Cancer 7 - External Factors controlling division and behaviour of normal and cancerous cells

Question 1

What is cell behaviour

Answer 1

The way cells interact with external environment and their reactions to this - especially proliferative/motile responses

Question 2

Which 3 factors contribute largely to cell proliferation

Answer 2

1. GFs
2. Cell-cell adhesion
3. Cell-ECM adhesion

Question 3

Cells often obtain polarity on ECM. Which part is usually the motile part?

Answer 3

The front part - contains lamellipod

Question 4

Cell spreading is not a gravity-dependent event. What prerequisite is needed for cell spreading?

Answer 4

Energy

Question 5

Cells need to be bound to ECM for?

Answer 5

In order to be fully competent to respond to soluble GFs - higher probability of entering S phase if they are able to spread more

Question 6

Do cells significantly synthesise protein or DNA in suspension (i.e. not attached to ECM or spread)

Answer 6

No - attachment to ECM may be crucial for cell survival - “Anchorage dependance”

Question 7

Cell phenotype can be determined by ECM composition. Give an example

Answer 7

Cultured mammary epithelium - in:
1. Interstitial matrix (type 1 collagen) - no differentiation to secretory cells

2. Basal lamina matrix (basement membrane) - mammary cells become “organoids” and produce milk proteins

Question 8

Cells have receptors that bind to ECM - give an example

Answer 8

Integrins

Question 9

Integrins are heterodimer complexes. What are their subunits and describe them

Answer 9

alpha subunit - consists of 2 parts with a disulphide bridge

beta subunit - 1 long chain with cysteine-rich domains

Question 10

Integrin complexes - which part associates with the extracellular region?

Answer 10

The “head” regions.

the leg regions span the plasma membrane

Question 11

Where does ligand binding occur in an integrin complex

Answer 11

At the junction of head regions

Question 12

On integrins, what does the a5B1 fibronectin receptor bind to?

Answer 12

Arg-Gly-Asp (RGD)

Question 13

Not all integrins bind to matrix - what else may integrins bind to?

Give an example

Answer 13

May also bind to specific adhesion molecules on other cells

e.g. ICAM-1 on endothelial cells in inflammation

Question 14

What do most integrins link to within the cell

Answer 14

Actin cytoskeleton via actin binding protein

Exception = a6b4 integrin - found in epithelial hemidesmosomes - linked to cytokeratin (intermediate filament network)

Question 15

Integrin complexes cluster. What may they form

Answer 15

1. Focal adhesions (most)

2. Hemidesmosomes (a6b4)

Question 16

Integrins can act as signal transducters. What 2 forms can this take?

Answer 16

“Outside-in” integrin signalling / “Inside out”

Question 17

Describe how outside in signalling works

Answer 17

1. ECM composition determines which integrin complexes binds
2. Upon binding - ECM composition determines which signals cells receive

This can alter cell phenotype

Question 18

What factors can determine the force generated at a focal adhesion point

Answer 18

1. Force generated by cytoskeleton

2. ECM stiffness

Question 19

Integrins recruit cytoplasmic proteins for 2 functions. What are the 2 functions

Answer 19

1. Promote signalling

2. Promote actin assembly

Question 20

“Flexed/bent” integrins are?

Answer 20

Inactive - i.e. dont bind to ligands, low affinity

Question 21

Blood clotting and inflammation are examples of what type of signalling

Answer 21

“Inside out signalling”

Question 22

How does inside out signalling work

Answer 22

Signal generated inside cell (e.g. through hormone binding on receptor) - causes integrin complex to alter its affinity for ECM binding

Question 23

The extended conformation is?

Answer 23

High affinity for ECM

Question 24

How can low affinity integrin become high affinity integrin

Answer 24

Signal from inside the cell acts on integrin complex - inside out activation

Question 25

Once integrin binds to ECM, there is further opening (extension) of the legs of integrin. Why

Answer 25

Exposes sites of binding for cytoplasmic signalling molecules - outside-in activation

Question 26

What is meant by density-dependance of cell division

Answer 26

Higher the density of cell division - the less proliferation there is (due to competition for GFs)

Question 27

Which 2 signals are needed for efficient stimulation of proliferation?

Answer 27

1. Gf | 2. ECM

Question 28

Why do GF receptors and integrin signalling complexes activate identical signalling pathways (e.g. MAPK)

Answer 28

Because individually, the activations are weak but together they are strong and sustained - hence why both pathways act synergistically

Question 29

Describe the 2 types of contact interactions between cells and their nature

Answer 29

Short term - transient interactions between cells - don't form stable cell-cell junctions Long term - stable interactions resulting in cell-cell junction formation

Question 30

How do cells ensure that they do not multilayer in culture and in vivo

Answer 30

"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

Question 31

Name some cells that form long term cell-cell contacts

Answer 31

Epithelial cells Endothelial cells Neurones forming synapses

Question 32

How can contact between epithelial cells result in a stable monolayer?

Answer 32

When 2 epithelial cells contact - there is a mutual induction of spreading - total spread area > 2xindividual spread area (if they were separate)

Question 33

Which ion influences the formation of cell-cell junctions

Answer 33

Ca2+

Question 34

How may the formation of cell-cell adhesion reduce cell proliferation (in some cell types)

Answer 34

1. Cell-cell junctions form 2. MAPK inactive 3. Increased p27KIP1 (inhibitor of proliferation) 4. Less/low proliferation

Question 35

What are cadherins associated to?

Answer 35

Cadherins are cell adhesion molecules - they are associated with B-catenin and a-catenin

Question 36

In APC (colon) - what protein is involved

Answer 36

Protein involved in degradation of b-catenin (which is associated with cell-cell junctions) (Not enough protein made)

Question 37

B-catenin can also act as a transcription factor when associated with?

Answer 37

LEF-1

Question 38

How does the APC complex influence the cells actions Usually APC active, if not APC happens in colon

Answer 38

IF APC ACTIVE: rapid degradation of b-catenin IF APC INACTIVE - b-catenin associates with LEF-1 and acts as. TF stimulating cell proliferation

Question 39

Clustering of cadherins after cell cell contact can alter GTPase activation. What consequence does this have

Answer 39

Rac activated, Rho inhibited - influences proliferation

Question 40

Some GF receptors are associated with cell cell junctions - What does this mean

Answer 40

Reduced capacity to promote proliferation

Question 41

What may cause a cell to proliferate uncontrollably?

Answer 41

Lost density dependence of proliferation

Question 42

What may cause cells to be less adherent and multilayer

Answer 42

Lost contact inhibition of locomotion and anchorage dependance

Question 43

When can cancer occur

Answer 43

if cells: 1. Proliferate uncontrollably 2. Less adherent - multilayer 3. Epithelia breakdown cell cell contacts 4. Not hay flick limited - express telomerase - immortalised

Question 44

What may add to the invasive property of cancerous tumours?

Answer 44

Loss of contact inhibition of locomotion

Question 45

Ras is mutated in approximately what percentage of cancers

Answer 45

30%

Question 46

Most adult cancers are cancers of?

Answer 46

Epithelia - i.e. carcinomas

Question 47

What does the degree of carcinoma cell-cell adhesion indicate?

Answer 47

1. How differentiated primary tumour is | 2. Invasiveness and prognosis

Question 48

What are 3 requirements for metastasis

Answer 48

1. Cell-cell adhesion downregulation 2. Cells must be motile 3. ECM degradation - e.g. through MMPs