A PML/retinoic acid receptor alpha fusion transcript is constantly detected by RNA-based polymerase chain reaction in acute promyelocytic leukemia

International audienceThe t(15;17) translocation is specifically observed in patients with promyelocytic leukemia (AML3). The chromosomal rearrangement juxtaposes the retinoic acid receptor alpha (RAR alpha) and PML genes, resulting in PML/RAR alpha fusion transcripts. Our previous studies have shown that a polymerase chain reaction (PCR) amplification product could be obtained from the cDNA of the NB4 promyelocytic cell line from which the chimaeric PML/RAR alpha was cloned. We report here that in all 14 AML3 patients tested, reverse transcriptase-PCR (RT-PCR) allows the detection of three specific fusion products. In eight patients, one amplification product was detected corresponding to the previously described abnormal fusion. Five patients displayed a different amplified fragment corresponding to a different fusion point. One other patient always showed a third different-sized product. The different types of fusion transcripts amplified were correlated to the size of the abnormal RAR alpha transcripts detected in these patients by Northern analysis, but did not prove determinant for either the phenotypic features or the retinoic acid responsiveness in AML3 cells in this group of patients. The consistent identification by RT-PCR of the fusion of the PML and RAR alpha genes in AML3 patients suggest that this method will provide a useful tool for the diagnosis and detection of minimal residual disease in these patients

Cyclin D3 is a cofactor of retinoic acid receptors, modulating their activity in the presence of cellular retinoic acid-binding protein II

International audienceLigand-induced transcription activation of retinoic acid (RA) target genes by nuclear receptors (retinoic acid (RAR) and retinoid X (RXR) receptors) depends on the recruitment of coactivators. We have previously demonstrated that the small 15-kDa cellular RA-binding protein II (CRABPII) is a coactivator present in the RA-dependent nuclear complex. As identifying cell-specific partners of CRABPII might help to understand the novel control of RA signaling, we performed a yeast two-hybrid screen of a hematopoietic HL-60 cDNA library using human CRABPII as bait and have subsequently identified human cyclin D3 as a partner of CRABPII. Cyclin D3 interacted with CRABPII in a ligand-independent manner and equally bound RAR alpha, but not RXR alpha, and only in the presence of RA. We further show that cyclin D3 positively modulated RA-mediated transcription through CRABPII. Therefore, cyclin D3 may be part of a ternary complex with CRABPII and RAR. Finally, we show that cyclin D3 expression paralleled HL-60 differentiation and arrest of cell growth. These findings led us to speculate that control of cell proliferation during induction of differentiation may directly involve, at the transcriptional level, nuclear receptors, coactivators, and proteins of the cell cycle in a cell- and nuclear receptor-specific manner

Poor response to all-trans retinoic acid therapy in a t(11;17) PLZF/RAR alpha patient.

All-trans retinoic acid (ATRA) is a potent inducer of differentiation and cell death in malignant cells. Its effect is known to be mediated through binding to specific nuclear (RARs and RXRs) or cytoplasmic (CRABP) proteins. ATRA is strikingly effective in acute promyelocytic leukemia (the AML3 subtype) inducing a high incidence of complete remissions. Paradoxically, most AML3 cells harbor an abnormal retinoic acid receptor (PML/RAR alpha) resulting from the t(15;17) translocation. Though few AML3 patients do not respond to ATRA therapy, individualization of these cases is of practical importance. Recently the RAR alpha gene has been demonstrated to be involved in a novel fusion transcript (PLZF/RAR alpha) through a t(11;17) translocation. We describe here the second case of such a patient with a t(11;17)-PLZF/RAR alpha leukemic clone. Southern analysis revealed that the breakpoint in the RAR alpha gene was within the second intron (as for PML/RAR alpha) and the intron separating the second and third zinc finger of the PLZF gene. In vitro, the leukemic cells did not show increased NBT reduction or loss of self-renewal after incubation with ATRA. After therapy with ATRA, only partial remission was obtained. These results suggest that the t(11;17) (PLZF/RAR alpha) case of this study was less responsive to ATRA therapy than t(15;17) (PML/RAR alpha) cases and raises the question of the definition of this novel AML subtype.Case ReportsJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.info:eu-repo/semantics/publishe

Toll-like receptor 3 regulates cord blood-derived endothelial cell function in vitro and in vivo

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Localization of the NRAS:BCL-2 complex determines anti-apoptotic features associated with progressive disease in myelodysplastic syndromes

We have previously demonstrated that two prognostic features of myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML), mutant NRAS and over-expressing BCL-2, cooperate physically and functionally in vivo. Screening of MDS patient bone marrow (BM) identified NRAS:BCL-2 co-localization in 64% cases, correlating with percentage BM blasts, apoptotic features and disease status (p < 0.0001). Localization of the complex at the plasma membrane or the mitochondria correlated with disease and apoptosis features in MDS patients, whilst caspase-9 mediated mechanism was elucidated in vivo and in vitro. The intensity and localization of the RAS:BCL-2 complex merits further evaluation as a novel biomarker of MDS