Variant translocations (9;11): identification of the critical genetic rearrangement

C/EBPbeta suppression by interruption of CUGBP1 resulting from a complex rearrangement of MLL

Translocations involving the mixed-lineage leukemia gene (MLL) confer a poor prognosis in acute leukemias. In t(1;11)(q21;q23), MLL is fused reciprocally with AF1q. Here we describe a t(1;11)(q21;q23) with a secondary event involving insertion of the telomeric portion of MLL into the p arm of chromosome 11 (11p11). We show that this latter event interrupts the CUG triplet repeat binding protein-1 (CUGBP1) gene, a translational enhancer of C/EBPbeta. We then showed that these cells have reduced expression of CUGBP1 and C/EBPbeta when compared to other AML blasts. This is the first report to describe insertional disruption of the CUGBP1 gene and to suggest a role for the CUGBP1-C/EBPbeta pathway in leukemogenesis.

MLL/ENL fusion in congenital acute lymphoblastic leukemia with a unique t(11;18;19)

To elucidate the events leading to a unique complex translocation involving chromosomes 11, 18, and 19 in a congenital progenitor B-cell acute lymphoblastic leukemia, we have performed comprehensive cytogenetic and fluorescence in situ hybridization (FISH) analyses as well as molecular genetic studies on the DNA and RNA level. We were able to confirm the cytogenetic interpretation of this complex t(11;18;19)(q23;q22;p13.3) by chromosome painting. Involvement of the MLL gene on 11q23 became evident by Southern blot analysis as well as by FISH with a YAC clone containing the respective gene. Despite the fact that the additional signals of the split YAC clone were observed on the abnormal chromosome 18, reverse transcription polymerase chain reaction (RT-PCR) revealed a MLL/ENL hybrid mRNA, which is specific for a t(11;19)(q23;p13.3). This gene fusion most probably represents the critical part of this rearrangement. The transfer of the translocated part of the split YAC clone onto chromosome 18 indicates that the second break must have occurred in the vicinity of the first one, at a distance too close to be resolved by FISH. Whether this break took place within chromosome 11 or 19 sequences, up- or downstream of the MLL/ENL fusion, and whether this translocation results from a concerted simultaneous exchange of material or from two separate sequential events in consecutive cell generations remains open.

Translocation (9;11;22)(p22;q23;q11). A new type of complex variant translocation of t(9;11)(p22;q23) with MLL rearrangement

We describe a patient with acute monocytic leukemia (M5a, FAB classification) associated with a new type of variant translocation (9;11). Southern blot analysis showed the rearrangement of the MLL (ALL-1/HRX) gene at 11q23. Fluorescence in situ hybridization (FISH) with painting probes of chromosomes 9, 11, and 22 revealed the translocation as t(9;11;22) (p22;q23;q11). This is more evidence that the production of chimeric mRNA following the translocation of the LTG9 (MLLT3/AF9) gene at 9p22 to 11q is a critical event in this leukemia subtype.

New variant t(9;11;14)(p22;q23;q24) suggests a translocation of 9p to 11q as the critical genetic event

We describe a patient with M5a (FAB classification) associated with a new type of variant translocation (9;11), namely t(9;11;14)(p22;q23;q24). The translocation of chromosome fragment from 9p to 11q is the common feature among the five variant translocations in the literature and our patient.

Involvement of a homolog of Drosophila trithorax by 11q23 chromosomal translocations in acute leukemias

We have identified a human homolog of the Drosophila trithorax protein that is structurally altered by 11q23 translocations in acute leukemias. Human trithorax (HRX) is a predicted 431 kd protein containing two potential DNA-binding motifs consisting of zinc fingers conserved with the fly protein and nonconserved amino-terminal "AT hook" motifs related to the DNA-binding motifs in HMG proteins. 11q23 translocations disrupt the HRX gene between these two motifs, and in a t(11;19)-carrying cell line fusion transcripts are expressed from both derivative chromosomes. The more abundant derivative 11 transcript codes for a chimeric protein containing the AT hook motifs fused to a previously undescribed protein (ENL) from chromosome 19. These data suggest a novel role for a trithorax-homologous protein in multilineage human leukemias that may be mediated by DNA binding within the minor groove at AT-rich sites, implicated to play an important role in bacterial IHF-, yeast datin-, and mammalian HMG-mediated gene activation.

The der(11) chromosome contains the critical breakpoint junction in the 4;11, 9;11, and 11;19 translocations in acute leukemia

Translocations involving 11q23 are recurring abnormalities in human acute leukemia cells of either lymphoid or myeloid lineage. Analysis of 13 variant translocations associated with four of these [t(4;11), t(6;11), t(9;11) and t(11;19)] reveals that the der(11) chromosome is conserved in all of them and therefore contains the critical genetic rearrangement. The MLL gene (myeloid/lymphoid leukemia) is involved in each of these translocations. It is transcribed from centromere to telomere. The present analysis indicates that the 5' region of MLL on the der(11) is juxtaposed to the coding sequences of genes on each of the other translocation partners.

Ewing's sarcoma t(11;22) in a case of acute nonlymphocytic leukemia

Chromosome analysis of bone marrow cells from a patient with acute nonlymphocytic leukemia M2 revealed the translocation t(11;22)(q24;q12) usually associated with Ewing's sarcoma. Molecular investigations ruled out the possibility that this was a variant Philadelphia translocation with breakpoints in the major breakpoint cluster region. Although cytogenetic analysis was not available at diagnosis, this abnormality was found both pre- and postallogeneic bone marrow transplant.

Unusual translocations and other changes in acute leukemia

We report three cases of ANLL and one case of ALL in which we found chromosome abnormalities not previously described. The first patient had a (9;11;16)(p22;q23;p13) translocation in the relapse after bone marrow transplantation. In the second case, a secondary leukemia following a Wilms' tumor, there was a single chromosome anomaly, an inversion of chromosome 13. The third case also presented an isochromosome 13q. In the fourth patient we observed a translocation between two achrocentric chromosomes, as in the third patient, but not of the Robertsonian type: t(21;21)(q22.1;q22.5).