Identification of a novel fusion gene MLL-MAML2 in secondary acute myelogenous leukemia and myelodysplastic syndrome with inv(11)(q21q23)

We have identified a novel fusion partner of MLL, namely the mastermind like 2 (MAML2 gene), in secondary acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) with inv(11)(q21q23). RT-PCR and sequencing revealed that exon 7 of MLL was fused to exon 2 of MAML2 in the AML and MDS cells. The inv(11)(q21q23) results in the creation of a chimeric RNA encoding a putative fusion protein containing 1,408 amino acids from the NH2-terminal part of MLL and 952 amino acids from the COOH-terminal part of MAML2. The NH2-terminal part of MAML2, a basic domain including a binding site of the intracellular domain of NOTCH, was deleted in MLL-MAML2. MLL-MAML2 in secondary AML/MDS and MECT1-MAML2 in mucoepithelioid carcinoma, benign Wartin's tumor, and clear cell hidradenoma consist of the same COOH-terminal part of MAML2. A luciferase assay revealed that MLL-MAML2 suppressed HES1 promoter activation by the NOTCH1 intracellular domain. MAML2 involving a chimeric gene might contribute to carcinogenesis in multiple neoplasms by the disruption of NOTCH signaling.     

Amplification of the 11q23 region in acute myeloid leukemia.

Cytogenetic abnormalities involving the 11q23 region are found in both acute lymphoblastic leukemia (ALL) and myeloid leukemia (AML). Molecular consequences of 11q23 translocations are the formation of chimeric genes, all of them involving the MLL (mixed-lineage leukemia) gene. To evaluate the usefulness of fluorescence in situ hybridization (FISH) in detecting MLL rearrangements in AML, we analyzed 181 patients with an MLL-specific probe. Among them, we detected three patients with multiple FISH signals, reflecting genomic amplification of this chromosomal region. Extra copies of MLL have been reported previously in four patients, but did not correspond to a true gene amplification. For the first time, we describe genomic amplification of the 11q23 region (up to more than 50 copies) in AML patients. This genomic amplification could affect MLL, but other genes in the vicinity could also be the primary target. Genes Chromosomes Cancer 26:166-170, 1999.     

Pediatric T-cell acute lymphoblastic leukemia with aberrations of both MLL loci

Translocations involving the MLL gene at 11q23 have been implicated in acute lymphoblastic leukemia (ALL), as well as acute myeloid leukemia (AML). Such translocations result in gain of function fusion proteins that drive cell proliferation. Except in cases of T-cell ALL, MLL rearrangement is typically associated with a poor prognosis. We report a case of T-cell ALL with a t(11;19)(q23;p13.3) and deletion of the other chromosome 11 homolog at band q23. Fluorescence in situ hybridization (FISH) analyses confirmed involvement of the MLL loci in both the translocation and deletion. This case is unique in that deletions of 11q23 reported in ALL generally do not involve MLL. We are unaware of a previous report showing rearrangement of the MLL loci on both chromosome 11 homologues.     

MLL-CBP fusion transcript in a therapy-related acute myeloid leukemia with the t(11;16)(q23;p13) which developed in an acute lymphoblastic leukemia patient with Fanconi anemia

We describe a boy with Fanconi anemia (FA) who developed acute lymphoblastic leukemia (ALL) (FAB-LI) followed by acute myeloid leukemia (AML) (FAB-M5) at relapse. The patient was diagnosed with early pre-B-cell ALL without preceding aplastic anemia and was treated with ALL-oriented chemotherapy which included doxorubicin (a total dose of 140 mg/m(2) administered), which is a topoisomerase II inhibitor. Complete remission was obtained, but after 38 weeks AML developed. The karyotype of ALL cells at diagnosis showed 46,XY, and that of AML cells at relapse was 46,XY, t(11;16)(q23;p13). An MLL gene rearrangement and MLL-CBP chimeric mRNA were found in AML, but not in ALL. A diagnosis of FA was confirmed by an increased number of chromosomal breaks and rearrangements in peripheral blood lymphocytes cultured with mitogen in the presence of mitomycin C. We conclude that this FA patient developed ALL followed by a therapy-related t(11;16)-AML resulting in an MLL-CBP fusion. Further examination of such patients would shed light on leukemogenesis in FA patients. Genes Chromosomes Cancer 27:264-269, 2000.     

Rearrangement of the MLL gene and a region proximal to the RARalpha gene in a case of acute myelocytic leukemia M5 with a t(11;17)(q23;q21)

A case of acute myelocytic leukemia (AML) M5 subtype (French-American-British classification), in a 13-year-old girl showed the abnormal karyotype 46,XX,t(11;17)(q23;q21) in all bone marrow cells analyzed. Rearrangements involving 11q23 are frequent in cases of AML M5 and often involve the MLL gene. Nevertheless, t(11;17)(q23;q21) is very rare in this type of leukemia. In acute promyelocytic leukemia, the RARalpha gene, located at 17q21, is involved in almost all cases. Fluorescence in situ hybridization studies revealed a deletion of the C-terminal part of the MLL gene and a translocation of the RARalpha gene on the derivative chromosome 11, proximal to the remaining part of the MLL gene. However, hybridization with the LSI RARA dual color break-apart rearrangement probe showed that the RARalpha gene was not rearranged in this translocation. This is the first study reporting a t(11;17)(q23;q21) with a deletion distal to MLL gene exon 6 in a case of AML M5. Furthermore, this is the second study that strongly suggests the implication of a gene proximal and close to the RARalpha locus in a case of AML M5. According to these results, the discovery of new fusion partner genes of MLL and the precise characterization of t(11;17) will be important for the understanding of neoplastic cell differentiation in AML M5.     

Translocation (4;11)(p12;q23) with rearrangement of FRYL and MLL in therapy-related acute myeloid leukemia

Reciprocal chromosomal translocations involving the MLL gene at chromosome region 11q23 are recurring cytogenetic abnormalities in both de novo and therapy-related acute myeloid leukemia (AML) and in acute lymphoblastic leukemia. We report a t(4;11)(p12;q23) with rearrangement of MLL and FRYL (also known as AF4p12), a human homolog to the furry gene of Drosophila, in an adult patient with therapy-related AML after fludarabine and rituximab therapy for small lymphocytic lymphoma and radiation therapy for breast carcinoma. To our knowledge, t(4;11)(p12;q23) has been reported in two previous patients, and MLL and FRYL rearrangement was demonstrated in one of them. Both of the previous patients had therapy-related leukemias after exposure to topoisomerase II inhibitors, whereas our patient had received cytotoxic therapy that did not include a topoisomerase II inhibitor. Thus, t(4;11)(p12;q23) with MLL and FRYL involvement represents a new recurring 11q23 translocation, to date seen only in therapy-related acute leukemias.     

Analysis of t(9;11) chromosomal breakpoint sequences in childhood acute leukemia: almost identical MLL breakpoints in therapy-related AML after treatment without etoposides

The translocation t(9;11)(p22;q23) is a recurring chromosomal abnormality in acute myeloid leukemia (AML) fusing two genes designated as MLL and AF9. Within MLL, almost all rearrangements cluster in an 8.3-kb restricted region and fuse 5' portions of MLL to a variety of heterologous genes in various 11q23 translocations. AF9 is one of the most common fusion partners of MLL. It spans more than 100 kb, and two breakpoint cluster regions (BCRs) have been identified in a telomeric region of intron 4 (BCR1) and within introns 7 and 8 (BCR2). We investigated 11 children's bone marrow or peripheral blood samples (3 AML, 5 t-AML, 2 ALL, 1 ALL relapse) and two cell lines (THP-1 and Mono-Mac-6) with cytogenetically diagnosed translocations t(9;11). By use of an optimized multiplex nested long-range PCR assay, a breakpoint-spanning DNA fragment from each sample was amplified and directly sequenced. In four patients and two cell lines, the AF9 breakpoints were located within BCR1 and in two patients within BCR2, respectively. However, in five patients the AF9 breakpoints were found outside the previously described BCRs within the centromeric region of intron 4 and even within intron 3 in one case. All five patients with a secondary AML, who had not received etoposides during treatment of the primary malignant disease, revealed almost identical MLL breakpoints very close to a breakage hot spot inducible by topoisomerase II inhibitors or apoptotic triggers in vitro. Sequence patterns around the breakpoints indicated involvement of a "damage-repair mechanism" in the development of t(9;11) similar to t(4;11) in infants' acute leukemia.