Chapter 15 - Signaling

• Communication by EC - steps

  1. Synthesis of molecule
  2. Release of molecule
  3. Transport of signal
  4. Detection of signal
  5. Change initiated by signal
  6. Removal of signal
• Endocrine Signaling - distant targets

  
• Paracrine Signaling

  • Local mediators
  • Contact dependent signaling
  • Synaptic signaling
• Local Mediators - close proximity

  
• Contact Dependent Signaling - GAP Junctions

  
• Synaptic Signaling - Neurotransmitters

  
• Autocrine signaling - self

  
• Receptor Structure

  • EC Domain - binds ligands
  • Transmembrane Domain
  • Cytoplasmic Domain - Enzymatic activity and Binds other proteins

  A) Extracellular Domain

  B) Transmembrane Domain

  C) Cytoplasmic Domain
• Types of Signaling Receptors

  • Nuclear receptors
  • G-linked Protein Receptor
  • Enzyme linked receptors
• Nuclear Receptors

  • function as TFs once activated

  
• G-linked Protein Receptors

  • 7 membrane pass proteins
  • Activated G protein
  • Inactive GDP becomes active GTP

  
• Enzyme Linked Receptors

  • Single pass TM domain
  • Receptor Tyrosine Kinase (RTK)
  • Tyrosine Kinase Associated Receptor
  • Receptor-like Tyrosine Phosphatase
  • Recepto Ser/Thr Kinase
  • Histidine Kinase Associated Receptor

  A) Receptor Tyrosine Kinase (RTK)

  B) Tyrosine Kinase Associated Receptor

  C) Receptor-like Tyrosine Phosphatase

  D) Receptor Ser/Thr Kinase

  E) Histidine Kinase Associated Receptor

  
• Signal Transduction Pathways

  1. Ligand binds to receptor (1st messenger)
  2. 1st messenger transmits the signal to a 2nd messenger (can be more than one 2nd messenger
  3. 2nd messenger transmits signal to TF
  4. TF activate/repress genes
  5. mRNA and protein is made/repressed
  6. Signal outcome (proliferation, differentiation, wound repair, etc.)
• Types of Second Messengers

  • Relay proteins
  • Messenger proteins
  • Adapter proteins
  • Transducer proteins
  • Bifurcation proteins
  • Integration protein
  • Latent Gene Regulatory protein
• Relay Proteins - pass message to next signaling component

  
• Messenger proteins - from one part of the cell to another

  
• Adapter proteins - links 2 signaling molecules together but don't convey a signal themselves

  
• Transducer proteins - coverts signal from one form to another

  
• Bifurcation proteins - sends signal to more than one pathway

  
• Integration proteins - receives signal from more than one pathway

  
• Latent Gene Regulatory Proteins - activated by receptors and go directly to nucleus to activate genes

  
• TGF-B Receptor

  • Receptor Ser/Thr Kinase

  1. Type II - binds TGF-B as homodimer
  2. Type I homodimer recruited
  3. Type II phosphorylates Type I on GS domain
  4. Activated tetrameric receptor

  
• Ras

  • Rat sarcoma
  • 20-25% of all human cancers

  1. Monomeric GTPase - Inactive bound to GDP
  2. Binds receptor indirectly
  3. Adaptor protein - Binds P-Ser in receptor / Binds Proline rich regions in GEF protein
  4. Ras binds GEF
  5. Raf and MEKK-1 pathways - Bifurcation, transducer, relay
• Ras - Adaptor proteins

  • Binds P-Ser in receptor
  • Binds Proline rich region in GEF proteins
• Ras - Ras binds GEF

  • Dissociation of GDP
  • Increase uptake of GTP from cytosol
  • Active
• Raf

  • Rat Fibrosarcoma
  • 15-30% of all human cancers
  • Serine/Threonine kinase - can phos.
  • 3 Conserved regions - CR-1, CR-2, CR-3
  • Activates MEK-1/2
  • Relay molecule
• Raf - 3 Conserved Regions

  • CR-1: RBD (binds to Ras) and CRD (anchors to cell membrane)
  • CR-2: Binding to MEK-1/2
  • CR-3: Catalytic domain (kinase activity does phosphorylating)
• MEK-1/2

  • MAP and ERK kinases
  • Dual Kinase (can phos. Ser/Thr and Tyr)
  • Activates ERK-1/2
  • Relay molecule
• MEK-1/2 Domains

  • Nuclear export signal
  • Kinase domain
  • Docking (D) domain - allows binding with other molecules
• ERK-1/2

  • Extracellular regulated kinase
  • Ser/Thr Kinase
  • c-myc (helix-loop-helix), c-fos (leucine zipper), p53
  • messenger and relay molecule
• ERK-1/2 mutations

  • Breast carcinoma
  • Leukemia
  • Melanoma
• ERK-1/2 Domains

  • Nuclear export signal
  • MEK-1/2 binding site
  • Kinase domain
  • Nuclear localization domain - allows entrance into nucleus
• ERK-1/2 - Domains: MEK-1/2 binding site

  1. Destabilizes P region in ERK-1/2 and allows for Tyr phosphate
  2. MEK then phosphates Thr residue
• MEK-1/2 mutations

  • Lung and colon carcinomas
  • melanomas
• MEK-1/2 Domains

  • Nuclear export signal
  • Kinase domain
  • Docking (D) domain
• SMADS - Latent gene regulatory protein second messengers
• R-SMADs - SMAD receptors

  • include 2 and 3
  • 2 MH domains connected by linear domain (N and C terminus)
• R-SMADs : MH-1

  • N-terminus
  • Binds DNA
  • NLS
  • Transcriptional activation domain - signaling molecule functioning as TF
• R-SMADs: MH-2

  • C-terminus
  • Associates with Type I TGF-B receptor
  • Homo/hetero dimerization domain - Binds SMADs 2/3 together and Binds SMAD 4 (co-SMAD)
• SMAD inactive state

  • MH-1/MH-2 interact - domains not exposed
  • SARA (SMAD anchoring for receptor activation) - Contains FYVE domains that binds P-lipids in membrane