Cell-Environment Interaction (inside-out)

Wagner Shin Nishitani04/13/2009

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Journal Papers

Arnaout, M. A., Goodman, S. L. & Xiong, J.-P. Structure and mechanics of integrin-based cell adhesion. Curr. Opin. Cell Biol. 19, 495–507 (2007)

Meshel, A. S., Wei, Q., Adelstein, R. S. & Sheetz, M. P. Basic mechanism of three-dimensional collagen fibre transport by fibroblasts. Nat. Cell Biol. 7, 157–164 (2005)

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Outline

Introduction (integrins) Structure Ligand binding Conformational regulation Inside-out activation Example

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Introduction

Adhesion by integrins Binds to extracellular matrix (ECM)

through large ectodomain Binds to cytoskeleton through short

cytoplasmic tail

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Introduction

Adhesion by integrins Major role in organization of

tissue/organs Cytoskeleton controls affinity of

ectodomain to ECM (inside-out) ECM binding changes cytoskeleton

(outside-in) Transmission of force across

membrane

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Structure

Components 18 α-subunits 8 β-subunits Total of 24 integrins

2 groups Containing or Lacking von Willebrand

factor type A domain (αA)

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Structure

von Willebrand factor type A domain (αA) GTPase-like domain with a metal-ion-

dependent adhesion site (MIDAS) instead of the catalytic site

Closed (low affinity) or Open (high affinity) conformations

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Structure

αVβ3 (αA-lacking): α - blue, β - red

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Structure

PartsHead(formation of dimer)

Legs

Knees

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Ligand binding

RGD binding (R – propeller, D – βA)

SpecificityDeterminingLoop

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Conformational regulation

Similarly to αA, βA affinity is assumed to be controlled by conformational change

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Conformational regulation

Switchblade model High affinity of βA

dependent on large Hybrid swing-out (~80°)

To provide space, knees fully extended

Allows access to binding site

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Conformational regulation

Deadbolt model High affinity of βA

possible with small changes between βTD and βA/Hybrid

Ligand binding provides energy for Hybrid swing-out (maybe knees not fully extended)

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Conformational regulation

Ligand-relay model Active βA changes conformation of αA

for high affinity αA is the ligand for βA

Consistent with deadbolt model

αA-containing αA-lacking

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Inside-out activation

Talin Actin binding protein Localized early with

high-affinity integrins Interaction β

Tail Close to membrane

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Inside-out activation

Talin Interaction close to

membrane Disrupts ionic bonds

between α and β tails Separation between

tails for inside-out activation

Unclear!

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Inside-out activation

Filamin Binds competitively with talin to β tails

Negatively regulates talin-induced activation

Calcium and integrin binding protein 1 (CIB1) Binds to αIIb peptide close to membrane

Potentially negatively regulates talin-induced activation

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Example

Collagen fiber transport by fibroblast Hand-over-hand cycle

Extension of lamellipodia Collagen bound by integrin Retraction of lamellipodia Collagen released

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Example

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Example

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Example

Collagen fiber transport by fibroblast Integrin α2β1 involved

Blocking antibody inhibited spreading on collagen-coated substrate

Bind/release cycle Inside-out control required