8: Regulation of Cell Motility (Invasion)

Question 1

Explain the different steps in tumor Progession

When do benign Tumors turn to malignant tumors?

Answer 1

1. Homeostasis (normal cells)
2. Genetic alteration
3. Hyper-proliferation

–> Benign

4. De-differentiation

• dissasembly of cell-cell contacts
• loss of polarity

5. Invasion

• increase motility
• cleavage of ECM proteins and basemsent membranes –> Metastisis

Question 2

What are the two main types of tumor cell migration?

How do they differ?

Answer 2

1. Individual cell migration
   
   1. Ameoboid cells
   2. Mesenchymal (single) cells
   3. Mesenchymal(chain) cells
2. Collective cell migration
   
   1. Cluster cohorts
   2. Multicellular strands/sheaths

Question 3

Which factors are needed in individual cell migration?

Answer 3

Individual cell migration requires

• integrins and proteases for Basememnt membrane cleavage

Question 4

What factors are needed in Cluser/multicellular cell migration of tumors?

Answer 4

1. Integrins and proteases to cleave basement membrane
2. Gap junctions and cadherins for coordination of movements

Question 5

What are the characteristics of tumor cell metastisis?

Answer 5

They mimic normal morpholigical movements

• as seen in angiogenesis
• branching morphogenseis like in mamillary gland
• etc.

Question 6

How does migration of a tumor differ from normal cell migration?

Answer 6

Often they try to mimic morphological cell movement but are different in

• deattaches from another (no cell-cell junctions and signaling)
• grow randomly + unorgansied
• fast growth

Question 7

How does the Gen profile of migrating tumor cells differn from those that don’t migrate?

Answer 7

Often:

• upregulation in cytoskeleton regulation
• and machinery

–> Normally they don’t have more oncogenic mutations but are just more mobile (EGF mouse experiment)

Question 8

When does a cell move?

Answer 8

Normally due to external stimuli like

• organogenesis and morphogenesis
• wounding
• growth factors/chemoattractants

But can also happen in oncogenesis

• dedifferentiation (tumor formation)

Question 9

What are focal adhesions?

Answer 9

They are connections between the cell and the extracellular matrix through integrins

• Extracellularly: integrins bind to extracellular ligands
• Intracellularly: multiproteins assemble (Plaque) and are connected to the actin cytoskeleton

Question 10

What is the role of focal adhesions?

Answer 10

Important in signaling of movement

1. anchor the cell
2. Signaling: inform the cell about the composition of the ECM –> influence behaviour of cell

Question 11

What are filopodia?

Answer 11

Finger like projections of cell membrane made of actin filaments, involved in cell motility

Question 12

Explain the structure of Fillopodia

Answer 12

They are organised in

• straight, crosslinked actin filaments
• fomed by
  
  • Polerymerisation
  • Bundling of actin filaments
  • Crosslinking of the filaments

Question 13

What are Lamellipodia?

Answer 13

Shee-like pertrusions of cell membrane, rich in actin filaments needed for cell motility

*

Question 14

What are the four steps that repetitively happen in cell movement?

Answer 14

1. Extention
   
   • Lamellipodia and Fillopodia grow into direction of movement
2. Adhesion
   
   1. New adhesions (focal adhesions) with ECM+ Basement membrane found
3. Translocation
   
   • Cell body is moves in the direction of the movement, via contraction of actin filaments on the side opposite of movement
4. De-adhesion of old adhesion

Question 15

How does the overall cell shape change in a migrating cell compated to a normal cell?

Answer 15

It will become a polerised (in shape) cell

Question 16

What are stress fibres?

What is their role in cell migration?

Answer 16

Antiparralel strucztures actin filaments needed in cell migration

–> contraction of the cell

Question 17

What are the different forms /organisations of actin (tip: differ in number)

Answer 17

1. G Actin
   
   • monomers, get assemblied to
2. F Actin
   
   • polymers, assembly to different structures

Question 18

When is the assembly and disassembly of G and F actin important in cell migration?

Answer 18

It is important to disassembyl the F actin to G proteins to make them available

• The G need to be converted to F to form new structures for migration (e.g. Filopodia, Laemlipodia)

Question 19

What is the first and rate limiting step in actin assembly?

What happens durin this step

Answer 19

Nucleation

• Attachment of actin to the inner cell membrane
• Arp proteins form a complex and bind actin monomers to create a nucleated actin filament
  
  • Actin monomers bind to Arp-complex

Question 20

Which proteins are important in the nucleation of actin filaments (other than G actin itself?)

Answer 20

Arp complexes

Question 21

After initial formation of a actin trimer, what is the next step in actin filament formation?

Which protein is neede for it?

Answer 21

Elongation

• Controlled by
  
  • +: profilin
  • inhibited by thymosin

Question 22

What are the different steps in formation of an actin filaments for cell movement?

Answer 22

1. Nucleation
2. Elongation
3. Capping
4. Severing
5. Cross linking and bundle formation
6. Branching
7. Gel-sol transition by actin filament severing

Question 23

What happens after the Elongation of actin monomers to form an actin filament?

Answer 23

Capping

• further elongation inhibited
• done by proteins like: (also Arp protein involved)

Question 24

After capping of Actin filaments, what is the next step?

Why is it importantn?

Answer 24

Severing

• enables quicker break down and reassembly of actin filaments (because chunks of actin are available, not jut monomeres)

Question 25

What is the role of Arp in the formation and disassembly of actin filaments?

Answer 25

It is involved in * nucleation * Capping * Branching of the filaments The same protein has different functions and do many things, dependant on their current regulation

Question 26

What ar the possible fates of single severed actin filaments?

Answer 26

1. De-polymerisation and monomer recylcling 2. Annealing to other parts 3. Elongation (at (+)Barbed-end with profilin actin filaments)

Question 27

What is the next step after formation of a fully functional indivudual actin filament?

Answer 27

Cross-linking and bundling of strands * functional dependant, many proteins can cross link e.g. * Bundling * Buckling if needed for contraction

Question 28

Explain the role and the protein involved in actin branching

Answer 28

Branching forms a stable network of actin filaments --\> needed in formation for Lemelipodia * 70° angle used Mediated by the **Arp complex**

Question 29

What happens during the Gel-Sol transition of actin filaments? Why does it happen?

Answer 29

A process of severing * a few actin filaments are cleaved to allow **movement** (sol-phase) from steady gel phase

Question 30

Which cytoskeletal changes occur during Extention of the cell during movement?

Answer 30

Cell polymerisation is needed and all processes happen to deassambly/re-assembly actin filaments(e..g for lamellae protrusion) * Disassembly * Nucleation * Branching * Severing * Capping * Bundling

Question 31

Which cytoskeletal changes occur durin lamellae portrusion?

Answer 31

Polymerization, disassembly, branching, capping

Question 32

Which cytoskeletal processes occur during Filopodia bulding?

Answer 32

1. Polimerization 2. Bundling 3. Crosslinkin

Question 33

Which signals regulate the actin cytoskeleton?

Answer 33

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

Question 34

What kind of proteins are Rho proteins? Which protein class do they belong to? What is their function?

Answer 34

Rho proteins are a subfamily of small GTPases, belonging to the RAS superfamily They are needed in regulation of the cytoskeleton

Question 35

Which proteins regulate the cytoskeleton? Name indivudual ones that controll

Answer 35

Overall: Rho proteins * Folopodia: Cdc42 * Lamellipodia: Rac * Stress fibres: Rho

Question 36

How do Rho proteins get activated?

Answer 36

activated by * receptor tyrosine kinase * adhesion receptors * signal transduction pathways. --\> Cause GTP binding and therefore acivation (quick indactivation via phosphorylation)

Question 37

What is the role of Rho protiens in cancer?

Answer 37

They might be upregulated in differenet kind of cancers ## Footnote --\> more cytoskeletal activity

Question 38

How do Rho proteins controll the cytoskeleton?

Answer 38

* They set of a set of intracellular messenger systems and activate actin bindin proteins * Lead to actin polerization/organisation * Arp2/3 in nucleation * Cofilin, Profilin * etc.

Question 39

What is the role of Cdc42 in cell migration?

Answer 39

They are involved in the regulation of the Fillopodia and therefore needed for * regulation of the **polerized motility** * regulation of **actin polymerization**

Question 40

Explain the role of Rac in cell migration and movement

Answer 40

Needed in the 1. Adhesion 2. and Extention phase of cell migration * controlles lamellipodia and therefore needed for * focal adhesion assembly * actin polimerizsation and branching

Question 41

Explain the role of Rho (specific protein, not family) in cell migration and movement

Answer 41

Controlls **stress fibres** therefore needed in 1. Adhesion 2. Translocation 3. De-adhstion of cell Via * tension and contraction of filamnents

Question 42

What is the role of the actin polarity?

Answer 42

Have a + and - end * different proteins can bind to the different ends * depending on the bound protein, fibres can have different functions