Chapter 19 - ECM

• Proteins that make up the ECM: Laminin, Fibronectin, Collagen, Vitronectin, Elastin, Proteoglycans
• Laminin - alpha, beta, and gamma subunits
• Laminin

  • major component of basal lamina
  • 1 form of congenital muscular dystrophy
• Fibronectin - protein dimer
• Fibronectin

  • soluble (blood stream) and insoluble (matrix) form
  • Glomerulopathy (kidney disease)
• Collagen - triple helix
• Collagen

  • Most abundant protein in mammals
  • Ehlers-Danlos Syndrome - Connective tissues defects
• Vitronectin - monomeric protein
• Vitronectin

  • soluble and insoluble form
  • liver disorders (cirrhosis)
• Elastin - cross-linked monomers
• Elastin

  • Primarily in connective tissue
  • Marfan syndrome
• Proteoglycans - glycosylated proteins
• Proteoglycans

  • ubiquitously found in ECM (a lot in CT)
  • Alzheimer disease
• Integrins

  • Receptors that link/bind the cell to ECM
  • Large family of homologous transmembrane receptors
  • EC domain
  • IC domain
• Integrins - homologous transmembrane receptors

  • 2 non-covalently associated subunits (alpha and beta)
  • 8 beta and 18 alpha subunits (mix and match)
  • Many proteins recognized by multiple integrins (8 integrins bind fibronectin)
• Integrins - 8B and 18a subunits

  • Forms different heterodimers
  • Each can be alternatively spliced
  • High degree of diversity
• Integrins - EC domain

  • N-terminal
  • Binds ECM or cells
• Integrins : IC domain

  • C-terminal
  • Binds cytoskeleton
• Muscular Dystrophy

  • Laminin mutation
  • alpha 7 (a7) and Beta 1 (B1)
• Glanzmann"s Disease

  • Fibrinogen mutation
  • alpha 11b (a11b) and beta 3 (B3)
  • Integrin binds fibrinogen
  • No aggregation/bridging of platelets
  • Prolonged bleeding time
• Leukocyte Adhesion Deficiency

  • ICAM-1/2
  • alpha x (ax) and beta 2 (B2)
  • White blood cells can't leave bloodstream and enter infected tissue
  • Chronic bacterial infections
• Integrin Adhesion - Migration

  • Wound repair - normal function
  • Metastasis - abnormal function
• Integrin Signaling - Direct

  • Signaling via FAK
• Integrin Signaling - Indirect

  • many pathways are not activated without adhesion
  • often can't survive or proliferate without adhesion
• Integrin movement

  1. Trailing/lagging edge and leading edge on ECM
  2. Leading edge moves forwards and forms interactions
  3. Trailing/lagging edge interactions are lost
  4. Cell body moves forwards
• Focal Adhesions

  • connect ECM to cytoskeleton
  • Signaling
• DAPI - stains nuclei blue
• Phalloidin conjugated to TRITC - stains actin red
• Anti-vinculin Ab conjugated to FITC - stains vinculin green
• Signaling through Integrins

  1. Integrin cluster
  2. Talin, Paxillin, and Vinculin bind to integrin tails (inside cell)
  3. FAK recruited to integrin tail by talin, paxillin, and vinculin
  4. FAK auto-phosphorylates on Tyr
  5. FAK's phospho-Tyr recruits Src
  6. Src phosphorylates FAK on Tyr
  7. Activated FAK can signal to PI3K pathway and Ras pathway