Down-stream regions of the POZ-domain influence the interaction of the t(11;17)-associated PLZF/RARalpha fusion protein with the histone-deacetylase recruiting co-repressor complex.
BACKGROUND
Acute promyelocytic leukemia (APL) patients with t(15;17)(PML/RARalpha positive) achieve remission upon t-RA treatment, whereas patients with t(11;17)(PLZF/RARalpha positive) do not. Both APL translocation products bind to the histone deacetylase (HD)-recruiting nuclear co-repressor complex (HD-NCR) in a ligand-dependent manner through their RARalpha portion. Differently to PML/RARalpha, PLZF/RARalpha also binds the HD-NCR in a ligand-independent manner through the PLZF portion of the fusion protein (PLZF#), which seems to be crucial for the t-RA resistance of t(11;17) APL patients.


METHODS
The t-RA sensitivity of U937 cells was tested by the nitro-blue tetrazolium reduction (NBT) assay and by analysis of t-RA-induced type II transglutaminase activity. The interaction between HD-NCR and PLZF/RARalpha was investigated by in vitro binding assays.


RESULTS
(i) Deletions in PLZF# convert PLZF/RARalpha from a repressor to an activator of t-RA response in U937 cells; (ii) the effect of PLZF/RARalpha on t-RA-signaling is regulated by the POZ-domain and its down-stream regions of PLZF#; (iii) there are additional binding sites for HD-NCR in PLZF# and (iv) PLZF# not only directly binds but also regulates the binding of PLZF/RARalpha to the HD-NCR.


CONCLUSIONS
At least two different mechanisms responsible for the aberrant recruitment of HD-NCR complexes by PLZF# are regulating the different t-RA-sensitivity of the PLZF/RARalpha and PML/RARalpha positive APL blasts: one is related to the direct binding of the different members of the HD-NCR complex to PLZF#; the other is an enforcing effect of PLZF# on the affinity of the PLZF/RARalpha fusion protein to the HD-NCR complex.
Puccetti
E
E
Med. Klinik III/Abtl. Hämatologie, Johann Wolfgang Goethe-Universität, D-60590 Frankfurt, Germany.
Sennewald
B
B
Fosca-Ferrara
F
F
Boehrer
S
S
Bianchini
A
A
Hoelzer
D
D
Ottmann
O G
OG
Nervi
C
C
Ruthardt
M
M
D002880:Chromosomes, Human, Pair 11; D002886:Chromosomes, Human, Pair 17; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology; D019008:Drug Resistance, Neoplasm; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D051741:Kruppel-Like Transcription Factors; D015473:Leukemia, Promyelocytic, Acute / Q000209:etiology / Q000235:genetics; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D000075722:Promyelocytic Leukemia Zinc Finger Protein; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology; D014178:Translocation, Genetic; D014212:Tretinoin / Q000494:pharmacology; D020298:U937 Cells; D016335:Zinc Fingers / Q000235:genetics
D004268:DNA-Binding Proteins; D051741:Kruppel-Like Transcription Factors; D009363:Neoplasm Proteins; D015514:Oncogene Proteins, Fusion; C118318:PLZF-RARalpha fusion protein, human; D000075722:Promyelocytic Leukemia Zinc Finger Protein; D012097:Repressor Proteins; D014157:Transcription Factors; C092037:ZBTB16 protein, human; D014212:Tretinoin; D006655:Histone Deacetylases