Lecture 22

Question 1

describe cytogenetics

Answer 1

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

Question 2

define cytogenetics

Answer 2

the study of inheritance in relation to the structure and function of chromosomes

Question 3

what is cml

Answer 3

chronic myeloid leukemia
characterized by Philadelphia chromosome

Question 4

describe philadelphia chromosome

Answer 4

translocation between chromosomes 9 and 22
usually chromosomes not supposed to recombine
generated fusion gene
improper event

Question 5

what is bcr and what is abl

Answer 5

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

Question 6

what is imatinib

Answer 6

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

Question 7

describe erbB2 signalling

Answer 7

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

Question 8

what is erbb2 aka

Answer 8

neuro/glioblastoma derived oncogene homolog (neu)
human epidermal growth factor receptor 2 (her2)

Question 9

describe rtks - parts

Answer 9

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

Question 10

describe rtks = normal vs mutations

Answer 10

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

Question 11

rtk overexpression

Answer 11

ex = erbb2
may cause cell to become hyperresponsive to low growth factor concentrations or cause ligand independent rtk dimerization due to mass action effect

Question 12

what happens when her 2 amplified

Answer 12

proliferation, survival high and resistant to apoptosis
if her2 amplified = survive less

Question 13

what is fish and describe

Answer 13

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

Question 14

describe fish analysis of erbb2/her2

Answer 14

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

Question 15

describe ihc analysis of erbb2/her2

Answer 15

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

Question 16

what is traztuzumab

Answer 16

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

Question 17

what is ras - describe

Answer 17

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

Question 18

Describe ras missense mutation

Answer 18

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

Question 19

what is role of proto onco genes

Answer 19

function to regulate normal cell prolife and differentiation

Question 20

what happens when proto onco altered

Answer 20

upreg expression or mutations that alter their structure can lead to overly active growth promoting genes which appear in cancer cells as activated oncogenes

Question 21

describe oncogenes

Answer 21

once formed = drive cell proliferation and play a central role in pathogenesis of cancer

Question 22

what is a tsg

Answer 22

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

Question 23

Describe rb - arises from and treatment

Answer 23

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

Question 24

Describe rb - how diagnosed

Answer 24

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

Question 25

describe knudson 2 hit hypothesis

Answer 25

alfred knudson
studied kinetics of retinal tumour appearance in children affected by either familial or sporadic versions of rb
1971= concluded that rate of appearance of familial was consistent with one random event and sporadic was consistent with 2 random event

Question 26

describe knudson 2 hit hypothesis - bi and uni

Answer 26

bilateral = only need 1 hit since already have one hit from familial - first somatic mutation will cause rb
unilateral = needs 2 hits in genome to get rb case

Question 27

what is G0

Answer 27

quiescent phase = stage where in cells remain metabolically active but do not proliferate unless called to do so

Question 28

what does rb do

Answer 28

cell cycle gatekeeper = regulates restriction points
r point denotes the point in time where cell must make the commitment to advance through the remainder of cell cycle through m phase, to remain in g1 or retreat from active cell cycel into g0
rb regulates restriction point, commit or go to g0 or cell death

Question 29

what is rb - how does it activate

Answer 29

nuclear protein that can be phosphorylated by number of mitogenic signalling pathways
rb acts as a transcriptional repressor that determines if cells will enter s phase
nuclear localization not heavily phosphorylated usally but can become hyperphosphorylated
if stress = no longer phosphorylated and binds to e2f and prevents transcription since bound to rb
if no rb at all = cell will go through cell cycle and e2f will continue to transcribe genes

Question 30

what are mitogenic pathways

Answer 30

pathways that regulate or stimulate mitosis

Question 31

what are transcription factors

Answer 31

proteins involved in process of converting or transcribing dna into rna

Question 32

describe knudson 2 hit and rb gene specifically

Answer 32

familial = only one hit needed = pops up earlier
sporadic = 2 somatic mutations in cells

Question 33

mab

Answer 33

all generic drugs that are monoclonal antibodies have names that end in mab