The critical role of chromosome translocations in human leukemias

SEC: A core hub during cell fate alteration

Pol II pause release is a rate-limiting step in gene transcription, influencing various cell fate alterations. Numerous proteins orchestrate Pol II pause release, thereby playing pivotal roles in the intricate process of cellular fate modulation. Super elongation complex (SEC), a large assembly comprising diverse protein components, has garnered attention due to its emerging significance in orchestrating physiological and pathological cellular identity changes by regulating the transcription of crucial genes. Consequently, SEC emerges as a noteworthy functional complex capable of modulating cell fate alterations. Therefore, a comprehensive review is warranted to systematically summarize the core roles of SEC in different types of cell fate alterations. This review focuses on elucidating the current understanding of the structural and functional basis of SEC. Additionally, we discuss the intricate regulatory mechanisms governing SEC in various models of cell fate alteration, encompassing both physiological and pathological contexts. Furthermore, leveraging the existing knowledge of SEC, we propose some insightful directions for future research, aiming to enhance our mechanistic and functional comprehension of SEC within the diverse landscape of cell fate alterations.

Regulation of HOX gene expression in AML

As key developmental regulators, HOX cluster genes have varied and context-specific roles in normal and malignant hematopoiesis. A complex interaction of transcription factors, epigenetic regulators, long non-coding RNAs and chromatin structural changes orchestrate HOX expression in leukemia cells. In this review we summarize molecular mechanisms underlying HOX regulation in clinical subsets of AML, with a focus on NPM1 mutated (NPM1mut) AML comprising a third of all AML patients. While the leukemia initiating function of the NPM1 mutation is clearly dependent on HOX activity, the favorable treatment responses in these patients with upregulation of HOX cluster genes is a poorly understood paradoxical observation. Recent data confirm FOXM1 as a suppressor of HOX activity and a well-known binding partner of NPM suggesting that FOXM1 inactivation may mediate the effect of cytoplasmic NPM on HOX upregulation. Conversely the residual nuclear fraction of mutant NPM has also been recently shown to have chromatin modifying effects permissive to HOX expression. Recent identification of the menin-MLL interaction as a critical vulnerability of HOX-dependent AML has fueled the development of menin inhibitors that are clinically active in NPM1 and MLL rearranged AML despite inconsistent suppression of the HOX locus. Insights into context-specific regulation of HOX in AML may provide a solid foundation for targeting this common vulnerability across several major AML subtypes.

Targeting Menin and CD47 to Address Unmet Needs in Acute Myeloid Leukemia

After forty years of essentially unchanged treatment in acute myeloid leukemia (AML), innovation over the past five years has been rapid, with nine drug approvals from 2016 to 2021. Increased understanding of the molecular changes and genetic ontology of disease have led to targeting mutations in isocitrate dehydrogenase, FMS-like tyrosine kinase 3 (FLT3), B-cell lymphoma 2 and hedgehog pathways. Yet outcomes remain variable; especially in defined molecular and genetic subgroups such as NPM1 (Nucleophosmin 1) mutations, 11q23/KMT2A rearranged and TP53 mutations. Emerging therapies seek to address these unmet needs, and all three of these subgroups have promising new therapeutic approaches. Here, we will discuss the normal biological roles of menin in acute leukemia, notably in KMT2A translocations and NPM1 mutation, as well as current drug development. We will also explore how CD47 inhibition may move immunotherapy into front-line settings and unlock new treatment strategies in TP53 mutated disease. We will then consider how these new therapeutic advances may change the management of AML overall.

Neoplasia-associated Chromosome Translocations Resulting in Gene Truncation

Chromosomal translocations in cancer as well as benign neoplasias typically lead to the formation of fusion genes. Such genes may encode chimeric proteins when two protein-coding regions fuse in-frame, or they may result in deregulation of genes via promoter swapping or translocation of the gene into the vicinity of a highly active regulatory element. A less studied consequence of chromosomal translocations is the fusion of two breakpoint genes resulting in an out-of-frame chimera. The breaks then occur in one or both protein-coding regions forming a stop codon in the chimeric transcript shortly after the fusion point. Though the latter genetic events and mechanisms at first awoke little research interest, careful investigations have established them as neither rare nor inconsequential. In the present work, we review and discuss the truncation of genes in neoplastic cells resulting from chromosomal rearrangements, especially from seemingly balanced translocations.

The impact of fusion genes on cancer stem cells and drug resistance

With ever increasing evidences on the role of fusion genes as the oncogenic protagonists in myriad cancers, it's time to explore if fusion genes can be the next generational drug targets in meeting the current demands of higher drug efficacy. Eliminating cancer stem cells (CSC) has become the current focus; however, we have reached a standstill in drug development owing to the lack of effective strategies to eradicate CSC. We believe that fusion genes could be the novel targets to overcome this limitation. The intriguing feature of fusion genes is that it dominantly impacts every aspect of CSC including self-renewal, differentiation, lineage commitment, tumorigenicity and stemness. Given the clinical success of fusion gene-based drugs in hematological cancers, our attempt to target fusion genes in eradicating CSC can be rewarding. As fusion genes are expressed explicitly in cancer cells, eradicating CSC by targeting fusion genes provides yet an another advantage of negligible patient side effects since normal cells remain unaffected by the drug. We hereby delineate the latest evidences on how fusion genes regulate CSC and drug resistance.

Interstitial Deletions Generating Fusion Genes

A fusion gene is the physical juxtaposition of two different genes resulting in a structure consisting of the head of one gene and the tail of the other. Gene fusion is often a primary neoplasia-inducing event in leukemias, lymphomas, solid malignancies as well as benign tumors. Knowledge about fusion genes is crucial not only for our understanding of tumorigenesis, but also for the diagnosis, prognostication, and treatment of cancer. Balanced chromosomal rearrangements, in particular translocations and inversions, are the most frequent genetic events leading to the generation of fusion genes. In the present review, we summarize the existing knowledge on chromosome deletions as a mechanism for fusion gene formation. Such deletions are mostly submicroscopic and, hence, not detected by cytogenetic analyses but by array comparative genome hybridization (aCGH) and/or high throughput sequencing (HTS). They are found across the genome in a variety of neoplasias. As tumors are increasingly analyzed using aCGH and HTS, it is likely that more interstitial deletions giving rise to fusion genes will be found, significantly impacting our understanding and treatment of cancer.

Fusion proteins in lung cancer: addressing diagnostic problems for deciding therapy

Introduction: Gene fusions are frequent chromosomal aberrations in solid tumors. In Lung cancer (LC) several druggable-fusions involving tyrosine kinase receptor genes have been described, including ALK, ROS1, RET and NTRK. In non-small cell lung cancer, testing for targetable fusions has become a part of routine clinical practice, greatly impacting therapeutic choice for patients with these aberrations. Although substantial technologies for gene fusion detection have been implemented over time including; cytogenetic, Fluorescence in situ hybridization (FISH), Immunohistochemistry (IHC), Retro-transcription Real-Time PCR (RT-qPCR), to Next Generation Sequencing (NGS), nCounter system (Nanostring technology), several critical issues remain. To date, only the companion diagnostic tests FISH and IHC for ALK-rearrangements and NGS for ROS1-rearrangments were approved. Other fusion approved tests are currently unavailable.Areas covered: In this review, we explore current diagnostic problems of gene fusion detection relative to the technologies available, in order to clarify future standardization of analyses which determine therapeutic choices.Expert opinion: The establishment of a gold standard, an effective diagnostic algorithm, and a standardized interpretation for the analysis of each druggable-fusions in lung cancer is essential for adequate therapeutic management.

Genome chaos: Creating new genomic information essential for cancer macroevolution

Cancer research has traditionally focused on the characterization of individual molecular mechanisms that can contribute to cancer. Due to the multiple levels of genomic and non-genomic heterogeneity, however, overwhelming molecular mechanisms have been identified, most with low clinical predictability. It is thus necessary to search for new concepts to unify these diverse mechanisms and develop better strategies to understand and treat cancer. In recent years, two-phased cancer evolution (comprised of the genome reorganization-mediated punctuated phase and gene mutation-mediated stepwise phase), initially described by tracing karyotype evolution, was confirmed by the Cancer Genome Project. In particular, genome chaos, the process of rapid and massive genome reorganization, has been commonly detected in various cancers-especially during key phase transitions, including cellular transformation, metastasis, and drug resistance-suggesting the importance of genome-level changes in cancer evolution. In this Perspective, genome chaos is used as a discussion point to illustrate new genome-mediated somatic evolutionary frameworks. By rephrasing cancer as a new system emergent from normal tissue, we present the multiple levels (or scales) of genomic and non-genomic information. Of these levels, evolutionary studies at the chromosomal level are determined to be of ultimate importance, since altered genomes change the karyotype coding and karyotype change is the key event for punctuated cellular macroevolution. Using this lens, we differentiate and analyze developmental processes and cancer evolution, as well as compare the informational relationship between genome chaos and its various subtypes in the context of macroevolution under crisis. Furthermore, the process of deterministic genome chaos is discussed to interpret apparently random events (including stressors, chromosomal variation subtypes, surviving cells with new karyotypes, and emergent stable cellular populations) as nonrandom patterns, which supports the new cancer evolutionary model that unifies genome and gene contributions during different phases of cancer evolution. Finally, the new perspective of using cancer as a model for organismal evolution is briefly addressed, emphasizing the Genome Theory as a new and necessary conceptual framework for future research and its practical implications, not only in cancer but evolutionary biology as a whole.

Mutagenicity monitoring in humans: Global versus specific origin of mutations

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.e., traditional analyses of aberrations, translocation studies involving chromosome painting and fluorescence in situ hybridization (FISH) and determinations of micronuclei (MN). Other T-cell assays measure gene mutations. i.e., hypoxanthine-guanine phosphoriboslytransferase (HPRT) and phosphoribosylinositol glycan class A (PIGA). In addition to the T-cell assays, also reviewed are those assays that measure events in peripheral blood cells that necessarily arose in BM cells, i.e., MN in reticulocytes; glycophorin A (GPA) gene mutations in red blood cells (RBCs), and PIGA gene mutations in RBC or granulocytes. This review considers only cell culture- or cytometry-based assays to describe endpoints measured, methods, optimal sampling times, and sample summaries of typical quantitative and qualitative results. However, to achieve its intended focus on the target cells where events occur, kinetics of the cells of peripheral blood that derive at some point from precursor cells are reviewed to identify body sites and tissues where the genotoxic events originate. Kinetics indicate that in normal adults, measured events in T-cells afford global assessments of in vivo mutagenicity but are not specific for BM effects. Therefore, an agent's capacity for inducing mutations in BM cells cannot be reliably inferred from T-cell assays as the magnitude of effect in BM, if any, is unknown. By contrast, chromosome or gene level mutations measured in RBCs/reticulocytes or granulocytes must originate in BM cells, i.e. in RBC or granulocyte precursors, thereby making them specific indicators for effects in BM. Assays of mutations arising directly in BM cells may quantitatively reflect the mutagenicity of potential leukemogenic agents.

COMPASS and SWI/SNF complexes in development and disease

The Trithorax group (TrxG) of proteins is a large family of epigenetic regulators that form multiprotein complexes to counteract repressive developmental gene expression programmes established by the Polycomb group of proteins and to promote and maintain an active state of gene expression. Recent studies are providing new insights into how two crucial families of the TrxG - the COMPASS family of histone H3 lysine 4 methyltransferases and the SWI/SNF family of chromatin remodelling complexes - regulate gene expression and developmental programmes, and how misregulation of their activities through genetic abnormalities leads to pathologies such as developmental disorders and malignancies.

Learning from mouse models of MLL fusion gene-driven acute leukemia

5-10% of human acute leukemias carry chromosomal translocations involving the mixed lineage leukemia (MLL) gene that result in the expression of chimeric protein fusing MLL to >80 different partners of which AF4, ENL and AF9 are the most prevalent. In contrast to many other leukemia-associated mutations, several MLL-fusions are powerful oncogenes that transform hematopoietic stem cells but also more committed progenitor cells. Here, I review different approaches that were used to express MLL fusions in the murine hematopoietic system which often, but not always, resulted in highly penetrant and transplantable leukemias that closely phenocopied the human disease. Due to its simple and reliable nature, reconstitution of irradiated mice with bone marrow cells retrovirally expressing the MLL-AF9 fusion became the most frequently in vivo model to study the biology of acute myeloid leukemia (AML). I review some of the most influential studies that used this model to dissect critical protein interactions, the impact of epigenetic regulators, microRNAs and microenvironment-dependent signals for MLL fusion-driven leukemia. In addition, I highlight studies that used this model for shRNA- or genome editing-based screens for cellular vulnerabilities that allowed to identify novel therapeutic targets of which some entered clinical trials. Finally, I discuss some inherent characteristics of the widely used mouse model based on retroviral expression of the MLL-AF9 fusion that can limit general conclusions for the biology of AML. This article is part of a Special Issue entitled: The MLL family of proteins in normal development and disease edited by Thomas A Milne.

Godwin A, L. Hupert M, A. Witek M, A. Soper S. Microfluidic Device for On-Chip Immunophenotyping and Cytogenetic Analysis of Rare Biological Cells

The role of circulating plasma cells (CPCs) and circulating leukemic cells (CLCs) as biomarkers for several blood cancers, such as multiple myeloma and leukemia, respectively, have recently been reported. These markers can be attractive due to the minimally invasive nature of their acquisition through a blood draw (i.e., liquid biopsy), negating the need for painful bone marrow biopsies. CPCs or CLCs can be used for cellular/molecular analyses as well, such as immunophenotyping or fluorescence in situ hybridization (FISH). FISH, which is typically carried out on slides involving complex workflows, becomes problematic when operating on CLCs or CPCs due to their relatively modest numbers. Here, we present a microfluidic device for characterizing CPCs and CLCs using immunofluorescence or FISH that have been enriched from peripheral blood using a different microfluidic device. The microfluidic possessed an array of cross-channels (2-4 µm in depth and width) that interconnected a series of input and output fluidic channels. Placing a cover plate over the device formed microtraps, the size of which was defined by the width and depth of the cross-channels. This microfluidic chip allowed for automation of immunofluorescence and FISH, requiring the use of small volumes of reagents, such as antibodies and probes, as compared to slide-based immunophenotyping and FISH. In addition, the device could secure FISH results in <4 h compared to 2-3 days for conventional FISH.

Molecular mechanisms and pathobiology of oncogenic fusion transcripts in epithelial tumors

Recurrent fusion transcripts, which are one of the characteristic hallmarks of cancer, arise either from chromosomal rearrangements or from transcriptional errors in splicing. DNA rearrangements include intrachromosomal or interchromosomal translocation, tandem duplication, deletion, inversion, or result from chromothripsis, which causes complex rearrangements. In addition, fusion proteins can be created through transcriptional read-through. Fusion genes can be transcribed to fusion transcripts and translated to chimeric proteins, with many having demonstrated transforming activities through multiple mechanisms in cells. Fusion proteins represent novel therapeutic targets and diagnostic biomarkers of diagnosis, disease status, or progression. This review focuses on the mechanisms underlying the formation of oncogenic fusion genes and transcripts and their impact on the pathobiology of epithelial tumors.

Leukaemia and myeloid malignancy among people exposed to low doses (<100 mSv) of ionising radiation during childhood: a pooled analysis of nine historical cohort studies

BACKGROUND

Substantial evidence links exposure to moderate or high doses of ionising radiation, particularly in childhood, with increased risk of leukaemia. The association of leukaemia with exposure to low-dose (<100 mSv) radiation is less certain, although this is the dose range most relevant to the general population. We aimed to estimate the risk of leukaemia associated with low-dose radiation exposure in childhood (age <21 years).

METHODS

In this analysis of historical cohort studies, we pooled eligible cohorts reported up to June 30, 2014. We evaluated leukaemia and myeloid malignancy outcomes in these cohorts with the relevant International Classification of Diseases and International Classification of Diseases for Oncology definitions. The cohorts included had not been treated for malignant disease, had reported at least five cases of the relevant haematopoietic neoplasms, and estimated individual active bone marrow (ABM) doses. We restricted analysis to individuals who were younger than 21 years at first irradiation who had mean cumulative ABM doses of less than 100 mSv. Dose-response models were fitted by use of Poisson regression. The data were received in fully anonymised form by the statistical analyst.

FINDINGS

We identified nine eligible cohorts from Canada, France, Japan, Sweden, the UK, and the USA, including 262 573 people who had been exposed to less than 100 mSv enrolled between June 4, 1915, and Dec 31, 2004. Mean follow-up was 19·63 years (SD 17·75) and mean cumulative ABM dose was 19·6 mSv (SD 22·7). 154 myeloid malignancies were identified (which included 79 acute myeloid leukaemias, eight myelodysplastic syndromes, and 36 chronic myeloid leukaemias, in addition to other unspecified myeloid malignancies) and 40 acute lymphoblastic leukaemias, with 221 leukaemias (including otherwise unclassified leukaemias but excluding chronic lymphocytic leukaemia) identified overall. The fitted relative risks at 100 mSv were 3·09 (95% CI 1·41-5·92; p_trend=0·008) for acute myeloid leukaemia and myelodysplastic syndromes combined, 2·56 (1·09-5·06; p_trend=0·033) for acute myeloid leukaemia, and 5·66 (1·35-19·71; p_trend=0·023) for acute lymphoblastic leukaemia. There was no clear dose-response for chronic myeloid leukaemia, which had a relative risk at 100 mSv of 0·36 (0·00-2·36; p_trend=0·394). There were few indications of between-cohort heterogeneity or departure from linearity. For acute myeloid leukaemia and myelodysplastic syndromes combined and for acute lymphoblastic leukaemia, the dose-responses remained significant for doses of less than 50 mSv. Excess absolute risks at 100 mSv were in the range of 0·1-0·4 cases or deaths per 10 000 person-years.

INTERPRETATION

The risks of acute myeloid leukaemia and acute lymphoblastic leukaemia were significantly increased after cumulative doses of ionising radiation of less than 100 mSv in childhood or adolescence, with an excess risk also apparent for cumulative radiation doses of less than 50 mSv for some endpoints. These findings support an increased risk of leukaemia associated with low-dose exposure to radiation and imply that the current system of radiological protection is prudent and not overly protective.

FUNDING

National Cancer Institute Intramural Research Program, National Cancer Institute, and US National Institutes for Health.

An AML1-ETO/miR-29b-1 regulatory circuit modulates phenotypic properties of acute myeloid leukemia cells

Acute myeloid leukemia (AML) is characterized by an aggressive clinical course and frequent cytogenetic abnormalities that include specific chromosomal translocations. The 8;21 chromosomal rearrangement disrupts the key hematopoietic RUNX1 transcription factor, and contributes to leukemia through recruitment of co-repressor complexes to RUNX1 target genes, altered subnuclear localization, and deregulation of the myeloid gene regulatory program. However, a role of non-coding microRNAs (miRs) in t(8;21)-mediated leukemogenesis is minimally understood. We present evidence of an interplay between the tumor suppressor miR-29b-1 and the AML1-ETO (also designated RUNX1-RUNX1T1) oncogene that is encoded by the t(8;21). We find that AML1-ETO and corepressor NCoR co-occupy the miR-29a/b-1 locus and downregulate its expression in leukemia cells. Conversely, re-introduction of miR-29b-1 in leukemia cells expressing AML1-ETO causes significant downregulation at the protein level through direct targeting of the 3’ untranslated region of the chimeric transcript. Restoration of miR-29b-1 expression in leukemia cells results in decreased cell growth and increased apoptosis. The AML1-ETO-dependent differentiation block and transcriptional program are partially reversed by miR-29b-1. Our findings establish a novel regulatory circuit between the tumor-suppressive miR-29b-1 and the oncogenic AML1-ETO that controls the leukemic phenotype in t(8;21)-carrying acute myeloid leukemia.

MYB induces the expression of the oncogenic corepressor SKI in acute myeloid leukemia

Acute myeloid leukemia (AML) arises through clonal expansion of transformed myeloid progenitor cells. The SKI proto-oncogene is highly upregulated in different solid tumors and leukemic cells, but little is known about its transcriptional regulation during leukemogenesis. MYB is an important hematopoietic transcription factor involved in proliferation as well as differentiation and upregulated in most human acute leukemias. Here, we find that MYB protein binds within the regulatory region of the SKI gene in AML cells. Reporter gene assays using MYB binding sites present in the SKI gene locus show MYB-dependent transcriptional activation. SiRNA-mediated depletion of MYB in leukemic cell lines reveals that MYB is crucial for SKI gene expression. Consistently, we observed a positive correlation of MYB and SKI expression in leukemic cell lines and in samples of AML patients. Moreover, MYB and SKI both were downregulated by treatment with histone deacetylase inhibitors. Strikingly, differentiation of AML cells induced by depletion of MYB is attenuated by overexpression of SKI. Our findings identify SKI as a novel MYB target gene, relevant for the MYB-induced differentiation block in leukemic cells.

A Postgenomic Perspective on Molecular Cytogenetics

BACKGROUND

The postgenomic era is featured by massive data collection and analyses from various large scale-omics studies. Despite the promising capability of systems biology and bioinformatics to handle large data sets, data interpretation, especially the translation of -omics data into clinical implications, has been challenging.

DISCUSSION

In this perspective, some important conceptual and technological limitations of current systems biology are discussed in the context of the ultimate importance of the genome beyond the collection of all genes. Following a brief summary of the contributions of molecular cytogenetics/cytogenomics in the pre- and post-genomic eras, new challenges for postgenomic research are discussed. Such discussion leads to a call to search for a new conceptual framework and holistic methodologies.

CONCLUSION

Throughout this synthesis, the genome theory of somatic cell evolution is highlighted in contrast to gene theory, which ignores the karyotype-mediated higher level of genetic information. Since "system inheritance" is defined by the genome context (gene content and genomic topology) while "parts inheritance" is defined by genes/epigenes, molecular cytogenetics and cytogenomics (which directly study genome structure, function, alteration and evolution) will play important roles in this postgenomic era.

An unusual translocation, t(1;11)(q21;q23), in a case of chronic myeloid leukemia with a cryptic Philadelphia chromosome

Chronic myeloid leukemia (CML) is characterized by the translocation t(9;22)(q34;q11) [Philadelphia (Ph) chromosome). Although not frequently occurring, additional chromosome abnormalities (ACAs) can be detected at diagnosis and a number have been associated with an adverse cytogenetic and molecular outcome. The present study reports a case of CML presenting with the translocation t(1;11)(q21;q23) and a cryptic Ph chromosome. The presence of ACAs could generate greater genetic instability, promoting the emergence of further alterations. The present findings suggest that t(1;11)(q21;q23) can prevent a good response to tyrosine kinase inhibitor (TKI) therapy developing a primary resistance. In the present patient, at a recent follow-up, the T315I mutation was detected. This mutation confers full resistance to all available TKI, except ponatinib, which was not a therapeutic option due to comorbidities.

Drosophila melanogaster positive transcriptional elongation factors regulate metabolic and sex-biased expression in adults

Background

Transcriptional elongation is a generic function, but is also regulated to allow rapid transcription responses. Following relatively long initiation and promoter clearance, RNA polymerase II can pause and then rapidly elongate following recruitment of positive elongation factors. Multiple elongation complexes exist, but the role of specific components in adult Drosophila is underexplored.

Results

We conducted RNA-seq experiments to analyze the effect of RNAi knockdown of Suppressor of Triplolethal and lilliputian. We similarly analyzed the effect of expressing a dominant negative Cyclin-dependent kinase 9 allele. We observed that almost half of the genes expressed in adults showed reduced expression, supporting a broad role for the three tested genes in steady-state transcript abundance. Expression profiles following lilliputian and Suppressor of Triplolethal RNAi were nearly identical raising the possibility that they are obligatory co-factors. Genes showing reduced expression due to these RNAi treatments were short and enriched for genes encoding metabolic or enzymatic functions. The dominant-negative Cyclin-dependent kinase 9 profiles showed both overlapping and specific differential expression, suggesting involvement in multiple complexes. We also observed hundreds of genes with sex-biased differential expression following treatment.

Conclusion

Transcriptional profiles suggest that Lilliputian and Suppressor of Triplolethal are obligatory cofactors in the adult and that they can also function with Cyclin-dependent kinase 9 at a subset of loci. Our results suggest that transcriptional elongation control is especially important for rapidly expressed genes to support digestion and metabolism, many of which have sex-biased function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3755-x) contains supplementary material, which is available to authorized users.

Germline variants in ETV6 underlie reduced platelet formation, platelet dysfunction and increased levels of circulating CD34+ progenitors

Variants in ETV6, which encodes a transcription repressor of the E26 transformation-specific family, have recently been reported to be responsible for inherited thrombocytopenia and hematologic malignancy. We sequenced the DNA from cases with unexplained dominant thrombocytopenia and identified six likely pathogenic variants in ETV6, of which five are novel. We observed low repressive activity of all tested ETV6 variants, and variants located in the E26 transformation-specific binding domain (encoding p.A377T, p.Y401N) led to reduced binding to corepressors. We also observed a large expansion of megakaryocyte colony-forming units derived from variant carriers and reduced proplatelet formation with abnormal cytoskeletal organization. The defect in proplatelet formation was also observed in control CD34+ cell-derived megakaryocytes transduced with lentiviral particles encoding mutant ETV6. Reduced expression levels of key regulators of the actin cytoskeleton CDC42 and RHOA were measured. Moreover, changes in the actin structures are typically accompanied by a rounder platelet shape with a highly heterogeneous size, decreased platelet arachidonic response, and spreading and retarded clot retraction in ETV6 deficient platelets. Elevated numbers of circulating CD34+ cells were found in p.P214L and p.Y401N carriers, and two patients from different families suffered from refractory anemia with excess blasts, while one patient from a third family was successfully treated for acute myeloid leukemia. Overall, our study provides novel insights into the role of ETV6 as a driver of cytoskeletal regulatory gene expression during platelet production, and the impact of variants resulting in platelets with altered size, shape and function and potentially also in changes in circulating progenitor levels.

Loss of p53 induces leukemic transformation in a murine model of Jak2 V617F-driven polycythemia vera

As leukemic transformation of myeloproliferative neoplasms (MPNs) worsens the clinical outcome, reducing the inherent risk of the critical event in MPN cases could be beneficial. Among genetic alterations concerning the transformation, the frequent one is TP53 mutation. Here we show that retroviral overexpression of Jak2 V617F mutant into wild-type p53 murine bone marrow cells induced polycythemia vera (PV) in the recipient mice, whereas Jak2 V617F-transduced p53-null mice developed lethal leukemia after the preceding PV phase. The leukemic mice had severe anemia, hepatosplenomegaly, pulmonary hemorrhage and expansion of dysplastic erythroid progenitors. Primitive leukemia cells (c-kit⁺Sca1⁺Lin^- (KSL) and CD34^-CD16/32^-c-kit⁺Sca1^-Lin^- (megakaryocyte-erythroid progenitor; MEP)) and erythroid progenitors (CD71⁺) from Jak2 V617F-transduced p53-null leukemic mice had leukemia-initiating capacity, however, myeloid differentiated populations (Mac-1⁺) could not recapitulate the disease. Interestingly, recipients transplanted with CD71⁺ cells rapidly developed erythroid leukemia, which was in sharp contrast to leukemic KSL cells to cause lethal leukemia after the polycythemic state. The leukemic CD71⁺ cells were more sensitive to INCB18424, a potent JAK inhibitor, than KSL cells. p53 restoration could ameliorate Jak2 V617F-transduced p53-null erythroleukemia. Taken together, our results show that p53 loss is sufficient for inducing leukemic transformation in Jak2 V617F-positive MPN.

High chromosomal instability in workers occupationally exposed to solvents and paint removers

BACKGROUND

Painters are exposed to an extensive variety of harmful substances like aromatic hydrocarbons used as solvents and paint removers, some of which have shown clastogenic activity. These substances constitute a complex mixture of chemicals which contain well-known genotoxicants, such as Benzene, Toluene and Xylene. Thus, chronic occupational exposure to such substances may be considered to possess genotoxic risk. In Colombia the information available around the genotoxic damage (Chromosomal and DNA damage) in car paint shop workers is limited and the knowledge of this damage could contribute not only to a better understanding of the carcinogenic effect of this kind of substances but also could be used as biomarkers of occupational exposure to genotoxic agents.

RESULTS

In this study, the genotoxic effect of aromatic hydrocarbons was assessed in peripheral blood lymphocytes of 24 workers occupationally exposed and 24 unexposed donors, by using Cytogenetic analysis and comet assay. A high frequency of Chromosomal alterations was found in the exposed group in comparison with those observed in the unexposed group. Among the total of CAs observed in the exposed group, fragilities were most frequently found (100 %), followed by chromosomal breaks (58 %), structural (41.2 %) and numerical chromosomal alterations (21 %). Numerical chromosomal alterations, fragilities and chromosomal breaks showed significant differences between exposed and unexposed groups. Among the fragilities, fra(9)(q12) was the most frequently observed. DNA damage index was also significantly higher in the exposed group compared to the unexposed group (p < 0.000).

CONCLUSIONS

Our results revealed that occupational exposure to aromatic hydrocarbons is significantly associated with Chromosomal and DNA damage in car paint shops workers and are also indicative of high chromosomal instability. The high frequency of both Chromosomal Alterations and DNA Damage Index observed in this study indicates an urgent need of intervention not only to prevent the increased risk of developing cancer but also to the application of strict health control and motivation to the use of appropriate protecting devices during work.

Reconstruction of ancestral chromosome architecture and gene repertoire reveals principles of genome evolution in a model yeast genus

Reconstructing genome history is complex but necessary to reveal quantitative principles governing genome evolution. Such reconstruction requires recapitulating into a single evolutionary framework the evolution of genome architecture and gene repertoire. Here, we reconstructed the genome history of the genus Lachancea that appeared to cover a continuous evolutionary range from closely related to more diverged yeast species. Our approach integrated the generation of a high-quality genome data set; the development of AnChro, a new algorithm for reconstructing ancestral genome architecture; and a comprehensive analysis of gene repertoire evolution. We found that the ancestral genome of the genus Lachancea contained eight chromosomes and about 5173 protein-coding genes. Moreover, we characterized 24 horizontal gene transfers and 159 putative gene creation events that punctuated species diversification. We retraced all chromosomal rearrangements, including gene losses, gene duplications, chromosomal inversions and translocations at single gene resolution. Gene duplications outnumbered losses and balanced rearrangements with 1503, 929, and 423 events, respectively. Gene content variations between extant species are mainly driven by differential gene losses, while gene duplications remained globally constant in all lineages. Remarkably, we discovered that balanced chromosomal rearrangements could be responsible for up to 14% of all gene losses by disrupting genes at their breakpoints. Finally, we found that nonsynonymous substitutions reached fixation at a coordinated pace with chromosomal inversions, translocations, and duplications, but not deletions. Overall, we provide a granular view of genome evolution within an entire eukaryotic genus, linking gene content, chromosome rearrangements, and protein divergence into a single evolutionary framework.

Current Role of Genetics in Hematologic Malignancies

Rapidly changing field of genetic technology and its application in the management of hematological malignancies has brought significant improvement in treatment and outcome of these disorders. Today, genetics plays pivotal role in diagnosis and prognostication of most hematologic neoplasms. The utilization of genetic tests in deciding specific treatment of various hematologic malignancies as well as for evaluation of depth of treatment response is rapidly advancing. Therefore, it is imperative for practitioners working in the field of hemato-oncology to have sufficient understanding of the basic concepts of genetics in order to comprehend upcoming molecular research in this area and to translate the same for patient care.

Why it is crucial to analyze non clonal chromosome aberrations or NCCAs?

Current cytogenetics has largely focused its efforts on the identification of recurrent karyotypic alterations, also known as clonal chromosomal aberrations (CCAs). The rationale of doing so seems simple: recurrent genetic changes are relevant for diseases or specific physiological conditions, while non clonal chromosome aberrations (NCCAs) are insignificant genetic background or noise. However, in reality, the vast majority of chromosomal alterations are NCCAs, and it is challenging to identify commonly shared CCAs in most solid tumors. Furthermore, the karyotype, rather than genes, represents the system inheritance, or blueprint, and each NCCA represents an altered genome system. These realizations underscore the importance of the re-evaluation of NCCAs in cytogenetic analyses. In this concept article, we briefly review the definition of NCCAs, some historical misconceptions about them, and why NCCAs are not insignificant "noise," but rather a highly significant feature of the cellular population for providing genome heterogeneity and complexity, representing one important form of fuzzy inheritance. The frequencies of NCCAs also represent an index to measure both internally- and environmentally-induced genome instability. Additionally, the NCCA/CCA cycle is associated with macro- and micro-cellular evolution. Lastly, elevated NCCAs are observed in many disease/illness conditions. Considering all of these factors, we call for the immediate action of studying and reporting NCCAs. Specifically, effort is needed to characterize and compare different types of NCCAs, to define their baseline in various tissues, to develop methods to access mitotic cells, to re-examine/interpret the NCCAs data, and to develop an NCCA database.

Saliva as a sampling source for the detection of leukemic fusion transcripts

Background

Saliva has long been used as a sampling source for clinical diagnosis of oral disease such as oral squamous cell carcinoma, or therapeutic drug monitoring. The aims of this study was to ascertain if saliva RNA could be stored at room temperature and to study if saliva could be a convenient source for fusion transcripts in leukemic patients.

Methods

This is a cross-sectional diagnostic study. We first developed a Saliva RNA tube for stable storage of whole saliva RNA at room temperature. Then we detected the leukemic fusions in the whole saliva from seven leukemic patients and twenty healthy volunteers, and compared with the results obtained from the bone marrow of the patients.

Results

Human gene transcripts could be reproducibly detected in the whole saliva for at least four weeks when stored in the developed composition at room temperature. Concordant results of the fusion transcripts were obtained between the saliva and the bone marrow in the seven leukemic patients and no fusions were detected in the healthy controls.

Conclusions

The results support our hypothesis that human whole saliva could be a reliable and convenient sampling source for the detection of leukemic fusions.

Chromosomal instability (CIN): what it is and why it is crucial to cancer evolution

Results of various cancer genome sequencing projects have "unexpectedly" challenged the framework of the current somatic gene mutation theory of cancer. The prevalence of diverse genetic heterogeneity observed in cancer questions the strategy of focusing on contributions of individual gene mutations. Much of the genetic heterogeneity in tumors is due to chromosomal instability (CIN), a predominant hallmark of cancer. Multiple molecular mechanisms have been attributed to CIN but unifying these often conflicting mechanisms into one general mechanism has been challenging. In this review, we discuss multiple aspects of CIN including its definitions, methods of measuring, and some common misconceptions. We then apply the genome-based evolutionary theory to propose a general mechanism for CIN to unify the diverse molecular causes. In this new evolutionary framework, CIN represents a system behavior of a stress response with adaptive advantages but also serves as a new potential cause of further destabilization of the genome. Following a brief review about the newly realized functions of chromosomes that defines system inheritance and creates new genomes, we discuss the ultimate importance of CIN in cancer evolution. Finally, a number of confusing issues regarding CIN are explained in light of the evolutionary function of CIN.

Interaction of c-Myb with p300 is required for the induction of acute myeloid leukemia (AML) by human AML oncogenes

A mutation preventing interaction between c-Myb and p300 prevents transformation and leukemia induction by MLL-AF9 and AML1-ETO9a oncogenes. Identifying agents that block the c-Myb-p300 interaction may be a valuable approach to developing a therapy for acute myeloid leukemia.

Control of transcriptional elongation

Elongation is becoming increasingly recognized as a critical step in eukaryotic transcriptional regulation. Although traditional genetic and biochemical studies have identified major players of transcriptional elongation, our understanding of the importance and roles of these factors is evolving rapidly through the recent advances in genome-wide and single-molecule technologies. Here, we focus on how elongation can modulate the transcriptional outcome through the rate-liming step of RNA polymerase II (Pol II) pausing near promoters and how the participating factors were identified. Among the factors we describe are the pausing factors--NELF (negative elongation factor) and DSIF (DRB sensitivity-inducing factor)--and P-TEFb (positive elongation factor b), which is the key player in pause release. We also describe the high-resolution view of Pol II pausing and propose nonexclusive models for how pausing is achieved. We then discuss Pol II elongation through the bodies of genes and the roles of FACT and SPT6, factors that allow Pol II to move through nucleosomes.

The little elongation complex functions at initiation and elongation phases of snRNA gene transcription

The small nuclear RNA (snRNA) genes have been widely used as a model system for understanding transcriptional regulation due to the unique aspects of their promoter structure, selectivity for either RNA polymerase (Pol) II or III, and because of their unique mechanism of termination that is tightly linked with the promoter. Recently, we identified the little elongation complex (LEC) in Drosophila that is required for the expression of Pol II-transcribed snRNA genes. Here, using Drosophila and mammalian systems, we provide genetic and molecular evidence that LEC functions in at least two phases of snRNA transcription: an initiation step requiring the ICE1 subunit, and an elongation step requiring ELL.

Understanding spatial organizations of chromosomes via statistical analysis of Hi-C data

Understanding how chromosomes fold provides insights into the transcription regulation, hence, the functional state of the cell. Using the next generation sequencing technology, the recently developed Hi-C approach enables a global view of spatial chromatin organization in the nucleus, which substantially expands our knowledge about genome organization and function. However, due to multiple layers of biases, noises and uncertainties buried in the protocol of Hi-C experiments, analyzing and interpreting Hi-C data poses great challenges, and requires novel statistical methods to be developed. This article provides an overview of recent Hi-C studies and their impacts on biomedical research, describes major challenges in statistical analysis of Hi-C data, and discusses some perspectives for future research.

[Models of oncogenesis: an endless world?]

From the second part of the 20th century, our knowledge of tumor biology widely benefited of tremendous progress in genetics (oncogenes, tumor suppressor genes, chromosomal abnormalities, etc), then in complex epigenetic process that regulates gene expression. Other players have entered the field of oncology and are now considered for their potential therapeutic interest: energetic metabolism, cancer stem cells as sources of tumor recurrence, microenvironment and above all intratumor heterogeneity. A better understanding of these domains of fundamental oncology should not mask the notion that a tumor is a living entity, which obeys the rules of Darwinian evolution.

Topoisomerase II-mediated DNA cleavage and mutagenesis activated by nitric oxide underlie the inflammation-associated tumorigenesis

AIMS

Both cancer-suppressing and cancer-promoting properties of reactive nitrogen and oxygen species (RNOS) have been suggested to play a role in tumor pathology, particularly those activities associated with chronic inflammation. Here, we address the impact of nitric oxide (NO) on the induction of DNA damage and genome instability with a specific focus on the involvement of topoisomerase II (TOP2). We also investigate the contribution of NO to the formation of skin melanoma in mice.

RESULTS

Similar to the TOP2-targeting drug, etoposide (VP-16), the NO-donor, S-nitrosoglutathione (GSNO), induces skin melanomas formation in 7,12-dimethyl- benz[a]anthracene (DMBA)-initiated mice. To explore the mechanism(s) underlying this NO-induced tumorigenesis, we use a co-culture model system to demonstrate that inflamed macrophages with inducible NO synthase (iNOS) expression cause γ-H2AX activation, p53 phosphorylation, and chromosome DNA breaks in the target cells. Inhibitor experiments revealed that NO and TOP2 isozymes are responsible for the above described cellular phenotypes. Notably, NO, unlike VP-16, preferentially induces the formation of TOP2β cleavable complexes (TOP2βcc) in cells. Moreover, GSNO induced TOP2-dependent DNA sequence rearrangements and cytotoxicity. Furthermore, the incidences of GSNO- and VP-16-induced skin melanomas were also observed to be lower in the skin-specific top2β-knockout mice. Our results suggest that TOP2 isozymes contribute to NO-induced mutagenesis and subsequent cancer development during chronic inflammation.

INNOVATION AND CONCLUSIONS

We provide the first experimental evidence for the functional role of TOP2 in NO-caused DNA damage, mutagenesis, and carcinogenesis. Notably, these studies contribute to our molecular understanding of the cancer-promoting actions of RNOS during chronic inflammation.

Leukemic transformation by the MLL-AF6 fusion oncogene requires the H3K79 methyltransferase Dot1l

The t(6;11)(q27;q23) is a recurrent chromosomal rearrangement that encodes the MLLAF6 fusion oncoprotein and is observed in patients with diverse hematologic malignancies. The presence of the t(6;11)(q27;q23) has been linked to poor overall survival in patients with AML. In this study, we demonstrate that MLL-AF6 requires continued activity of the histone-methyltransferase DOT1L to maintain expression of the MLL-AF6-driven oncogenic gene-expression program. Using gene-expression analysis and genome-wide chromatin immunoprecipitation studies followed by next generation sequencing, we found that MLL-fusion target genes display markedly high levels of histone 3 at lysine 79 (H3K79) dimethylation in murine MLL-AF6 leukemias as well as in ML2, a human myelomonocytic leukemia cell line bearing the t(6;11)(q27;q23) translocation. Targeted disruption of Dot1l using a conditional knockout mouse model inhibited leukemogenesis mediated by the MLL-AF6 fusion oncogene. Moreover, both murine MLL-AF6-transformed cells as well as the human MLL-AF6-positive ML2 leukemia cell line displayed specific sensitivity to EPZ0004777, a recently described, selective, small-molecule inhibitor of Dot1l. Dot1l inhibition resulted in significantly decreased proliferation, decreased expression of MLL-AF6 target genes, and cell cycle arrest of MLL-AF6-transformed cells. These results indicate that patients bearing the t(6;11)(q27;q23) translocation may benefit from therapeutic agents targeting aberrant H3K79 methylation.

New fusion transcripts identified in normal karyotype acute myeloid leukemia

Genetic aberrations contribute to acute myeloid leukemia (AML). However, half of AML cases do not contain the well-known aberrations detectable mostly by cytogenetic analysis, and these cases are classified as normal karyotype AML. Different outcomes of normal karyotype AML suggest that this subgroup of AML could be genetically heterogeneous. But lack of genetic markers makes it difficult to further study this subgroup of AML. Using paired-end RNAseq method, we performed a transcriptome analysis in 45 AML cases including 29 normal karyotype AML, 8 abnormal karyotype AML and 8 AML without karyotype informaiton. Our study identified 134 fusion transcripts, all of which were formed between the partner genes adjacent in the same chromosome and distributed at different frequencies in the AML cases. Seven fusions are exclusively present in normal karyotype AML, and the rest fusions are shared between the normal karyotype AML and abnormal karyotype AML. CIITA, a master regulator of MHC class II gene expression and truncated in B-cell lymphoma and Hodgkin disease, is found to fuse with DEXI in 48% of normal karyotype AML cases. The fusion transcripts formed between adjacent genes highlight the possibility that certain such fusions could be involved in oncological process in AML, and provide a new source to identify genetic markers for normal karyotype AML.

Deregulated expression of EVI1 defines a poor prognostic subset of MLL-rearranged acute myeloid leukemias: a study of the German-Austrian Acute Myeloid Leukemia Study Group and the Dutch-Belgian-Swiss HOVON/SAKK Cooperative Group

PURPOSE

To evaluate the prognostic value of ecotropic viral integration 1 gene (EVI1) overexpression in acute myeloid leukemia (AML) with MLL gene rearrangements.

PATIENTS AND METHODS

We identified 286 patients with AML with t(11q23) enrolled onto German-Austrian Acute Myeloid Leukemia Study Group and Dutch-Belgian-Swiss Hemato-Oncology Cooperative Group prospective treatment trials. Material was available from 177 AML patients for EVI1 expression analysis.

RESULTS

We divided 286 MLL-rearranged AMLs into three subgroups: t(9;11)(p22;q23) (44.8%), t(6;11)(q27;q23) (14.7%), and t(v;11q23) (40.5%). EVI1 overexpression (EVI1(+)) was found in 45.8% of all patients with t(11q23), with t(6;11) showing the highest frequency (83.9%), followed by t(9;11) at 40.0%, and t(v;11q23) at 34.8%. Concurrent gene mutations were rare or absent in all three subgroups. Within all t(11q23) AMLs, EVI1(+) was the sole prognostic factor, predicting for inferior overall survival (OS; hazard ratio [HR], 2.06; P = .003), relapse-free survival (HR, 2.28; P = .002), and event-free survival (HR, 1.79; P = .009). EVI1(+) AMLs with t(11q23) in first complete remission (CR) had a significantly better outcome after allogeneic transplantation compared with other consolidation therapies (5-year OS, 54.7% v 0%; Mantel-Byar, P = .0006). EVI1(-) t(9;11) AMLs had lower WBC counts, more commonly FAB M5 morphology, and frequently had additional trisomy 8 (39.6%; P < .001). Among t(9;11) AMLs, EVI1(+) again was the sole independent adverse prognostic factor for survival.

CONCLUSION

Deregulated EVI1 expression defines poor prognostic subsets among AML with t(11q23) and AML with t(9;11)(p22;q23). Patients with EVI1(+) MLL-rearranged AML seem to benefit from allogeneic transplantation in first CR.

BET domain co-regulators in obesity, inflammation and cancer

The bromodomain is a highly conserved motif of 110 amino acids that is bundled into four anti-parallel α-helices and found in proteins that interact with chromatin, such as transcription factors, histone acetylases and nucleosome remodelling complexes. Bromodomain proteins are chromatin 'readers'; they recruit chromatin-regulating enzymes, including 'writers' and 'erasers' of histone modification, to target promoters and to regulate gene expression. Conventional wisdom held that complexes involved in chromatin dynamics are not 'druggable' targets. However, small molecules that inhibit bromodomain and extraterminal (BET) proteins have been described. We examine these developments and discuss the implications for small molecule epigenetic targeting of chromatin networks in cancer.

Oncogenomics methods and resources

Today, cancer is viewed as a genetic disease and many genetic mechanisms of oncogenesis are known. The progression from normal tissue to invasive cancer is thought to occur over a timescale of 5-20 years. This transformation is driven by both inherited genetic factors and somatic genetic alterations and mutations, and it results in uncontrolled cell growth and, in many cases, death. In this article, we review the main types of genomic and genetic alterations involved in cancer, namely copy-number changes, genomic rearrangements, somatic mutations, polymorphisms, and epigenomic alterations in cancer. We then discuss the transcriptomic consequences of these alterations in tumor cells. The use of "next-generation" sequencing methods in cancer research is described in the relevant sections. Finally, we discuss different approaches for candidate prioritization and integration and analysis of these complex data.

Evolutionary mechanisms and diversity in cancer

The recently introduced genome theory of cancer evolution provides a new framework for evolutionary studies on cancer. In particular, the established relationship between the large number of individual molecular mechanisms and the general evolutionary mechanism of cancer calls upon a change in our strategies that have been based on the characterization of common cancer gene mutations and their defined pathways. To further explain the significance of the genome theory of cancer evolution, a brief review will be presented describing the various attempts to illustrate the evolutionary mechanism of cancer, followed by further analysis of some key components of somatic cell evolution, including the diversity of biological systems, the multiple levels of information systems and control systems, the two phases (the punctuated or discontinuous phase and gradual Darwinian stepwise phase) and dynamic patterns of somatic cell evolution where genome replacement is the driving force. By linking various individual molecular mechanisms to the level of genome population diversity and tumorigenicity, the general mechanism of cancer has been identified as the evolutionary mechanism of cancer, which can be summarized by the following three steps including stress-induced genome instability, population diversity or heterogeneity, and genome-mediated macroevolution. Interestingly, the evolutionary mechanism is equal to the collective aggregate of all individual molecular mechanisms. This relationship explains why most of the known molecular mechanisms can contribute to cancer yet there is no single dominant mechanism for the majority of clinical cases. Despite the fact that each molecular mechanism can serve as a system stress and initiate the evolutionary process, to achieve cancer, multiple cycles of genome-mediated macroevolution are required and are a stochastically determined event. Finally, the potential clinical implications of the evolutionary mechanism of cancer are briefly reviewed.

The COMPASS family of histone H3K4 methylases: mechanisms of regulation in development and disease pathogenesis

The Saccharomyces cerevisiae Set1/COMPASS was the first histone H3 lysine 4 (H3K4) methylase identified over 10 years ago. Since then, it has been demonstrated that Set1/COMPASS and its enzymatic product, H3K4 methylation, is highly conserved across the evolutionary tree. Although there is only one COMPASS in yeast, Drosophila possesses three and humans bear six COMPASS family members, each capable of methylating H3K4 with nonredundant functions. In yeast, the histone H2B monoubiquitinase Rad6/Bre1 is required for proper H3K4 and H3K79 trimethylations. The machineries involved in this process are also highly conserved from yeast to human. In this review, the process of histone H2B monoubiquitination-dependent and -independent histone H3K4 methylation as a mark of active transcription, enhancer signatures, and developmentally poised genes is discussed. The misregulation of histone H2B monoubiquitination and H3K4 methylation result in the pathogenesis of human diseases, including cancer. Recent findings in this regard are also examined.

Functionally recurrent rearrangements of the MAST kinase and Notch gene families in breast cancer

Breast cancer is a heterogeneous disease, exhibiting a wide range of molecular aberrations and clinical outcomes. Here we employed paired-end transcriptome sequencing to explore the landscape of gene fusions in a panel of breast cancer cell lines and tissues. We observed that individual breast cancers harbor an array of expressed gene fusions. We identified two classes of recurrent gene rearrangements involving microtubule associated serine-threonine kinase (MAST) and Notch family genes. Both MAST and Notch family gene fusions exerted significant phenotypic effects in breast epithelial cells. Breast cancer lines harboring Notch gene rearrangements are uniquely sensitive to inhibition of Notch signaling, and over-expression of MAST1 or MAST2 gene fusions had a proliferative effect both in vitro and in vivo. These findings illustrate that recurrent gene rearrangements play significant roles in subsets of carcinomas and suggest that transcriptome sequencing may serve to identify patients with rare, actionable gene fusions.

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.