Cancer 3 Flashcards
What is melanoma?
Skin cancer- derived from melanocytes (moles)
What are the risk factors for skin cancer?
Age- accumulate mutations
Sex- higher risk in makes- psychosocial? hormones?
Skin colour- 24x higher risk for white skin
Sunburn UV exposure
GENETICS
Which mutations can predispose you to develop skin cancer?
Mutated DNA repair genes- xeroderma pigmentosum
Mutated melanocortin receptor
Mutated CDKN2A/P16/P14- send cells to apoptosis when theyre damaged
Rare TERT promoter mutations- activate TERT expression- cells which shouldve died survive
What do melanoma cells constitutively express?
MAPK
What are the 2 types of initiator mutations of melanoma?
BRAFV600E
NRAS
Mutations often seen in progressing stages
TERT
SWI/ SNF- involved in chromatin remodelling
CDKN2A
Later stage mutations in melanomas
P53
PTEN
Why was yeast used to study melanomas? what was its drawback
To look at the cell cycle machinery
Yeast do not have upstream signals that activate genes
What are the upstream signals we’re interested in and what model animal can we study them with?
EGF/RAS/MAPK
Drosophila and C.elegans
When do we need to use a vertebrate model animal?
To look at tumour growth and metastasis- specifically angiogenesis and the immune system
Explain: Tyr:CreERT2
Tyrosinase promoter (only in melanoctyes) activatable by tamoxifen
Explain: Brafca
Cre-activatable form of BRAF
Explain: PTENlox
a loxed allele of PTEN- inactivated by Cre mediated excision
What happens to CreERT2 when tamoxifen is introduced?
Cre-ERT2 will go into the nucleus and activate BRAF
PTEN will be will be activated
Need BRAF with the loss of PTEN to create a melanoma
Whats characteristic of a mutant foxn1 mouse? Why are they not great in studying cancer?
Defective immune system
The immune system plays an important role in cancer- these mice are immunocompromised
Whats an inhibitor of the BRAFV600E mutation? Which animal was involved in its discovery
PLX4032 is temporarily very effective against melanoma
The mouse
Whats the downfall of PLX4032?
Only effective temporarily
And only inhibits the function of the BRAFV600E mutant
What transgenic animal was used to screen for compounds that intefered with melanocyte precursor formation? What was the discovery?
Zebrafish
Tg mitfa:braf(V600E)
Melanomas have a neural crest progenitor sequence
What followed the discovery that neural crest progenitor cells were involved in melanomas?
Chemical screen of 2000 chemicals that inhibited crestin
What is crestin?
A marker for neural crest progenitors
What was found to inhbit crestin? What drug is based on this compounds and hat does it do
NSC21067 - an inhibitor of DHODH
Leflunomide- increases the potency of PLX4032
Which genes cause progression of melanomas? What was done to answer this question?
They knew it was a gene found in a region of chromosome 1 - tested candidate genes from this region
Melanoma assay on zebrafish
mitfa:braf (V600E) fish
test fish used: mitfa-/- fish in a P53-/- background
Engineered a vector- miniCoopR
What did they do with the miniCoopR and what was the result?
injected each plasmid in the eggs of test line and found one that significantly enhanced cancer formation compared to mitfa alone - SETDB1
What are the advantages of using zebrafish?
Cheaper than mice- can use greater numbers
can visualise cells etc using GFP
Can effectively do genetic/ chemical screens
