Activation of HLXB9 by juxtaposition with MYB via formation of t(6;7)(q23;q36) in an AML-M4 cell line (GDM-1)

Altered enhancer-promoter interaction leads to MNX1 expression in pediatric acute myeloid leukemia with t(7;12)(q36;p13)

ABSTRACT

Acute myeloid leukemia (AML) with the t(7;12)(q36;p13) translocation occurs only in very young children and has a poor clinical outcome. The expected oncofusion between break point partners (motor neuron and pancreas homeobox 1 [MNX1] and ETS variant transcription factor 6 [ETV6]) has only been reported in a subset of cases. However, a universal feature is the strong transcript and protein expression of MNX1, a homeobox transcription factor that is normally not expressed in hematopoietic cells. Here, we map the translocation break points on chromosomes 7 and 12 in affected patients to a region proximal to MNX1 and either introns 1 or 2 of ETV6. The frequency of MNX1 overexpression in pediatric AML is 2.4% and occurs predominantly in t(7;12)(q36;p13) AML. Chromatin interaction assays in a t(7;12)(q36;p13) induced pluripotent stem cell line model unravel an enhancer-hijacking event that explains MNX1 overexpression in hematopoietic cells. Our data suggest that enhancer hijacking may be a more widespread consequence of translocations in which no oncofusion product was identified, including t(1;3) or t(4;12) AML.

The effect of LNCRNA SHANK3 on the malignant development of gastric cancer cells by regulating the miR-4530/MNX1

Gastric cancer (GC) has become the first malignant tumor with highest incidence rate and mortality of cancer in China, finding therapeutic targets for gastric cancer is of great significant for improving the survival rate of patients with GC. Recently, many of studies have shown that LncRNAs is involved in multiple biological progresses in the development of GC. This study, we screened for abnormally high expression of LncSHANK3 in GC through the TCGA database, and found that LncSHANK3 sponge adsorbs miR-4530, further competing with MNX1 and binding to miR-4530. We demonstrated the interaction between LncSHANK3 and miR-4530 through luciferase reporting analysis, with miR-4530 negatively regulating MNX1.Through CCK8, colony formation, transwell, and wound healing assays, it was found that LncSHANK3 affects the occurrence of GC through cell proliferation, migration and invasion. In conclusion, LncSHANK3/miR-4530/MNX1 axis is a potential mechanism for the treatment of GC.

Mechanisms associated with t(7;12) acute myeloid leukaemia: from genetics to potential treatment targets

Acute myeloid leukaemia (AML), typically a disease of elderly adults, affects 8 children per million each year, with the highest paediatric incidence in infants aged 0-2 of 18 per million. Recurrent cytogenetic abnormalities contribute to leukaemia pathogenesis and are an important determinant of leukaemia classification. The t(7;12)(q36;p13) translocation is a high-risk AML subtype exclusively associated with infants and represents the second most common abnormality in this age group. Mechanisms of t(7;12) leukaemogenesis remain poorly understood. The translocation relocates the entire MNX1 gene within the ETV6 locus, but a fusion transcript is present in only half of the patients and its significance is unclear. Instead, research has focused on ectopic MNX1 expression, a defining feature of t(7;12) leukaemia, which has nevertheless failed to produce transformation in conventional disease models. Recently, advances in genome editing technologies have made it possible to recreate the t(7;12) rearrangement at the chromosomal level. Together with recent studies of MNX1 involvement using murine in vivo, in vitro, and organoid-based leukaemia models, specific investigation on the biology of t(7;12) can provide new insights into this AML subtype. In this review, we provide a comprehensive up-to-date analysis of the biological features of t(7;12), and discuss recent advances in mechanistic understanding of the disease which may deliver much-needed therapeutic opportunities to a leukaemia of notoriously poor prognosis.

DNA Methylation Clusters and Their Relation to Cytogenetic Features in Pediatric AML

Acute Myeloid Leukemia (AML) is characterized by recurrent genetic and cytogenetic lesions that are utilized for risk stratification and for making treatment decisions. In recent years, methylation dysregulation has been extensively studied and associated with risk groups and prognosis in adult AML, however, such studies in pediatric AML are limited. Moreover, the mutations in epigenetic genes such as DNMT3A, IDH1 or IDH2 are almost absent or rare in pediatric patients as compared to their abundance in adult AML. In the current study, we evaluated methylation patterns that occur with or independent of the well-defined cytogenetic features in pediatric AML patients enrolled on multi-site AML02 clinical trial (NCT00136084). Our results demonstrate that unlike adult AML, cytosine DNA methylation does not result in significant unique clusters in pediatric AML, however, DNA methylation signatures correlated significantly with the most common and recurrent cytogenetic features. Paired evaluation of DNA methylation and expression identified genes and pathways of biological relevance that hold promise for novel therapeutic strategies. Our results further demonstrate that epigenetic signatures occur complimentary to the well-established chromosomal/mutational landscape, implying that dysregulation of oncogenes or tumor suppressors might be leveraging both genetic and epigenetic mechanisms to impact biological pathways critical for leukemogenesis.

The impact of At1r inhibition via losartan on the anti-leukaemic effects of doxorubicin in acute myeloid leukaemia

Introduction:

Bone marrow renin–angiotensin system(RAS) modulates acute myeloid leukaemia(AML).The aim of this study is to clarify the relationships between RAS and AML, and to show the effect of losartan and doxorubicin treatment in AML cell lines.

Methods:

AML cell lines including CESS, HL-60, MO-1, P31/FUJ, GDM-1 and KASUMI-3 were used as models in this study.

Results:

After treating the six AML cell lines with a combination of losartan and doxorubicin, they were divided into two groups based on their behaviour: one became more sensitive to drug treatment (Group A) and the other had no change observed in behaviour after drug treatment (Group B). In silico analyses showed that Group A is involved in cellular apoptosis, while Group B is involved in tumour angiogenesis further supporting the in vitro results.

Conclusion:

The combined treatment of the AML cell lines with losartan and doxorubicin resulted in an increase in sensitivity of some of the cell lines. Those leukaemic cells are modulated via the induction of apoptosis, whereas the other cells resistant to the drug treatment are closely related to tumour angiogenesis indicating that RAS-AT1R seems to be differently expressed in different leukaemic blast cells and tumour microenvironments. Pharmaco-biological actions of RAS inhibitors may be different in distinct leukaemic cells based on the pathological behaviour of AML genomic subtypes.

Motor Neuron and Pancreas Homeobox 1 (MNX1) Is Involved in Promoting Squamous Cervical Cancer Proliferation via Regulating Cyclin E

Background

Cervical cancer is one of the most lethal gynecologic malignancies worldwide. The objective of this study was to assess the role of MNX1 in cervical cancer and its underlying mechanisms.

Material/Methods

The expression of motor neuron and pancreas homeobox 1 (MNX1) in immortal epithelial cervical cell line ECT, cervical cancer cell HeLa, and SiHa and cervical cancer, as well as in adjacent noncancer tissues, was detected and analyzed. CCK-8 and colony formation assays were performed to evaluate the effects of MNX1 overexpression on cervical cancer cell proliferation. Transwell assay was used to detect migration and invasion after MNX1 knockdown or overexpression. Real-time PCR and Western blotting were used to examine MNX1 and cell cycle regulator expression.

Results

Data from our study indicated that MNX1 was upregulated both in cervical cancer cell lines and cervical cancer tissues. The high levels of MNX1 are related to advanced stages and lymph nodes metastasis. The overexpression of MNX1 promoted cervical cancer cells proliferation, migration, and invasion. Moreover, MNX1 upregulated 2 critical cell cycle regulators, CCNE1 and CCNE2.

Conclusions

These findings reveal MNX1 as a novel oncogene of cervical cancer and indicate MNX1 is a promising therapeutic and prognostic biomarker.

The homeobox transcription factor HB9 induces senescence and blocks differentiation in hematopoietic stem and progenitor cells

The homeobox gene HLXB9 encodes for the transcription factor HB9, which is essential for pancreatic as well as motor neuronal development. Beside its physiological expression pattern, aberrant HB9 expression has been observed in several neoplasias. Especially in infant translocation t(7;12) acute myeloid leukemia, aberrant HB9 expression is the only known molecular hallmark and is assumed to be a key factor in leukemic transformation. However, so far, only poor functional data exist addressing the oncogenic potential of HB9 or its influence on hematopoiesis. We investigated the influence of HB9 on cell proliferation and cell cycle in vitro, as well as on hematopoietic stem cell differentiation in vivo using murine and human model systems. In vitro, HB9 expression led to premature senescence in human HT1080 and murine NIH3T3 cells, providing for the first time evidence for an oncogenic potential of HB9. Onset of senescence was characterized by induction of the p53–p21 tumor suppressor network, resulting in growth arrest, accompanied by morphological transformation and expression of senescence-associated β-galactosidase. In vivo, HB9-transduced primary murine hematopoietic stem and progenitor cells underwent a profound differentiation arrest and accumulated at the megakaryocyte/erythrocyte progenitor stage. In line, gene expression analyses revealed de novo expression of erythropoiesis-related genes in human CD34⁺hematopoietic stem and progenitor cells upon HB9 expression. In summary, the novel findings of HB9-dependent premature senescence and myeloid-biased perturbed hematopoietic differentiation, for the first time shed light on the oncogenic properties of HB9 in translocation t(7;12) acute myeloid leukemia.

Motor neuron and pancreas homeobox 1/HLXB9 promotes sustained proliferation in bladder cancer by upregulating CCNE1/2

Background

Uncontrolled proliferation is thought to be the most fundamental characteristic of cancer. Detailed knowledge of cancer cell proliferation mechanisms would not only benefit understanding of cancer progression, but may also provide new clues for developing novel therapeutic strategies.

Methods

In vitro function of MNX1 (Motor neuron and pancreas homeobox 1) in bladder cancer cell was evaluated using MTT assay, colony formation assay, and bromodeoxyuridine incorporation assay. Real-time PCR and western blotting were performed to detect MNX1 and CCNE1/2 expressions. In vivo tumor growth was conducted in BALB/c-nu mice.

Results

We reported that MNX1 is responsible for sustaining bladder cancer cell proliferation. Abnormal MNX1 upregulation in bladder cancer cell lines and 167 human tissue specimens; high MNX1 expression levels correlated significantly with shorter 5-year overall and relapse-free survival in the bladder cancer patients. Furthermore, MNX1 overexpression accelerated bladder cancer cell proliferation and tumorigenicity both in vitro and in vivo, whereas MNX1 downregulation arrested it. In addition, MNX1 transcriptionally upregulated CCNE1 and CCNE2 by directly bounding to their promoters, which promoted G1–S transition in the bladder cancer cells.

Conclusion

These findings reveal an oncogenic role and novel regulatory mechanism of MNX1 in bladder cancer progression and suggest that MNX1 is a potential prognostic biomarker and therapeutic target.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0829-9) contains supplementary material, which is available to authorized users.

Paediatric acute myeloid leukaemia with the t(7;12)(q36;p13) rearrangement: a review of the biological and clinical management aspects

The presence of chromosomal abnormalities is one of the most important criteria for leukaemia diagnosis and management. Infant leukaemia is a rare disease that affects children in their first year of life. It has been estimated that approximately one third of infants with acute myeloid leukaemia harbour the t(7;12)(q36;p13) rearrangement in their leukaemic blasts. However, the WHO classification of acute myeloid leukaemia does not yet include the t(7;12) as a separate entity among the different genetic subtypes, although the presence of this chromosomal abnormality has been associated with an extremely poor clinical outcome. Currently, there is no consensus treatment for t(7;12) leukaemia patients. However, with the inferior outcome with the standard induction therapy, stem cell transplantation may offer a better chance for disease control. A better insight into the chromosome biology of this entity might shed some light into the pathogenic mechanisms arising from this chromosomal translocation, that at present are not fully understood. Further work is needed to improve our understanding of the molecular and genetic basis of this disorder. This will hopefully open some grounds for possible tailored treatment for this subset of very young patients with inferior disease outcome. This review aims at highlighting the cytogenetic features that characterise the t(7;12) leukaemias for a better detection of the abnormality in the diagnostic setting. We also review treatment and clinical outcome in the cases reported to date.

HLXB9 gene expression, and nuclear location during in vitro neuronal differentiation in the SK-N-BE neuroblastoma cell line

Different parts of the genome occupy specific compartments of the cell nucleus based on the gene content and the transcriptional activity. An example of this is the altered nuclear positioning of the HLXB9 gene in leukaemia cells observed in association with its over-expression. This phenomenon was attributed to the presence of a chromosomal translocation with breakpoint proximal to the HLXB9 gene. Before becoming an interesting gene in cancer biology, HLXB9 was studied as a developmental gene. This homeobox gene is also known as MNX1 (motor neuron and pancreas homeobox 1) and it is relevant for both motor neuronal and pancreatic beta cells development. A spectrum of mutations in this gene are causative of sacral agenesis and more broadly, of what is known as the Currarino Syndrome, a constitutional autosomal dominant disorder. Experimental work on animal models has shown that HLXB9 has an essential role in motor neuronal differentiation. Here we present data to show that, upon treatment with retinoic acid, the HLXB9 gene becomes over-expressed during the early stages of neuronal differentiation and that this corresponds to a reposition of the gene in the nucleus. More precisely, we used the SK-N-BE human neuroblastoma cell line as an in vitro model and we demonstrated a transient transcription of HLXB9 at the 4th and 5th days of differentiation that corresponded to the presence, predominantly in the cell nuclei, of the encoded protein HB9. The nuclear positioning of the HLXB9 gene was monitored at different stages: a peripheral location was noted in the proliferating cells whereas a more internal position was noted during differentiation, that is while HLXB9 was transcriptionally active. Our findings suggest that HLXB9 can be considered a marker of early neuronal differentiation, possibly involving chromatin remodeling pathways.

Oncogenic deregulation of NKL homeobox gene MSX1 in mantle cell lymphoma

NKL homeobox gene MSX1 is physiologically expressed during embryonic hematopoiesis. Here, we detected MSX1 overexpression in three examples of mantle cell lymphoma (MCL) and one of acute myeloid leukemia (AML) by screening 96 leukemia/lymphoma cell lines via microarray profiling. Moreover, in silico analysis identified significant overexpression of MSX1 in 3% each of patients with MCL and AML, confirming aberrant activity in subsets of both types of malignancies. Comparative expression profiling analysis and subsequent functional studies demonstrated overexpression of histone acetyltransferase PHF16 together with transcription factors FOXC1 and HLXB9 as activators of MSX1 transcription. Additionally, we identified regulation of cyclin D1/CCND1 by MSX1 and its repressive cofactor histone H1C. Fluorescence in situ hybridization in MCL cells showed that t(11;14)(q13;q32) results in detachment of CCND1 from its corresponding repressive MSX1 binding site. Taken together, we uncovered regulators and targets of homeobox gene MSX1 in leukemia/lymphoma cells, supporting the view of a recurrent genetic network that is reactivated in malignant transformation.

The embryonic transcription factor Hlxb9 is a menin interacting partner that controls pancreatic β-cell proliferation and the expression of insulin regulators

The multiple endocrine neoplasia type 1 (MEN1) syndrome is caused by germline mutations in the MEN1 gene encoding menin, with tissue-specific tumors of the parathyroids, anterior pituitary, and enteropancreatic endocrine tissues. Also, 30-40% of sporadic pancreatic endocrine tumors show somatic MEN1 gene inactivation. Although menin is expressed in all cell types of the pancreas, mouse models with loss of menin in either pancreatic α-cells, or β-cells, or total pancreas develop β-cell-specific endocrine tumors (insulinomas). Loss of widely expressed tumor suppressor genes may produce tissue-specific tumors by reactivating one or more embryonic-specific differentiation factors. Therefore, we determined the effect of menin overexpression or knockdown on the expression of β-cell differentiation factors in a mouse β-cell line (MIN6). We show that the β-cell differentiation factor Hlxb9 is posttranscriptionally upregulated upon menin knockdown, and it interacts with menin. Hlxb9 reduces cell proliferation and causes apoptosis in the presence of menin, and it regulates genes that modulate insulin level. Thus, upon menin loss or from other causes, dysregulation of Hlxb9 predicts a possible combined mechanism for β-cell proliferation and insulin production in insulinomas. These observations help to understand how a ubiquitously expressed protein such as menin might control tissue-specific tumorigenesis. Also, our findings identify Hlxb9 as an important factor for β-cell proliferation and insulin regulation.

Homeobox protein HB9 binds to the prostaglandin E receptor 2 promoter and inhibits intracellular cAMP mobilization in leukemic cells

BACKGROUND

HB9 is highly expressed in translocation t(7;12) positive infant AML.

RESULTS

HB9 binds to the PTGER2 promoter, down-regulates PTGER2 gene expression and subsequently represses cAMP synthesis in hematopoietic cells.

CONCLUSION

Expression of HLXB9 represses PTGER2 mediated signaling.

SIGNIFICANCE

First molecular report of HB9-dependent target gene regulation in hematopoietic cells. The transcription factor HB9, encoded by the homeobox gene B9 (HLXB9), is involved in the development of pancreatic beta- and motor neuronal cells. In addition, HLXB9 is recurrently rearranged in young children with acute myeloid leukemia characterized by a chromosomal translocation t(7;12)-HLXB9/TEL and concomitant high expression of the unrearranged, wild-type HLXB9 allele. However, target genes of HB9 in hematopoietic cells are not known to date. In this study, we used ChIP-on-chip analysis together with expression profiling and identified PTGER2 (prostaglandin E receptor 2) as a target gene of HB9 in a hematopoietic cell line. The functional HB9 homeodomain as well as the HB9 binding domain within the PTGER2 promoter are essential for binding of HB9 to the PTGER2 promoter region and down-regulation of PTGER2 expression. Functionally, HB9 conducted down-regulation of PTGER2 results in a reduced content of intracellular cAMP mobilization and furthermore the decreased PTGER2 gene expression is valid in bone marrow cells from translocation t(7;12) positive patients. Among the primary and secondary target genes of HB9 in the myeloid cell line HL60, 78% of significantly regulated genes are down-regulated, indicating an overall repressive function of HB9. Differentially regulated genes were preferentially confined to pathways involved in cell-adhesion and cell-cell interactions, similar to the gene expression footprint of HLXB9-expressing cells from t(7;12) positive patients.

Novel chromosomal rearrangements and break points at the t(6;9) in salivary adenoid cystic carcinoma: association with MYB-NFIB chimeric fusion, MYB expression, and clinical outcome

OBJECTIVE

To investigate the molecular genetic heterogeneity associated with the t(6:9) in adenoid cystic carcinoma (ACC) and correlate the findings with patient clinical outcome.

EXPERIMENTAL DESIGN

Multimolecular and genetic techniques complemented with massive pair-ended sequencing and single-nucleotide polymorphism array analyses were used on tumor specimens from 30 new and 52 previously analyzed fusion transcript-negative ACCs by reverse transcriptase PCR (RT-PCR). MYB mRNA expression level was determined by quantitative RT-PCR. The results of 102 tumors (30 new and 72 previously reported cases) were correlated with the clinicopathologic factors and patients' survival.

RESULTS

The FISH analysis showed 34 of 82 (41.5%) fusion-positive tumors and molecular techniques identified fusion transcripts in 21 of the 82 (25.6%) tumors. Detailed FISH analysis of 11 out the 15 tumors with gene fusion without transcript formation showed translocation of NFIB sequences to proximal or distal sites of the MYB gene. Massive pair-end sequencing of a subset of tumors confirmed the proximal translocation to an NFIB sequence and led to the identification of a new fusion gene (NFIB-AIG1) in one of the tumors. Overall, MYB-NFIB gene fusion rate by FISH was in 52.9% whereas fusion transcript forming incidence was 38.2%. Significant statistical association between the 5' MYB transcript expression and patient survival was found.

CONCLUSIONS

We conclude that: (i) t(6;9) results in complex genetic and molecular alterations in ACC, (ii) MYB-NFIB gene fusion may not always be associated with chimeric transcript formation, (iii) noncanonical MYB-NFIB gene fusions occur in a subset of tumors, (iv) high MYB expression correlates with worse patient survival.

The dual role of HLXB9 in leukemia

BACKGROUND

The HLXB9 gene encodes a homeodomain containing transcription factor which has been implicated in the development of both solid and hematological malignancies. In leukemia it is one of the two fused genes, along with ETV6, in a recurrent translocation frequently observed in infant AML.

PROCEDURE

Here we investigate the role of epigenetic inactivation of the HLXB9 gene in leukemia. Quantitative DNA methylation analysis was performed using the COBRA assay, and qRT-PCR was used to assess the effects of methylation on expression in hematological cell lines and primary ALL samples.

RESULTS

Hypermethylation of the HLXB9 gene was found to be a frequent event in childhood ALL, occurring in 33% of cases. However, it was rarely or never observed in other types of leukemia, including AML, CML, and CLL, with the exception of adult ALL, in which 39% of cases were hypermethylated. Furthermore, hypermethylation of HLXB9 results in loss of expression in hematological cell lines and primary ALL samples.

CONCLUSION

These results suggest that HLXB9 may have a dual role in childhood leukemia, as an oncogene in infant AML but as a tumor suppressor in childhood ALL.

Imatinib sensitivity as a consequence of a CSF1R-Y571D mutation and CSF1/CSF1R signaling abnormalities in the cell line GDM1

Imatinib is usually a highly effective treatment for myeloproliferative neoplasms (MPNs) associated with ABL, PDGFRA or PDGFRB gene fusions; however, occasional imatinib-responsive patients have been reported without abnormalities of these genes. To identify novel imatinib-sensitive lesions, we screened 11 BCR-ABL-negative cell lines and identified GDM1, derived from a patient with an atypical MPN (aMPN), as being responsive to imatinib. Screening of genes encoding known imatinib targets revealed an exon 12 mutation in the colony-stimulating factor 1 receptor (CSF1R; c-FMS) with a predicted Y571D amino-acid substitution. CSF1R in GDM1 was constitutively phosphorylated, but rapidly dephosphorylated on exposure to imatinib. Y571D did not transform FDCP1 cells to growth factor independence, but resulted in a significantly increased colony growth compared with controls, constitutive CSF1R phosphorylation and elevated CSF1R signaling. We found that GDM1 expresses CSF1, and CSF1 neutralization partially inhibited proliferation, suggesting the importance of both autocrine and intrinsic mechanisms of CSF1R activation. An extensive screen of CSF1R in aMPNs and acute myeloid leukemia identified three additional novel missense variants. None of these variants were active in transformation assays and are therefore likely to be previously unreported rare polymorphisms or non-pathogenic passenger mutations.

Comprehensive analysis of homeobox genes in Hodgkin lymphoma cell lines identifies dysregulated expression of HOXB9 mediated via ERK5 signaling and BMI1

Many members of the nearly 200-strong homeobox gene family have been implicated in cancer, mostly following ectopic expression. In this study we analyzed homeobox gene expression in Hodgkin lymphoma (HL) cell lines. Both reverse transcription-polymerase chain reaction (RT-PCR) using degenerate primers and microarray profiling identified consistently up-regulated HOXB9 expression. Analysis of HOXB9 regulation in HL cells revealed E2F3A and BMI1 as activator and repressor, respectively. Furthermore, a constitutively active ERK5 pathway was identified in all HL cell lines analyzed as well as primary HL cells. Our data show that ERK5 probably mediates HOXB9 expression by repressing BMI1. In addition, expression analysis of the neighboring microRNA gene mir-196a1 revealed coregulation with HOXB9. Functional analysis of HOXB9 by knockdown and overexpression assays indicated their influence on both proliferation and apoptosis in HL cells. In summary, we identified up-regulation of HOXB9 in HL mediated by constitutively active ERK5 signaling which may represent novel therapeutic targets in HL.

High incidence of t(7;12)(q36;p13) in infant AML but not in infant ALL, with a dismal outcome and ectopic expression of HLXB9

The t(7;12)(q36;p13) is a recurrent translocation involving the ETV6/TEL gene (12p13) and a heterogeneous breakpoint at 7q36. A fusion transcript between HLXB9 and ETV6 in AML with t(7;12) is occasionally found. To study the incidence of t(7;12) in infant and childhood acute leukemia, we screened 320 cases <36 months using FISH. Additionally, 28 pediatric cases >36 months with cytogenetic breakpoints at 12p and 7q were investigated. We studied the presence of an HXLB9-ETV6 fusion transcript and quantified the expression of various genes located in the 7q36 breakpoint region. In total, six AML patients carried the t(7;12) of which five were infants and one child of 18 months. Only one out of 99 infant ALL patients harbored the t(7;12). No t(7;12) was found in older children with AML or ALL. AML patients carrying a t(7;12) had a poor outcome with a 3-year EFS of 0%. A fusion of HLXB9 to ETV6 was found in four AML cases with t(7;12). The 7q36 genes NOM1, LMBR1, RNF32, and SHH were equally expressed among t(7;12)-positive AML versus t(7;12)-negative AML, t(7;12)-negative ALL, or normal bone marrow. However, the HLXB9 expression was highly increased in t(7;12)-positive cases, including those with an HLXB9-ETV6 fusion. We conclude that the t(7;12) is almost exclusively present in infant AML and covers 30% of infant AML, while it is extremely rare in infant ALL and older children. The t(7;12) is associated with a poor outcome and an ectopic expression of HLXB9 is commonly involved in this genetic subtype of leukemia.

Genome-wide analysis of menin binding provides insights into MEN1 tumorigenesis

Multiple endocrine neoplasia type I (MEN1) is a familial cancer syndrome characterized primarily by tumors of multiple endocrine glands. The gene for MEN1 encodes a ubiquitously expressed tumor suppressor protein called menin. Menin was recently shown to interact with several components of a trithorax family histone methyltransferase complex including ASH2, Rbbp5, WDR5, and the leukemia proto-oncoprotein MLL. To elucidate menin's role as a tumor suppressor and gain insights into the endocrine-specific tumor phenotype in MEN1, we mapped the genomic binding sites of menin, MLL1, and Rbbp5, to approximately 20,000 promoters in HeLa S3, HepG2, and pancreatic islet cells using the strategy of chromatin-immunoprecipitation coupled with microarray analysis. We found that menin, MLL1, and Rbbp5 localize to the promoters of thousands of human genes but do not always bind together. These data suggest that menin functions as a general regulator of transcription. We also found that factor occupancy generally correlates with high gene expression but that the loss of menin does not result in significant changes in most transcript levels. One exception is the developmentally programmed transcription factor, HLXB9, which is overexpressed in islets in the absence of menin. Our findings expand the realm of menin-targeted genes several hundred-fold beyond that previously described and provide potential insights to the endocrine tumor bias observed in MEN1 patients.

In multiple endocrine neoplasia type I, absence of the nuclear factor menin gives rise to endocrine tumors by a mechanism that is poorly understood. Using state-of-the-art genome-wide chromatin-immunoprecipitation coupled with microarray analysis technology, this paper significantly enlarges our understanding of the role of menin by greatly extending the number of gene targets where menin binds. The authors show that while menin frequently colocalizes with a protein complex that modifies chromatin structure, menin can also bind to many other promoters by an alternative mechanism. They also present data that potentially implicate one of the menin target genes, HLXB9, in the endocrine specificity of tumorigenesis in multiple endocrine neoplasia, type 1. Further experiments to confirm the role of HLXB9 in tumorigenesis are necessary and may help explain how the loss of a ubiquitously expressed tumor suppressor gene can give rise to tumors in specific tissues.

HLXB9 activates IL6 in Hodgkin lymphoma cell lines and is regulated by PI3K signalling involving E2F3

Multiple cytokines are secreted by Hodgkin lymphoma (HL) cells, notably interleukin-6 (IL6), which is believed to play a significant pathobiological role in this and certain other tumors. Previous work on prostate carcinoma cells has shown that IL6 expression is activated therein by the homeodomain protein GBX2, which we found to be absent in HL cells. Instead, we observed expression of a closely related gene, HLXB9, albeit restricted to HL cells coexpressing IL6. Treatment of HL cell lines with antisense-oligonucleotides directed against HLXB9, forced expression of recombinant HLXB9, and analysis of reporter gene constructs containing IL6 promoter sequences all confirmed the potential of HLXB9 to drive expression of IL6. Chromosomal rearrangements of the HLXB9 locus at 7q36 were not detected in HL cells unlike AML subsets expressing HLXB9. However, inhibition of certain signal transduction pathways revealed that the phosphatidylinositol 3 kinase (PI3K) pathway contributes to HLXB9 expression. AKT/phospho-AKT analysis revealed constitutively active PI3K signalling in HL cell lines. Downstream analysis of PI3K revealed that E2F3 may mediate activation of HLXB9. Taken together, our data show that the PI3K signalling pathway in HL cells is constitutively activated and promotes HLXB9 expression, probably via E2F3, thereby enhancing malignant expression of IL6.