Cytogenetic and molecular analysis of chromosome 11q23 abnormalities in leukaemia

MLL/AF10(OM-LZ)-immortalized cells expressed cytokines and induced host cell proliferation in a mouse bone marrow transplantation model

Several mouse models studying the MLL fusion-induced leukemic transformation showed that a myeloproliferation stage precedes leukemia or occurred as the only phenotype of hematological disorder in mice. We established 6 MLL/AF10(OM-LZ)-immortalized cell lines by retrovirally transducing the fusion gene into bone marrow cells from B6 or congenic GFP-B6 mice. Immunophenotypic and cytological analyses revealed that the immortalized cell lines could be divided into 2 types. Type I had a high percentage of cells expressing monocytic lineage marker CD115 in the medium containing IL3 and could terminally differentiate into granulocytes and monocytes in response to granulocyte colony-stimulating factor (G-CSF) and macrophage colony-stimulating factor (M-CSF) treatments, respectively. On the other hand, type II had a low percentage of cells expressing CD115. The type II cell lines could not differentiate into granulocytes by G-CSF treatment and died rapidly in response to M-CSF treatment. Transplantation of both types I and II cells induced lethal myeloproliferative disease (MPD)-like myeloid leukemia in most of the sublethally irradiated B6 mice. Flow cytometric analysis of GFP and lineage markers of the peripheral blood cells from MPD mice revealed that the monocytes and granulocytes were generated not only from the donor cells but also from the host cells. RT-PCR analysis revealed that the MLL/AF10(OM-LZ)-immortalized cells expressed mRNAs encoding colony-stimulating factors (CSFs) of M-CSF and GM-CSF and inflammatory cytokines of IL-1alpha, IL-1beta and TNF-alpha. Our results showed that the MLL/AF10(OM-LZ)-immortalized cells could induce host cell proliferation in the transplanted mice, probably through stimulation by CSFs or cytokines produced by the donor cells.

Translocation (10;11)(p12;q23) in childhood acute myeloid leukemia: incidence and complex mechanism

Using both conventional and molecular cytogenetic methods, we found five new cases of t(10;11)(p12;q23). This translocation represented 28% of all cases of childhood AML treated at our center in 2004, and 63% of AML with rearrangements of 11q23. We describe three mechanisms for the translocation. Different fragments of 11q were involved in four of the five cases. One patient showed a cytogenetically cryptic insertion of 5' part of MLL into the 3' part of MLLT10 in 10p12. The median event-free survival of patients was 8.1 months, and we conclude that the t(10;11)(p12;q23) is associated with unfavorable prognosis in childhood acute myeloid leukemia.

[Application of molecular biology techniques to malignant haematology]

Malignant hemopathies, although heterogeneous in their prognosis and oncogenesis, represent an interesting model for studying cancer genesis mechanisms in man through the recurrent presence of genetic abnormalities involved in oncogenesis and the availability of tumour material. Nowadays, molecular biology techniques are very much used for the diagnosis, the treatment and the follow-up of these diseases. Firstly used for research, the new techniques have completely changed our ability to characterise malignant hemopathies and to understand the cancer-inducing processes, permitting us to perform the biological assessment of patients with malignant hemopathies, the diagnosis, and to estimate and follow the outcome of patients after treatment. At a more fundamental level, the structural and functional analysis of the deregulated genes implied in leukaemia and lymphoma has improved our knowledge and understanding of oncogenic and physiologic mechanisms significantly.

Platelet-activating factor acetylhydrolase

Platelet-activating factor (PAF) is one of the most potent lipid mediators and is involved in a variety of physiological events. The acetyl group at the sn-2 position of its glycerol backbone is required for its biological activity, and deacetylation of PAF induces loss of activity. The deacetylation reaction is catalyzed by PAF-acetylhydrolase (PAF-AH). A series of biochemical and enzymological studies have revealed that there are at least three types of PAF-AH in mammals, namely the intracellular type I and II and plasma type. Type I PAF-AH is a G-protein-like complex of two catalytic subunits (alpha1 and alpha2) and a regulatory beta subunit. The beta subunit is a product of the LIS1 gene, mutations of which cause type I lissencephaly. Recent studies indicate that LIS1/beta is important in cellular functions such as induction of nuclear movement and control of microtubule organization. Although circumstantial evidence is accumulating supporting the idea that the catalytic subunits are also involved in microtubule function, it is still not known what role PAF plays in the process and whether PAF is a native endogenous substrate of this enzyme. Type II PAF-AH is a single polypeptide and shows significant sequence homology with plasma PAF-AH. Type II PAF-AH is myristoylated at the N-terminus and like other N-myristoylated proteins, is distributed in both the cytosol and membranes. Plasma PAF-AH is also a single polypeptide and exists in association with plasma lipoproteins. Type II PAF-AH as well as plasma PAF-AH may play roles as scavengers of oxidized phospholipids which are thought to be involved in diverse pathological processes, including disorganization of membrane structure and PAF-like proinflammatory actions. In this chapter, author focuses on the structures and possible biological functions of intracellular PAF-AHs.

Molecular analysis of an unstable genomic region at chromosome band 11q23 reveals a disruption of the gene encoding the alpha2 subunit of platelet-activating factor acetylhydrolase (Pafah1a2) in human lymphoma

A region of 150 kb has been analysed around a previously isolated, lymphoma associated, translocation breakpoint located at chromosome band 11q23. This balanced and reciprocal translocation, t(11;14)(q32;q23), has been shown to result in the fusion between chromosome 11 specific sequence and the switch gamma4 region of the IGH locus. The LPC gene, encoding a novel proprotein convertase belonging to the furin family, has been identified in this region. In order to characterize further the region surrounding the translocation, we have determined the detailed structure of LPC. Here we show that LPC consists of at least 16 exons covering 25 kb, and that there is a partial duplication, involving mobile genetic elements and containing LPC exons 13-17 in a tail-tail configuration at 65 kb downstream. Since the chromosomal breakpoint lay between these two structures, the intervening region was further analysed and shown to contain at least two unrelated genes. The previously known SM22 gene was localized close to the 3' tail of LPC. Furthermore, we identified the gene encoding the alpha2 subunit of platelet-activating factor acetylhydrolase (Pafah1a2) at the chromosomal breakpoint. The position of another previously identified breakpoint was also located to within the first intron of this gene. Altogether, our results give evidence of a genomic instability of this area of 11q23 and show that Pafah1a2 and not LPC is the gene disrupted by the translocation, suggesting that deregulated Pafah1a2 may have a role in lymphomagenesis.

AF6q21, a Novel Partner of the MLL Gene in t(6; 11)(q21; q23), Defines a Forkhead Transcriptional Factor Subfamily

Fusion genes implicating the MLL gene have been recently demonstrated in various 11q23 chromosomal abnormalities in human hematopoietic malignancies. We analyzed a t(6; 11)(q21; q23) translocation detected in a secondary acute myeloblastic leukemia. This translocation results in fusion of the MLL gene on 11q23 to a previously unknown gene on chromosome 6 that differs from the previously reported MLL partner gene AF6q. The novel gene, named AF6q21, encodes a forkhead (FH) protein with strong similarities to the two FH family members whose genes are already known to be involved in chromosomal translocations of human malignancies, AFX and FKHR. Strikingly, in these translocations the breakpoints are located at the same position within the FH domains. Therefore, AF6q21, AFX, and FKHR could define a new FH subfamily particularly involved in human malignancies.

Molecular cytogenetics of childhood acute myelogenous leukaemias

Chromosome abnormalities of childhood acute myeloblastic leukaemia, observed at least in 70-80% of cases, are presently recognized as important parameters for diagnostic, prognostic and follow-up purposes. These abnormalities are numerical, structural or both numerical and structural. They are also classified in "primary" abnormalities, usually more or less related with one subtype of leukaemia, and "secondary" abnormalities thought to appear in a second time. Chromosome abnormalities of childhood acute myeloblastic leukaemia (AML) are not basically qualitatively different from those of adult AML. The main difference lies in the incidence of the various types of abnormalities, and these differences appear to be more marked for age extremes such as infants and elderly patients. In total, 3 common abnormalities are more frequently observed in childhood than in adult AML; t(8;21) in AML-M2, monosomy 7 in AML-M4, der(11q) in AML-M5. In addition, molecular rearrangements associated with chromosomal abnormalities are dependent on the type of rearrangement and not on age. As in adult AML, the prognostic value of chromosome abnormalities has been diversely evaluated; some anomalies seem to be related to a shorter survival than others independent of the various therapeutic protocols used. In the present work, chromosome abnormalities of childhood AML have been reviewed according to cytologic subtypes as well as to some clinical settings. Special attention has been paid to abnormalities frequently or exclusively encountered in children.

Gene BR140, which is related to AF10 and AF17, maps to chromosome band 3p25

The genes AF10 and AF17 have been identified as the basis of the t(10;11) and t(11;17) translocations, events that result in their fusion to the MLL/HRX gene in acute myeloid leukaemias. AF10 and AF17 bear significant homology to each other within their putative zinc finger and leucine zipper domains, although they are diverged outside these regions. The BR140 gene encodes a 140 kDa protein of unknown function that contains a putative zinc finger domain, a leucine zipper region, and, in addition, a bromo domain. The zinc finger and leucine zipper domains of BR140 have significant homology to those of AF10 and AF17, suggesting that it belongs to this newly described gene family and, therefore, could be a target for chromosome translocation. To assess the potential involvement of BR140 in chromosome translocations in leukaemia, the chromosomal location of the BR140 gene has been determined by using several independent methods. A combination of Southern analysis, polymerase chain reactions (PCR) on monochromosomal cell hybrids, and fluorescence in situ hybridisation (FISH) has been used to show that the BR140 gene maps to chromosome band 3p25.

Distribution of TP53 mutations among acute leukemias with MLL rearrangements

Acute leukemias carrying MLL rearrangements are characterized by a high degree of clinical and immunologic heterogeneity, as demonstrated by variability in their immunophenotype, consistent with lymphoid or myeloid/monoblastic derivation, as well as their occurrence in distinct age groups from infancy to adulthood. Recently, it was shown that inactivation of the TP53 tumor suppressor gene occurs frequently in cases of acute lymphoblastic leukemia carrying MLL rearrangements. In order to assess the extent of TP53 inactivation throughout the immunophenotypic and clinical spectrum of MLL+ acute leukemias, we tested for TP53 mutations 29 cases of MLL+ acute leukemias displaying lymphoid (13 cases) or myeloid/monoblastic (16 cases) features and belonging to different age groups. Mutations were detected in 6/16 myeloid/monoblastic cases and in 3/13 lymphoid cases. Among myeloid/monoblastic leukemias, the TP53 mutations occurred in 3/4 infants, but only in 3/16 cases in other age groups. Overall, our data suggest that (1) TP53 inactivation is a relatively common event in leukemias with MLL rearrangements irrespective of the leukemic phenotype and of the patients' age; (2) at least two genetic lesions (i.e., MLL rearrangement and TP53 mutation) have accumulated in the short time (few weeks after the birth or conception of the child) corresponding to the development of acute leukemias of infancy.

Characterization of a t(10;11)(p13-14;q14-21) in the monoblastic cell line U937

Previous analysis of the monoblastic cell line U937 has shown that several sublines contain a rearranged chromosome arm 11q. In order to determine the true nature of the rearrangement, fluorescence in situ hybridization (FISH) was carried out with various combinations of single copy anonymous markers, clones containing genes, a chromosome 10 paint, and an 11 centromere specific sequence. The rearrangement was deduced to be a reciprocal translocation between chromosomes 10 and 11 described as t(10;11)(p13-14;q14-21). The breakpoint on chromosome 11 is telomeric to the INT2 gene and the pHS11 probe at 11q13, and centromeric to the marker D11S36 localized to 11q14.3-q22.1 and the MLL gene at 11q23. Similar translocations have been reported in various acute leukemias, principally of the monocytic lineage, and also in T-cell precursor acute lymphocytic leukemias. Further characterization of the genetic rearrangements in U937 may lead to the isolation of genes important in leukemogenesis and provide an in vitro system for their study.

Molecular basis of 11q23 rearrangements in hematopoietic malignant proliferations

Chromosomal abnormalities of the 11q23 band occur frequently in various hematopoietic malignant disorders. Because numerous partner chromosomes have been previously described, it is now important to determine the number of genes involved at 11q23 and to clarify the role of the partner genes. Recent efforts in several laboratories have identified a trithorax-related gene that is involved in most of the 11q23 abnormalities. The aim of this review is to summarize the recent data concerning these 11q23 rearrangements and the understanding of their consequences.

Chromosome 11q23 abnormalities in leukaemia

Breakpoints on chromosome 11 at band q23 have been observed in patients with primary or secondary leukaemia. Recent data have shown that these breakpoints are clustered in a approximately 15kb region of a gene named HRX. This gene product has homology to the Drosophila trithorax gene product, which suggests it may play a role in regulating transcription control. Disruption of HRX as a result of chromosomal translocation is thought to contribute to the leukaemogenic process; this may occur in utero giving rise to infant acute leukaemia or may be induced by epipodophyllotoxic drugs resulting in secondary leukaemia. Translocations of 11q23 can involve a number of different partner chromosomes. The reciprocal genes on chromosomes 4q21, 9p22 and 19p13 have been recently cloned and are predicted to encode proline and serine rich proteins. Of particular interest is the high degree of homology observed between the genes on 9p22 and 19p13, which suggests that they too may have an important role to play in the generation of the leukaemic phenotype.

An odyssey in search of a cure: the evolution of treatment of childhood acute lymphoblastic leukemia in the United Kingdom

This review charts the evolution of therapy for childhood acute lymphoblastic leukaemia (ALL) in the United Kingdom. The present chemotherapeutic regimen is the result of experience gained from carefully planned randomised cooperative studies carried out during the last two decades. In common with the experience of the West German and American groups, the best results have been in those treated with post remission intensification blocks. With current chemotherapy protocols, almost 70% of children with ALL in U.K. can be cured but there may be a medical cost of such a cure, in terms of both acute and long term toxicity. This was especially true when central nervous system (CNS) therapy with cranial irradiation was used. Therefore present regimens are examining chemotherapeutic options for CNS disease control and the efficacy of additional post remission intensification. Failure of chemotherapy is most often seen in those children with a presenting white cell count of more than 50 x 10(9)/l, very young children and/or the presence of certain chromosomal rearrangements (e.g. t4: 11, t9: 22). At present the optimum therapeutic option for such high risk patients and for the majority of those in second remission, is an allogenic bone marrow transplant if an HLA-matched sibling is available. Modern day therapy is both complicated and costly and will be beyond the resources available for most children with ALL in developing countries. A significant decrease in worldwide mortality due to ALL will only occur if either the disease can be prevented or a simpler cure devised.