Hedgehog pathway and cancer

Question 1

What does hedgehog binding relieve the inhibition of?

Answer 1

Smoothened activity

Question 2

What term would you use to describe the basic structure of cyclopamine?

Answer 2

Steroidal

Question 3

Does cyclopamine act upstream or downstream of patched?

Answer 3

Downstream

Question 4

What happens in the absence of patched and why?

Answer 4

Constitutive activation of target genes as patched is not there to repress smoothened activity

Question 5

Experimentally, how would you monitor the activity of the patched pathway?

Answer 5

Using a reporter gene fused to a Gli-sensitive promoter

Question 6

Is the reporter gene expressed in fibroblasts of mouse embryos derived from homozygous mutants of patched? And what happens to the expression of the reporter when cyclopamine is added?

Answer 6

Yes it is expressed, and adding cyclopamine inhibits the expression of the reporter gene

Question 7

Knowing that cyclopamine acts downstream of patched, what does it bind to?

Answer 7

Smoothened

Question 8

Is the patched sterol-sensing domain important?

Answer 8

Yes, it is involved in cholesterol transport and this is consistent with defects in cholesterol synthesis affecting hedgehog signalling

Question 9

What is patched?

Answer 9

The hedgehog receptor

Question 10

During development, stem cells can do what?

Answer 10

Either proliferate or differentiate

Question 11

Are there many or few pathways acting during development?

Answer 11

Many

Question 12

What disease are signalling systems important during development implicated in and why?

Answer 12

Cancer

Can cause dedifferentiation of cells and proliferation instead

Question 13

Give two examples demonstrating that sonic hedgehog has mitogenic activity in a number of settings

Answer 13

Proliferation of granule neuron precursors during brain development
Epithelial cells

Question 14

What is inappropriate activation of the hedgehog pathway often associated with? Give an example

Answer 14

Some human tumours, e.g. inherited dominant syndrome (Gorlin)

Question 15

What does inherited dominant syndrome (Gorlin) cause?

Answer 15

An increase appearance of many tumours, particularly basal cell carcinoma (BCC)

Question 16

What is inherited dominant syndrome (Gorlin) caused by?

Answer 16

Heterozygous loss of function mutations in patched

Question 17

What is the most common cancer in developed countries accounting for 8E5 new cases per year in the USA?

Answer 17

Non-familial basal cell carcinoma

Question 18

What mutations do you often find in 40% of sporadic basal cell carcinomas and 25% of primitive neuroectodermal tumours?

Answer 18

Loss of function mutations in patched or gain of function mutations in smoothened

Question 19

When is oncogenic activation of signalling pathways important?

Answer 19

During embryonic development

Question 20

What is the disadvantage of targeting agents to repress the signalling pathway in adults with cancer?

Answer 20

The agents might not be very damaging

Question 21

What is the biggest disadvantage of traditional treatments?

Answer 21

They are toxic to normal proliferating tissues

Question 22

What agent might be useful as a way of suppressing the hedgehog pathway in tumours and what limitation to this agent might there be?

Answer 22

Cyclopamine, but oncogenic forms of smoothened are much more resistant

Question 23

Are chemically synthesised derivatives of cyclopamine more or less potent at inhibiting the hedgehog pathway?

Answer 23

More potent, 10-20 times more potent

Question 24

What agent, that is a derivative of cyclopamine, can inhibit pathway activation caused by oncogenic smoothened?

Answer 24

KAAD cyclopamine

Question 25

What is SmoA?

Answer 25

The activated oncogenic form of smoothened

Question 26

How does KAAD cyclopamine work and what does this mean it can be potentially useful for?

Answer 26

Inhibits cell growth cased by oncogenic mutations of patched so can be potentially useful as a therapeutic agent for tumours caused by loss of function mutations of patched or gain of function mutations of smoothened

Question 27

Why is the inhibition of the hedgehog pathway by cyclopamine a bad thing during embryonic development?

Answer 27

Because the pathway is used in many contexts, e.g:
Neural tube differentiation
Midline development of the brain and face
Proliferation of neural precursors
Limb development

Question 28

Why is the use of cyclopamine a potential good thing to treat tumours?

Answer 28

Because the pathway is inappropriately activated by oncogenic mutations such as loss of function mutations in patched and gain of function mutations in smoothened

Question 29

Experimentally, how can you look for better pathway-specific inhibitors?

Answer 29

Using light-emitting assays for the hedgehog pathway in cultured cells, allowing for repaid mechanised testing of up to E6 small compounds

Question 30

If the hedgehog pathway is able to promote cell invasiveness then what can this lead to?

Answer 30

Tumour metastasis

Question 31

In which organism was the hedgehog pathway and tumour spread looked at?

Answer 31

Rodent prostate cancer cell lines

Question 32

How does a high hedgehog pathway influence the metastatic potential of a tumour?

Answer 32

A high hedgehog pathway gives a high metastatic potential

Question 33

How does a low hedgehog pathway influence the metastatic potential of a tumour?

Answer 33

A low hedgehog pathway gives a low metastatic potential

Question 34

Can hedgehog pathway inhibition prevent metastasis?

Answer 34

Yes, cyclopamine prevented metastasis

Question 35

What part of the hedgehog pathway promotes metastasis?

Answer 35

The over-expression of Gli

Question 36

What is the main opportunity for using hedgehog pathway inhibitors as cancer therapy?

Answer 36

Ligand-dependent hedgehog signalling involved in other tumours, as hedgehog pathway inhibitors may be useful for a wider spectrum of cancers

Question 37

What sorts of tissues are affected by cytotoxins?

Answer 37

All rapidly dividing tissues, e.g. gut, hair, skin

Question 38

What are cytotoxic treatments?

Answer 38

Generally quite crude and toxic, having a drastic but effective affect

Question 39

What is KAAD?

Answer 39

An extra complex hydrocarbon

Question 40

What is IC50 a measure of?

Answer 40

Potency

Question 41

What are basaloid nests a simple model for?

Answer 41

Basal cells

Question 42

What does TUNEL staining test for?

Answer 42

Binds to the ends of chromosomes
If there are lots of ends of chromosomes this gives a dark stain, which indicates the DNA is broken and the cell is undergoing apoptosis

Question 43

Give examples of stromal cells

Answer 43

Fibroblasts

Cells of the connective tissue