Invasion - Regulation of Cell Migration Flashcards
What is the sequence of steps that lead to tumour formation and spread
- Homeostasis
- Genetic Alterations
- Hyper-proliferation
- De-differentiation
- Invasion
- Metastasis
Describe the epithelial tissue in the homeostasis stage of tumour progression
In homeostatic epithelial tissue there is a layer of cells tightly attached to each other lying on a basement membrane
Beneath is a stroma consisting of blood vessels and supportive tissues
What is the consequence of genetic alterations in tumour progression
If there are a cumulation of genetic alterations, there may be hyperproliferation of some cells – this leads to the formation of a benign tumour
Explain the de-differentiation stage of tumour progression
Progression from a benign to malignant tumour involves the cells de-differentiating (losing their identity and function as epithelial cells)
disassembling cell-cell contacts
losing polarity
Explain the invasion stage of tumour progression
Malignant cells invade the basement membrane, requires:
Cleavage of ECM proteins
Increase motility
Describe metastatic cells under the microscope
Cell migrate much faster
No attachment to neighbours
Movement in every direction, over each other
Do not stop by contact inhibition
Describe the sequential events of metastasis
- Epithelial cells in primary tumours are tightly bound together
- Metastatic tumour cells become mobile mesenchyme-type cells and enter the bloodstream
- Metastatic blood cells then travel through the bloodstream to a new location in the body
- Metastatic cells exit the circulation and invade a new organ
- Cancer cells lose their mesenchymal characteristics and form a new tumour
How are tumour cells profiled
Tumour cells are inoculated in a mouse, and they form a primary tumour. Growth factors can then be used to stimulate cell migration
How is the extraction of both the primary tumour cells, and the more invasive cells compared with regards to their expression profile ≈
By measuring mRNA levels
It is found that there is upregulation of genes involved
Which genes are upregulated in comparison of expression profile of invasive cells vs primary tumours
Cytoskeleton regulation
Motility machinery
What are the stimuli for cell movement
organogenesis and morphogenesis
Wounding
Growth factors/chemoattractants
Dedifferentiation (tumours)
What are the factors involved in regulation of cell movement
Direction (polarity)
Contact-inhibition motility
Specialised structure formation (focal adhesion, lamellae, filopodium)
What are focal adhesions
Focal adhesions are the sites at which the cell attaches to proteins which make the ECM
Explain how ECM proteins cause cell attachment to the substratum
Filamentous actin lies beneath the membrane, and hooks the focal adhesions to the
cytoskeletons via integrins
On the intracellular side, integrins interact with various cytoskeletal proteins to form a plaque
What are filopodia and what do they do
Finger-like protrusions rich in actin
Protrude from the cell to sense where they want to attach, and direction of movement
Which structures in actin filaments attach to the substratum and what is the name given to them when they move back
Lamellipodia
Ruffles
What is vinuncilin
Proteins that overlie the protrutions of filopodia
Control is needed:
Within a cell to coordinate what is happening in different parts
To regulate adhesion/release of cell-ECM receptors
From outside to respond to external influences
What are the 2 types of cell motility
Hapoptatic motility - movement with no direction
Chemotactic movement - movement in which the cell senses a stimulus and goes towards it
Both involve changes in cell shape
How do cells regulate their shape changes
Regulation of actin cytoskeleton
- Signal (e.g. nutrient source) at one end
- F-actin at the other end disassembles
- Subunits diffuse to the signal side
- Reassembly of the subunits at the new site
- Movement facilitation
What structure can actin be found as in the cytoskeleton
Can be found as small soluble globular monomers (G-actin)
Or
in a large polymerized filamentous polymer (F-actin)
How does actin facilitate movement
- Signal (e.g. nutrient source) at one end
- F-actin at the other end disassembles
- Subunits diffuse to the signal side
- Reassembly of the subunits at the new site
- Movement facilitation
Describe the actin filament arrangement in the cell cortex
random gel-like arrangement to provide support to the plasma membrane
Describe the actin filament arrangement in the stress fibres
anti-parallel arrangement, forming contractile bundles
Describe the actin filament arrangement in the filopodium
tight parallel bundles
What is remodelling of actin filaments driven by and what does actin dynamics refer to
Different actin binding proteins
The cycle between G-actin monomers
Describe the G-actin monomers in solution and what is the solution to the problem it poses
Polymerises very quickly, because the lowest energetic state is as a filament (but you can’t just have loads of filaments in the cell)
The solution to this is to have sequestering proteins, which store the G-actin monomers until they are required.
What are capping and severing proteins
Stop signals which prevent further growth.
Severing proteins act like scissors, and various proteins regulate how the filaments are arranged
Draw a diagram that illustrates the remodelling of actin filaments
(refer to notes)
What is nucleation in actin filament remodelling
Rate limiting step in actin dynamics
Formation of trimers to initate polymerisation
Explain what occurs in nucleation during actin filament remodelling
Arp 2 + 3 (actin-related proteins) are similar to actin, and form a complex on which trimers of actin can attach (on the minus end)
Elongation of the filament can then occur from the Arp2/3 complex
Explain what occurs in the elongation stage of actin filament remodelling
Profilin binds to the monomers and helps to elongate the filament.
Thymosin is a sequestering protein which prevents polymerisation.
There is a balance between these two proteins to regulate filament growth, as
profilin competes with thymosin for binding to actin monomers and promote
assembly.
Explain what occurs in the branching stage of actin filament remodelling
branched filaments form a precise 70 degree angle.
Arp complex binds to the
ide of the filament, providing nucleation at a different site
What do capping proteins do
Prevents further growth of the filament
Can be used to regulate directionality of growth
Which proteins are in the plus end of capping proteins
Cap Z
Gelsolin
Fragmin
Severin
Which proteins are in the minus end of capping proteins
Tropomodulin
Arp complex
What are the two types of cross-linking and bundling
- Actin filaments and alpha-actinin, which forms a contractile bundle, which a loose packing allowing myosin-II to enter the bundle
- Actin filaments and fimbrin, which forms parallel bundling with tight packing
What is the role of severing during action filament remodelling
Prevents low rate of growth/shrinking of very long filaments
Give examples of severing proteins
Gelsolin
AF/Cofilin
Fragmin/severin
What do membrane connections allow the cell to do
Sense surfaces and suitable environments for protrusions
What do membrane connections involve
Transmembrane protein, and a intracellular plaque which is attached to the cytoskeleton
Connections are then mediated by cell-cell and cell-ECM receptors
Give examples of proteins that membrane connections involve
Talin Alpha-catenin Spectrin Ezrin All of these proteins are perturbed (Changed, or truncated) in cancer
Which actin activities occur in cell movement
Disassembly Nucleation Branching Severing Capping Bundling
Give an example of participation of action in cell movement and what actin activities does it involve
Lamellae protrusion
Involves polymerisation, disassembly, branching and capping.
What are the signalling mechanisms that regulate the actin cytoskeleton
Ion flux changes (i.e. intracellular calcium)
Phosphoinositide signalling (phospholipid binding)
Kinases/phosphatases (phosphorylation cytoskeletal proteins)
Signalling cascades via small GTPases
Explain how ion flux changes regulate the actin cytoskeleton
Gelsolin severing is Ca2+ dependent, as this exposes the fast depolymerising end
Alpha-actinin crosslinks actin filaments, and this is decreased in high Ca2+ levels
Explain how signalling cascades via small GTPases regulates the actin cytoskeleton
Uses Rho (subfamily from Ras) to participate in cytoskeletal processes Activated by receptor tyrosine kinase, adhesion receptors and signal transduction pathways
What are filopodia, lamellae and stress fibres activated by
Filopodia - Cdc42
Lamellae - Rac
Stress fibres - Rho
What do the G-proteins )GTP-ases) of the Ras super family cdc42, Rac, and Rho activate
Filopodia - Cdc42
Lamellae - Rac
Stress fibres - Rho
What occurs during protrusion in lamellar protrusion
Net filament assembly at the leading edge, and net filament disassembly behind the leading edge.
What do filopodia involve
Polymerisation / growth
Bundling
Fimbrin cross-linking
