Invasion and regulation of motility Flashcards
Describe the Tumour Progression from homeostasis to metastasis
Describe the Tumour Progression
Steps of tumour progression:
- Homeostasis
- Genetic alterations
- Hyper-proliferation (primary tumours start as tighlty bound cells)
- De-differentiation:
- Disassembly of cell-cell contacts. (loose their epithelial cells properties)
- Loss of cell polarity.
- Invasion:
- Increased motility, form a mass and invade
- Cleavage of ECM proteins.
What are the different Types of Migration?
What are the different Types of Migration?
- Individual cell migration: (require integrins and proteases)
- Amoeboid – e.g. lymphomas.
- Mesenchymal (single) – e.g. Fibrosarcoma.
- Collective cell migration: (require cadherins and gap juncitons)
- Mesenchymal (chains) – e.g. Fibrosarcoma.
- Cluster/cohorts – e.g. Epithelial cancers.
- Multicellular strands/sheets – e.g. Epithelial cancers.
- Collective cell migration requires more coordination to metastasise and so still has some cell-cell junctions that communicate
What does the metastatic process resmble? What are the mutations that are found?
Tumour cell metastasis/migration MIMICS PHYSIOLOGICAL morphogenic events.
- E.G. Branching morphogenesis in the mammary glands.
- E.G. Migration of primary glial cells to repair a scratch wound (the cells stop migrating when the contact is made) – conversely, tumour cells will have no clear migration front and no sense of direction.
The metastatic process results in upregulation of the genes involved in:
- Cytoskeleton regulation.
- Motility machinery.
How is cell movement guided?
What inhibits the progression of the cell movement
Where to go?
- Polarity
When to stop?
- Contact-inhibition
- How?
- Filopodium
- Lamellae
- Local adhesions
- How?
What are the structures used in motility ?
What is the purpose of motility?
Which structures are used in Motility and how are they coordinated?
- The cells attach to the ECM via integrins.
- For motility, the cell uses:
- Filopodia – finger-like projections rich in actin filaments.
- A bundle of parallel filaments. (result from remodelling the cytoskeletone)
- Lamellipodia – sheet-like protrusions rich in actin filaments.
- Branched and crosslinked filaments. (contact is formed on a larger area)
- Filopodia – finger-like projections rich in actin filaments.
Control is needed in motility for/to:
- Coordinate happenings inside the cell itself.
- Regulate adhesion/release of cell-ECM.
- To respond to external influences.
How are focal adhesions broken to ensure motility?
What are the possible signals that can initiate movement?
- Contraction of Filopodia and Lamellipodia can break old facal adhesions, allowing the cell to maintain a motion.
- A signal to move could be a nutrient source and the filaments can rapidly disassemble and then reassemble at a new site to move the cell.
- Actin filaments have a polarity – there is a plus and minus end on which different proteins can bind.
- Depending on the proteins that bind, the actin filaments can carry out different functions.
Steps:
- Nucleation
- Elongation
- Severing
- Capping
- Cross-linking and Bundling
- Branching
Describe the nucleation step:
NUCLEATION
- Arp2 and Arp3 come together with some other proteins to form the ARP complex
- Actin monomers come together to form trimers and then begin attaching themselves to this complex (this is the rate limmiting step)
Describe the Elongation step:
Profilin facilitates actin monomer binding to the actin filament.
- Thymosin reduces actin monomer binding by sequestering the free monomers so they are not available to bind to the actin filament.
- VASP helps to recruit profilin to the area that is needed (necessary for the formation of the new branch)
- ARP/2/3: looks like a preformed dimer that helps to initiate the elongation (this and profilin is initiates the creation of a new branch)
- To elomgate you need the free actin monomers and the short filaments
- It is continuously broken down and turn over because it can more easily be regulated
- It is ATP dependent, (you need to add a phospate to the monomer to be addded to the structure, adn then it is remouved)
- The first steps id thermodinamacally difficult to avoid the formation of small dimers all the time
Describe the Capping and Severing step:
- Capping – addition of a capping molecule (to + or – end) to limit elongation.
- Plus-end caps – Cap Z, Gelsolin, Fragmin/Severin.
- Minus-end caps – Tropomodulin, Arp complex.
- Severing – breaking up actin filaments:
- Chop the filament up which generates more ends so that the filaments can grow more rapidly
- Proteins – gelsolin, ADF/cofilin, fragmin/severin.
- Chop the filament up which generates more ends so that the filaments can grow more rapidly
Gelosin caps and severs filaments
Describe the
- Crosslinking and Bundling
- Branching
of actin:
Crosslinking & bundling:
- Fascin, Fimbrin and Alpha-actinin bind filaments together
1. Spectrin, Filamin and dystrophin will cross-link the filaments at angles
Dystrophin mutated in muscular diseases, they will link filaments in the plasma membrane, mainly in boys, X chromosome, instead fatty tissue
Fibrin different spaces between them
- Branching:
- This protein enables branches of actin to come off at 70degree angles.
- Protein – Arp complex (Arp2)
Describe Gel-Sol Transition by Actin Severing
Gel the membrane has some rigidity but if you need to protrude and change their shape they need to become SOL and this is done by clipping the filaments at certain points
LO: explain the role of second messengers as control mechanisms for cytoskeletal components
GTPases - e.g. Rho subfamily (Rac, Rho, Cdc42)
- Inactivated when GTP → GDP
Rho proteins are upreg in tumours
When activated they form these actin cytoskeletal structures by activating other proteins
- Cdc42 → WASP → Arp2/3 → filopodia
- Rac → WAVE → Arp2/3 → lamellipodia
- Rho → stress fibres
Focal adhesion assembly is a RAC and RHO process and contraction is a RHO area
State the main types of actin and given an overview of the locomotion
2 types of actin:
- G (Globular) are small soluble subunits
- F (Filamentous) are large polymers
The process of movement depends on the disassembly of existing F actin and repolarisation to the direction of the stimulus and then subsequent polymerisation at that site
- The lamellipodium extends forward by actin polymerisation, putting the cortex under tension, resulting in the movement of intracellular components forward (by unpolymerized actin) to the direction of the lamellipodia to relieve the tension.
- The cell swells and moves forward, then subsequent retraction of the opposite pole of the cell restores normal structure.
- New focal contacts with the membrane anchors the cell, and the process repeats.
Which are the Signalling mechanisms that regulate the actin cytoskeleton?
- ion flux changes (i.e. intracellular calcium)
2 – Phosphoinositide signalling (phospholipid binding)
3 – Kinases/phosphatases (phosphorylation cytoskeletal proteins)
4 - Signalling cascades via small GTPases
How does signalling from small GTPases regulate actin cytoskeleton and motility?
The below pictures show how the above methods are used in the cell.
