receptor structure G-protein coupled receptors
G-protein-coupled receptor structure G-protein coupled receptors
  • Transmembrane proteins transduce extracellular signals
  • common structural motif of 7 membrane spanning regions
  • Receptor binding promotes interaction
    • between receptor
    • G protein on interior surface of membrane
  • induces an exchange of GDP for GTP on G protein α subunit and dissociation of the α subunit from the βγ heterodimer

GTP-α subunit complex mediates intracellular signaling, depending on isoform either

  • indirectly - by acting on effector molecules adenylyl cyclase (AC), phospholipaseC(PLC)
  • directly - by regulating ion channel or kinase function

Receptor associated with Kinase

Receptor and non-receptor tyrosine kinases
Endothelial cell signaling cartoon
  • many growth factors use this pathway
    • Vascular Endothelial Growth Factor
    • Epidermal Growth Factor
    • Nerve Growth Factor
    • Bone Morphogenic Protein
    • Transforming Growth Factor-beta

Pathway

  1. Ligand binding
  2. Receptor association
  3. Phosphorylation
  4. Kinase cascade

VEGF Receptor and Ligands (example) EGF Receptor Transduction Pathway Signaling Pathway of TGF-β

  • TGF-β receptor
  • include Type I and II subunits
  • are serine-threonine kinases
  • signal through SMAD family of proteins
  • binding of TGF-β to cell surface receptor Type II leads to phosphorylation of Type I receptor by Type II

TrkA Receptor

TrkA receptor.jpg The PI 3-kinase pathway and cell survival

  • trk (often pronounced 'track') stands for tropomyosin-receptor-kinase (not tyrosine kinase or tropomyosin-related kinase)
  • proteins with a single transmembrane helix
  • Trk proto-oncogenes – TrkA, TrkB, TrkC, TrkE
    • variably expressed in CNS and PNS

TrkA Pathway

  1. following neurotrophin binding
  2. dimeric Trk receptors
  3. phosphorylate one another at tyrosine residues (Y490 and Y785 for TrkA)
  4. phosphotyrosines bind adaptor molecules such as Shc and PLC-γ.
  5. these signaling intermediaries activate three major signaling pathways
    1. Ras/MAPK cascade
    2. PI3K/AKT
    3. IP3-dependent Ca2+ release (?)
  6. pathway activation results in transcriptional changes of different target genes

http://www.ncbi.nlm.nih.gov/pubmed/19126759 | http://en.wikipedia.org/wiki/Trk_receptor | Neurotrophin–receptor interactions | Neurotrophin signalling

Proto-oncogenes

  • Normal cell proteins that have potential to cause uncontrolled growth when mutated
    • loss of receptor regulation
    • cells grow out of control
    • mutation in TK Receptor – receptor always activated
    • mutation of activating protein – always active
    • Oncogenes – Ras
  • mutants detected in 30% cervical cancers

Movie: Methods Receptor/Ligand MCB ch20anim3.mov

Movie: Receptor Internalization

Phosphatases

The mechanism for dephosphorylation is through phosphatases.

Three main families of phosphatases

  1. phospho-Tyr phosphatases (PTP)
  2. phospho-Ser/Thr phosphatases
  3. those that cleave both

Phosphatase specificity by binding protein cofactors

  • facilitate translocation and binding to specific phosphoproteins
  • active phosphatase consists of a complex
    • phosphatase catalytic subunit
    • regulatory subunit
  • Regulatory subunits for Tyr phosphatases may contain a SH2 domain allowing binding of the binary complex to autophosphorylated membrane receptor Tyr kinases.

Protein Tyr phosphatases (PTPs)

  • consist of receptor-like (transmembrane) and intracellular Tyr phosphatases (about 100 PTPs)

PTP1B - dephosphorylates many cell surface receptors (insulin, EGF, PDGF) that have been phosphorylated on Tyr residues

References

Textbooks

Essential Cell Biology

  • Essential Cell Biology Chapter 15

Molecular Biology of the Cell

Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002

Molecular Cell Biology

Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999

The Cell- A Molecular Approach

Cooper, Geoffrey M. Sunderland (MA): Sinauer Associates, Inc.; c2000

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Books

PubMed

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  • Online Mendelian Inheritance in Man (OMIM) is a comprehensive compendium of human genes and genetic phenotypes. The full-text, referenced overviews in OMIM contain information on all known mendelian disorders and over 12,000 genes. OMIM
  • Entrez is the integrated, text-based search and retrieval system used at NCBI for the major databases, including PubMed, Nucleotide and Protein Sequences, Protein Structures, Complete Genomes, Taxonomy, and others Entrez

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Reviews

  • The great divide: coordinating cell cycle events during bacterial growth and division. Haeusser DP, Levin PA. Curr Opin Microbiol. 2008 Apr;11(2):94-9. Epub 2008 Apr 7. Review. PMID: 18396093 | PMC
  • Cell cycle studies based upon quantitative image analysis. Stacey DW, Hitomi M. Cytometry A. 2008 Apr;73(4):270-8. Review. PMID: 18163464
  • Analysis of cell cycle phases and progression in cultured mammalian cells. Schorl C, Sedivy JM. Methods. 2007 Feb;41(2):143-50. Review. PMID: 17189856
  • Cell cycle regulation of DNA replication. Sclafani RA, Holzen TM. Annu Rev Genet. 2007;41:237-80. Review. PMID: 17630848

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2010 Course Content

Lectures: Cell Biology Introduction | Cells Eukaryotes and Prokaryotes | Cell Membranes and Compartments | Cell Nucleus | Cell Export - Exocytosis | Cell Import - Endocytosis | Cell Mitochondria | Cell Junctions | Cytoskeleton Introduction | Cytoskeleton 1 Intermediate Filaments | Cytoskeleton 2 Microtubules | Cytoskeleton 3 Microfilaments | Extracellular Matrix 1 | Extracellular Matrix 2 | Cell Cycle | Cell Division | Cell Death 1 | Cell Death 2 | Signal 1 | Signal 2 | Stem Cells 1 | Stem Cells 2 | Development | Revision

Laboratories: Introduction to Lab | Microscopy Methods | Preparation/Fixation | Immunochemistry | Cell Knockout Methods | Cytoskeleton Exercise | Confocal Microscopy | Microarray Visit | Tissue Culture 1 | Tissue Culture 2 | Stem Cells Lab | Stem Cells Analysis

Dr Mark Hill 2015, UNSW Cell Biology - UNSW CRICOS Provider Code No. 00098G