CML Genetics

Question 1

philadelphia chromosome

Answer 1

t(9;22) creates new gene encoding constitutively active tyrosine kinase

Question 2

tx CML

Answer 2

Targeted molecular therapy based on mechanism: tyrosine kinase inhibitors, Imatinib

Question 3

stem cell

Answer 3

Undergoes self renewal Pluripotent- capable of generating all lineages Capable of proliferation

Question 4

progenitor cells

Answer 4

Capable of proliferation but not self renewal.
Multipotent- can generate more than one lineage.
Capacity becomes narrower as progress down pathway.

Question 5

committed cells

Answer 5

Do not proliferate.

Only one fate, to generate the next step in the path to the neutrophil.

Question 6

BCR-ABL1 genomic translocation in what cell

Answer 6

HSC

mutation passed down to all progeny

Question 7

what does BCR-ABL1 mutation create

Answer 7

Genetic chimera of parts of BCR gene and ABL1 gene–> constitutively active TK that activates proliferation and blocks apoptosis in absence of extracellular signals

Question 8

what does BCR-ABL1 confer to mutated cells (vs. normal cells)

Answer 8

Selective advantage for progenitor cells
- can proliferate more, survive longer, can acquire more mutations to become more oncogenic

Cannot self-renew, CAN continue to differentiate

Question 9

outcome of BCR-ABL mutation in general in chronic phase

Answer 9

expansion of progenitor and committed cells, mature cells still produced
disease relatively mild

Question 10

blast phase mutations and outcome

Answer 10

GMP acquires ability to self renew (Wnt-b catenin signaling activated), acquires block to differentiation (translation of CEBPa inhibited)

huge expansion of blasts, 30% extramedullary

Question 11

mechanism of BCR-ABL1 translocation

Answer 11

double stranded breaks occur in 2 chromosomes at specific breakpoints
NHEJ – ends of different chromosomes are joined

Question 12

two most common breakpoints

Answer 12

p210 found in CML, most common

p190 found in some ALL, less common

Question 13

Normal BCR

Answer 13

Ser/Thr kinase domain
role in inhibition of some inflammatory responses
key functional domains for oncogenic fusion protein (coiled-coil domain, tyrosine 177)

Question 14

ABL1 normal

Answer 14

tyrosine kinase = key functional domain for both normal and oncogenic fusion protein
in normal - inactive unless activated by external signals
long chain FA myristate maintains inhibition

functions in DNA repair, cytoskeletal organization

Question 15

differences between BCR-ABL1 and normal genes

Answer 15

Both ABL1 and BCR-ABL1 are tyrosine kinases
But ABL1 is normally inactive unless signaled, BCR-ABL1 is constitutively active
ABL1 mainly nuclear, BCR-ABL1 mainly cytoplasmic
Activate different signaling pathways

Question 16

Differences in structural changes in BCR ABL1

Answer 16

Coiled-coil domain from BCR promotes dimerization (required for activation)
Myristate attachment site lost from ABL1 (normal method of autoinhibition)
Tyrosine 177 added from BCR - phosophorylation of Y-177 creates new binding site for intracellular signaling proteins

Question 17

Y177 subject to tyrosine phosphorylation in BCR-ABL fusion protein but not in BCR protein why

Answer 17

BCR is not a tyrosine kinase

Question 18

what does BCR-ABL activate to lead to proliferation and anti-apoptosis

Answer 18

Stat5

Question 19

what does imatinib block

Answer 19

Imatinib specifically inactivates ABL1 kinase by blocking ATP binding .

Question 20

Imatinib and oncogenic cells selective advantage

Answer 20

Imatinib prevents selective advantage that comes from activated oncogenic signaling pathways
Also causes apoptosis (BCR-ABL cells dependent on BCR-ABL)
Loss of BCR-ABL mutant cells allow normal cells to repopulate

Question 21

limitations of imatinib

Answer 21

1. Many develop secondary resistance to imatinib d/t mutations in BCR-ABL
2. BCR-ABL1 TKIs not effective in blast phase (cells now independent of BCR-ABL)
3. CML Stem cells are resistant to TKIs (must take for life)

Question 22

If mutation in HSC, why is CML in neutrophil lineage?

Answer 22

Model- Specific signaling opportunities created by BCR-ABL protein benefit neutrophil progenitors more than others.