Ikaros dominant negative isoform (Ik6) induces IL-3-independent survival of murine pro-B lymphocytes by activating JAK-STAT and up-regulating Bcl-xl levels.

Ikaros is an essential regulator of lymphocyte differentiation. Mice transgenic for the Ikaros dominant negative (DN) mutation rapidly develop lymphoid malignancies. Various human leukemias have also been reported to express Ikaros DN isoforms, but its role in leukemogenesis is yet to be defined. We demonstrate that overexpressed Ikaros DN (Ik6) prolonged the survival of two different murine pro-B cell lines in cytokine deprived condition, and this was associated with increased expression of Bcl-xl. A survey of the upstream controller(s) of Bcl-xl expression revealed Ik6 overexpression enhanced the phosphorylation of JAK2 and STAT5. Interestingly, the Ik6 expressing cell lines showed reduced expression of B-cell differentiation surface marker CD45R (B220), which is also known as a JAK2 inhibitor. Although further evaluation with human clinical materials are required, these results propose a putative role of Ik6 in the development of B-lineage acute lymphoblastic leukemia, by activating the JAK2-STAT5 pathway and thus stimulating the production of Bcl-xl.

Early blastic transformation following complete cytogenetic response in a pediatric chronic myeloid leukemia patient treated with imatinib mesylate.

This article reports early blastic transformation of chronic myeloid leukemia (CML) in a child following a complete cytogenetic response induced by imatinib mesylate. A 14-year-old Japanese boy was diagnosed with t(9;22) cryptic CML in the chronic phase and treated with imatinib. His response to treatment was slow, but a major cytogenetic response was obtained at 142 days of therapy. However, he developed lymphoid blastic transformation at 9 months. He attained remission with acute lymphoblastic leukemia-type chemotherapy and then successfully received a non-T-cell-depleted allogeneic stem cell transplantation (allo-SCT) with his mother's two loci-mismatched donor cells. A sudden blastic transformation may occur even with a complete cytogenetic response induced by imatinib. CML patients who respond slowly to imatinib may still be candidates for allo-SCT, even when a major cytogenetic response is obtained.

Impact of glutathione S-transferase gene deletion on early relapse in childhood B-precursor acute lymphoblastic leukemia.

BACKGROUND AND OBJECTIVES: The glutathione-S-transferase (GST) polymorphism may affect the outcome of treatment of leukemia because GSTs play an important role in detoxifying the chemotherapeutic agents used to kill leukemia cells. However, results of previous reports have been controversial. This study was undertaken to clarify the influence of GST polymorphism on the outcome of childhood B-precursor acute lymphoblastic leukemia (ALL). DESIGN AND METHODS: Eighty-two patients with childhood B-precursor ALL treated during 1988-1999 with our ALL protocol (median follow-up time 89.5 months, range 31 -169 months) were examined for GST gene patterns. The effect of GSTM1 and GSTT1 deletion genotypes on the clinical features and therapeutic results was analyzed. RESULTS: All patients attained complete remission but 12 had an early relapse (within 30 months of the initiation of treatment). In univariate analysis, early relapse of ALL was correlated significantly with the presence of the t(9;22)(q34;q11) cytogenetic abnormality (p=0.0003), high white blood cell counts (p=0.015) and double null genotype (p=0.027). Multivariate analysis revealed that the GST double null genotype was the only significant independent predictor of early relapse (p=0.018). INTERPRETATION AND CONCLUSIONS: The simultaneous deletion of both the GSTM1 and GSTT1 genes is more predictive than any other parameter of early relapse of childhood B-precursor ALL.

Frequent co-expression of HoxA9 and Meis1 genes in infant acute lymphoblastic leukaemia with MLL rearrangement.

We studied the expression of HoxA9 and Meis1 by reverse transcriptase-polymerase chain reaction analysis in leukaemic cells from cases of infant acute lymphoblastic leukaemia (ALL, n = 27) and childhood ALL (n = 29). These two genes were co-expressed significantly more frequently in infant ALL than in childhood ALL (19/27 vs0/29 cases, P < 0.001) and were highly associated with MLL gene rearrangement in infant ALL cases (P < 0.001). These findings indicate that the HoxA9 and Meis1 genes are closely associated with MLL gene rearrangement in the development of infant ALL, which represents a distinct entity of childhood ALL.

Expression of the Ikaros gene family in childhood acute lymphoblastic leukaemia.

The Ikaros (Ik) gene family, which includes Ik, Aiolos (Ai), and Helios (He), is a primary regulator of lymphocyte differentiation, and is involved in the development of acute lymphoblastic leukaemia (ALL). We analysed the expression of the Ik gene family isoforms in 97 ALL cases, consisting of 64 childhood and 33 infant ALL cases, using reverse transcription-polymerase chain reaction (RT-PCR). Expression of Ik was detected in all cases, 87 of which expressed either Ik1 or Ik2, or both, five of which expressed Ik1/Ik2 and Ik6, and another five of which expressed only Ik6. Therefore, the dominant negative isoform of Ik6 was expressed in 10 of the 38 cases of childhood precursor B ALL, but was absent in other types of childhood ALL (26.3%, chi2-test, P = 0.0001). In terms of Aiolos and Helios expression, 49 (65.3%) out of the 75 and 40 (50%) out of the 80 ALL cases tested showed non-spliced Ai1 and He1 respectively. Only one case of T lineage ALL expressed a small-sized isoform of Helios (designated as He6). It was also found that the expression of Ai1 and He1 was low in Ik6-positive patients (Fisher's exact test; Ai1 P = 0.005, Hel P = 0.035).

High frequency of Ikaros isoform 6 expression in acute myelomonocytic and monocytic leukemias: implications for up-regulation of the antiapoptotic protein Bcl-XL in leukemogenesis.

While studying Ikaros proteins in childhood acute myeloid leukemia (AML), Ikaros isoform 6 (Ik6) expression was detected in 7 of 10 cases of M4 and M5 leukemia, but in none of the remaining French-American-British subtypes (M2, 8 cases; M7, 6 cases). The spliced Ikaros isoforms 4 to 8 (Ik4-8) suppress the function of full-length Ik1 or Ik2 in a dominant-negative manner, owing to their reduced numbers of DNA binding sites. Thus, dominant-negative Ikaros isoforms may inhibit the normal transcriptional regulation of hematopoietic cell development. To clarify the function of Ik6 in developing blood cells, this isoform was transiently transfected into an Ik2(+), interleukin-3 (IL-3)-dependent 32D murine myeloid precursor cell line and studied the expression of Bcl-2 family proteins in relation to in vitro cell growth, using a tetracycline-inducible TREx system. The possibility of aberrant cell regulation due to Ikaros functional changes was examined by cotransfecting both Ik2 and Ik6 into Ikaros/Aiolos/Helios triple-negative Cos-7 cells. The results demonstrated IL-3-independent growth by Ik6-transfected 32D clones coincident with up-regulation of the antiapoptotic protein Bcl-XL. Up-regulation of Bcl-XL, but not of other Bcl-2 family proteins, was associated with the suppression of functional Ik2 by Ik6 in a dominant-negative fashion. Thus, the pathogenesis of myelomonocytic/monocytic AML may involve aberrant regulation of apoptosis due to unscheduled expression of the Ik6 isoform.