Cell adhesion Adhesion molecule signaling Mechanotransduction Cell motility

Cell adhesion

• Adhesion molecule signaling

• Mechanotransduction

• Cell motility

Cell adhesion molecules

• Immunoglobulin-like

• Cadherin

• Integrin

• Selectin

• Dystroglycan

Integrins

• Alpha/Beta heterodimers

• Closed/Open/Ligated states– Couple cytoskeletal and extracellular

conformations

• Focal complex

Xiao et al., 2004

Insideout Ousidein

Integrin signaling

• Survival

• Focal Adhesion Kinase– PI-3K– Src/Grb2, Crk– RhoGAP

• PTEN/SHP– Phosphatase and tensin homolog on

chromosome 10

– PIP3->PIP2

– PI-3K antagonist

Integrin signaling: motility

Juliano 2002

Cadherins

• Cell-cell adhesion– Adherens junction– Desmosome

• Catenin signaling– p120 RhoGAP– Transcription factor– Cytoskeletal linker

• Differentiation/development– Tissue aggregation

Juliano 2002

Cadherin SignalingCadherin/catenin signaling interacts with traditional growth factor receptors, incl wnt/frz/dsh and HGF/c-Met

Juliano 2002

Immunoglobulin-like

• Ubiquitous class, CAM

• Several extracellular Ig like domains– Not antibodies

• Short cytoplasmic tail– Associates with ankyrin/

spectrin cytoskeleton– MAP kinases

• Function– Developmental guidance– Immune cell response

Juliano 2002

Mechanotransduction

• Mechanical conformational change– Force– Deformation– Opposition of internal and external forces

• CAM-matrix adhesion

• CAM-cytoskeleton adhesion

• Deformability of series structures

Elastic Domains

• EGF

• Fibronectin (FN)

• Immunoglobulin (Ig)

• Complement like

Complement like

Ig

EGF

CN3D, UIUC Theoretical and computational biophysics group

Mechanical conformational changes

• Mechanical energy disrupts H-bonding

• Modular elasticity

• nm stretch

• 100%+ strain

• pN force

Gao et al., 2002 PNAS

Cell growth-substrate interaction

• Substrate chemistry– Ligand matching– Integrin/CAM mediated differentiation

• Substrate mechanics– Improved differentiation on elastic

substrates– Fewer stress fibers on softer materials

Yeung et al 2005

Motility

• Motility vs. contraction

• Polymerization systems– Actin– Tubulin

• Filament – motor systems– Actin-myosin– Microtubule-kinesin/dynein

Structural reorganization

Motion of focal adhesions (white) and surrounding gel (red) in corneal fibroblasts. Petroll et al 2003

Crawling

• Pseudopodia– Lammelapodia– Filopodia

• Actin filament dynamics– Directional polymerization– Treadmilling

Photolabel actinmonomers

2 minutes

Cell moves relative to actin

Actin: polymerization dependent motion

• Disk shaped

• Adenine nucleotide binding– ATPase activity– Nucleotide exchange

• Promoted by Profilin• Inhibited by Cofilin

• Filament formation– Barbed/Pointed end– Myosin S-1 “decoration”– ADP maturation

Actin filament polymerization

• Asymmetric exchange of monomers

Myosin fragment

Filament regulation

• Exchange proteins– Profilin

• PROmotes filament growth towards barb• Nucleotide exchange factor

– Cofilin• ADP-Actin binding• Filament repair

• Monomer recycling– Cofilin disassembles ADP-actin– Profilin regenerates ATP-actin

Monomer recycling

• Facilitates “treadmilling”

• Membrane extension

ATP-ADP conversion as filament matures

Cofilin disassembles ADP-actin

Profilin carries ATP-actin to leading edge

Rho family GTPases

• GTP dependent cofactors, like G subunits– Rho Kinase, mDia,

• Components of shape-dependent processes– Motility, cell cycle,

phagocytosis

Heasman & Ridley 2008

Rho family GTPases

• Rho– Stress fibers, integrin, selectin

• Rac– Lamellipodia, growth factors

• cdc42– Filopodia, cytokines

Constitutively active cdc42 Rac Rho

Normal cell

Rho family signaling diversity

cdc42

WASP IRSp53 mDia2 PAK

LIMK

coflin

Actinturnover

ARP2/3

Actinpolymerization

Actinbranching

Lamellipodia Filopodia

Rac

WAVE mDia2 PAK

LIMK

coflin

Actinturnover

ARP2/3

Actinpolymerization

Filopodia

formin

Rho

RhoK

Stress fiber

MLCK MLP

myosin

Microtubule

• Regular array of a/b dimers

• Spontaneous tube formation

• Polar

Motor Proteins

• Myosin-actin

• Kinesin-tubulin

• Dynein-tubulin

Motor step cycle

• One head

• Two head “Hand-over-hand”

Motor step systems

MtK1 MtK1T MtK1DP MtK1DK2 MtK2

K1T MtK1DPK2DK1 MtK1DPK2 Mt

T

T P

P

D

Shape Changes“Weak”

Binding K2

“Strong”Binding K2

AM AMT AMDP AMD AM

MT MDPM MD M

T

T P

P D

D

Shape Changes

“Weak”Binding

“Strong”Binding

Myo

sin

Kin

esin

Kinesin/Dynein motility

• Vesicular transport– Kinesin

• Toward +• Away from nucleus

– Dynein• Toward –• Toward Nuc

– 0.1-1 um/s

Myosin motility

• Cytoplasmic streaming (plants)– Transport of ER along actin tracks– 60 um/s

• Muscle– Specialized bipolar myosin filaments– Opposing motion in adjacent actin filaments– 1-10 um/s

Highly ordered filaments

• Crystalline polymerization facilitates molecular interaction

• Maximize density of force generating elements

Woodhead et al 2005

Double-headed Myosin

“J” structure on filament surface

Regulation of force (smooth muscle)

• Thick filament regulation

• Regulatory myosin light chain phos– Myosin light chain kinase (MLCK)– Calmodulin– Slow, sustained

Regulation of force (striated muscle)

• Thin filament regulation

• Steric availability of actin– Tropomyosin– Troponin I,C,T– Cooperative– Rapid

Weak myosin bindingStrong myosin bindingActinTropomyosin