Distinct molecular phenotype of malignant CD34(+) hematopoietic stem and progenitor cells in chronic myelogenous leukemia

Leukemia stem cell immunophenotyping tool for diagnostic, prognosis, and therapeutics

The existence of cancer stem cells is debatable in numerous solid tumors, yet in leukemia, there is compelling evidence of this cell population. Leukemic stem cells (LSCs) are altered cells in which accumulating genetic and/or epigenetic alterations occur, resulting in the transition between the normal, preleukemic, and leukemic status. These cells do not follow the normal differentiation program; they are arrested in a primitive state but with high proliferation potential, generating undifferentiated blast accumulation and a lack of a mature cell population. The identification of LSCs might guide stem cell biology research and provide key points of distinction between these cells and their normal counterparts. The identification and characterization of the main features of LSCs can be useful as tools for diagnosis and treatment. In this context, the aim of the present review was to connect immunophenotype data in the main types of leukemia to further guide technical improvements.

Transcriptional cofactors Ski and SnoN are major regulators of the TGF-β/Smad signaling pathway in health and disease

The transforming growth factor-β (TGF-β) family plays major pleiotropic roles by regulating many physiological processes in development and tissue homeostasis. The TGF-β signaling pathway outcome relies on the control of the spatial and temporal expression of >500 genes, which depend on the functions of the Smad protein along with those of diverse modulators of this signaling pathway, such as transcriptional factors and cofactors. Ski (Sloan-Kettering Institute) and SnoN (Ski novel) are Smad-interacting proteins that negatively regulate the TGF-β signaling pathway by disrupting the formation of R-Smad/Smad4 complexes, as well as by inhibiting Smad association with the p300/CBP coactivators. The Ski and SnoN transcriptional cofactors recruit diverse corepressors and histone deacetylases to repress gene transcription. The TGF-β/Smad pathway and coregulators Ski and SnoN clearly regulate each other through several positive and negative feedback mechanisms. Thus, these cross-regulatory processes finely modify the TGF-β signaling outcome as they control the magnitude and duration of the TGF-β signals. As a result, any alteration in these regulatory mechanisms may lead to disease development. Therefore, the design of targeted therapies to exert tight control of the levels of negative modulators of the TGF-β pathway, such as Ski and SnoN, is critical to restore cell homeostasis under the specific pathological conditions in which these cofactors are deregulated, such as fibrosis and cancer.

Proteins that repress molecular signaling through the transforming growth factor-beta (TGF-β) pathway offer promising targets for treating cancer and fibrosis. Marina Macías-Silva and colleagues from the National Autonomous University of Mexico in Mexico City review the ways in which a pair of proteins, called Ski and SnoN, interact with downstream mediators of TGF-β to inhibit the effects of this master growth factor. Aberrant levels of Ski and SnoN have been linked to diverse range of diseases involving cell proliferation run amok, and therapies that regulate the expression of these proteins could help normalize TGF-β signaling to healthier physiological levels. For decades, drug companies have tried to target the TGF-β pathway, with limited success. Altering the activity of these repressors instead could provide a roundabout way of remedying pathogenic TGF-β activity in fibrosis and oncology.

A review of orexin's unprecedented potential as a novel, highly-specific treatment for various localized and metastatic cancers

A systematic review was conducted to categorize the types of cancerous tissues that express orexin receptors and also to examine the effect of in vitro administration of orexin A or B to corresponding cell samples. Comprehensive literature analyses of primary experimental studies were performed. The results of the review included an increased frequency of orexin receptor expression in many colon and prostate cancer tissues and an upward trend of pro-apoptotic activity in these aggressive cell types.

Disease-stabilizing treatment based on all-trans retinoic acid and valproic acid in acute myeloid leukemia - identification of responders by gene expression profiling of pretreatment leukemic cells

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive malignancy only cured by intensive therapy. However, many elderly and unfit patients cannot receive such treatment due to an unacceptable risk of treatment-related morbidity and mortality. Disease-stabilizing therapy is then the only possible strategy, one alternative being treatment based on all-trans retinoic acid (ATRA) combined with the histone deacetylase inhibitor valproic acid and possibly low-toxicity conventional chemotherapy.

METHODS

Primary AML cells were derived from 43 patients included in two clinical studies of treatment based on ATRA, valproic acid and theophyllamine; low toxicity chemotherapy (low-dose cytarabine, hydroxyurea, 6-mercaptopurin) was also allowed. Pretreatment leukemic cells were analyzed by mutation profiling of 54 genes frequently mutated in myeloid malignancies and by global gene expression profiling before and during in vivo treatment.

RESULTS

Patients were classified as responders and non-responders to the treatment, however response to treatment showed no significant associations with karyotype or mutational profiles. Significance analysis of microarray (SAM) showed that responders and non-responders significantly differed with regard to the expression of 179 different genes. The differentially expressed genes encoding proteins with a known function were further classified based on the PANTHER (protein annotation through evolutionary relationship) classification system. The identified genes encoded proteins that are involved in several important biological functions, but a main subset of the genes were important for transcriptional regulation. These pretherapy differences in gene expression were largely maintained during treatment. Our analyses of primary AML cells during in vivo treatment suggest that ATRA modulates HOX activity (i.e. decreased expression of HOXA3, HOXA4 and HOXA5 and their regulator PBX3), but altered function of DNA methyl transferase 3A (DNMT3A) and G-protein coupled receptor signaling may also contribute to the effect of the overall treatment.

CONCLUSIONS

Responders and non-responders to AML stabilizing treatment based on ATRA and valproic acid differ in the pretreatment transcriptional regulation of their leukemic cells, and these differences may be important for the clinical effect of this treatment.

TRIAL REGISTRATIONS

ClinicalTrials.gov no. NCT00175812 ; EudraCT no. 2004-001663-22, registered September 9, 2005 and ClinicalTrials.gov no. NCT00995332 ; EudraCT no. 2007-2007-001995-36, registered October 14, 2009.

Chemokines as a Conductor of Bone Marrow Microenvironment in Chronic Myeloid Leukemia

All blood lineage cells are generated from hematopoietic stem cells (HSCs), which reside in bone marrow after birth. HSCs self-renew, proliferate, and differentiate into mature progeny under the control of local microenvironments including hematopoietic niche, which can deliver regulatory signals in the form of bound or secreted molecules and from physical cues such as oxygen tension and shear stress. Among these mediators, accumulating evidence indicates the potential involvement of several chemokines, particularly CXCL12, in the interaction between HSCs and bone marrow microenvironments. Fusion between breakpoint cluster region (BCR) and Abelson murine leukemia viral oncogene homolog (ABL)-1 gene gives rise to BCR-ABL protein with a constitutive tyrosine kinase activity and transforms HSCs and/or hematopoietic progenitor cells (HPCs) into disease-propagating leukemia stem cells (LSCs) in chronic myeloid leukemia (CML). LSCs can self-renew, proliferate, and differentiate under the influence of the signals delivered by bone marrow microenvironments including niche, as HSCs can. Thus, the interaction with bone marrow microenvironments is indispensable for the initiation, maintenance, and progression of CML. Moreover, the crosstalk between LSCs and bone marrow microenvironments can contribute to some instances of therapeutic resistance. Furthermore, evidence is accumulating to indicate the important roles of bone marrow microenvironment-derived chemokines. Hence, we will herein discuss the roles of chemokines in CML with a focus on bone marrow microenvironments.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Gene expression profile of circulating CD34(+) cells and granulocytes in chronic myeloid leukemia

PURPOSE

We compared the gene expression profile of peripheral blood CD34(+) cells and granulocytes in subjects with chronic myeloid leukemia (CML), with the accent on signaling pathways affected by BCR-ABL oncogene.

METHODS

The microarray analyses have been performed in circulating CD34(+) cells and granulocytes from peripheral blood of 7 subjects with CML and 7 healthy donors. All studied BCR-ABL positive CML patients were in chronic phase, with a mean value of 2012±SD of CD34(+)cells/μl in peripheral blood.

RESULTS

The gene expression profile was more prominent in CML CD34(+) cells (3553 genes) compared to granulocytes (2701 genes). The 41 and 39 genes were significantly upregulated in CML CD34(+) cells (HINT1, TXN, SERBP1) and granulocytes, respectively. BCR-ABL oncogene activated PI3K/AKT and MAPK signaling through significant upregulation of PTPN11, CDK4/6, and MYC and reduction of E2F1, KRAS, and NFKBIA gene expression in CD34(+) cells. Among genes linked to the inhibition of cellular proliferation by BCR-ABL inhibitor Imatinib, the FOS and STAT1 demonstrated significantly decreased expression in CML.

CONCLUSION

The presence of BCR-ABL fusion gene doubled the expression quantity of genes involved in the regulation of cell cycle, proliferation and apoptosis of CD34(+) cells. These results determined the modified genes in PI3K/AKT and MAPK signaling of CML subjects.

The implication of cancer progenitor cells and the role of epigenetics in the development of novel therapeutic strategies for chronic myeloid leukemia

SIGNIFICANCE

Chronic myeloid leukemia (CML) involves the malignant transformation of hematopoietic stem cells, defined largely by the Philadelphia chromosome and expression of the breakpoint cluster region-Abelson (BCR-ABL) oncoprotein. Pharmacological tyrosine kinase inhibitors (TKIs), including imatinib mesylate, have overcome limitations in conventional treatment for the improved clinical management of CML.

RECENT ADVANCES

Accumulated evidence has led to the identification of a subpopulation of quiescent leukemia progenitor cells with stem-like self renewal properties that may initiate leukemogenesis, which are also shown to be present in residual disease due to their insensitivity to tyrosine kinase inhibition.

CRITICAL ISSUES

The characterization of quiescent leukemia progenitor cells as a unique cell population in CML pathogenesis has become critical with the complete elucidation of mechanisms involved in their survival independent of BCR-ABL that is important in the development of novel anticancer strategies. Understanding of these functional pathways in CML progenitor cells will allow for their selective therapeutic targeting. In addition, disease pathogenesis and drug responsiveness is also thought to be modulated by epigenetic regulatory mechanisms such as DNA methylation, histone acetylation, and microRNA expression, with a capacity to control CML-associated gene transcription.

FUTURE DIRECTIONS

A number of compounds in combination with TKIs are under preclinical and clinical investigation to assess their synergistic potential in targeting leukemic progenitor cells and/or the epigenome in CML. Despite the collective promise, further research is required in order to refine understanding, and, ultimately, advance antileukemic therapeutic strategies.

Misfolding, Aggregation, and Disordered Segments in c-Abl and p53 in Human Cancer

The current understanding of the molecular mechanisms that lead to cancer is not sufficient to explain the loss or gain of function in proteins related to tumorigenic processes. Among them, more than 100 oncogenes, 20-30 tumor-suppressor genes, and hundreds of genes participating in DNA repair and replication have been found to play a role in the origins of cancer over the last 25 years. The phosphorylation of serine, threonine, or tyrosine residues is a critical step in cellular growth and development and is achieved through the tight regulation of protein kinases. Phosphorylation plays a major role in eukaryotic signaling as kinase domains are found in 2% of our genes. The deregulation of kinase control mechanisms has disastrous consequences, often leading to gains of function, cell transformation, and cancer. The c-Abl kinase protein is one of the most studied targets in the fight against cancer and is a hotspot for drug development because it participates in several solid tumors and is the hallmark of chronic myelogenous leukemia. Tumor suppressors have the opposite effects. Their fundamental role in the maintenance of genomic integrity has awarded them a role as the guardians of DNA. Among the tumor suppressors, p53 is the most studied. The p53 protein has been shown to be a transcription factor that recognizes and binds to specific DNA response elements and activates gene transcription. Stress triggered by ionizing radiation or other mutagenic events leads to p53 phosphorylation and cell-cycle arrest, senescence, or programed cell death. The p53 gene is the most frequently mutated gene in cancer. Mutations in the DNA-binding domain are classified as class I or class II depending on whether substitutions occur in the DNA contact sites or in the protein core, respectively. Tumor-associated p53 mutations often lead to the loss of protein function, but recent investigations have also indicated gain-of-function mutations. The prion-like aggregation of mutant p53 is associated with loss-of-function, dominant-negative, and gain-of-function effects. In the current review, we focused on the most recent insights into the protein structure and function of the c-Abl and p53 proteins that will provide us guidance to understand the loss and gain of function of these misfolded tumor-associated proteins.

The SKI proto-oncogene enhances the in vivo repopulation of hematopoietic stem cells and causes myeloproliferative disease

The proto-oncogene SKI is highly expressed in human myeloid leukemia and also in murine hematopoietic stem cells. However, its operative relevance in these cells remains elusive. We have over-expressed SKI to define its intrinsic role in hematopoiesis and myeloid neoplasms, which resulted in a robust competitive advantage upon transplantation, a complete dominance of the stem and progenitor compartments, and a marked enhancement of myeloid differentiation at the expense of other lineages. Accordingly, enforced expression of SKI induced a gene signature associated with hematopoietic stem cells and myeloid differentiation, as well as hepatocyte growth factor signaling. Here we demonstrate that, in contrast to what has generally been assumed, the significant impact of SKI on hematopoiesis is independent of its ability to inhibit TGF-beta signaling. Instead, myeloid progenitors expressing SKI are partially dependent on functional hepatocyte growth factor signaling. Collectively our results demonstrate that SKI is an important regulator of hematopoietic stem cell activity and its overexpression leads to myeloproliferative disease.

DNA damage response in CD133 + stem/progenitor cells from umbilical cord blood: low level of endogenous foci and high recruitment of 53BP1

Abstract Purpose: Human hematopoietic stem cells (HSC) are thought to be a major target of radiation-induced leukemogenesis and also provide a relevant cellular model for assessing cancer risk. Cluster of designation 133+ (CD133+) is a marker found in human progenitor and hematopoietic stem cells. Our study examined the repair of radiation-induced DNA double-strand breaks (DSB) in CD133 + umbilical cord blood cells (UCBC).

MATERIALS AND METHODS

After γ-irradiation, endogenous and induced DSB were evaluated in CD133 + UCBC, CD133 - UCBC and peripheral blood lymphocytes (PBL) in terms of phosphorylated histone 2A family member X (γH2AX) and tumor suppressor p53 binding protein 1 (53BP1) foci.

RESULTS

We found that repair signaling in CD133 + UCBC is different from CD133 - UCBC and PBL. These differences include lower endogenous DSB levels and higher 53BP1 recruitment.

CONCLUSIONS

Our data, together with a recent report on radiation-induced γH2AX and 53BP1 foci in CD34 + cells, indicate enhanced DNA repair capacity in HSC as compared to mature lymphocytes.

Physiology of the orexinergic/hypocretinergic system: a revisit in 2012

The neuropeptides orexins and their G protein-coupled receptors, OX(1) and OX(2), were discovered in 1998, and since then, their role has been investigated in many functions mediated by the central nervous system, including sleep and wakefulness, appetite/metabolism, stress response, reward/addiction, and analgesia. Orexins also have peripheral actions of less clear physiological significance still. Cellular responses to the orexin receptor activity are highly diverse. The receptors couple to at least three families of heterotrimeric G proteins and other proteins that ultimately regulate entities such as phospholipases and kinases, which impact on neuronal excitation, synaptic plasticity, and cell death. This article is a 10-year update of my previous review on the physiology of the orexinergic/hypocretinergic system. I seek to provide a comprehensive update of orexin physiology that spans from the molecular players in orexin receptor signaling to the systemic responses yet emphasizing the cellular physiological aspects of this system.

Tyrosine kinase chromosomal translocations mediate distinct and overlapping gene regulation events

Background

Leukemia is a heterogeneous disease commonly associated with recurrent chromosomal translocations that involve tyrosine kinases including BCR-ABL, TEL-PDGFRB and TEL-JAK2. Most studies on the activated tyrosine kinases have focused on proximal signaling events, but little is known about gene transcription regulated by these fusions.

Methods

Oligonucleotide microarray was performed to compare mRNA changes attributable to BCR-ABL, TEL-PDGFRB and TEL-JAK2 after 1 week of activation of each fusion in Ba/F3 cell lines. Imatinib was used to control the activation of BCR-ABL and TEL-PDGFRB, and TEL-JAK2-mediated gene expression was examined 1 week after Ba/F3-TEL-JAK2 cells were switched to factor-independent conditions.

Results

Microarray analysis revealed between 800 to 2000 genes induced or suppressed by two-fold or greater by each tyrosine kinase, with a subset of these genes commonly induced or suppressed among the three fusions. Validation by Quantitative PCR confirmed that eight genes (Dok2, Mrvi1, Isg20, Id1, gp49b, Cxcl10, Scinderin, and collagen Vα1(Col5a1)) displayed an overlapping regulation among the three tested fusion proteins. Stat1 and Gbp1 were induced uniquely by TEL-PDGFRB.

Conclusions

Our results suggest that BCR-ABL, TEL-PDGFRB and TEL-JAK2 regulate distinct and overlapping gene transcription profiles. Many of the genes identified are known to be involved in processes associated with leukemogenesis, including cell migration, proliferation and differentiation. This study offers the basis for further work that could lead to an understanding of the specificity of diseases caused by these three chromosomal translocations.

Insights into the stem cells of chronic myeloid leukemia

Chronic myeloid leukemia (CML) has long served as a paradigm for generating new insights into the cellular origin, pathogenesis and improved approaches to treating many types of human cancer. Early studies of the cellular phenotypes and genotypes represented in leukemic populations obtained from CML patients established the concept of an evolving clonal disorder originating in and initially sustained by a rare, multipotent, self-maintaining hematopoietic stem cell (HSC). More recent investigations continue to support this model, while also revealing new insights into the cellular and molecular mechanisms that explain how knowledge of CML stem cells and their early differentiating progeny can predict the differing and variable features of chronic phase and blast crisis. In particular, these emphasize the need for new agents that effectively and specifically target CML stem cells to produce non-toxic, but curative therapies that do not require lifelong treatments.

Senescence evasion by MCF-7 human breast tumor-initiating cells

Introduction

A subpopulation of cancer cells, tumor-initiating cells, is believed to be the driving force behind tumorigenesis and resistance to radiation and chemotherapy. The persistence of tumor-initiating cells may depend on altered regulation of DNA damage and checkpoint proteins, as well as a reduced propensity to undergo apoptosis or senescence.

Methods

To test this hypothesis, we isolated CD24^-/low/CD44⁺ tumor-initiating cells (as mammospheres) from MCF-7 breast cancer cells grown in adherent monolayer culture, and carried out a comprehensive comparison of cell death and DNA damage response pathways prior to and after exposure to ionizing radiation in mammospheres and monolayer MCF-7 cells. Single and double-strand break repair was measured by single-cell gel electrophoresis. The latter was also examined by phosphorylation of histone H2AX and formation of 53BP1 and Rad51 foci. Apoptosis was quantified by flow-cytometric analysis of annexin V-binding and senescence was analyzed on the basis of cellular β-galactosidase activity. We employed the telomeric repeat amplification protocol to quantify telomerase activity. Expression of key DNA repair and cell cycle regulatory proteins was detected and quantified by western blot analysis.

Results

Our data demonstrate that in comparison to the bulk population of MCF-7 cells (predominantly CD24⁺/CD44⁺), the MCF-7 mammosphere cells benefit from a multifaceted approach to cellular protection relative to that seen in monolayer cells, including a reduced level of reactive oxygen species, a more active DNA single-strand break repair (SSBR) pathway, possibly due to a higher level of expression of the key SSBR protein, human AP endonuclease 1 (Ape1), and a significantly reduced propensity to undergo senescence as a result of increased telomerase activity and a low level of p21 protein expression. No significant difference was seen in the rates of double-strand break repair (DSBR) between the two cell types, but DSBR in mammospheres appears to by-pass the need for H2AX phosphorylation.

Conclusions

Enhanced survival of MCF-7 tumor-initiating cells in response to ionizing radiation is primarily dependent on an inherent down-regulation of the senescence pathway. Since MCF-7 cells are representative of cancer cells that do not readily undergo apoptosis, consideration of senescence pathways may play a role in targeting stem cells from such tumors.

Bcl2 is not required for the development and maintenance of leukemia stem cells in mice

The existence of leukemia stem cells (LSCs) responsible for tumor maintenance has been firmly established. Therefore, therapeutic targeting of these LSCs may have a profound impact on cancer eradication. The anti-apoptotic protein Bcl2 has been proposed as a therapeutic target, but its role in LSC biology has not been investigated. In order to understand the role of Bcl2 in LSC generation and maintenance, we have taken advantage of our Sca1-BCRABLp210 mouse model of human chronic myeloid leukemia and bcl2 gene-targeted mice. This study provides genetic evidence that the inhibition of Bcl2 is not critical for the generation, selection or maintenance of the tumor initiating and maintaining cells in mice.

Molecular and functional analysis of the stem cell compartment of chronic myelogenous leukemia reveals the presence of a CD34- cell population with intrinsic resistance to imatinib

We show the molecular and functional characterization of a novel population of lineage-negative CD34-negative (Lin(-)CD34(-)) hematopoietic stem cells from chronic myelogenous leukemia (CML) patients at diagnosis. Molecular karyotyping and quantitative analysis of BCR-ABL transcript demonstrated that approximately one-third of CD34(-) cells are leukemic. CML Lin(-)CD34(-) cells showed kinetic quiescence and limited clonogenic capacity. However, stroma-dependent cultures induced CD34 expression on some cells and cell cycling, and increased clonogenic activity and expression of BCR-ABL transcript. Lin(-)CD34(-) cells showed hematopoietic cell engraftment rate in 2 immunodeficient mouse strains similar to Lin-CD34(+) cells, whereas endothelial cell engraftment was significantly higher. Gene expression profiling revealed the down-regulation of cell-cycle arrest genes and genes involved in antigen presentation and processing, while the expression of genes related to tumor progression, such as angiogenic factors, was strongly up-regulated compared with normal counterparts. Phenotypic analysis confirmed the significant down-regulation of HLA class I and II molecules in CML Lin(-)CD34(-) cells. Imatinib mesylate did not reduce fusion transcript levels, BCR-ABL kinase activity, and clonogenic efficiency of CML Lin(-)CD34(-) cells in vitro. Moreover, leukemic CD34(-) cells survived exposure to BCR-ABL inhibitors in vivo. Thus, we identified a novel CD34(-) leukemic stem cell subset in CML with peculiar molecular and functional characteristics.

Blood-forming stem cells are nervous: direct and indirect regulation of immature human CD34+ cells by the nervous system

The nervous system regulates immunity through hormonal and neuronal routes as part of host defense and repair mechanism. Here, we review the emerging evidence for regulation of human hematopoietic stem and progenitor cells (HSPC) by the nervous system both directly and indirectly via their bone marrow (BM) niche-supporting stromal cells. Functional expression of several neurotransmitter receptors was demonstrated on HSPC, mainly on the more primitive CD34(+)/CD38(-/low) fraction. The myeloid cytokines, G-CSF and GM-CSF, dynamically upregulate neuronal receptor expression on human HSPC. This is followed by an increased response to neurotransmitters, leading to enhanced proliferation and motility of human CD34(+) progenitors, repopulation of the murine BM and their egress to the circulation. Importantly, recent observations showed rapid mobilization of human HSPC to high SDF-1 expressing ischemic tissues of stroke individuals followed by neoangiogenesis, neurological and functional recovery. Along with decreased levels of circulating immature CD34(+) cells and SDF-1 blood levels found in patients with early-stage Alzheimer's disease, these findings suggest a possible involvement of human HSPC in brain homeostasis and thus their potential clinical applications in neuropathology.

Molecular biology of bcr-abl1-positive chronic myeloid leukemia

Chronic myeloid leukemia (CML) has been regarded as the paradigmatic example of a malignancy defined by a unique molecular event, the BCR-ABL1 oncogene. Decades of research zeroing in on the role of BCR-ABL1 kinase in the pathogenesis of CML have culminated in the development of highly efficacious therapeutics that, like imatinib mesylate, target the oncogenic kinase activity of BCR-ABL1. In recent years, most research efforts in CML have been devoted to developing novel tyrosine kinase inhibitors (TKIs) as well as to elucidating the mechanisms of resistance to imatinib and other TKIs. Nonetheless, primordial aspects of the pathogenesis of CML, such as the mechanisms responsible for the transition from chronic phase to blast crisis, the causes of genomic instability and faulty DNA repair, the phenomenon of stem cell quiescence, the role of tumor suppressors in TKI resistance and CML progression, or the cross-talk between BCR-ABL1 and other oncogenic signaling pathways, still remain poorly understood. Herein, we synthesize the most relevant and current knowledge on such areas of the pathogenesis of CML.

Cancer induction by restriction of oncogene expression to the stem cell compartment

In human cancers, all cancerous cells carry the oncogenic genetic lesions. However, to elucidate whether cancer is a stem cell-driven tissue, we have developed a strategy to limit oncogene expression to the stem cell compartment in a transgenic mouse setting. Here, we focus on the effects of the BCR-ABLp210 oncogene, associated with chronic myeloid leukaemia (CML) in humans. We show that CML phenotype and biology can be established in mice by restricting BCR-ABLp210 expression to stem cell antigen 1 (Sca1)⁺ cells. The course of the disease in Sca1-BCR-ABLp210 mice was not modified on STI571 treatment. However, BCR-ABLp210-induced CML is reversible through the unique elimination of the cancer stem cells (CSCs). Overall, our data show that oncogene expression in Sca1⁺ cells is all that is required to fully reprogramme it, giving rise to a full-blown, oncogene-specified tumour with all its mature cellular diversity, and that elimination of the CSCs is enough to eradicate the whole tumour.

BCR-ABL1-induced expression of HSPA8 promotes cell survival in chronic myeloid leukaemia

In order to determine new signal transduction pathways implicated in chronic myeloid leukaemia (CML), we performed a gene expression profile comparison between CD34+ cells from CML patients and healthy donors. Functional studies were performed using the Mo7e and Mo7e-p210 cell lines. Expression of CCND1 (Cyclin D1), as well as the chaperone HSPA8, which is important for regulation of CCND1, were significantly upregulated in CD34+ CML cells. Upregulation of HSPA8 was dependent, at least in part, on STAT5 (signal transducer and activator of transcrition 5)-dependent transcriptional activation, as demonstrated by chromatin immunoprecipitation. The presence of HSPA8 in the nuclear protein fraction as well as its binding to CCND1 suggests that it may contribute to stabilization of the CCND1/CDK4 complex, which, in turn, may participate in proliferation of CML cells. Treatment of CML cells with the specific HSPA8 inhibitor 15-deoxyspergualin induced inhibition of CML cell viability but did not induce apoptosis. In conclusion, our studies suggest that STAT5-mediated activation of HSPA8 induces nuclear translocation and activation of the CCND1/CDK4 complex leading to increased proliferation of CML cells, deciphering a new pathway implicated in CML and supporting a potential role of chaperone inhibitors in the treatment of CML.

Chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is typified by robust marrow and extramedullary myeloid cell production. In the absence of therapy or sometimes despite it, CML has a propensity to progress from a relatively well tolerated chronic phase to an almost uniformly fatal blast crisis phase. The discovery of the Philadelphia chromosome followed by identification of its BCR-ABL fusion gene product and the resultant constitutively active P210 BCR-ABL tyrosine kinase, prompted the unraveling of the molecular pathogenesis of CML. Ground-breaking research demonstrating that BCR-ABL was necessary and sufficient to initiate chronic phase CML provided the rationale for targeted therapy. However, regardless of greatly reduced mortality rates with BCR-ABL targeted therapy, most patients harbor quiescent CML stem cells that may be a reservoir for disease progression to blast crisis. While the hematopoietic stem cell (HSC) origin of CML was first suggested over 30 years ago, only recently have the HSC and progenitor cell-specific effects of the molecular mutations that drive CML been investigated. This has provided the impetus for investigating the genetic and epigenetic events governing HSC and progenitor cell resistance to therapy and their role in disease progression. Accumulating evidence suggests that the acquired BCR-ABL mutation initiates chronic phase CML and results in aberrant stem cell differentiation and survival. This eventually leads to the production of an expanded progenitor population that aberrantly acquires self-renewal capacity resulting in leukemia stem cell (LSC) generation and blast crisis transformation. Therapeutic recalcitrance of blast crisis CML provides the rationale for targeting the molecular pathways that drive aberrant progenitor differentiation, survival and self-renewal earlier in disease before LSC predominate.

Transcriptional Analysis of Quiescent and Proliferating CD34+ Human Hemopoietic Cells from Normal and Chronic Myeloid Leukemia Sources

Quiescent and dividing hemopoietic stem cells (HSC) display marked differences in their ability to move between the peripheral circulation and the bone marrow. Specifically, long-term engraftment potential predominantly resides in the quiescent HSC subfraction, and G-CSF mobilization results in the preferential accumulation of quiescent HSC in the periphery. In contrast, stem cells from chronic myeloid leukemia (CML) patients display a constitutive presence in the circulation. To understand the molecular basis for this, we have used microarray technology to analyze the transcriptional differences between dividing and quiescent, normal, and CML-derived CD34+ cells. Our data show a remarkable transcriptional similarity between normal and CML dividing cells, suggesting that the effects of BCR-ABL on the CD34+ cell transcriptome are more limited than previously thought. In addition, we show that quiescent CML cells are more similar to their dividing counterparts than quiescent normal cells are to theirs. We also show these transcriptional differences to be reflected in the altered proliferative activity of normal and CML CD34+ cells. Of the most interest is that the major class of genes that is more abundant in the quiescent cells compared with the dividing cells encodes members of the chemokine family. We propose a role for chemokines expressed by quiescent HSC in the orchestration of CD34+ cell mobilization. Disclosure of potential conflicts of interest is found at the end of this article.

Monocyte derived dendritic cells generated by IFN-alpha acquire mature dendritic and natural killer cell properties as shown by gene expression analysis

BACKGROUND

Dendritic cell (DC) vaccines can induce antitumor immune responses in patients with malignant diseases, while the most suitable DC culture conditions have not been established yet. In this study we compared monocyte derived human DC from conventional cultures containing GM-CSF and IL-4/TNF-alpha (IL-4/TNF-DC) with DC generated by the novel protocol using GM-CSF and IFN-alpha (IFN-DC).

METHODS

To characterise the molecular differences of both DC preparations, gene expression profiling was performed using Affymetrix microarrays. The data were conformed on a protein level by immunophenotyping, and functional tests for T cell stimulation, migration and cytolytic activity were performed.

RESULTS

Both methods resulted in CD11c+ CD86+ HLA-DR+ cells with a typical DC morphology that could efficiently stimulate T cells. But gene expression profiling revealed two distinct DC populations. Whereas IL-4/TNF-DC showed a higher expression of genes envolved in phagocytosis IFN-DC had higher RNA levels for markers of DC maturity and migration to the lymph nodes like DCLAMP, CCR7 and CD49d. This different orientation of both DC populations was confined by a 2.3 fold greater migration in transwell experiments (p = 0.01). Most interestingly, IFN-DC also showed higher RNA levels for markers of NK cells such as TRAIL, granzymes, KLRs and other NK cell receptors. On a protein level, intracytoplasmatic TRAIL and granzyme B were observed in 90% of IFN-DC. This translated into a cytolytic activity against K562 cells with a median specific lysis of 26% at high effector cell numbers as determined by propidium iodide uptake, whereas IL-4/TNF-DC did not induce any tumor cell lysis (p = 0.006). Thus, IFN-DC combined characteristics of mature DC and natural killer cells.

CONCLUSION

Our results suggest that IFN-DC not only stimulate adaptive but also mediate innate antitumor immune responses. Therefore, IFN-DC should be evaluated in clinical vaccination trials. In particular, this could be relevant for patients with diseases responsive to a treatment with IFN-alpha such as Non-Hodgkin lymphoma or chronic myeloid leukemia.

Ski can negatively regulates macrophage differentiation through its interaction with PU.1

In the hematopoietic cell system, the oncoprotein Ski dramatically affects growth and differentiation programs, in some cases leading to malignant leukemia. However, little is known about the interaction partners or signaling pathways involved in the Ski-mediated block of differentiation in hematopoietic cells. Here we show that Ski interacts with PU.1, a lineage-specific transcription factor essential for terminal myeloid differentiation, and thereby represses PU.1-dependent transcriptional activation. Consistent with this, Ski inhibits the biological function of PU.1 to promote myeloid cells to differentiate into macrophage colony-stimulating factor receptor (M-CSFR)-positive macrophages. Using a Ski mutant deficient in PU.1 binding, we demonstrate that Ski-PU.1 interaction is critical for Ski's ability to repress PU.1-dependent transcription and block macrophage differentiation. Furthermore, we provide evidence that Ski-mediated repression of PU.1 is due to Ski's ability to recruit histone deacetylase 3 to PU.1 bound to DNA. Since inactivation of PU.1 is closely related to the development of myeloid leukemia and Ski strongly inhibits PU.1 function, we propose that aberrant Ski expression in certain types of myeloid cell lineages might contribute to leukemogenesis.

Gene expression analysis identifies a genetic signature potentially associated with response to α-IFN in chronic phase CML patients

Microarray-based gene expression analysis was performed on diagnostic chronic phase CML patient samples prior to interferon treatment. Fifteen patient samples corresponding to six cytogenetic responders and nine non-responders were included. Genes differentially expressed between responder and non-responder patients were listed and a subsequent leave-one-out cross validation (LOOV) procedure showed that the top 20 genes allowed the highest prediction accuracy. The relevant genes were quantified by real-time PCR that supported the microarray results. We conclude that it might be possible to use gene expression analysis to predict future response to interferon in CML diagnostic samples.

Molecular signature of CD34+ hematopoietic stem and progenitor cells of patients with CML in chronic phase

In this study, we provide a molecular signature of highly enriched CD34+ cells from bone marrow of untreated patients with chronic myelogenous leukemia (CML) in chronic phase in comparison with normal CD34+ cells using microarrays covering 8746 genes. Expression data reflected several BCR-ABL-induced effects in primary CML progenitors, such as transcriptional activation of the classical mitogen-activated protein kinase pathway and the phosphoinositide-3 kinase/AKT pathway as well as downregulation of the proapoptotic gene IRF8. Moreover, novel transcriptional changes in comparison with normal CD34+ cells were identified. These include upregulation of genes involved in the transforming growth factorbeta pathway, fetal hemoglobin genes, leptin receptor, sorcin, tissue inhibitor of metalloproteinase 1, the neuroepithelial cell transforming gene 1 and downregulation of selenoprotein P. Additionally, genes associated with early hematopoietic stem cells (HSC) and leukemogenesis such as HoxA9 and MEIS1 were transcriptionally activated. Differential expression of differentiation-associated genes suggested an altered composition of the CD34+ cell population in CML. This was confirmed by subset analyses of chronic phase CML CD34+ cells showing an increase of the proportion of megakaryocyte-erythroid progenitors, whereas the proportion of HSC and granulocyte-macrophage progenitors was decreased in CML. In conclusion, our results give novel insights into the biology of CML and could provide the basis for identification of new therapeutic targets.

Gene expression profiling of CD34+ cells identifies a molecular signature of chronic myeloid leukemia blast crisis

Despite recent success in the treatment of early-stage disease, blastic phase (BP) of chronic myeloid leukemia (CML) that is characterized by rapid expansion of therapy-refractory and differentiation-arrested blasts, remains a therapeutic challenge. The development of resistance upon continuous administration of imatinib mesylate is associated with poor prognosis pointing to the need for alternative therapeutic strategies and a better understanding of the molecular mechanisms underlying disease progression. To identify transcriptional signatures that may explain pathological characteristics and aggressive behavior of BP blasts, we performed comparative gene expression profiling on CD34+ Ph+ cells purified from patients with untreated newly diagnosed chronic phase CML (CP, n=11) and from patients in BP (n=9) using Affymetrix oligonucleotide arrays. Supervised microarray data analysis revealed 114 differentially expressed genes (P<10(-4)), 34 genes displaying more than two-fold transcriptional changes when comparing CP and BP groups. While 24 of these genes were downregulated, 10 genes, especially suppressor of cytokine signalling 2 (SOCS2), CAMPATH-1 antigen (CD52), and four human leukocyte antigen-related genes were strongly overexpressed in BP. Expression of selected genes was validated by real-time-polymerase chain reaction and flow cytometry. Our data suggest the existence of a common gene expression profile of CML-BP and provide new insight into the molecular phenotype of blasts associated with disease progression and high malignancy.

P210 Bcr-abl tyrosine kinase interaction with histone deacetylase 1 modifies histone H4 acetylation and chromatin structure of chronic myeloid leukaemia haematopoietic progenitors

The BCR-ABL fusion gene, originating from the balanced (9;22) translocation, is the molecular hallmark and the causative event of chronic myeloid leukaemia (CML). The interactions of its p210 protein constitutively activated and improperly confined to the cytoplasm with multiple regulatory signals of cell cycle progression, apoptosis and self-renewal, induce the illegitimate enlargement of clonal haematopoiesis and genetic instability that drives its progression towards the fully transformed phenotype of blast crisis. However, its effects on the basic transcription machinery and chromatin remodelling are unknown. Our study underscored histone H4 hyperacetylation associated with p210 tyrosine kinase in vitro and in vivo and its role in BCR-ABL transcription. Histone H4 hyperacetylation proceeds, at least partly, from the 'loss of function' of histone deacetylase 1 protein, a critical component of Rb-mediated transcriptional repression, in consequence of its cytoplasmatic compartmentalisation.

Absence of the JAK2 mutation V617F in CD34+ hematopoietic stem and progenitor cells from patients with BCR-ABL-positive CML in chronic phase and blast crisis

In this study, we examined highly enriched CD34+ cells from patients with BCR-ABL-positve CML in chronic phase or blast crisis for the JAK2 V617F activation mutation by sequencing. The cells examined did not bear the mutation irrespective of the disease stage. This finding suggests that the previously described increase of expression and kinase activity of JAK2 in CML cells does not result from the JAK2 V617F activation mutation and that transformation into blast crisis is not associated with the occurrence of this mutation.