PML/RARα fusion protein mediates the unique sensitivity to arsenic cytotoxicity in acute promyelocytic leukemia cells: Mechanisms involve the impairment of cAMP signaling and the aberrant regulation of NADPH oxidase

2008 ◽  
Vol 217 (2) ◽  
pp. 486-493 ◽  
Author(s):  
Lingna Li ◽  
Jie Wang ◽  
Richard D. Ye ◽  
Guiying Shi ◽  
Huifang Jin ◽  
...  
Keyword(s):  
Nadph Oxidase ◽  
Fusion Protein ◽  
Acute Promyelocytic Leukemia ◽  
Promyelocytic Leukemia ◽  
Camp Signaling ◽  
Leukemia Cells

Impact of Protein Phosphatase PP2A on ATRA-Induced Activation of FoxO3a In Acute Promyelocytic Leukemia Cells

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2492-2492
Author(s):  
Yasuhiko Sakoe ◽  
Kumi Sakoe ◽  
Haruo Shimazaki ◽  
Keita Kirito ◽  
Norio Komatsu
Keyword(s):  
Retinoic Acid ◽  
Cell Growth ◽  
Fusion Protein ◽  
Acute Promyelocytic Leukemia ◽  
Cellular Responses ◽  
Promyelocytic Leukemia ◽  
Leukemia Cell Line ◽  
Leukemia Cells ◽  
Atra Treatment ◽  
Granulocytic Differentiation

Abstract Abstract 2492 Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia caused by reciprocal translocations of the long arms of chromosomes 15 and 17, which prevent cellular differentiation into mature neutrophils. The translocation of the promyelocytic leukemia (PML) gene on chromosome 15 and a retinoic acid receptor α (RARα) gene on chromosome 17 generates a PML-RARα fusion protein that inhibits PML-dependent apoptotic pathways in a dominant negative fashion. This fusion protein also blocks granulocytic differentiation by direct transcriptional inhibition of retinoic acid target genes. All-trans retinoic acid (ATRA) arrests cell growth, granulocytic differentiation, and apoptosis in APL cells via proteasome-dependent degradation of PML-RARα fusion protein and subsequent PML-nuclear body (NB) formation. Although PML is the essential component of PML-NBs and functions as a tumor suppressor, disruption of PML-NBs by the PML-RARα fusion protein inhibits endogenous PML tumor-suppressive functions in APL cells. Therefore, degradation of PML-RARα fusion protein and reorganization of PML-NBs during ATRA treatment are regarded as critical cellular responses, similar to the cell growth arrest and apoptosis of leukemia cells. Recently we demonstrated that FoxO3a (also named FKHRL1), a member of the Forkhead family of transcription factors, is a key molecule for the ATRA-induced cellular responses in APL cells (Blood 2010; 115: 3787–3795). In this study, we investigated the mechanism by which FoxO3a is activated by ATRA treatment in a human promyelocytic leukemia cell line NB4. Okadaic acid, a potent PP2A inhibitor, cancelled ATRA-induced dephosphorylation of AKT and its downstream molecule FoxO3a in NB4 cells. Knockdown of endogenous PP2A by siRNA significantly enhanced phosphorylation of both AKT and FoxO3a. These results suggested that PP2A is involved in ATRA-induced dephosphorylation of AKT and FoxO3a. Concomitantly, PP2AC, a catalytic subunit of PP2A, was dephoshorylated at tyrosine 307, and phosphatase activity of PP2A increased after ATRA treatment. Co-immunoprecipitation assay revealed that PP2A constitutively and directly binds to FoxO3a. Using artificial oligopeptides, we demonstrated that enhanced PP2A activity by ATRA directly dephosphorylates phosphothreonine 32 on FoxO3a. In addition, we found that 14-3-3 epsilon binded to phosphorylated FoxO3a in the cytoplasm in the absence of ATRA. After ATRA treatment, however, dephosphorylated FoxO3a dissociated from 14-3-3 epsilon and moved into the nucleus. Confocal microscopic analysis revealed that PP2A-FoxO3a complex partially co-localized with PML-NBs in the nucleus after ATRA treatment. Together, PML orchestrates nuclear networking with PP2A and FoxO3a for ATRA-induced granulocytic differentiation and apoptosis of APL cells. Disclosures: No relevant conflicts of interest to declare.

scholarly journals PML protein expression in hematopoietic and acute promyelocytic leukemia cells

Blood ◽  
1993 ◽  
Vol 82 (6) ◽  
pp. 1858-1867 ◽  
Author(s):  
MT Daniel ◽  
M Koken ◽  
O Romagne ◽  
S Barbey ◽  
A Bazarbachi ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Fusion Protein ◽  
Acute Promyelocytic Leukemia ◽  
Retinoic Acid Receptor ◽  
Promyelocytic Leukemia ◽  
Leukemia Cells ◽  
Cytoplasmic Localization ◽  
Wild Type ◽  
Retinoic Acid Receptor Alpha ◽  
Dominant Effect

Abstract Acute promyelocytic leukemia (APL) is thought to be caused by the t(15,17) translocation that fuses the PML gene to that of the retinoic acid receptor alpha (RAR alpha) and generates a PML/RAR alpha fusion protein. Yet, paradoxically, APL cells are exquisitely sensitive to retinoic acid (RA), as they terminally differentiate upon RA exposure. In this report, we have examined the expression of PML and PML/RAR alpha in normal and APL cells. By immunofluorescence or immunocytochemistry, we show that PML has a speckled nuclear pattern of expression that contrasts with that of PML/RAR alpha (mostly a micropunctuated nuclear pattern or a cytoplasmic localization). The APL- derived cell line NB4 that expresses both the PML and PML/RAR alpha genes also shows the fine micropunctuated nuclear pattern, suggesting a dominant effect of the fusion protein over the localization of wild- type PML. RA treatment of NB4 cells or clones expressing PML/RAR alpha gradually leads to a PML pattern before apparent morphologic maturation. In 14 untreated APL patients, the PML-reactive proteins were cytoplasmic (by immunocytochemistry) or both cytoplasmic and nuclear with a micropunctuated pattern (by immunofluorescence). Strikingly, in 4 patients, after 1 to 2 weeks of RA therapy, the speckled nuclear PML pattern reappeared concomitant with the onset of differentiation. These results establish that fusion of PML to RAR alpha results in an altered localization of PML that is reverted upon RA treatment. This observation, which highlights the importance of PML, is likely to be a key to unravelling the molecular mechanism of both leukemogenesis and RA-induced differentiation of APL.

scholarly journals PML protein expression in hematopoietic and acute promyelocytic leukemia cells

Blood ◽  
1993 ◽  
Vol 82 (6) ◽  
pp. 1858-1867 ◽  
Author(s):  
MT Daniel ◽  
M Koken ◽  
O Romagne ◽  
S Barbey ◽  
A Bazarbachi ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Fusion Protein ◽  
Acute Promyelocytic Leukemia ◽  
Retinoic Acid Receptor ◽  
Promyelocytic Leukemia ◽  
Leukemia Cells ◽  
Cytoplasmic Localization ◽  
Wild Type ◽  
Retinoic Acid Receptor Alpha ◽  
Dominant Effect

Acute promyelocytic leukemia (APL) is thought to be caused by the t(15,17) translocation that fuses the PML gene to that of the retinoic acid receptor alpha (RAR alpha) and generates a PML/RAR alpha fusion protein. Yet, paradoxically, APL cells are exquisitely sensitive to retinoic acid (RA), as they terminally differentiate upon RA exposure. In this report, we have examined the expression of PML and PML/RAR alpha in normal and APL cells. By immunofluorescence or immunocytochemistry, we show that PML has a speckled nuclear pattern of expression that contrasts with that of PML/RAR alpha (mostly a micropunctuated nuclear pattern or a cytoplasmic localization). The APL- derived cell line NB4 that expresses both the PML and PML/RAR alpha genes also shows the fine micropunctuated nuclear pattern, suggesting a dominant effect of the fusion protein over the localization of wild- type PML. RA treatment of NB4 cells or clones expressing PML/RAR alpha gradually leads to a PML pattern before apparent morphologic maturation. In 14 untreated APL patients, the PML-reactive proteins were cytoplasmic (by immunocytochemistry) or both cytoplasmic and nuclear with a micropunctuated pattern (by immunofluorescence). Strikingly, in 4 patients, after 1 to 2 weeks of RA therapy, the speckled nuclear PML pattern reappeared concomitant with the onset of differentiation. These results establish that fusion of PML to RAR alpha results in an altered localization of PML that is reverted upon RA treatment. This observation, which highlights the importance of PML, is likely to be a key to unravelling the molecular mechanism of both leukemogenesis and RA-induced differentiation of APL.

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