Pbx Family Research Articles

Three-amino acid loop extension homeodomain proteins regulate stress responses and encystation in Entamoeba.

It is interesting to identify factors involved in the regulation of the encystation of Entamoeba histolytica that differentiate trophozoites into cysts. Evolutionarily conserved three amino acid loop extension (TALE) homeodomain proteins act as transcription factors and execute a variety of functions that are essential for life. A TALE homeodomain (EhHbox) protein-encoding gene has been identified in E. histolytica (Eh) that is highly upregulated during heat shock, glucose, and serum starvation. Its ortholog, EiHbox1, a putative homeobox protein in E. invadens (Ei), is also highly upregulated during the early hours of encystation, glucose starvation, and heat shock. They belong to the PBX family of TALE homeobox proteins and have conserved residues in the homeodomain that are essential for DNA binding. Both are localized in the nucleus during encystation and under different stress conditions. The electrophoretic mobility shift assay confirmed that the recombinant GST-EhHbox binds to the reported TGACAG and TGATTGAT motifs. Down-regulation of EiHbox1 by gene silencing reduced Chitin synthase, Jacob, and increased Jessie gene expression, resulting in defective cysts and decreased encystation efficiency and viability. Overall, our results suggest that the TALE homeobox family has been conserved during evolution and acts as a transcription factor to control the differentiation of Entamoeba by regulating the key encystation-induced genes.

Correlation analysis of PBX family with immune invasion and drug sensitivity in colon adenocarcinoma

ObjedtivePre-B cell leukemia (PBX) has been found to be associated with cancer, but poorly studied with colon adenocarcinoma (COAD). In this study, the correlation between PBX family and COAD pathogenesis and immune cytokine infiltration was further explored by analyzing online tumor databases, in order to find new biomarkers for the diagnosis of COAD. MethodsThe online database was used to analyze gene differential expression, methylation level, gene mutation rate, immune infiltration difference, drug sensitivity, and so on. ResultsPBX1 and PBX3 decreased in COAD. PBX2 and PBX4 increased. The expression of PBX1 and PBX2 in different clinical stages was different. PBX4 was valuable for the prognosis of COAD. PBX family has correlation between COAD and immune infiltration. PBX2 was correlated with different pathological stages. PBX3 had the highest gene mutation rate, followed by PBX1, PBX2 and PBX4. PBX1, PBX2 and PBX4 were correlated with the sensitivity of multiple drugs. ConclusionThe PBX family is differentially expressed in COAD and has a genetic mutation, and its protein network is closely related to the HOX family and is associated with immune infiltration of COAD.

Research progress of PBX1 in developmental and regenerative medicine.

Pre-B-cell leukemia transcription factor 1 (PBX1) proteins are a subfamily of evolutionarily conserved atypical homeodomain transcription factors belonging to the superfamily of triple amino acid loop extension homeodomain proteins. PBX family members play crucial roles in the regulation of various pathophysiological processes. This article reviews the research progress on PBX1 in terms of structure, developmental function, and regenerative medicine. The potential mechanisms of development and research targets in regenerative medicine are also summarized. It also suggests a possible link between PBX1 in the two domains, which is expected to open up a new field for future exploration of cell homeostasis, as well as the regulation of endogenous danger signals. This would provide a new target for the study of diseases in various systems.

PBX3 promotes pentose phosphate pathway and colorectal cancer progression by enhancing G6PD expression.

Metabolic reprogramming is a hallmark of cancers crucial for fulfilling the needs of energy, building blocks, and antioxidants to support tumor cells' rapid proliferation and to cope with the harsh microenvironment. Pre-B-cell leukemia transcription factor 3 (PBX3) is a member of the PBX family whose expression is up-regulated in various tumors, however, whether it is involved in tumor cell metabolic reprogramming remains unclear. Herein, we report that PBX3 is a positive regulator of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway (PPP). PBX3 promoted G6PD transcriptional activity in tumor cells by binding directly to its promoter, leading to PPP stimulation and enhancing the production of nucleotides and NADPH, a crucial reductant, thereby promoting nucleic acid and lipid biosynthesis while decreasing intracellular reactive oxygen species levels. The PBX3/G6PD axis also promoted tumorigenic potential in vitro and in vivo. Collectively, these findings reveal a novel function of PBX3 as a regulator of G6PD, linking its oncogenic activity with tumor cell metabolic reprogramming, especially PPP. Furthermore, our results suggested that PBX3 is a potential target for metabolic-based anti-tumor therapeutic strategies.

Phosphorylation of PBX2, a novel downstream target of mTORC1, is determined by GSK3 and PP1.

Mechanistic target of rapamycin complex 1 (mTORC1) is a serine-threonine kinase that is activated by extracellular signals such as nutrients and growth factors. It plays a key role in the control of various biological processes such as protein synthesis and energy metabolism by mediating or regulating the phosphorylation of multiple target molecules, some of which remain to be identified. We have here reanalyzed a large-scale phosphoproteomics data set for mTORC1 target molecules and identified pre-B cell leukemia transcription factor 2 (PBX2) as such a novel target that is dephosphorylated downstream of mTORC1. We confirmed that PBX2, but not other members of the PBX family, is dephosphorylated in an mTORC1 activity-dependent manner. Furthermore, pharmacological and gene knockdown experiments revealed that glycogen synthase kinase 3 (GSK3) and protein phosphatase 1 (PP1) are responsible for the phosphorylation and dephosphorylation of PBX2, respectively. Our results thus suggest that the balance between the antagonistic actions of GSK3 and PP1 determines the phosphorylation status of PBX2 and its regulation by mTORC1.

The regulation of PBXs and their emerging role in cancer.

Pre‐B‐cell leukaemia transcription factor (PBX) proteins are a subfamily of evolutionarily conserved, atypical homeodomain transcription factors that belong to the superfamily of three amino acid loop extension (TALE) homeodomain proteins. Members of the PBX family play crucial roles in regulating multiple pathophysiological processes, such as the development of organs, congenital cardiac defects and carcinogenesis. The dysregulation of PBXs has been shown to be closely associated with many diseases, particularly cancer. However, the detailed mechanisms of PBX dysregulation in cancer progression are still inconclusive. In this review, we summarize the recent advances in the structures, functions and regulatory mechanisms of PBXs, and discuss their underlying mechanisms in cancer progression. We also highlight the great potential of PBXs as biomarkers for the early diagnosis and prognostic evaluation of cancer as well as their therapeutic applications. The information reviewed here may expand researchers’ understanding of PBXs and could strengthen the clinical implication of PBXs in cancer treatment.

SP1.1.7PBX4 functions as a novel oncogene and promotes angiogenesis in colorectal cancer: A comprehensive analysis of the PBX gene family

Abstract Aims Pre-B-cell Leukaemia (PBX) genes are important in organ development during embryogenesis. To date, four members of the PBX family (PBX1, PBX2, PBX3, PBX4) have been identified to be involved in human cancers, but little is known about their role in colorectal cancer (CRC). The aim of this study was to determine their differential expression, prognostic role and function in CRC. Methods Molecular and overall survival (OS) data from 614 patients with CRC were obtained from the National Cancer Institute, Tissue Cancer Genome Atlas (TCGA) database. To investigate the differential PBX gene mRNA expression, we performed a comparative cancer to normal computational analysis in edgeR. To determine PBXs prognostic value, we conducted Kaplan-Meier survival analysis and COX regression, selecting 10-year OS as primary outcome. Lastly, to explore the effect of PBX4 in CRC cell growth and angiogenesis, we performed gene expression modulation experiments using a PBX4-overexpressing plasmid-vector. Cell proliferation and VEGFA angiogenic factor expression were defined as primary and secondary in vitro outcomes respectively. Results Among PBXs only PBX4 was significantly upregulated showing a 4-fold increase in CRC vs normal colon (p < 0.0001). Survival analysis showed that only high PBX4 mRNA expression was associated with increased risk for worse OS in patients with CRC (HR:1.3 95%CI:1-1.6, p = 0.02). Functionally, overexpression of PBX4 significantly increased CRC cell proliferation in vitro (p < 0.001) and markedly upregulated the expression of VEGFA (p < 0.0001). Conclusions Comprehensive analysis of the PBX gene family identifies that PBX4 may function as a novel oncogene and may promote angiogenesis through VEGFA in CRC.

The transcription factor PBX3 promotes tumor cell growth through transcriptional suppression of the tumor suppressor p53.

Pre-B-cell leukemia transcription factor 3 (PBX3) is a member of the PBX family and contains a highly conserved homologous domain. PBX3 is involved in the progression of gastric cancer, colorectal cancer, and prostate cancer; however, the detailed mechanism by which it promotes tumor growth remains to be elucidated. Here, we found that PBX3 silencing induces the expression of the cell cycle regulator p21, leading to an increase in colorectal cancer (CRC) cell apoptosis as well as suppression of proliferation and colony formation. Furthermore, we found that PBX3 is highly expressed in clinical CRC patients, in whom p21 expression is aberrantly low. We found that the regulation of p21 transcription by PBX3 occurs through the upstream regulator of p21, the tumor suppressor p53, as PBX3 binds to the p53 promoter and suppresses its transcriptional activity. Finally, we revealed that PBX3 regulates tumor growth through regulation of the p53/p21 axis. Taken together, our results not only describe a novel mechanism regarding PBX3-mediated regulation of tumor growth but also provide new insights into the regulatory mechanism of the tumor suppressor p53.

PBX1 is a valuable prognostic biomarker for patients with breast cancer.

Pre-B-cell leukemia transcription factor (PBX) proteins have important roles in the development of numerous organs. To date, four members of the PBX family have been identified to be involved in human cancer but little is known about their expression patterns and precise functions in breast cancer (BC) progression. The aim of the present study was to determine whether they have the potential to be prognostic biomarkers in patients with BC. The expression patterns of PBXs were evaluated using Oncomine, Cancer Cell Line Encyclopedia and Gene expression-based Outcome for Breast cancer Online algorithm analyses. The prognostic value of PBX1 was determined by Kaplan-Meier plotter analysis. It was observed that, among all PBX family members, only PBX1 was significantly upregulated in BC vs. normal tissues. Meta-analysis in the Oncomine database revealed that PBX1 was significantly upregulated in invasive breast carcinoma stroma, ductal breast carcinoma, invasive lobular breast carcinoma, invasive mixed breast carcinoma and male breast carcinoma compared with normal tissues. In addition, PBX1 was significantly correlated with forkhead box protein A1. Subtype analysis indicated that PBX1 overexpression was associated with luminal-like and hormone receptor-sensitive subtypes. In the survival analysis, a high expression level of PBX1 was associated with poor prognosis of patients with estrogen receptor (ER)-positive, luminal A and luminal B subtypes of BC. The results of the present study indicate that PBX1 may serve as a specific biomarker and essential prognostic factor for ER-positive, luminal A and luminal B subtypes of BC.

Pbx loss in cranial neural crest, unlike in epithelium, results in cleft palate only and a broader midface.

Orofacial clefting represents the most common craniofacial birth defect. Cleft lip with or without cleft palate (CL/P) is genetically distinct from cleft palate only (CPO). Numerous transcription factors (TFs) regulate normal development of the midface, comprising the premaxilla, maxilla and palatine bones, through control of basic cellular behaviors. Within the Pbx family of genes encoding Three Amino‐acid Loop Extension (TALE) homeodomain‐containing TFs, we previously established that in the mouse, Pbx1 plays a preeminent role in midfacial morphogenesis, and Pbx2 and Pbx3 execute collaborative functions in domains of coexpression. We also reported that Pbx1 loss from cephalic epithelial domains, on a Pbx2‐ or Pbx3‐deficient background, results in CL/P via disruption of a regulatory network that controls apoptosis at the seam of frontonasal and maxillary process fusion. Conversely, Pbx1 loss in cranial neural crest cell (CNCC)‐derived mesenchyme on a Pbx2‐deficient background results in CPO, a phenotype not yet characterized. In this study, we provide in‐depth analysis of PBX1 and PBX2 protein localization from early stages of midfacial morphogenesis throughout development of the secondary palate. We further establish CNCC‐specific roles of PBX TFs and describe the developmental abnormalities resulting from their loss in the murine embryonic secondary palate. Additionally, we compare and contrast the phenotypes arising from PBX1 loss in CNCC with those caused by its loss in the epithelium and show that CNCC‐specific Pbx1 deletion affects only later secondary palate morphogenesis. Moreover, CNCC mutants exhibit perturbed rostro‐caudal organization and broadening of the midfacial complex. Proliferation defects are pronounced in CNCC mutants at gestational day (E)12.5, suggesting altered proliferation of mutant palatal progenitor cells, consistent with roles of PBX factors in maintaining progenitor cell state. Although the craniofacial skeletal abnormalities in CNCC mutants do not result from overt patterning defects, osteogenesis is delayed, underscoring a critical role of PBX factors in CNCC morphogenesis and differentiation. Overall, the characterization of tissue‐specific Pbx loss‐of‐function mouse models with orofacial clefting establishes these strains as unique tools to further dissect the complexities of this congenital craniofacial malformation. This study closely links PBX TALE homeodomain proteins to the variation in maxillary shape and size that occurs in pathological settings and during evolution of midfacial morphology.

Silencing Pre-B-cell leukemia homeobox 3 decreases the proliferation of human glioma cells in vitro and in vivo.

Among primary brain tumors, gliomas are the most common and most aggressive, with a poor prognosis and limited treatment options. Thus, it is essential to determine the mechanisms involved in glioma development to develop effective therapies for glioma patients. Pre-B-cell leukemia homeobox 3 (PBX3), a critical member of the PBX family, is frequently overexpressed in multiple human malignancies. However, the expression patterns and biological functions, as well as the involved molecular functions of PBX3 in human gliomas remain largely unknown. In this study, we demonstrate that PBX3 expression is increased in both human glioma tissues and cell lines compared with their normal counterparts. These results suggested that PBX3 might be involved in glioma progression. Thus, the role of PBX3 in glioma cell proliferation was investigated using genetic knockdown and overexpression methods. The results showed that PBX3 knockdown inhibited glioma cell proliferation and induced apoptosis, while PBX3 overexpression significantly promoted glioma cell proliferation. Mechanistically, we found that PBX3 promoted cell proliferation by modulating cell cycle progression. A xenograft LN229 model was used to confirm that PBX3 depletion decreased tumor growth in vivo. In summary, our findings reveal that PBX3 may be a potential therapeutic target in gliomas.

HOXA1 and TALE proteins display cross-regulatory interactions and form a combinatorial binding code on HOXA1 targets.

Hoxa1 has diverse functional roles in differentiation and development. We identify and characterize properties of regions bound by HOXA1 on a genome-wide basis in differentiating mouse ES cells. HOXA1-bound regions are enriched for clusters of consensus binding motifs for HOX, PBX, and MEIS, and many display co-occupancy of PBX and MEIS. PBX and MEIS are members of the TALE family and genome-wide analysis of multiple TALE members (PBX, MEIS, TGIF, PREP1, and PREP2) shows that nearly all HOXA1 targets display occupancy of one or more TALE members. The combinatorial binding patterns of TALE proteins define distinct classes of HOXA1 targets, which may create functional diversity. Transgenic reporter assays in zebrafish confirm enhancer activities for many HOXA1-bound regions and the importance of HOX-PBX and TGIF motifs for their regulation. Proteomic analyses show that HOXA1 physically interacts on chromatin with PBX, MEIS, and PREP family members, but not with TGIF, suggesting that TGIF may have an independent input into HOXA1-bound regions. Therefore, TALE proteins appear to represent a wide repertoire of HOX cofactors, which may coregulate enhancers through distinct mechanisms. We also discover extensive auto- and cross-regulatory interactions among the Hoxa1 and TALE genes, indicating that the specificity of HOXA1 during development may be regulated though a complex cross-regulatory network of HOXA1 and TALE proteins. This study provides new insight into a regulatory network involving combinatorial interactions between HOXA1 and TALE proteins.

Spleen hypoplasia leads to abnormal stress hematopoiesis in mice with loss of Pbx homeoproteins in splenic mesenchyme.

The spleen plays critical roles in immunity and also provides a permissive microenvironment for hematopoiesis. Previous studies have reported that the TALE-class homeodomain transcription factor Pbx1 is essential in hematopoietic stem and progenitor cells (HSPCs) for stem cell maintenance and progenitor expansion. However, the role of Pbx1 in the hematopoietic niche has not been investigated. Here we explored the effects that genetic perturbation of the splenic mesenchymal niche has on hematopoiesis upon loss of members of the Pbx family of homeoproteins. Splenic mesenchyme-specific inactivation of Pbx1 (SKO) on a Pbx2- or Pbx3-deficient genetic background (DKO) resulted in abnormal development of the spleen, which is dysmorphic and severely hypoplastic. This phenotype, in turn, affected the number of HSPCs in the fetal and adult spleen at steady state, as well as markedly impairing the kinetics of hematopoietic regeneration in adult mice after sub-lethal and lethal myelosuppressive irradiation. Spleens of mice with compound Pyx deficiency 8days following sublethal irradiation displayed significant downregulation of multiple cytokine-encoding genes, including KitL/SCF, Cxcl12/SDF-1, IL-3, IL-4, GM-CSF/Csf2 IL-10, and Igf-1, compared with controls. KitL/SCF and Cxcl12/SDF-1 were recently shown to play key roles in the splenic niche in response to various haematopoietic stresses such as myeloablation, blood loss, or pregnancy. Our results demonstrate that, in addition to their intrinsic roles in HSPCs, non-cell autonomous functions of Pbx factors within the splenic niche contribute to the regulation of hematopoiesis, at least in part via the control of KitL/SCF and Cxcl12/SDF-1. Furthermore, our study establishes that abnormal spleen development and hypoplasia have deleterious effects on the efficiency of hematopoietic recovery after bone marrow injury.

Classification and expression analyses of homeobox genes from Dictyostelium discoideum.

Homeobox genes are compared between genomes in an attempt to understand the evolution of animal development. The ability of the protist, Dictyostelium discoideum, to shift between uni- and multicellularity makes this group ideal for studying the genetic changes that may have occurred during this transition. We present here the first genome-wide classification and comparative genomic analysis of the 14 homeobox genes present in D. discoideum. Based on the structural alignment of the homeodomains, they can be broadly divided into TALE and non-TALE classes. When individual homeobox genes were compared with members of known class or family, we could further classify them into 3 groups, namely, TALE, OTHER and NOVEL classes, but no HOX family was found. The 5 members of TALE class could be further divided into PBX, PKNOX, IRX and CUP families; 4 homeobox genes classified as NOVEL did not show any similarity to any known homeobox genes; while the remaining 5 were classified as OTHERS as they did show certain degree of similarity to few known homeobox genes. No unique RNA expression pattern during development of D. discoideum emerged for members of an individual group. Putative promoter analysis revealed binding sites for few homeobox transcription factors among many probable factors.

A shift in c-Myb gene promoter usage correlates with leukaemic behaviour in myeloid cells

c-Myb is an important regulator of haematopoiesis expressed principally in haematopoietic stem cells and progenitors (HSC/HPC). Aberrant expression of c-Myb has been linked to the development of several types of leukaemia including Acute Lymphoblastic Leukaemia (ALL) and Acute Myeloid Leukaemia (AML). Previously, we demonstrated differential regulation of the c-myb gene in murine myeloid leukaemic cells compared to normal HSC. This differential pattern of regulation was shown to be mediated by HoxA9 and its cofactor Meis1 together with the proteins from the Pbx family, Pbx1 and Pbx2, and involved a shift in promoter usage from the conventional (P1) in normal HSC to a second promoter (P2) upstream of exon 2 in leukaemic cells.

PBX3 is overexpressed in gastric cancer and regulates cell proliferation

The pre-leukemia transcription factor 3 (PBX3) is a member of the PBX family of transcription factors, which is known to increase DNA-binding/transcriptional activity of HOX proteins and regulate genes involved in development. Recently, PBX3 was reported to be involved in a variety of cancers, while its implication in gastric cancer is unclear. This study aimed to investigate its clinical significance and biological function in gastric cancer. PBX3 expression was analyzed in 90 gastric cancer specimens using immunohistochemistry. PBX3 was overexpressed in 30 cases (33.33%). Importantly, PBX3 overexpression positively correlated with advanced invasion depth (p = 0.0017), Clinical stage (p = 0.0127) and grade of tumor differentiation (p = 0.0158). PBX3 was also overexpressed in gastric cancer cell lines. Plasmid transfection was performed in AGS and SGC-7901 gastric cancer cell line with low endogenous PBX3 expression. MTT and colony formation assay were carried out to assess the role of PBX3 in proliferation. PBX3 overexpression in gastric cancer cell lines accelerated cell proliferation rate and colony formation ability, with upregulation of PCNA expression. In addition, matrigel invasion assay showed that PBX3 transfection also increased cell-invading ability. These results validate the role of PBX3 as a clinically relevant oncoprotein and establish PBX3 as a promising therapeutic target of gastric cancer.

The HOXA/PBX3 Pathway Is an Attractive Therapeutic Target in MLL-Rearranged Acute Leukemia

AbstractAbstract 3522MLL (mixed lineage leukemia) gene rearrangements account for about 10% of human acute leukemias, including ∼80% of infant acute leukemia. At present, the majority of patients die within two years of diagnosis, and a more effective therapeutic strategy is thus urgently needed. MLL fusion proteins induce aberrant expression of a group of homeobox gene super-family members, including HOXA and co-factors such as MEIS1 and PBX3. Overexpression of individual HOXA genes can induce myeloproliferation and block differentiation. Co-expression of Meis1 and Hoxa9 is sufficient to transform normal hematopoietic progenitor cells and to induce a rapidly fatal leukemia in transplanted mice, and their aberrant overexpression is required for the induction and maintenance of MLL-rearranged leukemia. Although Pbx proteins are known to interact with Hox proteins, thereby increasing the DNA-binding affinity of the latter and enhancing the transcription of downstream target genes, little is known about the interaction between Pbx proteins and Hox proteins (e.g., Hoxa9) in cell transformation and leukemogenesis.Recently, we showed that increased expression of a four-homeobox-gene signature (HOXA7, HOXA9, HOXA11 and PBX3) was an independent predictor of shorter overall survival in patients with cytogenetically abnormal acute myeloid leukemia (CA-AML) (Li Z., et al., Blood. 2012). Our analysis of the expression profiles of three independent large-scale patient sets showed that PBX3 was the only member of the PBX family that was consistently co-expressed with HOXA9 in various subtypes of CA-AML, particularly in MLL-rearranged AML; in contrast, both PBX1 and PBX2 tended to exhibit an inverse correlation of expression with HOXA9 in CA-AML. We then investigated the role of PBX3 in CA-AML, because its function in leukemia was unclear. We found a similar pattern of co-expression of Hoxa9 and Pbx3 in MLL fusion-mediated mouse leukemia models. We then showed that depletion of Pbx3 (but not Pbx1 and Pbx2) by Pbx3 shRNA dramatically inhibited MLL-AF9 induced transformation/immortalization of mouse normal bone marrow progenitor cells (about 50% reduction in colony numbers and about 70% reduction of number of cells in each colony). Furthermore, we demonstrated that forced expression of PBX3 exhibited a significantly synergistic effect with HOXA9 in promoting cell transformation/immortalization in vitro. In mouse bone marrow reconstitution/transplantation assay, the PBX3+HOXA9 mice developed leukemia significantly faster than HOXA9 alone with overall median survival of 71 days versus 140 days (P<0.0001). Finally, we treated leukemia cell lines and cells with HXR9, a small, cell-permeable peptide, previously shown to specifically disrupt the formation of HOX/PBX heterodimers, and to be effective in treating various cancers with minimal toxicity. We found that leukemia cells with higher levels of HOXA/PBX3 expression were more sensitive to HXR9 treatment than those with lower levels. Thus, targeting the HOXA/PBX3 pathway may provide a new strategy to substantially improve outcomes of patients with MLL-rearranged leukemia and possibly, non-favorable CA-AML. Disclosures:No relevant conflicts of interest to declare.

C-terminal domain of MEIS1 converts PKNOX1 (PREP1) into a HOXA9-collaborating oncoprotein

AbstractThe three-amino-acid loop extension (TALE) class homeodomain proteins MEIS1 and PKNOX1 (PREP1) share the ability to interact with PBX and HOX family members and bind similar DNA sequences but appear to play opposing roles in tumor development. Elevated levels of MEIS1 accelerate development of HOX- and MLL-induced leukemias, and this pro-tumorigenic property has been associated with transcriptional activity of MEIS1. In contrast, reduction of PKNOX1 levels has been linked with cancer development despite the absence of an identifiable transactivating domain. In this report, we show that a chimeric protein generated by fusion of the MEIS1 C-terminal region encompassing the transactivating domain with the full-length PKNOX1 (PKNOX1-MC) acquired the ability to accelerate the onset of Hoxa9-induced leukemia in the mouse bone marrow transduction/transplantation model. Gene expression profiling of primary bone marrow cells transduced with Hoxa9 plus Meis1, or Hoxa9 plus Pknox1-MC revealed perturbations in overlapping functional gene subsets implicated in DNA packaging, chromosome organization, and in cell cycle regulation. Together, results presented in this report suggest that the C-terminal domain of MEIS1 confers to PKNOX1 an ectopic transactivating function that promotes leukemogenesis by regulating expression of genes involved in chromatin accessibility and cell cycle progression.

Regulation of PBX3 expression by androgen and Let-7d in prostate cancer

BackgroundThe pre-leukemia transcription factor 3 (PBX) is part of the PBX family of transcription factors, which is known to regulate genes involved in differentiation of urogenital organs and steroidogenesis. This is of interest with regard to prostate cancer progression as regulation of steroidogenesis is one of the mechanisms involved in the development of castration-resistant prostate cancer. In light of this we wanted to investigate the possible involvement of androgen regulation of PBX3 expression in prostate cancer.ResultsIn this study, we show that PBX3 is post-transcriptionally regulated by androgen in prostate cancer cells and that the effect might be independent of the androgen receptor. Furthermore, PBX3 was identified as a target of Let-7d, an androgen regulated microRNA. Let-7d was down-regulated in malignant compared to benign prostate tissue, whereas up-regulation of PBX3 expression was observed.ConclusionsWe demonstrate that PBX3 is up-regulated in prostate cancer and post- transcriptionally regulated by androgen through Let-7d.

Control of pelvic girdle development by genes of the Pbx family and Emx2

Genes expressed in the somatopleuric mesoderm, the embryonic domain giving rise to the vertebrate pelvis, appear important for pelvic girdle formation. Among such genes, Pbx family members and Emx2 were found to genetically interact in hindlimb and pectoral girdle formation. Here, we generated compound mutant embryos carrying combinations of mutated alleles for Pbx1, Pbx2, and Pbx3, as well as Pbx1 and Emx2, to examine potential genetic interactions during pelvic development. Indeed, Pbx genes share overlapping functions and Pbx1 and Emx2 genetically interact in pelvic formation. We show that, in compound Pbx1;Pbx2 and Pbx1;Emx2 mutants, pelvic mesenchymal condensation is markedly perturbed, indicative of an upstream control by these homeoproteins. We establish that expression of Tbx15, Prrx1, and Pax1, among other genes involved in the specification and development of select pelvic structures, is altered in our compound mutants. Lastly, we identify potential Pbx1-Emx2-regulated enhancers for Tbx15, Prrx1, and Pax1, using bioinformatics analyses.