Evidence that the Pim1 kinase gene is a direct target of HOXA9

PIM1 kinase and its diverse substrate in solid tumors

The PIM kinase family, consisting of PIM1, PIM2, and PIM3, is a group of serine/threonine protein kinases crucial for cellular growth, immunoregulation, and oncogenesis. PIM1 kinase is often overexpressed in solid and hematopoietic malignancies, promoting cell survival, proliferation, migration, and senescence by activating key genes. In vitro and in vivo studies have established the oncogenic potential of PIM1 kinases. These kinases have been implicated in tumor progression, metastasis, and resistance to chemotherapy, underscoring their potential as a therapeutic target for cancer therapy. This review delves into the intricate molecular mechanisms through which PIM1 interacts with specific substrates in different tumor tissues, leading to diverse outcomes in various human cancers. Over the past decade, the inhibition of PIM1 in cancers has garnered significant attention as a potential standalone treatment. Various in vitro, in vivo, and early clinical trial data have provided support for this approach to varying extents. Novel compounds that inhibit PIM1 kinase have shown effectiveness and a favorable toxicity profile in preclinical studies. Several of these substances are now being studied in clinical trials due to their promising outcomes. This article provides a thorough examination of the PIM1 kinase pathways and the recent advancements in producing PIM1 kinase inhibitors for the treatment of cancer.

HOXA9 transcription factor is a double-edged sword: from development to cancer progression

The HOXA9 transcription factor serves as a molecular orchestrator in cancer stemness, epithelial-mesenchymal transition (EMT), metastasis, and generation of the tumor microenvironment in hematological and solid malignancies. However, the multiple modes of regulation, multifaceted functions, and context-dependent interactions responsible for the dual role of HOXA9 as an oncogene or tumor suppressor in cancer remain obscure. Hence, unravelling its molecular complexities, binding partners, and interacting signaling molecules enables us to comprehend HOXA9-mediated transcriptional programs and molecular crosstalk. However, it is imperative to understand its central role in fundamental biological processes such as embryogenesis, foetus implantation, hematopoiesis, endothelial cell proliferation, and tissue homeostasis before designing targeted therapies. Indeed, it presents an enormous challenge for clinicians to selectively target its oncogenic functions or restore tumor-suppressive role without altering normal cellular functions. In addition to its implications in cancer, the present review also focuses on the clinical applications of HOXA9 in recurrence and drug resistance, which may provide a broader understanding beyond oncology, open new avenues for clinicians for accurate diagnoses, and develop personalized treatment strategies. Furthermore, we have also discussed the existing therapeutic options and accompanying challenges in HOXA9-targeted therapies in different cancer types.

HOXA9 gene inhibits proliferation and differentiation and promotes apoptosis of bovine preadipocytes

BACKGROUND

Hox gene family is an important transcription factor that regulates cell process, and plays a role in the process of adipocytes differentiation and fat deposition. Previous transcriptome sequencing studies have indicated that the Homeobox A9 gene (HOXA9) is a candidate gene for regulating the process of bovine lipid metabolism, but the function and specific mechanism of action remain unclear. Therefore, this study aims to explore the role of HOXA9 in the proliferation, differentiation and apoptosis of bovine preadipocytes through gain-of-function and lose-of-function.

RESULT

It found HOXA9 highly expressed in bovine adipose tissue, and its expression level changed significantly during adipocytes differentiation process. It gave a hint that HOXA9 may be involved in the process of bovine lipid metabolism. The results of HOXA9 gain-of-function experiments indicated that HOXA9 appeared to act as a negative regulator not only in the differentiation but also in the proliferation of bovine preadipocytes, which is mainly reflected that overexpression of HOXA9 down-regulate the mRNA and protein expression level of PPARγ, CEBPα and FABP4 (P < 0.05). The mRNA expression level of CDK1, CDK2, PCNA, CCNA2, CCNB1, CCND1 and CCNE2, as well as the protein expression of CDK2 also significantly decreased. The decrease of lipid droplets content was the main characteristic of the phenotype (P < 0.01), which further supported the evidence that HOXA9 was a negative regulator of preadipocytes differentiation. The decrease of cell proliferation rate and EdU positive rate, as well as the limitation of transition of preadipocytes from G0/G1 phase to S phase also provided evidence for the inhibition of proliferation. Apart from this above, we noted an interesting phenomenon that overexpression of HOXA9 showed in a significant upregulation of both mRNA and protein level of apoptosis markers, accompanied by a significant increase in cell apoptosis rate. These data led us not to refute the fact that HOXA9 played an active regulatory role in apoptosis. HOXA9 loss-of-function experiments, however, yielded the opposite results. Considering that HOXA9 acts as a transcription factor, we predicted its target genes. Dual luciferase reporter assay system indicated that overexpression of HOXA9 inhibits activity of PCNA promoter.

CONCLUSION

Taken together, we demonstrated for the first time that HOXA9 played a role as a negative regulatory factor in the differentiation and proliferation of preadipocytes, but played a positive regulatory role in apoptosis, and it may play a regulatory role by targeting PCNA. This study provides basic data for further exploring the regulatory network of intramuscular fat deposition in bovine.

Pim Kinases: Important Regulators of Cardiovascular Disease

Pim Kinases; Pim-1, Pim-2, and Pim-3, are a family of constitutively active serine/threonine kinases, widely associated with cell survival, proliferation, and migration. Historically considered to be functionally redundant, independent roles for the individual isoforms have been described. Whilst most established for their role in cancer progression, there is increasing evidence for wider pathological roles of Pim kinases within the context of cardiovascular disease, including inflammation, thrombosis, and cardiac injury. The Pim kinase isoforms have widespread expression in cardiovascular tissues, including the heart, coronary artery, aorta, and blood, and have been demonstrated to be upregulated in several co-morbidities/risk factors for cardiovascular disease. Pim kinase inhibition may thus be a desirable therapeutic for a multi-targeted approach to treat cardiovascular disease and some of the associated risk factors. In this review, we discuss what is known about Pim kinase expression and activity in cells of the cardiovascular system, identify areas where the role of Pim kinase has yet to be fully explored and characterised and review the suitability of targeting Pim kinase for the prevention and treatment of cardiovascular events in high-risk individuals.

Osteoprogenitor-GMP crosstalk underpins solid tumor-induced systemic immunosuppression and persists after tumor removal

Remote tumors disrupt the bone marrow (BM) ecosystem (BME), eliciting the overproduction of BM-derived immunosuppressive cells. However, the underlying mechanisms remain poorly understood. Herein, we characterized breast and lung cancer-induced BME shifts pre- and post-tumor removal. Remote tumors progressively lead to osteoprogenitor (OP) expansion, hematopoietic stem cell dislocation, and CD41- granulocyte-monocyte progenitor (GMP) aggregation. The tumor-entrained BME is characterized by co-localization between CD41- GMPs and OPs. OP ablation abolishes this effect and diminishes abnormal myeloid overproduction. Mechanistically, HTRA1 carried by tumor-derived small extracellular vesicles upregulates MMP-13 in OPs, which in turn induces the alterations in the hematopoietic program. Importantly, these effects persist post-surgery and continue to impair anti-tumor immunity. Conditional knockout or inhibition of MMP-13 accelerates immune reinstatement and restores the efficacies of immunotherapies. Therefore, tumor-induced systemic effects are initiated by OP-GMP crosstalk that outlasts tumor burden, and additional treatment is required to reverse these effects for optimal therapeutic efficacy.

Homeobox A9 is a novel mediator of vascular smooth muscle cell phenotypic switching and proliferation by regulating methyl-CpG binding protein 2

Aberrant proliferation and phenotypic switching of vascular smooth muscle cells (VSMCs) are considered to be the main pathological processes of atherosclerotic plaque formation. Methyl-CpG binding protein 2 (MECP2) affects cell differentiation via modulating VSMC-specific gene expression and acts as a driver for the development of atherosclerosis (AS). Here, we aimed to elucidate (Rafieian-Kopaei et al., 2014 [1]) the role of homeobox A9 (HOXA9) on aberrant VSMCs upon injury or AS, and (Rana et al., 2021 [2]) whether HOXA9-mediated VSMC injury was associated with MECP2. Adeno-associated virus serotype 8-mediated knockdown of HOXA9 rescued aortic pathological injury of apolipoprotein E-deficient (ApoE^-/-) mice fed a high-fat diet (HFD), characterized by the reduction of lipid accumulation and foam cell formation. Further in vitro evidence suggested that proliferation and migration of primary mouse VSMCs (mVSMCs) stimulated by oxidized low-density lipoprotein (ox-LDL) were inhibited after HOXA9 silencing. In addition, HOXA9 silencing blocked VSMC phenotypic switching from contractile to a pathological synthetic state. HOXA9 overexpression caused opposite alterations in ox-LDL-stimulated mVSMCs. Mechanistically, MECP2 was transcriptionally activated by HOXA9. Forced expression of MECP2 impaired the anti-proliferation, anti-migration, and phenotypic switching abilities of HOXA9 silencing in VSMCs upon ox-LDL stimulation. Collectively, our findings reveal that the role of HOXA9 in pathological vascular remodeling may attribute to transcriptional regulation of MECP2.

Targeting Pim kinases in hematological cancers: molecular and clinical review

Decades of research has recognized a solid role for Pim kinases in lymphoproliferative disorders. Often up-regulated following JAK/STAT and tyrosine kinase receptor signaling, Pim kinases regulate cell proliferation, survival, metabolism, cellular trafficking and signaling. Targeting Pim kinases represents an interesting approach since knock-down of Pim kinases leads to non-fatal phenotypes in vivo suggesting clinical inhibition of Pim may have less side effects. In addition, the ATP binding site offers unique characteristics that can be used for the development of small inhibitors targeting one or all Pim isoforms. This review takes a closer look at Pim kinase expression and involvement in hematopoietic cancers. Current and past clinical trials and in vitro characterization of Pim kinase inhibitors are examined and future directions are discussed. Current studies suggest that Pim kinase inhibition may be most valuable when accompanied by multi-drug targeting therapy.

Role of HOXA9 in solid tumors: mechanistic insights and therapeutic potential

HOXA9 functioning as a transcription factor is one of the members of HOX gene family, which governs multiple cellular activities by facilitating cellular signal transduction. In addition to be a driver in AML which has been widely studied, the role of HOXA9 in solid tumor progression has also received increasing attention in recent years, where the aberrant expression of HOXA9 is closely associated with the prognosis of patient. This review details the signaling pathways, binding partners, post-transcriptional regulation of HOXA9, and possible inhibitors of HOXA9 in solid tumors, which provides a reference basis for further study on the role of HOXA9 in solid tumors.

The Role of PIM Kinases in Pediatric Solid Tumors

PIM kinases have been identified as potential therapeutic targets in several malignancies. Here, we provide an in-depth review of PIM kinases, including their structure, expression, activity, regulation, and role in pediatric carcinogenesis. Also included is a brief summary of the currently available pharmaceutical agents targeting PIM kinases and existing clinical trials.

Proviral Integration of Moloney Virus-2 (PIM-2) Expression Level as a Prognostic Marker in Patients with Acute Myeloid Leukemia

Purpose

This study aimed to assess PIM-2 gene expression level as a prognostic marker in AML patients and to correlate the results with their clinical outcome.

Patients and Methods

This study was conducted on 50 de novo younger AML patients (median age 44). Quantitative real-time polymerase chain reaction (QRT-PCR) was used to assess the expression level of the PIM-2 gene. The transcription level of the target gene (PIM-2) was normalized to that of the reference gene (GAPDH). Twenty control samples were withdrawn from 20 age- and sex-matched individuals for the analysis of the results using the 2^−ΔΔCT method. On day 28 following induction chemotherapy, patients’ bone marrow (BM) was examined for evaluation of their remission status.

Results

PIM-2 gene expression was higher among AML patients who did not achieve complete remission (CR); also, it was higher in patients in the intermediate and poor cytogenetic risk groups. A significant positive correlation was found between PIM-2 level and BM blasts on day 28. In AML patients, PIM-2 has been discovered to be an independent predictive factor for achieving CR following standard induction treatment. Receiver operating characteristic curve (ROC) and area under the curve (AUC) were performed for PIM-2 level at diagnosis to evaluate its role in achieving remission after induction. It was found that PIM-2 at cutoff ≤1.6 had an AUC (0.903) with a sensitivity (90.48%) and specificity (86.21%), P <0.001.

Conclusion

Overexpression of the PIM-2 gene is associated with induction failure and low CR.

PIM Kinase Inhibitors Block the Growth of Primary T-cell Acute Lymphoblastic Leukemia: Resistance Pathways Identified by Network Modeling Analysis

Despite significant progress in understanding the genetic landscape of T-cell acute lymphoblastic leukemia (T-ALL), the discovery of novel therapeutic targets has been difficult. Our results demonstrate that the levels of PIM1 protein kinase is elevated in early T-cell precursor ALL (ETP-ALL) but not in mature T-ALL primary samples. Small-molecule PIM inhibitor (PIMi) treatment decreases leukemia burden in ETP-ALL. However, treatment of animals carrying ETP-ALL with PIMi was not curative. To model other pathways that could be targeted to complement PIMi activity, HSB-2 cells, previously characterized as a PIMi-sensitive T-ALL cell line, were grown in increasing doses of PIMi. Gene set enrichment analysis of RNA sequencing data and functional enrichment of network modules demonstrated that the HOXA9, mTOR, MYC, NFκB, and PI3K-AKT pathways were activated in HSB-2 cells after long-term PIM inhibition. Reverse phase protein array-based pathway activation mapping demonstrated alterations in the mTOR, PI3K-AKT, and NFκB pathways, as well. PIMi-tolerant HSB-2 cells contained phosphorylated RelA-S536 consistent with activation of the NFκB pathway. The combination of NFκB and PIMis markedly reduced the proliferation in PIMi-resistant leukemic cells showing that this pathway plays an important role in driving the growth of T-ALL. Together these results demonstrate key pathways that are activated when HSB-2 cell line develop resistance to PIMi and suggest pathways that can be rationally targeted in combination with PIM kinases to inhibit T-ALL growth.

HoxA9 transforms murine myeloid cells by a feedback loop driving expression of key oncogenes and cell cycle control genes

Ectopic expression of the oncogenic transcription factor HoxA9 is a major cause of acute myeloid leukemia (AML). Here, we demonstrate that HoxA9 is a specific substrate of granule proteases. Protease knockout allowed the comprehensive determination of genome-wide HoxA9 binding sites by chromatin immunoprecipitation sequencing in primary murine cells and a human AML cell line. The kinetics of enhancer activity and transcription rates in response to alterations of an inducible HoxA9 were determined. This permitted identification of HoxA9-controlled enhancers and promoters, allocation to their respective transcription units, and discrimination against HoxA9-bound, but unresponsive, elements. HoxA9 triggered an elaborate positive-feedback loop that drove expression of the complete Hox-A locus. In addition, it controlled key oncogenic transcription factors Myc and Myb and directly induced the cell cycle regulators Cdk6 and CyclinD1, as well as telomerase, drawing the essential blueprint for perturbation of proliferation by leukemogenic HoxA9 expression.

Direct and Indirect Targeting of HOXA9 Transcription Factor in Acute Myeloid Leukemia

HOXA9 (Homeobox A9) is a homeotic transcription factor known for more than two decades to be associated with leukemia. The expression of HOXA9 homeoprotein is associated with anterior-posterior patterning during embryonic development, and its expression is then abolished in most adult cells, with the exception of hematopoietic progenitor cells. The oncogenic function of HOXA9 was first assessed in human acute myeloid leukemia (AML), particularly in the mixed-phenotype associated lineage leukemia (MPAL) subtype. HOXA9 expression in AML is associated with aggressiveness and a poor prognosis. Since then, HOXA9 has been involved in other hematopoietic malignancies and an increasing number of solid tumors. Despite this, HOXA9 was for a long time not targeted to treat cancer, mainly since, as a transcription factor, it belongs to a class of protein long considered to be an "undruggable" target; however, things have now evolved. The aim of the present review is to focus on the different aspects of HOXA9 targeting that could be achieved through multiple ways: (1) indirectly, through the inhibition of its expression, a strategy acting principally at the epigenetic level; or (2) directly, through the inhibition of its transcription factor function by acting at either the protein/protein interaction or the protein/DNA interaction interfaces.

Heterocyclic Diamidine DNA Ligands as HOXA9 Transcription Factor Inhibitors: Design, Molecular Evaluation, and Cellular Consequences in a HOXA9-Dependant Leukemia Cell Model

Most transcription factors were for a long time considered as undruggable targets because of the absence of binding pockets for direct targeting. HOXA9, implicated in acute myeloid leukemia, is one of them. To date, only indirect targeting of HOXA9 expression or multitarget HOX/PBX protein/protein interaction inhibitors has been developed. As an attractive alternative by inhibiting the DNA binding, we selected a series of heterocyclic diamidines as efficient competitors for the HOXA9/DNA interaction through binding as minor groove DNA ligands on the HOXA9 cognate sequence. Selected DB818 and DB1055 compounds altered HOXA9-mediated transcription in luciferase assays, cell survival, and cell cycle, but increased cell death and granulocyte/monocyte differentiation, two main HOXA9 functions also highlighted using transcriptomic analysis of DB818-treated murine Hoxa9-transformed hematopoietic cells. Altogether, these data demonstrate for the first time the propensity of sequence-selective DNA ligands to inhibit HOXA9/DNA binding both in vitro and in a murine Hoxa9-dependent leukemic cell model.

A novel, dual pan-PIM/FLT3 inhibitor SEL24 exhibits broad therapeutic potential in acute myeloid leukemia

Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is one of the most common genetic lesions in acute myeloid leukemia patients (AML). Although FLT3 tyrosine kinase inhibitors initially exhibit clinical activity, resistance to treatment inevitably occurs within months. PIM kinases are thought to be major drivers of the resistance phenotype and their inhibition in relapsed samples restores cell sensitivity to FLT3 inhibitors. Thus, simultaneous PIM and FLT3 inhibition represents a promising strategy in AML therapy. For such reasons, we have developed SEL24-B489 - a potent, dual PIM and FLT3-ITD inhibitor. SEL24-B489 exhibited significantly broader on-target activity in AML cell lines and primary AML blasts than selective FLT3-ITD or PIM inhibitors. SEL24-B489 also demonstrated marked activity in cells bearing FLT3 tyrosine kinase domain (TKD) mutations that lead to FLT3 inhibitor resistance. Moreover, SEL24-B489 inhibited the growth of a broad panel of AML cell lines in xenograft models with a clear pharmacodynamic-pharmacokinetic relationship. Taken together, our data highlight the unique dual activity of the SEL24-B489 that abrogates the activity of signaling circuits involved in proliferation, inhibition of apoptosis and protein translation/metabolism. These results underscore the therapeutic potential of the dual PIM/FLT3-ITD inhibitor for the treatment of AML.

HOXA9 Cooperates with Activated JAK/STAT Signaling to Drive Leukemia Development

Leukemia is caused by the accumulation of multiple genomic lesions in hematopoietic precursor cells. However, how these events cooperate during oncogenic transformation remains poorly understood. We studied the cooperation between activated JAK3/STAT5 signaling and HOXA9 overexpression, two events identified as significantly co-occurring in T-cell acute lymphoblastic leukemia. Expression of mutant JAK3 and HOXA9 led to a rapid development of leukemia originating from multipotent or lymphoid-committed progenitors, with a significant decrease in disease latency compared with JAK3 or HOXA9 alone. Integrated RNA sequencing, chromatin immunoprecipitation sequencing, and Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) revealed that STAT5 and HOXA9 have co-occupancy across the genome, resulting in enhanced STAT5 transcriptional activity and ectopic activation of FOS/JUN (AP1). Our data suggest that oncogenic transcription factors such as HOXA9 provide a fertile ground for specific signaling pathways to thrive, explaining why JAK/STAT pathway mutations accumulate in HOXA9-expressing cells.Significance: The mechanism of oncogene cooperation in cancer development remains poorly characterized. In this study, we model the cooperation between activated JAK/STAT signaling and ectopic HOXA9 expression during T-cell leukemia development. We identify a direct cooperation between STAT5 and HOXA9 at the transcriptional level and identify PIM1 kinase as a possible drug target in mutant JAK/STAT/HOXA9-positive leukemia cases. Cancer Discov; 8(5); 616-31. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 517.

Intrinsic resistance to PIM kinase inhibition in AML through p38α-mediated feedback activation of mTOR signaling

Although conventional therapies for acute myeloid leukemia (AML) and diffuse large B-cell lymphoma (DLBCL) are effective in inducing remission, many patients relapse upon treatment. Hence, there is an urgent need for novel therapies. PIM kinases are often overexpressed in AML and DLBCL and are therefore an attractive therapeutic target. However, in vitro experiments have demonstrated that intrinsic resistance to PIM inhibition is common. It is therefore likely that only a minority of patients will benefit from single agent PIM inhibitor treatment. In this study, we performed an shRNA-based genetic screen to identify kinases whose suppression is synergistic with PIM inhibition. Here, we report that suppression of p38α (MAPK14) is synthetic lethal with the PIM kinase inhibitor AZD1208. PIM inhibition elevates reactive oxygen species (ROS) levels, which subsequently activates p38α and downstream AKT/mTOR signaling. We found that p38α inhibitors sensitize hematological tumor cell lines to AZD1208 treatment in vitro and in vivo. These results were validated in ex vivo patient-derived AML cells. Our findings provide mechanistic and translational evidence supporting the rationale to test a combination of p38α and PIM inhibitors in clinical trials for AML and DLBCL.

HOXA9 transcriptionally regulates the EPHB4 receptor to modulate trophoblast migration and invasion

INTRODUCTION

Functional placenta formation is crucially dependent on extravillous trophoblast migration and invasion. EPHB4 has been identified to play a negative but important role in regulating trophoblast biological function, whereas the upstream regulation mechanism remains unknown. As reported, there is a transcriptional stimulation of EPHB4 expression consequent to HOXA9 activation in endothelial cells (ECs). Therefore, this study is conducted to investigate the role of HOXA9 and its relationship with EPHB4 in trophoblast cells.

METHOD

Both mRNA and protein expression levels of HOXA9 and EPHB4 were measured in preeclamptic placenta (n = 15) and normal placenta (n = 15). Next, the expression and location of HOXA9 and EPHB4 in first-trimester villi were shown via immunohistochemistry. Trophoblast cell line HTR-8/SVneo was used to explore the effect of HOXA9 on EPHB4 expression and trophoblast bioactivity by gain- and loss-of function studies. In addition, chromatin immunoprecipitation (ChIP) and luciferase assays were conducted to clarify the regulation mechanism of HOXA9 on EPHB4 expression in HTR-8/SVneo.

RESULT

HOXA9 and EPHB4 expression were increased in preeclamptic placenta compared with normal placenta. HOXA9 could promote EPHB4 expression and impaired HTR-8/SVneo cells migration and invasion. ChIP and luciferase assays revealed that HOXA9 could directly bind to EPHB4 promoter and promoted its transcription.

CONCLUSION

HOXA9 transcriptionally regulated EPHB4 expression to modulate trophoblasts migration and invasion, which may suggest a contribution of HOXA9-EPHB4 in the poor placentation in the pathogenesis of preeclampsia.

Pediatric non-Down syndrome acute megakaryoblastic leukemia is characterized by distinct genomic subsets with varying outcomes

Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia (AML) in which cells morphologically resemble abnormal megakaryoblasts. While rare in adults, AMKL accounts for 4-15% of newly diagnosed childhood AML cases. AMKL in individuals without Down syndrome (non-DS-AMKL) is frequently associated with poor clinical outcomes. Previous efforts have identified chimeric oncogenes in a substantial number of non-DS-AMKL cases, including RBM15-MKL1, CBFA2T3-GLIS2, KMT2A gene rearrangements, and NUP98-KDM5A. However, the etiology of 30-40% of cases remains unknown. To better understand the genomic landscape of non-DS-AMKL, we performed RNA and exome sequencing on specimens from 99 patients (75 pediatric and 24 adult). We demonstrate that pediatric non-DS-AMKL is a heterogeneous malignancy that can be divided into seven subgroups with varying outcomes. These subgroups are characterized by chimeric oncogenes with cooperating mutations in epigenetic and kinase signaling genes. Overall, these data shed light on the etiology of AMKL and provide useful information for the tailoring of treatment.

Developmental stage-specific effects of Pim-1 dysregulation on murine bone marrow B cell development

Background

The serine threonine kinase Pim-1 has documented roles in hematopoietic progenitor and B cell precursor proliferation and survival. Pim-1 is a molecular target of the transcription factor Hoxa9. Previous studies showed that Pim-1 deficiency phenocopied the hematopoietic progenitor defect in hoxa9-/- mice and forced expression of Pim-1 normalized the in vitro proliferation defect inherent to hoxa9-/- hematopoietic progenitors. Pim-1 is induced by cytokine signaling, including the early lymphoid/B lineage regulators Flt3 and IL-7, and expression levels were shown to influence the size of the B cell compartment in bone marrow (BM).

Results

In this study, we sought to determine if transgenic expression of Pim-1, driven by the immunoglobulin enhancer, Eμ, was sufficient to rescue the lymphoid/B cell precursor defect in hoxa9 or flt3-ligand (flt3l) deficient mice. Unexpectedly, expression of Eμ − Pim1 exacerbated lymphoid progenitor deficiencies in flt3l-/-, and to a lesser extent, hoxa9-/- mice. Furthermore, Eμ − Pim1 expression alone reduced early myeloid and lymphoid, but not erythroid, progenitors. In contrast, Pim-1 deficiency had no significant effect on early lymphoid/B cell development through the Pre-Pro-B cell stage, but caused a significant reduction in IgM⁻ B cell precursors. Importantly, loss of Pim-1 did not phenocopy hoxa9- or flt3l-deficiency on the lymphoid/early B cell progenitor pools.

Conclusions

These experimental findings demonstrate that Pim-1 overexpression has developmental-stage-specific effects on B lymphopoiesis and myelopoiesis. Importantly, these suggest that Pim-1 deficiency does not contribute significantly to the early lymphoid/B cell developmental deficiency in hoxa9-/- or flt3l-/- mice.

MicroRNA-196b is transcribed from an autonomous promoter and is directly regulated by Cdx2 and by posterior Hox proteins during embryogenesis

The miR-196 miRNA gene family located within the Hox gene clusters has been shown to function during embryogenesis and to be aberrantly expressed in various malignancies, including leukaemia, melanoma, and colorectal cancer. Despite its involvement in numerous biological processes, the control of miR-196 expression is still poorly defined. We identified the miR-196b promoter and found that the mature miR-196b originates from a large, non-coding primary transcript, which starts within an autonomous TATA box promoter and is not in physical continuity with either the Hoxa10 or Hoxa9 main primary transcripts. A ~680bp genomic fragment, spanning the pri-miR-196b transcription start site, is sufficient to recapitulate the neural tube expression pattern of miR-196 during embryogenesis. This region contains potential binding sites for Cdx and 5'Hox transcription factors. Two of these sites revealed to be necessary for neural tube expression and were bound in vivo by Cdx2 and Hoxd13. We show that Cdx2 is required for miR-196 expression and that both Cdx2 and 5'Hox, but not 3'Hox, are able to activate the miR-196b promoter. The possible role of Cdx2- and 5'Hox-mediated regulation of miR-196 expression in vertebrate anterior-posterior (AP) axis formation during embryogenesis is discussed.

Role of HOXA9 in leukemia: dysregulation, cofactors and essential targets

HOXA9 is a homeodomain-containing transcription factor that has an important role in hematopoietic stem cell expansion and is commonly deregulated in acute leukemias. A variety of upstream genetic alterations in acute myeloid leukemia lead to overexpression of HOXA9, which is a strong predictor of poor prognosis. In many cases, HOXA9 has been shown to be necessary for maintaining leukemic transformation; however, the molecular mechanisms through which it promotes leukemogenesis remain elusive. Recent work has established that HOXA9 regulates downstream gene expression through binding at promoter distal enhancers along with a subset of cell-specific cofactor and collaborator proteins. Increasing efforts are being made to identify both the critical cofactors and target genes required for maintaining transformation in HOXA9-overexpressing leukemias. With continued advances in understanding HOXA9-mediated transformation, there is a wealth of opportunity for developing novel therapeutics that would be applicable for greater than 50% of AML with overexpression of HOXA9.

CDK4/6 Inhibitor PD 0332991 Sensitizes Acute Myeloid Leukemia to Cytarabine-Mediated Cytotoxicity

Cyclin-dependent kinase (CDK)4 and CDK6 are frequently overexpressed or hyperactivated in human cancers. Targeting CDK4/CDK6 in combination with cytotoxic killing therefore represents a rational approach to cancer therapy. By selective inhibition of CDK4/CDK6 with PD 0332991, which leads to early G1 arrest and synchronous S-phase entry upon release of the G1 block, we have developed a novel strategy to prime acute myeloid leukemia (AML) cells for cytotoxic killing by cytarabine (Ara-C). This sensitization is achieved in part through enrichment of S-phase cells, which maximizes the AML populations for Ara-C incorporation into replicating DNA to elicit DNA damage. Moreover, PD 0332991 triggered apoptosis of AML cells through inhibition of the homeobox (HOX)A9 oncogene expression, reducing the transcription of its target PIM1. Reduced PIM1 synthesis attenuates PIM1-mediated phosphorylation of the proapoptotic BAD and activates BAD-dependent apoptosis. In vivo, timely inhibition of CDK4/CDK6 by PD 0332991 and release profoundly suppresses tumor growth in response to reduced doses of Ara-C in a xenograft AML model. Collectively, these data suggest selective and reversible inhibition of CDK4/CDK6 as an effective means to enhance Ara-C killing of AML cells at reduced doses, which has implications for the treatment of elderly AML patients who are unable to tolerate high-dose Ara-C therapy.

Pim kinases in hematological malignancies: where are we now and where are we going?

The proviral insertion in murine (PIM) lymphoma proteins are a serine/threonine kinase family composed of three isoformes: Pim-1, Pim-2 and Pim-3. They play a critical role in the control of cell proliferation, survival, homing and migration. Recently, overexpression of Pim kinases has been reported in human tumors, mainly in hematologic malignancies. In vitro and in vivo studies have confirmed their oncogenic potential. Indeed, PIM kinases have shown to be involved in tumorgenesis, to enhance tumor growth and to induce chemo-resistance, which is why they have become an attractive therapeutic target for cancer therapy. Novel molecules inhibiting Pim kinases have been evaluated in preclinical studies, demonstrating to be effective and with a favorable toxicity profile. Given the promising results, some of these compounds are currently under investigation in clinical trials. Herein, we provide an overview of the biological activity of PIM-kinases, their role in hematologic malignancies and future therapeutic opportunities.

EBNA3C augments Pim-1 mediated phosphorylation and degradation of p21 to promote B-cell proliferation

Epstein–Barr virus (EBV), a ubiquitous human herpesvirus, can latently infect the human population. EBV is associated with several types of malignancies originating from lymphoid and epithelial cell types. EBV latent antigen 3C (EBNA3C) is essential for EBV-induced immortalization of B-cells. The Moloney murine leukemia provirus integration site (PIM-1), which encodes an oncogenic serine/threonine kinase, is linked to several cellular functions involving cell survival, proliferation, differentiation, and apoptosis. Notably, enhanced expression of Pim-1 kinase is associated with numerous hematological and non-hematological malignancies. A higher expression level of Pim-1 kinase is associated with EBV infection, suggesting a crucial role for Pim-1 in EBV-induced tumorigenesis. We now demonstrate a molecular mechanism which reveals a direct role for EBNA3C in enhancing Pim-1 expression in EBV-infected primary B-cells. We also showed that EBNA3C is physically associated with Pim-1 through its amino-terminal domain, and also forms a molecular complex in B-cells. EBNA3C can stabilize Pim-1 through abrogation of the proteasome/Ubiquitin pathway. Our results demonstrate that EBNA3C enhances Pim-1 mediated phosphorylation of p21 at the Thr¹⁴⁵ residue. EBNA3C also facilitated the nuclear localization of Pim-1, and promoted EBV transformed cell proliferation by altering Pim-1 mediated regulation of the activity of the cell-cycle inhibitor p21/WAF1. Our study demonstrated that EBNA3C significantly induces Pim-1 mediated proteosomal degradation of p21. A significant reduction in cell proliferation of EBV-transformed LCLs was observed upon stable knockdown of Pim-1. This study describes a critical role for the oncoprotein Pim-1 in EBV-mediated oncogenesis, as well as provides novel insights into oncogenic kinase-targeted therapeutic intervention of EBV-associated cancers.

The oncogenic serine/threonine kinase Pim-1 is upregulated in a number of human cancers including lymphomas, gastric, colorectal and prostate carcinomas. EBV nuclear antigen 3C (EBNA3C) is essential for EBV-induced transformation of human primary B-lymphocytes. Our current study revealed that EBNA3C significantly enhances Pim-1 kinase expression at both the transcript and protein levels. EBNA3C also interacts with Pim-1 and can form a complex in EBV-transformed cells. Moreover, EBNA3C increases nuclear localization of Pim-1 and stabilizes Pim-1 protein levels by inhibiting its poly-ubiquitination. Additionally, EBNA3C augments Pim-1 mediated phosphorylation of p21 and its proteosomal degradation. Stable knockdown of Pim-1 using si-RNA showed a significant decrease in proliferation of EBV transformed lymphoblastoid cell lines and subsequent induction of apoptosis by triggering the intrinsic apoptotic pathway. Therefore, our study demonstrated a new mechanism by which the oncogenic Pim-1 kinase targeted by EBV latent antigen 3C can inhibit p21 function, and is therefore a potential therapeutic target for the treatment of EBV-associated malignancies.

Therapeutic antagonists of microRNAs deplete leukemia-initiating cell activity

Acute myelogenous leukemia (AML) subtypes that result from oncogenic activation of homeobox (HOX) transcription factors are associated with poor prognosis. The HOXA9 transcription activator and growth factor independent 1 (GFI1) transcriptional repressor compete for occupancy at DNA-binding sites for the regulation of common target genes. We exploited this HOXA9 versus GFI1 antagonism to identify the genes encoding microRNA-21 and microRNA-196b as transcriptional targets of HOX-based leukemia oncoproteins. Therapeutic inhibition of microRNA-21 and microRNA-196b inhibited in vitro leukemic colony forming activity and depleted in vivo leukemia-initiating cell activity of HOX-based leukemias, which led to leukemia-free survival in a murine AML model and delayed disease onset in xenograft models. These data establish microRNA as functional effectors of endogenous HOXA9 and HOX-based leukemia oncoproteins, provide a concise in vivo platform to test RNA therapeutics, and suggest therapeutic value for microRNA antagonists in AML.

AZD1208, a potent and selective pan-Pim kinase inhibitor, demonstrates efficacy in preclinical models of acute myeloid leukemia

Upregulation of Pim kinases is observed in several types of leukemias and lymphomas. Pim-1, -2, and -3 promote cell proliferation and survival downstream of cytokine and growth factor signaling pathways. AZD1208 is a potent, highly selective, and orally available Pim kinase inhibitor that effectively inhibits all three isoforms at <5 nM or <150 nM in enzyme and cell assays, respectively. AZD1208 inhibited the growth of 5 of 14 acute myeloid leukemia (AML) cell lines tested, and sensitivity correlates with Pim-1 expression and STAT5 activation. AZD1208 causes cell cycle arrest and apoptosis in MOLM-16 cells, accompanied by a dose-dependent reduction in phosphorylation of Bcl-2 antagonist of cell death, 4EBP1, p70S6K, and S6, as well as increases in cleaved caspase 3 and p27. Inhibition of p4EBP1 and p-p70S6K and suppression of translation are the most representative effects of Pim inhibition in sensitive AML cell lines. AZD1208 inhibits the growth of MOLM-16 and KG-1a xenograft tumors in vivo with a clear pharmacodynamic-pharmacokinetic relationship. AZD1208 also potently inhibits colony growth and Pim signaling substrates in primary AML cells from bone marrow that are Flt3 wild-type or Flt3 internal tandem duplication mutant. These results underscore the therapeutic potential of Pim kinase inhibition for the treatment of AML.

Hoxa9 and Flt3 signaling synergistically regulate an early checkpoint in lymphopoiesis

Hoxa9 and Flt3 signaling are individually important for the generation of lymphoid lineage precursors from multipotent hematopoietic progenitors (MPP) in bone marrow. Mice deficient for Hoxa9, Flt3, or Flt3 ligand (FL) have reduced numbers of lymphoid-primed multipotential progenitors (LMPP), common lymphoid progenitors (CLP), and B/T cell precursors. Hoxa9 regulates lymphoid development, in part, through transcriptional regulation of Flt3. However, it was unclear whether Hoxa9 has functions in lymphopoiesis independent of, or alternatively, synergistically with Flt3 signaling. In this study, we show that Hoxa9(-/-)Flt3l(-/-) mice have more severe deficiencies in all B lineage cells, CLP, LMPP, and total Flt3(+) MPP in bone marrow than the single knockouts. Although LMPP and Flt3(+) CLP contain precursors for NK and dendritic cell lineage cells, no deficiencies in these lineages beyond that in Flt3l(-/-) mice was found. Thymocyte cellularity was significantly reduced in the compound knockout, although peripheral T cell numbers mirrored Flt3l(-/-) mice. Analysis of the hematopoietic progenitor compartment revealed elevated numbers of CD150(+hi)CD34(-)CD41(+) myeloid-biased stem cells in Hoxa9(-/-)Flt3l(-/-) mice. In contrast, CD150(-) MPP enriched for lymphoid potential were synergistically reduced, suggesting Hoxa9 and Flt3 signaling function coordinately to regulate lymphopoiesis at a very early stage. Real-time PCR analysis of CD150(-)Flt3(+) cells from wild-type control, Hoxa9(-/-), and Flt3l(-/-) single knockouts revealed decreased lymphoid transcripts, corroborating the importance of these regulators in lymphoid development. Taken together, these studies reveal a very early checkpoint in lymphopoiesis dependent on the combinatorial activities of Hoxa9 function and Flt3 signaling.

Pim1 serine/threonine kinase regulates the number and functions of murine hematopoietic stem cells

The genes and pathways that govern the functions and expansion of hematopoietic stem cells (HSC) are not completely understood. In this study, we investigated the roles of serine/threonine Pim kinases in hematopoiesis in mice. We generated PIM1 transgenic mice (Pim1-Tx) overexpressing human PIM1 driven by vav hematopoietic promoter/regulatory elements. Compared to wild-type littermates, Pim1-Tx mice showed enhanced hematopoiesis as demonstrated by increased numbers of Lin(-) Sca-1 (+) c-Kit (+) (LSK) hematopoietic stem/progenitor cells and cobblestone area forming cells, higher BrdU incorporation in long-term HSC population, and a better ability to reconstitute lethally irradiated mice. We then extended our study using Pim1(-/-), Pim2(-/-), Pim3(-/-) single knockout (KO) mice. HSCs from Pim1(-/-) KO mice showed impaired long-term hematopoietic repopulating capacity in secondary and competitive transplantations. Interestingly, these defects were not observed in HSCs from Pim2(-/-) or Pim3(-/-) KO mice. Limiting dilution competitive transplantation assay estimated that the frequency of LSKCD34(-) HSCs was reduced by approximately 28-fold in Pim1(-/-) KO mice compared to wild-type littermates. Mechanistic studies demonstrated an important role of Pim1 kinase in regulating HSC cell proliferation and survival. Finally, our polymerase chain reaction (PCR) array and confirmatory real-time PCR (RT-PCR) studies identified several genes including Lef-1, Pax5, and Gata1 in HSCs that were affected by Pim1 deletion. Our data provide the first direct evidence for the important role of Pim1 kinase in the regulation of HSCs. Our study also dissects out the relative role of individual Pim kinase in HSC functions and regulation.

The PIM family of serine/threonine kinases in cancer

The proviral insertion site in Moloney murine leukemia virus, or PIM proteins, are a family of serine/threonine kinases composed of three different isoforms (PIM1, PIM2, and PIM3) that are highly evolutionarily conserved. These proteins are regulated primarily by transcription and stability through pathways that are controlled by Janus kinase/Signal transducer and activator of transcription, JAK/STAT, transcription factors. The PIM family proteins have been found to be overexpressed in hematological malignancies and solid tumors, and their roles in these tumors were confirmed in mouse tumor models. Furthermore, the PIM family proteins have been implicated in the regulation of apoptosis, metabolism, cell cycle, and homing and migration, which has led to the postulation of these proteins as interesting targets for anticancer drug discovery. In the present work, we review the importance of PIM kinases in tumor growth and as drug targets.

Abnormal hematopoietic phenotypes in Pim kinase triple knockout mice

Background

Pim (proviral insertion in murine lymphoma) kinases are a small family of constitutively active, highly conservative serine/threonine oncogenic kinases and have 3 members: Pim1, Pim2, and Pim3. Pim kinases are also implicated in the regulation of B- and T- cell responses to cytokines and hematopoietic growth factors. The roles of Pim kinases in the regulation of primitive hematopoietic stem cells (HSCs) are largely unknown.

Methods

In the current study, Pim1^−/−2^−/−3^−/− triple knockout (TKO) mice were used to determine the role of Pim kinases in hematopoiesis. Peripheral blood hematological parameters were measured in Pim TKO mice and age-matched wild-type (WT) controls. Primary, secondary, and competitive transplantations were performed to assay the long-term repopulating HSCs in Pim TKO mice. In vivo BrdU incorporation assay and ex vivo Ki67 staining and caspase 3 labeling were performed to evaluate the proliferation and apoptosis of HSCs in Pim TKO mice.

Results

Compared to age-matched WT controls, Pim TKO mice had lower peripheral blood platelet count and exhibited erythrocyte hypochromic microcytosis. The bone marrow cells from Pim TKO mice demonstrated decreased hematopoietic progenitor colony-forming ability. Importantly, Pim TKO bone marrow cells had significantly impaired capacity in rescuing lethally irradiated mice and reconstituting hematopoiesis in primary, secondary and competitive transplant models. In vivo BrdU incorporation in long-term HSCs was reduced in Pim TKO mice. Finally, cultured HSCs from Pim TKO mice showed reduced proliferation evaluated by Ki67 staining and higher rate of apoptosis via caspase 3 activation.

Conclusions

Pim kinases are not only essential in the hematopoietic lineage cell development, but also important in HSC expansion, self-renewal, and long-term repopulation.

The role of HOX genes in normal hematopoiesis and acute leukemia

The homeobox (HOX) genes are a highly conserved family of homeodomain-containing transcription factors that specify cell identity in early development and, subsequently, in a number of adult processes including hematopoiesis. The dysregulation of HOX genes is associated with a number of malignancies including acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL), where they have been shown to support the immortalization of leukemic cells both as chimeric partners in fusion genes and when overexpressed in their wild-type form. This review covers our current understanding of the role of HOX genes in normal hematopoiesis, AML and ALL, with particular emphasis on the similarities and differences of HOX function in these contexts, their hematopoietic downstream gene targets and implications for therapy.

Pim kinases in cancer: diagnostic, prognostic and treatment opportunities

PIM proteins belong to a family of ser/thr kinases composed of 3 members, PIM1, PIM2 and PIM3, with greatly overlapping functions. PIM kinases are mainly responsible for cell cycle regulation, antiapoptotic activity and the homing and migration of receptor tyrosine kinases mediated via the JAK/STAT pathway. PIM kinases have been found to be upregulated in many hematological malignancies and solid tumors. Although these kinases have been described as weak oncogenes, they are heavily targeted for anticancer drug discovery. The present review summarizes the discoveries made to date regarding PIM kinases as driving oncogenes in the process of tumorigenesis and their validation as drug targets.

Regulation of HOXA9 activity by predominant expression of DACH1 against C/EBPα and GATA-1 in myeloid leukemia with MLL-AF9

Although MLL-AF9 caused by the chromosomal translocation t(9;11) has a critical role in acute myeloid leukemia, the molecular pathogenesis is poorly understood. Here, we identified that the cell fate determination factor DACH1 is directly up-regulated by MLL-AF9. Recently we showed that the forced expression of DACH1 in myeloid cells induced p27(Kip1) and repressed p21(Cip1), which is a pivotal characteristic of the myeloid progenitor. Consistent with our previous study, ectopic expression of DACH1 contributed to the maintenance of colonogenic activity and blocked the differentiation of myeloid progenitors. Moreover, we here identified an endogenous HOXA9-DACH1 complex mediated by the carboxyl terminus of DACH1 in t(9;11) leukemia cells. qRT-PCR revealed that DACH1 has a stronger transcription-promoting activity with HOXA9 than does PBX2 with HOXA9. Furthermore, C/EBPα and GATA-1 can directly bind to the promoter of DACH1 and act as a transcriptional suppressor. Expression of DACH1 is down-regulated during myeloid differentiation and shows an inverse pattern compared to C/EBPα and GATA-1 expression. However, ectopic expression of C/EBPα and/or GATA-1 could not abrogate the over-expression of DACH1 induced by MLL-AF9. Therefore, we postulate that the inability of C/EBPα and GATA-1 to down-regulate DACH1 expression induced by MLL-AF9 during myeloid differentiation may contribute to t(9;11) leukemogenesis.

Asymmetric chromatid segregation in cardiac progenitor cells is enhanced by Pim-1 kinase

RATIONALE

Cardiac progenitor cells (CPCs) in the adult heart are used for cell-based treatment of myocardial damage, but factors determining stemness, self-renewal, and lineage commitment are poorly understood. Immortal DNA strands inherited through asymmetric chromatid segregation correlate with self-renewal of adult stem cells, but the capacity of CPCs for asymmetric segregation to retain immortal strands is unknown. Cardioprotective kinase Pim-1 increases asymmetric cell division in vivo, but the ability of Pim-1 to enhance asymmetric chromatid segregation is unknown.

OBJECTIVE

We aimed to demonstrate immortal strand segregation in CPCs and the enhancement of asymmetric chromatid distribution by Pim-1 kinase.

METHODS AND RESULTS

Asymmetric segregation is tracked by incorporation of bromodeoxyuridine. The CPC DNA was labeled for several generations and then blocked in second cytokinesis during chase to determine distribution of immortal versus newly synthesized strands. Intensity ratios of binucleated CPCs with bromodeoxyuridine of ≥70:30 between daughter nuclei indicative of asymmetric chromatid segregation occur with a frequency of 4.57, and asymmetric chromatid segregation is demonstrated at late mitotic phases. Asymmetric chromatid segregation is significantly enhanced by Pim-1 overexpression in CPCs (9.19 versus 4.79 in eGFP-expressing cells; P=0.006).

CONCLUSIONS

Asymmetric segregation of chromatids in CPCs is increased nearly two-fold with Pim-1 kinase overexpression, indicating that Pim-1 promotes self-renewal of stem cells.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.

Mechanisms of cytotoxicity to Pim kinase inhibitor, SGI-1776, in acute myeloid leukemia

Pim kinases are Ser/Thr kinases with multiple substrates that affect survival pathways. These proteins are overexpressed in acute myeloid leukemia (AML) blasts and we hypothesized that Pim kinase inhibition would affect AML cell survival. Imidazo[1,2-b]pyridazine compound, SGI-1776 inhibits Pim-1, Pim-2 and Pim-3, and was evaluated in AML-cell line, -xenograft model, and -primary blasts. Treatment of AML cells with SGI-1776 results in a concentration-dependent induction of apoptosis and we investigated its effect on Pim kinase functions. Phosphorylation of traditional Pim kinase targets, c-Myc(Ser62) and 4E-BP1 (Thr36/Thr47), were both decreased in actively cycling AML cell lines MV-4-11, MOLM-13 and OCI-AML-3. Levels of antiapoptotic proteins Bcl-2, Bcl-x(L), XIAP, and proapoptotic Bak and Bax were unchanged; however, a significant reduction in Mcl-1 was observed. This was correlated with inhibition of global RNA and protein synthesis and MCL-1 transcript decline after SGI-1776 treatment. These data suggest that SGI-1776 mechanism in AML involves Mcl-1 protein reduction. Consistent with cell line data, xenograft model studies with mice bearing MV-4-11 tumors showed efficacy with SGI-1776. Importantly, SGI-1776 was also cytotoxic in AML primary cells, irrespective of FLT3 mutation status and resulted in Mcl-1 protein decline. Pim kinase inhibition may be a new strategy for AML treatment.

HoxA10 activates CDX4 transcription and Cdx4 activates HOXA10 transcription in myeloid cells

HoxA10 is a homeodomain transcription factor that influences a number of developmental processes, including hematopoiesis. During definitive hematopoiesis, expression of HoxA10 is maximal in committed myeloid progenitor cells and decreases as differentiation proceeds. Aberrantly increased expression of HoxA10 was found in bone marrow cells in a poor prognosis subset of human acute myeloid leukemia (AML). Consistent with this, AML developed in mice transplanted with HoxA10-overexpressing bone marrow. However, relatively few target genes have been identified that explain the role of HoxA10 in leukemogenesis. In the current study, we identified CDX4 as a HoxA10 target gene. Cdx4 is a homeodomain transcription factor that was also implicated in myeloid leukemogenesis. Although relatively few Cdx4 target genes have been identified, Cdx4 was known to influence HOX gene transcription. We identified a HoxA10-binding cis element in the CDX4 promoter that activated transcription. We also identified a Cdx4-binding cis element that activated the HOXA10 promoter. Therefore, increased Cdx4 expression in HoxA10-overexpressing cells augmented transcription of the endogenous HOXA10 gene. Increased endogenous HoxA10 in these cells induced additional CDX4 transcription. We found that Cdx4 influenced transcription of HoxA10 target genes in a HoxA10-dependent manner. Similarly, HoxA10 influenced transcription of HOX genes in a Cdx4-dependent manner. We previously found that HoxA10-overexpressing myeloid progenitors were hypersensitive to a variety of cytokines. In the current studies, we found that Cdx4 knockdown decreased cytokine hypersensitivity of HoxA10-overexpressing cells. Therefore, these studies identified a positive feedback relationship between HoxA10 and Cdx4, which potentially amplified the contribution of either transcription factor to the pathogenesis of AML.

Ischemia-reperfusion injury up-regulates Pim-3 gene expression in myocardial tissue

This study examined the effect of ischemia-reperfusion injury on the expression of Pim-3 gene in myocardial tissues and their underlying mechanism. Rat models of myocardial ischemia-reperfusion injury were established by ligating the left anterior descending coronary artery of the rats. A total of 30 SD male adult rats were randomly divided into 5 groups: group A (sham operation, n=6); group B (in which the rats were subjected to 15 min of ischemia by ligation of the left anterior descending coronary artery, n=6); group C (in which the rats received 30 min of ischemia, n=6), group D and group E (in which the left anterior descending coronary artery of the rats were ligated for 30 min and then reperfused for 30 min or 120 min, n=6 in each). The left ventricular tissues were removed immediately after the ischemia-reperfusion injury. Neonatal cardiomyocytes were cultured and treated with different concentrations of H(2)O(2) (0, 5, 10, 20 μmol/L) or tumor necrosis factor-α (TNF-α, 0, 1, 5, 10 ng/mL). The mRNA and protein expression of Pim-3 gene was determined by using RT-PCR, western blotting and immunohistochemistry. Additionally, neonatal cardiomyocytes were transfected with Pim-3 siRNA, and induced to develop apoptosis by using H(2)O(2). The results showed that normal myocardial tissues expressed a quantity of Pim-3 gene mRNA and protein. Ischemia-reperfusion injury could up-regulate the mRNA and protein expression of Pim-3 gene in myocardial tissues. Furthermore, H(2)O(2) but not TNF-α up-regulated the Pim-3 gene expression in cultured cardiomyocytes. And Pim-3 silencing failed to strengthen the H(2)O(2)-inducing apoptosis in cardiomyocytes. It was concluded that ischemia-reperfusion injury up-regulated the Pim-3 gene expression through oxidative stress signaling pathway in myocardial tissues.

Hoxa9 regulates Flt3 in lymphohematopoietic progenitors

Early B cell factor (EBF) is a transcription factor essential for specification and commitment to the B cell fate. In this study, we show downregulation of a developmentally regulated cluster of hoxa genes, notably hoxa9, coincides with induction of EBF at the Pro-B cell stage of B cell differentiation. Analysis of the hematopoietic progenitor compartment in Hoxa9(-/-) mice revealed significantly reduced frequencies and expression levels of Flt3, a cytokine receptor important for lymphoid priming and the generation of B cell precursors (BCPs). We show that Hoxa9 directly regulates the flt3 gene. Chromatin immunoprecipitation analysis revealed binding of Hoxa9 to the flt3 promoter in a lymphoid progenitor cell line. Knockdown of Hoxa9 significantly reduced Flt3 transcription and expression. Conversely, forced expression of Hoxa9 increased Flt3 transcription and expression in a Pro-B cell line that expressed low levels of Flt3. Hoxa9 inversely correlated with ebf1 in ex vivo-isolated bone marrow progenitors and BCPs, suggesting that EBF might function to silence a Hoxa9 transcriptional program. Restoration of EBF function in an EBF(-/-) cell line induced B lineage gene expression but did not directly suppress hoxa9 transcription, revealing alternate mechanisms of Hoxa9 regulation in BCPs. These data provide new insight into Hoxa9 function and regulation during lymphoid and B cell development. Furthermore, they suggest that failure to upregulate Flt3 provides a molecular basis for the lymphoid/early B cell deficiencies in Hoxa9(-/-) mice.

p53-dependent induction of prostate cancer cell senescence by the PIM1 protein kinase

The PIM family of serine threonine protein kinases plays an important role in regulating both the growth and transformation of malignant cells. However, in a cell line-dependent manner, overexpression of PIM1 can inhibit cell and tumor growth. In 22Rv1 human prostate cells, but not in Du145 or RWPE-2, PIM1 overexpression was associated with marked increases in cellular senescence, as shown by changes in the levels of beta-galactosidase (SA-beta-Gal), p21, interleukin (IL)-6 and IL-8 mRNA and protein. During early cell passages, PIM1 induced cellular polyploidy. As the passage number increased, markers of DNA damage, including the level of gammaH2AX and CHK2 phosphorylation, were seen. Coincident with these DNA damage markers, the level of p53 protein and genes transcriptionally activated by p53, such as p21, TP53INP1, and DDIT4, increased. In these 22Rv1 cells, the induction of p53 protein was associated not only with senescence but also with a significant level of apoptosis. The importance of the p53 pathway to PIM1-driven cellular senescence was further shown by the observation that expression of dominant-negative p53 or shRNA targeting p21 blocked the PIM1-induced changes in the DNA damage response and increases in SA-beta-Gal activity. Likewise, in a subcutaneous tumor model, PIM1-induced senescence was rescued when the p53-p21 pathways are inactivated. Based on these results, PIM1 will have its most profound effects on tumorigenesis in situations where the senescence response is inactivated.

Gfi1-cells and circuits: unraveling transcriptional networks of development and disease

PURPOSE OF REVIEW

The review will integrate current knowledge of transcriptional circuits whose dysregulation leads to autoimmunity, neutropenia and leukemia.

RECENT FINDINGS

Growth factor independent-1 (Gfi1) is a transcriptional repressor with essential roles in controlling hematopoietic stem cell biology, myeloid and lymphoid differentiation and lymphocyte effector functions. Recent work has suggested that Gfi1 competes or collaborates with other transcription factors to modulate transcription programs and lineage decisions.

SUMMARY

Gfi1 is central to several transcriptional circuits whose dysregulation leads to abnormal or malignant hematopoiesis. These functional relationships are conserved from Drosophila development. Such conserved pathways represent central oncogenic or 'gatekeeper' pathways that are pivotal to understanding the process of cellular transformation, and illustrate key targets for clinical intervention.

HOXA9 regulates miR-155 in hematopoietic cells

HOXA9-mediated up-regulation of miR-155 was noted during an array-based analysis of microRNA expression in Hoxa9(-/-)bone marrow (BM) cells. HOXA9 induction of miR-155 was confirmed in these samples, as well as in wild-type versus Hoxa9-deficient marrow, using northern analysis and qRT-PCR. Infection of wild-type BM with HOXA9 expressing or GFP(+) control virus further confirmed HOXA9-mediated regulation of miR-155. miR-155 expression paralleled Hoxa9 mRNA expression in fractionated BM progenitors, being highest in the stem cell enriched pools. HOXA9 capacity to induce myeloid colony formation was blunted in miR-155-deficient BM cells, indicating that miR-155 is a downstream mediator of HOXA9 function in blood cells. Pu.1, an important regulator of myelopoiesis, was identified as a putative down stream target for miR-155. Although miR-155 was shown to down-regulate the Pu.1 protein, HOXA9 did not appear to modulate Pu.1 expression in murine BM cells.

PIM serine/threonine kinases in the pathogenesis and therapy of hematologic malignancies and solid cancers

The identification as cooperating targets of Proviral Integrations of Moloney virus in murine lymphomas suggested early on that PIM serine/threonine kinases play an important role in cancer biology. Whereas elevated levels of PIM1 and PIM2 were mostly found in hematologic malignancies and prostate cancer, increased PIM3 expression was observed in different solid tumors. PIM kinases are constitutively active and their activity supports in vitro and in vivo tumor cell growth and survival through modification of an increasing number of common as well as isoform-specific substrates including several cell cycle regulators and apoptosis mediators. PIM1 but not PIM2 seems also to mediate homing and migration of normal and malignant hematopoietic cells by regulating chemokine receptor surface expression. Knockdown experiments by RNA interference or dominant-negative acting mutants suggested that PIM kinases are important for maintenance of a transformed phenotype and therefore potential therapeutic targets. Determination of the protein structure facilitated identification of an increasing number of potent small molecule PIM kinase inhibitors with in vitro and in vivo anticancer activity. Ongoing efforts aim to identify isoform-specific PIM inhibitors that would not only help to dissect the kinase function but hopefully also provide targeted therapeutics. Here, we summarize the current knowledge about the role of PIM serine/threonine kinases for the pathogenesis and therapy of hematologic malignancies and solid cancers, and we highlight structural principles and recent progress on small molecule PIM kinase inhibitors that are on their way into first clinical trials.

HOXA9 modulates its oncogenic partner Meis1 to influence normal hematopoiesis

While investigating the mechanism of action of the HOXA9 protein, we serendipitously identified Meis1 as a HOXA9 regulatory target. Since HOXA9 and MEIS1 play key developmental roles, are cooperating DNA binding proteins and leukemic oncoproteins, and are important for normal hematopoiesis, the regulation of Meis1 by its partner protein is of interest. Loss of Hoxa9 caused downregulation of the Meis1 mRNA and protein, while forced HOXA9 expression upregulated Meis1. Hoxa9 and Meis1 expression was correlated in hematopoietic progenitors and acute leukemias. Meis1(+/-) Hoxa9(-/-) deficient mice, generated to test HOXA9 regulation of endogenous Meis1, were small and had reduced bone marrow Meis1 mRNA and significant defects in fluorescence-activated cell sorting-enumerated monocytes, mature and pre/pro-B cells, and functional B-cell progenitors. These data indicate that HOXA9 modulates Meis1 during normal murine hematopoiesis. Chromatin immunoprecipitation analysis did not reveal direct binding of HOXA9 to Meis1 promoter/enhancer regions. However, Creb1 and Pknox1, whose protein products have previously been reported to induce Meis1, were shown to be direct targets of HOXA9. Loss of Hoxa9 resulted in a decrease in Creb1 and Pknox1 mRNA, and forced expression of CREB1 in Hoxa9(-/-) bone marrow cells increased Meis1 mRNA almost as well as HOXA9, suggesting that CREB1 may mediate HOXA9 modulation of Meis1 expression.

Gfi1 integrates progenitor versus granulocytic transcriptional programming

In patients with severe congenital neutropenia (SCN) and mice with growth factor independent-1 (Gfi1) loss of function, arrested myeloid progenitors accumulate, whereas terminal granulopoiesis is blocked. One might assume that Gfi-null progenitors accumulate because they lack the ability to differentiate. Instead, our data indicate that Gfi1 loss of function deregulates 2 separable transcriptional programs, one of which controls the accumulation and lineage specification of myeloid progenitors, but not terminal granulopoiesis. We demonstrate that Gfi1 directly represses HoxA9, Pbx1, and Meis1 during normal myelopoiesis. Gfi1-/- progenitors exhibit elevated levels of HoxA9, Pbx1 and Meis1, exaggerated HoxA9-Pbx1-Meis1 activity, and progenitor transformation in collaboration with oncogenic K-Ras. Limiting HoxA9 alleles corrects, in a dose-dependent manner, in vivo and in vitro phenotypes observed with loss of Gfi1 in myeloid progenitor cells but did not rescue Gfi1-/- blocked granulopoiesis. Thus, Gfi1 integrates 2 events during normal myeloid differentiation; the suppression of a HoxA9-Pbx1-Meis1 progenitor program and the induction of a granulopoietic transcription program.

Ki67 and PIM1 expression predict outcome in mantle cell lymphoma treated with high dose therapy, stem cell transplantation and rituximab: a Cancer and Leukemia Group B 59909 correlative science study

The proliferation index in mantle cell lymphoma (MCL) has not been validated in the context of aggressive therapy regimens in the rituximab era. We assessed Ki67 and PIM1 (a cell cycle-related gene upregulated in blastoid MCL) expression by immunohistochemistry in a phase II study Cancer and Leukemia Group B 59909 of aggressive chemotherapy and rituximab followed by autologous stem cell transplantation plus rituximab in untreated MCL patients <70 years of age. As a continuous variable or using a cutoff of 35%, higher image analysis (IA Ki67, n = 52) was associated with shorter progression free survival (PFS) (P < or = 0.030) and event free survival (EFS) (P < or = 0.017). PIM1 expression (n = 50) was associated with PFS (P = 0.033) and EFS (P = 0.043). Bivariate Cox models showed IA Ki67 and PIM1 were independent of clinical factors. High Ki67 (>35%) is an important independent prognostic marker in aggressively treated MCL in the rituximab era. PIM1 expression predicts poor outcome and, given its potential role as a therapeutic target, deserves further study.