Invasion – Regulation of Cell Motility Flashcards
What changes occur in the cells that occur during tumour progression?
Genetic alterations lead to: hyperproliferation disassembly of cell-cell contacts loss of polarity increased motility cleavage of ECM proteins
What are the different types of tumour cell migration? Give examples of types of cancer that behave in this way
Single cell migration (ameboid) e.g. Leukaemia
Mesenchymal single cells e.g. Fibrosarcoma
Mesenchymal chains e.g. Glioblastoma
Clusters/cohorts e.g. Melanoma
Multicellular strands/sheets e.g. Vascular tumours
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?
Cytoskeleton regulation
Motility machinery
What makes normal migrating cells stop moving? How are tumour cells different in migrating?
Contact inhibition of locomotion
Tumour cells lose contact inhibition of locomotion so can multilayer
What is another term for ECM proteins?
Substratum
What are filopodia?
Finger-like protrusions rich in actin filaments
Sense the local environment
What are lamellipodia?
Sheet-like protrusions rich in actin filaments
What are the four main stages of cell movement?
Extension
Adhesion
Translocation
De-adhesion
What are the attachments between the cell and the surface that it is moving along called?
Focal adhesions
What are the monomers and polymers of actin filaments?
Monomers: G-actin
Polymers: F-actin
Describe the polarity of actin filaments.
They have a plus end + a minus end
Monomers preferentially get added on at the plus end
What protein complex is important in initiating polymerisation?
Arp2/3
Forms a trimer with actin, cell thinks there is a trimer, this facilitate rapid nucleation + initiates polymerisation
What is the limiting step in actin dynamics?
Formation of Arp2/3-actin trimers to initiate polymerisation
State two proteins that bind to free G-actin and describe how they affect elongation.
Promote elongation: profilin (deliver G-actin to the growing filament)
Sequesters G-actin: Beta–4 thymosin, ADF, cofilin
Name 3 + end capping proteins.
CapZ
Gelsolin
Fragmin/ severin
Name 2 – end capping proteins.
Tropomodulin
Arp2/3
Name 3 severing proteins.
Gelsolin
Framin/ severin
ADF/ Cofilin
What are the features of the actin filaments in severed populations?
Actin filaments can grow + shrink more rapidly (than unsevered populations)
What can happen to single filaments of actin to improve their structural integrity?
They can be bundled or cross-linked
Name 6 proteins involved in cross linking and bundling actin.
Alpha-actinin Fimbrin Filamin Spectrin Villin Vinculin
Which protein allows branching of the actin filaments?
Arp2/3
At what angle do actin filaments branch?
70 degrees
Summarise the actions of Arp2/3.
Initiate nucleation
Cap filaments
Cause branching
Describe what causes the gel-sol transition.
Actin filaments can be severed to make the cell more fluid
Describe the actin processes that take place during the protusion of lamellipodia.
Polymerisation, disassembly, branching + capping
Net filament assembly at the leading edge + net filament disassembly behind leading edge
Describe the actin processes that take place during the formation of filopodia.
Actin polymerisation
Bundling + cross-linking
(NO branching)
Capping at the projecting end + disassembly at the bottom of the protrusion allows retraction back to the membrane
State four signalling mechanisms that regulate the actin cytoskeleton.
Ion flux changes (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: filopodia
Rac: lamellipodia
Rho: stress fibres
(all part of the Rho family)
Explain how Rac causes actin polymerisation/organisation.
Rac binds to + activates WAVE
WAVE then activates Arp2/3 (important in actin organisation)
Explain how Cdc42 causes actin polymerisation/organisation.
Cdc42 binds to WASP
WASP activates Arp2/3 (important in actin organisation)
Which small GTPases are involved in lamellipodia protrusion?
Rac
Which small GTPases are involved in focal adhesion assembly?
Rac + Rho
Which small GTPases are involved in contraction?
Rho (assembles stress fibres, important for contraction)
What molecules are involved in all types of tumour cell migration? (Individual and collective)
Integrins
Proteases
What molecules are only involved in collective tumour cell migration?
Cadherins
Gap junctions
What are the main roles of integrins?
Signalling port to connect the cytoskeleton to the ECM
To structurally support the cell
What are the 2 types of motility?
Hapoptatic: Aimless, non directional movement
Chemotactic: Purposeful, polar movement
Describe the different filament organisations and structures found in motile cells
Filopodium: Bundle of parallel filaments
Lamellipodium: Branched + cross linked filaments
Stress fibres: Antiparallel contractile structures that form focal adhesions
What are the 2 ways in which G-actin can be remodelled?
Nucleating
Sequestering
Which molecule helps contraction of cells?
Myosin
How are the Rho subfamily of small GTPases activated?
By receptor tyrosine kinase, adhesion receptors + signal transduction pathways
What is the importance of Cdc42 in cell migration?
Generation of filopodia to sense appropriate direction of movement
Receptors to chemotractants need Cdc42 to transduce signalling that occurs in the cell
Important for actin polymerisation as with Rac control Arp2/3 complex formation
