Meis1-mediated apoptosis is caspase dependent and can be suppressed by coexpression of HoxA9 in murine and human cell lines

The impact of MEIS1 TALE homeodomain transcription factor knockdown on glioma stem cell growth

Myeloid ecotropic virus insertion site 1 (MEIS1) is a HOX co-factor necessary for organ development and normal hematopoiesis. Recently, MEIS1 has been linked to the development and progression of various cancers. However, its role in gliomagenesis particularly on glioma stem cells (GSCs) remains unclear. Here, we demonstrate that MEIS1 is highly upregulated in GSCs compared to normal, and glioma cells and to its differentiated counterparts. Inhibition of MEIS1 expression by shRNA significantly reduced GSC growth in both in vitro and in vivo experiments. On the other hand, integrated transcriptomics analyses of glioma datasets revealed that MEIS1 expression is correlated to cell cycle-related genes. Clinical data analysis revealed that MEIS1 expression is elevated in high-grade gliomas, and patients with high MEIS1 levels have poorer overall survival outcomes. The findings suggest that MEIS1 is a prognostic biomarker for glioma patients and a possible target for developing novel therapeutic strategies against GBM.

PBX1: a key character of the hallmarks of cancer

Pre-B-cell leukemia homeobox transcription factor 1 (PBX1) was first identified as part of a fusion protein resulting from the chromosomal translocation t(1;19) in pre-B cell acute lymphoblastic leukemias. Since then, PBX1 has been associated with important developmental programs, and its expression dysregulation has been related to multifactorial disorders, including cancer. As PBX1 overexpression in many cancers is correlated to poor prognosis, we sought to understand how this transcription factor contributes to carcinogenesis, and to organize PBX1's roles in the hallmarks of cancer. There is enough evidence to associate PBX1 with at least five hallmarks: sustaining proliferative signaling, activating invasion and metastasis, inducing angiogenesis, resisting cell death, and deregulating cellular energetics. The lack of studies investigating a possible role for PBX1 on the remaining hallmarks made it impossible to defend or refute its contribution on them. However, the functions of some of the PBX1's transcription targets indicate a potential engagement of PBX1 in the avoidance of immune destruction and in the tumor-promoting inflammation hallmarks. Interestingly, PBX1 might be a player in tumor suppression by activating the transcription of some DNA damage response genes. This is the first review organizing PBX1 roles into the hallmarks of cancer. Thus, we encourage future studies to uncover the PBX1's underlying mechanisms to promote carcinogenesis, for it is a promising diagnostic and prognostic biomarker, as well as a potential target in cancer treatment.

MEIS1 and its potential as a cancer therapeutic target (Review)

Meis homeobox 1 (Meis1) was initially discovered in 1995 as a factor involved in leukemia in an animal model. Subsequently, 2 years later, MEIS1, the human homolog, was cloned in the liver and cerebellum, and was found to be highly expressed in myeloid leukemia cells. The MEIS1 gene, located on chromosome 2p14, encodes a 390-amino acid protein with six domains. The expression of homeobox protein MEIS1 is affected by cell type, age and environmental conditions, as well as the pathological state. Certain types of modifications of MEIS1 and its protein interaction with homeobox or pre-B-cell leukemia homeobox proteins have been described. As a transcription factor, MEIS1 protein is involved in cell proliferation in leukemia and some solid tumors. The present review article discusses the molecular biology, modifications, protein-protein interactions, as well as the role of MEIS1 in cell proliferation of cancer cells and MEIS1 inhibitors. It is suggested by the available literature MEIS1 has potential to become a cancer therapeutic target.

Oncogenic and tumor suppressor function of MEIS and associated factors

MEIS proteins are historically associated with tumorigenesis, metastasis, and invasion in cancer. MEIS and associated PBX-HOX proteins may act as tumor suppressors or oncogenes in different cellular settings. Their expressions tend to be misregulated in various cancers. Bioinformatic analyses have suggested their upregulation in leukemia/lymphoma, thymoma, pancreas, glioma, and glioblastoma, and downregulation in cervical, uterine, rectum, and colon cancers. However, every cancer type includes, at least, a subtype with high MEIS expression. In addition, studies have highlighted that MEIS proteins and associated factors may function as diagnostic or therapeutic biomarkers for various diseases. Herein, MEIS proteins and associated factors in tumorigenesis are discussed with recent discoveries in addition to how they could be modulated by noncoding RNAs or newly developed small-molecule MEIS inhibitors.

The Role of HOX Transcription Factors in Cancer Predisposition and Progression

Homeobox (HOX) transcription factors, encoded by a subset of homeodomain superfamily genes, play pivotal roles in many aspects of cellular physiology, embryonic development, and tissue homeostasis. Findings over the past decade have revealed that mutations in HOX genes can lead to increased cancer predisposition, and HOX genes might mediate the effect of many other cancer susceptibility factors by recognizing or executing altered genetic information. Remarkably, several lines of evidence highlight the interplays between HOX transcription factors and cancer risk loci discovered by genome-wide association studies, thereby gaining molecular and biological insight into cancer etiology. In addition, deregulated HOX gene expression impacts various aspects of cancer progression, including tumor angiogenesis, cell autophagy, proliferation, apoptosis, tumor cell migration, and metabolism. In this review, we will discuss the fundamental roles of HOX genes in cancer susceptibility and progression, highlighting multiple molecular mechanisms of HOX involved gene misregulation, as well as their potential implications in clinical practice.

CBAP modulates Akt-dependent TSC2 phosphorylation to promote Rheb-mTORC1 signaling and growth of T-cell acute lymphoblastic leukemia

High-frequency relapse remains a clinical hurdle for complete remission of T-cell acute lymphoblastic leukemia (T-ALL) patients, with heterogeneous dysregulated signaling profiles—including of Raf-MEK-ERK and Akt-mTORC1-S6K signaling pathways—recently being implicated in disease outcomes. Here we report that GM-CSF/IL-3/IL-5 receptor common β-chain-associated protein (CBAP) is highly expressed in human T-ALL cell lines and many primary tumor tissues and is required to bolster leukemia cell proliferation in tissue culture and for in vivo leukemogenesis in a xenograft mouse model. Downregulation of CBAP markedly restrains expansion of leukemia cells and alleviates disease aggravation of leukemic mice. Transcriptomic profiling and molecular biological analyses suggest that CBAP acts upstream of Ras and Rac1, and functions as a modulator of both Raf-MEK–ERK and Akt-mTORC1 signaling pathways to control leukemia cell growth. Specifically, CBAP facilitated Akt-dependent TSC2 phosphorylation in cell-based assays and in vitro analysis, decreased lysosomal localization of TSC2, and elevated Rheb-GTP loading and subsequent activation of mTORC1 signaling. Taken together, our findings reveal a novel oncogenic contribution of CBAP in T-ALL leukemic cells, in addition to its original pro-apoptotic function in cytokine-dependent cell lines and primary hematopoietic cells, by demonstrating its functional role in the regulation of Akt-TSC2-mTORC1 signaling for leukemia cell proliferation. Thus, CBAP represents a novel therapeutic target for many types of cancers and metabolic diseases linked to PI3K-Akt-mTORC1 signaling.

HOXA9 inhibits HIF-1α-mediated glycolysis through interacting with CRIP2 to repress cutaneous squamous cell carcinoma development

Glycolytic reprogramming is a typical feature of many cancers; however, key regulators of glucose metabolism reengineering are poorly understood, especially in cutaneous squamous cell carcinoma (cSCC). Here, Homeobox A9 (HOXA9), a direct target of onco-miR-365, is identified to be significantly downregulated in cSCC tumors and cell lines. HOXA9 acts as a tumor suppressor and inhibits glycolysis in cSCC in vitro and in vivo by negatively regulating HIF-1α and its downstream glycolytic regulators, HK2, GLUT1 and PDK1. Mechanistic studies show that HOXA9-CRIP2 interaction at glycolytic gene promoters impeds HIF-1α binding, repressing gene expression in trans. Our results reveal a miR-365-HOXA9-HIF-1α regulatory axis that contributes to the enhanced glycolysis in cSCC development and may represent an intervention target for cSCC therapy.

Hypoxia-inducible transcription factor HIF-1α promotes glycolysis allowing cell survival under stress. Here the authors show, using both cell lines and animal models, that in cutaneous squamous cell carcinoma HOXA9 acts as a tumor suppressor and inhibits glycolysis by associating with CRIP2 to repress HIF-1α binding to target genes.

Role of MAML1 and MEIS1 in Esophageal Squamous Cell Carcinoma Depth of Invasion

Homeobox (HOX) transcription factors and NOTCH signaling pathway are critical regulators of stem cell functions, cell fate in development and homeostasis of gastrointestinal tissues. In the present study, we analyzed cross talk between NOTCH pathway and HOX genes through assessment of probable correlation betweenMAML1 and MEIS1 as the main transcription factor of NOTCH pathway and enhancer of HOX transcriptional machinery, respectively in esophageal squamous cell carcinoma (ESCC) patients. Fifty one ESCC cases were enrolled to assess the levels of Meis1 and Maml1 mRNA expression using real-time polymerase chain reaction (PCR). Only 3 out of 51 (5.9%) cases had MEIS1/MAML1 under expression and 2/51 (3.9%) cases had MEIS1/MAML1over expression. Nine out of 51 samples (17.6%) have shown MEIS1 under expression and MAML1 over expression. There was a significant correlation between MAML1and MEIS1mRNA expressions (p ≤ 0.05). There were significant correlations between MEIS1 under/MAML1 over expressed cases and tumor location (p = 0.05), tumor depth of invasion (p = 0.011), and sex (p = 0.04). Our results showed that MEIS1 may have a negative role in regulation of MAML1expression during the ESCC progression.

RE-IIBP Methylates H3K79 and Induces MEIS1-mediated Apoptosis via H2BK120 Ubiquitination by RNF20

Histone lysine methylation contributes to transcriptional regulation by serving as a platform for the recruitment of various cofactors. Intense studies have been conducted for elucidating the functional meaning of H3K79 methylation, and to date, the only known HMTase responsible for the modification was DOT1L. In this study, we report that the MMSET isoform RE-IIBP has HMTase activity for H3K79. It was uncovered that RE-IIBP up-regulates MEIS1 transcription through H3K79 methylation via recruitment to the MEIS1 promoter. By means of proteomic and biochemical analysis, association of RE-IIBP with the E3 ubiquitin ligase RNF20 was demonstrated for synergistic activation of MEIS1 transcription via H3K79 HMTase activity. Furthermore, It was observed that RE-IIBP induces MEIS1-mediated apoptosis, which was dependent on H2BK120 ubiquitination by RNF20. These findings suggest RE-IIBP as another candidate for further studies to elucidate the mechanism of H3K79 methylation and its biological functions.

Quantitative multiplex quantum dot in-situ hybridisation based gene expression profiling in tissue microarrays identifies prognostic genes in acute myeloid leukaemia

Measurement and validation of microarray gene signatures in routine clinical samples is problematic and a rate limiting step in translational research. In order to facilitate measurement of microarray identified gene signatures in routine clinical tissue a novel method combining quantum dot based oligonucleotide in situ hybridisation (QD-ISH) and post-hybridisation spectral image analysis was used for multiplex in-situ transcript detection in archival bone marrow trephine samples from patients with acute myeloid leukaemia (AML). Tissue-microarrays were prepared into which white cell pellets were spiked as a standard. Tissue microarrays were made using routinely processed bone marrow trephines from 242 patients with AML. QD-ISH was performed for six candidate prognostic genes using triplex QD-ISH for DNMT1, DNMT3A, DNMT3B, and for HOXA4, HOXA9, Meis1. Scrambled oligonucleotides were used to correct for background staining followed by normalisation of expression against the expression values for the white cell pellet standard. Survival analysis demonstrated that low expression of HOXA4 was associated with poorer overall survival (p=0.009), whilst high expression of HOXA9 (p<0.0001), Meis1 (p=0.005) and DNMT3A (p=0.04) were associated with early treatment failure. These results demonstrate application of a standardised, quantitative multiplex QD-ISH method for identification of prognostic markers in formalin-fixed paraffin-embedded clinical samples, facilitating measurement of gene expression signatures in routine clinical samples.

MEIS1, PREP1, and PBX4 are differentially expressed in acute lymphoblastic leukemia: association of MEIS1 expression with higher proliferation and chemotherapy resistance

Background

The Three-amino acid-loop-extension (TALE) superfamily of homeodomain-containing transcription factors have been implicated in normal hematopoiesis and in leukemogenesis and are important survival, differentiation, and apoptosis pathway modulators. In this work, we determined the expression levels of TALE genes in leukemic-derived cell lines, in blood samples of patients with Acute lymphoblastic leukemia (ALL), and in the blood samples of healthy donors.

Results

Here we show increased expression of MEIS1, MEIS2, and PREP1 genes in leukemia-derived cell lines compared with blood normal cells. High levels of MEIS1 and PREP1, and low levels of PBX4 expression were also founded in samples of patients with ALL. Importantly, silencing of MEIS1 decreases the proliferation of leukemia-derived cells but increases their survival after etoposide treatment. Etoposide-induced apoptosis induces down-regulation of MEIS1 expression or PREP1 up-regulation in chemotherapy-resistant cells.

Conclusions

Our results indicate that up-regulation of MEIS1 is important for sustaining proliferation of leukemic cells and that down-regulation of MEIS1 or up-regulation of PREP1 and PBX genes could be implicated in the modulation of the cellular response to chemotherapeutic-induced apoptosis.

NUP98-HOXA9-transgenic zebrafish develop a myeloproliferative neoplasm and provide new insight into mechanisms of myeloid leukaemogenesis

NUP98-HOXA9 [t(7;11) (p15;p15)] is associated with inferior prognosis in de novo and treatment-related acute myeloid leukaemia (AML) and contributes to blast crisis in chronic myeloid leukaemia (CML). We have engineered an inducible transgenic zebrafish harbouring human NUP98-HOXA9 under the zebrafish spi1(pu.1) promoter. NUP98-HOXA9 perturbed zebrafish embryonic haematopoiesis, with upregulated spi1 expression at the expense of gata1a. Markers associated with more differentiated myeloid cells, lcp1, lyz, and mpx were also elevated, but to a lesser extent than spi1, suggesting differentiation of early myeloid progenitors may be impaired by NUP98-HOXA9. Following irradiation, NUP98-HOXA9-expressing embryos showed increased numbers of cells in G2-M transition compared to controls and absence of a normal apoptotic response, which may result from an upregulation of bcl2. These data suggest NUP98-HOXA9-induced oncogenesis may result from a combination of defects in haematopoiesis and an aberrant response to DNA damage. Importantly, 23% of adult NUP98-HOXA9-transgenic fish developed a myeloproliferative neoplasm (MPN) at 19-23 months of age. In summary, we have identified an embryonic haematopoietic phenotype in a transgenic zebrafish line that subsequently develops MPN. This tool provides a unique opportunity for high-throughput in vivo chemical modifier screens to identify novel therapeutic agents in high risk AML.

Trib1 links the MEK1/ERK pathway in myeloid leukemogenesis

Trib1 is a myeloid oncogene that cooperates with Hoxa9 and Meis1. Although the MAPK pathway and C/EBP transcription factors are known to interact with Trib proteins, the mechanisms by which Trib1 contributes to myeloid leukemogenesis remains to be clarified. Here we report that interaction between Trib1 and MEK1 is required for Trib1-induced leukemogenesis. The C-terminal ILLHPWF motif that is well conserved among Trib family proteins is required for MEK1 binding, enhancement of ERK phosphorylation, enhanced self-renewal activity of bone marrow cells and leukemogenic activity by Trib1. The motif is also important for Trib1-induced C/EBPα degradation though interaction between Trib1 and C/EBPα is not necessary. Inhibition of ERK phosphorylation suppressed Trib1-induced C/EBPα degradation, indicating an important role for Trib1/MEK1 interaction. These results suggest that Trib1 may be a key mediator between the RTK-MAPK pathway and the C/EBP transcription factor in myeloid leukemogenesis.

HOXA9 is required for survival in human MLL-rearranged acute leukemias

Leukemias that harbor translocations involving the mixed lineage leukemia gene (MLL) possess unique biologic characteristics and often have an unfavorable prognosis. Gene expression analyses demonstrate a distinct profile for MLL-rearranged leukemias with consistent high-level expression of select Homeobox genes, including HOXA9. Here, we investigated the effects of HOXA9 suppression in MLL-rearranged and MLL-germline leukemias using RNA interference. Gene expression profiling after HOXA9 suppression demonstrated co-down-regulation of a program highly expressed in human MLL-AML and murine MLL-leukemia stem cells, including HOXA10, MEIS1, PBX3, and MEF2C. We demonstrate that HOXA9 depletion in 17 human AML/ALL cell lines (7 MLL-rearranged, 10 MLL-germline) induces proliferation arrest and apoptosis specifically in MLL-rearranged cells (P = .007). Similarly, assessment of primary AMLs demonstrated that HOXA9 suppression induces apoptosis to a greater extent in MLL-rearranged samples (P = .01). Moreover, mice transplanted with HOXA9-depleted t(4;11) SEMK2 cells revealed a significantly lower leukemia burden, thus identifying a role for HOXA9 in leukemia survival in vivo. Our data indicate an important role for HOXA9 in human MLL-rearranged leukemias and suggest that targeting HOXA9 or downstream programs may be a novel therapeutic option.

MEIS and PBX homeobox proteins in ovarian cancer

Three amino-acid loop extension (TALE) homeobox proteins MEIS and PBX are cofactors for HOX-class homeobox proteins, which control growth and differentiation during embryogenesis and homeostasis. We showed that MEIS and PBX expression are related to cisplatin resistance in ovarian cancer cell lines. Therefore, MEIS1, MEIS2 and PBX expression were investigated immunohistochemically in a tissue microarray (N=232) of ovarian cancers and ovarian surface epithelium (N=15). Results were related to clinicopathologic characteristics and survival. All cancers expressed MEIS1, MEIS2 and PBX in nucleus and cytoplasm. MEIS1 and 2 only stained nuclear in surface epithelium. Nuclear MEIS2 was negatively related to stage, grade and overall survival in univariate analyses. Additionally, MEIS and PBX RNA expression in ovarian surface epithelium and other normal tissues and ovarian cancer versus other tumour types using public array data sets were studied. In ovarian cancer, MEIS1 is highly expressed compared to other cancer types. In conclusion, MEIS and PBX are extensively expressed in ovarian carcinomas and may play a role in ovarian carcinogenesis.

Histone deacetylase inhibitors deplete enhancer of zeste 2 and associated polycomb repressive complex 2 proteins in human acute leukemia cells

Human enhancer of zeste 2 (EZH2) protein belongs to the multiprotein polycomb repressive complex 2, which also includes suppressor of zeste 12 (SUZ12) and embryonic ectoderm development (EED). The polycomb repressive complex 2 complex possesses histone methyltransferase activity mediated by the Su(var)3-9, enhancer of zeste, and trithorax domain of EZH2, which methylates histone H3 on lysine (K)-27 (H3K27). In the present studies, we determined that treatment with the hydroxamate histone deacetylase inhibitor LBH589 or LAQ824 depleted the protein levels of EZH2, SUZ12, and EED in the cultured (K562, U937, and HL-60) and primary human acute leukemia cells. This was associated with decreased levels of trimethylated and dimethylated H3K27, with concomitant depletion of the homeobox domain containing HOXA9 and of MEIS1 transcription factors. Knockdown of EZH2 by EZH2 small interfering RNA also depleted SUZ12 and EED, inhibited histone methyltransferase activity, and reduced trimethylated and dimethylated H3K27 levels, with a concomitant loss of clonogenic survival of the cultured acute myelogenous leukemia (AML) cells. EZH2 small interfering RNA sensitized the AML cells to LBH589-mediated depletion of EZH2, SUZ12, and EED; loss of clonogenic survival; and LBH589-induced differentiation of the AML cells. These findings support the rationale to test anti-EZH2 treatment combined with hydroxamate histone deacetylase inhibitors as an antileukemia epigenetic therapy, especially against AML with coexpression of EZH2, HOXA9, and MEIS1 genes.

Jpk, a novel cell death inducer, regulates the expression of Hoxa7 in F9 teratocarcinoma cells, but not during apoptosis

Hox proteins play critical role in animal pattern formation during embryogenesis. During the study on the regulation of Hox gene expression, a novel gene, Jpk, has been isolated as a putative regulatory factor associating with the upstream regulatory sequence of murine Hoxa7. Since overexpression of Jpk caused cell death in bacteria as well as in eukaryotic cells and Hox has been reported to participate in apoptosis, we tried to analyze the relationship between Jpk and Hoxa7 during apoptosis after confirming the regulatory effect of Jpk on the expression of Hoxa7 in F9 teratocarcinoma cells. For that purpose, an effector (pEGFP-Jpk) and reporter (pGL2-NM307) plasmid containing a luciferase gene under the 307 bp (NM307) of Hoxa7 upstream regulatory sequence was constructed. In the presence of Jpk (effector), luciferase activity was increased and this enhancement was decreased by siRNA against Jpk, suggesting that Jpk is a regulatory factor of Hoxa7. In order to see whether Jpk still regulates the expression of Hoxa7 during apoptosis, F9 cells were transiently transfected with pcDNA-Jpk, and the expression of Jpk, Hoxa7, and CHOP-10 was analyzed using RT-PCR. Hoxa7 and CHOP-10 were not upregulated in the presence of Jpk although Jpk seemed to cause apoptosis, indicating that the regulatory mechanism of Jpk on the expression of Hoxa7 might be different depending on the cell status, that is, an apoptotic or proliferative condition.

Differential Expression of Neuronal Genes Defines Subtypes of Disseminated Neuroblastoma with Favorable and Unfavorable Outcome

PURPOSE

Identification of molecular characteristics of spontaneously regressing stage IVS and progressing stage IV neuroblastoma to improve discrimination of patients with metastatic disease following favorable and unfavorable clinical courses.

EXPERIMENTAL DESIGN

Serial analysis of gene expression profiles were generated from five stage IVS and three stage IV neuroblastoma. Differential expression of candidate genes was evaluated by real-time quantitative reverse transcription-PCR in 76 pretreatment tumor samples (stage IVS n=27 and stage IV n=49). Gene expression-based outcome prediction was determined by Prediction Analysis for Microarrays using 38 tumors as a training set and 38 tumors as a test set.

RESULTS

Comparison of serial analysis of gene expression profiles from stage IV and IVS neuroblastoma revealed approximately 500 differentially expressed transcripts. Genes related to neuronal differentiation were observed more frequently in stage IVS tumors as determined by associating transcripts to Gene Ontology annotations. Forty-one candidate genes were evaluated by quantitative reverse transcription-PCR and 18 were confirmed to be differentially expressed (P<or=0.001). Classification of patients according to expression patterns of these 18 genes using Prediction Analysis for Microarrays discriminated two subgroups with significantly differing event-free survival (96+/-6% versus 40+/-8% at 3 years; P<0.0001) and overall survival (100% versus 72+/-7% at 3 years; P=0.0003). This classifier was the only independent covariate marker in a multivariate analysis considering the variables stage, age, MYCN amplification, and gene signature.

CONCLUSIONS

Spontaneously regressing and progressing metastatic neuroblastoma differ by specific gene expression patterns, indicating distinct levels of neuronal differentiation and allowing for an improved risk estimation of children with disseminated disease.

Targeting MLL-AF4 with short interfering RNAs inhibits clonogenicity and engraftment of t(4;11)-positive human leukemic cells

The chromosomal translocation t(4;11) marks infant acute lymphoblastic leukemia associated with a particularly dismal prognosis. The leukemogenic role of the corresponding fusion gene MLL-AF4 is not well understood. We show that transient inhibition of MLL-AF4 expression with small interfering RNAs impairs the proliferation and clonogenicity of the t(4; 11)-positive human leukemic cell lines SEM and RS4;11. Reduction of mixed-lineage leukemia (MLL)-ALL-1 fused gene from chromosome 4 (AF4) levels induces apoptosis associated with caspase-3 activation and diminished BCL-X(L) expression. Suppression of MLL-AF4 is paralleled by a decreased expression of the homeotic genes HOXA7, HOXA9, and MEIS1. MLL-AF4 depletion inhibits expression of the stem-cell marker CD133, indicating hematopoietic differentiation. Transfection of leukemic cells with MLL-AF4 siRNAs reduces leukemia-associated morbidity and mortality in SCID mice that received a xenotransplant, suggesting that MLL-AF4 depletion negatively affects leukemia-initiating cells. Our findings demonstrate that MLL-AF4 is important for leukemic clonogenicity and engraftment of this highly aggressive leukemia. Targeted inhibition of MLL-AF4 fusion gene expression may lead to an effective and highly specific treatment of this therapy-resistant leukemia.

Converging pathways in leukemogenesis and stem cell self-renewal

Studies over the last 40 years have led to an understanding of the hierarchical organization of the hematopoietic system and the role of the pluripotential hematopoietic stem cell. Earlier recognition of the importance of bone marrow hematopoietic microenvironments has evolved into the recognition of specific niches that regulate stem cell pool size, proliferative status, mobilization, and differentiation. The discovery of the role of multiple hematopoietic growth factors and their receptors in the orchestration of stem cell self-renewal and differentiation has been followed by recognition of the importance of the Notch and Wnt pathways. The homeobox family of transcription factors serve as master regulators of development and are increasingly found to be critical regulators of hematopoiesis. In parallel with this understanding of normal hematopoiesis has come a recognition that stem cell dysregulation at various levels is involved in leukemogenesis. Furthermore, the progression from chronic leukemia or myelodysplasia to acute leukemia involves accumulation of at least two mutational events that lead to enhancement of stem cell proliferation, or acquisition of stem cell behavior by a progenitor cell, coupled with maturation inhibition. Translocations resulting in development of oncogenic fusion genes are found in AML and the transforming potential of two of these, AML1-ETO and NUP98-HOXA9, will be discussed. Secondary, constitutively activating mutations of the Flt3 and c-kit receptors and of K- and N-ras are found with high frequency in AML, and the transforming potential of mutated FLT3 and the role of STAT5A activation in human stem cell transformation will be reviewed.

Hox regulation of normal and leukemic hematopoietic stem cells

PURPOSE OF REVIEW

Herein we focus on recent studies of knock out mice that demonstrate a function for the clustered homeobox (Hox) genes in normal hematopoiesis, on papers that point to their general involvement in human leukemia, and discuss the advances in the understanding of the mechanisms underlying their role in these processes.

RECENT FINDINGS

Expression analysis and gain- or loss- of function studies have shown that Hox play an important role in the regulation of early stages of hematopoiesis, including the self-renewal of hematopoietic stem cells (HSCs)/early progenitors. In the area of leukemia, numerous models of murine leukemia have demonstrated a role for Hox in the pathobiology of the disease. Moreover, the identification of multiple Hox genes as partners of chromosomal translocations and the observed global deregulation of Hox genes and cofactors demonstrated by gene profiling of cells from leukemic patients, have unequivocally shown a major function for Hox genes and cofactors in a wide spectrum of human leukemia.

SUMMARY

The identification of Hox genes as HSC regulators has been exploited to develop strategies to efficiently expand HSCs ex vivo, a key step to the success of therapies based on HSC transplantation and the understanding of mechanisms underlying HSC regulation. As leukemia is the result of deregulation of normal HSC development, the elucidation of the role of Hox in the pathobiology of the disease is helping to understand how HSCs self-renew and differentiate, and moreover, should facilitate the development of strategies for the management of leukemia.

Differential Gene Expression Profiling of CD34+CD133+Umbilical Cord Blood Hematopoietic Stem Progenitor Cells

Umbilical cord blood (CB)-derived primitive hematopoietic stem progenitor cells (HSPC) are a promising source for stem cell-based gene therapy due to the reduced incidence and severity of graftversus- host disease (GVHD) after human leukocyte antigen (HLA)-disparate CB transplantation. Cell-surface markers such as CD34 and CD133 have been used in combination to enrich primitive HSPC for research and clinical applications. To understand the molecular characteristics of the CB HSPC, we compared the global gene expression of freshly isolated CB CD34+ CD133+ cells with their progenies using a cDNA microarray containing 22,000 human cDNA clones printed on a single chip. A total of 139 genes were differentially expressed between CB HSPC and their progenies. These transcripts included a number of known genes that might play roles in key functions of CB HSPC as well as many genes of unknown function. Among the genes showing the greatest differential expression levels in HSPC were: psoriasin 1, CRHBP, HDAC3, MLLT3, HBEX2, SPINK2, c-kit, H2BFQ, CD133, HHEX, TCF4, ALDH1A1, and FHL1. These data provide more information on the molecular phenotype of CB HSPC and may lead to the identification of new genes critical to stem cell function.