Cancer 11: Invasion - regulation of cell migration Flashcards
2) What are the molecular mechanisms that regulate
microfilaments
regulation of actin dynamics
cytoskeletal proteins
signalling proteins
Describe the process of tumour progression
- homeostasis
- genetic alterations
- hyper - proliferation (due to mutation)
- de-differentiation
- -> cells lose their identity
- -> lose contact w each other
- -> and lose polarity (no longer cuboidal epithelium) - invasion
- -> cells break down BM
- -> acquire increased motility
Metastasis requires distinct and sequential events
give a general overview of these events
benign = cells still attached
- -> then invades surrounding stroma
- -> travel via circulation
- -> invade new organ
- -> forms a new tumour
compare between the 2different types of tumour cell migration/ motility ?
a) single cell
- Amoeboid (circular) or mesenchymal
- Require integrins + proteases
b) collective cell migration
- Group of cells detach + form clusters/cohorts or multicellular strands/sheets (where cells follow leader cell)
- Require cadherins + gap junctions
note: Tumour cell metastasis mimic morphogenetic events
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Comparison of expression profile of invasive cells Vs primary tumours
needle w EGF = haemotactic
–> invasive cells go up needle –>
What are main stimuli for cells to migrate ?
- organogenesis + morphogenesis
- wounding
- growth factors/chemoattractants
- dedifferentiation (tumours)
What is direction of movement of cells controlled by?
Direction controlled by polarity (directionality)
What controls Stop of movement of cells?
Stop of movement = controlled by contact-inhibition motility
How do cells actually move?
via specialised structures (focal adhesion, lamellae, filopodium)
–> allows them to move
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 rich in actin filaments
- used for motility
- important for sensing environment ( senses stimulus + site of attachment )
What are Lamellipodia ?
Sheet-like protrusions rich in actin filaments
- used for motility
Why is control need in cell movement?
a) to coordinate what is happening in different parts
b) to regulate adhesion/release of cell-extracellular matrix receptors
c) to respond to external influences from outside –
needs:
- -> sensors
- -> directionality
Compare between the 2 types of cell motility :
hapoptatic vs chemotatic
hapoptatic - cell roaming around
chemotatic - cells have a purpose
–> but same machinery
What are the processes of cell motility?
Cell motility (movement to R):
- Extension: of cell body in direction of movement
- Adhesion: led by lamellipodium, then filopodia hook onto ECM –> form new focal adhesion
- Translocation: contraction of cell body –> bring back of cell forwards; needs energy
- De-adhesion of previous focal adhesions
describe how Actin filament polarity affects the cell movement.
actin filaments = made of polymers
- G actin –> soluble –> forms F actin (has polarity)
- in response to signs, e.g nutrients,
F actin on one side –> disassembles
and reassembles on the side with the signal –> allows polarity –> allows movement
Describe the organization and structure of the Filament ?
- Filopodia filled with bundles of parallel actin filaments
- Stress fibres have antiparallel organisation – when contract, affect whole cell body; have focal adhesions on endings
- Lamellipodia have branched + cross-linked filaments –> provides support to big membrane sheet
describe the Remodelling of actin filaments.
- Nucleation: (occurs at -ve end for +ve end to have polymerization)
= rate-limiting step in organisation of cytoskeleton/actin,
–> high energy needed
- Arp = actin-related proteins, like actin
–> Arp 2 + Arp3 = resembles actin structure –> helps actin monomers form initial trimers –>initiates polymerization –> eventually form filaments
- Elongation:
- Profilin binds G-actin –> brings it to actin filament
- Thymosin binds G-actin, but doesn’t bring to filaments –> inhibits polymerisation
- Sequestering: b4-thymosin, ADF/cofilin (doesn’t inhibit polymerization)
- Capping: capping proteins regulate elongation of actin filament: (capping protein = blocks polymerization)
- At + end: Cap Z, Gelsolin, Fragmin/severin; At – end: Tropomodulin, Arp complex
- When blocked at front by capping proteins –> causes shortening/disassembly of filament at back - Severing: regulate filament size, filaments may grow + shrink
- Severing proteins:
o Gelsolin, ADF/cofilin, fragmin/severin
- Gelsolin also is capping protein; function determined by regulation e.g. post-translational modification or signalling protein
after being cut 3 pathways
- continue elongation
- annealing –> join fragments back together
- capping cut end ( to prevent elongation)
- Cross-linking + bundling of newly formed filaments:
- e.g Fascin bundles filaments together
- Fimbrin does same but at longer distances
- Spectrin, filamin, dystrophin cross-link multiple filaments at particular angles;
6. Branching: - Branching in lamella occurs at particular angles (70 °)
- Arp2/3 complex = responsible for branching appearance of filaments in lamella as cells move forward
- Thus, Arp2 does both nucleation + filament elongation/angling
- Gel-sol transition by actin filament severing:
- Cross-linking proteins hold cytoskeleton to make rigid mesh/scaffold
- to release + protrude to memb –> they need cytoplasm to flow (gel status –> sol status)
- Can severe filaments (not cross-linking proteins) to allow cytoplasm flow in parts of cell to allow expansion of membranek
how does cooperation of actin help in generating filaments?
- Profilin-(G)actin binds plus end for elongation
- When filaments broken down, cell can glue pieces back together (annealing)
- Or short filament can grow new separate fibre
Which one of these diseases is not caused by deregulation of actin cytoskeleton?
a) High blood pressure
b) Wiskott-Aldrich Syndrome – WAS (immunodeficiency, eczma, autoimmunity)
c) Duchenne Muscular Dystrophy (muscle wasting)
d) Bullous Pemphigoid (autoimmune disease)
e) Alzheimer (neurodegenerative)
e) Alzheimer (neurodegenerative)
Participation of different actin activities during cell movement
i.f list the various stages
- disassembly
- nucleation
- branching
- severing
- capping
- bundling
What is lamallae protrusion?
- controlled by polymerization + formation of branched filaments
- -> allows sheer of memb to be protruded
- -> movement of monomer to the front
- -> allows incorporation of new filaments
what do you need to form the filopodia?
you need
- actin polymerisation
- bundling
- crosslinking
describe the regulation of cytoskeleton by small G proteins.
- Rho subfamily of small GTPases belongs to the Ras super-family
–> Family members: Rac, Rho, Cdc42 best known
- Participate in a variety of cytoskeletal processes.
- These proteins are activated by: receptor tyrosine kinase/ adhesion receptors / signal transduction pathways.
- Expression = up-regulated in different human tumours.
How do small GTPases participate on cell migration?
- Deadhesion is action of Rho, so if block Rho –> block movement
- Lamellipodium controlled by Rac
- Focal adhesion controlled by Rac + Rho
- Contraction + deadhesion controlled by Rho
types of tumour cell migration
- ameoboid –> round
mesenchymal –> - cluster / cohorts –> synchronise motility
- multicellular strands/ sheets –>
- -> integrins + protease = found in all types of cell migration
- -> cahejrins + gap junctions = found in cluster cohorts + multicellular strands - which mediates cell to cell contact
note: compared to wound healing, migration in tumour = faster + more dysregulated
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What are 3 structures used for motility?
Lamellipodia
filopodia
Attachment of cells to substratum
what are the 4 signalling mechanisms that regulate actin cytoskeleton
1 - ion flux changes (i.e. intracellular calcium)
2 – Phosphoinositide signalling (phospholipid binding)
3 – Kinases/phosphatases (phosphorylation cytoskeletal proteins)
4 - Signalling cascades via small GTPases
note:
Rho activation –> formed stress fibres
Rac –> forms lamellipodia
CDC42 –> forms filopodia
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- actin polymerisation + branching of lamellipodium = controlled by _____
- focal adhesion + assembly = controlled by _____
- contraction = controlled by ____
- detachment at back = controlled by ____
- formation of filopodia + polarisatied motility + actin polymoeration = controlled by ______
- actin polymerisation + branching of lamellipodium = controlled by Rac
- focal adhesion + assembly = controlled by rac + rho
- contraction = controlled by rho
- detachment at back = controlled by rho
- formation of filopodia + polarisatied motility + actin polymoeration = controlled by cdc 42
