Invasion – Regulation of Cell Motility

Question 1

What are the changes that 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 and cleavage of ECM proteins

Question 2

What are the different types of tumour cell migration?

Answer 2

Single cell migration (ameboid) 
Mesenchymal single cells  
Mesenchymal chains  
Clusters/cohorts 
Multicellular strands/sheets

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?

Answer 5

Contact inhibition of locomotion

Question 6

How are tumour cells different in this aspect?

Answer 6

They lose contact inhibition of locomotion so they can multilayer

Question 7

What is another term for ECM proteins?

Answer 7

Substratum

Question 8

What are filopodia?

Answer 8

Finger-like protrusions that are rich in actin filaments

They sense the local environment

Question 9

What are lamellipodia?

Answer 9

Sheet-like protrusions that are rich in actin filaments

Question 10

What are the four main stages of cell movement?

Answer 10

Extension
Adhesion
Translocation
De-adhesion

Question 11

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

Answer 11

Focal adhesions

Question 12

What are the monomers of actin filaments?

Answer 12

G-actin

Question 13

Describe the polarity of acting filaments.

Answer 13

They have a plus end and a minus end

The monomers preferentially get added on at the plus end

Question 14

What protein complex is important in initiating polymerisation?

Answer 14

Arp2/3

This forms a trimer with actin and is good at initiating polymerisation

Question 15

What is the limiting step in actin dynamics?

Answer 15

Formation of Arp2/3-actin trimers to initiate polymerisation

Question 16

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

Answer 16

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

Question 17

Name some + end capping proteins.

Answer 17

CapZ
Gelsolin
Fragmin/severin

Question 18

Name some – end capping proteins.

Answer 18

Tropomodulin

Arp2/3

Question 19

Name some severing proteins.

Answer 19

Gelsolin ADF
Framin/severin
Cofilin

Question 20

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

Answer 20

Actin filaments can grow and shrink more rapidly

Question 21

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

Answer 21

They can be bundled or cross-linked

Question 22

Name some proteins involved in these processes.

Answer 22

Alpha-actinin 
Fimbrin 
Filamin 
Spectrin 
Villin 
Vinculin

Question 23

Which protein allows branching of the actin filaments?

Answer 23

Arp2/3

Question 24

At what angle do they branch?

Answer 24

70 degrees

Question 25

Summarise the actions of Arp2/3.

Answer 25

They initiate nucleation They cap filaments They cause branching

Question 26

Describe what causes the gel-sol transition.

Answer 26

The actin filaments can be severed to make the cell more fluid

Question 27

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

Answer 27

There is polymerisation, disassembly, branching and capping There is net filament assembly at the leading edge

Question 28

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

Answer 28

Actin polymerisation Bundling and cross-linking (NO branching) As soon as the finger wants to retract it will collapse at the base

Question 29

State four signalling mechanisms that regulate the actin cytoskeleton.

Answer 29

Ion flux changes Phosphoinositide signalling Kinases/phosphatases Small GTPases

Question 30

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

Answer 30

Cdc42 – filopodia Rac – lamellipodia Rho – stress fibres NOTE: these are all part of the Rho family

Question 31

Explain how Rac causes actin polymerisation/organisation.

Answer 31

Rac binds to and activates WAVE | WAVE then activates Arp2/3, which is important in actin organisation

Question 32

Explain how Cdc42 causes actin polymerisation/organisation.

Answer 32

Cdc42 binds to WASP | WASP also activates Arp2/3

Question 33

Which small GTPases are involved in lamellipodia protrusion?

Answer 33

Rac

Question 34

Which small GTPases are involved in focal adhesion assembly?

Answer 34

Rac and Rho

Question 35

Which small GTPases are involved in contraction?

Answer 35

Rho (stress fibres are important for contraction)