Cancer 7: External factors controlling division and behavior Flashcards
Define Cell behaviour
the way cells interact with their external environment and their reactions to this, particularly proliferative and motile responses of cells.
What are some EXTERNAL chemical influence detected by cells ?
Chemical:- hormones, growth factors, ion concs, ECM, molecules on other cells, nutrients and dissolved gas (O2/CO2) concs.
What are some EXTERNAL physical influence detected by cells ?
Physical:- mechanical stresses, temperature, the topography or “layout” of the ECM and other cells
What are 3 Important (regarding cancer cells) external factors influencing cell division?
- GFs
- cell-cell adhesion
- cell-ECM adhesion
What is Cell spreading needed for?
- Cell spreading needed for cell survival + growth, otherwise cell in single spot dies by apoptosis
- -> provides polarity + motility
- -> cell can spread, survive + grows
–>cell front = lamellipod
Why do cancer cells need to be attached to ECM?
- In suspension (no spread), cells don’t significantly synthesise protein/DNA
- Cells must be attached to ECM to begin protein synthesis + proliferation (DNA synthesis)
– ECM attachment may be needed for cell survival
(Anchorage dependence)
give an example showing how phenotype of cell = depends on environment
phenotype of cell = depends on environment
e.g Cultured Mammary Epithelium
A) in interstitial matrix (type 1 collagen), mammary epithelium does not differentiate to secretory cells;
(B) in basal lamina (basement membrane) matrix, mammary cells organise into “organoids” and produce milk proteins.
A cell can receive information about its surroundings from its adhesion to ECM
How do they do that?
Cells have receptors on their cell surface which bind specifically to ECM molecules
these molecule = often linked, to their cytoplasmic domains, to the cytoskeleton
this arrangement means that there is mechanical continuity between ECM and the cell interior
What are integrins ?
integrin = heterodimer complexes of a and b subunits that associate extracellularly by their “head” regions (ligand binding occurs here)
the “leg” region –> spans the plasma memb
–> relatively short cytosolic domains
What is the significance of integrins?
integrins –> Recognise short, specific peptide sequences
- Integrin complexes cluster to form focal adhesions (mostly) or hemidesmosomes (in a6b4)
–> These clusters = involved in signal transduction
- Most integrins linked to _____________ (via actin-binding proteins)
- Most integrins linked to actin cytoskeleton (via actin-binding proteins)
note: ECM receptors (e.g. integrins) can act to transduce signals
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How can cell-ECM adhesion, and signals, can be switched on and off?
- Integrin complexes can adopt “flexed” OR “extended” molecular confirmations.
Switching between these confirmations affects their ability to bind their ligands, and their signalling
–> allows it to be switched on/off
How can a Cell receive environmental information from its adhesion to ECM?
o E.g. composition of ECM determines which integrin complexes bind + which signals it receives –> this can alter cell phenotype
The amount of force that is generated at a focal adhesion depends on what 2 things?
- force generated by the cytoskeleton (F cell)
- stiffness of the ECM
Upon binding certain ECM molecules, what happens to the integrins?
- causes opening of legs of integrin –> exposes binding sites for recruitment of cytoplasmic signalling molecules
integrin recruits cytoplasmic proteins + form clusters –> which in turn recruits actin cytoskeleton + signalling molecules (e.g FAK) –> which promotes signalling + actin assembly/interaction
describe the concept of Inside-Out Integrin Signalling:
Inside-Out Integrin Signalling:
- Signal generated intracellularly (e.g. due to hormone binding to receptor) can act on an integrin complex to alter affinity (for ECM binding) of the integrin
o E.g. in inflammation or clotting, switching on adhesion of circulating leukocytes
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bent confirmation of integrin = low/high affinity
extended confirmation of integrin = low/high affinity
a) what causes this switch in conformation
bent confirmation of intern = low affinity
extended confirmation of intern = high affinity
–> allows cytoplasmic signalling molecules to bind
a) signals from inside the cell –> promotes switch in conformation
what is meant by density dependence of cell division
When cells in culture form a confluent monolayer, they cease proliferating and slow down many other metabolic activities –> competition for external growth factors and not cell-cell contact responsible:-
aka Density-dependence of cell division.
higher cell density = less cell proliferation
ERK MAP Kinase cascade:
GF binding to receptor tyrosine kinase –>causes phosphorylation which recruits RAS –> initiates cascade –> causes MAPK activation –> acts on nucleus –> cause proliferation
What are the 2 signals needed for efficient stimulation of proliferation of tissue cells?
signals from:
1) Growth factor (density dependence)
2) ECM (anchorage dependence)
Describe the mechanism of anchorage dependence.
o GF receptors + integrin signalling complexes both activate identical signalling pathways (e.g. MAPK)
o Individually –> activation weak and/or transient
o Together –> activation strong + sustained
o The separate signalling pathways –> act synergistically –> to stimulate proliferation
in terms of contact interaction btw cells, what is meant by :
a) Short term
b) Long term
short-term: transient interactions between cells which do not form stable cell-cell junctions
long term: stable interactions resulting in formation of cell-cell junctions
What is the significance of contact inhibition of locomotion?
- it is responsible for preventing multilayering of cells in culture and in vivo.
i. e Cells making contact-repel one another to prevent multilayering.
give examples of long term cell-cell contacts
E.g. adherens junctions, desmosomes, tight + gap junctions (tissues 1)
–> Arranged as continuous belts (zonulae) or discrete spots (maculae)
- E.g. in epithelial + endothelial cells –> form layers
and neurones –> form synapses
describe what happens in contact induced spreading of epithelial cells
Contact btw epithelial cells –> causes mutual induction of
spreading,
so that total spread area of the contacted cells =
greater than sum of the two separated cells.
–> This could result in a stable monolayer.
What is the effect of cell-cell adhesion on cell proliferation with:
a) increased Ca2+
b) reduced adhesion blocking antibody
c) reduced Ca2+
d) increased adhesion blocking antibody
increased Ca2+ / reduced adhesion blocking antibody:
formation of cell-cell junction –> MAPK activity is reduced –> there is increase in Increased P27KIP1 (inhibits proliferation)
–> low proliferation
reduce Ca2+ / increased adhesion blocking antibody :
increased cell-cell junction
–> increase in MAPK activity –> decrease in P27KIP1 –> high proliferation
Describe te molecular organisation of adherents junctions .
- Involve cadherin
- -> binds to identical molecule
- -> Ca2+ dependent
- Cytoplasmic tail = associated with beta-Catenin, alpha-catenin + actin
Adenomatous polyposis coli (APC)
genetic disorder where colon massively produces too much tissue –> thousands of polyps
- APC gene product = protein that causes –> degradation of B catenin (molecule involved in cell-cell junction)
What happens in the
a) absence of APC
b) presence of APC
on B-Catenin
APC absent –> no rapid degradation of B catenin
–> binds to LEF-1 –> complex enters the nucleus –> increases gene expression –> to cause cell proliferation
APC present –> B catenin –> rapidly degraded
when bound to cadherin at the membrane –>
b-catenin = not available for LEF-1 binding and nuclear effects
What other adhesion-associated signalling pathways can influence contact-induced inhibition of proliferation?
- Clustering of cadherins after cell-cell contact alters activation of small GTPases
o e.g. Rac activated, Rho inhibited: affects proliferation.
- Some GF receptors associated with cell-cell junctions –> reduces capacity to promote proliferation.
What happens when cells lose their behavior restraints? (e.g due to cancer)
Cells:
- proliferate uncontrollably (lose density dependence of proliferation)
- less adherent and will multilayer (lose contact inhibition of locomotion and anchorage dependence)
- epithelia breakdown cell-cell contacts
- Not Hayflick limited, express telomerase –> unlimited number of divisions
Other than promoting the formation of solid tumours, what is an important consequence of loss of contact inhibition of locomotion for the progression of cancer?
helps in invasion properties of cancer cells
Note:
Many components of signal trannduction = proto-oncogenes:
e.g. receptors, signalling intermediates + targets (e.g. transcription factors)
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Define oncogene
Oncogene:
mutant gene which promotes uncontrolled cell proliferation
Define Proto-oncogene
Proto-oncogene:
normal cellular gene corresponding to the oncogene
–> Ras = common proto-oncogene that commonly mutates –> to cause cancer
How does a primary carcinoma cell metastasise?
- cell-cell adhesion must be down-regulated (e.g. cadherin levels reduced)
o Less differentiated –> more likely to spread
- Cells need to be motile
- ECM degradation must occur MEtrix metaloproteinase (MMP) levels increased to migrate through basement membrane + interstitial ECM
o Degree of carcinoma cell-cell adhesion = indicator of:
o Degree of carcinoma cell-cell adhesion = indicator of:
- how differentiated primary tumour is,
- its invasiveness,
- prognosis
What difference might you observe in a cell in contract / no contact w the ECM?
no contact with ECM = blebbing
contact with ECM = less blebbing
how would cells in
a) agar
b) small adhesive patch
c) large adhesive patch
differ in proliferation
in terms of cell spreading?
d) what does this experiment show?
Cells in agar –> low probability of entering S phase (cant proliferate)
Cells on small adhesive patch –> some degree of proliferation
Cells on large adhesive patch –> that could fully spread –> almost all enters S phase (can proliferate a lot )
d) what does this experiment show?
- shows that cells need to be bound to ECM to be fully competent for responding to soluble GFs
What is the RGD Motif?
peptide sequence
a5b1 fibronectin receptor binds arg-gly-asp
What is outside-in signalling?
outside-in signalling = cell binds to matrix –> generates signal within the cell
–> so composition of matrix determines with integrin complex bind + which signals it receives
–> this is one of the ways the matrix can influences / alters the phenotype of the cell
What is inside out signalling?
- signals from inside the cell –> can act on integrin complex to change its confirmation –> increase activity
–> important in inflammation / blood clotting /switching on adhesion of circulating leucocytes (as in blood clotting)
Note: uncontrolled proliferation of tissues cells (cancer cells) –> doesn’t require GF or anchorage in order to proliferate
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