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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