8: Invasion - Regulation of Cell Migration Flashcards
What are the molecular mechanisms that regulate motility?
microfilaments
regulation of actin dynamics
cytoskeletal proteins
signalling proteins
What are the steps that make a benign tumour go to malignant?
De-differentiation
- disassembly of cell-cell contacts (don’t recognise neighbouring cells anymore)
- loss of polarity
Invasion
- increased motility
- cleavage of ECM proteins
What are the 4 main steps in metastasis?
- epithelial cells in primary tumours are tightly bound toegether
- metastatic tumour cells become mesenchyme-type cells and enter the bloodstream.
- metastasic cells 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 in the new tumour.
What are the types of tumour migration?
A. Individual
- ameboid (mostly lymphoma, leukemia, SCLC)
- mesenchymal (single cells)
- mesenchymal (chains)
e. g. glioblastoma, aplastic
B. Collective
(- clusters/cohorts -> 3-20 cells (in epithelial cancer and melanoma)
- multicellular strands/sheets (epithelial and vascular tumours)
- cadherins, contact between the neighbours, gap junctions
=> even with the same number of cells, there is a higher metastatic potential in clusters of cells than in single cells.
=> different signalling, different molecules. - proteases and integrins in both
Tumour cell metastasis - mimicking morphogenic events
a) 2D sheet
b) branching morphogenesis - mammary gland (has a leader cell)
c) vascular sprouting
d) multicellular 3D invasion
e) Border cells (e.g. ovary) - there are nurse cells around that are responsible for feeding
f) detached cluseter
In experiments on rodents, what was seen in terms of differences in cells of primary tumours and invasive cells?
- invasive cells have a higher expression of genes for cytoskeleton regulation and motility machinery
What are stimuli for cells to move?
- organogenesis and morphogenesis
- wounding
- growth factors/chemoattractants
- dedifferentiation (tumours)
What determines where a cell will go?
Polarity / Directionality (due to factors like chemoattractants)
What determines when the cell should stop moving?
contact-inhibition motility
How does a cell move?
specialised structures e.g.:
- focal adhesions
- lamellae
- filopodium
What are focal adhesions?
- dynamic protein complexes through which the cytoskeleton of a cell connects to the ECM.
- form mechanical links with (filamentous) actin inside the cell
- filamentous actin hooks to focal adhesions
- there is no enzymatic action on the ic side of integrins so a plaque of cytoskeletal proteins on the inside is responsible for the actions -> signalling port and connection to cytoskeleton
Filopodia
- structures used for motility
- Finger-like protrusions rich in actin filaments
- “fingers”
- contain filaments
- sense surrounding of cells
- are all over the cell
- also at the bottom of the cells if they are attached
Lamellipodia
- structures used for motility
- sheet-like protrusions rich in actin filaments / broad sheets of membrane
Cell movement control - why is it needed?
- within a cell to coordinate what is happening in different parts (e.g. if cell is moving in one direction, on the other end the cell has to detach to allow for movement)
- regulate adhesion/release of cell-extracellular matrix receptors
- from outside to respond to external influences –
sensors
directionality
How is cell movement mediated?
- change of cell shape
- focal adhesions with ECM
- extension -> lamellipodium lands on ECM
- adhesion -> lamellipodium forms new (focal) adhesion on ECM
- Translocation - cell body moves
- De-adhesion (old adhesion on the opposite side of direction of movement detatches from ECM)
=> here also small GTPases like Rho and Raf play a role. Also there are different actin activities such as polymerisation, gel/sol transition and contraction)
Motility types
Hapoptatic: you just go for the sake of moving
Chemotatic: there is a purpose and direction to move, there is a stimulus that drives the cell to a particular location
What is the difference between G- and F-actin?
- G: small, soluble subunits
- F: long, filamentous polymer
How does actin change to allow for cell shape change?
- signal such as nutrient source
- disassembly of filaments and rapid diffusion of subunits
- reassembly of filaments at a new site (actin can polymerase to large units fast!)
In what ways can actin filaments be remodelled?
- constant flow between G and F-actin pool
- proteins involved e.g. sequestering proteins, motor proteins that will contract, capping, cross linking, severing, nucleating
F-actin
- severing
- cross linking
- capping
- side binding
- motor proteins
- bundling
G-actin
- nucleating
- sequestering
vinculin
- one of the main components of the integration plaque
- binds to filamentous actin
- high concentration of forms fingers of the cell (filopodia)
What is a key difference between stress fibers and filipodium?
- stress fibres have antiparallel fibers
- filopodia have parallel filaments
Nucleation of actin
- key limiting factor in the transition form g to filamentous actin pool is the initial step of nucleation
- in order for polymerisation to occur you need nucleation of 3 monomers together (this is not very stable)
- proteins called nucdelators are needed
- Arp2 and Arp 3 resemble actin but they are not actin
- > bind to monomer -> polymerisation starts
- > facilitate rapid nucleation to start polymerisation.
- Arp2 and Arp3 are the minus end. Elongation is at the plus end.
What is the limiting step in actin dynamics? (g -> f)
formation of trimers to initiate polymerization
Elongation of actin
- after you have the trimer, elongation is needed
- requires 2 types of protein:
- profilin
- thymosin
- thymosin binds to actin and hold it for itself
- profilin facilitates rapid incorporation of actin
- profilin competes with thymidine for binding to actin monomers and promotes assembly
beta-4-thymosinf and ADF/cofilin are sequestering (the second one does not inhibit polymerisation)
