Lecture 22 Flashcards
describe cytogenetics
process of pairing and ordering a cells chromosomes - looking at them
add colchicine and hypotonic saline = prevents cells from going from metaphase to anaphase = screws up microtubule polarization
analyze metaphase spread = karyotype
define cytogenetics
the study of inheritance in relation to the structure and function of chromosomes
what is cml
chronic myeloid leukemia
characterized by Philadelphia chromosome
describe philadelphia chromosome
translocation between chromosomes 9 and 22
usually chromosomes not supposed to recombine
generated fusion gene
improper event
what is bcr and what is abl
bcr = break point cluster region
abl = tyrosine kinase - proto oncogene
when abl translocated next to bcr region = becomes oncogene
fusion leads to abl kinase constitutive activity = emoits strong growth promoting signals in a dysregulated manner = hyperactivated, unable to turn off
what is imatinib
gleevec
kills cml cells but not normal cells
inhibits kinase and treats cml
binds to atp binding site on fusion protein - so cannot bind atp and cannot phosphorylate = blocks bcr able protein from binding atp = cannot phosphorylate
Competitive inhibitor
if do not have fusion = would not give drug
wont work for all cancer
describe erbB2 signalling
rtk
responds to epidermal growth factor (EGFR)
dimerization activities proliferation and survival gene expression signalling pathways
her2 can lead to ras activator = down signalling cascade to promote cell growth proliferation
what is erbb2 aka
neuro/glioblastoma derived oncogene homolog (neu)
human epidermal growth factor receptor 2 (her2)
describe rtks - parts
ectodomain = protrudes in extracellular space to recognize and bind ligand
egf receptor - has kinase and more
hydrophobic transmembrane domain threads through plasma membrane lipid bilayer - into pm
kinase domain sits inside cell - inner membrane, src kinase domain
describe rtks = normal vs mutations
growth factor binding normally leads to rtk dimerization and activation of kinase domain = dimerization on its own since crowded cell
mutations can result in ligand independent kinase activation
rtk overexpression
ex = erbb2
may cause cell to become hyperresponsive to low growth factor concentrations or cause ligand independent rtk dimerization due to mass action effect
what happens when her 2 amplified
proliferation, survival high and resistant to apoptosis
if her2 amplified = survive less
what is fish and describe
fluorescence in situ hybridization
probe dna = make adjacent erbb2 gene
labeling with florescent dye - fluorochrome
coverslip and denature and hybridize = add in ss probe and will hybridize
can detect copies of erbb2 under microscope, since diploid = should have 2 copies in each cell
describe fish analysis of erbb2/her2
erbb2 amplified in breast cancer
many cases where her2 is just highly expressed
= not always case that it is amplified at gene level
like if promotor hyperactive - can still make large amount of protein without being amplified
describe ihc analysis of erbb2/her2
look at protein levels
antibody that recognizes erbb2, binds to cover slip and amount of protein corresponds to staining level - high protein levels = see its in pm not tucked in nucleus, see localization
what is traztuzumab
herceptin
antibody recognizes extracellular component of her2 - domain
binds to extracellular domain of this receptor and inhibits her2 homodimerization = prevents her2 mediated signalling - wont respond to signals and decrease ability of rtk to fire off downstream
only if has her2 (positive)
drugs give side effects
only used if her2 positive
personalize medical approach by treating her2 positive breast cancer
what is ras - describe
not a kinase
ras gene picked up by being associated with diff sarcoma viruses back in day
2 ras gene = k-ras, h-ras, n-ras
gtp protein activated when bound to gtp
uses gtpase function to hydrolyze - cleave gtp to gdp to inactivate itself
turns itself on and off like a light
inactive –> gef –> active
active –> gap –> inactive
Signalling cascades on many downstream prosignalling pathways = chromatin remodelling, transcription, protein synthesis, cell growth and prolife
Describe ras missense mutation
one of most highly mutated in cancer
missense in gly 12 and 61 turn ras from a protoonco to onco
lead to gtpase neg feeback mechanism being inactivated
mutated ras genes are found in many cancers, in particular 50% of colorectal cancers and 95% pancreatic cancer
what is role of proto onco genes
function to regulate normal cell prolife and differentiation
what happens when proto onco altered
upreg expression or mutations that alter their structure can lead to overly active growth promoting genes which appear in cancer cells as activated oncogenes
describe oncogenes
once formed = drive cell proliferation and play a central role in pathogenesis of cancer
what is a tsg
gene when inactivated or lost leads to increase in selective growth advantage of cell in which it resides - rb and p53
often considered to be recessive to oncogenes which are dominant
Describe rb - arises from and treatment
arises from photoreceptor cell precursors in 1 in 20,000 children
radiation/surgery can treat bilateral rb - these children have higher risk of bone cancers (osteosarcoma) and other tumours later in life
Describe rb - how diagnosed
children with no fam history = sporadic form - can have single tumour in one eye, with radiation and surgery = effective
children with fam history = familial form, often have multiple foci of tumours in both eyes = bilateral
