Expression of AML/Runx and ETO/MTG family members during hematopoietic differentiation of embryonic stem cells

Concordant Androgen-Regulated Expression of Divergent Rhox5 Promoters in Sertoli Cells

Concordant transcriptional regulation can generate multiple gene products that collaborate to achieve a common goal. Here we report a case of concordant transcriptional regulation that instead drives a single protein to be produced in the same cell type from divergent promoters. This gene product-the RHOX5 homeobox transcription factor-is translated from 2 different mRNAs with different 5' untranslated regions (UTRs) transcribed from alternative promoters. Despite the fact that these 2 promoters-the proximal promoter (Pp) and the distal promoter (Pd)-exhibit different patterns of tissue-specific activity, share no obvious sequence identity, and depend on distinct transcription factors for expression, they exhibit a remarkably similar expression pattern in the testes. In particular, both depend on androgen signaling for expression in the testes, where they are specifically expressed in Sertoli cells and have a similar stage-specific expression pattern during the seminiferous epithelial cycle. We report evidence for 3 mechanisms that collaborate to drive concordant Pp/Pd expression. First, both promoters have an intrinsic ability to respond to androgen receptor and androgen. Second, the Pp acts as an enhancer to promote androgen-dependent transcription from the Pd. Third, Pd transcription is positively autoregulated by the RHOX5 protein, which is first produced developmentally from the Pp. Together, our data support a model in which the Rhox5 homeobox gene evolved multiple mechanisms to activate both of its promoters in Sertoli cells to produce Rhox5 in an androgen-dependent manner during different phases of spermatogenesis.

RUNX1T1 rs34269950 is associated with obesity and metabolic syndrome

BACKGROUND

Runt-related transcription factor 1 (RUNX1T1) isoforms are involved in adipogenesis. RUNX1T1 is mediated by the fat mass and obesity-associated (FTO). However, the extent to which RUNX1T1 single-nucleotide polymorphisms (SNPs) are associated with obesity risk or metabolic abnormalities in a community population basis is unknown.

METHODS

Samples were obtained from the Australian Crossroads study bio-bank. SNPs located in the coding region and 3'untranslated regions of RUNX1T1 with minor allele frequency ≥0.05 were analysed using Taqman genotyping assays.

RESULTS

Eight candidate SNPs were genotyped successfully in 1440 participants. Of these SNPs only rs34269950 located in the 'RRACH' motif, the most common N6-methyladenosine (m6A) methylation modification site (recognized by FTO), was significantly associated with obesity risk and metabolic abnormalities. Specifically, compared to AA genotype, rs34269950 del/del genotype was associated with a 1.47 [95% confidence interval (CI): 1.01-2.14, P = 0.042] fold higher rate of obesity risk. Additionally, the del/del genotype was associated with a 60% increased risk of metabolic syndrome (MetS) [odds ratio (OR) = 1.60, 95% CI: 1.10-2.32, P = 0.015], in comparison to the AA genotype. Finally, rs34269950 del/del increased the risk of a larger waist circumference (OR = 1.65, 95% CI: 1.15-2.36, P = 0.007), but not other components of MetS.

CONCLUSION

Our study demonstrates that RUNX1T1 rs34269950, located in a potential FTO recognition motif, is significantly associated with waist circumference. This provides novel evidence to suggest SNPs located in RRACH motif may be involved in RNA m6A modification and mechanistic pathways that influence abdominal obesity.

Leukemia associated RUNX1T1 gene reduced proliferation and invasiveness of glioblastoma cells

RUNX1T1 has been found to be mutated in different cancers such as prostate, lung, colon, and breast cancer. A recent computational study involving the TCGA database of glioma patients found RUNX1T1 as one of the downregulated driver genes associated with poor overall survival of glioma patients. Hypoxia-inducible factor 1α (HIF1α) is upregulated in glioma and has been associated with the severity and drug resistance of glioma. Previously, we have shown that RUNX1T3 degrades HIF1α affecting the proliferation of leukemia cells. We hypothesize that RUNX1T1 might be associated with the growth and development of glioma through the regulation of HIF1α. We have evaluated the expression level of RUNX1T1 at different stages of glioma and the effect of RUNX1T1 on the proliferation and invasiveness of glioblastoma cells in vitro. We further looked at the effect of RUNX1T1 on the expression and stability of HIF1α in vitro. Expression of RUNX1T1 was significantly downregulated, both at RNA and protein levels in glioma samples as studied by quantitative real-time polymerase chain reaction and immunohistochemistry. While expression of HIF1α was higher in glioma tissues compared with its level in the normal brain. In vitro studies demonstrated that RUNX1T1 interacted with HIF1α and recruited HIF1α modification factor such as PHD2 and GSK3β causing hydroxylation of HIF1α following ubiquitination by FBW7. RUNX1T1 led to the degradation of HIF1α and decreased proliferation/invasiveness of glioblastoma cell lines. Further, RUNX1T1 increased the effectiveness of temozolomide (TMZ), a conventional glioma drug toward glioblastoma cell lines. This study indicates that downregulation of RUNX1T1 might play an important role in the severity and development of glioma.

RUNX1T1, a potential prognostic marker in breast cancer, is co-ordinately expressed with ERα, and regulated by estrogen receptor signalling in breast cancer cells

BACKGROUND

RUNX1T1 is extensively studied in the context of AML1-RUNX1T1 fusion protein in acute myeloid leukemia. Little is known about the function of RUNX1T1 itself, although data on its function and regulation have begun to emerge from clinical, and in vitro studies. It is a putative tumor suppressor, whose expression is altered in a variety of solid tumors. Recently, reduced expression of RUNX1T1 in triple-negative breast tumors, and its influence on prognosis was reported.

METHODS AND RESULTS

The Kaplan-Meier Plotter online tool was used to study the relationship between RUNX1T1 expression and survival of breast cancer patients. High RUNX1T1 expression was associated with longer overall survival (OS), relapse-free survival (RFS) and distant metastasis free survival (DMFS). RUNX1T1 expression positively and negatively influenced OS of patients with ERα-positive and ERα-negative breast tumors, respectively. It was also associated with prolonged RFS, and DMFS in tamoxifen-treated patients. Expression of RUNX1T1 and ERα mRNA was analyzed in 40 breast tumor samples, and breast cancer cell lines using RT-PCR. TCGA-BRCA data was mined to study the relationship between RUNX1T1 and ERα mRNA expression. ERα-positive breast tumors showed significantly higher RUNX1T1 mRNA expression compared to ERα-negative tumors. RUNX1T1 mRNA expression was analyzed by qRT-PCR in MCF-7 or T47D cells, which were treated with 17β-estradiol, or the ERα agonist PPT, alone or in combination with 4-hydroxytamoxifen. Effect of ERα knockdown was also investigated. Results indicate that estrogen downmodulated RUNX1T1 mRNA expression via ERα.

CONCLUSION

Higher expression of RUNX1T1 in breast tumors is associated with favourable prognosis. RUNX1T1 and ERα show co-ordinated expression in breast tumors, and breast cancer cell lines. Estrogen-ERα signalling downmodulates the expression of RUNX1T1 mRNA in ERα-positive breast cancer cells. In-depth investigations on the interaction between RUNX1T1 and ERα are warranted to unravel the role and relevance of RUNX1T1 in breast cancer.

Runx1t1 promotes the neuronal differentiation in rat hippocampus

Background

Runt-related transcription factor 1 translocated to 1 (Runx1t1) is one of the members of the myeloid translocation gene family. Our previous work showed that Runx1t1 induced the neuronal differentiation of radial glia cells in vitro.

Methods

To better uncover the role of Runx1t1 in hippocampal neurogenesis, in this study, we further explore its localization and function during the hippocampal neurogenesis.

Results

Our results showed that insufficient expression of Runx1t1 reduced the neuronal differentiation, and overexpression of Runx1t1 promoted the neuronal differentiation in vitro. We also found that Runx1t1 localized in neurons but not astrocytes both in vivo and in vitro. Furthermore, we found that Runx1t1 overexpression elevated the number of newborn neurons in the hippocampal dentate gyrus.

Conclusions

Taken together, our results further proved that Runx1t1 could be worked as a regulator in the process of hippocampal neurogenesis.

Compatibility of RUNX1/ETO fusion protein modules driving CD34+ human progenitor cell expansion

Chromosomal translocations represent frequent events in leukemia. In t(8;21)+ acute myeloid leukemia, RUNX1 is fused to nearly the entire ETO protein, which contains four conserved nervy homology regions, NHR1-4. Furthermore RUNX1/ETO interacts with ETO-homologous proteins via NHR2, thereby multiplying NHR domain contacts. As shown recently, RUNX1/ETO retains oncogenic activity upon either deletion of the NHR3 + 4 N-CoR/SMRT interaction domain or substitution of the NHR2 tetramer domain. Thus, we aimed to clarify the specificities of the NHR domains. A C-terminally NHR3 + 4 truncated RUNX1/ETO containing a heterologous, structurally highly related non-NHR2 tetramer interface translocated into the nucleus and bound to RUNX1 consensus motifs. However, it failed to interact with ETO-homologues, repress RUNX1 targets, and transform progenitors. Surprisingly, transforming capacity was fully restored by C-terminal fusion with ETO's NHR4 zinc-finger or the repressor domain 3 of N-CoR, while other repression domains failed. With an inducible protein assembly system, we further demonstrated that NHR4 domain activity is critically required early in the establishment of progenitor cultures expressing the NHR2 exchanged truncated RUNX1/ETO. Together, we can show that NHR2 and NHR4 domains can be replaced by heterologous protein domains conferring tetramerization and repressor functions, thus showing that the NHR2 and NHR4 domain structures do not have irreplaceable functions concerning RUNX1/ETO activity for the establishment of human CD34+ cell expansion. We could resemble the function of RUNX1/ETO through modular recomposition with protein domains from RUNX1, ETO, BCR and N-CoR without any NHR2 and NHR4 sequences. As most transcriptional repressor proteins do not comprise tetramerization domains, our results provide a possible explanation as to the reason that RUNX1 is recurrently found translocated to ETO family members, which all contain tetramer together with transcriptional repressor moieties.

Characterization of RUNX1T1, an Adipogenesis Regulator in Ovine Preadipocyte Differentiation

Runt-related transcription factor 1 translocation partner 1 (RUNX1T1), a potential novel regulator of adipogenesis, exists in two splice variants: a long (RUNX1T1-L) and a short (RUNX1T1-S) isoform. However, there is no data showing the existence of RUNX1T1 in ovine subcutaneous fat at different stages of developmental and its role on ovine adipogenesis. Therefore, the objectives of this study were to evaluate the presence of RUNX1T1 in subcutaneous fat of five-day-old to 24-month-old sheep and to investigate the role of RUNX1T1 in ovine adipogenesis. In this study, we detected a 1829 bp cDNA fragment of RUNX1T1 which contains a 1815 bp coding sequence that encodes 602-amino acid and 14 bp of 5′ untranslated region, respectively. The amino acid sequence of RUNX1T1 has 31.18–94.21% homology with other species’ protein sequences. During fat development, the RUNX1T1 protein expression was higher in subcutaneous fat of 24-month-old Hu sheep. In addition, the expression of RUNX1T1-L mRNA decreased first, then subsequently increased during ovine preadipocyte differentiation. Knockdown of RUNX1T1-L in ovine preadipocytes promoted preadipocyte differentiation and lipid accumulation. Taken together, our data suggests that RUNX1T1 is an important functional molecule in adipogenesis. Moreover, it showed for the first time that RUNX1T1-L was negatively correlated with the ovine preadipocyte differentiation.

Integrated Analyses Reveal Overexpressed Notch1 Promoting Porcine Satellite Cells' Proliferation through Regulating the Cell Cycle

Notch signaling as a conserved cell fate regulator is involved in the regulation of cell quiescence, proliferation, differentiation and postnatal tissue regeneration. However, how Notch signaling regulates porcine satellite cells (PSCs) has not been elucidated. We stably transfected Notch1 intracellular domain (N1ICD) into PSCs to analyze the gene expression profile and miRNA-seq. The analysis of the gene expression profile identified 295 differentially-expressed genes (DEGs) in proliferating-N1ICD PSCs (P-N1ICD) and nine DEGs on differentiating-N1ICD PSCs (D-N1ICD), compared with that in control groups (P-Control and D-Control, respectively). Analyzing the underlying function of DEGs showed that most of the upregulated DEGs enriched in P-N1ICD PSCs are related to the cell cycle. Forty-four and 12 known differentially-expressed miRNAs (DEMs) were identified in the P-N1ICD PSCs and D-N1ICD PSCs group, respectively. Furthermore, we constructed the gene-miRNA network of the DEGs and DEMs. In P-N1ICD PSCs, miR-125a, miR-125b, miR-10a-5p, ssc-miR-214, miR-423 and miR-149 are downregulated hub miRNAs, whose corresponding hub genes are marker of proliferation Ki-67 (MKI67) and nuclear receptor binding SET domain protein 2 (WHSC1). By contrast, miR-27a, miR-146a-5p and miR-221-3p are upregulated hub miRNAs, whose hub genes are RUNX1 translocation partner 1 (RUNX1T1) and fibroblast growth factor 2 (FGF2). All the hub miRNAs and genes are associated with cell proliferation. Quantitative RT-PCR results are consistent with the gene expression profile and miRNA-seq results. The results of our study provide valuable information for understanding the molecular mechanisms underlying Notch signaling in PSCs and skeletal muscle development.

Emerging Roles of MTG16 in Cell-Fate Control of Hematopoietic Stem Cells and Cancer

MTG16 (myeloid translocation gene on chromosome 16) and its related proteins, MTG8 and MTGR1, define a small family of transcriptional corepressors. These corepressors share highly conserved domain structures yet have distinct biological functions and tissue specificity. In vivo studies have shown that, of the three MTG corepressors, MTG16 is uniquely important for the regulation of hematopoietic stem/progenitor cell (HSPC) proliferation and differentiation. Apart from this physiological function, MTG16 is also involved in carcinomas and leukemias, acting as the genetic target of loss of heterozygosity (LOH) aberrations in breast cancer and recurrent translocations in leukemia. The frequent involvement of MTG16 in these disease etiologies implies an important developmental role for this transcriptional corepressor. Furthermore, mounting evidence suggests that MTG16 indirectly alters the disease course of several leukemias via its regulatory interactions with a variety of pathologic fusion proteins. For example, a recent study has shown that MTG16 can repress not only wild-type E2A-mediated transcription, but also leukemia fusion protein E2A-Pbx1-mediated transcription, suggesting that MTG16 may serve as a potential therapeutic target in acute lymphoblastic leukemia expressing the E2A-Pbx1 fusion protein. Given that leukemia stem cells share similar regulatory pathways with normal HSPCs, studies to further understand how MTG16 regulates cell proliferation and differentiation could lead to novel therapeutic approaches for leukemia treatment.

Endothelial angiogenesis is directed by RUNX1T1-regulated VEGFA, BMP4 and TGF-β2 expression

Tissue angiogenesis is intimately regulated during embryogenesis and postnatal development. Defected angiogenesis contributes to aberrant development and is the main complication associated with ischemia-related diseases. We previously identified the increased expression of RUNX1T1 in umbilical cord blood-derived endothelial colony-forming cells (ECFCs) by gene expression microarray. However, the biological relevance of RUNX1T1 in endothelial lineage is not defined clearly. Here, we demonstrate RUNX1T1 regulates the survival, motility and tube forming capability of ECFCs and EA.hy926 endothelial cells by loss-and gain-of function assays, respectively. Second, embryonic vasculatures and quantity of bone marrow-derived angiogenic progenitors are found to be reduced in the established Runx1t1 heterozygous knockout mice. Finally, a central RUNX1T1-regulated signature is uncovered and VEGFA, BMP4 as well as TGF-β2 are demonstrated to mediate RUNX1T1-orchested angiogenic activities. Taken together, our results reveal that RUNX1T1 serves as a common angiogenic driver for vaculogenesis and functionality of endothelial lineage cells. Therefore, the discovery and application of pharmaceutical activators for RUNX1T1 will improve therapeutic efficacy toward ischemia by promoting neovascularization.

Core binding factor (CBF) is required for Epstein-Barr virus EBNA3 proteins to regulate target gene expression

ChIP-seq performed on lymphoblastoid cell lines (LCLs), expressing epitope-tagged EBNA3A, EBNA3B or EBNA3C from EBV-recombinants, revealed important principles of EBNA3 binding to chromatin. When combined with global chromatin looping data, EBNA3-bound loci were found to have a singular character, each directly associating with either EBNA3-repressed or EBNA3-activated genes, but not with both. EBNA3A and EBNA3C showed significant association with repressed and activated genes. Significant direct association for EBNA3B loci could only be shown with EBNA3B-repressed genes. A comparison of EBNA3 binding sites with known transcription factor binding sites in LCL GM12878 revealed substantial co-localization of EBNA3s with RUNX3-a protein induced by EBV during B cell transformation. The beta-subunit of core binding factor (CBFβ), that heterodimerizes with RUNX3, could co-immunoprecipitate robustly EBNA3B and EBNA3C, but only weakly EBNA3A. Depletion of either RUNX3 or CBFβ with lentivirus-delivered shRNA impaired epitope-tagged EBNA3B and EBNA3C binding at multiple regulated gene loci, indicating a requirement for CBF heterodimers in EBNA3 recruitment during target-gene regulation. ShRNA-mediated depletion of CBFβ in an EBNA3C-conditional LCL confirmed the role of CBF in the regulation of EBNA3C-induced and -repressed genes. These results reveal an important role for RUNX3/CBF during B cell transformation and EBV latency that was hitherto unexplored.

Runx1t1 regulates the neuronal differentiation of radial glial cells from the rat hippocampus

The brain has the highest Runx1t1 level relative to the levels in other organs. Runx1t1 might have a regulatory function as a transcriptional corepressor in the differentiation/development of the nervous system. Neurogenesis requires factors that regulate the proliferation of progenitors and activate the neuronal differentiation process. However, the precise role of Runx1t1 in hippocampal neurogenesis is unclear. We knocked down Runx1t1 in hippocampal radial glial cells (RGCs) with Runx1t1-RNA interference using lentiviral vectors. We also used LV-Runx1t1 to induce Runx1t1 overexpression in vitro. We have provided experimental evidence that decreased Runx1t1 expression reduced the neuronal differentiation of RGCs, and increased Runx1t1 expression caused a greater number of RGCs to differentiate into neurons. We have concluded that Runx1t1 could be involved in the process through which RGCs differentiate into neurons.

Runx1t1 (Runt-related transcription factor 1; translocated to, 1) epigenetically regulates the proliferation and nitric oxide production of microglia

Background

Microglia, the resident immune cells of the brain, undergo rapid proliferation and produce several proinflammatory molecules and nitric oxide (NO) when activated in neuropathological conditions. Runx1t1 (Runt-related transcription factor 1, translocated to 1) has been implicated in recruiting histone deacetylases (HDACs) for transcriptional repression, thereby regulating cell proliferation. In the present study, Runx1t1 expression was shown to localize in amoeboid microglial cells of the postnatal rat brain, being hardly detectable in ramified microglia of the adult brain. Moreover, a marked expression of Runx1t1was induced and translocated to nuclei in activated microglia in vitro and in vivo. In view of these findings, it was hypothesized that Runx1t1 regulates microglial functions during development and in neuropathological conditions.

Methods and Findings

siRNA-mediated knockdown of Runx1t1 significantly decreased the expression level of cell cycle-related gene, cyclin-dependent kinase 4 (Cdk4) and proliferation index in activated BV2 microglia. It was also shown that HDAC inhibitor (HDACi) treatment mimics the effects of Runx1t1 knockdown on microglial proliferation, confirming that microglial proliferation is associated with Runx1t1 expression and HDACs activity. Further, Runx1t1 and HDACs were shown to promote neurotoxic effect of microglia by repressing expression of LAT2, L-aminoacid transporter-2 (cationic amino acid transporter, y+ system), which normally inhibits NO production. This was confirmed by chromatin immunoprecipitation (ChIP) assay, which revealed that Runx1t1 binds to the promoter region of LAT2 and this binding increased upon microglial activation. However, the enhanced binding of Runx1t1 to the LAT2 promoter could not repress the LAT2 expression when the BV2 microglia cells were treated with HDACi, indicating that Runx1t1 requires HDACs to transcriptionally repress the expression of LAT2.

Conclusion/Interpretation

In conclusion, it is suggested that Runx1t1 controls proliferation and the neurotoxic effect of microglia by epigenetically regulating Cdk4 and LAT2 via its interaction with HDACs.

CEH-20/Pbx and UNC-62/Meis function upstream of rnt-1/Runx to regulate asymmetric divisions of the C. elegans stem-like seam cells

Caenorhabditis elegans seam cells divide in the stem-like mode throughout larval development, with the ability to both self-renew and produce daughters that differentiate. Seam cells typically divide asymmetrically, giving rise to an anterior daughter that fuses with the hypodermis and a posterior daughter that proliferates further. Previously we have identified rnt-1 (a homologue of the mammalian cancer-associated stem cell regulator Runx) as being an important regulator of seam development, acting to promote proliferation; rnt-1 mutants have fewer seam cells whereas overexpressing rnt-1 causes seam cell hyperplasia. We isolated the interacting CEH-20/Pbx and UNC-62/Meis TALE-class transcription factors during a genome-wide RNAi screen for novel regulators of seam cell number. Animals lacking wild type CEH-20 or UNC-62 display seam cell hyperplasia, largely restricted to the anterior of the worm, whereas double mutants have many additional seam cells along the length of the animal. The cellular basis of the hyperplasia involves the symmetrisation of normally asymmetric seam cell divisions towards the proliferative stem-like fate. The hyperplasia is completely suppressed in rnt-1 mutants, and rnt-1 is upregulated in ceh-20 and unc-62 mutants, suggesting that CEH-20 and UNC-62 function upstream of rnt-1 to limit proliferative potential to the appropriate daughter cell. In further support of this we find that CEH-20 is asymmetrically localised in seam daughters following an asymmetric division, being predominantly restricted to anterior nuclei whose fate is to differentiate. Thus, ceh-20 and unc-62 encode crucial regulators of seam cell division asymmetry, acting via rnt-1 to regulate the balance between proliferation and differentiation.

RUNX1a enhances hematopoietic lineage commitment from human embryonic stem cells and inducible pluripotent stem cells

Advancements in human pluripotent stem cell (hPSC) research have potential to revolutionize therapeutic transplantation. It has been demonstrated that transcription factors may play key roles in regulating maintenance, expansion, and differentiation of hPSCs. In addition to its regulatory functions in hematopoiesis and blood-related disorders, the transcription factor RUNX1 is also required for the formation of definitive blood stem cells. In this study, we demonstrated that expression of endogenous RUNX1a, an isoform of RUNX1, parallels with lineage commitment and hematopoietic emergence from hPSCs, including both human embryonic stem cells and inducible pluripotent stem cells. In a defined hematopoietic differentiation system, ectopic expression of RUNX1a facilitates emergence of hematopoietic progenitor cells (HPCs) and positively regulates expression of mesoderm and hematopoietic differentiation-related factors, including Brachyury, KDR, SCL, GATA2, and PU.1. HPCs derived from RUNX1a hPSCs show enhanced expansion ability, and the ex vivo-expanded cells are capable of differentiating into multiple lineages. Expression of RUNX1a in embryoid bodies (EBs) promotes definitive hematopoiesis that generates erythrocytes with β-globin production. Moreover, HPCs generated from RUNX1a EBs possess ≥9-week repopulation ability and show multilineage hematopoietic reconstitution in vivo. Together, our results suggest that RUNX1a facilitates the process of producing therapeutic HPCs from hPSCs.

The leukemia associated nuclear corepressor ETO homologue genes MTG16 and MTGR1 are regulated differently in hematopoietic cells

Background

MTG16, MTGR1 and ETO are nuclear transcriptional corepressors of the human ETO protein family. MTG16 is implicated in hematopoietic development and in controlling erythropoiesis/megakaryopoiesis. Furthermore, ETO homologue genes are 3'participants in leukemia fusions generated by chromosomal translocations responsible of hematopoietic dysregulation. We tried to identify structural and functional promoter elements of MTG16 and MTGR1 genes in order to find associations between their regulation and hematopoiesis.

Results

5' deletion examinations and luciferase reporter gene studies indicated that a 492 bp sequence upstream of the transcription start site is essential for transcriptional activity by the MTG16 promoter. The TATA- and CCAAT-less promoter with a GC box close to the start site showed strong reporter activity when examined in erythroid/megakaryocytic cells. Mutation of an evolutionary conserved GATA -301 consensus binding site repressed promoter function. Furthermore, results from in vitro antibody-enhanced electrophoretic mobility shift assay and in vivo chromatin immunoprecipitation indicated binding of GATA-1 to the GATA -301 site. A role of GATA-1 was also supported by transfection of small interfering RNA, which diminished MTG16 expression. Furthermore, expression of the transcription factor HERP2, which represses GATA-1, produced strong inhibition of the MTG16 promoter reporter consistent with a role of GATA-1 in transcriptional activation. The TATA-less and CCAAT-less MTGR1 promoter retained most of the transcriptional activity within a -308 to -207 bp region with a GC-box-rich sequence containing multiple SP1 binding sites reminiscent of a housekeeping gene with constitutive expression. However, mutations of individual SP1 binding sites did not repress promoter function; multiple active SP1 binding sites may be required to safeguard constitutive MTGR1 transcriptional activity. The observed repression of MTG16/MTGR1 promoters by the leukemia associated AML1-ETO fusion gene may have a role in hematopoietic dysfunction of leukemia.

Conclusions

An evolutionary conserved GATA binding site is critical in transcriptional regulation of the MTG16 promoter. In contrast, the MTGR1 gene depends on a GC-box-rich sequence for transcriptional regulation and possible ubiquitous expression. Our results demonstrate that the ETO homologue promoters are regulated differently consistent with hematopoietic cell-type- specific expression and function.

Runx2 in normal tissues and cancer cells: A developing story

The Runx transcription factors are essential for mammalian development, most notably in the haematopoietic and osteogenic lineages. Runx1 and its binding partner, CBFbeta, are frequently targeted in acute leukaemia but evidence is accumulating that all three Runx genes may have a role to play in a wider range of cancers, either as tumour promoters or tumour suppressors. Whilst Runx2 is renowned for its role as a master regulator of bone development we discuss here its expression pattern and putative functions beyond this lineage. Furthermore, we review the evidence that RUNX2 promotes neoplastic development in haematopoietic lineages and in advanced mammary and prostate cancer.

Assessment of transmission distortion on chromosome 6p in healthy individuals using tagSNPs

The best-documented example for transmission distortion (TD) to normal offspring are the t haplotypes on mouse chromosome 17. In healthy humans, TD has been described for whole chromosomes and for particular loci, but multiple comparisons have presented a statistical obstacle in wide-ranging analyses. Here we provide six high-resolution TD maps of the short arm of human chromosome 6 (Hsa6p), based on single-nucleotide polymorphism (SNP) data from 60 trio families belonging to two ethnicities that are available through the International HapMap Project. We tested all approximately 70,000 previously genotyped SNPs within Hsa6p by the transmission disequilibrium test. TagSNP selection followed by permutation testing was performed to adjust for multiple testing. A statistically significant evidence for TD was observed among male parents of European ancestry, due to strong and wide-ranging skewed segregation in a 730 kb long region containing the transcription factor-encoding genes SUPT3H and RUNX2, as well as the microRNA locus MIRN586. We also observed that this chromosomal segment coincides with pronounced linkage disequilibrium (LD), suggesting a relationship between TD and LD. The fact that TD may be taking place in samples not selected for a genetic disease implies that linkage studies must be assessed with particular caution in chromosomal segments with evidence of TD.

Characterization of a t(5;8)(q31;q21) translocation in a patient with mental retardation and congenital heart disease: implications for involvement of RUNX1T1 in human brain and heart development

The chromosome break points of the t(8;21)(q21.3;q22.12) translocation associated with acute myeloid leukemia disrupt the RUNX1 gene (also known as AML1) and the RUNX1T1 gene (also known as CBFA2T3, MTG8 and ETO) and generate a RUNX1-RUNX1T1 fusion protein. Molecular characterization of the translocation break points in a t(5;8)(q32;q21.3) patient with mild-to-moderate mental retardation and congenital heart disease revealed that one of the break points was within the RUNX1T1 gene. Analysis of RUNX1T1 expression in human embryonic and fetal tissues suggests a role of RUNX1T1 in brain and heart development and support the notion that disruption of the RUNX1T1 gene is associated with the patient's phenotype.

Transcriptional repression of the RUNX3/AML2 gene by the t(8;21) and inv(16) fusion proteins in acute myeloid leukemia

RUNX3/AML2 is a Runt domain transcription factor like RUNX1/AML1 and RUNX2/AML3. Regulated by 2 promoters P1 and P2, RUNX3 is frequently inactivated by P2 methylation in solid tumors. Growing evidence has suggested a role of this transcription factor in hematopoiesis. However, genetic alterations have not been reported in blood cancers. In this study on 73 acute myeloid leukemia (AML) patients (44 children and 29 adults), we first showed that high RUNX3 expression among childhood AML was associated with a shortened event-free survival, and RUNX3 was significantly underexpressed in the prognostically favorable subgroup of AML with the t(8;21) and inv(16) translocations. We further demonstrated that this RUNX3 repression was mediated not by P2 methylation, but RUNX1-ETO and CBFbeta-MYH11, the fusion products of t(8;21) and inv(16), via a novel transcriptional mechanism that acts directly or indirectly in collaboration with RUNX1, on 2 conserved RUNX binding sites in the P1 promoter. In in vitro studies, ectopically expressed RUNX1-ETO and CBFbeta-MYH11 also inhibited endogenous RUNX3 expression. Taken together, RUNX3 was the first transcriptional target found to be commonly repressed by the t(8;21) and inv(16) fusion proteins and might have an important role in core-binding factor AML.

t(8;21)(q22;q22) Fusion proteins preferentially bind to duplicated AML1/RUNX1 DNA-binding sequences to differentially regulate gene expression

Chromosome abnormalities are frequently associated with cancer development. The 8;21(q22;q22) chromosomal translocation is one of the most common chromosome abnormalities identified in leukemia. It generates fusion proteins between AML1 and ETO. Since AML1 is a well-defined DNA-binding protein, AML1-ETO fusion proteins have been recognized as DNA-binding proteins interacting with the same consensus DNA-binding site as AML1. The alteration of AML1 target gene expression due to the presence of AML1-ETO is related to the development of leukemia. Here, using a 25-bp random double-stranded oligonucleotide library and a polymerase chain reaction (PCR)-based DNA-binding site screen, we show that compared with native AML1, AML1-ETO fusion proteins preferentially bind to DNA sequences with duplicated AML1 consensus sites. This finding is further confirmed by both in vitro and in vivo DNA-protein interaction assays. These results suggest that AML1-ETO fusion proteins have a selective preference for certain AML1 target genes that contain multimerized AML1 consensus sites in their regulatory elements. Such selected regulation provides an important molecular mechanism for the dysregulation of gene expression during cancer development.

The functional consequences of alternative promoter use in mammalian genomes

We are beginning to appreciate the increasing complexity of mammalian gene structure. A phenomenon that adds an important dimension to this complexity is the use of alternative gene promoters that drive widespread cell type, tissue type or developmental gene regulation. Recent annotations of the human genome suggest that almost one half of the protein-coding genes contain alternative promoters, including those of many disease-associated genes. Aberrant use of one promoter over another has been found to be associated with various diseases, including cancer. Here we discuss the functional consequences of use and misuse of alternative promoters in normal and disease genomes and review the molecular mechanisms regulating alternative promoter use in mammalian genomes.

Inability of RUNX1/AML1 to breach AML1-ETO block of embryonic stem cell definitive hematopoiesis

The t(8;21)(q22:q22) translocation associated with acute myeloid leukemia fuses the AML1/RUNX1 N-terminal portion located on chromosome 21 to most of the ETO/MTG8 gene on chromosome 8. Various investigators have shown that the fusion product AML1-ETO on its own is unable to promote leukemia. Early studies using transgenic mouse models demonstrated that the direct knock-in of the fusion protein expression is embryonic lethal, similar to the AML1 knockout, suggesting that AML1-ETO has a dominant negative role over AML1. Using the embryonic stem cells generated for such studies, we show here that the presence of the fusion product AML1-ETO blocks definitive hematopoiesis in vitro as well, in both one and two step methylcellulose methods of embryonic stem cell hematopoietic differentiation. However, there is a very low occurrence of macrophage colonies, similar to the knock-in mice that display macrophages in cell cultures of yolk sac derived cells. In addition, we show that exogenous expression of AML1 is unable to bypass this AML1-ETO induced definitive hematopoietic block in these cells. This inability is not linked to an inability to reverse gene expression inhibition by AML1-ETO of the PU.1 gene associated with stem cell maintenance and myeloid differentiation. Our results suggest that AML1-ETO functions in a complex competitive manner with AML1 involving transcriptional regulation, protein-protein interactions and post-transcriptional mechanism(s) affecting early embryonic hematopoiesis and possibly leukemogenesis.