Search

The promyelocytic leukemia retinoic acid receptor alpha (PMLRARalpha) chimeric protein is associated with acute promyelocytic leukemia (APL). PMLRARalpha transgenic mice develop leukemia only after several months, suggesting that PMLRARalpha does not by itself confer a fully malignant phenotype. Suppression of apoptosis can have a central role in tumorigenesis; therefore, we assessed whether BCL-2 influenced the ability of PMLRARalpha to initiate leukemia. Evaluation of preleukemic animals showed that whereas PMLRARalpha alone modestly altered neutrophil maturation, the combination of PMLRARalpha and BCL-2 caused a marked accumulation of immature myeloid cells in bone marrow. Leukemias developed more rapidly in mice coexpressing PMLRARalpha and BCL-2 than in mice expressing PMLRARalpha alone, and all mice expressing both transgenes succumbed to leukemia by 7 mo. Although both preleukemic, doubly transgenic mice and leukemic animals had abundant promyelocytes in the bone marrow, only leukemic mice exhibited thrombocytopenia and dissemination of immature cells. Recurrent gain of chromosomes 7, 8, 10, and 15 and recurrent loss of chromosome 2 were identified in the leukemias. These chromosomal changes may be responsible for the suppression of normal hematopoiesis and dissemination characteristic of the acute leukemias. Our results indicate that genetic changes that inhibit apoptosis can cooperate with PMLRARalpha to initiate APL.

Arsenic, an ancient drug used in traditional Chinese medicine, has attracted worldwide interest because it shows substantial anticancer activity in patients with acute promyelocytic leukemia (APL). Arsenic trioxide ([As.sub.2][O.sub.3]) exerts its therapeutic effect by promoting degradation of an oncogenic protein that drives the growth of APL cells, PML-RAR[alpha] (a fusion protein containing sequences from the PML zinc finger protein and retinoic acid receptor alpha). PML and PML-RAR[alpha] degradation is triggered by their SUMOylation, but the mechanism by which As203 induces this posttranslational modification is unclear. Here we show that arsenic binds directly to cysteine residues in zinc fingers located within the RBCC domain of PML-RAR[alpha] and PML. Arsenic binding induces PML oligomerization, which increases its interaction with the small ubiquitin-like protein modifier (SUMO)--conjugating enzyme UBC9, resulting in enhanced SUMOylation and degradation. The identification of PML as a direct target of [As.sub.2][O.sub.3] provides new insights into the drug's mechanism of action and its specificity for APL. 10.1126/science.1183424

Retinoic acid and arsenic trioxide target the protein stability and transcriptional repression activity of the fusion oncoprotein PML-RARA, resulting in regression of acute promyelocytic leukemia (APL). Phenotypically, retinoic acid induces differentiation of APL cells. Here we show that retinoic acid also triggers growth arrest of leukemia-initiating cells (LICs) ex vivo and their clearance in PML-RARA mouse APL in vivo. Retinoic acid treatment of mouse APLs expressing the fusion protein PLZF-RARA triggers full differentiation, but not LIC loss or disease remission, establishing that differentiation and LIC loss can be uncoupled. Although retinoic acid and arsenic synergize to clear LICs through cooperative PML-RARA degradation, this combination does not enhance differentiation. A cyclic AMP (CAMP)-dependent phosphorylation site in PML-RARA is crucial for retinoic acid-induced PML-RARA degradation and LIC clearance. Moreover, activation of cAMP signaling enhances LIC loss by retinoic acid, identifying cAMP as another potential APL therapy. Thus, whereas transcriptional activation of PML-RARA is likely to control differentiation, its catabolism triggers LIC eradication and long-term remission of mouse APL. Therapy-triggered degradation of oncoproteins could be a general strategy to eradicate cancer stem cells., APL is characterized by a specific t(15;17) translocation that encodes a fusion of the promyelocytic leukemia (PML) and retinoic acid receptor-[alpha] (RARA) proteins. PML-RARA is a transcriptional repressor with both [...]

An attempt is made to investigate casein kinase 2 (CK2), a kinase associated with cancer promotion, phosphorylates PML protein, which causes senescence and on oncogenic stress, its absence promotes cellular transformation. Tumor establishment can be offset by the pharmacological inhibition of CK-2 induced PML.

Rihab Nasr, Marie-Claude Guillemin, Omar Ferhi, Hassan Soilihi, Laurent Peres, Caroline Berthier, Philippe Rousselot, Macarena Robledo-Sarmiento, Valerie Lallemand-Breitenbach, Bernard Gourmel, Dominique Vitoux, Pier Paolo Pandolfi, Cecile Rochette-Egly, Jun Zhu & [...]

Acute promyelocytic leukemia (APL) is a hematological malignancy driven by the PML/RARA oncogene. The prognosis for patients with APL was revolutionized by two treatments: retinoic acid (RA) and As2O3 (arsenic trioxide). These were both shown a posteriori to target PML/RARA, explaining their exquisite specificity for APL. Arsenic, as a single agent, cures up to 70% of patients, whereas APL patients treated with the combination of RA and As2O3 reach a stunning 90% cure rate. Recent physiopathological models highlight the key role of RA- and As2O3-triggered PML/RARA degradation, and the molecular mechanisms underlying As2O3-induced PML/RARA degradation have been recently clarified. As discussed below, arsenic binding, oxidation, sumoylation on PML nuclear bodies, and RNF4-mediated ubiquitination all contribute to the As2O3-triggered catabolism of PML/RARA. [ABSTRACT FROM AUTHOR]

We recently have identified a new cytoplasmic linker protein (CLIP), CLIPR-59, which is involved in the regulation of early endosome/trans-Golgi network dynamics. In contrast with CLIP-170, CLIPR-59 is not localized to microtubules at steady state but is associated with the trans-Golgi network and the plasma membrane. Here we show that the last 30 amino acids (C30) are sufficient for membrane targeting and that two cysteines in the C30 domain are palmitoylated. We demonstrate that CLIPR-59 is associated with lipid rafts via its C-terminal palmitoylated domain. In vitro experiments suggest that CLIPR-59 and its microtubule-binding domain alone have a better affinity for unpolymerized tubulin or small oligomers than for microtubules. In contrast with the CLIP-170 microtubule-binding domain, the CLIPR-59 microtubule-binding domain diminishes microtubule regrowth after nocodazole washout in vivo, showing that this domain can prevent microtubule polymerization. In contrast with the role of linker between membranes and microtubules that was proposed for CLIP function, CLIPR-59 thus may have an "anti-CLIP" function by preventing mierotubule-raft interactions. [ABSTRACT FROM AUTHOR]

Arsenic, an ancient drug used in traditional Chinese medicine, has attracted worldwide interest because it shows substantial anticancer activity in patients with acute promyelocytic leukemia (APL). Arsenic trioxide (As2O3) exerts its therapeutic effect by promoting degradation of an oncogenic protein that drives the growth of APL cells, PML-RARα (a fusion protein containing sequences from the PML zinc finger protein and retinoic acid receptor alpha). PML and PML-RARα degradation is triggered by their SUMOylation, but the mechanism by which As2O3induces this posttranslational modification is unclear. Here we show that arsenic binds directly to cysteine residues in zinc fingers located within the RBCC domain of PML-RARα and PML. Arsenic binding induces PML oligomerization, which increases its interaction with the small ubiquitin-like protein modifier (SUMO)--conjugating enzyme UBC9, resulting in enhanced SUMOylation and degradation. The identification of PML as a direct target of As2O3 provides new insights into the drug's mechanism of action and its specificity for APL. [ABSTRACT FROM AUTHOR]