Invasion – Regulation of Cell Motility

Question 1

What changes occur in the cells that occur during tumour progression?

Answer 1

Genetic alterations lead to:
hyperproliferation
disassembly of cell-cell contacts
loss of polarity
increased motility
cleavage of ECM proteins

Question 2

What are the different types of tumour cell migration? Give examples of types of cancer that behave in this way

Answer 2

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

Question 3

What physiological phenomena does tumour migration mimic?

Answer 3

Morphogenesis e.g. angiogenesis

Question 4

What did a comparison of the expression profile of invasive cells vs primary tumours show to be upregulated in invasive cells?

Answer 4

Cytoskeleton regulation

Motility machinery

Question 5

What makes normal migrating cells stop moving? How are tumour cells different in migrating?

Answer 5

Contact inhibition of locomotion

Tumour cells lose contact inhibition of locomotion so can multilayer

Question 6

What is another term for ECM proteins?

Answer 6

Substratum

Question 7

What are filopodia?

Answer 7

Finger-like protrusions rich in actin filaments

Sense the local environment

Question 8

What are lamellipodia?

Answer 8

Sheet-like protrusions rich in actin filaments

Question 9

What are the four main stages of cell movement?

Answer 9

Extension
Adhesion
Translocation
De-adhesion

Question 10

What are the attachments between the cell and the surface that it is moving along called?

Answer 10

Focal adhesions

Question 11

What are the monomers and polymers of actin filaments?

Answer 11

Monomers: G-actin
Polymers: F-actin

Question 12

Describe the polarity of actin filaments.

Answer 12

They have a plus end + a minus end

Monomers preferentially get added on at the plus end

Question 13

What protein complex is important in initiating polymerisation?

Answer 13

Arp2/3

Forms a trimer with actin, cell thinks there is a trimer, this facilitate rapid nucleation + initiates polymerisation

Question 14

What is the limiting step in actin dynamics?

Answer 14

Formation of Arp2/3-actin trimers to initiate polymerisation

Question 15

State two proteins that bind to free G-actin and describe how they affect elongation.

Answer 15

Promote elongation: profilin (deliver G-actin to the growing filament)
Sequesters G-actin: Beta–4 thymosin, ADF, cofilin

Question 16

Name 3 + end capping proteins.

Answer 16

CapZ
Gelsolin
Fragmin/ severin

Question 17

Name 2 – end capping proteins.

Answer 17

Tropomodulin

Arp2/3

Question 18

Name 3 severing proteins.

Answer 18

Gelsolin
Framin/ severin
ADF/ Cofilin

Question 19

What are the features of the actin filaments in severed populations?

Answer 19

Actin filaments can grow + shrink more rapidly (than unsevered populations)

Question 20

What can happen to single filaments of actin to improve their structural integrity?

Answer 20

They can be bundled or cross-linked

Question 21

Name 6 proteins involved in cross linking and bundling actin.

Answer 21

Alpha-actinin 
Fimbrin 
Filamin 
Spectrin 
Villin 
Vinculin

Question 22

Which protein allows branching of the actin filaments?

Answer 22

Arp2/3

Question 23

At what angle do actin filaments branch?

Answer 23

70 degrees

Question 24

Summarise the actions of Arp2/3.

Answer 24

Initiate nucleation
Cap filaments
Cause branching

Question 25

Describe what causes the gel-sol transition.

Answer 25

Actin filaments can be severed to make the cell more fluid

Question 26

Describe the actin processes that take place during the protusion of lamellipodia.

Answer 26

Polymerisation, disassembly, branching + capping | Net filament assembly at the leading edge + net filament disassembly behind leading edge

Question 27

Describe the actin processes that take place during the formation of filopodia.

Answer 27

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

Question 28

State four signalling mechanisms that regulate the actin cytoskeleton.

Answer 28

Ion flux changes (intracellular calcium) Phosphoinositide signalling (phospholipid binding) Kinases/phosphatases (phosphorylation cytoskeletal proteins) Signalling cascades via small GTPases

Question 29

What are the three most important small GTPases in terms of the actin cytoskeleton and what does activation of each cause?

Answer 29

Cdc42: filopodia Rac: lamellipodia Rho: stress fibres (all part of the Rho family)

Question 30

Explain how Rac causes actin polymerisation/organisation.

Answer 30

Rac binds to + activates WAVE | WAVE then activates Arp2/3 (important in actin organisation)

Question 31

Explain how Cdc42 causes actin polymerisation/organisation.

Answer 31

Cdc42 binds to WASP | WASP activates Arp2/3 (important in actin organisation)

Question 32

Which small GTPases are involved in lamellipodia protrusion?

Answer 32

Rac

Question 33

Which small GTPases are involved in focal adhesion assembly?

Answer 33

Rac + Rho

Question 34

Which small GTPases are involved in contraction?

Answer 34

Rho (assembles stress fibres, important for contraction)

Question 35

What molecules are involved in all types of tumour cell migration? (Individual and collective)

Answer 35

Integrins | Proteases

Question 36

What molecules are only involved in collective tumour cell migration?

Answer 36

Cadherins | Gap junctions

Question 37

What are the main roles of integrins?

Answer 37

Signalling port to connect the cytoskeleton to the ECM | To structurally support the cell

Question 38

What are the 2 types of motility?

Answer 38

Hapoptatic: Aimless, non directional movement Chemotactic: Purposeful, polar movement

Question 39

Describe the different filament organisations and structures found in motile cells

Answer 39

Filopodium: Bundle of parallel filaments Lamellipodium: Branched + cross linked filaments Stress fibres: Antiparallel contractile structures that form focal adhesions

Question 40

What are the 2 ways in which G-actin can be remodelled?

Answer 40

Nucleating | Sequestering

Question 41

Which molecule helps contraction of cells?

Answer 41

Myosin

Question 42

How are the Rho subfamily of small GTPases activated?

Answer 42

By receptor tyrosine kinase, adhesion receptors + signal transduction pathways

Question 43

What is the importance of Cdc42 in cell migration?

Answer 43

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