Identification and molecular characterization of CALM/AF10fusion products in T cell acute lymphoblastic leukemia and acute myeloid leukemia

Genetics and Diagnostic Approach to Lymphoblastic Leukemia/Lymphoma

Our understanding of the genetics and biology of lymphoblastic leukemia/lymphoma (acute lymphoblastic leukemia, ALL) has advanced rapidly in the past decade with advances in sequencing and other molecular techniques. Besides recurrent chromosomal abnormalities detected by karyotyping or fluorescence in situ hybridization, these leukemias/lymphomas are characterized by a variety of mutations, gene rearrangements as well as copy number alterations. This is particularly true in the case of Philadelphia-like (Ph-like) ALL, a major subset which has the same gene expression signature as Philadelphia chromosome-positive ALL but lacks BCR-ABL1 translocation. Ph-like ALL is associated with a worse prognosis and hence its detection is critical. However, techniques to detect this entity are complex and are not widely available. This chapter discusses various subsets of ALL and describes our approach to the accurate classification and prognostication of these cases.

Enhanced anticancer activity and endocytic mechanisms by polymeric nanocarriers of n-butylidenephthalide in leukemia cells

PURPOSE

The purpose of this study was to investigate the antitumor mechanisms of n-butylidenephthalide (BP) and to further examine the delivery efficacy of polycationic liposome containing PEI and polyethylene glycol complex (LPPC)-encapsulated BP in leukemia cells.

METHODS

MTS, flow cytometric and TUNEL assays were performed to assess cell viability and apoptosis. BP and BP/LPPC complex delivery efficiency was analyzed by full-wavelength fluorescent scanner and fluorescence microscope. The expressions of cell cycle- and apoptosis-related proteins were conducted by Western blotting.

RESULTS

The results showed that BP inhibited leukemia cell growth by inducing cell cycle arrest and cell apoptosis. LPPC-encapsulated BP rapidly induced endocytic pathway activation, resulting in the internalization of BP into leukemia cells, causing cell apoptosis within 1 h.

CONCLUSIONS

LPPC encapsulation enhanced the cytotoxic activity of BP and did not influence the effects of BP induction that suggested LPPC-encapsulated BP might be developed as anti-leukemia drugs in future.

The Genetics and Mechanisms of T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T-cell progenitors. The recognition of clinical, genetic, transcriptional, and biological heterogeneity in this disease has already translated into new prognostic biomarkers, improved leukemia animal models, and emerging targeted therapies. This work reviews our current understanding of the molecular mechanisms of T-ALL.

CATS (FAM64A) abnormal expression reduces clonogenicity of hematopoietic cells

The CATS (FAM64A) protein interacts with CALM (PICALM) and the leukemic fusion protein CALM/AF10. CATS is highly expressed in leukemia, lymphoma and tumor cell lines and its protein levels strongly correlates with cellular proliferation in both malignant and normal cells. In order to obtain further insight into CATS function we performed an extensive analysis of CATS expression during differentiation of leukemia cell lines. While CATS expression decreased during erythroid, megakaryocytic and monocytic differentiation, a markedly increase was observed in the ATRA induced granulocytic differentiation. Lentivirus mediated silencing of CATS in U937 cell line resulted in somewhat reduced proliferation, altered cell cycle progression and lower migratory ability in vitro; however was not sufficient to inhibit tumor growth in xenotransplant model. Of note, CATS knockdown resulted in reduced clonogenicity of CATS-silenced cells and reduced expression of the self-renewal gene, GLI-1. Moreover, retroviral mediated overexpression of the murine Cats in primary bone marrow cells lead to decreased colony formation. Although our in vitro data suggests that CATS play a role in cellular processes important for tumorigenesis, such as cell cycle control and clonogenicity, these effects were not observed in vivo.

The target cell of transformation is distinct from the leukemia stem cell in murine CALM/AF10 leukemia models

The CALM/AF10 fusion gene is found in various hematological malignancies including acute myeloid leukemia (AML), T-cell acute lymphoblastic leukemia and malignant lymphoma. We have previously identified the leukemia stem cell (LSC) in a CALM/AF10-driven murine bone marrow transplant AML model as B220+ lymphoid cells with B-cell characteristics. To identify the target cell for leukemic transformation or 'cell of origin of leukemia' (COL) in non-disturbed steady-state hematopoiesis, we inserted the CALM/AF10 fusion gene preceded by a loxP-flanked transcriptional stop cassette into the Rosa26 locus. Vav-Cre-induced panhematopoietic expression of the CALM/AF10 fusion gene led to acute leukemia with a median latency of 12 months. Mice expressing CALM/AF10 in the B-lymphoid compartment using Mb1-Cre or CD19-Cre inducer lines did not develop leukemia. Leukemias had a predominantly myeloid phenotype but showed coexpression of the B-cell marker B220, and had clonal B-cell receptor rearrangements. Using whole-exome sequencing, we identified an average of two to three additional mutations per leukemia, including activating mutations in known oncogenes such as FLT3 and PTPN11. Our results show that the COL for CALM/AF10 leukemia is a stem or early progenitor cell and not a cell of B-cell lineage with a phenotype similar to that of the LSC in CALM/AF10+ leukemia.

Hox gene dysregulation in acute myeloid leukemia

ABSTRACT: 

In humans, class I homeobox genes (HOX genes) are distributed in four clusters. Upstream regulators include transcriptional activators and members of the CDX family of transcription factors. HOX genes encode proteins and need cofactor interactions, to increase their specificity and selectivity. HOX genes contribute to the organization and regulation of hematopoiesis by controlling the balance between proliferation and differentiation. Changes in HOX gene expression can be associated with chromosomal rearrangements generating fusion genes, such as those involving MLL and NUP98, or molecular defects, such as mutations in NPM1 and CEBPA for example. Several miRNAs are involved in the control of HOX gene expression and their expression correlates with HOX gene dysregulation. HOX genes dysregulation is a dominant mechanism of leukemic transformation. A better knowledge of their target genes and the mechanisms by which their dysregulated expression contributes to leukemogenesis could lead to the development of new drugs.

The prognosis of CALM-AF10-positive adult T-cell acute lymphoblastic leukemias depends on the stage of maturation arrest

CALM-AF10 (also known as PICALM-MLLT10) is the commonest fusion protein in T-cell acute lymphoblastic leukemia, but its prognostic impact remains unclear. Molecular screening at diagnosis identified CALM-AF10 in 30/431 (7%) patients with T-cell acute lymphoblastic leukemia aged 16 years and over and in 15/234 (6%) of those aged up to 15 years. Adult CALM-AF10-positive patients were predominantly (72%) negative for surface (s)CD3/T-cell receptor, whereas children were predominantly (67%) positive for T-cell receptor. Among 22 adult CALM-AF10-positive patients treated according to the LALA94/GRAALL03-05 protocols, the poor prognosis for event-free survival (P=0.0017) and overall survival (P=0.0014) was restricted to the 15 T-cell receptor-negative cases. Among CALM-AF10-positive, T-cell receptor-negative patients, 82% had an early T-cell precursor phenotype, reported to be of poor prognosis in pediatric T-cell acute lymphoblastic leukemia. Early T-cell precursor acute lymphoblastic leukemia corresponded to 22% of adult LALA94/GRAALL03-05 T-cell acute lymphoblastic leukemias, but had no prognostic impact per se. CALM-AF10 fusion within early T-cell precursor acute lymphoblastic leukemia (21%) did, however, identify a group with a poor prognosis with regards to event-free survival (P=0.04). CALM-AF10 therefore identifies a poor prognostic group within sCD3/T-cell receptor negative adult T-cell acute lymphoblastic leukemias and is over-represented within early T-cell precursor acute lymphoblastic leukemias, in which it identifies patients in whom treatment is likely to fail. Its prognosis and overlap with early T-cell precursor acute lymphoblastic leukemia in pediatric T-cell acute lymphoblastic leukemia merits analysis. The clinical trial GRAALL was registered at Clinical Trials.gov number NCT00327678.

The NOTCH signaling pathway: role in the pathogenesis of T-cell acute lymphoblastic leukemia and implication for therapy

T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) is characterized by aberrant activation of NOTCH1 in over 60% of T-ALL cases. The high prevalence of activating NOTCH1 mutations highlights the critical role of NOTCH signaling in the pathogenesis of this disease and has prompted the development of therapeutic approaches targeting the NOTCH signaling pathway. Small molecule gamma secretase inhibitors (GSIs) can effectively inhibit oncogenic NOTCH1 and are in clinical testing for the treatment of T-ALL. Treatment with GSIs and glucocorticoids are strongly synergistic and may overcome the gastrointestinal toxicity associated with systemic inhibition of the NOTCH pathway. In addition, emerging new anti-NOTCH1 therapies include selective inhibition of NOTCH1 with anti-NOTCH1 antibodies and stapled peptides targeting the NOTCH transcriptional complex in the nucleus.

HOX-mediated LMO2 expression in embryonic mesoderm is recapitulated in acute leukaemias

The Lim Domain Only 2 (LMO2) leukaemia oncogene encodes an LIM domain transcriptional cofactor required for early haematopoiesis. During embryogenesis, LMO2 is also expressed in developing tail and limb buds, an expression pattern we now show to be recapitulated in transgenic mice by an enhancer in LMO2 intron 4. Limb bud expression depended on a cluster of HOX binding sites, while posterior tail expression required the HOX sites and two E-boxes. Given the importance of both LMO2 and HOX genes in acute leukaemias, we further demonstrated that the regulatory hierarchy of HOX control of LMO2 is activated in leukaemia mouse models as well as in patient samples. Moreover, Lmo2 knock-down impaired the growth of leukaemic cells, and high LMO2 expression at diagnosis correlated with poor survival in cytogenetically normal AML patients. Taken together, these results establish a regulatory hierarchy of HOX control of LMO2 in normal development, which can be resurrected during leukaemia development. Redeployment of embryonic regulatory hierarchies in an aberrant context is likely to be relevant in human pathologies beyond the specific example of ectopic activation of LMO2.

New recurrent balanced translocations in acute myeloid leukemia and myelodysplastic syndromes: cancer and leukemia group B 8461

Acquired chromosome abnormalities in patients with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) are among the most valuable determinants of diagnosis and prognosis. In search of new recurrent balanced translocations, we reviewed the Cancer and Leukemia Group B (CALGB) cytogenetics database containing pretreatment and relapse karyotypes of 4,701 adults with AML and 565 with MDS who were treated on CALGB trials. We identified all cases with balanced structural rearrangements occurring as a sole abnormality or in addition to one other abnormality, excluded abnormalities known to be recurrent, and then reviewed the literature to determine whether any of what we considered unique, previously unknown abnormalities had been reported. As a result, we identified seven new recurrent balanced translocations in AML or MDS: t(7;11)(q22;p15.5), t(10;11)(q23;p15), t(2;12)(p13;p13), t(12;17)(p13;q12), t(2;3)(p21;p21), t(5;21)(q31;q22), and t(8;14)(q24.1;q32.2), and additionally, t(10;12)(p11;q15), a new translocation in AML previously reported in a case of acute lymphoblastic leukemia. Herein, we report hematologic and clinical characteristics and treatment outcomes of patients with these newly recognized recurrent translocations. We also report 52 unique balanced translocations, together with the clinical data of patients harboring them, which to our knowledge have not been previously published. We hope that once the awareness of their existence is increased, some of these translocations may become recognized as novel recurring abnormalities. Identification of additional cases with both the new recurrent and the unique balanced translocations will enable determination of their prognostic significance and help to provide insights into the mechanisms of disease pathogenesis in patients with these rare abnormalities.

Investigation of transcriptional responses of juvenile mouse bone marrow to power frequency magnetic fields

To seek alterations in gene transcription in bone marrow cells following in vivo exposure of juvenile mice to power frequency magnetic fields, young (21-24-day old) C57BL/6 mice were exposed to a 100μT 50Hz magnetic field for 2h. Transcription was analysed by three methods, High Coverage Expression Profiling (HiCEP), Illumina microarrays and quantitative real-time polymerase chain reaction (QRT-PCR). A pilot HiCEP experiment with 6 exposed (E) and 6 non-exposed (NE) mice identified four candidate responsive transcripts (two unknown transcripts (AK152075 and F10-NED), phosphatidylinositol binding clathrin assembly protein (Picalm) and exportin 7 (Xpo7)). A larger experiment compared 19 E and 15 NE mice using two independent QRT-PCR assays and repeated microarray assays. No significant field-dependent changes were seen, although Picalm showed a trend to significance in one QRT-PCR assay (E/NE=0.91; P=0.06). However, the study was underpowered to detect an effect of this magnitude (52% power at P=0.05). These data indicate the current experimental constraints in detecting small changes in transcription that may occur in response to magnetic fields. These constraints result from technical limitations in the accuracy of assays and biological variation, which together were sufficient to account statistically for the number of differentially expressed transcripts identified in the pilot experiment.

CALM/AF10-positive leukemias show upregulation of genes involved in chromatin assembly and DNA repair processes and of genes adjacent to the breakpoint at 10p12

The t(10;11)(p12;q14) is a recurring chromosomal translocation that gives rise to the CALM/AF10 fusion gene, which is found in acute myeloid leukemia, acute lymphoblastic leukemia and malignant lymphoma. We analyzed the fusion transcripts in 20 new cases of CALM/AF10-positive leukemias, and compared the gene expression profile of 10 of these to 125 patients with other types of leukemia and 10 normal bone marrow samples. Based on gene set enrichment analyses, the CALM/AF10-positive samples showed significant upregulation of genes involved in chromatin assembly and maintenance and DNA repair process, and downregulation of angiogenesis and cell communication genes. Interestingly, we observed a striking upregulation of four genes located immediately centromeric to the break point of the t(10;11)(p12;q14) on 10p12 (COMMD3 (COMM domain containing 3), BMI1 (B lymphoma Mo-MLV insertion region 1 homolog), DNAJC1 (DnaJ (Hsp40) homolog subfamily C member 1) and SPAG6 (sperm associated antigen 6)). We also conducted semiquantitative reverse transcriptase-PCR analysis on leukemic blasts from a murine CALM/AF10 transplantation model that does not have the translocation. Commd3, Bmi1 and Dnajc1, but not Spag6 were upregulated in these samples. These results strongly indicate that the differential regulation of these three genes is not due to the break point effect but as a consequence of the CALM/AF10 fusion gene expression, though the mechanism of regulation is not well understood.

The clathrin-binding domain of CALM-AF10 alters the phenotype of myeloid neoplasms in mice

The PICALM (CALM) gene, whose product is involved in clathrin-mediated endocytosis, has been identified in two recurring chromosomal translocations, involving either MLL or MLLT10 (AF10). We developed a mouse model of CALM-AF10⁺ leukemia to examine the hypothesis that disruption of endocytosis contributes to leukemogenesis. Exclusion of the C-terminal portion of CALM from the fusion protein, which is required for optimal binding to clathrin, resulted in the development of a myeloproliferative disease, while inclusion of this domain led to the development of acute myeloid leukemia and changes in gene expression of several cancer-related genes, notably Pim1 and Crebbp. Nonetheless, the development of leukemia could not be attributed directly to interference with endocytosis or consequential changes in proliferation and signaling. In leukemia cells, full-length CALM-AF10 localized to the nucleus with no consistent effect on growth factor endocyctosis, and suppressed H3K79 methylation regardless of the presence of clathrin. Using FRET analysis, we show that CALM-AF10 has a propensity to homo-oligomerize, raising the possibility that the function of endocytic proteins involved in chimeric fusions may be to provide dimerization properties, a recognized mechanism for unleashing oncogenic properties of chimeric transcription factors, rather than disrupting the internalization of growth factor receptors.

The clathrin-binding domain of CALM and the OM-LZ domain of AF10 are sufficient to induce acute myeloid leukemia in mice

The t(10;11)(p13-14;q14-21) translocation, giving rise to the CALM-AF10 fusion gene, is a recurrent chromosomal rearrangement observed in patients with poor prognosis acute myeloid leukemia (AML). Although splicing of the CALM-AF10 fusion transcripts has been described in AML patients, the contribution of different CALM and AF10 domains to in vivo leukemogenesis remains to be defined. We therefore performed detailed structure-function studies of the CALM-AF10 fusion protein. We demonstrate that fusion of the C-terminal 248 amino acids of CALM, which include the clathrin-binding domain, to the octapeptide motif-leucine-zipper (OM-LZ) domain of AF10 generated a fusion protein (termed CALM-AF10 minimal fusion (MF)), with strikingly enhanced transformation capabilities in colony assays, providing an efficient system for the expeditious assessment of CALM-AF10-mediated transformation. Leukemias induced by the CALM-AF10 (MF) mutant recapitulated multiple aspects of full-length CALM-AF10-induced leukemia, including aberrant Hoxa cluster upregulation, a characteristic molecular lesion of CALM-AF10 leukemias. In summary, this study indicates that collaboration of the clathrin-binding and the OM-LZ domains of CALM-AF10 is sufficient to induce AML. These findings further suggest that future approaches to antagonize CALM-AF10-induced transformation should incorporate strategies, which aim at blocking these key domains.

The leukemia-associated Mllt10/Af10-Dot1l are Tcf4/β-catenin coactivators essential for intestinal homeostasis

Wnt signaling maintains the undifferentiated state of intestinal crypt progenitor cells by inducing the formation of nuclear TCF4/β-catenin complexes. In colorectal cancer, activating mutations in Wnt pathway components cause inappropriate activation of TCF4/β-catenin-driven transcription. Despite the passage of a decade after the discovery of TCF4 and β-catenin as the molecular effectors of the Wnt signal, few transcriptional activators essential and unique to the regulation of this transcription program have been found. Using proteomics, we identified the leukemia-associated Mllt10/Af10 and the methyltransferase Dot1l as Tcf4/β-catenin interactors in mouse small intestinal crypts. Mllt10/Af10-Dot1l, essential for transcription elongation, are recruited to Wnt target genes in a β-catenin-dependent manner, resulting in H3K79 methylation over their coding regions in vivo in proliferative crypts of mouse small intestine in colorectal cancer and Wnt-inducible HEK293T cells. Depletion of MLLT10/AF10 in colorectal cancer and Wnt-inducible HEK293T cells followed by expression array analysis identifies MLLT10/AF10 and DOT1L as essential activators to a large extent dedicated to Wnt target gene regulation. In contrast, previously published β-catenin coactivators p300 and BRG1 displayed a more pleiotropic target gene expression profile controlling Wnt and other pathways. tcf4, mllt10/af10, and dot1l are co-expressed in Wnt-driven tissues in zebrafish and essential for Wnt-reporter activity. Intestinal differentiation defects in apc-mutant zebrafish can be rescued by depletion of Mllt10 and Dot1l, establishing these genes as activators downstream of Apc in Wnt target gene activation in vivo. Morpholino-depletion of mllt10/af10-dot1l in zebrafish results in defects in intestinal homeostasis and a significant reduction in the in vivo expression of direct Wnt target genes and in the number of proliferative intestinal epithelial cells. We conclude that Mllt10/Af10-Dot1l are essential, largely dedicated activators of Wnt-dependent transcription, critical for maintenance of intestinal proliferation and homeostasis. The methyltransferase DOT1L may present an attractive candidate for drug targeting in colorectal cancer.

Molecular pathogenesis and targeted therapies for NOTCH1-induced T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic tumor resulting from the malignant transformation of immature T-cell progenitors. Originally associated with a dismal prognosis, the outcome of T-ALL patients has improved remarkably over the last two decades as a result of the introduction of intensified chemotherapy protocols. However, these treatments are associated with significant acute and long-term toxicities, and the treatment of patients presenting with primary resistant disease or those relapsing after a transient response remains challenging. T-ALL is a genetically heterogeneous disease in which numerous chromosomal and genetic alterations cooperate to promote the aberrant proliferation and survival of leukemic lymphoblasts. However, the identification of activating mutations in the NOTCH1 gene in over 50% of T-ALL cases has come to define aberrant NOTCH signaling as a central player in this disease. Therefore, the NOTCH pathway represents an important potential therapeutic target. In this review, we will update our current understanding of the molecular basis of T-ALL, with a particular focus on the role of the NOTCH1 oncogene and the development of anti-NOTCH1 targeted therapies for the treatment of this disease.

Clathrin assembly lymphoid myeloid leukemia-AF10-positive acute leukemias: a report of 2 cases with a review of the literature

The translocation t(10;11)(p13;q14q21) has been found to be recurrent in acute lymphoblastic and myeloid leukemias, and results in the fusion of the clathrin assembly lymphoid myeloid leukemia (CALM) gene with the AF10 gene; these genes are present on chromosomes 11 and 10, respectively. Because the CALM-AF10 rearrangement is a rare chromosomal abnormality, it is not included in routine molecular tests for acute leukemia. Here, we describe the cases of 2 patients with the CALM-AF10 fusion gene. The first patient (case 1) was diagnosed with T-cell ALL, and the second patient (case 2) was diagnosed with AML. Both patient samples showed expression of the homeobox A gene cluster and the histone methyltransferase hDOT1L, which suggests that they mediate leukemic transformation in CALM-AF10-positive and mixed-lineage leukemia-AF10-positive leukemias. Both patients achieved complete remission after induction chemotherapy. The first patient (case 1) relapsed after double-unit cord blood transplantation; there was no evidence of relapse in the second patient (case 2) after allogenic peripheral blood stem cell transplantation. Since CALM-AF10- positive leukemias have been shown to have poor prognosis with conventional therapy, molecular tests for CALM-AF10 rearrangement would be necessary to detect minimal residual disease during follow-up.

Endocytic proteins in the regulation of nuclear signaling, transcription and tumorigenesis

Accumulating evidence argues that many proteins governing membrane sorting during endocytosis participate also in nuclear signaling and transcriptional regulation, mostly by modulating the activity of various nuclear factors. Some adaptors and accessory proteins acting in clathrin-mediated internalization, as well as endosomal sorting proteins can undergo nuclear translocation and affect gene expression directly, while for others the effects may be more indirect. Although it is often unclear to what extent the endocytic and nuclear functions are interrelated, several of such proteins are implicated in the regulation of cell proliferation and tumorigenesis, arguing that their dual-function nature may be of physiological importance.

The CALM and CALM/AF10 interactor CATS is a marker for proliferation

The CATS protein was recently identified as a novel CALM interacting protein. CATS increases the nuclear and specifically the nucleolar localization of the leukemogenic CALM/AF10 fusion protein. We cloned and characterized the murine Cats gene. Detailed analysis of murine Cats expression during mouse embryogenesis showed an association with rapidly proliferating tissues. Interestingly, the Cats transcript is highly expressed in murine hematopoietic cells transformed by CALM/AF10. The CATS protein is highly expressed in leukemia, lymphoma and tumor cell lines but not in non-proliferating T-cells or human peripheral blood lymphocytes. CATS protein levels are cell cycle dependent and it is induced by mitogens, suggesting a role of CATS in the control of cell proliferation and possibly CALM/AF10-mediated leukemogenesis.

The role of CALM-AF10 gene fusion in acute leukemia

Chromosomal translocations are important genetic perturbations frequently associated with hematologic malignancies; characterization of these events has been a rich source of insights into the mechanisms that lead to malignant transformation. The t(10;11)(p13;q14-21) results in a recently identified rare but recurring chromosomal translocation seen in patients with ALL as well as AML, and results in the production of a CALM-AF10 fusion gene. Although the details by which the CALM-AF10 fusion protein exerts its leukemogenic effect remain unclear, emerging data suggests that the CALM-AF10 fusion impairs differentiation of hematopoietic cells, at least in part via an upregulation of HOXA cluster genes. This review discusses the normal structure and function of CALM and AF10, describes the spectrum of clinical findings seen in patients with CALM-AF10 fusions, summarizes recently published CALM-AF10 mouse models and highlights the role of HOXA cluster gene activation in CALM-AF10 leukemia.

Expression of a CALM-AF10 fusion gene leads to Hoxa cluster overexpression and acute leukemia in transgenic mice

To assess the role of the CALM-AF10 fusion gene in leukemic transformation in vivo, we generated transgenic mice that expressed a CALM-AF10 fusion gene. Depending on the transgenic line, at least 40% to 50% of the F(1) generation mice developed acute leukemia at a median age of 12 months. Leukemic mice typically had enlarged spleens, invasion of parenchymal organs with malignant cells, and tumors with myeloid markers such as myeloperoxidase, Mac1, and Gr1. Although most leukemias were acute myeloid leukemia, many showed lymphoid features, such as CD3 staining, or clonal Tcrb or Igh gene rearrangements. Mice were clinically healthy for the first 9 months of life and had normal peripheral blood hemograms but showed impaired thymocyte differentiation, manifested by decreased CD4(+)/CD8(+) cells and increased immature CD4(-)/CD8(-) cells in the thymus. Hematopoietic tissues from both clinically healthy and leukemic CALM-AF10 mice showed up-regulation of Hoxa cluster genes, suggesting a potential mechanism for the impaired differentiation. The long latency period and incomplete penetrance suggest that additional genetic events are needed to complement the CALM-AF10 transgene and complete the process of leukemic transformation.

Leukaemic transformation by CALM-AF10 involves upregulation of Hoxa5 by hDOT1L

Chromosomal translocation is a common cause of leukaemia and the most common chromosome translocations found in leukaemia patients involve the mixed lineage leukaemia (MLL) gene. AF10 is one of more than 30 MLL fusion partners in leukaemia. We have recently demonstrated that the H3K79 methyltransferase hDOT1L contributes to MLL-AF10-mediated leukaemogenesis through its interaction with AF10 (ref. 5). In addition to MLL, AF10 has also been reported to fuse to CALM (clathrin-assembly protein-like lymphoid-myeloid) in patients with T-cell acute lymphoblastic leukaemia (T-ALL) and acute myeloid leukaemia (AML). Here, we analysed the molecular mechanism of leukaemogenesis by CALM-AF10. We demonstrate that CALM-AF10 fusion is both necessary and sufficient for leukaemic transformation. Additionally, we provide evidence that hDOT1L has an important role in the transformation process. hDOT1L contributes to CALM-AF10-mediated leukaemic transformation by preventing nuclear export of CALM-AF10 and by upregulating the Hoxa5 gene through H3K79 methylation. Thus, our study establishes CALM-AF10 fusion as a cause of leukaemia and reveals that mistargeting of hDOT1L and upregulation of Hoxa5 through H3K79 methylation is the underlying mechanism behind leukaemia caused by CALM-AF10 fusion.

Notch signaling in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a form of pediatric leukemia that is thought to be caused by approximately 12 distinct chromosomal translocations that lead to aberrant expression of as many different cellular genes. Development of novel, rational therapies against such a diverse set of mechanistic targets has thus been a formidable challenge. Recent studies, however, have identified a large fraction of T-ALL cases carrying mutations in one of these genes, Notch1, suggesting for the first time that many cases may share a common pathogenic etiology, and perhaps may allow the development of targeted therapies that benefit the majority of patients with this disease.

Notch 1 activation in the molecular pathogenesis of T-cell acute lymphoblastic leukaemia

The chromosomal translocation t(7;9) in human T-cell acute lymphoblastic leukaemia (T-ALL) results in deregulated expression of a truncated, activated form of Notch 1 (TAN1) under the control of the T-cell receptor-beta (TCRB) locus. Although TAN1 efficiently induces T-ALL in mouse models, t(7;9) is present in less than 1% of human T-ALL cases. The recent discovery of novel activating mutations in NOTCH1 in more than 50% of human T-ALL samples has made it clear that Notch 1 is far more important in human T-ALL pathogenesis than previously suspected.

The novel CALM interactor CATS influences the subcellular localization of the leukemogenic fusion protein CALM/AF10

The Clathrin Assembly Lymphoid Myeloid leukemia gene (CALM or PICALM) was first identified as the fusion partner of AF10 in the t(10;11)(p13;q14) translocation, which is observed in acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL) and malignant lymphoma. The CALM/AF10 fusion protein plays a crucial role in t(10;11)(p13;q14) associated leukemogenesis. Using the N-terminal half of CALM as a bait in a yeast two-hybrid screen, a novel protein named CATS (CALM interacting protein expressed in thymus and spleen) was identified. Multiple tissue Northern blot analysis showed predominant expression of CATS in thymus, spleen and colon. CATS codes for two protein isoforms of 238 and 248 amino acids (aa). The interaction between CALM and CATS could be confirmed using pull down assays, co-immunoprecipitation and colocalization experiments. The CATS interaction domain of CALM was mapped to aa 221-335 of CALM. This domain is contained in the CALM/AF10 fusion protein. CATS localizes to the nucleus and shows a preference for nucleoli. Expression of CATS was able to markedly increase the nuclear localization of CALM and of the leukemogenic fusion protein CALM/AF10. The possible implications of these findings for CALM/AF10-mediated leukemogenesis are discussed.

Molecular genetics of acute lymphoblastic leukemia

From its beginnings two decades ago with the analysis of chromosomal translocation breakpoints, research into the molecular pathogenesis of acute lymphoblastic leukemia (ALL) has now progressed to the large-scale resequencing of candidate oncogenes and tumor suppressor genes in the genomes of ALL cases blocked at various developmental stages within the B- and T-cell lineages. In this review, we summarize the findings of these investigations and highlight how this information is being integrated into multistep mutagenesis cascades that impact specific signal transduction pathways and synergistically lead to leukemic transformation. Because of these advances, fueled by improved technology for mutational analysis and the development of small-molecule drugs and monoclonal antibodies, the future is bright for a new generation of targeted therapies. Best illustrated by the successful introduction of imatinib mesylate, these new treatments will interfere with disordered molecular pathways specific for the leukemic cells, and thus should exhibit much less toxicity and fewer long-term adverse effects than currently available therapeutic modalities.

Identification of novel Myc target genes with a potential role in lymphomagenesis

The c-Myc transcription factor regulates a wide set of genes involved in processes such as proliferation, differentiation and apoptosis. Therefore, altered expression of Myc leads to deregulation of a large number of target genes and, as a consequence, to tumorigenesis. For understanding Myc-induced transformation, identification of these target genes is essential. In this study, we searched for Myc target genes involved in lymphomagenesis using different mouse T and B cell lymphoma cell lines transformed by a conditional Myc-allele. Target genes obtained by microarray experiments were further subjected to a kinetic analysis of mRNA expression upon Myc inactivation/reactivation, bioinformatic examination of Myc binding sites and chromatin immunoprecipitation. This approach allowed us to define targets whose activation is a direct consequence of Myc binding. Among the 38 novel Myc targets, we identified several genes implicated in the tumor development. These genes are not only relevant for mouse lymphomas because we observed their upregulation in human lymphomas as well. Our findings further the understanding of Myc-induced lymphomagenesis and help toward developing more efficient antitumor strategies.

Prognostic implications of t(10;11) translocations in childhood acute myelogenous leukemia: a report from the Children's Cancer Group

PURPOSE

This was a retrospective analysis of outcome based on cytogenetics for a Children's Cancer Group phase 3 trial of acute myelogenous leukemia (AML) (CCG-2891).

PATIENTS AND METHODS

A retrospective analysis of outcome for newly diagnosed children with AML and myelodysplastic syndrome (MDS) was performed using data collected from CCG-2891. The authors identified 11 patients whose blasts carried t(10;11) reciprocal translocations or other complex rearrangements involving 10p and 11q among 470 eligible patients entered with acceptable, centrally reviewed cytogenetics. A bone marrow specimen was used for each case of cytogenetic analysis in which 20 banded (either G-banded or Q-banded) metaphases were completed on each subject. All 11 patients had characteristic monocytoid morphology (M4 or M5) and tended to be young (0.1-7.9 years; median 0.9 years).

RESULTS

All 11 patients entered remission, but remissions tended to be short; 9 patients relapsed within 12 months (median 4 months). The relapse rate of 82% was significantly higher for this group of patients compared with 46% for the group at large. The relapse rate for this group of patients having t(10;11) reciprocal translocations or other complex rearrangements involving 10p and 11q was also significantly higher compared with subjects with other 11q23 chromosomal abnormalities. The CNS relapse rate of 55% was higher for this group of patients compared with 3% for all other patients in the study. The CNS relapse rate was higher for the subjects who had t(10;11) reciprocal translocations or other complex rearrangements involving 10p and 11q compared with subjects with all other chromosome 11 abnormalities. Three children survived, two in second remissions (4.7 and 6.3 years after relapse) and one in first remission (7.0 years after diagnosis). Survival and event-free survival for the patients with t(10;11) reciprocal translocations or other complex rearrangements involving 10p and 11q was 27 +/- 27% and 9 +/- 17% at 6 years, respectively, and was not statistically different from all other patients with cytogenetics. Similarly, the survival and event-free survival for the patients with t(10;11) translocations and other rearrangements of chromosomes 10 and 11 was 27 +/- 27% and 9 +/- 17% at 6 years, respectively, and was not statistically different from the 11q23 group of subjects.

CONCLUSIONS

Further research is needed to determine the various changes that are occurring at the molecular level for patients with t(10;11) translocations and other rearrangements of chromosomes 10 and 11 to gain insight into the mechanisms causing this clinical phenotype associated with a poor prognosis.

Mutations in the clathrin-assembly gene Picalm are responsible for the hematopoietic and iron metabolism abnormalities in fit1 mice

Recessive N-ethyl-N-nitrosourea (ENU)-induced mutations recovered at the fitness-1 (fit1) locus in mouse chromosome 7 cause hematopoietic abnormalities, growth retardation, and shortened life span, with varying severity of the defects in different alleles. Abnormal iron distribution and metabolism and frequent scoliosis have also been associated with an allele of intermediate severity (fit14R). We report that fit14R, as well as the most severe fit15R allele, are nonsense point mutations in the mouse ortholog of the human phosphatidylinositol-binding clathrin assembly protein (PICALM) gene, whose product is involved in clathrin-mediated endocytosis. A variety of leukemias and lymphomas have been associated with translocations that fuse human PICALM with the putative transcription factor gene AF10. The Picalmfit1-5R and Picalmfit1-4R mutations are splice-donor alterations resulting in transcripts that are less abundant than normal and missing exons 4 and 17, respectively. These exon deletions introduce premature termination codons predicted to truncate the proteins near the N and C termini, respectively. No mutations in the genes encoding Picalm, clathrin, or components of the adaptor protein complex 2 (AP2) have been previously described in which the suite of disorders present in the Picalmfit1 mutant mice is apparent. These mutants thus provide unique models for exploring how the endocytic function of mouse Picalm and the transport processes mediated by clathrin and the AP2 complex contribute to normal hematopoiesis, iron metabolism, and growth.

Cytogenetic, spectral karyotyping, fluorescence in situ hybridization, and comparative genomic hybridization characterization of two new secondary leukemia cell lines with 5q deletions, and MYC and MLL amplification

Cytogenetic studies of patients with therapy-induced acute myeloid leukemia (t-AML) have demonstrated whole chromosome loss or q-arm deletion of chromosomes 5 and/or 7 in a majority of cases. We have established two cell lines, SAML-1 and SAML-2, from two patients who developed t-AML after radiation and chemotherapy for Hodgkin disease. In both cases, the leukemia cells contained 5q deletions. SAML-1 has 58 chromosomes and numerous abnormalities, including der(1)(1qter-->1p22::5q31-->5qter), der(5)(5pter-->5q22::1p22-->1pter), +8, der(13)i(13)(q10)del(13)(q11q14.1), and t(10;11). Fluorescence in situ hybridization (FISH) with unique sequence probes for the 5q31 region showed loss of IL4, IL5, IRF1, and IL3, and translocation of IL9, DS5S89, EGR1, and CSFIR to 1p. SAML-2 has 45 chromosomes, del(5)(q11.2q31) with a t(12;13)ins(12;5), leading to the proximity of IRF1 and RB1, and complex translocations of chromosomes 8 and 11, resulting in amplification of MYC and MLL. Comparative genomic hybridization and spectral karyotyping were consistent with the G-banding karyotype and FISH analyses. Because a potential tumor suppressor(s) in the 5q31 region has yet to be identified, these cell lines should prove useful in the study of the mechanisms leading to the development of t-AML.

Monocytic leukemia with CALM/AF10 rearrangement showing mediastinal emphysema

The t(10;11)(p12-14;q14-21) is a non-random translocation that results in the fusion of CALM gene on chromosome 11 with AF10 gene on chromosome 10. This translocation is observed in acute myeloid leukemia, acute lymphoblastic leukemia, and lymphoblastic lymphoma. Here we report a patient with t(10;11) who was diagnosed with AML-M4. Reverse transcriptase-polymerase chain reaction (RT-PCR) assay revealed one type of CALM/AF10 and three types of AF10/CALM fusion transcripts. Sequencing analysis for these RT-PCR products determined the breakpoint in CALM at nucleotide (nt) 1926-1927 and in AF10 at nt 423-424. The latter breakpoint was the same as that identified in three monocytic cell lines carrying t(10;11). After achieving complete remission, the patient developed mediastinal emphysema during the course of consolidation therapy, possibly due to the necrosis of his mediastinal mass. Monocytic leukemias with CALM/AF10 fusion are frequently associated with mediastinal invasion. We need to pay special attention to such a complication, even if the chest X-ray is normal at presentation.

A novel chromosomal inversion at 11q23 in infant acute myeloid leukemia fuses MLL to CALM, a gene that encodes a clathrin assembly protein

Rearrangements involving the MLL gene at chromosome band 11q23 are common in infant acute myeloid leukemias (AMLs). We recently encountered an infant patient with rapidly progressive AML whose leukemic cells harbored a previously undescribed MLL rearrangement involving an inversion of 11q [inv(11)(q14q23)]. We used panhandle PCR to determine that this rearrangement juxtaposed the MLL (Mixed-Lineage Leukemia) gene to the CALM (Clathrin Assembly Lymphoid Myeloid leukemia) gene at 11q14-q21. The CALM protein participates in recruitment of clathrin to internal membrane surfaces, thereby regulating vesicle formation in both endocytosis and intracellular protein transport. Intriguingly, CALM has been identified in other cases of AML as a translocation partner for the AF10 gene, which has independently been found to be an MLL partner in AML. We identified the MLL-CALM fusion transcript (but not the reciprocal CALM-MLL transcript) in leukemia cell RNA by RT-PCR. The predicted 1803 amino acid MLL-CALM fusion protein includes amino-terminal MLL domains involved in transcriptional repression, and carboxy-terminal CALM-derived clathrin-binding domains. The genomic breakpoint in MLL is in the 7th intron (within the breakpoint cluster region); the corresponding CALM breakpoint is in the 7th CALM intron. In contrast, breakpoints in CALM-AF10 translocations lie in the 17th-19th CALM introns (30 kb downstream); also, in these translocations, CALM provides the 5' end of the fusion transcript. Together with its previously recognized association with AF10 in AML, the identification of CALM as an MLL fusion partner suggests that interference with clathrin-mediated trafficking pathways may be an underappreciated mechanism in leukemogenesis.

The leucine zipper motif of the Drosophila AF10 homologue can inhibit PRE-mediated repression: implications for leukemogenic activity of human MLL-AF10 fusions

In a screen for Drosophila genes that interfere with transcriptional repression mediated by the Polycomb group of genes, we identified a dominant mutation affecting the Alhambra (Alh) gene, the fly homologue of the human AF10 gene. AF10 has been identified as a fusion partner of both MLL and CALM in infant leukemias. Both fusion proteins retain the leucine zipper domain of AF10 but not its PHD domain. We show here that, while the full-length ALH protein has no activity on Polycomb group-responsive elements (PREs), overexpression of the isolated ALH leucine zipper domain activates several PREs. Within the ALH full-length protein, the PHD domain inhibits the PRE deregulation mediated by the leucine zipper domain. This deregulation is conserved in the human AF10 leucine zipper domain, which confers the same activity on an oncogenic MLL-AF10 fusion protein expressed in Drosophila melanogaster. These data reveal new properties for the leucine zipper domain and thus might provide new clues to understanding the mechanisms by which AF10 fusion proteins in which the PHD domain is lost might trigger leukemias in humans.

Rare recurring balanced chromosome abnormalities in therapy-related myelodysplastic syndromes and acute leukemia: report from an international workshop

Seventy-seven patients were identified with Rare recurring (excluding 11q23, 21q22, inv(16), and t(15;17)) chromosome abnormalities among 511 patients with treatment-related myelodysplastic syndromes and acute leukemia accepted from centers in the United States, Europe, and Japan. The abnormality subsets included 3q21q26 (17 patients), 11p15 (17 patients), t(9;22)(q34;q11) (10 patients), 12p13 (9 patients), t(8;16)(p11;p13) (9 patients), and an "other" subset, which included t(6;9)(p23;q34) (3 patients), t(10;11)(p13;q13 approximately q21) (3 patients), t(1;17)(p36;q21) (2 patients), t(8;14)(q24;q32) (2 patients), t(11;19)(q13;q13) (2 patients), t(1;3)(p36;q21) (2 patients), and t(3;5)(q21;q31) (1 patient). Increased karyotypic complexity with additional balanced and unbalanced rearrangements was observed in 70% of cases. Among 54 cases with secondary abnormalities, chromosome 5 and/or 7 abnormalities were observed in 59%. The most frequent primary diseases were breast cancer (24 cases), Hodgkin disease (14 cases), non-Hodgkin lymphoma (10 cases), and de novo ALL (5 cases). Thirty-seven patients received alkylating agents plus topoisomerase II inhibitors with or without radiation therapy. The presenting diagnosis was t-AML in 47 cases, t-MDS in 23 cases (10 progressed to t-AML), and t-ALL in seven cases, five of whom had a t(9;22). The median latency time from initiation of original therapy to therapy-related disease diagnosis was quite long (69 months), and the overall median survival from the date of therapy-related disease diagnosis was very short (7 months). The 1-year survival rate was 34 +/- 7%, with no significant differences among subsets. Comparison with previously reported cases showed increased karyotypic complexity and adult presentation of pediatric-associated chromosome abnormalities.

The MLL fusion partner AF10 binds GAS41, a protein that interacts with the human SWI/SNF complex

The AF10 gene encodes a putative transcription factor containing an N-terminal LAP/PHD zinc finger motif, a functional nuclear localization signal, an AT-hook domain, and a leucine zipper toward the C-terminus. AF10 is involved in 2 distinct chromosomal translocations associated with hematologic malignancy. The chimeric fusion proteins MLL/AF10 and CALM/AF10, resulting from the t(10;11)(p12;q23) and the t(10;11)(p12;q14), respectively, consistently retain the leucine zipper motif of AF10. This part of the C-terminal region was used as bait in a yeast 2 hybrid screening of a testis complementary DNA library. The leucine zipper interacted with GAS41, a protein previously identified as the product of an amplified gene in a glioblastoma. GAS41 shows significant homology to the Saccharomyces cerevisiae protein ANC1 and to the human MLL fusion partners AF9 and ENL. The interaction was confirmed in vivo. Furthermore, the study showed by coimmunoprecipitation that GAS41 interacts with INI1 (Integrase Interactor 1) and that INI1 was present in the AF10 immunoprecipitate. INI1 is the human homologue of the yeast SNF5 protein, a component of the SWI/SNF complex, which acts to remodel chromatin and to modulate transcription. The retention of the leucine zipper in the MLL and CALM fusions suggests that a key feature of these chimeric proteins may be their ability to interfere in normal gene regulation through interaction with the adenosine triphosphate-dependent chromatinremodeling complexes.

Incidence of MLL rearrangement in acute myeloid leukemia, and a CALM-AF10 fusion in M4 type acute myeloblastic leukemia

To determine the incidence of the mixed lineage leukemia (MLL) gene rearrangements in acute myeloid leukemia (AML) without cytogenetically-detected 11q23 abnormalities, we screened 64 cases of AML at diagnosis for MLL rearrangement by FISH. Three cases (4.7%) had a MLL rearrangement detected; one was shown to have a cryptic t(11;22)(q23;q11) and another to have a t(9;11)(p21-22;q23) which had been missed by the conventional cytogenetic study. No 11q23 structural abnormality was visible in the third case. Twenty-six of the 64 cases were further studied by Southern blotting and DNA hybridization, and four of these cases (15%) were found to have MLL rearrangement: in three of these, FISH had not detected any abnormality. FISH was also used to confirm MLL involvement in eight cases of AML that had a cytogenetic abnormality at 11q23; in one of these, Southern blot did not show a rearrangement. The survival of patients with MLL abnormalities identified by cytogenetics, FISH and/or DNA analysis was significantly worse than that of patients without MLL abnormalities (event-free survival p = 0.016) although two patients with a t(9;11)(p21-22;q23) were long-term survivors, consistent with this particular translocation having a better prognosis. One further case with a cytogenetic abnormality close to 11q23 was studied; it was found to have a t(10;11)(p13;q21), and the breakpoints were shown by FISH to involve the Clathrin Assembly Lymphoid Myeloid (CALM) gene at 11q21 and the AF10 gene at 10p13. Our data confirm the value of combining cytogenetic, FISH and molecular analyses to define the incidence and precise nature of MLL and 11q23 abnormalities in AML.

t(10;11)-acute leukemias with MLL-AF10 and MLL-ABI1 chimeric transcripts: specific expression patterns of ABI1 gene in leukemia and solid tumor cell lines

The recurrent translocation t(10;11) is associated with acute myeloid leukemia (AML). The AF10 gene on chromosome 10 at band p12 and MLL at 11q23 fuse in the t(10;11)(p12;q23). Recently, we have identified ABI1 as a new partner gene for MLL in an AML patient with a t(10;11)(p11.2;q23). The ABI1 is a human homologue of the mouse Abl-interactor 1 (Abi1), encoding an Abl-binding protein. The ABI1 protein exhibits sequence similarity to homeotic genes, and contains several polyproline stretches and a src homology 3 (SH3) domain. To clarify the clinical features of t(10;11)-leukemias, we investigated 6 samples from acute leukemia patients with t(10;11) and MLL rearrangement and detected MLL-AF10 chimeric transcripts in 5 samples and MLL-ABI1 in one. The patient with MLL-ABI1 chimeric transcript is the second case described, thus confirming that the fusion of the MLL and ABI1 genes is a recurring abnormality. Both of the patients with MLL-ABI1 chimeric transcript are surviving, suggesting that these patients have a better prognosis than the patients with MLL-AF10. To investigate the roles of AF10 and ABI1 further, we examined the expression of these genes in various cell lines and fresh tumor samples using the reverse transcriptase-polymerase chain reaction method. Although AF10 was expressed in almost all cell lines similarly, the expression patterns of ABI1 were different between leukemia and solid tumor cell lines, suggesting the distinctive role of each isoform of ABI1 in these cell lines. We also determined the complete mouse Abi1 sequence and found that the sequence matched with human ABI1 better than the originally reported Abi1 sequence. Further functional analysis of the MLL-AF10 and MLL-ABI1 fusion proteins will provide new insights into the leukemogenesis of t(10;11)-AML.

Identification and molecular characterisation of a CALM-AF10 fusion in acute megakaryoblastic leukaemia

The t(10;11)(p13;q14-21) is a non-random translocation described in acute lymphoblastic and myeloid leukaemias. It results in the fusion of the gene CALM, which encodes a clathrin assembly protein, on 11q14 to the gene AF10, a putative transcription factor on 10p13. Here we describe for the first time, the occurrence of a CALM-AF10 fusion in a case of acute megakaryoblastic leukaemia. Fluorescence in situ hybridisation and reverse transcriptase polymerase chain reaction were used to confirm the presence of a CALM-AF10 fusion. A novel splice variant of CALM missing nt 1927-2091 was also detected. Though CALM is a cytoplasmic protein, the chimaeric fusion product is able to localise to both the nucleus and cytoplasm. Analysis of the fusion variants suggests, however, that the critical fusion product is likely to be cytoplasmic and contain the interactive leucine zipper of AF10.

Lymphoblastic lymphoma

Recent advances in the unique clinicopathologic entity of lymphoblastic lymphoma (and its variants) are discussed in this article, which details the natural history, molecular biology, prognosis, and outcome with various chemotherapy regimens. Improved outcome with the newer intensive chemotherapy regimens and the role of modalities such as autologous intensification, allogeneic bone marrow transplant, and radiotherapy are discussed.

Protean clinical manifestations in children with leukemias containing MLL-AF10 fusion

Translocations involving the MLL gene on chromosome 11q23 occur in 5-10% of human leukemias, and involve fusion with more than 30 different partner genes. The MLL-AF10 fusion produced by the t(10;11)(p12;q23) or ins(10;11)(p12;q23q13) occurs in a small percentage of acute leukemias, most commonly acute myelogenous leukemia (AML) of the M5 FAB subtype. We report two cases of AML (M5a and M0) and one case of acute lymphoblastic leukemia containing MLL-AF10 fusion. Each case had varied clinical characteristics, despite expressing similar MLL-AF10 fusion transcripts. Including the three cases described in this report, we identified a total of 38 cases of leukemia with MLL-AF10 fusion. Approximately one-third of these are not M5 AML. Taken together, these findings emphasize that while the sentinel molecular event may be identical in a disease, the clinical presentation and outcome can vary widely.

CALM-AF10 fusion gene in leukemias: simple and inversion-associated translocation (10;11)

A translocation (10;11)(p12;q14) was observed in two children, one with acute eosinophilic leukemia and the other with acute T-cell lymphoblastic leukemia. The presence of CALM-AF10 fusion was ascertained by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Fluorescence in situ hybridization (FISH) analysis showed that AF10 gene splitting was associated with partial inversion of chromosome 11 in the first patient. In addition, FISH analysis also determined the orientation of the CALM gene, 5' telomere to 3' centromere on 11q.

Clinical implications of recurring chromosomal and associated molecular abnormalities in acute lymphoblastic leukemia

Comprehensive study of the major chromosomal/molecular abnormalities in children and adults with acute lymphoblastic leukemia (ALL) has demonstrated prognostic utility for many of these anomalies, to the extent that cytogenetic and molecular genetic evaluations are now required for optimal clinical management of newly diagnosed cases. For example, the t(12;21)/TEL-AML1 (ETV6-CBFA2) or hyperdiploid karyotypes each identifies subgroups of children who can be cured with well-tolerated chemotherapy based primarily on drugs with few long-term toxicities, such as L-asparaginase and antimetabolites. By contrast, the t(1;19)/E2A-PBX1 identifies a subtype of ALL that responds much better to more intensive regimens that rely on genotoxic drugs. At the extreme end of the risk spectrum, the t(4;11)/MLL-AF4 and t(9;22)/BCR-ABL almost always confer a dire prognosis in both children and adults with ALL, who warrant high-dose chemotherapy and hematopoietic stem cell rescue to sustain or even induce first remission. Such chromosomal/molecular markers are being incorporated into risk classification schemes, as they convey prognostic information that cannot be gleaned from conventional risk factors such as immunophenotype, presenting age, and the initial circulating leukemic blast cell count. The most exciting prospect is the discovery of drugs that inhibit specific oncogenes, as illustrated by the BCR-ABL tyrosine kinase inhibitor STI-571.

Molecular analysis of the CALM/AF10 fusion: identical rearrangements in acute myeloid leukemia, acute lymphoblastic leukemia and malignant lymphoma patients

The recurring translocation t(10;11)(p13;q14) which is found in acute myeloid leukemia (AML) and in acute lymphoblastic leukemia (ALL) results in the fusion of the putative transcription factor AF10 to CALM encoding a clathrin assembly protein. Previous studies using mainly fluorescence in situ hybridization (FISH) analysis have shown that the CALM/AF10 rearrangement is found in immature acute myeloid leukemia (AML) of subtype M0 and M1 and in T cell ALL. In this study we analyzed the CALM/AF10 and AF10/CALM fusion mRNAs in a series of three patients with AML, one patient with T-ALL and two patients with precusor T lymphoblastic lymphoma. In all six patients the breakpoint in CALM is at the 3' end of the coding region (nt1926/1927 or nt 2091/2092). Three breakpoints could be identified in AF10 (nt 588/589, nt 882/883 and nt 978/979). These data demonstrate that the CALM/AF10 fusions found in patients differ only slightly with respect to the portion of AF10 present and that there is no obvious difference between the fusions found in AML patients compared to those found in patients with lymphoid malignancies. Leukemia (2000) 14, 93-99.