Cancer 7 - External Factors controlling division and behaviour of normal and cancerous cells Flashcards
What is cell behaviour
The way cells interact with external environment and their reactions to this - especially proliferative/motile responses
Which 3 factors contribute largely to cell proliferation
- GFs
- Cell-cell adhesion
- Cell-ECM adhesion
Cells often obtain polarity on ECM. Which part is usually the motile part?
The front part - contains lamellipod
Cell spreading is not a gravity-dependent event. What prerequisite is needed for cell spreading?
Energy
Cells need to be bound to ECM for?
In order to be fully competent to respond to soluble GFs - higher probability of entering S phase if they are able to spread more
Do cells significantly synthesise protein or DNA in suspension (i.e. not attached to ECM or spread)
No - attachment to ECM may be crucial for cell survival - “Anchorage dependance”
Cell phenotype can be determined by ECM composition. Give an example
Cultured mammary epithelium - in:
1. Interstitial matrix (type 1 collagen) - no differentiation to secretory cells
- Basal lamina matrix (basement membrane) - mammary cells become “organoids” and produce milk proteins
Cells have receptors that bind to ECM - give an example
Integrins
Integrins are heterodimer complexes. What are their subunits and describe them
alpha subunit - consists of 2 parts with a disulphide bridge
beta subunit - 1 long chain with cysteine-rich domains
Integrin complexes - which part associates with the extracellular region?
The “head” regions.
the leg regions span the plasma membrane
Where does ligand binding occur in an integrin complex
At the junction of head regions
On integrins, what does the a5B1 fibronectin receptor bind to?
Arg-Gly-Asp (RGD)
Not all integrins bind to matrix - what else may integrins bind to?
Give an example
May also bind to specific adhesion molecules on other cells
e.g. ICAM-1 on endothelial cells in inflammation
What do most integrins link to within the cell
Actin cytoskeleton via actin binding protein
Exception = a6b4 integrin - found in epithelial hemidesmosomes - linked to cytokeratin (intermediate filament network)
Integrin complexes cluster. What may they form
- Focal adhesions (most)
2. Hemidesmosomes (a6b4)
Integrins can act as signal transducters. What 2 forms can this take?
“Outside-in” integrin signalling / “Inside out”
Describe how outside in signalling works
- ECM composition determines which integrin complexes binds
- Upon binding - ECM composition determines which signals cells receive
This can alter cell phenotype
What factors can determine the force generated at a focal adhesion point
- Force generated by cytoskeleton
2. ECM stiffness
Integrins recruit cytoplasmic proteins for 2 functions. What are the 2 functions
- Promote signalling
2. Promote actin assembly
“Flexed/bent” integrins are?
Inactive - i.e. dont bind to ligands, low affinity
Blood clotting and inflammation are examples of what type of signalling
“Inside out signalling”
How does inside out signalling work
Signal generated inside cell (e.g. through hormone binding on receptor) - causes integrin complex to alter its affinity for ECM binding
The extended conformation is?
High affinity for ECM
How can low affinity integrin become high affinity integrin
Signal from inside the cell acts on integrin complex - inside out activation
Once integrin binds to ECM, there is further opening (extension) of the legs of integrin. Why
Exposes sites of binding for cytoplasmic signalling molecules - outside-in activation
What is meant by density-dependance of cell division
Higher the density of cell division - the less proliferation there is (due to competition for GFs)
Which 2 signals are needed for efficient stimulation of proliferation?
- Gf
2. ECM
Why do GF receptors and integrin signalling complexes activate identical signalling pathways (e.g. MAPK)
Because individually, the activations are weak but together they are strong and sustained - hence why both pathways act synergistically
Describe the 2 types of contact interactions between cells and their nature
Short term - transient interactions between cells - don’t form stable cell-cell junctions
Long term - stable interactions resulting in cell-cell junction formation
How do cells ensure that they do not multilayer in culture and in vivo
“Contact inhibition of locomotion”
When 2 non-epithelial cells collide - they repel one another by paralysing motility at the contact site, and form motile front at a different site in the cell and move off
Name some cells that form long term cell-cell contacts
Epithelial cells
Endothelial cells
Neurones forming synapses
How can contact between epithelial cells result in a stable monolayer?
When 2 epithelial cells contact - there is a mutual induction of spreading - total spread area > 2xindividual spread area (if they were separate)
Which ion influences the formation of cell-cell junctions
Ca2+
How may the formation of cell-cell adhesion reduce cell proliferation
(in some cell types)
- Cell-cell junctions form
- MAPK inactive
- Increased p27KIP1 (inhibitor of proliferation)
- Less/low proliferation
What are cadherins associated to?
Cadherins are cell adhesion molecules - they are associated with B-catenin and a-catenin
In APC (colon) - what protein is involved
Protein involved in degradation of b-catenin (which is associated with cell-cell junctions)
(Not enough protein made)
B-catenin can also act as a transcription factor when associated with?
LEF-1
How does the APC complex influence the cells actions
Usually APC active, if not APC happens in colon
IF APC ACTIVE: rapid degradation of b-catenin
IF APC INACTIVE - b-catenin associates with LEF-1 and acts as. TF stimulating cell proliferation
Clustering of cadherins after cell cell contact can alter GTPase activation. What consequence does this have
Rac activated, Rho inhibited - influences proliferation
Some GF receptors are associated with cell cell junctions - What does this mean
Reduced capacity to promote proliferation
What may cause a cell to proliferate uncontrollably?
Lost density dependence of proliferation
What may cause cells to be less adherent and multilayer
Lost contact inhibition of locomotion and anchorage dependance
When can cancer occur
if cells:
- Proliferate uncontrollably
- Less adherent - multilayer
- Epithelia breakdown cell cell contacts
- Not hay flick limited - express telomerase - immortalised
What may add to the invasive property of cancerous tumours?
Loss of contact inhibition of locomotion
Ras is mutated in approximately what percentage of cancers
30%
Most adult cancers are cancers of?
Epithelia - i.e. carcinomas
What does the degree of carcinoma cell-cell adhesion indicate?
- How differentiated primary tumour is
2. Invasiveness and prognosis
What are 3 requirements for metastasis
- Cell-cell adhesion downregulation
- Cells must be motile
- ECM degradation - e.g. through MMPs
