Down-regulation of the myeloid homeobox protein Hex is essential for normal T-cell development

Overcoming effector T cell exhaustion in ovarian cancer ascites with a novel adenovirus encoding for a MUC1 bispecific antibody engager and IL-2 cytokine

T cell-focused cancer immunotherapy including checkpoint inhibitors and cell therapies has been rapidly evolving over the past decade. Nevertheless, there remains a major unmet medical need in oncology generally and immuno-oncology specifically. We have constructed an oncolytic adenovirus, Ad5/3-E2F-d24-aMUC1aCD3-IL-2 (TILT-322), which is armed with a human aMUC1aCD3 T cell engager and IL-2. TILT-322 treatment stimulated T cell cytotoxicity through the increased presence of granzyme B, perforin, and interferon-gamma. Additional immune profiling indicated TILT-322 increased gamma delta T cell activation and impacted other cell types such as natural killer cells and natural killer-like T cells that are traditionally involved in cancer immunotherapy. TILT-322 treatment also decreased the proportion of exhausted CD8+ T cells as demarked by immune checkpoint expression in ovarian ascites samples. Overall, our data showed that TILT-322 treatment led to an enhanced T cell activation and reversed T cell exhaustion translating into high antitumor efficacy when given locally or intravenously. The analysis of blood and tumors isolated from an in vivo patient-derived ovarian cancer xenograft model suggested TILT-322 mediated tumor control through improved T cell functions. Therefore, TILT-322 is a promising novel anti-tumor agent for clinical translation.

The Haematopoietically-expressed homeobox transcription factor: roles in development, physiology and disease

The Haematopoietically expressed homeobox transcription factor (Hhex) is a transcriptional repressor that is of fundamental importance across species, as evident by its evolutionary conservation spanning fish, amphibians, birds, mice and humans. Indeed, Hhex maintains its vital functions throughout the lifespan of the organism, beginning in the oocyte, through fundamental stages of embryogenesis in the foregut endoderm. The endodermal development driven by Hhex gives rise to endocrine organs such as the pancreas in a process which is likely linked to its role as a risk factor in diabetes and pancreatic disorders. Hhex is also required for the normal development of the bile duct and liver, the latter also importantly being the initial site of haematopoiesis. These haematopoietic origins are governed by Hhex, leading to its crucial later roles in definitive haematopoietic stem cell (HSC) self-renewal, lymphopoiesis and haematological malignancy. Hhex is also necessary for the developing forebrain and thyroid gland, with this reliance on Hhex evident in its role in endocrine disorders later in life including a potential role in Alzheimer's disease. Thus, the roles of Hhex in embryological development throughout evolution appear to be linked to its later roles in a variety of disease processes.

The Role of NKL Homeobox Genes in T-Cell Malignancies

Homeobox genes encode transcription factors controlling basic developmental processes. The homeodomain is encoded by the homeobox and mediates sequence-specific DNA binding and interaction with cofactors, thus operating as a basic regulatory platform. Similarities in their homeobox sequences serve to arrange these genes in classes and subclasses, including NKL homeobox genes. In accordance with their normal functions, deregulated homeobox genes contribute to carcinogenesis along with hematopoietic malignancies. We have recently described the physiological expression of eleven NKL homeobox genes in the course of hematopoiesis and termed this gene expression pattern NKL-code. Due to the developmental impact of NKL homeobox genes these data suggest a key role for their activity in the normal regulation of hematopoietic cell differentiation including T-cells. On the other hand, aberrant overexpression of NKL-code members or ectopical activation of non-code members has been frequently reported in lymphoid and myeloid leukemia/lymphoma, demonstrating their oncogenic impact in the hematopoietic compartment. Here, we provide an overview of the NKL-code in normal hematopoiesis and discuss the oncogenic role of deregulated NKL homeobox genes in T-cell malignancies.

NKL Homeobox Gene VENTX Is Part of a Regulatory Network in Human Conventional Dendritic Cells

Recently, we documented a hematopoietic NKL-code mapping physiological expression patterns of NKL homeobox genes in human myelopoiesis including monocytes and their derived dendritic cells (DCs). Here, we enlarge this map to include normal NKL homeobox gene expressions in progenitor-derived DCs. Analysis of public gene expression profiling and RNA-seq datasets containing plasmacytoid and conventional dendritic cells (pDC and cDC) demonstrated HHEX activity in both entities while cDCs additionally expressed VENTX. The consequent aim of our study was to examine regulation and function of VENTX in DCs. We compared profiling data of VENTX-positive cDC and monocytes with VENTX-negative pDC and common myeloid progenitor entities and revealed several differentially expressed genes encoding transcription factors and pathway components, representing potential VENTX regulators. Screening of RNA-seq data for 100 leukemia/lymphoma cell lines identified prominent VENTX expression in an acute myelomonocytic leukemia cell line, MUTZ-3 containing inv(3)(q21q26) and t(12;22)(p13;q11) and representing a model for DC differentiation studies. Furthermore, extended gene analyses indicated that MUTZ-3 is associated with the subtype cDC2. In addition to analysis of public chromatin immune-precipitation data, subsequent knockdown experiments and modulations of signaling pathways in MUTZ-3 and control cell lines confirmed identified candidate transcription factors CEBPB, ETV6, EVI1, GATA2, IRF2, MN1, SPIB, and SPI1 and the CSF-, NOTCH-, and TNFa-pathways as VENTX regulators. Live-cell imaging analyses of MUTZ-3 cells treated for VENTX knockdown excluded impacts on apoptosis or induced alteration of differentiation-associated cell morphology. In contrast, target gene analysis performed by expression profiling of knockdown-treated MUTZ-3 cells revealed VENTX-mediated activation of several cDC-specific genes including CSFR1, EGR2, and MIR10A and inhibition of pDC-specific genes like RUNX2. Taken together, we added NKL homeobox gene activities for progenitor-derived DCs to the NKL-code, showing that VENTX is expressed in cDCs but not in pDCs and forms part of a cDC-specific gene regulatory network operating in DC differentiation and function.

NKL-Code in Normal and Aberrant Hematopoiesis

Simple Summary

Gene codes represent expression patterns of closely related genes in particular tissues, organs or body parts. The NKL-code describes the activity of NKL homeobox genes in the hematopoietic system. NKL homeobox genes encode transcription factors controlling basic developmental processes. Therefore, aberrations of this code may contribute to deregulated hematopoiesis including leukemia and lymphoma. Normal and abnormal activities of NKL homeobox genes are described and mechanisms of (de)regulation, function, and diseases exemplified.

Abstract

We have recently described physiological expression patterns of NKL homeobox genes in early hematopoiesis and in subsequent lymphopoiesis and myelopoiesis, including terminally differentiated blood cells. We thereby systematized differential expression patterns of eleven such genes which form the so-called NKL-code. Due to the developmental impact of NKL homeobox genes, these data suggest a key role for their activity in normal hematopoietic differentiation processes. On the other hand, the aberrant overexpression of NKL-code-members or the ectopical activation of non-code members have been frequently reported in lymphoid and myeloid leukemia/lymphoma, revealing the oncogenic potential of these genes in the hematopoietic compartment. Here, I provide an overview of the NKL-code in normal hematopoiesis and instance mechanisms of deregulation and oncogenic functions of selected NKL genes in hematologic cancers. As well as published clinical studies, our conclusions are based on experimental work using hematopoietic cell lines which represent useful models to characterize the role of NKL homeobox genes in specific tumor types.

Homeobox protein Hhex negatively regulates Treg cells by inhibiting Foxp3 expression and function

Regulatory T (Treg) cells play an essential role in maintaining immune homeostasis, but the suppressive function of Treg cells can be an obstacle in the treatment of cancer and chronic infectious diseases. Here, we identified the homeobox protein Hhex as a negative regulator of Treg cells. The expression of Hhex was lower in Treg cells than in conventional T (Tconv) cells. Hhex expression was repressed in Treg cells by TGF-β/Smad3 signaling. Retroviral overexpression of Hhex inhibited the differentiation of induced Treg (iTreg) cells and the stability of thymic Treg (tTreg) cells by significantly reducing Foxp3 expression. Moreover, Hhex-overexpressing Treg cells lost their immunosuppressive activity and failed to prevent colitis in a mouse model of inflammatory bowel disease (IBD). Hhex expression was increased; however, Foxp3 expression was decreased in Treg cells in a delayed-type hypersensitivity (DTH) reaction, a type I immune reaction. Hhex directly bound to the promoters of Foxp3 and other Treg signature genes, including Il2ra and Ctla4, and repressed their transactivation. The homeodomain and N-terminal repression domain of Hhex were critical for inhibiting Foxp3 and other Treg signature genes. Thus, Hhex plays an essential role in inhibiting Treg cell differentiation and function via inhibition of Foxp3.

Deregulated NKL Homeobox Genes in B-Cell Lymphoma

Recently, we have described physiological expression patterns of NKL homeobox genes in early hematopoiesis and in subsequent lymphopoiesis. We identified nine genes which constitute the so-called NKL-code. Aberrant overexpression of code-members or ectopically activated non-code NKL homeobox genes are described in T-cell leukemia and in T- and B-cell lymphoma, highlighting their oncogenic role in lymphoid malignancies. Here, we introduce the NKL-code in normal hematopoiesis and focus on deregulated NKL homeobox genes in B-cell lymphoma, including HLX, MSX1 and NKX2-2 in Hodgkin lymphoma; HLX, NKX2-1 and NKX6-3 in diffuse large B-cell lymphoma; and NKX2-3 in splenic marginal zone lymphoma. Thus, the roles of various members of the NKL homeobox gene subclass are considered in normal and pathological hematopoiesis in detail.

NKL homeobox gene activities in hematopoietic stem cells, T-cell development and T-cell leukemia

T-cell acute lymphoblastic leukemia (T-ALL) cells represent developmentally arrested T-cell progenitors, subsets of which aberrantly express homeobox genes of the NKL subclass, including TLX1, TLX3, NKX2-1, NKX2-5, NKX3-1 and MSX1. Here, we analyzed the transcriptional landscape of all 48 members of the NKL homeobox gene subclass in CD34+ hematopoietic stem and progenitor cells (HSPCs) and during lymphopoiesis, identifying activities of nine particular genes. Four of these were expressed in HSPCs (HHEX, HLX1, NKX2-3 and NKX3-1) and three in common lymphoid progenitors (HHEX, HLX1 and MSX1). Interestingly, our data indicated downregulation of NKL homeobox gene transcripts in late progenitors and mature T-cells, a phenomenon which might explain the oncogenic impact of this group of genes in T-ALL. Using MSX1-expressing T-ALL cell lines as models, we showed that HHEX activates while HLX1, NKX2-3 and NKX3-1 repress MSX1 transcription, demonstrating the mutual regulation and differential activities of these homeobox genes. Analysis of a public T-ALL expression profiling data set comprising 117 patient samples identified 20 aberrantly activated members of the NKL subclass, extending the number of known NKL homeobox oncogene candidates. While 7/20 genes were also active during hematopoiesis, the remaining 13 showed ectopic expression. Finally, comparative analyses of T-ALL patient and cell line profiling data of NKL-positive and NKL-negative samples indicated absence of shared target genes but instead highlighted deregulation of apoptosis as common oncogenic effect. Taken together, we present a comprehensive survey of NKL homeobox genes in early hematopoiesis, T-cell development and T-ALL, showing that these genes generate an NKL-code for the diverse stages of lymphoid development which might be fundamental for regular differentiation.

Hhex is Required at Multiple Stages of Adult Hematopoietic Stem and Progenitor Cell Differentiation

Hhex encodes a homeodomain transcription factor that is widely expressed in hematopoietic stem and progenitor cell populations. Its enforced expression induces T-cell leukemia and we have implicated it as an important oncogene in early T-cell precursor leukemias where it is immediately downstream of an LMO2-associated protein complex. Conventional Hhex knockouts cause embryonic lethality precluding analysis of adult hematopoiesis. Thus, we induced highly efficient conditional knockout (cKO) using vav-Cre transgenic mice. Hhex cKO mice were viable and born at normal litter sizes. At steady state, we observed a defect in B-cell development that we localized to the earliest B-cell precursor, the pro-B-cell stage. Most remarkably, bone marrow transplantation using Hhex cKO donor cells revealed a more profound defect in all hematopoietic lineages. In contrast, sublethal irradiation resulted in normal myeloid cell repopulation of the bone marrow but markedly impaired repopulation of T- and B-cell compartments. We noted that Hhex cKO stem and progenitor cell populations were skewed in their distribution and showed enhanced proliferation compared to WT cells. Our results implicate Hhex in the maintenance of LT-HSCs and in lineage allocation from multipotent progenitors especially in stress hematopoiesis.

Trisomy 8 Acute Myeloid Leukemia Analysis Reveals New Insights of DNA Methylome with Identification of HHEX as Potential Diagnostic Marker

Trisomy 8 acute myeloid leukemia (AML) is the commonest numerical aberration in AML. Here we present a global analysis of trisomy 8 AML using methylated DNA immunoprecipitation-sequencing (MeDIP-seq). The study is based on three diagnostic trisomy 8 AML and their parallel relapse status in addition to nine non-trisomic AML and four normal bone marrows (NBMs). In contrast to non-trisomic DNA samples, trisomy 8 AML showed a characteristic DNA methylation distribution pattern because an increase in the frequency of the hypermethylation signals in chromosome 8 was associated with an increase in the hypomethylation signals in the rest of the chromosomes. Chromosome 8 hypermethylation signals were found mainly in the CpG island (CGI) shores and interspersed repeats. Validating the most significant differentially methylated CGI (P = 7.88 × 10(-11)) identified in trisomy 8 AML demonstrated a specific core region within the gene body of HHEX, which was significantly correlated with HHEX expression in both diagnostic and relapse trisomy 8 AMLs. Overall, the existence of extra chromosome 8 was associated with a global impact on the DNA methylation distribution with identification of HHEX gene methylation as a potential diagnostic marker for trisomy 8 AML.

A mouse model for inducible overexpression of Prdm14 results in rapid-onset and highly penetrant T-cell acute lymphoblastic leukemia (T-ALL)

PRDM14 functions in embryonic stem cell (ESC) maintenance to promote the expression of pluripotency-associated genes while suppressing differentiation genes. Expression of PRDM14 is tightly regulated and typically limited to ESCs and primordial germ cells; however, aberrant expression is associated with tumor initiation in a wide variety of human cancers, including breast cancer and leukemia. Here, we describe the generation of a Cre-recombinase-inducible mouse model for the spatial and temporal control of Prdm14 misexpression [ROSA26 floxed-stop Prdm14 (R26PR)]. When R26PR is mated to either of two Cre lines, Mx1-cre or MMTV-cre, mice develop early-onset T-cell acute lymphoblastic leukemia (T-ALL) with median overall survival of 41 and 64 days for R26PR;Mx1-cre and R26PR;MMTV-cre, respectively. T-ALL is characterized by the accumulation of immature single-positive CD8 cells and their widespread infiltration. Leukemia is preceded by a dramatic expansion of cells resembling hematopoietic stem cells and lymphoid-committed progenitors prior to disease onset, accompanied by a blockage in B-cell differentiation at the early pro-B stage. Rapid-onset PRDM14-induced T-ALL requires factors that are present in stem and progenitor cells: R26PR;dLck-cre animals, which express Prdm14 starting at the double-positive stage of thymocyte development, do not develop disease. PRDM14-induced leukemic cells contain high levels of activated NOTCH1 and downstream NOTCH1 targets, including MYC and HES1, and are sensitive to pharmacological inhibition of NOTCH1 with the γ-secretase inhibitor DAPT. Greater than 50% of human T-ALLs harbor activating mutations in NOTCH1; thus, our model carries clinically relevant molecular aberrations. The penetrance, short latency and involvement of the NOTCH1 pathway will make this hematopoietic R26PR mouse model ideal for future studies on disease initiation, relapse and novel therapeutic drug combinations. Furthermore, breeding R26PR to additional Cre lines will allow for the continued development of novel cancer models.

New MLLT10 gene recombinations in pediatric T-acute lymphoblastic leukemia

The MLLT10 gene, located at 10p13, is a known partner of MLL and PICALM in specific leukemic fusions generated from recurrent 11q23 and 11q14 chromosome translocations. Deep sequencing recently identified NAP1L1/12q21 as another MLLT10 partner in T-cell acute lymphoblastic leukemia (T-ALL). In pediatric T-ALL, we have identified 2 RNA processing genes, that is, HNRNPH1/5q35 and DDX3X/Xp11.3 as new MLLT10 fusion partners. Gene expression profile signatures of the HNRNPH1- and DDX3X-MLLT10 fusions placed them in the HOXA subgroup. Remarkably, they were highly similar only to PICALM-MLLT10-positive cases. The present study showed MLLT10 promiscuity in pediatric T-ALL and identified a specific MLLT10 signature within the HOXA subgroup.

NKL homeobox genes in leukemia

NK-like (NKL) homeobox genes code for transcription factors, which can act as key regulators in fundamental cellular processes. NKL genes have been implicated in divergent types of cancer. In this review, we summarize the involvement of NKL genes in cancer and leukemia in particular. NKL genes can act as tumor-suppressor genes and as oncogenes, depending on tissue type. Aberrant expression of NKL genes is especially common in T-cell acute lymphoblastic leukemia (T-ALL). In T-ALL, 8 NKL genes have been reported to be highly expressed in specific T-ALL subgroups, and in ~30% of cases, high expression is caused by chromosomal rearrangement of 1 of 5 NKL genes. Most of these NKL genes are normally not expressed in T-cell development. We hypothesize that the NKL genes might share a similar downstream effect that promotes leukemogenesis, possibly due to mimicking a NKL gene that has a physiological role in early hematopoietic development, such as HHEX. All eight NKL genes posses a conserved Eh1 repressor motif, which has an important role in regulating downstream targets in hematopoiesis and possibly in leukemogenesis as well. Identification of a potential common leukemogenic NKL downstream pathway will provide a promising subject for future studies.

Multilayered specification of the T-cell lineage fate

T-cell development from stem cells has provided a highly accessible and detailed view of the regulatory processes that can go into the choice of a cell fate in a postembryonic, stem cell-based system. But it has been a view from the outside. The problems in understanding the regulatory basis for this lineage choice begin with the fact that too many transcription factors are needed to provide crucial input: without any one of them, T-cell development fails. Furthermore, almost all the factors known to provide crucial functions during the climax of T-lineage commitment itself are also vital for earlier functions that establish the pool of multilineage precursors that would normally feed into the T-cell specification process. When the regulatory genes that encode them are mutated, the confounding effects on earlier stages make it difficult to dissect T-cell specification genetically. Yet both the positive and the negative regulatory events involved in the choice of a T-cell fate are actually a mosaic of distinct functions. New evidence has emerged recently that finally provides a way to separate the major components that fit together to drive this process. Here, we review insights into T-cell specification and commitment that emerge from a combination of molecular, cellular, and systems biology approaches. The results reveal the regulatory structure underlying this lineage decision.

Phosphorylation of HOX11/TLX1 on Threonine-247 during mitosis modulates expression of cyclin B1

BACKGROUND

The HOX11/TLX1 (hereafter referred to as HOX11) homeobox gene was originally identified at a t(10;14)(q24;q11) translocation breakpoint, a chromosomal abnormality observed in 5-7% of T cell acute lymphoblastic leukemias (T-ALLs). We previously reported a predisposition to aberrant spindle assembly checkpoint arrest and heightened incidences of chromosome missegregation in HOX11-overexpressing B lymphocytes following exposure to spindle poisons. The purpose of the current study was to evaluate cell cycle specific expression of HOX11.

RESULTS

Cell cycle specific expression studies revealed a phosphorylated form of HOX11 detectable only in the mitotic fraction of cells after treatment with inhibitors to arrest cells at different stages of the cell cycle. Mutational analyses revealed phosphorylation on threonine-247 (Thr247), a conserved amino acid that defines the HOX11 gene family and is integral for the association with DNA binding elements. The effect of HOX11 phosphorylation on its ability to modulate expression of the downstream target, cyclin B1, was tested. A HOX11 mutant in which Thr247 was substituted with glutamic acid (HOX11 T247E), thereby mimicking a constitutively phosphorylated HOX11 isoform, was unable to bind the cyclin B1 promoter or enhance levels of the cyclin B1 protein. Expression of the wildtype HOX11 was associated with accelerated progression through the G2/M phase of the cell cycle, impaired synchronization in prometaphase and reduced apoptosis whereas expression of the HOX11 T247E mutant restored cell cycle kinetics, the spindle checkpoint and apoptosis.

CONCLUSIONS

Our results demonstrate that the transcriptional activity of HOX11 is regulated by phosphorylation of Thr247 in a cell cycle-specific manner and that this phosphorylation modulates the expression of the target gene, cyclin B1. Since it is likely that Thr247 phosphorylation regulates DNA binding activity to multiple HOX11 target sequences, it is conceivable that phosphorylation functions to regulate the expression of HOX11 target genes involved in the control of the mitotic spindle checkpoint.

CK2 phosphorylation of the PRH/Hex homeodomain functions as a reversible switch for DNA binding

The proline-rich homeodomain protein (PRH/Hex) regulates transcription by binding to specific DNA sequences and regulates mRNA transport by binding to translation initiation factor eIF4E. Protein kinase CK2 plays multiple roles in the regulation of gene expression and cell proliferation. Here, we show that PRH interacts with the β subunit of CK2 in vitro and in cells and that CK2 phosphorylates PRH. Phosphorylation of PRH by CK2 inhibits the DNA binding activity of this protein and dephosphorylation restores DNA binding indicating that this modification acts as a reversible switch. We show that phosphorylation of the homeodomain is sufficient to block DNA binding and we identify two amino acids within this the domain that are phosphorylated by CK2: S163 and S177. Site-directed mutagenesis demonstrates that mutation of either of these residues to glutamic acid partially mimics phosphorylation but is insufficient to completely block DNA binding whereas an S163E/S177E double mutation severely inhibits DNA binding. Significantly, the S163E and S177E mutations and the S163E/S177E double mutation all inhibit the ability of PRH to regulate transcription in cells. Since these amino acids are conserved between many homeodomain proteins, our results suggest that CK2 may regulate the activity of several homeodomain proteins in this manner.

The PRH/Hex repressor protein causes nuclear retention of Groucho/TLE co-repressors

The PRH (proline-rich homeodomain) [also known as Hex (haematopoietically expressed homeobox)] protein is a transcription factor that functions as an important regulator of vertebrate development and many other processes in the adult including haematopoiesis. The Groucho/TLE (transducin-like enhancer) family of co-repressor proteins also regulate development and modulate the activity of many DNA-binding transcription factors during a range of diverse cellular processes including haematopoiesis. We have shown previously that PRH is a repressor of transcription in haematopoietic cells and that an Eh-1 (Engrailed homology) motif present within the N-terminal transcription repression domain of PRH mediates binding to Groucho/TLE proteins and enables co-repression. In the present study we demonstrate that PRH regulates the nuclear retention of TLE proteins during cellular fractionation. We show that transcriptional repression and the nuclear retention of TLE proteins requires PRH to bind to both TLE and DNA. In addition, we characterize a trans-dominant-negative PRH protein that inhibits wild-type PRH activity by sequestering TLE proteins to specific subnuclear domains. These results demonstrate that transcriptional repression by PRH is dependent on TLE availability and suggest that subnuclear localization of TLE plays an important role in transcriptional repression by PRH.

PRH/Hex: an oligomeric transcription factor and multifunctional regulator of cell fate

The PRH (proline-rich homeodomain) [also known as Hex (haematopoietically expressed homeobox)] protein is a critical regulator of vertebrate development. PRH is able to regulate cell proliferation and differentiation and is required for the formation of the vertebrate body axis, the haematopoietic and vascular systems and the formation of many vital organs. PRH is a DNA-binding protein that can repress and activate the transcription of its target genes using multiple mechanisms. In addition, PRH can regulate the nuclear transport of specific mRNAs making PRH a member of a select group of proteins that control gene expression at the transcriptional and translational levels. Recent biophysical analysis of the PRH protein has shown that it forms homo-oligomeric complexes in vivo and in vitro and that the proline-rich region of PRH forms a novel dimerization interface. Here we will review the current literature on PRH and discuss the complex web of interactions centred on this multifunctional protein.

Molecular profiling reveals distinct functional attributes of CD1d-restricted natural killer (NK) T cell subsets

CD1d-restricted natural killer T (NKT) cells can have multiple effects on an immune response, including the activation, regulation and attraction of innate immune cells, and modulation of adaptive immunity. Recent studies reveal that there are distinct subsets of NKT cells which selectively perform some of the functions attributed to CD1d-restricted cells, but the mechanisms underlying these functional differences have not been resolved. Our aim in this study was to identify novel NKT cell associated traits that would provide important insight into NKT cell activation and function. To this end, we have performed gene expression profiling of two separate subsets of NKT cells, analyzing genes differentially expressed in these cells compared to conventional CD4(+)NK1.1(-) T cells. We identify different sets of genes over expressed in each of the two NKT cell types, as well as genes that are common to the two CD1d-restricted NKT cell populations analyzed. A large number of these genes are highly relevant for NKT cell development, activation and function. Each NKT subtype displayed a unique set of chemokine receptors, integrins and molecules related to effector function, supporting the notion that distinct NKT cells can be selectively engaged and have diverse functions in different types of immune reactions.

Overexpression of a hematopoietic transcriptional regulator EDAG induces myelopoiesis and suppresses lymphopoiesis in transgenic mice

Erythroid differentiation-associated gene (EDAG) is a hematopoietic tissue-specific gene that is highly expressed in the earliest CD34+ lin- bone marrow (BM) cells and involved in the proliferation and differentiation of hematopoietic cells. To investigate the role of EDAG in hematopoiesis, we established an EDAG transgenic mouse model driven by human CD11a promoter. The transgenic mice showed increased mortality with severe organ infiltration by neutrophils, and the homeostasis of hematopoiesis was broken. The myelopoiesis was enhanced with expansion of myeloid cells in BM, increased peripheral granulocytes and extramedullary myelopoiesis in spleen. In contrast to myeloid cells, the lymphoid commitment was severely impaired with the B lymphopoiesis blocked at the transition from pro/pre-B I to pre-B II stage in BM and T thymocytes development blocked at the most immature stage (DN I). Moreover, we showed that EDAG was a transcriptional regulator which had transactivation activity and regulated the expression of several key transcription factors such as PU.1 and Pax5 in transgenic hematopoietic stem cells. These data suggested that EDAG was a key transcriptional regulator in maintaining the homeostasis of hematopoietic lineage commitment.

Oligomerisation of the developmental regulator proline rich homeodomain (PRH/Hex) is mediated by a novel proline-rich dimerisation domain

Homeodomain proteins regulate multiple developmental pathways by altering gene expression temporally and in a tissue-specific fashion. The Proline Rich Homeodomain protein (PRH/Hex) is a transcription factor and an essential regulator of embryonic development and haematopoiesis. Recent discoveries have implicated self-association as an important feature of transcription factor function. Here, we show using a variety of techniques including gel-filtration, analytical ultracentrifugation, electron microscopy and in vitro cross-linking, that purified recombinant PRH is oligomeric and we use in vivo cross-linking to confirm that this protein exists as oligomers in cells. This is the first demonstration that a homeodomain protein can oligomerise in vivo. Consistent with these findings we show that a fraction of endogenous and exogenous PRH appears as discrete foci within the nucleus and at the nuclear periphery. The N-terminal domain of PRH is involved in the regulation of cell proliferation and transcriptional repression and can make multiple protein-protein interactions. We show that this region of PRH contains a novel proline-rich dimerisation domain that mediates oligomerisation. We propose a model that explains how PRH forms oligomers and we discuss how these oligomers might control transcription.

Purification and characterisation of the PRH homeodomain: Removal of the N-terminal domain of PRH increases the PRH homeodomain-DNA interaction

The Proline-Rich Homeodomain (PRH) protein is a regulator of transcription and translation and plays a key role in the control of cell proliferation and cell differentiation. PRH contains an N-terminal proline-rich domain that can repress transcription when expressed as a fusion protein with an unrelated DNA binding domain, a central homeodomain that binds to specific DNA sequences and an acidic C-terminal domain of no known function. In order to investigate the structure and functions of PRH we have purified the full-length protein and truncated proteins corresponding to different domains of PRH fused to histidine tags. Here we compare the effects of elution conditions and column volume on protein purification and we investigate the DNA binding activity of these proteins. We show that the PRH homeodomain co-purifies with nucleic acids even after nuclease treatment and that a high salt-wash is required to remove bound nucleic acids. In contrast with the full-length PRH protein, the PRH homeodomain binds to DNA with high affinity. We show that a truncated protein comprising the homeodomain and C-terminal domain also binds to DNA with high affinity and we conclude that the N-terminal domain of PRH inhibits the homeodomain-DNA interaction.

The proline-rich homeodomain (PRH/HEX) protein is down-regulated in liver during infection with lymphocytic choriomeningitis virus

The proline-rich homeodomain protein, PRH/HEX, participates in the early development of the brain, thyroid, and liver and in the later regenerative processes of damaged liver, vascular endothelial, and hematopoietic cells. A virulent strain of lymphocytic choriomeningitis virus (LCMV-WE) that destroys hematopoietic, vascular, and liver functions also alters the transcription and subcellular localization of PRH. A related virus (LCMV-ARM) that does not cause disease in primates can infect cells without affecting PRH. Biochemical experiments demonstrated the occurrence of binding between the viral RING protein (Z) and PRH, and genetic experiments mapped the PRH-suppressing phenotype to the large (L) segment of the viral genome, which encodes the Z and polymerase genes. The Z protein is clearly involved with PRH, but other viral determinants are needed to relocate PRH and to promote disease. By down-regulating PRH, the arenavirus is able to eliminate the antiproliferative effects of PRH and to promote liver cell division. The interaction of an arenavirus with a homeodomain protein suggests a mechanism for viral teratogenic effects and for the tissue-specific manifestations of arenavirus disease.

Identification and Characterization of the Hematopoietic Cell-Specific Enhancer-Like Element of the Mouse Hex Gene

Hex is one of the homeobox genes suggested to be important for hematopoietic cell differentiation. However, its biological function and mechanism of transcriptional regulation in hematopoietic cells remain elusive. We have identified the regulatory region necessary for transcription of the mouse Hex gene in K562 leukemia cells through transient reporter assays involving various deletion mutants. This region, comprising +775 to +1177 in the first intron, had enhancer-like properties and showed high activity in other hematopoietic cell lines such as U937, HEL, and RAW264.7, but little activity in other Hex-expressing cell lines such as MH(1)C(1) and H4IIE hepatoma cells, suggesting that this region functions as a hematopoietic cell-specific enhancer-like element. Binding site mutation of hematopoietic transcription factors, such as GATAs and c-Myb present in the enhancer-like element, significantly decreased the luciferase reporter gene expression in K562 cells. Electrophoretic mobility shift assays showed that GATA-1, GATA-2, or c-Myb actually binds to three of these putative binding sites, and also suggested that several unidentified factors might interact with the enhancer-like element. Overexpression of GATA-1, GATA-2, or c-Myb stimulated the enhancer-like activity via these three binding sites. Thus, we conclude that Hex expression in hematopoietic cells is mainly regulated by GATA-1, GATA-2, and c-Myb via this intronic enhancer-like element.

The homeobox gene Hex induces T-cell-derived lymphomas when overexpressed in hematopoietic precursor cells

Proviral insertions at the viral insertion site Lvis1 occur frequently in B- and T-cell leukemias and lymphomas in AKXD mice and activate two nearby genes, the divergent homeobox gene Hex and the kinesin-related spindle protein gene Eg5. To determine whether Hex misexpression results in the altered differentiation or neoplastic transformation of hematopoietic lineages, we have transplanted mice with bone marrow cells transduced with retrovirus containing the Hex coding region. High levels of Hex expression in hematopoietic precursor cells inhibit contribution to mature blood cell lineages by these precursors. Hex bone marrow transplant recipient mice also develop hematologic neoplasms that appear to originate in the bone marrow. The tumors have clonal rearrangements of the TCR locus, are Thy1+, and are CD4+CD8+, CD4-CD8-, or mixed, indicating tumor origin from a precursor T-cell population. Tumors in transplant mice contain clonal and transcriptionally active Hex proviral insertions, demonstrating a causal role for Hex misexpression in the onset of these neoplasms. Our results demonstrate that Hex can act as a T lineage oncogene when misexpressed in hematopoietic precursor cells.