Bmi-1 and SALL4 are putative oncogenes that modulate stem cell pluripotency and play a role in leukemogenesis. Murine Sall4 also has been shown to play an essential role in maintaining the properties of ES cells and governing the fate of the primitive inner cell mass. Here, we demonstrate that transcription from the Bmi-1 promoter is strikingly activated by SALL4 in a dose-dependent manner by using a luciferase reporter gene assay. Both promoter deletion construct studies and ChIP from a myeloid stem cell line, 32D, demonstrate that SALL4 binds to a specific region of the Bmi-1 promoter. Deletion of one copy of Sall4 by gene targeting in mouse bone marrow significantly reduced Bmi-1 expression. Reducing SALL4 expression by siRNA in the HL-60 leukemia cell line also results in significant down-regulation of Bmi-1. Furthermore, Bmi-1 expression is up-regulated in transgenic mice that constitutively overexpress human SALL4, and the levels of Bmi-1 in these mice increase as they progress from normal to preleukemic (myelodysplastic syndrome) and leukemic (acute myeloid leukemia) stages. High levels of H3-K4 trimethylation and H3-K79 dimethylation were observed in the SALL4 binding region of the Bmi-1 promoter. These findings suggest a novel link between SALL4 and Bmi-1 in regulating self-renewal of normal and leukemic stem cells. An increase in histone H3-K4 and H3-K79 methylation within the Bmi-1 promoter provides an epigenetic mechanism for histone modifications in SALL4-mediated Bmi-1 gene deregulation.leukemia ͉ methylation ͉ stem cells

Key Points CML patients can be stratified into 4 subgroups with different risk of blastic transformation based on cytogenetic abnormalities. TKI therapy mitigates risk of blastic transformation associated with low-risk ACAs or no ACAs but not that associated with HR ACAs.

• The emergence of 3q26.2 rearrangements in CML is associated with resistance to TKI treatment and poor prognosis.• 3q26.2 rearrangements play a predominant role in determining prognosis, irrelevant to the presence or absence of other additional chromosomal abnormalities in CML.Chromosome 3q26.2 abnormalities in acute myeloid leukemia, including inv(3)/t(3;3) and t(3;21), have been studied and are associated with a poor prognosis. Their prevalence, response to tyrosine kinase inhibitor (TKI) treatment, and prognostic significance in chronic myelogenous leukemia (CML) are largely unknown. In this study, we explored these aspects using a cohort of 2013 patients with CML diagnosed in the era of TKI therapy. Chromosome 3 abnormalities were observed in 116 (5.8%) of 2013 cases. These cases were divided into 5 distinct groups: A, inv(3)(q21q26.2)/t(3;3)(q21;q26.2), 26%; B, t(3;21)(q26.2;q22), 17%; C, other 3q26.2 rearrangements, 7%; D, rearrangements involving chromosome 3 other than 3q26.2 locus, 32%; and E, gain or loss of partial or whole chromosome 3, 18%. In all, 3q26.2 rearrangements were the most common chromosome 3 abnormalities (50%, groups A-C). 3q26.2 rearrangements emerged at different leukemic phases. For cases with 3q26.2 rearrangements that initially emerged in chronic or accelerated phase, they had a high rate of transformation to blast phase. Patients with 3q26.2 abnormalities showed a marginal response to TKI treatment, and no patients achieved a long-term sustainable response at a cytogenetic or molecular level. Compared with other chromosomal abnormalities in CML, patients with 3q26.2 rearrangements had poorer overall survival. The presence or absence of other concurrent chromosomal abnormalities did not affect survival in these patients, reflecting the predominant role of 3q26.2 rearrangements in determining prognosis. Interestingly, although heterogeneous, chromosome 3 abnormalities involving non-3q26.2 loci (groups D, E) also conferred a worse prognosis compared with changes involving other chromosomes in this cohort.

Acute myeloid leukemia with t(8;21)(q22;q22) is a distinct type of leukemia considered to have a favorable prognosis. However, some patients rapidly succumb to disease despite chemotherapy. We studied 56 patients with acute myeloid leukemia associated with t(8;21) and correlated clinicopathologic, cytogenetic and molecular findings with outcome to identify markers of prognosis. In a subset of patients, we also assessed the status of the c-KIT, FLT3 and RAS genes. There were 31 men and 25 women, with a median age of 38 years (range 4-76). The follow-up period ranged from 17 to 104 months (median 52). At the last follow-up, 29 patients had died, 25 patients were in complete remission and two patients were alive with disease. The median survial was 38 months. The 5-year overall survival rate of newly diagnosed patients was 56%. Most patients (39/56, 70%) had chromosomal aberrations in addition to t(8;21), with loss of a sex chromosome (39%) being most common followed by del(9q)(q21-22) (11%) and trisomy 8 (7%). These aberrations, however, did not predict survival. C-KIT (D816V or D816Y), FLT3 (ITD or D835) and RAS mutations were detected in 26, 10 and 7%, respectively, of cases assessed. The 5-year overall survival rate of patients with mutated leukemia was 20%. No mutations were observed in three patients who died within 7 months of diagnosis. Leukocytosis or CD56 expression did not correlate with a poor survival nor did the levels of CD19 expression predict c-KIT mutation status. We conclude that acute myeloid leukemia associated with t(8;21) is a heterogeneous disease with poor survival in a subset of patients unrelated to common secondary cytogenetic aberrations. Keywords: t(8;21); cytogenetics; c-KIT mutation The t(8;21)(q22;q22) is the most common cytogenetic abnormality in acute myeloid leukemia (AML), occurring in up to 12% of patients. 1 As a result of t(8;21), the ETO (MTG8) gene on chromosome 8 is fused to the AML1 (RUNX1) gene on chromosome 21, producing a novel chimeric gene, AML1-ETO. The AML1 gene encodes the alpha subunit of core-binding factor (CBF) that is essential for normal hematopoiesis. AML1-ETO fusion gene disrupts the CBF transcription complex, thus initiating the first step of leukemogenesis. 2 The AML1-ETO fusion protein is a multifunctional cellular protein that affects cell differentiation, proliferation, apoptosis and self-renewal. 3 Evidence suggests that additional cytogenetic aberrations may act synergistically with AML-ETO in leukemogenesis. 3 AML with t(8;21), similar to AML with inv(16) or t(15;17), is generally considered a disease with an overall favorable prognosis characterized by a higher response rate and longer median survival compared with other types of AML. This concept is adopted in the current World Health Organization Classification. 4 Of the two references cited by the WHO classification, both published in 1998, 5,6 one was a British study of 1612 AML patients in which 122 patients had AML with t(8;21). The 5-year overall survival (OS) rate of patients with t(8;21) ...

Summary FLT3 gene mutations, either internal tandem duplication or point mutation type, are common in acute myeloid leukaemia (AML). We describe 21 AML cases with both types of gene mutations, so‐called dual mutations, representing approximately 1% of all cases. Most newly diagnosed AML with FLT3 dual mutations had monocytic differentiation and a normal karyotype. Over the disease course, changes in FLT3 mutation status were seen in 89% of cases, and were associated with cytogenetic changes. We conclude that FLT3 dual mutations occur rarely in AML, and appear to be related to clonal evolution.