Phenotypic and genotypic characterization of 14 leukemia and lymphoma cell lines with 11q23 translocations

Establishment and characterization of a DOT1L inhibitor-sensitive human acute monocytic leukemia cell line YBT-5 with a novel KMT2A-MLLT3 fusion

Immortalized cell lines are useful for deciphering the pathogenesis of acute leukemia and developing novel therapeutic agents against this malignancy. In this study, a new human myeloid leukemia cell line YBT-5 was established. After more than 1-year cultivation from the bone marrow of a patient with acute monocytic leukemia, YBT cell line was established. Then a subclone, YBT-5, was isolated from YBT using single cell sorting. Morphological and cytogenetical characterizations of the YBT-5 cell line were determined by cytochemical staining, flow cytometry analysis, and karyotype analysis. Molecular features were identified by transcriptomic analysis and reverse transcription-polymerase chain reaction. To establish a tumor model, 5 × 10⁶ YBT-5 cells were injected subcutaneously in nonobese diabetic/severe combined immune-deficiency (NOD/SCID) mice. DOT1L has been proposed as a potential therapeutic target for KMT2A-related leukemia; therefore, to explore the potential application of this new cell line, its sensitivity to a specific DOT1L inhibitor, EPZ004777 was measured ex vivo. The growth of YBT-5 does not depend on granulocyte-macrophage colony-stimulating factor. Cytochemical staining showed that α-naphthyl acetate esterase staining was positive and partially inhibited by sodium fluoride, while peroxidase staining was negative. Flow cytometry analysis of YBT-5 cells showed positive myeloid and monocytic markers. Karyotype analysis of YBT-5 showed 48,XY,+8,+8. The breakpoints between KMT2A exon 10 and exon 11 (KMT2A exon 10/11) and MLLT3 exon 5 and exon 6 (MLLT3 exon 5/6) were identified, which was different from all known breakpoint locations, and a novel fusion transcript KMT2A exon 10/MLLT3 exon 6 was formed. A tumor model was established successfully in NOD/SCID mice. EPZ004777 could inhibit the proliferation and induce the differentiation of YBT-5 cells. Therefore, a new acute monocytic leukemia cell line with clear biological and molecular features was established and may be used in the research and development of new agents targeting KMT2A-associated leukemia.

Synergistic effect of all‑trans retinoic acid in combination with protein kinase C 412 in FMS-like tyrosine kinase 3-mutated acute myeloid leukemia cells

Acute myeloid leukemia (AML) is a heterogeneous disease. Numerous molecular abnormalities have been identified in AML and, amongst these, FMS‑like tyrosine kinase 3 (FLT3) mutations are one of the most common somatic alterations detected. In the present study, an in vitro investigation was performed to evaluate the effects of all‑trans retinoic acid (ATRA) and PKC412, alone and in combination, in FLT3‑mutated AML cell lines. Trypan blue exclusion test, as well as morphological, western blot and isobologram analyses were conducted. The results indicated that the combined ATRA and PKC412 treatment exhibited additive or synergistic effects in FLT3‑mutated AML cell lines. These results provided in vitro evidence for the future clinical trials evaluating the effects of a combination treatment using PKC412 and ATRA on AML patients with FLT3‑mutations.

Inhibition of FLT3 expression by green tea catechins in FLT3 mutated-AML cells

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by a block in differentiation and uncontrolled proliferation. FLT3 is a commonly mutated gene found in AML patients. In clinical trials, the presence of a FLT3-ITD mutation significantly correlates with an increased risk of relapse and dismal overall survival. Therefore, activated FLT3 is a promising molecular target for AML therapies. In this study, we have shown that green tea polyphenols including (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin-3-gallate (ECG) suppress the proliferation of AML cells. Interestingly, EGCG, EGC and ECG showed the inhibition of FLT3 expression in cell lines harboring FLT3 mutations. In the THP-1 cells harboring FLT3 wild-type, EGCG showed the suppression of cell proliferation but did not suppress the expression of FLT3 even at the concentration that suppress 100% cell proliferation. Moreover, EGCG-, EGC-and ECG-treated cells showed the suppression of MAPK, AKT and STAT5 phosphorylation. Altogether, we suggest that green tea polyphenols could serve as reagents for treatment or prevention of leukemia harboring FLT3 mutations.

t(11;14)(q23;q32) involving IGH and DDX6 in nodal marginal zone lymphoma

Nodal marginal zone lymphoma (NMZL) is a primary nodal B-cell lymphoma that shares morphological and immunophenotypic characteristics with extranodal and splenic marginal zone lymphoma. Data on altered genes and signaling pathways are scarce in this rare tumor entity. To gain further insights into the genetic background of NMZL, seven cases were investigated by microarray analysis, G-banding, and FISH. Chromosomal imbalances were observed in 3/7 cases (43%) with gains of chromosome arms 1q, 8q, and 12q being the most frequent findings. Furthermore, we identified a translocation t(11;14)(q23;q32) involving IGH and DDX6. Chromosomal walking, expression analysis, siRNA-mediated gene knockdown and a yeast two hybrid screen were performed for further characterization of the translocation in vitro. In siRNA experiments, DDX6 appeared not to be involved in NF-κB activation as frequently observed for genes promoting lymphomagenesis but was found to interfere with the expression of BCL6 and BCL2 in an NF-κB independent manner. In conclusion, we identified several unbalanced aberrations and a t(11;14) involving IGH and DDX6 providing evidence for a contribution of DDX6 to lymphomagenesis by deregulation of BCL6 in NMZL.

MicroRNA expression signatures accurately discriminate acute lymphoblastic leukemia from acute myeloid leukemia

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, whereas acute myeloid leukemia (AML) is the most common acute leukemia in adults. In general, ALL has a better prognosis than AML. To understand the distinct mechanisms in leukemogenesis between ALL and AML and to identify markers for diagnosis and treatment, we performed a large-scale genome-wide microRNA (miRNA, miR) expression profiling assay and identified 27 miRNAs that are differentially expressed between ALL and AML. Among them, miR-128a and -128b are significantly overexpressed, whereas let-7b and miR-223 are significantly down-regulated in ALL compared with AML. They are the most discriminatory miRNAs between ALL and AML. Using the expression signatures of a minimum of two of these miRNAs resulted in an accuracy rate of >95% in the diagnosis of ALL and AML. The differential expression patterns of these four miRNAs were validated further through large-scale real-time PCR on 98 acute leukemia samples covering most of the common cytogenetic subtypes, along with 10 normal control samples. Furthermore, we found that overexpression of miR-128 in ALL was at least partly associated with promoter hypomethylation and not with an amplification of its genomic locus. Taken together, we showed that expression signatures of as few as two miRNAs could accurately discriminate ALL from AML, and that epigenetic regulation might play an important role in the regulation of expression of miRNAs in acute leukemias.

Malignant hematopoietic cell lines: in vitro models for the study of MLL gene alterations

Human tumor cell lines are powerful tools for investigating basic and applied aspects of cell biology. Leukemia-lymphoma cell lines have been instrumental in the cytogenetic and molecular analysis of recurring chromosome rearrangements, notably translocations and inversions, thus illuminating the pathogenesis of hematological malignancy. Chromosomal translocations targeting the MLL gene at 11q23 have come to represent a paradigm in acute leukemias. These translocations result in the in-frame joining of the MLL gene with a partner gene to generate unique fusion proteins of putatively novel function. More than 30 partner genes that participate with MLL in the more than 60 known 11q23 translocations have been reported. Cell lines provide territory to both explore the detailed structures of 11q23 translocations and investigate the leukemogenic activities of MLL fusion proteins. We review here the leukemia cell lines that have been described to carry 11q23 translocations and MLL fusion genes. Except for the t(10;11)(p12;q23), each of the following relatively frequent 11q23/MLL translocations is represented by one or more cell lines: 16 cell lines with t(4;11)(q21;q23), two cell lines with t(6;11)(q27;q23), seven cell lines with t(9;11)(p22;q23), and eight cell lines with t(11;19)(q23;p13). For each of three rare translocations, one cell line has been reported: t(5;11)(q15;q23), t(11;16)(q23;p13), and t(X;11)(q13;q23). Of these 36 cell lines with 11q23 translocations, 17 have been made available to us; we confirmed the occurrence of the alterations reported in these cell lines at the chromosomal and/or gene level. A second type of MLL gene alteration is the partial tandem duplication (PTD), which occurs in acute myeloid leukemia (AML). We found four AML cell lines with an MLL PTD; one acute lymphoblastic leukemia-derived cell line was reported to show a partial nontandem duplication. Finally, a third rearrangement involves intrachromosomal amplification of the unrearranged MLL gene leading to multiple copies of the gene and (presumably) increased expression. Three cell lines carrying such MLL amplifications have been described. The availability of these cell lines as model systems provides the opportunity to explore the altered expression or functions of MLL genes and their partners in oncogenesis.

MLL-AF4 gene rearrangement in a child with Epstein-Barr virus-related posttransplant B-cell lymphoma

Recipients of solid organ allografts are known to be at increased risk of developing Epstein-Barr virus-related posttransplant lymphoproliferative diseases. A 28-month-old boy who had received a heterotopic liver transplant presented with lymphadenopathy in the abdomen, multiple nodules in the liver, and bilateral renal infiltration 19 months after transplantation. He was diagnosed with a Burkitt-like lymphoma based on bone marrow examination and the finding that the blastic cells in bone marrow were EBER-1 positive. Cytogenetic analysis of the bone marrow cells showed an MLL-AF4 rearrangement. He was treated with a combined chemotherapy regimen. He has been in continuous complete remission for 15 months now.

Sensitization by 5-aza-2'-deoxycytidine of leukaemia cells with MLL abnormalities to induction of differentiation by all-trans retinoic acid and 1alpha,25-dihydroxyvitamin D3

Most chromosomal abnormalities associated with breakage at 11q23 in acute leukaemia involve the MLL gene, and the presence of this breakage strongly predicts a poor clinical outcome. We assessed the possibility of differentiation-inducing therapy for acute leukaemias with chromosomal translocations involving 11q23. Among the cell lines with MLL translocations that we examined, KOCL48 and KOPN-1 cells were induced to differentiate into granulocytes by all-trans retinoic acid (ATRA) or into monocytes by 1alpha,25-dihydroxyvitamin D3 (VD3). These cells expressed p16 mRNA before treatment with 5-aza-2'-deoxycytidine (5-AZA), an inhibitor of DNA methylation. On the other hand, differentiation was not induced in SN-1, KOCL33, KOCL51 or KOCL44 cells by ATRA or VD3, and these cells did not express mRNA of this gene. However, these cells were effectively induced to differentiate by ATRA or VD3 in the presence of 5-AZA, and concomitantly exhibited p16 gene expression, suggesting an association between DNA demethylation and restoration of sensitivity to differentiation-inducing activity of ATRA or VD3 in leukaemia cells with MLL abnormalities. Based on these findings, combined treatment with ATRA or VD3 plus 5-AZA may be clinically useful in therapy for acute leukaemia with MLL abnormalities.

Arsenic induces apoptosis in B-cell leukaemic cell lines in vitro: activation of caspases and down-regulation of Bcl-2 protein

We showed that arsenic inhibited the cell growth of four B-cell leukaemia cell lines of 11 various cell lines in vitro. In two of these four lines, KOCL44 and LyH7, apoptosis was identified by morphological and nucleosomal DNA fragmentation studies. Three of the four B-cell lines that were growth inhibited were acute infantile leukaemia with t(11;19)(q23;p13) translocations involving the MLL gene that encodes the transcriptional factor Drosophila trithorax. The arsenic-induced apoptosis in KOCL44 and LyH7 cells was found to be linked to caspases by Western blot and enzymological analyses. The amount of Bcl-2 was reduced during apoptosis in LyH7 as judged by Western blot analysis. We concluded that combined activation of the caspases and down-regulation of Bcl-2 could determine the fate of B-cell leukaemic cells in response to arsenic.

The structure of the human ALL-1/MLL/HRX gene

The human ALL-1/MLL/HRX gene on chromosome 11q23 is the site of many locally clustered chromosomal alterations associated with several types of acute leukemias, including deletions. partial duplications and reciprocal translocations. Structurally variant proteins derived from an altered ALL-1 gene presumably make essential contributions to the malignant transformation of hematopoietic progenitor cells. The ALL-1 gene is spread over approximately 92 kb and consists of at least 37 exons. An exon/intron map including the position of the 3'-end of the gene and a detailed restriction map were produced and an updated map is presented. Data from other laboratories were incorporated where compatible. Exon/intron boundaries were sequenced and an intron-phase analysis was performed. The results are expected to contribute to a better understanding of those structural alterations of the gene that conserve the open reading frame and produce presumably oncogenic variants of the ALL-1 protein. They will also facilitate the rapid molecular diagnosis of structural alterations of this gene and the choice of therapeutic options. Mechanisms that may potentially account for the striking clustering of the translocation breakpoints in the breakpoint cluster region of the gene are discussed.

Molecular analysis of the chromosomal breakpoint and fusion transcripts in the acute lymphoblastic SEM cell line with chromosomal translocation t(4;11)

The chromosomal breakpoint and fusion transcripts of the pre-B-leukaemia-derived SEM cell line carrying a reciprocal t(4;11)(q21;q23) translocation were analysed. The breakpoint from derivative chromosome der4 was cloned and sequenced. The crossover site was localized in intron 7 of the ALL-1 gene on chromosome 11q23 and in a large intron of the AF-4 (FEL) gene. RNA transcripts from both wild-type genes and both hybrid genes were detected by reverse transcriptase polymerase chain reaction (RT-PCR) assays. In addition, alternatively spliced mRNA species derived from the der4 chromosome were found. They were generated by using the exon 5' of the breakpoint on der4 as a common splice donor site and the 5' boundaries of exons 8 or 9 of the ALL-1 gene as alternative splice acceptor sites. The hypothesis is proposed that selective pressure operators to maintain the presence of both derivative chromosomes as important elements in the leukaemogenic process.

Molecular cloning of 19p13 breakpoint region in infantile leukemia with t(11;19)(q23;p13) translocation

We studied the breakpoint regions involved in t(11;19)(q23;p13) translocation associated with infantile leukemias. Southern blot analysis with the partial cDNA clone for the MLL gene at 11q23 which we had isolated previously detected gene rearrangements in all three cell lines and three leukemia samples from the patients with t(11;19) translocation, indicating that these breakpoints were clustered within the 8.5 kb BamHI germline fragment detected by the probe. To study the breakpoint region, a genomic library of one of the cell lines, KOCL-33, was made. We have isolated the der(19) allele containing the breakpoint as well as the germline alleles at 19p13 and 11q23. Using the genomic probes on chromosome 19 near the breakpoint, Southern blot analysis was performed. The breakpoints at 19p13 of the two other cell lines and the three leukemia samples were not located within 36 kilobases of the KOCL-33 breakpoint, although pulsed-field gel electrophoresis showed that the breakpoints of all three cell lines were on the same NruI fragment of 230 kilobases. These results showed that the breakpoints at 19p13 were not clustered like those at 11q23 in t(11;19) translocation.