Establishment of a novel human myeloid leukemia cell line, AMU-AML1, carrying t(12;22)(p13;q11) without chimeric MN1-TEL and with high expression of MN1

Intrinsically disordered Meningioma-1 stabilizes the BAF complex to cause AML

Meningioma-1 (MN1) overexpression in AML is associated with poor prognosis, and forced expression of MN1 induces leukemia in mice. We sought to determine how MN1 causes AML. We found that overexpression of MN1 can be induced by translocations that result in hijacking of a downstream enhancer. Structure predictions revealed that the entire MN1 coding frame is disordered. We identified the myeloid progenitor-specific BAF complex as the key interaction partner of MN1. MN1 over-stabilizes BAF on enhancer chromatin, a function directly linked to the presence of a long polyQ-stretch within MN1. BAF over-stabilization at binding sites of transcription factors regulating a hematopoietic stem/progenitor program prevents the developmentally appropriate decommissioning of these enhancers and results in impaired myeloid differentiation and leukemia. Beyond AML, our data detail how the overexpression of a polyQ protein, in the absence of any coding sequence mutation, can be sufficient to cause malignant transformation.

Menin is necessary for long term maintenance of meningioma-1 driven leukemia

Translocations of Meningioma-1 (MN1) occur in a subset of acute myeloid leukemias (AML) and result in high expression of MN1, either as a full-length protein, or as a fusion protein that includes most of the N-terminus of MN1. High levels of MN1 correlate with poor prognosis. When overexpressed in murine hematopoietic progenitors, MN1 causes an aggressive AML characterized by an aberrant myeloid precursor-like gene expression program that shares features of KMT2A-rearranged (KMT2A-r) leukemia, including high levels of Hoxa and Meis1 gene expression. Compounds that target a critical KMT2A-Menin interaction have proven effective in KMT2A-r leukemia. Here, we demonstrate that Menin (Men1) is also critical for the self-renewal of MN1-driven AML through the maintenance of a distinct gene expression program. Genetic inactivation of Men1 led to a decrease in the number of functional leukemia-initiating cells. Pharmacologic inhibition of the KMT2A-Menin interaction decreased colony-forming activity, induced differentiation programs in MN1-driven murine leukemia and decreased leukemic burden in a human AML xenograft carrying an MN1-ETV6 translocation. Collectively, these results nominate Menin inhibition as a promising therapeutic strategy in MN1-driven leukemia.

Ectopia associated MN1 fusions and aberrant activation in myeloid neoplasms with t(12;22)(p13;q12)

Chromosome translocation t(12;22)(p13;q12)/MN1-ETV6 and MN1 overexpression confer a subset of adverse prognostic AML but so far lack in-depth research. We focused on the clinical course and comprehensive genetic analysis of eight cases with t(12;22)(p13;q12) and one with t(12;17;22) (p13;q21;q13) to elucidate their molecular etiology and outcomes of allogeneic hemopoietic stem cell transplantation (allo-HSCT). The total incidence of t(12;22)(p13;q12) and related translocations was 0.32% in myeloid neoplasms. These patients were confirmed to have dismal prognosis when treated only with chemotherapy, and we firstly provided evidence that they can significantly benefit from timely allo-HSCT. Five cases were MN1-ETV6 positive, and a novel MN1-STAT3 fusion was identified in the patient with triadic translocation. Significant MN1 overexpression was observed in all three MN1-fusion-negative cases. Genetic analysis highlighted the evidence of an ectopic super-enhancer associated orchestrated mechanism of MN1 overexpression and ETV6 haploinsufficiency in t(12;22)(p13;q12) myeloid neoplasms, rather than the conventional thought of MN1-ETV6 fusion formation. We also disclosed the high concomitance of trisomy 8 and 531 Kbps focal 8q duplication in t(12;22)(p13;q12) cases. The new perspective about this entity of disease will enlighten further research to define the mechanism of tumorigenesis and discover effective treatments for MN1-driven malignancies.

Establishment and characterization of a novel vincristine-resistant diffuse large B-cell lymphoma cell line containing the 8q24 homogeneously staining region

Chromosome band 8q24 is the most frequently amplified locus in various types of cancers. MYC has been identified as the primary oncogene at the 8q24 locus, whereas a long noncoding gene, PVT1, which lies adjacent to MYC, has recently emerged as another potential oncogenic regulator at this position. In this study, we established and characterized a novel cell line, AMU‐ML2, from a patient with diffuse large B‐cell lymphoma (DLBCL), displaying homogeneously staining regions at the 8q24 locus. Fluorescence in situ hybridization clearly detected an elevation in MYC copy numbers corresponding to the homogenously staining region. In addition, a comparative genomic hybridization analysis using high‐resolution arrays revealed that the 8q24 amplicon size was 1.4 Mb, containing the entire MYC and PVT1 regions. We also demonstrated a loss of heterozygosity for TP53 at 17p13 in conjunction with a TP53 frameshift mutation. Notably, AMU‐ML2 cells exhibited resistance to vincristine, and cell proliferation was markedly inhibited by MYC‐shRNA‐mediated knockdown. Furthermore, genes involved in cyclin D, mTOR, and Ras signaling were downregulated following MYC knockdown, suggesting that MYC expression was closely associated with tumor cell growth. In conclusion, AMU‐ML2 cells are uniquely characterized by homogenously staining regions at the 8q24 locus, thus providing useful insights into the pathogenesis of DLBCL with 8q24 abnormalities.

Establishment and characterization of a rare atypical chronic myeloid leukemia cell line NT-1

Human leukemia cell lines are of great value in leukemia research. In this study, we established and described the biological characteristics of a rare atypical chronic myeloid (aCML) leukemia cell line (NT-1). Mononuclear cells were isolated from the bone marrow of a patient with atypical chronic myeloid leukemia (Ph(-)/bcr(-)/abl(-)), and were passaged by liquid culture. Cells were maintained without any cytokines for over 1 year, and named NT-1. This cell line was extensively characterized using morphological assays, flow cytometry, cytogenetic analysis, clonogenic culture, quantitative fluorescent PCR, short tandem repeating sequence PCR (STR-PCR) and array-CGH. Its tumorigenic capacity was also examined in nude mice. The NT-1 cell line had morphological features of chronic myeloid leukemia and major myeloid markers (CD13, CD33, CD11b). Additionally, NT-1 expressed progenitor cells and natural killer cell-related antigens such as CD34, CD117, CD56. Cytogenetic analysis initially demonstrated two abnormalities: 47, xx, +8 and 47, xx, +8 accompanied by t(5;12)(q31;p13) translocation. The one-year passage process did not alter the karyotype. NT-1 cells maintained the same morphology, immunophenotyping and cytogenetic features as primary leukemia cells, which was strongly supported by STR-PCR results. Neither Epstein-Barr virus nor mycoplasma was detected in the NT-1 line. In addition, NT-1 cells showed high tumorigenic capacity in nude mice. NT-1 is a new atypical chronic myeloid leukemia cell line with the +8 and t(5,12) translocation, and exhibits high tumorigenicity in nude mice. This new cell line provides a useful tool for the study of leukemogenesis.