Retroviral insertional mutagenesis identifies genes that collaborate with NUP98-HOXD13 during leukemic transformation

Summary of animal models of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a malignant tumor of the hematological system characterized by long-term, progressive refractory hemocytopenia. In addition, the risk of leukemia is high, and once it develops, the course of acute leukemia is short with poor curative effect. Animal models are powerful tools for studying human diseases and are highly effective preclinical platforms. Animal models of MDS can accurately show genetic aberrations and hematopoietic clone phenotypes with similar cellular features (such as impaired differentiation and increased apoptosis), and symptoms can be used to assess existing treatments. Animal models are also helpful for understanding the pathogenesis of MDS and its relationship with acute leukemia, which helps with the identification of candidate genes related to the MDS phenotype. This review summarizes the current status of animal models used to research myelodysplastic syndrome (MDS).

A unique mutator phenotype reveals complementary oncogenic lesions leading to acute leukemia

Mice homozygous for a hypomorphic allele of DNA replication factor minichromosome maintenance protein 2 (designated Mcm2cre/cre) develop precursor T cell lymphoblastic leukemia/lymphoma (pre-T LBL) with 4-32 small interstitial deletions per tumor. Mice that express a NUP98-HOXD13 (NHD13) transgene develop multiple types of leukemia, including myeloid and T and B lymphocyte. All Mcm2cre/cre NHD13+ mice develop pre-T LBL, and 26% develop an unrelated, concurrent B cell precursor acute lymphoblastic leukemia (BCP-ALL). Copy number alteration (CNA) analysis demonstrated that pre-T LBLs were characterized by homozygous deletions of Pten and Tcf3 and partial deletions of Notch1 leading to Notch1 activation. In contrast, BCP-ALLs were characterized by recurrent deletions involving Pax5 and Ptpn1 and copy number gain of Abl1 and Nup214 resulting in a Nup214-Abl1 fusion. We present a model in which Mcm2 deficiency leads to replicative stress, DNA double strand breaks (DSBs), and resultant CNAs due to errors in DNA DSB repair. CNAs that involve critical oncogenic pathways are then selected in vivo as malignant lymphoblasts because of a fitness advantage. Some CNAs, such as those involving Abl1 and Notch1, represent attractive targets for therapy.

Transforming activities of the NUP98-KMT2A fusion gene associated with myelodysplasia and acute myeloid leukemia

Inv(11)(p15q23), found in myelodysplastic syndromes and acute myeloid leukemia, leads to expression of a fusion protein consisting of the N-terminal of nucleoporin 98 (NUP98) and the majority of the lysine methyltransferase 2A (KMT2A). To explore the transforming potential of this fusion we established inducible iNUP98-KMT2A transgenic mice. After a median latency of 80 weeks, over 90% of these mice developed signs of disease, with anemia and reduced bone marrow cellularity, increased white blood cell numbers, extramedullary hematopoiesis, and multilineage dysplasia. Additionally, induction of iNUP98-KMT2A led to elevated lineage marker-negative Sca-1⁺ c-Kit⁺ cell numbers in the bone marrow, which outcompeted wildtype cells in repopulation assays. Six iNUP98-KMT2A mice developed transplantable acute myeloid leukemia with leukemic blasts infiltrating multiple organs. Notably, as reported for patients, iNUP98-KMT2A leukemic blasts did not express increased levels of the HoxA-B-C gene cluster, and in contrast to KMT2A-AF9 leukemic cells, the cells were resistant to pharmacological targeting of menin and BET family proteins by MI-2-2 or JQ1, respectively. Expression of iNUP98-KMT2A in mouse embryonic fibroblasts led to an accumulation of cells in G1 phase, and abrogated replicative senescence. In bone marrow-derived hematopoietic progenitors, iNUP98-KMT2A expression similarly resulted in increased cell numbers in the G1 phase of the cell cycle, with aberrant gene expression of Sirt1, Tert, Rbl2, Twist1, Vim, and Prkcd, mimicking that seen in mouse embryonic fibroblasts. In summary, we demonstrate that iNUP98-KMT2A has in vivo transforming activity and interferes with cell cycle progression rather than primarily blocking differentiation.

Meningioma 1 is indispensable for mixed lineage leukemia-rearranged acute myeloid leukemia

Mixed lineage leukemia (MLL/KMT2A) rearrangements (MLL-r) are one of the most frequent chromosomal aberrations in acute myeloid leukemia. We evaluated the function of Meningioma 1 (MN1), a co-factor of HOXA9 and MEIS1, in human and murine MLL-rearranged leukemia by CRISPR-Cas9 mediated deletion of MN1. MN1 was required for in vivo leukemogenicity of MLL positive murine and human leukemia cells. Loss of MN1 inhibited cell cycle and proliferation, promoted apoptosis and induced differentiation of MLL-rearranged cells. Expression analysis and chromatin immunoprecipitation with sequencing from previously reported data sets demonstrated that MN1 primarily maintains active transcription of HOXA9 and HOXA10, which are critical downstream genes of MLL, and their target genes like BCL2, MCL1 and Survivin. Treatment of MLL-rearranged primary leukemia cells with anti-MN1 siRNA significantly reduced their clonogenic potential in contrast to normal CD34⁺ hematopoietic progenitor cells, suggesting a therapeutic window for MN1 targeting. In summary, our findings demonstrate that MN1 plays an essential role in MLL fusion leukemias and serve as a therapeutic target in MLL-rearranged acute myeloid leukemia.

Paralogous HOX13 Genes in Human Cancers

Hox genes (HOX in humans), an evolutionary preserved gene family, are key determinants of embryonic development and cell memory gene program. Hox genes are organized in four clusters on four chromosomal loci aligned in 13 paralogous groups based on sequence homology (Hox gene network). During development Hox genes are transcribed, according to the rule of “spatio-temporal collinearity”, with early regulators of anterior body regions located at the 3’ end of each Hox cluster and the later regulators of posterior body regions placed at the distal 5’ end. The onset of 3’ Hox gene activation is determined by Wingless-type MMTV integration site family (Wnt) signaling, whereas 5’ Hox activation is due to paralogous group 13 genes, which act as posterior-inhibitors of more anterior Hox proteins (posterior prevalence). Deregulation of HOX genes is associated with developmental abnormalities and different human diseases. Paralogous HOX13 genes (HOX A13, HOX B13, HOX C13 and HOX D13) also play a relevant role in tumor development and progression. In this review, we will discuss the role of paralogous HOX13 genes regarding their regulatory mechanisms during carcinogenesis and tumor progression and their use as biomarkers for cancer diagnosis and treatment.

The Meningioma 1 (MN1) Gene is an Independent Poor Prognostic Factor in Adult Egyptian Acute Myeloid Leukemia Patients

Aim:

To determine the prognostic importance of meningioma 1 (MN1) gene expression levels in the context of other predictive markers for acute myeloid leukemia (AML) cases.

Methods:

MN1 expression was measured in 85 newly diagnosed adults younger than 60 years by real-time reverse-transcriptase polymerase chain reaction.

Results:

At diagnosis 67.4% of cases had elevated MN1 expression, this being associated with a worse prognosis, higher incidence of lymphadenopathy and CD34 transcript expression (p=0.02 and <0.001, respectively). No other molecular or clinical characteristics were significantly associated with MN1expression. Patients with high MN1 expression had lower complete response rate at day 15 compared to patients with low MN1 expression (p=0.09) and a significantly higher relapse rate (21.1% versus 7.7%, respectively, p=0.04). Patients with high MN1 expression had shorter TTP compared to those with low expression, p= 0.07.

Conclusion:

MN1 expression may predict outcome in AML patients. The MN1 gene and micro RNA expression suggest a biological feature that could be used as therapeutic targets.

NUP98 Fusion Proteins Interact with the NSL and MLL1 Complexes to Drive Leukemogenesis

The nucleoporin 98 gene (NUP98) is fused to a variety of partner genes in multiple hematopoietic malignancies. Here, we demonstrate that NUP98 fusion proteins, including NUP98-HOXA9 (NHA9), NUP98-HOXD13 (NHD13), NUP98-NSD1, NUP98-PHF23, and NUP98-TOP1 physically interact with mixed lineage leukemia 1 (MLL1) and the non-specific lethal (NSL) histone-modifying complexes. Chromatin immunoprecipitation sequencing illustrates that NHA9 and MLL1 co-localize on chromatin and are found associated with Hox gene promoter regions. Furthermore, MLL1 is required for the proliferation of NHA9 cells in vitro and in vivo. Inactivation of MLL1 leads to decreased expression of genes bound by NHA9 and MLL1 and reverses a gene expression signature found in NUP98-rearranged human leukemias. Our data reveal a molecular dependency on MLL1 function in NUP98-fusion-driven leukemogenesis.

The Ras/Rap GTPase activating protein RASA3: from gene structure to in vivo functions

RASA3 (or GTPase Activating Protein III, R-Ras GTPase-activating protein, GAP1(IP4BP)) is a GTPase activating protein of the GAP1 subfamily which targets Ras and Rap1. RASA3 was originally purified from pig platelet membranes through its intrinsic ability to bind inositol 1,3,4,5-tetrakisphosphate (I(1,3,4,5)P4) with high affinity, hence its first name GAP1(IP4BP) (for GAP1 subfamily member which binds I(1,3,4,5)P4). RASA3 was thus the first I(1,3,4,5)P4 receptor identified and cloned. The in vitro and in vivo functions of RASA3 remained somewhat elusive for a long time. However, recently, using genetically-modified mice and cells derived from these mice, the function of RASA3 during megakaryopoiesis, megakaryocyte adhesion and migration as well as integrin signaling has been reported. The goal of this review is thus to summarize and comment recent and less recent data in the literature on RASA3, in particular on the in vivo function of this specific GAP1 subfamily member.

Constitutive IRF8 expression inhibits AML by activation of repressed immune response signaling

Myeloid differentiation is blocked in acute myeloid leukemia (AML), but the molecular mechanisms are not well characterized. Meningioma 1 (MN1) is overexpressed in AML patients and confers resistance to all-trans retinoic acid-induced differentiation. To understand the role of MN1 as a transcriptional regulator in myeloid differentiation, we fused transcriptional activation (VP16) or repression (M33) domains with MN1 and characterized these cells in vivo. Transcriptional activation of MN1 target genes induced myeloproliferative disease with long latency and differentiation potential to mature neutrophils. A large proportion of differentially expressed genes between leukemic MN1 and differentiation-permissive MN1VP16 cells belonged to the immune response pathway like interferon-response factor (Irf) 8 and Ccl9. As MN1 is a cofactor of MEIS1 and retinoic acid receptor alpha (RARA), we compared chromatin occupancy between these genes. Immune response genes that were upregulated in MN1VP16 cells were co-targeted by MN1 and MEIS1, but not RARA, suggesting that myeloid differentiation is blocked through transcriptional repression of shared target genes of MN1 and MEIS1. Constitutive expression of Irf8 or its target gene Ccl9 identified these genes as potent inhibitors of murine and human leukemias in vivo. Our data show that MN1 prevents activation of the immune response pathway, and suggest restoration of IRF8 signaling as therapeutic target in AML.

Determining common insertion sites based on retroviral insertion distribution across tumors

A CIS (common insertion site) indicates a genome region that is hit more frequently by retroviral insertions than expected by chance. Such a region is strongly related to cancer gene loci, which leads to the detection of cancer genes. An algorithm for detecting CISs should satisfy the following: (1) it does not require any prior knowledge of underlying insertion distribution; (2) it can resolve the insertion biases caused by hotspots; (3) it can detect CISs of any biological width; (4) it can identify noises resulting from statistic mistakes and non-CIS insertions; and (5) it can identify the widths of CISs as accurately as possible. We develop a method to resolve these difficulties. We verify a region's significance from two perspectives: distribution width and distribution depth. The former indicates how many insertions in a region while the latter evaluates the insertion distribution across the tumors in a region. We compare our method with kernel density estimation and sliding window on the simulated data, showing that our method not only identifies cancer-related insertions effectively, but also filters noises correctly. The experiments on the real data show that taking insertion distribution into account can highlight significant CISs. We detect 53 novel CISs, some of which have been proven correct by the biological literature.

Nucleoporins and nucleocytoplasmic transport in hematologic malignancies

Hematologic malignancies are often associated with chromosomal rearrangements that lead to the expression of chimeric fusion proteins. Rearrangements of the genes encoding two nucleoporins, NUP98 and NUP214, have been implicated in the pathogenesis of several types of hematologic malignancies, particularly acute myeloid leukemia. NUP98 rearrangements result in fusion of an N-terminal portion of NUP98 to one of numerous proteins. These rearrangements often follow treatment with topoisomerase II inhibitors and tend to occur in younger patients. They have been shown to induce leukemia in mice and to enhance proliferation and disrupt differentiation in primary human hematopoietic precursors. NUP214 has only a few fusion partners. DEK-NUP214 is the most common NUP214 fusion in AML; it tends to occur in younger patients and is usually associated with FLT3 internal tandem duplications. The leukemogenic activity of NUP214 fusions is less well characterized. Normal nucleoporins, including NUP98 and NUP214, have important functions in nucleocytoplasmic transport, transcription, and mitosis. These functions and their disruptions by oncogenic nucleoporin fusions are discussed.

Animal models of leukemia: any closer to the real thing?

Animal models have been invaluable in the efforts to better understand and ultimately treat patients suffering from leukemia. While important insights have been gleaned from these models, limitations must be acknowledged. In this review, we will highlight the various animal models of leukemia and describe their contributions to the improved understanding and treatment of these cancers.

Haploinsufficiency of SAMD9L, an endosome fusion facilitator, causes myeloid malignancies in mice mimicking human diseases with monosomy 7

Monosomy 7 and interstitial deletion of 7q (-7/7q-) are well-recognized nonrandom chromosomal abnormalities frequently found among patients with myelodysplastic syndromes (MDSs) and myeloid leukemias. We previously identified candidate myeloid tumor suppressor genes (SAMD9, SAMD9-like = SAMD9L, and Miki) in the 7q21.3 subband. We established SAMD9L-deficient mice and found that SAMD9L(+/-) mice as well as SAMD9L(-/-) mice develop myeloid diseases resembling human diseases associated with -7/7q-. SAMD9L-deficient hematopoietic stem cells showed enhanced colony formation potential and in vivo reconstitution ability. SAMD9L localizes in early endosomes. SAMD9L-deficient cells showed delays in homotypic endosome fusion, resulting in persistence of ligand-bound cytokine receptors. These findings suggest that haploinsufficiency of SAMD9L and/or SAMD9 gene(s) contributes to myeloid transformation.

Association between genetic variants in pre-miRNA and colorectal cancer risk in a Chinese population

INTRODUCTION

Single-nucleotide polymorphisms (SNPs) in pre-miRNAs may alter microRNA expression levels or processing and then contribute to the susceptibility of cancer development. We hypothesized that SNPs in pre-miRNAs may be associated with the risk of colorectal cancer (CRC).

MATERIALS AND METHODS

We genotyped four common polymorphisms (i.e., rs11614913, rs3746444, rs2910164, and rs2292832) in pre-miRNAs of 353 CRC patients and 540 healthy controls to investigate the association between the SNPs and the risk of CRC using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay.

RESULTS

The rs11614913 CT, TT genotypes, and T allele were associated with an increased risk of CRC compared with the CC genotype and C allele (CT vs. CC: OR = 7.34, 95% CI 3.76-14.34; TT vs. CC: OR = 13.66, 95% CI 6.76-27.6; T vs. C: OR = 1.99, 95% CI 1.63-2.42, respectively). Interestingly, using the rs2910164 GG genotype as a reference, the rs2910164 GC genotype was associated with an increased risk of CRC (OR = 1.49, 95% CI 1.02-2.18), whereas the rs2910164 CC genotype was associated with a decreased risk of CRC (OR = 0.58, 95% CI 0.37-0.93). When compared with the rs2910164G allele, rs2910164 C allele was associated with a reduced risk of CRC (OR = 0.80, 95% CI 0.66-0.97, p = 0.02).

CONCLUSION

These findings suggest that rs11614913 and rs2910164 polymorphisms may be associated with the etiology of CRC.

Myelodysplastic syndrome: an inability to appropriately respond to damaged DNA?

Myelodysplastic syndrome (MDS) is considered a hematopoietic stem cell disease that is characterized by abnormal hematopoietic differentiation and a high propensity to develop acute myeloid leukemia. It is mostly associated with advanced age, but also with prior cancer therapy and inherited syndromes related to abnormalities in DNA repair. Recent technologic advances have led to the identification of a myriad of frequently occurring genomic perturbations associated with MDS. These observations suggest that MDS and its progression to acute myeloid leukemia is a genomic instability disorder, resulting from a stepwise accumulation of genetic abnormalities. The notion is now emerging that the underlying mechanism of this disease could be a defect in one or more pathways that are involved in responding to or repairing damaged DNA. In this review, we discuss these pathways in relationship to a large number of studies performed with MDS patient samples and MDS mouse models. Moreover, in view of our current understanding of how DNA damage response and repair pathways are affected by age in hematopoietic stem cells, we also explore how this might relate to MDS development.

Mapping of MN1 sequences necessary for myeloid transformation

The MN1 oncogene is deregulated in human acute myeloid leukemia and its overexpression induces proliferation and represses myeloid differentiation of primitive human and mouse hematopoietic cells, leading to myeloid leukemia in mouse models. To delineate the sequences within MN1 necessary for MN1-induced leukemia, we tested the transforming capacity of in-frame deletion mutants, using retroviral transduction of mouse bone marrow. We found that integrity of the regions between amino acids 12 to 458 and 1119 to 1273 are required for MN1's in vivo transforming activity, generating myeloid leukemia with some mutants also producing T-cell lympho-leukemia and megakaryocytic leukemia. Although both full length MN1 and a mutant that lacks the residues between 12-228 (Δ12-228 mutant) repressed myeloid differentiation and increased myeloproliferative activity in vitro, the mutant lost its transforming activity in vivo. Both MN1 and Δ12-228 increased the frequency of common myeloid progentiors (CMP) in vitro and microarray comparisons of purified MN1-CMP and Δ12-228-CMP cells showed many differentially expressed genes including Hoxa9, Meis1, Myb, Runx2, Cebpa, Cebpb and Cebpd. This collection of immediate MN1-responsive candidate genes distinguishes the leukemic activity from the in vitro myeloproliferative capacity of this oncoprotein.

A variant in microRNA-196a2 is not associated with susceptibility to and progression of colorectal cancer in Chinese

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNAs with regulatory functions as tumour suppressors and oncogenes. Although single nucleotide polymorphism (SNP) in miRNA regions have been reported to be rare and unlikely to be functionally important, recent evidence suggested that rs11614913 SNP in miR-196a2 was associated with the susceptibility of lung cancer, breast cancer, congenital heart disease and shortened survival time of non-small-cell lung cancer.

AIMS

The aim of this study was to investigate the association between this genetic variant and the risk and/or progression of colorectal cancer (CRC).

METHODS

A total of 126 CRC patients and 407 healthy controls was periodically enrolled. DNA was extracted from blood specimens, and miR-196a2 polymorphism was genotyped by polymerase chain reaction-ligation detection reaction (PCR-LDR).

RESULTS

Although the frequency of CC homozygotes or miR-196a2C allele-containing genotypes (CT and CC) was lower in CRC patients than in the healthy controls, no significant association between miR-196a2 polymorphism and the risk of CRC was found. The frequency of the 'C' allele in CRC patients was also not significantly lower than in healthy controls. In a subsequent analysis of the association between this polymorphism and the progression of CRC, there was still no significant difference in both genotype and allelic frequency.

CONCLUSIONS

Our results suggest that miR-196a2 polymorphism is not associated with both an increased risk and progression of CRC in Chinese.

Genetic and epigenetic factors in regulation of microRNA in colorectal cancers

Studies on miRNA profiling revealed that a large number of them are significantly deregulated in human cancers. The molecular mechanisms of this deregulation are not totally clarified, even if genetics and epigenetics are frequently involved. Single nucleotide polymorphisms (SNPs) are the most common type of genetic variation in the human genome. A SNP into miRNA gene might affect the transcription of primary miRNA, its processing and miRNA-mRNA interaction. We investigated the distribution of sequence variants of miR-146a, miR-196a2, miR-499 and miR-149 in colorectal cancer (CRC) and their effect on miRNA expression. Each variant was identified with HRM. For miR-499 we demonstrated a significant reduction of its expression in CRC connected to a specific genotype. To evaluate the epigenetic effects on miRNA genes in CRC, we investigated the influence of DNA methylation on miR-34b, miR-34c and miR-9-1 expression. We aimed to verify the relationship between the methylation status of these miRNA genes and their relative expression in tumor samples. For the quantification of DNA methylation we adopted a method based on Differential High Resolution Melting (D-HRM).

Three murine leukemia virus integration regions within 100 kilobases upstream of c-myb are proximal to the 5' regulatory region of the gene through DNA looping

Retroviruses integrated into genomic DNA participate in long-range gene activation from as far away as several hundred kilobases. Hypotheses have been put forth to account for these phenomena, but data have not been provided to support a physical mechanism that explains long-range activation. In murine leukemia virus-induced myeloid leukemia in mice, integrated proviruses have been found upstream of c-myb in three regions, named Mml1, Mml2, and Mml3 (25, 50, and 70 kb upstream, respectively). The transcription factor c-Myb is an oncogene whose dysregulation and/or mutation can lead to human leukemia. We hypothesized that the murine c-myb upstream region contains regulatory elements accessed by the retrovirus. To identify regulatory sites in the murine c-myb upstream region, we looked by chromatin immunoprecipitation with microarray technology (ChIP-on-chip) for histone modifications implicating gene activation in normal cells. H3K4me3, H3K4me1, and H3K9/14ac were enriched at Mml1 and/or Mml2 in the myeloblastic cell line M1, which expresses c-myb. The enrichment of all of these histone marks decreased with differentiation-induced downregulation of the gene in M1 cells but increased and spread in tumor cells containing integrated provirus. Importantly, using chromosome conformation capture (3C)-quantitative PCR assays, interactions between the 5' region, including the promoter and all Mml sites (Mml1, Mml2, and Mml3), were detected due to DNA looping in M1 cells and tumor cells with provirus in Mml1, Mml2, or Mml3. Therefore, our study provides a new mechanism of retrovirus insertional mutagenesis whereby spatial chromatin organization allows distally located provirus, with its own enhancer elements, to access the 5' regulatory region of the gene.

Sox4 cooperates with CREB in myeloid transformation

The cAMP response element-binding protein (CREB) is a nuclear transcription factor that is critical for normal and neoplastic hematopoiesis. Previous studies have demonstrated that CREB is a proto-oncogene whose overexpression promotes cellular proliferation in hematopoietic cells. Transgenic mice that overexpress CREB in myeloid cells develop a myeloproliferative disease with splenomegaly and aberrant myelopoiesis. However, CREB overexpressing mice do not spontaneously develop acute myeloid leukemia. In this study, we used retroviral insertional mutagenesis to identify genes that accelerate leukemia in CREB transgenic mice. Our mutagenesis screen identified several integration sites, including oncogenes Gfi1, Myb, and Ras. The Sox4 transcription factor was identified by our screen as a gene that cooperates with CREB in myeloid leukemogenesis. We show that the transduction of CREB transgenic mouse bone marrow cells with a Sox4 retrovirus increases survival and self-renewal of cells in vitro. Furthermore, leukemic blasts from the majority of acute myeloid leukemia patients have higher CREB, phosphorylated CREB, and Sox 4 protein expression. Sox4 transduction of mouse bone marrow cells results in increased expression of CREB target genes. We also demonstrate that CREB is a direct target of Sox4 by chromatin immunoprecipitation assays. These results indicate that Sox4 and CREB cooperate and contribute to increased proliferation of hematopoietic progenitor cells.

An insertional mutagenesis screen identifies genes that cooperate with Mll-AF9 in a murine leukemogenesis model

Patients with a t(9;11) translocation (MLL-AF9) develop acute myeloid leukemia (AML), and while in mice the expression of this fusion oncogene also results in the development of myeloid leukemia, it is with long latency. To identify mutations that cooperate with Mll-AF9, we infected neonatal wild-type (WT) or Mll-AF9 mice with a murine leukemia virus (MuLV). MuLV-infected Mll-AF9 mice succumbed to disease significantly faster than controls presenting predominantly with myeloid leukemia while infected WT animals developed predominantly lymphoid leukemia. We identified 88 candidate cancer genes near common sites of proviral insertion. Analysis of transcript levels revealed significantly elevated expression of Mn1, and a trend toward increased expression of Bcl11a and Fosb in Mll-AF9 murine leukemia samples with proviral insertions proximal to these genes. Accordingly, FOSB and BCL11A were also overexpressed in human AML harboring MLL gene translocations. FOSB was revealed to be essential for growth in mouse and human myeloid leukemia cells using shRNA lentiviral vectors in vitro. Importantly, MN1 cooperated with Mll-AF9 in leukemogenesis in an in vivo BM viral transduction and transplantation assay. Together, our data identified genes that define transcription factor networks and important genetic pathways acting during progression of leukemia induced by MLL fusion oncogenes.

Master regulatory GATA transcription factors: mechanistic principles and emerging links to hematologic malignancies

Numerous examples exist of how disrupting the actions of physiological regulators of blood cell development yields hematologic malignancies. The master regulator of hematopoietic stem/progenitor cells GATA-2 was cloned almost 20 years ago, and elegant genetic analyses demonstrated its essential function to promote hematopoiesis. While certain GATA-2 target genes are implicated in leukemogenesis, only recently have definitive insights emerged linking GATA-2 to human hematologic pathophysiologies. These pathophysiologies include myelodysplastic syndrome, acute myeloid leukemia and an immunodeficiency syndrome with complex phenotypes including leukemia. As GATA-2 has a pivotal role in the etiology of human cancer, it is instructive to consider mechanisms underlying normal GATA factor function/regulation and how dissecting such mechanisms may reveal unique opportunities for thwarting GATA-2-dependent processes in a therapeutic context. This article highlights GATA factor mechanistic principles, with a heavy emphasis on GATA-1 and GATA-2 functions in the hematopoietic system, and new links between GATA-2 dysregulation and human pathophysiologies.

PIM1 gene cooperates with human BCL6 gene to promote the development of lymphomas

Diffuse large B-cell lymphomas in humans are associated with chromosomal rearrangements (∼40%) and/or mutations disrupting autoregulation (∼16%) involving the BCL6 gene. Studies of lymphoma development in humans and mouse models have indicated that lymphomagenesis evolves through the accumulation of multiple genetic alterations. Based on our prior studies, which indicated that carcinogen-induced DNA mutations enhance the incidence of lymphomas in our mouse model expressing a human BCL6 transgene, we hypothesized that mutated genes are likely to play an important cooperative role in BCL6-associated lymphoma development. We used retroviral insertional mutagenesis in an effort to identify which genes cooperate with BCL6 in lymphomagenesis in our BCL6 transgenic mice. We identified PIM1 as the most frequently recurring cooperating gene in our murine BCL6-associated lymphomas (T- and B-cell types), and we observed elevated levels of PIM1 mRNA and protein expression in these neoplasms. Further, immunohistochemical staining, which was performed in 20 randomly selected BCL6-positive human B- and T-cell lymphomas, revealed concurrent expression of BCL6 and PIM1 in these neoplasms. As PIM1 encodes a serine/threonine kinase, PIM1 kinase inhibition may be a promising therapy for BCL6/PIM1-positive human lymphomas.

Update on cytogenetic and molecular changes in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis and a high propensity to transform to acute myeloid leukemia (AML). In the pathogenesis of the disease, both gene mutations and cytogenetic changes play an important role. The latter have been integrated into prognostic scoring systems including the IPSS (International Prognostic Scoring System) and WPSS (World Health Organization [WHO] classification-based Prognostic Scoring System). In these systems and in multivariate analyses comparing clinical and genetic data, complex karyotypes are associated with a particularly poor prognosis. del(5q) plays a distinct role by classifying the only genetically defined WHO subtype. Also, due to advancement in technology such as whole genome sequencing, the number of known mutations occurring in MDS is steadily increasing. Important recent discoveries include mutations in EZH2, DNMT3A, ASXL1 and IDH1/2. Like TET2, the most commonly mutated gene in MDS, all are involved in epigenetic regulation. Mutations such as ASXL1, RUNX1, EZH2, ETV6/TEL and TP53 have an adverse impact on patient overall survival. Early evidence suggests that some mutations might influence treatment response, necessitating reassessment of the prognostic effect of genetic alterations in the light of every new treatment. This review discusses clinical and biological effects of the most common cytogenetic and molecular aberrations in patients with MDS.

NUP98 gene fusions and hematopoietic malignancies: common themes and new biologic insights

Structural chromosomal rearrangements of the Nucleoporin 98 gene (NUP98), primarily balanced translocations and inversions, are associated with a wide array of hematopoietic malignancies. NUP98 is known to be fused to at least 28 different partner genes in patients with hematopoietic malignancies, including acute myeloid leukemia, chronic myeloid leukemia in blast crisis, myelodysplastic syndrome, acute lymphoblastic leukemia, and bilineage/biphenotypic leukemia. NUP98 gene fusions typically encode a fusion protein that retains the amino terminus of NUP98; in this context, it is important to note that several recent studies have demonstrated that the amino-terminal portion of NUP98 exhibits transcription activation potential. Approximately half of the NUP98 fusion partners encode homeodomain proteins, and at least 5 NUP98 fusions involve known histone-modifying genes. Several of the NUP98 fusions, including NUP98-homeobox (HOX)A9, NUP98-HOXD13, and NUP98-JARID1A, have been used to generate animal models of both lymphoid and myeloid malignancy; these models typically up-regulate HOXA cluster genes, including HOXA5, HOXA7, HOXA9, and HOXA10. In addition, several of the NUP98 fusion proteins have been shown to inhibit differentiation of hematopoietic precursors and to increase self-renewal of hematopoietic stem or progenitor cells, providing a potential mechanism for malignant transformation.

Association between microRNA196a2 rs11614913 genotypes and the risk of non-small cell lung cancer in Korean population

Objectives

The microRNA (miRNA) miR-196a2 may play an important role in lung cancer development and survival by altering binding activity of target mRNA. In this study, we evaluated their associations with the susceptibility of non-small cell lung cancers (NSCLC) by case-control study in a Korean population.

Methods

We performed genotyping analyses for miR-196a2 rs11614913 T/C at miRNA regions in a case-control study using blood samples of 406 NSCLC patient and 428 cancer-free control groups.

Results

The total C allele frequencies for miR-196a2 were 48.8% for the patients and 45.6% for the controls; and the genotype frequencies of TT, TC, and CC were 23.7%, 55.2%, and 21.1% for the patients and 31.1%, 46.35%, and 22.4% for the controls (p<0.05). Participants who possesses TC/CC genotypes showed high risk for NSCLC compared to those possessed TT genotypes (OR, 1.42; 95% CI, 1.03 to 1.96). The association was persisted in 60 and older age group, male, smokers, those without family history for cancer. However, no significant association of CC genotypes in recessive genetic model was observed.

Conclusions

In conclusion, this case-control study provides evidence that miR-196a2 rs11614913 C/T polymorphisms are associated with a significantly increased risk of NSCLC in a dominant model, indicating that common genetic polymorphisms in miR-196a2 rs11614913 are associated with NSCLC. The association of miR196a2 rs11614913 polymorphisms and NSCLC risk require confirmation through additional larger studies.

Genetic variants in miR-146a, miR-149, miR-196a2, miR-499 and their influence on relative expression in lung cancers

BACKGROUND

The presence of sequence variants in miRNA genes may influence their processing, expression and binding to target mRNAs. Since single miRNA can have a large number of potential mRNA targets, even minor variations in its expression can have influences on hundreds of putative mRNAs.

METHODS

Here, we evaluated 101 paired samples (cancer and normal tissues) from non-small cell lung carcinoma (NSCLC) patients to study the genotype distribution of single nucleotide polymorphisms (SNPs) in miR-146a (rs2910164 C-G), miR-149 (rs2292832 C-T), miR-196a2 (rs11614913 C-T) and miR-499 (rs3746444 G-A) and their influence on the expression of respective miRNAs.

RESULTS

Relative expression of miR-146a, miR-149 and miR-499 were comparable in NSCLC and in paired control tissues. On the contrary, we clearly detected a significant increase (p<0.001) of miR-196a2 expression in NSCLC. In particular we found a significant association between miR-196a2 CC genotype and high expression, whereas TT geno-type showed a very low expression in comparison to both CT (p<0.005) and CC patients (p<0.01). We did not find any association between miR-149, miR-196a2 and miR-499 genotype and risk of NSCLC. Conversely, CG genotype of miR-146a appeared associated to an increased risk for NSCLC (p=0.042 and 1.77 OR).

CONCLUSIONS

Our results seem to demonstrate that sequence variants of miR-196a2 can have an influence on its expression, while miR-146a can have a role in increasing the risk of NSCLC.

Heritable GATA2 mutations associated with familial myelodysplastic syndrome and acute myeloid leukemia

We report the discovery of the GATA2 gene as a new myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML) predisposition gene. We found the same, novel heterozygous c.1061C>T (p.Thr354Met) missense mutation in the GATA2 transcription factor gene segregating with the multigenerational transmission of MDS/AML in three families, and a GATA2 c.1063_1065delACA (p.Thr355del) mutation at an adjacent codon in a fourth MDS/AML family. The mutations reside within the second zinc finger of GATA2 which mediates DNA-binding and protein-protein interactions. We show differential effects of the mutants on transactivation of target genes, cellular differentiation, apoptosis and global gene expression. Identification of such predisposing genes to familial forms of MDS and AML is critical for more effective diagnosis and prognosis, counselling, selection of related bone marrow transplant donors, and development of therapies.

Cell of origin in AML: susceptibility to MN1-induced transformation is regulated by the MEIS1/AbdB-like HOX protein complex

Pathways defining susceptibility of normal cells to oncogenic transformation may be valuable therapeutic targets. We characterized the cell of origin and its critical pathways in MN1-induced leukemias. Common myeloid (CMP) but not granulocyte-macrophage progenitors (GMP) could be transformed by MN1. Complementation studies of CMP-signature genes in GMPs demonstrated that MN1-leukemogenicity required the MEIS1/AbdB-like HOX-protein complex. ChIP-sequencing identified common target genes of MN1 and MEIS1 and demonstrated identical binding sites for a large proportion of their chromatin targets. Transcriptional repression of MEIS1 targets in established MN1 leukemias demonstrated antileukemic activity. As MN1 relies on but cannot activate expression of MEIS1/AbdB-like HOX proteins, transcriptional activity of these genes determines cellular susceptibility to MN1-induced transformation and may represent a promising therapeutic target.

Association between SNPs in pre-miRNA and risk of chronic obstructive pulmonary disease

OBJECTIVES

Chronic obstructive pulmonary disease (COPD) is characterized by irreversible airway obstruction and persistent chronic airway inflammation and is influenced by genetic and environmental factors. This study aimed to explore the genetic aspect of its initial occurrence.

DESIGN AND METHODS

We conducted a case-control study of 432 COPD patients and 511 control subjects frequency-matched in age and gender distribution. We genotyped three single nucleotide polymorphisms (SNPs) in pre-miRNAs using a PCR-RFLP assay and evaluated their relevance to COPD susceptibility.

RESULTS

We found that the TT genotype and T allele of miR-196a2 rs11614913 were significantly associated with a decreased risk for COPD, compared with the CC genotype and C allele. Similarly, the GG genotype and G allele of miR-499 rs3746444 were associated with a decreased risk for COPD, compared with the AA genotype and A allele.

CONCLUSIONS

These findings suggest that both rs11614913 and rs3746444 may be involved in susceptibility to COPD.

Mouse models of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are hematopoietic malignancies characterized by peripheral cytopenias in the face of normo- or hypercellular, dysplastic bone marrow that arise from mutations in the hematopoietic stem/progenitor cell (HSPC). The disease is characterized by multiple cytogenetic and molecular defects, which result in an extremely heterogeneous phenotype. Recently, significant efforts have been made to develop appropriate mouse models to study this complex disease. Because of the heterogeneity of MDS, no single model is able to capture the MDS phenotype in its entirety. In this review, we describe several MDS mouse models and discuss the advances made in our understanding of the different disease mechanisms within the malignant clone and the marrow microenvironment. In addition, we describe progress in xenotransplantation models of MDS and discuss questions that remain to be answered.

Transcriptional deregulation of oncogenic myocyte enhancer factor 2C in T-cell acute lymphoblastic leukemia

Myocyte enhancer factor 2C (MEF2C) encodes a transcription factor which is ectopically expressed in T-cell acute lymphoblastic leukemia (T-ALL) cell lines, deregulated directly by ectopically expressed homeodomain protein NKX2-5 or by loss of promoter regions via del(5)(q14). Here, we analyzed the MEF2C 5'-region, thus identifying potential regulatory binding sites for GFI1B, basic helix-loop-helix proteins, STAT5, and HOXA9/HOXA10. Chromatin immunoprecipitation and overexpression analyses demonstrated direct activation by GFI1B and LYL1 and inhibition by STAT5. HOXA9/HOXA10 activated expression of NMYC which in turn mediated MEF2C repression, indicating an indirect mode of regulation via NMYC interactor (NMI) and STAT5. Lacking comma: Chromosomal deletion of the STAT5 binding site in LOUCY cells reduced protein levels of STAT5 in some MEF2C-positve T-ALL cell lines, and the presence of inhibitory IL7-JAK-STAT5 signaling highlighted the repressive impact of this factor in MEF2C regulation. Taken together, our results indicate that the expression of MEF2C in T-ALL cells is principally deregulated via activating leukemic transcription factors GFI1B or NKX2-5 and by escaping inhibitory developmental STAT5 signaling.

Identification of Hematopoietic Stem Cell Engraftment Genes in Gene Therapy Studies

Hematopoietic stem cell (HSC) therapy using replication-incompetent retroviral vectors is a promising approach to provide life-long correction for genetic defects. HSC gene therapy clinical studies have resulted in functional cures for several diseases, but in some studies clonal expansion or leukemia has occurred. This is due to the dyregulation of endogenous host gene expression from vector provirus insertional mutagenesis. Insertional mutagenesis screens using replicating retroviruses have been used extensively to identify genes that influence oncogenesis. However, retroviral mutagenesis screens can also be used to determine the role of genes in biological processes such as stem cell engraftment. The aim of this review is to describe the potential for vector insertion site data from gene therapy studies to provide novel insights into mechanisms of HSC engraftment. In HSC gene therapy studies dysregulation of host genes by replication-incompetent vector proviruses may lead to enrichment of repopulating clones with vector integrants near genes that influence engraftment. Thus, data from HSC gene therapy studies can be used to identify novel candidate engraftment genes. As HSC gene therapy use continues to expand, the vector insertion site data collected will be of great interest to help identify novel engraftment genes and may ultimately lead to new therapies to improve engraftment.

Mouse models of myelodysplastic syndromes

Three general approaches have been used to model myelodysplastic syndrome (MDS) in mice, including treatment with mutagens or carcinogens, xenotransplantation of human MDS cells, and genetic engineering of mouse hematopoietic cells. This article discusses the phenotypes observed in available mouse models for MDS with a concentration on a model that leads to aberrant expression of conserved homeobox genes that are important regulators of normal hematopoiesis. Using these models of MDS should allow a more complete understanding of the disease process and provide a platform for preclinical testing of therapeutic approaches.

Myeloid-specific inactivation of p15Ink4b results in monocytosis and predisposition to myeloid leukemia

Inactivation of p15INK4b, an inhibitor of cyclin-dependent kinases, through DNA methylation is one of the most common epigenetic abnormalities in myeloid leukemia. Although this suggests a key role for this protein in myeloid disease suppression, experimental evidence to support this has not been reported. To address whether this event is critical for premalignant myeloid disorders and leukemia development, mice were generated that have loss of p15Ink4b specifically in myeloid cells. The p15Ink4b(fl/fl)-LysMcre mice develop nonreactive monocytosis in the peripheral blood accompanied by increased numbers of myeloid and monocytic cells in the bone marrow resembling the myeloproliferative form of chronic myelomonocytic leukemia. Spontaneous progression from chronic disease to acute leukemia was not observed. Nevertheless, MOL4070LTR retrovirus integrations provided cooperative genetic mutations resulting in a high frequency of myeloid leukemia in knockout mice. Two common retrovirus insertion sites near c-myb and Sox4 genes were identified, and their transcript up-regulated in leukemia, suggesting a collaborative role of their protein products with p15Ink4b-deficiency in promoting malignant disease. This new animal model demonstrates experimentally that p15Ink4b is a tumor suppressor for myeloid leukemia, and its loss may play an active role in the establishment of preleukemic conditions.

Association of a variant in MIR 196A2 with susceptibility to hepatocellular carcinoma in male Chinese patients with chronic hepatitis B virus infection

MicroRNAs (miRNAs) are small noncoding RNAs with regulatory functions as tumor suppressors and oncogenes. Recent studies have implicated that the rs11614913 SNP in MIR196A2 was associated with susceptibility of lung cancer, congenital heart disease, breast cancer and shortened survival time of nonsmall cell lung cancer. To assess whether this polymorphism is associated with susceptibility to and clinicopathologic characteristics of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC), a total of 560 patients with chronic HBV infection and 391 healthy volunteers were enrolled, and MIR196A2 polymorphism was genotyped by polymerase chain reaction-ligation detection reaction (PCR-LDR). In our study group, there was no significant association between MIR196A2 polymorphism and the risk of HBV-related HCC in all subjects, however, the risk of HCC was significantly higher with MIR196A2 rs11614913 CC genotype or C allele compared with those with the TT genotype or T allele in male patients. Furthermore, in a subsequent analysis of the association between this polymorphism and clinicopathologic characteristics, there was still no significant difference in both the distribution of genotype or allelic frequency. However, we observed that the T allele was significantly more frequent in male HCC patients with lymphatic metastasis. Our results suggested that MIR196A2 polymorphism was associated with susceptibility to HBV-related HCC in a male Chinese population.

Gene profiling of the erythro- and megakaryoblastic leukaemias induced by the Graffi murine retrovirus

Background

Acute erythro- and megakaryoblastic leukaemias are associated with very poor prognoses and the mechanism of blastic transformation is insufficiently elucidated. The murine Graffi leukaemia retrovirus induces erythro- and megakaryoblastic leukaemias when inoculated into NFS mice and represents a good model to study these leukaemias.

Methods

To expand our understanding of genes specific to these leukaemias, we compared gene expression profiles, measured by microarray and RT-PCR, of all leukaemia types induced by this virus.

Results

The transcriptome level changes, present between the different leukaemias, led to the identification of specific cancerous signatures. We reported numerous genes that may be potential oncogenes, may have a function related to erythropoiesis or megakaryopoiesis or have a poorly elucidated physiological role. The expression pattern of these genes has been further tested by RT-PCR in different samples, in a Friend erythroleukaemic model and in human leukaemic cell lines.

We also screened the megakaryoblastic leukaemias for viral integrations and identified genes targeted by these integrations and potentially implicated in the onset of the disease.

Conclusions

Taken as a whole, the data obtained from this global gene profiling experiment have provided a detailed characterization of Graffi virus induced erythro- and megakaryoblastic leukaemias with many genes reported specific to the transcriptome of these leukaemias for the first time.

Functional characterization of high levels of meningioma 1 as collaborating oncogene in acute leukemia

Retroviral expression of leukemogenic oncogenes in the murine hematopoietic system is essential but not sufficient to induce acute leukemia. Proviral integration-mediated elevated expression of the meningioma 1 (MN1) oncogene suggested MN1 acting as cooperating event in mixed-lineage leukemia 1 (MLL) and eleven nineteen leukemia (ENL)-induced murine leukemia. Indeed, co-expression of MN1 with MLL-ENL enhanced transformation in vivo, and resulted in a significantly reduced latency for induction of an aggressive acute leukemia when compared with MN1 or MLL-ENL alone. In addition, co-expression of MN1 increased the granulocyte macrophage progenitor cell population with leukemia-initiating properties as shown in secondary transplantation experiments. Gene expression profiling experiments identified putative downstream MN1 targets, of which FMS-like tyrosine kinase 3 (FLT3) and CD34 were upregulated in both MN1-overexpressing murine leukemias and in pediatric acute leukemias with high MN1 levels. Interestingly, small interfering RNA (siRNA)-mediated MN1 knockdown resulted in cell cycle arrest and impaired clonogenic growth of human leukemia cell lines with high MN1 levels. Our work shows for the first time that high MN1 levels are important for the growth of leukemic cells, and that increased MN1 expression can synergize with MLL-ENL and probably other transforming fusion genes in leukemia induction through a distinct gene expression program that is able to expand the leukemia-initiating cell population.

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.

Modeling the functional heterogeneity of leukemia stem cells: role of STAT5 in leukemia stem cell self-renewal

Although the cancer stem cell (CSC) concept implies that CSCs are rare, recent reports suggest that CSCs may be frequent in some cancers. We hypothesized that the proportion of leukemia stem cells would vary as a function of the number of dysregulated pathways. Constitutive expression of MN1 served as a 1-oncogene model, and coexpression of MN1 and a HOX gene served as a 2-oncogene model. Leukemia-initiating cell (LIC) number and in vitro expansion potential of LICs were functionally assessed by limiting dilution analyses. LIC expansion potential was 132-fold increased in the 2- compared with the 1-oncogene model, although phenotypically, both leukemias were similar. The 2-oncogene model was characterized by granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity and activated STAT/ERK signaling. GM-CSF hypersensitivity of the 2-oncogene model (MN1/HOXA9) was lost in Stat5b(-/-) cells, and the LIC expansion potential was reduced by 86- and 28-fold in Stat5b(-/-) and Stat1(-/-) cells, respectively. Interestingly, in 201 acute myeloid leukemia (AML) patients, coexpression of MN1 and HOXA9 was restricted to patients with the poorest prognosis and was associated with highly active STAT signaling. Our data demonstrate the functional heterogeneity of LICs and show that STAT signaling is critical for leukemia stem cell self-renewal in MN1- and HOXA9-expressing leukemias.

Standardization of flow cytometry in myelodysplastic syndromes: report from the first European LeukemiaNet working conference on flow cytometry in myelodysplastic syndromes

The myelodysplastic syndromes are a group of clonal hematopoietic stem cell diseases characterized by cytopenia(s), dysplasia in one or more cell lineages and increased risk of evolution to acute myeloid leukemia (AML). Recent advances in immunophenotyping of hematopoietic progenitor and maturing cells in dysplastic bone marrow point to a useful role for multiparameter flow cytometry (FCM) in the diagnosis and prognostication of myelodysplastic syndromes. In March 2008, representatives from 18 European institutes participated in a European LeukemiaNet (ELN) workshop held in Amsterdam as a first step towards standardization of FCM in myelodysplastic syndromes. Consensus was reached regarding standard methods for cell sampling, handling and processing. The group also defined minimal combinations of antibodies to analyze aberrant immunophenotypes and thus dysplasia. Examples are altered numbers of CD34(+) precursors, aberrant expression of markers on myeloblasts, maturing myeloid cells, monocytes or erythroid precursors and the expression of lineage infidelity markers. When applied in practice, aberrant FCM patterns correlate well with morphology, the subclassification of myelodysplastic syndromes, and prognostic scoring systems. However, the group also concluded that despite strong evidence for an impact of FCM in myelodysplastic syndromes, further (prospective) validation of markers and immunophenotypic patterns are required against control patient groups as well as further standardization in multi-center studies. Standardization of FCM in myelodysplastic syndromes may thus contribute to improved diagnosis and prognostication of myelodysplastic syndromes in the future.

High-throughput insertional mutagenesis screens in mice to identify oncogenic networks

Retroviral insertional mutagenesis screens have been used for many years as a tool for cancer gene discovery. In recent years, completion of the mouse genome sequence as well as improved technologies for cloning and sequencing of retroviral insertions have greatly facilitated the retrieval of more complete data sets from these screens. The concomitant increase of the size of the screens allows researchers to address new questions about the genes and signalling networks involved in tumour development. In addition, the development of new insertional mutagenesis tools such as DNA transposons enables screens for cancer genes in tissues that previously could not be analysed by retroviral insertional mutagenesis.

Molecular bases of myelodysplastic syndromes: lessons from animal models

Myelodysplastic syndrome (MDS) is a clonal disorder of hematopietic stem cells characterized by ineffective hematopoiesis, peripheral blood cytopenia, morphologic dysplasia, and susceptibility to acute myeloid leukemia. Several mechanisms have been suggested as causes of MDS: unbalanced chromosomal abnormalities reflecting a gain or loss of chromosomal material, point mutations of transcription factors, and inactivation of p53. However, appropriate animal models that mimic MDS have long been lacking. We recently reported a novel murine model of MDS that recapitulates trilineage dysplasia and transformation to AML. In this review, we summarize the animal models of MDS and discuss the molecular bases of MDS as well as those of leukemia and myeloproliferative disorders (MPD). J. Cell. Physiol. 219: 529-534, 2009. (c) 2009 Wiley-Liss, Inc.

Runx2 induces acute myeloid leukemia in cooperation with Cbfbeta-SMMHC in mice

The core-binding factor (CBF) is a master regulator of developmental and differentiation programs, and CBF alterations are frequently associated with acute leukemia. The role of the CBF member RUNX2 in hematopoiesis is poorly understood. Genetic evidence suggests that deregulation of Runx2 may cause myeloid leukemia in mice expressing the fusion oncogene Cbfb-MYH11. In this study, we show that sustained expression of Runx2 modulates Cbfbeta-smooth muscle myosin heavy chain (SMMHC)-mediated myeloid leukemia development. Expression of Runx2 is high in the hematopoietic stem cell compartment and decreases during myeloid differentiation. Sustained Runx2 expression hinders myeloid progenitor differentiation capacity and represses expression of CBF targets Csf1R, Mpo, Cebpd, the cell cycle inhibitor Cdkn1a, and myeloid markers Cebpa and Gfi1. In addition, full-length Runx2 cooperates with Cbfbeta-SMMHC in leukemia development in transplantation assays. Furthermore, we show that the nuclear matrix-targeting signal and DNA-binding runt-homology domain of Runx2 are essential for its leukemogenic activity. Conversely, Runx2 haplo-insufficiency delays the onset and reduces the incidence of acute myeloid leukemia. Together, these results indicate that Runx2 is expressed in the stem cell compartment, interferes with differentiation and represses CBF targets in the myeloid compartment, and modulates the leukemogenic function of Cbfbeta-SMMHC in mouse leukemia.

Cancer gene discovery in mouse and man

The elucidation of the human and mouse genome sequence and developments in high-throughput genome analysis, and in computational tools, have made it possible to profile entire cancer genomes. In parallel with these advances mouse models of cancer have evolved into a powerful tool for cancer gene discovery. Here we discuss the approaches that may be used for cancer gene identification in both human and mouse and discuss how a cross-species 'oncogenomics' approach to cancer gene discovery represents a powerful strategy for finding genes that drive tumourigenesis.

MicroRNAs in cancer

Within the past few years, studies on microRNA (miRNA) and cancer have burst onto the scene. Profiling of the miRNome (global miRNA expression levels) has become prevalent, and abundant miRNome data are currently available for various cancers. The pattern of miRNA expression can be correlated with cancer type, stage, and other clinical variables, so miRNA profiling can be used as a tool for cancer diagnosis and prognosis. miRNA expression analyses also suggest oncogenic (or tumor-suppressive) roles of miRNAs. miRNAs play roles in almost all aspects of cancer biology, such as proliferation, apoptosis, invasion/metastasis, and angiogenesis. Given that many miRNAs are deregulated in cancers but have not yet been further studied, it is expected that more miRNAs will emerge as players in the etiology and progression of cancer. Here we also discuss miRNAs as a tool for cancer therapy.

MN1 affects expression of genes involved in hematopoiesis and can enhance as well as inhibit RAR/RXR-induced gene expression

The oncoprotein meningioma 1 (MN1) is overexpressed in several subtypes of acute myeloid leukemia (AML) and overexpression was associated with a poor response to chemotherapy. MN1 is a cofactor of retinoic acid receptor/retinoic x receptor (RAR/RXR)-mediated transcription and this study identified genes in the promonocytic cell line U937 that were regulated by MN1. We found that MN1 can both stimulate and inhibit transcription. Combining MN1 expression with all-trans retinoic acid (ATRA), the ligand of the RAR/RXR dimer, showed that MN1 could both enhance and repress ATRA effects. Many of the identified genes are key players in hematopoiesis and leukemogenesis (e.g. MEIS1 and BMI1). Another interesting target is DHRS9. DHRS9 is involved in the synthesis of ATRA from vitamin A. MN1 inhibited DHRS9 expression and completely abolished its induction by ATRA. MN1 is also the target of a rare AML-causing translocation encoding the MN1-TEL protein. MN1-TEL induces expression of only a few genes and its most pronounced effect is inhibition of a large group of ATRA-induced genes including DHRS9. In conclusion, both MN1 and MN1-TEL interfere with the ATRA pathway and this might explain the differentiation block in leukemias in which these genes are involved.

Cancer-associated genomic regions (CAGRs) and noncoding RNAs: bioinformatics and therapeutic implications

MicroRNAs (miRNAs) are small noncoding RNAs (ncRNAs, RNAs that do not code for proteins) that regulate the expression of target genes at the posttranscriptional or posttranslational level. Many miRNAs have conserved sequences between distantly related organisms, suggesting that these molecules participate in essential developmental and physiologic processes. miRNAs can act as tumor suppressor genes or oncogenes in human cancers. Mutations, deletions, or amplifications have been found in human cancers and shown to alter expression levels of mature and/or precursor miRNA transcripts. Moreover, a large fraction of genomic ultraconserved regions (UCRs) encode a particular set of ncRNAs whose expression is altered in human cancers. Both miRNAs and UCRs are frequently located at fragile sites and genomic regions affected in various cancers, named cancer-associated genomic regions (CAGRs). Bioinformatics studies are emerging as important tools to identify associations and/or correlations between miRNAs/ncRNAs and CAGRs. ncRNA profiling has allowed the identification of specific signatures associated with diagnosis, prognosis, and response to treatment of human tumors. Several abnormalities could contribute to the alteration of miRNA expression profiles in each kind of tumor and in each kind of tissue. This review is focused on the miRNAs and ncRNAs as genes affecting cancer risk, and we provided an updated catalog of miRNAs and UCRs located at fragile sites or at cancer susceptibility loci. These types of studies are the first step toward discoveries leading to novel approaches for cancer therapies.