Scott-CML Module

Question 1

What chromosomal translocation is associated w/ CML?

Answer 1

t (9;22)

Philadelphia chromosome

Question 2

What is the oncogenic mechanism by which the translocation affects cells?

Answer 2

BCR-ABL translocation creates new gene encoding constitutively active TK

Question 3

CML arises from defects in what pathway….

Answer 3

Neutrophil differentiation pathway

Question 4

What are the three stages of neutrophil differentiation?

Answer 4

Stem cells
Progenitor cells
Committed cells

Question 5

What are the characteristics of stem cells?

Answer 5

Undergo self renewal
pluripotent–> generate all ineages
capable of proliferation

Question 6

What are the characteristics of progenitor cells?

Answer 6

Lymphoid, erythroid, monocyte lineage

Proliferation but NO self renewal
Multipotent–can generate more than one lineage
Capacity becomes narrower as progress down pathway

Question 7

What are the characteristics of committed cells?

Answer 7

Myeloblast–> Neutrophil

Don’t proliferate
Only one fate to generate the next step in the path to the neutrophil.

Question 8

CML distorts what 2 processes in the Neutrophil pathway?

Answer 8

Differentiation

proliferation

Question 9

What initiates differentiation?

Answer 9

extracellular signals in the bone marrow–> TFs in hematpoietic cells

*each stage has a specific set of TFs which determine its characteristics

Question 10

What drives differentiation?

Answer 10

Sequential expression of TF

Question 11

What drives proliferation?

Answer 11

extracellular signaling form BM and Immune system

Question 12

What cells have the highest capacity for proliferation?

Answer 12

progenitor cells

Question 13

Self renewal and proliferation are tightly regulated by _________from ________ and leads to _______________.

Answer 13

extracellular signaling
bone marrow
appropriate number of mature neutrophils produced

Question 14

What happens to the neutrophil lineage in CML?

Answer 14

All the regulation is thrown out the window and normal neutrophil differentiation is disrupted.

Question 15

How does the BCR-ABL1 lead to proliferation and the blocking of apoptosis?

Answer 15

BCR-ABL1>
genetic chimera of parts of BCR gene and ABL1 gene>
BCR-ABL1 fusion protein= constitutively active TK>
activates proliferation and blocks apoptosis

Question 16

Where does the translocation occur? is it passed down?

Answer 16

Arises in hematopoietic stem cell

Passed down to ALL progeny

Question 17

What is the selective advantage for cells containing the BCR-ABL1 mutation?

Answer 17

Progenitor cells:

1) proliferate more, survive longer
2) have the opportunity to acquire more mutations–> make cells more oncogenic

Question 18

How does the BCR-ABL1 mutation relate to the ability to self renew and differentiate?

Answer 18

Progenitor cells
DO NOT self renew
DO continue to differentiate

Question 19

What is the outcome of BCR-ABL1 mutation?

Answer 19

Expansion of progenitor and committed cells

Mature cells still produced

Question 20

What happens in the chronic phase of CML?

Answer 20

Increased proliferation and survival of progenitor cells

Opportunity to acquire more mutations

Question 21

What happens in the blast phase of CML?

Answer 21

GMP acquires the ability to self renew
Acquires block to differentiation

Huge expansion of blast–> 30% extramedullary

Question 22

What is the outcome of accelerated CML w/ a blast phase?

Answer 22

EXTREME expansion of blasts
production of functional mature cells blocked
severe disease

Question 23

What causes progression from chronic to blast phase?

Answer 23

Additional mutations
GMP acquired self renewal capability
GMP lose ability to differentiate

Question 24

What is the mechanism of BCR-ABL1 translocation?

Answer 24

Double strand breaks occur in 2 chromosomes at specific break points

Question 25

What are the two most common break points?

Answer 25

P210- found in CML most common | P190- found in some ALL, less common

Question 26

What is the mechanism used for BCR-ABL1 translocation?

Answer 26

Non-homologous end joining - common DNA repair mechanism - doesn't require extensive homology

Question 27

What is the common initiating defect in CML?

Answer 27

reciprocal chromosomal translocation t(9:22) DNA is physically rearranged-->fusion protein w/ constitutive TK activity

Question 28

What are the normal domains in the BCR gene?

Answer 28

Ser/THR kinase domain | Coiled-coil domain, tyrosisne 177

Question 29

What are the normal functions of the BCR gene?

Answer 29

Inhibition of some inflammatory responses

Question 30

What are the normal domains in ABL1?

Answer 30

tyrosine kinase held inactive unless activated by external signals by myristate

Question 31

What are the normal functions of ABL1?

Answer 31

DNA repair | cytoskeletal organization

Question 32

What are tyrosine kinases?

Answer 32

regulator molecules in INTRAcellular signaling pathways that stimulate proliferatoin

Question 33

What are the main differences between normal ABL1 and BCR-ABL1?

Answer 33

ABL1 in normal cells is inactivated unless activated by intracellular signaling. BCR-ABL1 in CML cells is constitutively active. ABL1 and BCR-ABL1 activate different intracellular signaling pathways

Question 34

What are the different structural changes made to form BCR-ABL1?

Answer 34

1. coiled-coil domain is added from BCR--> dimerization necessary for activation 2. Myristate attachement site lost form ABL1-->Necessary for autoinhibition of ABL1 TK activity 3. Tyrosine-177- added from BCR phosphorylation of y-177 to create a new binding site for intracellular signaling proteins

Question 35

What is needed to initiate cell signaling in normal ABL cells?

Answer 35

Extracellular signaling is NECESSARY to initiate signaling by ABL1 ``` ABL in inactive conf> myristate inhibits> Extracellular signaling open conformation> dimerization> TK transphosphorylation> Initiation of signaling pathways ```

Question 36

What is needed to activated BACR-ABL to initiate signaling?

Answer 36

NO external signaling ``` BCR-ABL has NO myristate> always in open conf> coiled-coil domain promotes dimerization> TK active> Initiate cell signaling ```

Question 37

Why is the role of Y177 different in the BCR-ABL fusion protein from the BCR protein?

Answer 37

Y177 is subject to tyrosine phosphorylation in the fusion protein but NOT In BCR b/c BCR is NOT a tyrosine kinase.

Question 38

What does Stat5 do?

Answer 38

Binds to specific promoters to activate transcription of target genes that promote proliferation and impede apoptosis

Question 39

What is the role of JAK STAT in normal neutrophil development?

Answer 39

``` Cytokines (GM-CSF) are secreted by bone marrow--> bind to receptors on progenitor cells> initiates signaling through Jak 2> phosphorylates Stat 5 on tyrosine> activates it ```

Question 40

What is the activation of Stat 5 unique in CML cells? What does this do for cells?

Answer 40

BCR-ABL1 kinase activates Stat5 INDEPENDENTLY of external signals> trxn of proliferation factors and anti-apoptotic factors are downregulated This gives selective advantage to cells carrying this mutation so they can proliferate and create MORE mutations. Boooo.

Question 41

What does Imatinib do?

Answer 41

Inactivates ABL1 kinase by blocking ATP binding

Question 42

What leads to apoptosis in BCR-ABL mutant cells?

Answer 42

BCR-ABL mutant cells are dependent on BCR-ABL for proliferation and anti-apoptosis signaling. When BCR-ABL gets inactivated those cells are shit out of luck and it leads to APOPTOSIS. Loss of BCR-ABL mutatnt cells allows normal cells to repopulate.

Question 43

How does the BCR-ABL TK work?

Answer 43

Binding ATP> Transferring P from ATP to substrate> proliferation and block of apoptosis

Question 44

How does Imantib effect survival rates?

Answer 44

5 year survival for pts newly diagnosed w/ chronic CMLA nd treated w/ TK inhibitors 85-90% Normally 3-4 years

Question 45

What are the limitations of Imantib?

Answer 45

1. Secondary resistand d/t mut in BCR-ABL 2. NOT effective against blast phase disease 3. CML stem cells are resistant to TK inhibitors