Actin, Intermediate Filaments, Cell Adhesion Flashcards
Smooth Muscle
- phosphorylate myosin light chain = persistent contraction
- regulated by extracellular signals
Myosin and Vesicle Transport
- myosin V bound vesicles carried along actin filaments
- actin is capped by formin
- actin pulls on MTs to pull nucleus
- myosin V needs cargo to be active
Myosin V and Yeast Budding
- material transported into bud by myosin V
- formin activated at end and entry of bud
- actin added at (+) end = growing
Cytoplasmic Streaming
- transport along actin cytoskeleton = cytoplasm move
- used with diffusion in gas exchange
- cortical cytoplasmic actin around plant cell
- myosin V moves organelles along actin
Cell Migration
- pushing PM forward b/c actin polymerization
- Leading Edge = filopodia and lamellipodia
- Stress Fibers = focal adhesions (anchors cell to substrate)
Chemotaxis
- cells respond to cAMP
- cells have receptor for chemoattractant around cell surface
- activates actin polymerization at leading edge
Steps of Cell Movement
- cell on substrate attached to focal adhesions + cAMP
1) Extension = actin polymerization at leading edge
2) Adhesion = lamellipodia forms NEW focal adhesion
3) Translocation = cell moves
4) De-adhesion & Endocytic Recycling = remove old adhesion
Signalling Molecules
Rho-GTP ==> formin
Cdc42-GTP ==> activates WASp ==> activate Arp2/3
Rac-GTP ==> activates WAVE ==> activate Arp2/3
Mutations to Signalling Molecules
Dominant-active Rho = stress fibers
Dominant-active Cdc42 = lamellipodia
Dominant-active Rac = filopodia
Scratch Closure Assay
Cdc42 –> Rac –> Rho –| Rac
- confluent cells scratched = wound
- control = wound closure
- experimental (inactive form ANY signalling molecule) = wound does not close
Intermediate Filaments
- not globular
- not need ATP or GTP
- no polarity
- no motor proteins
- tetramer = basic subunit
Class I of Intermediate Filaments
acidic keratins
epithelial cells
tissue strength
Class II of Intermediate Filaments
basic keratins
epithelial cells
tissue strength
Class III of Intermediate Filaments
desmin, GFAP, vimentin
muscle & mesenchymal cells
sarcomere organization
Class IV of Intermediate Filaments
neurofilaments
nucleus
axon organization
Class V of Intermediate Filaments
lamins
nucleus
nuclear organization
Proteins Associated with Intermediate Filaments
plectin cross-links intermediate filament vimentin and MT
Functions of Intermediate Filaments
- structural support for cell (links to PM)
- lamins support nuclear membrane
Dynamic State
- proteins within filament are exchanged
- N-terminal domain of lamin A phosphorylated at serine = disassembly and prevents reassembly
- break nuclear membrane –> mitotic apparatus
Tissue Integrity
- transgenic mice w/ mutant keratin gene = skin blistering
- epithelial cells have IF anchored to desmosomes and hemidesmosomes
Epithelial Cells Polarity
- apical surface = microvilli
- basal surface = connect to ECM
Tight Junctions
- hold cells together to prevent material going through
- rows of occludin, claudin, JAM proteins in each cell
Gap Junctions
- hold cells together for communication
- 6 connexins = connexon
- 2 connexons = gap junction channel
- channel closes when exposed to Ca2+
Cadherins (Homophilic Interactions)
- single transmembrane domain + cytosolic C-terminal tail
- Ca2+ dependent
- linked to intermediate filament = desmosome
- linked to actin (via adapter proteins) = adherens junction
Ig-Superfamily CAMs (Homophilic Interactions)
- mediate Ca2+ independent homophilic interactions
Integrins (Heterophilic Interactions)
- heterodimeric transmembrane protein
- α1β1 binds collagen
- α5β1 binds fibronectin
- α6β1 binds laminin
- bind to core RGD amino acids
Selectins (Heterophilic Interactions)
- leukocyte extravasation (WBC leave bloodstream)
- endothelial cells secrete P-selectin and PAF
- P-selectin binds to oligosaccharides on leukocyte
- PAF binds to PAF receptor on leukocyte – activate integrin
- integrin binds to ICAM
- push endothelial cells apart and enter
Extracellular Matrix Proteins
Proteoglycans = hydrophilic (absorb water) Collagen = structural (strength) Laminin = adhesive (recognized by integrins) Fibronectin = adhesive (recognized by integrins)
Extracellular Matrix Functions (5)
- anchor + surround cells —> shape
- control cell polarity, survival, differentiation
- inhibit/facilitate cell migration
- binding growth factors
- activating cell surface receptors
Integrins + Extracellular Matrix
Bind to ECM
Cytoskeleton (actin = stress fiber) (IF = hemidesmosome)
Active form to bind to substrate
- inactive not bind to RGD
