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Canc > Cancer 11: Invasion > Flashcards

Cancer 11: Invasion Flashcards

1
Q

What are the molecular mechanisms that regulate motility

A

microfilaments
regulation of actin dynamics
cytoskeletal proteins
signalling proteins

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2
Q

What are the steps of tumour progression

A
  1. Homeostasis
  2. Genetic alterations
  3. Hyperproliferation
  4. Dedifferentiation
  5. Invasion
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3
Q

What is involved in dedifferentiation

A

disassembly of cell-cell contacts

loss of polarity

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4
Q

What is inolved in invasion

A

increased motility

cleavage ECM proteins

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5
Q

Outline how cells change property during metastasis

A

Tightly bound together in priary tumours

Become mobile mesenchyme type cells and enter blood stream

Exit circulation and lose mesenchymal characteristics to form new tumour

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6
Q

Classify the types of tumour cell migratin

A

Amoeboid (small collection of cells) e.g. lymphoma

Mesenchymal (single cells or in chains) e.g. breast sarcoma

Cluster/cohorts e.g. epithelial cancer/melanoma, SCC

Multicecellular strands/sheets e.g. epithelial cancer/vascu tumours, SCC

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7
Q

Outline the the important proteins in each category of tumour cell migration

A

The individual (amoeboid and mesenchymal) and collective (cluster/cohort and multicellular strands) both require integrins and protease

The collective also require cadherins and gap junctions

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8
Q

Tumour cell metastasis is similar to what

A

Mimics morphogenetic events:

The cancer cell is de-differentiated and taken back to a stage of development in which cells would physiologically invade tissue

e. g.
- Branching morphogenesis
- Vascular sprouting
- Border cells (collective migration)

In these processes, there is a tip cell which is pushed up and degrades tissue (i.e. in lung development). SImilar to clusters and invasion

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9
Q

…

A

…

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10
Q

Differentiate the scratch wound assay with primary glial cells vs with glial tumour cell line

A

In primary glial cells, the cells can sense a gap, but they maintain cell-cell contacts and migrate coherently (collective migration)

In the cancer cell line, the cells can sense the gap, but do not migrate together and do not maintain any cell cell contacts

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11
Q

Compare the expression profile of invasive cells vs primary tumour cells

How was the experiment performed

A

Inject tumour cells into a mouse. Then insert a needle with EGF, which is chemotactic for the tumour cells (but only those which can METASTASISE, as we only want to look at the proteins in the cells that can invade… othe tumour cells that can’t migrate are left in the primary tumour)

There was upregulation (so more mRNA) of genes (in invasive compared to primary tumour) involved in:

  1. CYTOSKELETON REGULATION
  2. MOTILITY MACHINERY

Especially Arp2/3 and EGFR

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12
Q

What can stimualte cells to move

A

organogenesis and morphogenesis

wounding

growth factors/chemoattractants (i.e. like how EGF was injected into the mouse to attract cells from the primary tumour)

dedifferentiation (tumours)

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13
Q

What determines where the cells go

How do cells know when to stop

A

Where to go: directionality (polarity occurs so that the cells become the mesenchymal type in the slide, the thicker end is the direciton of movement)

When to stop: contact inhibition motility

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14
Q

How do cells move

A

specialized structures (focal adhesion, lamellae, filopodium)

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15
Q

How are cells atttached to ECM proteins

A

Via integrins, there is an intracellular plaque linking the cytoskelon to the ECM

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16
Q

What are focal adhesions

A

Focal adhesions are large, dynamic protein complexes through which the cytoskeleton of a cell connects to the ECM

Filamentous actin converges onto the plaque which, through which it links to integrin molecules (look at the image, where there are focal adhesions, there is convergence of filamentous actin )

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17
Q

What is vinculin

A

vinculin is a membrane-cytoskeletal protein in focal adhesion plaques that is involved in linkage of integrin adhesion molecules to the actin cytoskeleton

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18
Q

Differentiate filipodia and lamellipodia

A

Filopodia: Finger-like protrusions rich in actin filaments. Parallel filaments

Lamellipodia_ Sheet-like protrusions rich in actin filaments. Branched and crosslinked filaments.

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19
Q

Where can filipodia and where can lamallipodia be found

A

During extension of the cell in migration , there is the ‘leading edge of lamellipodia’ (see rock climbing image)

Filopodia (also microspikes) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells

Note, filopodia are not included on this diagram

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20
Q

What control is needed in cell movement

A

Control within a cell to coordinate what is happening in different parts

Control to regulate adhesion/release of cell-extracellular matrix receptors (i.e. to allow attachment to the ECM and then degrade these attachments at the back of the cell)

Control from outside to respond to external influences –

sensors
directionality

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21
Q

What allows for cell movement

A

Changing cell shape

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22
Q

Differentiate the types of motility in cell movement

A

Motility:
hapoptatic (cell moving in different direction)

chemotatic (all of the cell moving in one direction… required control)…

determined by external influences (sensors and directionality)

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23
Q

What are the stages of cell motility

A

Extension, adhesion, trnaslocation, deadhesion

Like rock climbing….. look at the diagram slide 15

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24
Q

What are the two types of actin

A

G actin and F actin

G is small soluble subinity

F is large filamentous polymer

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25
Q

What can hppen to actin in response to signal such as nutrient source

A

Disassembly of filments and rapid diffusion of subunits

Then reassemby of filaments at a new site (i.e. where the signal was detected)

Basically, filamentous actin in one part of the cell will break down into monomeric actin and then reassemble at the site that the migration is required

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26
Q

Explain the relationship between lamellipodia, filopodia, stressfibres and focal adhesions.

Ensure you compare the organisaiton of actin in each structure too

A

Lamellipodia= leading front of the migrating cell.

Filopodia= extensions of the lamellipodia branching out

Stress fibres=actin filaments which converge at focal adhesions with integrin molecules

Stress fibres have anti-parallel contractile strucutres.

These allow for the contraction at the back of the cell which drives the cell forward.

Relate slide 17 to slide 15
……

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27
Q

How can G-actin start being converted to F-actin

A

Nucleating (formation of a stable multimer of actin monomers)

28
Q

F-actin can be modified. How?

A

After nucleation ,

severing, cross linking, capping, side binding, motor proteins and bundling

29
Q

…

A

……..

30
Q

Outline nucleation stage of actin polymerisation

A

Arp2 and Arp3 bind to other proteins and form an ARP compex

Then, at the MINUS end of the actin monomers which are forming into an actin filament, the ARP complex attaches

This leads to a NUCLEATED ACTIN FILMANET

31
Q

Why is nucleation important in actin polymerisation

A

Limiting step in actin dynamics – formation of trimers to initiate polymerization

32
Q

What happens in elongation stage of actin polymerisation

A

Addition and loss of G actin (dynamic) from the F actin chain.

Profilin binds to G- actin monomers and allows monomer binding to the forming actin filament

33
Q

What is sequestering and what is it carried out by

A

Sequestering:

Think this refers to either the prevention of binding of G actin to the extending F-actin

Or the removal of G actin from the F actin chain

Look at which molecules

34
Q

What can reduce the elongation process

A

SEQUESTERING:

  1. Profilin competes with thymosin for binding to actin monomers and promotes assembly

So thymosin binds to G-actin, but doesn’t allow monomers to be added to the forming actin filament.

Note that the Arp2/3 complex occurs at the negative end, but this means that the actin monomers are added on the positive end

They are reducing profilin action and thus reducing the polymerisation of monomers. They are a brake on polymerisation

  1. ADF/cofilin can also reduce elongation by severing monomers, therefore breaking down the actin filament
35
Q

What occurs in capping, give examples of these proteins

A

The capping protein binds the end of the filament and prevent monomers from being added on.

The filaments are very dynamic. Once adding is blocked, there is a disassembly process that results that &shortening of the filament

Proteins:

+ve end capping: Cap Z, gelosin, fragmin/severin

-ve end: tropomodulin and Arp complex (technically caps in the nucleation stage)

36
Q

What occurs in severing

A

The unsevered actin filament grows and shrinks, adding and removing monomers. Severing proteins chop the filament up

37
Q

T/f severing actually speeds up the elongation process

A

T

In usevered popultin, actin filaments grow and shrink slowly

In severed population, they grow and shrink more rapidly

38
Q

What is the function of gelsolin

A

Both caps at the +ve end and also severs

39
Q

Give examples of severing proteins

A

gelsolin
ADF/cofilin
fragmin/severin

40
Q

Elongation happens where on the filamentous actin

A

On the barbed end (requires energy, profilin-actin barbed end elongation)

41
Q

Outline the fates of a cut actin filament`

A
  1. Barbed-end Capped (remains a shorter actin filament now)
  2. Elongation of the cut part of the filament
  3. Annealing to a new actin
42
Q

Outline cross-linking and bundling

A

Note that everything up to this point has been involved in GENERATION OF THE ACTIN FILAMENT, whereas this stage involves ORGANISIATION of the generated ACTIN FILAMENTS

Some proteins can link separate actin polymers together in a parallel way, but at different distances apart
(fascin, fimbrin, a-actinin)

Spectrin links actin in a radiating structure

Filamin links actin in a non-parallel way

Dystrophin links actin to the membrane

43
Q

Give examples of proteins involved in cross-linking and bundling

A 
a-actinin
fimbrin
filamin
spectrin
villin
vinculin
44
Q

What occurs in buckling

A

When myosin acts between two actin polymers. It causes movements of the top strands together, allowing slack in the bottom strand

45
Q

What is involved in branching

A

Arp complexes which allow for the polymerisation of actin (nucleation stage) attach to existing actin filaments always at 70 degree angle

in the lamellipod

(in fillipodia, which branch off of the leading edge of the lamellipodia, the actin filaments are now in parallel bundles, not branched/in this way, but there is still cross-linking between bundles)

46
Q

What is the function of the arp complex

A

Nucleation of actin and also the branching

47
Q

What is gel-sol trnastion

A

Conversion from a relatively rigid cytoplasm gel to flowing cytoplasm

Severing of actin is used (HENCE THE GELSOLIN PROTEIN! INVOLVED IN CAPPING AND SEVERING!) . The actin cross linking proteins (e.g. fascin) are still present, but the filaments are no longer forming a mesh, so it allows a sol that can flow

Allows cytoplasm to move into another area

48
Q

Which of the following diseases is the actin cytoskeleton not involved in:

High blood pressure
Wiskott-Aldrich Syndrome – WAS (immunodeficiency, eczma, autoimmunity)
Duchenne Muscular Dystrophy (muscle wasting)
Bullous Pemphigoid (autoimmune disease)
Alzheimer (neurodegenerative)

A

Involved in all apart from alzheimers

49
Q

Which cell activities need to occur during cell movement

A

The cell is adhered to the ECM through focal adhesion (involing integrin+actin filaments in the cell (stress fibres)

There is disassembly of actin then POLYERMISATION: nucleation, brancing, severing, capping, bundling etc. At the lamellipodium, the actin cytoskeleton will be branching, elongating, capping, severing etc. At the back of the cell, there will be severing and bundling etc

There is then gel/sol transition to allow the cytoplasm to flow into the lamellipodium

Then there must be a new attachment to the ECM at this point

Then contraction at the back of the cell

Then detachment fro the adhesion at the back of the cell

50
Q

What will happen if there is no detachment of the focal adhesion at the back of the cell when the cell is moving forward

A

The cell will rip apart

51
Q

Outline the process of lamellar protrusion

A

There is asembly of filaments due to brancing and capping at when the lamellipod protrudes in the direction of mocement

At the back of the lamellar there is severing, reasing G actin from the actin filaments which can move to the leading edge

NET FOLAMENT ASSEMBLY AT LEADING EDGE

NET FILAMENT DISSAMBLY BEHHIND THE LEADING EGE

Use of FILAMIN for cross linking (NOT parallel, but crosslinked)

52
Q

What occurs in filipodia

A

There is actin polymerisation

There is lots of bundling and crosslinking of the actin to allow parallel actin strands with fascin. FAST ELONGATION

Then, upon removal of the stimulus, there is capping of the actin, and there is then retrograde flow and retraction as the base of the actin polymers are broken down

53
Q

What are the important proteins in filipodia and in lamellipodia

A

Filipodia: fascin, a actinin

Lamellippdia: Arp2/3, fliamin (BRANCHED)

54
Q

Which signallng mechanisms regulate the actin cytoskeleton

A

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

Think KIPS

55
Q

How do small G proteins work

A

Once activated, small G proteins bind to specific proteins (known as effectors). These effectors are the messengers that carry out actions. Proteins are inactivated by hydrolysis of GTP –> GDP.

56
Q

Give examples of the small G proteins

A

Rho subfamily of small GTPases belongs to the Ras super-family. Family members: Rac, Rho, Cdc42 best known

57
Q

Which is the most important signalling mechanism in regulation the actin cytoskeleton

A

Small GTPases

58
Q

What are small G proteins activated by

A

Proteins are activated by receptor tyrosine kinase, adhesion receptors & signal transduction pathways

59
Q

T/F although some small G proteins are upregulated in some cancers, no mtations have been found yet

A

F:

Expression levels upregulated in different human tumours

Rho proteins are upregulated in tumours – mutations have been found that lead to hyper-activation

60
Q

Give examples of how the Rho family of small GTPases can affect the cytoskeleton

A

Form cytoskeletal structures:

cdc42: induces filopodia

Rac; expansion and flattening of cell

Rho: induces stress fibres

61
Q

Give an example of the mechanism by which a Rho family GTPase affects cytoskeleton

A

Rac protein activates WAVE and Arp-2/3, so Rac will induce polymerisation.

cdc42 will upregute WASP which increases Arp2/3 too

62
Q

Actin binding proteins (arp) are regulated by which genes

A

Rac/Cdc42 GTPases

63
Q

Outline the involvement of RAC, RHO and cdc42 at each stage of cell movement

A

Cdc42: filopodia, polarised motility and actin polierisation

RAC: forms lamellipodia. Focal adhesion assembly (with RHO)

RHO: contraction of stress fibres/tension at the end of the cell not moving. Also detaches the back of the cell from the old adhesion to allow forward movement

64
Q

What could happen f you block Rho

A

Cell maybe ripped apart

65
Q

Give 2 examples of molecules which are involved in the filopodia

A

Vinculin and actin

Canc (16 decks)

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