Invasion - regulation of cell migration Flashcards
State the steps of (epithelial) tumour progression
- Homeostasis
- Genetic alterations
- Hyper-proliferation
- De-differentiation (disassembly of cell-cell contacts and loss of polarity)
- Invasion (increased motility and cleavage of ECM proteins)
What are the 5 different types of tumour cell migration? State important cell membrane proteins/structures required for collective and individual cell migration
- Single cell migration (as an ameboid)
- Mesenchymal single cells
- Mesenchymal chains
- Clusters/cohorts
- Multicellular strands/sheets
- Integrins and proteases for both collective and individual migration
- Cadherins and gap junctions for just collective migration
What physiological phenomena does tumour migration mimic?
Morphogenesis e.g. angiogenesis
What did a comparison of the expression profile of invasive cells vs primary tumours show to be upregulated in invasive cells?
Upregulation of genes involved in:
- Cytoskeleton regulation
- Motility machinery
What give normal migrating cells directionality and what makes normal migrating cells stop moving?
How are tumour cells different in this aspect?
Polarity determines what direction they move in. Contact inhibition of locomotion = STOP.
They lose contact inhibition of locomotion so they can multilayer.
What are main stimuli for cells to migrate?
- organogenesis + morphogenesis
- wounding
- growth factors/chemoattractants
- dedifferentiation (tumours)
Define substratum
A surface (ECM proteins) in which the cell attaches to, especially when the cell is growing or moving
Attachment of cells to substratum
allows them to move - how?
- Focal adhesions hook onto ECM + provide holding for cell whilst move
- Hooking mostly done by integrins
- Focal adhesions are on terminal ends of actin filament
What are filopodia?
Finger-like protrusions that are rich in actin filaments
They sense the local environment
What are lamellipodia?
Sheet-like protrusions that are rich in actin filaments
Define haptotaxis
Haptotaxis is a directional cell movement in response to adhesive substrates such as ECM
What are the processes of cell motility?
- Extension of cell in direction of movement
- Adhesion: led by lamellipodium, then filopodia hook onto ECM to form new focal adhesion
- Translocation: active contraction of cell to bring the rear of the cell forwards
- De-adhesion of previous focal adhesion
What are the small subunits/monomers that make up the actin filament polymers/F-actin?
G-actin
Describe how Actin filament polarity affects the cell movement.
In response to signal (e.g. nutrients) F actin disassembles and then reassembles on the side of the cell near the signal => cell polarity => allows movement
Describe the organisation and structure of the filament in the filopodia and lamellipodia? What are stress fibres?
- Filopodia filled with bundles of parallel actin filaments
- Lamellipodia have branched and cross-linked filaments
- Stress fibres have antiparallel filament organisation; they are contractile structures and have focal adhesions on endings
What protein complex is important in initiating polymerisation? What is the name of the process?
How do the monomers get added on?
ARP complex (composed of Arp2, Arp3 and other proteins)
Arp 2 and 3 form a trimer with actin to initiate polymerisation - called nucleation.
They have a plus end and a minus end; monomers preferentially get added on at the plus end
Hence, what is the limiting step in actin dynamics?
Formation of Arp2/3-actin trimers to initiate polymerisation
State proteins that bind to free G-actin and describe how they affect elongation.
Profilin - these deliver the G-actin to the growing filament => promote elongation
Beta4 thymosin and ADF/cofilin - they sequester G-actin but do not inhibit polymerisation
Name some capping proteins that bind at the plus end.
CapZ
Gelsolin
Fragmin/severin
Name some capping proteins that bind at the minus end
Tropomodulin
Arp2/3
Name some F-actin severing proteins.
Gelsolin
Fragmin/severin
ADF/Cofilin
What are the features of the actin filaments in severed populations?
Actin filaments can grow and shrink more rapidly
What can happen to single filaments of actin to improve their structural integrity?
They can be bundled or cross-linked
Name some proteins involved in actin filament bundling and cross-linking. How are they involved?
- Alpha-actinin (dimers cross link filaments)
- Fimbrin
- Filamin (filaments are at angles from each other => mesh)
- Spectrin (filaments are at angles from each other => mesh)
- Villin
- Vinculin
- Dystrophin (links filaments to plasma membrane)
Which protein allows branching of the actin filaments?
Arp complex (binds somewhere along the filament and initiates new polymerisation at an angle)
At what angle do the filaments branch (due to Arp)?
70 degrees
Summarise the actions of the Arp complex.
They bring about nucleation
They cap filaments (minus end)
They cause branching
Describe what causes the gel-sol transition.
The actin filaments can be severed to make the cell more fluid
Gel (rigid) => Sol (can flow)
Describe the actin processes that take place during the protusion of lamellipodia.
There is disassembly, nucleation, branching, severing, capping and bundling
There is net filament assembly at the leading edge and net filament disassembly behind the leading edge
Describe the actin processes that take place during the formation of filopodia.
Actin polymerisation
Bundling and cross-linking
(NO branching)
As soon as the finger wants to retract it will collapse at the base
State four signalling mechanisms that regulate the actin cytoskeleton.
- Ion flux changes (i.e. intracellular calcium)
- Phosphoinositide signalling (phospholipid binding)
- Kinases/phosphatases (phosphorylation cytoskeletal proteins)
- Signalling cascades via small GTPases
What are the three most important small GTPases in terms of the actin cytoskeleton and what does activation of each cause?
Cdc42 – for filopodia
Rac – for lamellipodia protrusion
Rho – for stress fibres
NOTE: these are all part of the Rho sub-family which belongs to the Ras super-family
Explain how Rac causes actin polymerisation/organisation.
Rac binds to and activates WAVE
WAVE then activates Arp2/3, which is important in actin organisation
Explain how Cdc42 causes actin polymerisation/organisation.
Cdc42 binds to WASP
WASP also activates Arp2/3
Which small GTPases are involved in focal adhesion assembly?
Rac and Rho
Which of the small GTPases are involved in contraction required for cell movement?
Rho (as stress fibres are important for contraction)
