Signal transduction and activator of transcription (STAT) proteins are extracellular ligand-responsive transcription factors that mediate cell proliferation, apoptosis, differentiation, development and the immune response. Aberrant signals of STAT induce uncontrolled cell proliferation and apoptosis resistance and are strongly involved in cancer. STAT has been identified as a promising target for antitumor drugs, but to date most trials have not been successful. Here, we demonstrated that a novel STAT inhibitor, OPB-31121, strongly inhibited STAT3 and STAT5 phosphorylation without upstream kinase inhibition, and induced significant growth inhibition in various hematopoietic malignant cells. Investigation of various cell lines suggested that OPB-31121 is particularly effective against multiple myeloma, Burkitt lymphoma and leukemia harboring BCR–ABL, FLT3/ITD and JAK2 V617F, oncokinases with their oncogenicities dependent on STAT3/5. Using an immunodeficient mouse transplantation system, we showed the significant antitumor effect of OPB-31121 against primary human leukemia cells harboring these aberrant kinases and its safety for normal human cord blood cells. Finally, we demonstrated a model to overcome drug resistance to upstream kinase inhibitors with a STAT inhibitor. These results suggested that OPB-31121 is a promising antitumor drug. Phase I trials have been performed in Korea and Hong Kong, and a phase I/II trial is underway in Japan.

PAX5 is a transcription factor required for B-cell development and maintenance. PML is a tumor suppressor and a pro-apoptotic factor. A fusion gene, PAX5-PML, was found in acute lymphoblastic leukemia (ALL) with chromosomal translocation t(9;15)(p13;q24), but no functional analysis has been reported. Here, we demonstrate that PAX5-PML had a dominant-negative effect on both PAX5 and PML. PAX5-PML dominant negatively inhibited PAX5 transcriptional activity in the luciferase reporter assay and suppressed the expression of the PAX5 transcriptional targets in B-lymphoid cell line. Surprisingly, PAX5-PML hardly showed DNA-binding activity in vitro although it retained the DNA-binding domain of PAX5. Additional experiments, including chromatin immunoprecipitation (ChIP) assay, suggested that PAX5-PML bound to the promoter through the association with PAX5 on the promoter. On the other hand, coexpression of PAX5-PML inhibited PML sumoylation, disrupted PML nuclear bodies (NBs), and conferred apoptosis resistance on HeLa cells. Furthermore, treatment with arsenic trioxide (ATO) induced PML sumoylation and reconstitution of PML NBs, and overcame the anti-apoptotic effect of PAX5-PML in HeLa cells. These data suggest the possible involvement of this fusion protein in the leukemogenesis of B-ALL in a dual dominant-negative manner and the possibility that ALL with PAX5-PML can be treated with ATO.

Plasma cell differentiation is initiated by Ag stimulation of BCR. Until BCR stimulation, B lymphocyte-induced maturation protein 1 (BLIMP1), a master regulator of plasma cell differentiation, is suppressed by PAX5, which is a key transcriptional repressor for maintaining B cell identity. After BCR stimulation, upregulation of BLIMP1 and subsequent suppression of PAX5 by BLIMP1 are observed and thought to be the trigger of plasma cell differentiation; however, the trigger that derepresses BLIMP1 expression is yet to be revealed. In this study, we demonstrated PAX5 phosphorylation by ERK1/2, the main component of the BCR signal. Transcriptional repression on BLIMP1 promoter by PAX5 was canceled by PAX5 phosphorylation. BCR stimulation induced ERK1/2 activation, phosphorylation of endogenous PAX5, and upregulation of BLIMP1 mRNA expression in B cells. These phenomena were inhibited by MEK1 inhibitor or the phosphorylation-defective mutation of PAX5. These data imply that PAX5 phosphorylation by the BCR signal is the initial event in plasma cell differentiation.

POEMS syndrome is a rare plasma cell dyscrasia presenting with polyneuropathy, λ-type M protein, vascular endothelial growth factor elevation, and systemic manifestations. The standard treatment has not been established, but autologous stem cell transplantation (ASCT) has exhibited effectiveness in this syndrome. However, the efficacy and long-term outcomes of ASCT have not been systematically studied. To clarify the efficacy and long-term outcomes of ASCT-treated patients in Japan, we performed a multicenter retrospective study assessing the clinical course of patients registered to the Japan Society for Hematopoietic Cell Transplantation Transplant Registry Unified Management Program (TRUMP) database. Between January 2000 and December 2011, 95 patients (58 men) were registered to the TRUMP database with a median age of 53 years (range, 28 to 72). The conditioning regimen was melphalan in 93 of 94 patients (99%), and 69 patients (74.2%) received a melphalan dose ≥ 200 mg/m. The median CD34 cell dose was 2.47 × 10/kg (range, .31 to 20). After ASCT, patient performance status was dramatically improved (Eastern Cooperative Oncology Group performance status 0 to 1: 20.0% versus 71.6%, P < .0001). Over a median follow-up of 46.6 months 10 patients died, and 5-year overall survival was 88.8% (n = 95). Progression-free survival at 3 years was 78.3% (n = 70; median follow-up, 54.4 months). These data support the promising role of ASCT in patients with POEMS syndrome for both prolonging survival and improving quality of life. However, disease recurrence remains a major issue for long-term survivors.

PAX5 is a transcription factor that is required for the development and maintenance of B cells. Promyelocytic leukemia (PML) is a tumor suppressor and proapoptotic factor. The fusion gene PAX5-PML has been identified in acute lymphoblastic leukemia with chromosomal translocation t(9;15)(p13; q24). We have reported previously that PAX5-PML dominantnegatively inhibited PAX5 transcriptional activity and impaired PML function by disrupting PML nuclear bodies (NBs). Here we demonstrated the leukemogenicity of PAX5-PML by introducing it into normal mouse pro-B cells. Arrest of differentiation was observed in PAX5-PML-introduced pro-B cells, resulting in the development of acute lymphoblastic leukemia after a long latency in mice. Among the transactivation targets of PAX5, B cell linker protein (BLNK) was repressed selectively in leukemia cells, and enforced BLNK expression abrogated the differentiation block and survival induced by PAX5-PML, indicating the importance of BLNK repression for the formation of preleukemic state. We also showed that PML NBs were intact in leukemia cells and attributed this to the low expression of PAX5-PML, indicating that the disruption of PML NBs was not required for the PAX5-PML-induced onset of leukemia. These results provide novel insights into the molecular mechanisms underlying the onset of leukemia by PAX5 mutations.PAX5 is a member of the highly conserved paired box (PAX) 2 domain family of transcription factors. PAX5 is expressed exclusively from the pro-B to mature B cell stage and is downregulated during terminal differentiation into plasma cells (1). PAX5 is indispensable for B lineage commitment by the transcriptional activation of B lineage-specific genes (2), such as CD19 (3), CD79A (4), and B cell linker protein (BLNK) (5), and its target disruption has been shown to cause B lymphoid maturation arrest at the pro-B cell stage (6). Previous studies have identified the PAX5 gene as the most frequent target of somatic mutations in childhood and adult B-progenitor acute lymphoblastic leukemia (ALL), being altered in 38.9% and 34% of cases, respectively (7,8), and these findings further emphasized the essential role of PAX5 in the proper development of B cells. Somatic mutations consist of partial or complete hemizygous deletions, homozygous deletions, partial or complete amplifications, point mutations, or fusion genes (7). These aberrations in the PAX5 gene are considered to impair PAX5 function and play a role in blocking B cell differentiation. PAX5 fusion proteins such as PAX5-TEL, PAX5-ENL, PAX5-PML, and PAX5-C20S have been shown previously to have dominant-negative effects on PAX5 transcriptional activity and have been suggested to be mainly responsible for the differentiation disorder of ALL with these fusion genes (9 -12). Consistently, a previous study has reported that PAX5 haploinsufficiency cooperated with the constitutive activation of STAT5 to initiate ALL in mice (13). However, the oncogenicity of PAX5 mutations, including fusion genes, has yet to be demonstrated...

We identified two novel GATA2 mutations in acute myeloid leukemia (AML). One mutation (p.R308P-GATA2) was a R308P substitution within the zinc finger (ZF)-1 domain, and the other (p.A350_N351ins8-GATA2) was an eight-amino-acid insertion between A350 and N351 residues within the ZF-2 domain. p.R308P-GATA2 did not affect DNA-binding and transcriptional activities, while p.A350_N351ins8-GATA2 reduced them, and impaired G-CSF-induced granulocytic differentiation of 32D cells. Although p.A350_N351ins8-GATA2 did not show a dominant-negative effect over wild-type (Wt)-GATA2 by the reporter assay, it might be involved in the pathophysiology of AML by impairing myeloid differentiation because of little Wt-GATA2 expression in primary AML cells harboring the p.A350_N351ins8 mutation.

We report a case of long-term remission following auto-PBSCT in a relapsed IVL patient. Our report suggests that auto-PBSCT could be a therapeutic option in chemosensitive patients with relapsed IVL. Due to her atypical clinical course, further careful long-term follow-up of our patient is needed.

No abstract