Acute Promyelocytic Leukaemia Flashcards
What is APML caused by?
Fusion of PML-RARA
What % of AMLs does it account for?
Who is it mainly diagnosed in?
5-8%
Adults but can occur at any age
What is it associated with?
Disseminated Intravascular Coagulation (DIC)
What is DIC
Massive stimulation of coagulation in the blood.
Massive internal bleeding
Describe DIC
Deregulation of homeostasis: widespread activation of the clotting cascade
Formation of small blood clots throughout body (cause damage to vital organs)
Mutiple organ damage
Coagulation process also consumes clotting factors and platelets - normal clotting is disrupted and severe bleeding can occur from various sites.
10-50% mortality
Urgent treatment required
Does RARA always fuse with PML?
No
RARA can also fuse with 8 other genes causing 5% of APML
Where is RARA
WHere is PML
RARA = 17q12
PML = 15q22
What are breakapart probes used for?
Detect if rearrangement is present
Done in combination of DUal fusion for PML-RARA
How is breakapart different to Dual fusion FISH?
Dual usion looks for two signals coming together
Breakapart looks for two signals breaking apart
How do we anaylse PML-RAR fusion using breakapart FISH
Upstream RARA (close to centromere) painted red, then RARA gen pained in green.
In normal individual - two normal copies of 17. SHould seen two red-green signals together.
In mutated - A red and green signal will be broken apart. Greeen signal will be on the abnormal chromosome 15.
What is the classic marker for PML-RARA in karytype analysis?
3 chromosome 14 and a missing chromosome 15.
Need to do further genetic analysis to characterise at the molecular level
Why do we need to do a dual fusion as well?
To know which gene RARA has fused to
This is so the correct rational therapy can be recomended. As therapy used for PML-RARA does not work as well for other RARA gene fusions.
Could also mean RARA gene has just moved to another region on chromosome.
Where does the fusion gene PML-RARA sit?
On abnormal 15
Limitation of FISH
Looking at 3D nucleus.
Could get colocalisation event of red and green signal in 1% of nuclei (if you rotate the red and green signal will eventually overlap)
However if you do this with 2 red spots or 2 green spots
What is used to treat APML RARA-PML gene fusion?
ATRa and ATO
mechanism of PML_RARA fusion gene
On the one hand, PML-RARA produces a block of myeloid differentiation at the promyelocytic stage
In this case, PML-RARA represses the transcription of several genes implicated in myeloid differentiation, such as those involved in the differentiation towards the granulocyte lineage, in a manner insensitive to physiological levels of retinoic ligands
On the other hand, PML-RARA confers a survival and proliferative advantage to leukemic cells, resulting in the progressive accumulation of promyelocytes in the bone marrow of APL patients
In this case, PML-RARA-RXR complexes mainly recognize atypical RAREs and interact with genomic regions characterized by a distinct pattern of chromatin modifications
(Liquori, 2020)
Mechanism of ATRA and ATO
These induce the PML-RARA degradation by binding to the RARA and PML parts of the fusion protein, respectively. Therefore, ATRA turns PML-RARA into a transcriptional activator, as a consequence of the release of several corepressors, including epigenetic enzymes (e.g., HDACs and DNA methyltransferases) and the interaction with a series of coactivators (e.g., coactivator-1, multi-protein complex including the cellular coactivator p300), leading to a more accessible chromatin
On the other side, ATO induces different posttranscriptional modifications at the second B-box (B2) domain of the PML moiety, resulting in the change of the PML-RARA organization from microspeckles to NBs
(Liquori, 2020)
