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

PICALM as a Novel Prognostic Biomarker and Its Correlation with Immune Infiltration in Breast Cancer

PICALM (phosphatidylinositol-binding clathrin assembly protein) mutations have been linked to a number of human disorders, including leukemia, Alzheimer's disease, and Parkinson's disease. Nevertheless, the effect of PICALM on cancer, particularly on prognosis and immune infiltration in individuals with BRCA, is unknown. We obtained the data of breast cancer patients from The Cancer Genome Atlas (TCGA) database, and analyzed the expression of PICALM in breast cancer, its impact on survival' and its role in tumor immune invasion. Finally, in vitro cellular experiments were performed to validate the results. Research has found that PICALM expression was shown to be downregulated in BRCA and to be substantially linked with clinical stage, histological type, PAM50, and age. PICALM downregulation was linked to a lower overall survival (OS) and disease-specific survival (DSS) in BRCA patients. A multivariate Cox analysis revealed that PICALM is an independent predictor of OS. The enriched pathways revealed by functional enrichment analysis included oxidative phosphorylation, angiogenesis, the TGF signaling pathway, and the IL-6/JAK/STAT3 signaling system. Furthermore, the amount of immune cell infiltration by B cells, eosinophils, mast cells, neutrophils, and T cells was positively linked with PICALM expression. Finally, we experimentally verified that low expression of PICALM can reduce proliferation, migration, and invasion in tumor cells. This evidence shows that PICALM expression impacts prognosis, immune infiltration, and pathway expression in breast cancer patients, and it might be a potential predictive biomarker for the disease.

Bacillamide F, Extracted from Marine Bacillus atrophaeus C89, Preliminary Effects on Leukemia Cell Lines

Developing new treatments for leukemia is essential since current therapies often suffer from drug resistance and toxicity. Bacillamides are very promising, naturally occurring compounds with various bioactivities. In the present study, we investigated the use of bacillamide analogues, a new thiazole alkaloid bacillamide F that was isolated from marine Bacillus atrophaeus C89 associated with sponge Dysidea avara. The structure of the new compound bacillamide F with indolyl−thiazolyl−pyrrolidine ring was determined by high resolution mass spectrometry, secondary mass spectrometry, and nuclear magnetic resonance analyses. Intriguingly, bacillamide F is able to inhibit the proliferation of an acute myeloid leukemia cell line HL60 (IC50 (24 h) 21.82 µM), and an acute T-cell leukemia Jurkat (IC50 (24 h) 46.90 µM), rather than inhibit the proliferation of the acute histiocytic lymphoma U-937 cell line, human fetal lung fibroblast MRC-5 cell line, and some solid tumor cell lines (IC50 (24 h) > 100 µM). The study provides a new indication of the pharmacological activity of natural product bacillamides.

MLLT10 rearranged acute leukemia: Incidence, prognosis, and possible therapeutic strategies

Rearrangements of the MLLT10 gene occur in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), most commonly T-lineage ALL (T-ALL), in patients of all ages. MLLT10 rearranged (MLLT10r) acute leukemia presents a complex diagnostic and therapeutic challenge due to frequent presentation of immature or mixed phenotype, and a lack of consensus regarding optimal therapy. Cases of MLLT10r AML or T-ALL bearing immature phenotype are at high risk of poor outcome, but the underlying molecular mechanisms and sensitivity to targeted therapies remain poorly characterized. This review addresses the incidence and prognostic significance of MLLT10r in acute leukemia, and how the aberrant gene expression profile of this disease can inform potential targeted therapeutic strategies. Understanding the underlying genomics of MLLT10r acute leukemia, both clinically and molecularly, will improve prognostic stratification and accelerate the development of targeted therapeutic strategies, to improve patient outcomes.

Acute myeloid leukemia driven by the CALM-AF10 fusion gene is dependent on BMI1

A subset of acute myeloid and lymphoid leukemia cases harbor a t(10;11)(p13;q14) translocation resulting in the CALM-AF10 fusion gene. Standard chemotherapeutic strategies are often ineffective in treating patients with CALM-AF10 fusions. Hence, there is an urgent need to identify molecular pathways dysregulated in CALM-AF10-positive leukemias which may lay the foundation for novel targeted therapies. Here we demonstrate that the Polycomb Repressive Complex 1 gene BMI1 is consistently overexpressed in adult and pediatric CALM-AF10-positive leukemias. We demonstrate that genetic Bmi1 depletion abrogates CALM-AF10-mediated transformation of murine hematopoietic stem and progenitor cells (HSPCs). Furthermore, CALM-AF10-positive murine and human AML cells are sensitive to the small-molecule BMI1 inhibitor PTC-209 as well as to PTC-596, a compound in clinical development that has been shown to result in downstream degradation of BMI1 protein. PTC-596 significantly prolongs survival of mice injected with a human CALM-AF10 cell line in a xenograft assay. In summary, these results validate BMI1 as a bona fide candidate for therapeutic targeting in AML with CALM-AF10 rearrangements.

CCAAT/enhancer-binding protein alpha (CEBPA) gene haploinsufficiency does not alter hematopoiesis or induce leukemia in Lck-CALM/AF10 transgenic mice

Although rare, CALM/AF10 is a chromosomal rearrangement found in immature T-cell acute lymphoblastic leukemia (T-ALL), acute myeloid leukemia, and mixed phenotype acute leukemia of T/myeloid lineages with poor prognosis. Moreover, this translocation is detected in 50% of T-ALL patients with gamma/delta T cell receptor rearrangement, frequently associated with low expression of transcription factor CCAAT/enhancer-binding protein alpha (CEBPA). However, the relevance of CEBPA low expression for CALM/AF10 leukemogenesis has not yet been evaluated. We generated double mutant mice, which express the Lck-CALM/AF10 fusion gene and are haploinsufficient for the Cebpa gene. To characterize the hematopoiesis, we quantified hematopoietic stem cells, myeloid progenitor cells, megakaryocyte-erythrocyte progenitor cells, common myeloid progenitor cells, and granulocyte-macrophage progenitor cells. No significant difference was detected in any of the progenitor subsets. Finally, we tested if Cebpa haploinsufficiency would lead to the expansion of Mac-1+/B220+/c-Kit+ cells proposed as the CALM/AF10 leukemic progenitor. Less than 1% of bone marrow cells expressed Mac-1, B220, and c-Kit with no significant difference between groups. Our results showed that the reduction of Cebpa gene expression in Lck-CALM/AF10 mice did not affect their hematopoiesis or induce leukemia. Our data corroborated previous studies suggesting that the CALM/AF10 leukemia-initiating cells are early progenitors with lymphoid/myeloid differentiating potential.

MLLT10 promotes tumor migration, invasion, and metastasis in human colorectal cancer

OBJECTIVES

Colorectal cancer (CRC), one of the most aggressive gastrointestinal malignancies, is a frequently diagnosed life-threatening cancer worldwide. Most CRC patients have poor prognosis mainly because of frequent metastasis and recurrence. Thus, it is crucial to find out some new biomarkers and to show deeper insights into the mechanisms of CRC. MLLT10, Myeloid/lymphoid or mixed-lineage leukemia translocated to 10, also known as AF10, a recurrent MLL partner. In this study, we found that MLLT10 promotes CRC tumor invasion and metastasis both in vitro and in vivo.

METHODS

Here, the expression of MLLT10 was evaluated by immunohistochemistry. Then, the plasmid and lentivirus particles for MLLT10 overexpression or knockdown were designed and constructed into SW620 and HT29 cells. Finally, cell proliferation assay, cell adhesion assay, transwell migration, and invasion assay were used to detect the migration and invasion ability of MLLT10 in CRC cells. A tail vein injection assay was employed to evaluate the role of MLLT10 in tumor metastases.

RESULTS

MLLT10 expression was significantly higher in CRC tissues than in noncancerous tissues and was associated with some clinicopathological factors. In vitro, the overexpression of MLLT10 promoted CRC cell migration and invasion, while after MLLT10 was knocked down, the opposite results were observed. Furthermore, we used animal metastasis models to detect the function of MLLT10 in vivo, the results are same with the outcomes in vitro. In lung metastasis sites, the knockdown of MLLT10 in SW620 cells significantly inhibited Vimentin expression, whereas the E-Cadherin was increased.

CONCLUSIONS

These results indicate that MLLT10 regulates the metastasis of CRC cells via EMT.

The development of targeted new agents to improve the outcome for children with leukemia

INTRODUCTION

Survival rates in pediatric leukemia have greatly improved in the last decades but still a substantial number of patients will relapse and die. New agents are necessary to overcome the limitations of conventional chemotherapy and hematopoietic stem cell transplantation and to reduce their undesirable long-term toxicities. The identification of driving molecular alterations of leukemogenesis in subsets of patients will allow the incorporation of new-targeted therapies. Areas covered: In this article the authors present a detailed review of the most recent advances in targeted therapies for pediatric leukemias. A comprehensive description of the biological background, adult data and early clinical trials in pediatrics is provided. Expert opinion: Clinical trials are the way to evaluate new agents in pediatric cancer. The development of new drugs in pediatric leukemia must be preceded by a solid biological rationale. Agents in development exploit all possible vulnerabilities of leukemic cells. Drugs targeting cell surface antigens, intracellular signaling pathways and cell cycle inhibitors or epigenetic regulators are most prominent. Major advances have occurred thanks to new developments in engineering leading to optimized molecules such as anti-CD19 bi-specific T-cell engagers (e.g. blinatumomab) and antibody-drug conjugates. The integration of new-targeted therapies in pediatric chemotherapy-based regimens will lead to improved outcomes.

An early thymic precursor phenotype predicts outcome exclusively in HOXA-overexpressing adult T-cell acute lymphoblastic leukemia: a Group for Research in Adult Acute Lymphoblastic Leukemia study

Gene expression studies have consistently identified a HOXA-overexpressing cluster of T-cell acute lymphoblastic leukemias, but it is unclear whether these constitute a homogeneous clinical entity, and the biological consequences of HOXA overexpression have not been systematically examined. We characterized the biology and outcome of 55 HOXA-positive cases among 209 patients with adult T-cell acute lymphoblastic leukemia uniformly treated during the Group for Research on Adult Acute Lymphoblastic Leukemia (GRAALL)-2003 and -2005 studies. HOXA-positive patients had markedly higher rates of an early thymic precursor-like immunophenotype (40.8% versus 14.5%, P=0.0004), chemoresistance (59.3% versus 40.8%, P=0.026) and positivity for minimal residual disease (48.5% versus 23.5%, P=0.01) than the HOXA-negative group. These differences were due to particularly high frequencies of chemoresistant early thymic precursor-like acute lymphoblastic leukemia in HOXA-positive cases harboring fusion oncoproteins that transactivate HOXA Strikingly, the presence of an early thymic precursor-like immunophenotype was associated with marked outcome differences within the HOXA-positive group (5-year overall survival 31.2% in HOXA-positive early thymic precursor versus 66.7% in HOXA-positive non-early thymic precursor, P=0.03), but not in HOXA-negative cases (5-year overall survival 74.2% in HOXA-negative early thymic precursor versus 57.2% in HOXA-negative non-early thymic precursor, P=0.44). Multivariate analysis further revealed that HOXA positivity independently affected event-free survival (P=0.053) and relapse risk (P=0.039) of chemoresistant T-cell acute lymphoblastic leukemia. These results show that the underlying mechanism of HOXA deregulation dictates the clinico-biological phenotype, and that the negative prognosis of early thymic precursor acute lymphoblastic leukemia is exclusive to HOXA-positive patients, suggesting that early treatment intensification is currently suboptimal for therapeutic rescue of HOXA-positive chemoresistant adult early thymic precursor acute lymphoblastic leukemia.

TRIAL REGISTRATION

The GRAALL-2003 and -2005 studies were registered at http://www.clinicaltrials.gov as #NCT00222027 and #NCT00327678, respectively.

Modulation of PICALM Levels Perturbs Cellular Cholesterol Homeostasis

PICALM (Phosphatidyl Inositol Clathrin Assembly Lymphoid Myeloid protein) is a ubiquitously expressed protein that plays a role in clathrin-mediated endocytosis. PICALM also affects the internalization and trafficking of SNAREs and modulates macroautophagy. Chromosomal translocations that result in the fusion of PICALM to heterologous proteins cause leukemias, and genome-wide association studies have linked PICALM Single Nucleotide Polymorphisms (SNPs) to Alzheimer's disease. To obtain insight into the biological role of PICALM, we performed gene expression studies of PICALM-deficient and PICALM-expressing cells. Pathway analysis demonstrated that PICALM expression influences the expression of genes that encode proteins involved in cholesterol biosynthesis and lipoprotein uptake. Gas Chromatography-Mass Spectrometry (GC-MS) studies indicated that loss of PICALM increases cellular cholesterol pool size. Isotopic labeling studies revealed that loss of PICALM alters increased net scavenging of cholesterol. Flow cytometry analyses confirmed that internalization of the LDL receptor is enhanced in PICALM-deficient cells as a result of higher levels of LDLR expression. These findings suggest that PICALM is required for cellular cholesterol homeostasis and point to a novel mechanism by which PICALM alterations may contribute to disease.

A cryptic three-way translocation t(10;19;11)(p12.31;q13.31;q23.3) with a derivative Y-chromosome in an infant with acute myeloblastic leukemia (M5b)

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by the malignant transformation of hematopoietic precursors to a pathogenic cell clone. Chromosomal band 11q23 harboring MLL (=mixed lineage leukemia) gene is known to be involved in rearrangements with variety of genes as activating partners of MLL in different AML subtypes. Overall, an unfavorable prognosis is associated with MLL abnormalities. Here we investigated an 11-month-old male presenting with hyperleukocytosis being diagnosed with AML subtype FAB-M5b. In banding cytogenetics a der(19)t(19;?)(q13.3;?) and del(Y)(q11.23) were found as sole aberrations. Molecular cytogenetics revealed that the MLL gene was disrupted and even partially lost due to a t(10;19;11)(p12.31;q13.31;q23.3), an MLL/MLLT10 fusion appeared, and the der(Y) was an asymmetric inverted duplication with breakpoints in Yp11.2 and Yq11.23. The patient got hematopoietic stem cell transplantation from his haploidentical mother. Still three months afterwards 15% of blasts were detected in bone marrow and later the patient was lost during follow-up. The present case highlights the necessity to exclude MLL rearrangements, even when there seems to be no actual hint from banding cytogenetics.

A critical role for CRM1 in regulating HOXA gene transcription in CALM-AF10 leukemias

The leukemogenic CALM-AF10 fusion protein is found in patients with immature acute myeloid and T-lymphoid malignancies. CALM-AF10 leukemias display abnormal H3K79 methylation and increased HOXA cluster gene transcription. Elevated expression of HOXA genes is critical for leukemia maintenance and progression; however, the precise mechanism by which CALM-AF10 alters HOXA gene expression is unclear. We previously determined that CALM contains a CRM1-dependent nuclear export signal (NES), which is both necessary and sufficient for CALM-AF10-mediated leukemogenesis. Here, we find that interaction of CALM-AF10 with the nuclear export receptor CRM1 is necessary for activating HOXA gene expression. We show that CRM1 localizes to HOXA loci where it recruits CALM-AF10, leading to transcriptional and epigenetic activation of HOXA genes. Genetic and pharmacological inhibition of the CALM-CRM1 interaction prevents CALM-AF10 enrichment at HOXA chromatin, resulting in immediate loss of transcription. These results provide a comprehensive mechanism by which the CALM-AF10 translocation activates the critical HOXA cluster genes. Furthermore, this report identifies a novel function of CRM1: the ability to bind chromatin and recruit the NES-containing CALM-AF10 transcription factor.

The Biochemical Properties and Functions of CALM and AP180 in Clathrin Mediated Endocytosis

Clathrin-mediated endocytosis (CME) is a fundamental process for the regulated internalization of transmembrane cargo and ligands via the formation of vesicles using a clathrin coat. A vesicle coat is initially created at the plasma membrane by clathrin assembly into a lattice, while a specific cargo sorting process selects and concentrates proteins for inclusion in the new vesicle. Vesicles formed via CME traffic to different parts of the cell and fuse with target membranes to deliver cargo. Both clathrin assembly and cargo sorting functions are features of the two gene family consisting of assembly protein 180 kDa (AP180) and clathrin assembly lymphoid myeloid leukemia protein (CALM). In this review, we compare the primary structure and domain organization of CALM and AP180 and relate these properties to known functions and roles in CME and disease.

Characterization and inhibition of AF10-mediated interaction

The non-random chromosomal translocations t(10;11)(p13;q23) and t(10;11)(p13;q14-21) result in leukemogenic fusion proteins comprising the coiled coil domain of the transcription factor AF10 and the proteins MLL or CALM, respectively, and subsequently cause certain types of acute leukemia. The AF10 coiled-coil domain, which is crucial for the leukemogenic effect, has been shown to interact with GAS41, a protein previously identified as the product of an amplified gene in glioblastoma. Using sequential synthetic peptides, we mapped the potential AF10/GAS41 interaction site, which was subsequently be used as scaffold for a library targeting the AF10 coiled-coil domain. Using phage display, we selected a peptide that binds the AF10 coiled-coil domain with higher affinity than the respective coiled-coil region of wild-type GAS41, as demonstrated by phage ELISA, CD, and PCAs. Furthermore, we were able to successfully deploy the inhibitory peptide in a mammalian cell line to lower the expression of Hoxa genes that have been described to be overexpressed in these leukemias. This work dissects molecular determinants mediating AF10-directed interactions in leukemic fusions comprising the N-terminal parts of the proteins MLL or CALM and the C-terminal coiled-coil domain of AF10. Furthermore, it outlines the first steps in recognizing and blocking the leukemia-associated AF10 interaction in histiocytic lymphoma cells and therefore, may have significant implications in future diagnostics and therapeutics.

Nuclear export signal within CALM is necessary for CALM-AF10-induced leukemia

The CALM–AF10 fusion gene, which results from a t(10;11) translocation, is found in a variety of hematopoietic malignancies. Certain HOXA cluster genes and MEIS1 genes are upregulated in patients and mouse models that express CALM-AF10. Wild-type clathrin assembly lymphoid myeloid leukemia protein (CALM) primarily localizes in a diffuse pattern within the cytoplasm, whereas AF10 localizes in the nucleus; however, it is not clear where CALM-AF10 acts to induce leukemia. To investigate the influence of localization on leukemogenesis involving CALM-AF10, we determined the nuclear export signal (NES) within CALM that is necessary and sufficient for cytoplasmic localization of CALM-AF10. Mutations in the NES eliminated the capacity of CALM-AF10 to immortalize murine bone-marrow cells in vitro and to promote development of acute myeloid leukemia in mouse models. Furthermore, a fusion of AF10 with the minimal NES can immortalize bone-marrow cells and induce leukemia in mice. These results suggest that during leukemogenesis, CALM-AF10 plays its critical roles in the cytoplasm.

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.

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.

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.

A CALM-derived nuclear export signal is essential for CALM-AF10-mediated leukemogenesis

The t(10;11) chromosomal translocation gives rise to the CALM-AF10 fusion gene and is found in patients with aggressive and difficult-to-treat hematopoietic malignancies. CALM-AF10-driven leukemias are characterized by HOXA gene up-regulation and a global reduction in H3K79 methylation. DOT1L, the H3K79 methyltransferase, interacts with the octapeptide/leucine zipper domain of AF10, and this region has been shown to be necessary and sufficient for CALM-AF10-mediated transformation. However, the precise role of CALM in leukemogenesis remains unclear. Here, we show that CALM contains a nuclear export signal (NES) that mediates cytoplasmic localization of CALM-AF10 and is necessary for CALM-AF10-dependent transformation. Fusions of the CALM NES (NES(CALM)-AF10) or NES motifs from heterologous proteins (ABL1, Rev, PKIA, APC) in-frame with AF10 are sufficient to immortalize murine hematopoietic progenitors in vitro. The CALM NES is essential for CALM-AF10-dependent Hoxa gene up-regulation and aberrant H3K79 methylation, possibly by mislocalization of DOT1L. Finally, we observed that CALM-AF10 leukemia cells are selectively sensitive to inhibition of nuclear export by Leptomycin B. These findings uncover a novel mechanism of leukemogenesis mediated by the nuclear export pathway and support further investigation of the utility of nuclear export inhibitors as therapeutic agents for patients with CALM-AF10 leukemias.

Design and feasibility of a novel, rapid, and simple fluorescence 26-plex rt-PCR assay for simultaneous detection of 24 fusion transcripts in adult acute myeloid leukemia

Identification of chromosomal abnormalities is mandatory for classification of acute myeloid leukemia (AML), and the abnormalities have to be determined quickly, to allow patient enrollment in multicenter protocols and/or for selecting therapeutic strategies. Rapid AML molecular diagnosis is often difficult to achieve, however, because it is based on numerous different RT-PCR protocols. We developed a new RT-PCR method, one that does not require a nested step, to simultaneously detect all AML fusion transcripts from six major recurrent translocations found in adults: t(15;17)(q22;q12), inv(16)(p13.1q22) [t(16;16)(p13.1;q22)], t(8;21)(q22;q22), t(6;9)(p23;q34), t(9;22)(q34;q11), and t(10;11)(p13;q14). Specific primers for RT-PCR detection of the 24 fusion transcripts, along with two transcripts for controls, were designed for this 26-plex RT-PCR. Each PCR product had a different size and was separated by capillary electrophoresis. We also designed a multiplex positive control with 24 chimeric RNAs, corresponding to all chimeric RNAs tested. Compared with classical molecular biology protocols and cytogenetic analyses used as reference standards, results of the 26-plex RT-PCR method were concordant in all 204 (100%) cases of adult AML tested. Results were obtained in less than 24 hours. Because of the multiplex positive control, interpretation of the peaks was very easy, without any ambiguity. The tumor cell detection threshold was 1.5%.

AF10 plays a key role in the survival of uncommitted hematopoietic cells

Hematopoiesis is a complex process regulated by both cell intrinsic and cell extrinsic factors. Alterations in the expression of critical genes during hematopoiesis can modify the balance between stem cell differentiation and proliferation, and may ultimately give rise to leukemia and other diseases. AF10 is a transcription factor that has been implicated in the development of leukemia following chromosomal rearrangements between the AF10 gene and one of at least two other genes, MLL and CALM. The link between AF10 and leukemia, together with the known interactions between AF10 and hematopoietic regulators, suggests that AF10 may be important in hematopoiesis and in leukemic transformation. Here we show that AF10 is important for proper hematopoietic differentiation. The induction of hematopoietic differentiation in both human hematopoietic cell lines and murine total bone marrow cells triggers a decrease of AF10 mRNA and protein levels, particularly in stem cells and multipotent progenitors. Gain- and loss-of-function studies demonstrate that over- or under-expression of AF10 leads to apoptotic cell death in stem cells and multipotent progenitors. We conclude that AF10 plays a key role in the maintenance of multipotent hematopoietic cells.

Abrogation of MLL-AF10 and CALM-AF10-mediated transformation through genetic inactivation or pharmacological inhibition of the H3K79 methyltransferase Dot1l

The t(10;11)(p12;q23) translocation and the t(10;11)(p12;q14) translocation, which encode the MLL (mixed lineage leukemia)-AF10 and CALM (clathrin assembly lymphoid myeloid leukemia)-AF10 fusion oncoproteins, respectively, are two recurrent chromosomal rearrangements observed in patients with acute myeloid leukemia and acute lymphoblastic leukemia. Here, we demonstrate that MLL-AF10 and CALM-AF10-mediated transformation is dependent on the H3K79 methyltransferase Dot1l using genetic and pharmacological approaches in mouse models. Targeted disruption of Dot1l using a conditional knockout mouse model abolished in vitro transformation of murine bone marrow cells and in vivo initiation and maintenance of MLL-AF10 or CALM-AF10 leukemia. The treatment of MLL-AF10 and CALM-AF10 transformed cells with EPZ004777, a specific small-molecule inhibitor of Dot1l, suppressed expression of leukemogenic genes such as Hoxa cluster genes and Meis1, and selectively impaired proliferation of MLL-AF10 and CALM-AF10 transformed cells. Pretreatment with EPZ004777 profoundly decreased the in vivo spleen-colony-forming ability of MLL-AF10 or CALM-AF10 transformed bone marrow cells. These results show that patients with leukemia-bearing chromosomal translocations that involve the AF10 gene may benefit from small-molecule therapeutics that inhibit H3K79 methylation.

The radial nuclear positioning of genes correlates with features of megabase-sized chromatin domains

A nonrandom radial nuclear organization of genes has been well documented. This study provides further evidence that radial positioning depends on features of corresponding ∼1 Mbp chromatin domains (CDs), which represent the basic units of higher-order chromatin organization. We performed a quantitative three-dimensional analysis of the radial nuclear organization of three genes located on chromosome 1 in a DG75 Burkitt lymphoma-derived cell line. Quantitative real-time polymerase chain reaction revealed similar transcription levels for the three selected genes, whereas the total expression strength (TES) calculated as the sum of transcription of all genes annotated within a surrounding window of about 1 Mbp DNA differed for each region. Radial nuclear position of the studied CDs correlated with TES, i.e., the domain with the highest TES occupied the most interior position. Positions of CDs with stable TES values were stably maintained even under experimental conditions, resulting in genome-wide changes of the expression levels of many other genes. Our results strongly support the hypothesis that knowledge of the local chromatin environment is essential to predict the radial nuclear position of a gene.

FHL2 interacts with CALM and is highly expressed in acute erythroid leukemia

The t(10;11)(p13;q14) translocation results in the fusion of the CALM (clathrin assembly lymphoid myeloid leukemia protein) and AF10 genes. This translocation is observed in acute myeloblastic leukemia (AML M6), acute lymphoblastic leukemia (ALL) and malignant lymphoma. Using a yeast two-hybrid screen, the four and a half LIM domain protein 2 (FHL2) was identified as a CALM interacting protein. Recently, high expression of FHL2 in breast, gastric, colon, lung as well as in prostate cancer was shown to be associated with an adverse prognosis. The interaction between CALM and FHL2 was confirmed by glutathione S-transferase-pulldown assay and co-immunoprecipitation experiments. The FHL2 interaction domain of CALM was mapped to amino acids 294–335 of CALM. The transcriptional activation capacity of FHL2 was reduced by CALM, but not by CALM/AF10, which suggests that regulation of FHL2 by CALM might be disturbed in CALM/AF10-positive leukemia. Extremely high expression of FHL2 was seen in acute erythroid leukemia (AML M6). FHL2 was also highly expressed in chronic myeloid leukemia and in AML with complex aberrant karyotype. These results suggest that FHL2 may play an important role in leukemogenesis, especially in the case of AML M6.

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.

Up a lymphoid blind alley: Does CALM/AF10 disturb Ikaros during leukemogenesis?

The Ikaros gene is required for normal development of lymphocytes and frequent intragenic deletions of Ikaros have been identified in acute lymphoblastic leukemia. However, little is known about the role of Ikaros in myeloid malignancies. Here we discuss the role of Ikaros as a lineage master regulator during the onset and progression of myeloid leukemias, namely CALM-AF10 positive acute myeloid leukemia and chronic myeloid leukemia. Alterations of Ikaros at the gene or protein level may act as a bi-directional lineage switch subverting developmental plasticity for malignant transformation. Finally, we propose that promiscuous signaling involving Ikaros and FOXO transcription factors might be a critical link between early lineage fate and uncontrolled proliferation.

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.

PHF6 mutations in adult acute myeloid leukemia

Loss of function mutations and deletions encompassing the plant homeodomain finger 6 (PHF6) gene are present in about 20% of T-cell acute lymphoblastic leukemias (ALLs). Here, we report the identification of recurrent mutations in PHF6 in 10/353 adult acute myeloid leukemias (AMLs). Genetic lesions in PHF6 found in AMLs are frameshift and nonsense mutations distributed through the gene or point mutations involving the second plant homeodomain (PHD)-like domain of the protein. As in the case of T-ALL, where PHF6 alterations are found almost exclusively in males, mutations in PHF6 were seven times more prevalent in males than in females with AML. Overall, these results identify PHF6 as a tumor suppressor gene mutated in AML and extend the role of this X-linked tumor suppressor gene in the pathogenesis of hematologic tumors.

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.

A modified "cross-talk" between histone H2B Lys-120 ubiquitination and H3 Lys-79 methylation

Western blot analysis is currently the major method utilized for quantitatively assessing histone global modifications. However, there is a growing need to develop a highly specific, accurate, and multisite quantitative method. Herein, we report a liquid chromatography-tandem mass spectrometry-multiple reaction monitoring method to simultaneously quantify multisite modifications with unmatched specificity, sensitivity, and throughput. With one set of purification of histones by high pressure liquid chromatography or SDS-PAGE, nearly 20 modification sites including acetylation, propionylation, methylation, and ubiquitination were quantified within 2 h for two samples to be compared. Using this method, the relative levels of H2B ubiquitination and H3 Lys-79 methylation were quantified in the U937 human leukemia cell line, U937 derivative cell lines overexpressing anti-secretory factor 10 (AF10) and mutant AF10 with the deletion of the hDot1 binding domain OM-LZ. We found that H2B ubiquitination is inversely correlated with H3 Lys-79 methylation. Therefore, we propose that a catalytic and inhibitory loop mechanism may better describe the cross-talk relationship between H2B ubiquitination and H3 Lys-79 methylation.

Early T cell differentiation lessons from T-cell acute lymphoblastic leukemia

T cells develop from bone marrow-derived self-renewing hematopoietic stem cells (HSC). Upon entering the thymus, these cells undergo progressive commitment and differentiation driven by the thymic stroma and the pre-T cell receptor (pre-TCR). These processes are disrupted in T-cell acute lymphoblastic leukemia (T-ALL). More than 70% of recurring chromosomal rearrangements in T-ALL activate the expression of oncogenic transcription factors, belonging mostly to three families, basic helix-loop-helix (bHLH), homeobox (HOX), and c-MYB. This prevalence is indicative of their importance in the T lineage, and their dominant mechanisms of transformation. For example, bHLH oncoproteins inhibit E2A and HEB, revealing their tumor suppressor function in the thymus. The induction of T-ALL, nonetheless, requires collaboration with constitutive NOTCH1 signaling and the pre-TCR, as well as loss-of-function mutations for CDKN2A and PTEN. Significantly, NOTCH1, the pre-TCR pathway, and E2A/HEB proteins control critical checkpoints and branchpoints in early thymocyte development whereas several oncogenic transcription factors, HOXA9, c-MYB, SCL, and LYL-1 control HSC self-renewal. Together, these genetic lesions alter key regulatory processes in the cell, favoring self-renewal and subvert the normal control of thymocyte homeostasis.

Retroviral insertional mutagenesis identifies Zeb2 activation as a novel leukemogenic collaborating event in CALM-AF10 transgenic mice

The t(10;11) translocation results in a CALM-AF10 fusion gene in a subset of leukemia patients. Expression of a CALM-AF10 transgene results in leukemia, with prolonged latency and incomplete penetrance, suggesting that additional events are necessary for leukemic transformation. CALM-AF10 mice infected with the MOL4070LTR retrovirus developed acute leukemia, and ligation-mediated polymerase chain reaction was used to identify retroviral insertions at 19 common insertion sites, including Zeb2, Nf1, Mn1, Evi1, Ift57, Mpl, Plag1, Kras, Erg, Vav1, and Gata1. A total of 26% (11 of 42) of the mice had retroviral integrations near Zeb2, a transcriptional corepressor leading to overexpression of the Zeb2-transcript. A total of 91% (10 of 11) of mice with Zeb2 insertions developed B-lineage acute lymphoblastic leukemia, suggesting that Zeb2 activation promotes the transformation of CALM-AF10 hematopoietic precursors toward B-lineage leukemias. More than half of the mice with Zeb2 integrations also had Nf1 integrations, suggesting cooperativity among CALM-AF10, Zeb2, and Ras pathway mutations. We searched for Nras, Kras, and Ptpn11 point mutations in the CALM-AF10 leukemic mice. Three mutations were identified, all of which occurred in mice with Zeb2 integrations, consistent with the hypothesis that Zeb2 and Ras pathway activation promotes B-lineage leukemic transformation in concert with CALM-AF10.

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.

Global reduction of the epigenetic H3K79 methylation mark and increased chromosomal instability in CALM-AF10-positive leukemias

Chromosomal translocations generating fusion proteins are frequently found in human leukemias. The fusion proteins play an important role in leukemogenesis by subverting the function of one or both partner proteins. The leukemogenic CALM-AF10 fusion protein is capable of interacting with the histone H3 lysine 79 (H3K79)-specific methyltransferase hDOT1L through the fused AF10 moiety. This interaction leads to local H3K79 hypermethylation on Hoxa5 loci, which up-regulates the expression of Hoxa5 and contributes to leukemogenesis. However, the long latency of leukemogenesis of CALM-AF10 transgenic mice suggests that the direct effects of fusion oncogene are not sufficient for the induction of leukemia. In this study, we show that the CALM-AF10 fusion protein can also greatly reduce global H3K79 methylation in both human and murine leukemic cells by disrupting the AF10-mediated association of hDOT1L with chromatin. Cells with reduced H3K79 methylation are more sensitive to gamma-irradiation and display increased chromosomal instability. Consistently, leukemia patients harboring CALM-AF10 fusion have more secondary chromosomal aberrations. These findings suggest that chromosomal instability associated with global epigenetic alteration contributes to malignant transformation in certain leukemias, and that leukemias with this type of epigenetic alteration might benefit from treatment regimens containing DNA-damaging agents. This study is registered with www.clinicaltrials.gov as NCT00266136.

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.

Molecular-genetic insights in paediatric T-cell acute lymphoblastic leukaemia

Paediatric T-cell acute lymphoblastic leukaemia (T-ALL) is an aggressive malignancy of thymocytes that accounts for about 15% of ALL cases and for which treatment outcome remains inferior compared to B-lineage acute leukaemias. In T-ALL, leukemic transformation of maturating thymocytes is caused by a multistep pathogenesis involving numerous genetic abnormalities that drive normal T-cells into uncontrolled cell growth and clonal expansion. This review provides an overview of the current knowledge on onco- and tumor suppressor genes in T-ALL and suggests a classification of these genetic defects into type A and type B abnormalities. Type A abnormalities may delineate distinct molecular-cytogenetic T-ALL subgroups, whereas type B abnormalities are found in all major T-ALL subgroups and synergize with these type A mutations during T-cell pathogenesis.

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.

The leukemogenic CALM/AF10 fusion protein alters the subcellular localization of the lymphoid regulator Ikaros

The t(10;11)(p13;q14) translocation leads to the fusion of the CALM and AF10 genes. This translocation can be found as the sole cytogenetic abnormality in acute lymphoblastic leukemia, acute myeloid leukemia and in malignant lymphomas. The expression of CALM/AF10 in primary murine bone marrow cells results in the development of an aggressive leukemia in a murine bone marrow transplantation model. Using a yeast two-hybrid screen, we identified the lymphoid regulator Ikaros as an AF10 interacting protein. Interestingly, Ikaros is required for normal development of lymphocytes, and aberrant expression of Ikaros has been found in leukemia. In a murine model, the expression of a dominant negative isoform of Ikaros causes leukemias and lymphomas. The Ikaros interaction domain of AF10 was mapped to the leucine zipper domain of AF10, which is required for malignant transformation both by the CALM/AF10 and the MLL/AF10 fusion proteins. The interaction between AF10 and Ikaros was confirmed by GST pull down and co-immunoprecipitation. Coexpression of CALM/AF10 but not of AF10 alters the subcellular localization of Ikaros in murine fibroblasts. The transcriptional repressor activity of Ikaros is reduced by AF10. These results suggest that CALM/AF10 might interfere with normal Ikaros function, and thereby block lymphoid differentiation in CALM/AF10 positive leukemias.

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.

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.

T-Cell lymphoblastic lymphoma presenting as bilateral multinodular breast masses: a case report and review of the literature

Non-Hodgkin lymphoma of T-cell lineage involving the breast is rare. We report on a 41-year-old woman with T-cell lymphoblastic lymphoma who presented with multiple bilateral breast masses. The patient was treated with intensive chemotherapy and mediastinal and whole-brain irradiation. She remains in complete remission 24 months after diagnosis. The clinical, histologic, phenotypic, and cytogenetic features are described, with a review of the literature.

Cytogenetic findings in pediatric T-lymphoblastic lymphomas: one institution's experience and a review of the literature

Cytogenetic analyses of lymphomas commonly reveal nonrandom chromosomal abnormalities, but there are relatively few reports in childhood lymphoblastic lymphoma (LL). We retrospectively reviewed G-banded karyotypic analyses performed at Arkansas Children's Hospital between 1990 and 2004. Six children (2 to 20 years old) had LL that presented as mediastinal or cervical masses and had a T-cell immunophenotype and clonal abnormalities. The cytogenetic findings in these 6 patients were as follows: 46,XX,-7,inv(9)(p11q12),der (12)t(7;12)(q11.2;p13),t(16;18)(p13.1;q21),+22 in patient 1; 47,XX,+9,del(9)(q11q22)x2 in patient 2; 72-119, XY,+X,+1,+1, inv(2) (p11q13),-3,+5,+6,+7,+10,-12,-16, -21,-21,-22,+mar in patient 3; 48,XY,+5,+20,t(7;9) (q32;q34) in patient 4; 47 approximately 48,XX,der(10)t(10;14)(q23; q11.2),+12, del(12)(p12)x2, -14,del(16)(q22q22),+?add (19)(p13.3) in patient 5; and 48 approximately 49,XY,+7,+8,t(11;19) (q23;p?13.3),+der(19)t(11;19)[cp20] in patient 6. Eleven chromosome breakpoints in 6 of our patients (7q11, 12p13, 16p13, 18q21, 9q11, 2p11, 2q13, 7q32, and 7q23) have been reported in other patients with acute lymphoblastic leukemia or LL and involved regions containing TEL, ABL, E2A, MLL, and T-cell receptor-alpha genes. A review of the cytogenetic findings of these and other cases of LL reveals that clonal aberrations are common and most frequently involve T-cell receptor gene regions. The aberrations show some features similar to those of acute lymphoblastic leukemia and are not unique to LL, thus furnishing additional evidence of the equivalence of these two diseases. The cytogenetic features of LL may be helpful in the diagnosis of pediatric lymphomas and undifferentiated neoplasms.

Met receptor dynamics and signalling

The receptor for hepatocyte growth factor (HGF), Met, controls a programme of invasive growth that combines proliferation with various moto- and morphogenetic processes. This process is important for development and organ regeneration, but dysregulation in transformed tissues can contribute to cancer progression and metastasis. Acute stimulation of tissue culture cells with HGF leads to Met downregulation via degradation through an endocytic mechanism that also requires proteasome activity. Perturbation of Met trafficking on the endocytic pathway, either at the level of the internalisation step or during sorting at the early endosome, leads to altered signalling outputs. Ubiquitination of Met through the E3-ligase Cbl is required for receptor downregulation, and a mutant receptor defective in Cbl binding is able to transform cells. We discuss the hypothesis that some naturally occurring Met mutants implicated in cancer may transform cells owing to defects in their trafficking along the endosomal degradation pathway.

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.

Cytogenetics, fluorescence in situ hybridization, and reverse transcriptase polymerase chain reaction are necessary to clarify the various mechanisms leading to an MLL-AF10 fusion in acute myelocytic leukemia with 10;11 rearrangement

In acute myelocytic leukemia (AML), predominantly in AML M5a, a recurrent chromosome aberration involves 11q23/MLL and the short arm of chromosome 10. Molecular studies have shown that the AF10 gene at 10p12 is consistently a partner gene in cases with 10;11 rearrangement. A simple reciprocal translocation cannot lead to the known MLL-AF10 fusion transcript because the 3' part of the MLL gene is orientated to the telomere and the 3' part of the AF10 gene to the centromere. In a series of 1897 AML samples, 14 cases (0.74%) showed 10;11 rearrangements leading to a MLL-AF10 fusion transcript. These cases were analyzed in detail with G banding analyses, fluorescence in situ hybridization, and molecular investigation in a single center. Five different mechanisms of (10;11) rearrangements leading to a MLL-AF10 fusion transcript can be observed (i.e., reciprocal translocations, insertions of either 10p into 11q or 11q into 10p, as well as complex and cryptic rearrangements). Compared to translocations involving MLL and other partner genes, complex rearrangements are unique for MLL-AF10 fusions. This may result from the opposite orientation of MLL and AF10.