Interferon regulatory factor-2 protects quiescent hematopoietic stem cells from type I interferon–dependent exhaustion

Type I interferons modulate vascular function, repair, thrombosis, and plaque progression in murine models of lupus and atherosclerosis

OBJECTIVE

Patients with systemic lupus erythematosus (SLE) have a notable increase in atherothrombotic cardiovascular disease (CVD) which is not explained by the Framingham risk equation. In vitro studies indicate that type I interferons (IFNs) may play prominent roles in increased CV risk in SLE. However, the in vivo relevance of these findings, with regard to the development of CVD, has not been characterized. This study was undertaken to examine the role of type I IFNs in endothelial dysfunction, aberrant vascular repair, and atherothrombosis in murine models of lupus and atherosclerosis.

METHODS

Lupus-prone New Zealand mixed 2328 (NZM) mice and atherosclerosis-prone apolipoprotein E- knockout (apoE(-/-) ) mice were compared to mice lacking type I IFN receptor (INZM and apoE(-/-) IFNAR(-/-) mice, respectively) with regard to endothelial vasodilatory function, endothelial progenitor cell (EPC) function, in vivo neoangiogenesis, plaque development, and occlusive thrombosis. Similar experiments were performed using NZM and apoE(-/-) mice exposed to an IFNα-containing or empty adenovirus.

RESULTS

Loss of type I IFN receptor signaling improved endothelium-dependent vasorelaxation, lipoprotein parameters, EPC numbers and function, and neoangiogenesis in lupus-prone mice, independent of disease activity or sex. Further, acute exposure to IFNα impaired endothelial vasorelaxation and EPC function in lupus-prone and non-lupus-prone mice. Decreased atherosclerosis severity and arterial inflammatory infiltrates and increased neoangiogenesis were observed in apoE(-/-) IFNAR(-/-) mice, compared to apoE(-/-) mice, while NZM and apoE(-/-) mice exposed to IFNα developed accelerated thrombosis and platelet activation.

CONCLUSION

These results support the hypothesis that type I IFNs play key roles in the development of premature CVD in SLE and, potentially, in the general population, through pleiotropic deleterious effects on the vasculature.

In vivo divisional tracking of hematopoietic stem cells

Hematopoietic stem cell (HSC) division leads to self-renewal, differentiation, or death of HSCs, and adequate balance of this process results in sustained, lifelong, high-throughput hematopoiesis. Despite their contribution to hematopoietic cell production, the majority of cells within the HSC population are quiescent at any given time. Recent studies have tackled the questions of how often HSCs divide, how divisional history relates to repopulating potential, and how many HSCs contribute to hematopoiesis. Here, we summarize these recent findings on HSC turnover from different experimental systems and discuss hypothetical models for HSC cycling and maintenance in steady-state and upon hematopoietic challenge.

Adaptive immune responses associated with breast cancer relapse

The generation, survival, and differentiation of breast cancer stem cells (BCSC) in immunocompetent hosts remain elusive. Some investigators have shown that BCSC can be induced from epithelial tumor cells by the pathologic epithelial to mesenchymal transition (EMT). Emerging evidence suggests that the induction of EMT among epithelial tumor cells originates from signals produced by the non-tumor cells that constitute the tumor microenvironment, including the immune effectors that infiltrate the tumors. Thus, this suggests that the immune system not only has anti-tumor function, but also paradoxically immunoedits tumors, facilitating tumor escape and progression. Indeed, many studies in human breast cancers show both positive and negative associations between the infiltration of various immune effectors (e.g., CD4 and CD8 T cells) and the propensity to relapse with metastatic disease. These observations suggest that distinct types of immune effector cells may induce or inhibit tumor relapse. This review focuses on recent advances in identifying components of the immune system that may directly induce tumor escape and relapse. We propose that levels of interferon (IFN)-γ production or levels of the expression of IFN-γ receptor α on tumor cells may determine whether tumor inhibitory or relapse-promoting effect of IFN-γ may prevail.

Gene Expression Profile Changes After Short-activating RNA-mediated Induction of Endogenous Pluripotency Factors in Human Mesenchymal Stem Cells

It is now recognized that small noncoding RNA sequences have the ability to mediate transcriptional activation of specific target genes in human cells. Using bioinformatics analysis and functional screening, we screened short-activating RNA (saRNA) oligonucleotides designed to target the promoter regions of the pluripotency reprogramming factors, Kruppel-like factor 4 (KLF4) and c-MYC. We identified KLF4 and c-MYC promoter-targeted saRNA sequences that consistently induced increases in their respective levels of nascent mRNA and protein expression in a time- and dose-dependent manner, as compared with scrambled sequence control oligonucleotides. The functional consequences of saRNA-induced activation of each targeted reprogramming factor were then characterized by comprehensively profiling changes in gene expression by microarray analysis, which revealed significant increases in mRNA levels of their respective downstream pathway genes. Notably, the microarray profile after saRNA-mediated induction of endogenous KLF4 and c-MYC showed similar gene expression patterns for stem cell- and cell cycle-related genes as compared with lentiviral vector-mediated overexpression of exogenous KLF4 and c-MYC transgenes, while divergent gene expression patterns common to viral vector-mediated transgene delivery were also noted. The use of promoter-targeted saRNAs for the activation of pluripotency reprogramming factors could have broad implications for stem cell research.

The sixth sense: hematopoietic stem cells detect danger through purinergic signaling

Over the past decade, extracellular nucleotides (such as ATP and UTP) have emerged as key immunomodulators. This family of molecules, already known for its key metabolic functions, has been the focus of intense investigation that has unambiguously shown its crucial role as mediators of cell-to-cell communication. More recently, in addition to its involvement in inflammation and immunity, purinergic signaling has also been shown to modulate BM-derived stem cells. Extracellular nucleotides promote proliferation, CXCL12-driven migration, and BM engraftment of hematopoietic progenitor and stem cells. In addition, purinergic signaling acts indirectly on hematopoietic progenitor and stem cells by regulating differentiation and release of proinflammatory cytokines in BM-derived human mesenchymal stromal cells, which are part of the hematopoietic stem cell (HSC) niche. HSC research has recently blended into the field of immunology, as new findings highlighted the role played by immunologic signals (such as IFN-α, IFN-γ, or TNF-α) in the regulation of the HSC compartment. In this review, we summarize recent reports unveiling a previously unsuspected ability of HSCs to integrate inflammatory signals released by immune and stromal cells, with particular emphasis on the dual role of extracellular nucleotides as mediators of both immunologic responses and BM stem cell functions.

IRF-2 regulates B-cell proliferation and antibody production through distinct mechanisms

Interferon regulatory factor (IRF)-2 is a transcription factor involved in type I (IFN- α/β) signaling. It has been reported that IRF-2 deficiency results in various immune dysfunctions. However, the role of IRF-2 in B-cell functions needs to be elucidated. Unlike wild-type (WT) B cells, IRF-2(-/-) B2 cells were refractory to anti-IgM, but not LPS. Such a defect in proliferation was dependent on IFN- α/β receptor (IFNAR). Marginal zone B cells increased in the proportion relative to B2 cells in IRF-2(-/-) mice produced IgM normally to LPS stimulation. However, IRF-2(-/-) B2 cells were defective in IgM production in an IFNAR-independent manner, although both B-cell subsets differentiated phenotypically to plasma cells at elevated efficiencies. Class switch recombination of IRF-2(-/-) B2 cells by LPS plus IL-4 was also impaired. Their reduced IgM production was conceivably due to an inefficient up-regulation of Blimp-1. Consistent with these in vitro observations, specific antibody production in vivo to a T-dependent antigen by B2 cells was severely impaired in IRF-2(-/- )mice. However, a low, but significant, level of IgG was detected at a late time point, and this IgG exhibited comparable binding affinity to that in WT mice. Follicular helper T-cell development and germinal center formation were normal. A similar tendency was observed when µ chain(-/-) mice were reconstituted with IRF-2(-/- )B cells. These results revealed a multi-faceted role of IRF-2 in the function of B cells, particularly B2 cells, through regulating proliferation in an IFNAR-dependent manner and antibody production via up-regulation of Blimp-1.

Hematopoietic stem and progenitor cells as effectors in innate immunity

Recent research has shed light on novel functions of hematopoietic stem and progenitor cells (HSPC). While they are critical for maintenance and replenishment of blood cells in the bone marrow, these cells are not limited to the bone marrow compartment and function beyond their role in hematopoiesis. HSPC can leave bone marrow and circulate in peripheral blood and lymph, a process often manipulated therapeutically for the purpose of transplantation. Additionally, these cells preferentially home to extramedullary sites of inflammation where they can differentiate to more mature effector cells. HSPC are susceptible to various pathogens, though they may participate in the innate immune response without being directly infected. They express pattern recognition receptors for detection of endogenous and exogenous danger-associated molecular patterns and respond not only by the formation of daughter cells but can themselves secrete powerful cytokines. This paper summarizes the functional and phenotypic characterization of HSPC, their niche within and outside of the bone marrow, and what is known regarding their role in the innate immune response.

Signal transduction pathways, intrinsic regulators, and the control of cell fate choice

BACKGROUND

Information regarding changes in organismal status is transmitted to the stem cell regulatory machinery by a limited number of signal transduction pathways. Consequently, these pathways derive their functional specificity through interactions with stem cell intrinsic master regulators, notably transcription factors. Identifying the molecular underpinnings of these interactions is critical to understanding stem cell function.

SCOPE OF REVIEW

This review focuses on studies in Drosophila that identify the gene regulatory basis for interactions between three different signal transduction pathways and an intrinsic master transcriptional regulator in the context of hematopoietic stem-like cell fate choice. Specifically, the interface between the GATA:FOG regulatory complex and the JAK/STAT, BMP, and Hedgehog pathways is examined.

MAJOR CONCLUSIONS

The GATA:FOG complex coordinates information transmitted by at least three different signal transduction pathways as a means to control stem-like cell fate choice. This illustrates emerging principles concerning regulation of stem cell function and describes a gene regulatory link between changes in organismal status and stem cell response.

GENERAL SIGNIFICANCE

The Drosophila model system offers a powerful approach to identify the molecular basis of how stem cells receive, interpret, and then respond to changes in organismal status. This article is part of a Special Issue entitled: Biochemistry of Stem Cells.

Myelofibrosis 2012: it's complicated

Major advances in myeloproliferative neoplasms in the last decade have cast light on their complexity. The identification of JAK2 (V617F) briefly promised a unifying mechanism of pathogenesis with a single pathway that could be efficiently targeted. Instead, there have been major advances in understanding acquired and background genetic and epigenetic contributors to this group of disorders, with refined risk prediction models and experimental therapeutics that have provided a more nuanced model of disease. In aggregate these observations likely explain the heterogeneity of these disorders and their generally unpredictable response to therapy. Molecular studies, beginning with the identification of JAK2 (V617F), have led to a concept of MPN subtypes existing on a continuum, and additional discoveries such as TET2 and EZH2 mutations have provided the molecular underpinnings to begin to explain overlapping phenotypes in myeloid malignancies more generally. In many ways the pace of molecular discovery is outstripping our ability to integrate these observations into clinical care, both in terms of molecular diagnostics and medical decision making. This review will attempt to summarize, within a clinical context, our evolving understanding of myeloproliferative neoplasms. It focuses on biology, histopathology, prognostic scoring systems, stem cell transplantation as well as selected clinical/preclinical therapeutic observations.

Constitutive type I interferon modulates homeostatic balance through tonic signaling

Interferons (IFNs) were discovered as cytokines induced during and protecting from viral infection. They have been documented to play essential roles in numerous physiological processes beyond antiviral and antimicrobial defense, including immunomodulation, cell cycle regulation, cell survival, and cell differentiation. Recent data have also uncovered a potentially darker side to IFN, including roles in inflammatory diseases, such as autoimmunity and diabetes. IFN can have effects in the absence of acute infection, highlighting a physiologic role for constitutive IFN. Type I IFNs are constitutively produced at vanishingly low quantities and yet exert profound effects, mediated in part through modulation of signaling intermediates required for responses to diverse cytokines. We review evidence for a yin-yang of IFN function through its role in modulating crosstalk between multiple cytokines by both feedforward and feedback regulation of common signaling intermediates and postulate a homeostatic role for IFN through tonic signaling in the absence of acute infection.

IFNβ impairs extracellular matrix formation leading to inhibition of mineralization by effects in the early stage of human osteoblast differentiation

Osteoimmunology is an emerging field of research focused on the interaction of the immune system and bone. In this study we demonstrate that human osteoblasts are sensitive to the immune cytokine interferon (IFN)β. Osteoblasts respond to IFNβ as shown by the induction of several known IFN target genes such as interferon-induced (IFI) proteins (IFIT1, IFI44L), interferon-stimulated gene factor 3 (ISGF3) complex and the induction of IFNβ itself. We demonstrated that IFNβ has severe inhibitory effects on mineralization of osteoblast-derived extracellular matrix (ECM). Analysis of the timing of the IFNβ effects revealed that committed osteoblasts in early stage of differentiation are most sensitive to IFNβ inhibition of mineralization. A single IFNβ treatment was as effective as multiple treatments. During the progress of differentiation osteoblasts become desensitized for IFNβ. This pinpoints to a complex pattern of IFNβ sensitivity in osteoblasts. Focusing on early osteoblasts, we showed that IFNβ decreased gene expression of ECM-related genes, such as type I Collagen (COL1A1), fibronectin (FN1), fibullin (FBLN1), fibrillin (FBN2), and laminin (LAMA1). Additionally, ECM produced by IFNβ-treated osteoblasts contained less collagen protein. IFNβ stimulated gene expression of osteopontin (OPN), annexin2 (ANXA2), and hyaluronan synthase 1 (HAS1), which are important factors in the adhesion of hematopoietic stem cells (HSC) in the HSC niche. In conclusion, IFNβ directly modifies human osteoblast function by inhibiting ECM synthesis eventually resulting in delayed bone formation and mineralization and induces a HSC niche supporting phenotype. These effects are highly dependent on timing of treatment in the early phase of osteoblast differentiation.

Differential requirements for IRF-2 in generation of CD1d-independent T cells bearing NK cell receptors

NK cell receptors (NKRs) such as NK1.1, NKG2D, and Ly49s are expressed on subsets of CD1d-independent memory phenotype CD8(+) and CD4(-)CD8(-) T cells. However, the mechanism for the generation and functions of these NKR(+) T cells remained elusive. In this study, we found that CD1d-independent Ly49(+) T cells were reduced severely in the spleen, bone marrow, and liver, but not thymus, in mice doubly deficient for IFN regulatory factor-2 (IRF-2) and CD1d, in which the overall memory phenotype T cell population was contrastingly enlarged. Because a large fraction of Ly49(+) T cells coexpressed NK1.1 or NKG2D, the reduction of Ly49(+) T cells resulted indirectly in underrepresentation of NK1.1(+) or NKG2D(+) cells. Ly49(+) T cell deficiency was observed in IRF-2(-/-) mice additionally lacking IFN-α/βR α-chain (IFNAR1) as severely as in IRF-2(-/-) mice, arguing against the involvement of the accelerated IFN-α/β signals due to IRF-2 deficiency. Rather, mice lacking IFN-α/βR alone also exhibited relatively milder Ly49(+) T cell reduction, and IL-2 could expand Ly49(+) T cells from IFNAR1(-/-), but not from IRF-2(-/-), spleen cells in vitro. These results together indicated that IRF-2 acted in Ly49(+) T cell development in a manner distinct from that of IFN-α/β signals. The influence of IRF-2 deficiency on Ly49(+) memory phenotype T cells observed in this study suggested a unique transcriptional program for this T cell population among other NKR(+) T and memory phenotype T cells.

HIF1α is required for survival maintenance of chronic myeloid leukemia stem cells

Hypoxia-inducible factor-1α (HIF1α), a master transcriptional regulator of the cellular and systemic hypoxia response, is essential for the maintenance of self-renewal capacity of normal HSCs. It is still unknown whether HIF1α has a role in survival regulation of leukemia stem cells (LSCs) in chronic myeloid leukemia (CML). Using a mouse model of CML, here we report that HIF1α plays a crucial role in survival maintenance of LSCs. Deletion of HIF1α impairs the propagation of CML through impairing cell-cycle progression and inducing apoptosis of LSCs. Deletion of HIF1α results in elevated expression of p16(Ink4a) and p19(Arf) in LSCs, and knockdown of p16(Ink4a) and p19(Arf) rescues the defective colony-forming ability of HIF1α(-/-) LSCs. Compared with normal HSCs, LSCs appear to be more dependent on the HIF1α pathway. Together, these results demonstrate that HIF1α represents a critical pathway in LSCs and inhibition of the HIF1α pathway provides a therapeutic strategy for eradicating LSCs in CML.

Demand-adapted regulation of early hematopoiesis in infection and inflammation

During systemic infection and inflammation, immune effector cells are in high demand and are rapidly consumed at sites of need. Although adaptive immune cells have high proliferative potential, innate immune cells are mostly postmitotic and need to be replenished from bone marrow (BM) hematopoietic stem and progenitor cells. We here review how early hematopoiesis has been shaped to deliver efficient responses to increased need. On the basis of most recent findings, we develop an integrated view of how cytokines, chemokines, as well as conserved pathogen structures, are sensed, leading to divisional activation, proliferation, differentiation, and migration of hematopoietic stem and progenitor cells, all aimed at efficient contribution to immune responses and rapid reestablishment of hematopoietic homeostasis. We also outline how chronic inflammatory processes might impinge on hematopoiesis, potentially fostering hematopoietic stem cell diseases, and, how clinical benefit is and could be achieved by learning from nature.

The role of protein phosphorylation in therapy resistance and disease progression in chronic myelogenous leukemia

This review focuses on the central role that protein phosphorylation plays in the pathogenesis of chronic myelogenous leukemia (CML). It will cover the signaling pathways that are dysregulated by the oncogenic tyrosine kinase, BCR-ABL1, which both defines and drives the disease, and the barriers to disease control. These will include the mechanisms that underlie drug resistance, as well as the features of CML that prevent its cure by tyrosine kinase inhibitors. In the second section, we will cover the proteins and pathways that lead to the transformation of early chronic-phase CML to the more advanced blast phase of the disease. Here, we will outline the key pathophysiologic differences between the chronic and the blast phase, the mechanisms that contribute to these differences, and how these might be therapeutically targeted in patients. In the final section, we will summarize the major lessons learnt from the CML clinic. We will focus on how these observations have impacted our understanding of the therapeutic potential of modulating protein phosphorylation in human diseases and areas in which future research in CML pathophysiology may be important.

The hematopoietic stem cell niche

Hematopoietic stem cells (HSCs) possess the ability to self-renew and to differentiate to mature progeny along multiple different hematopoietic lineages. The function of HSCs depends upon the signals from surrounding cells found within the highly specialized microenvironment termed the hematopoietic stem cell niche. Understanding and exploiting the HSC niche is a goal of basic scientists and clinicians alike. Recent studies have focused on defining the cellular components and molecular factors critical to this microenvironment. Here we review recent findings, discuss unresolved questions, and examine the clinical implications of our current knowledge of the HSC niche.

Expansion of functionally defined mouse hematopoietic stem and progenitor cells by a short isoform of RUNX1/AML1

Self-renewal activity is essential for the maintenance and regeneration of the hematopoietic system. The search for molecules capable of promoting self-renewal and expanding hematopoietic stem cells (HSCs) has met with limited success. Here, we show that a short isoform (AML1a) of RUNX1/AML1 has such activities. Enforced AML1a expression expanded functionally defined HSCs, with an efficiency that was at least 20 times greater than that of the control in vivo and by 18-fold within 7 days ex vivo. The ex vivo-expanded HSCs could repopulate hosts after secondary transplantations. Moreover, AML1a expression resulted in vigorous and long-term (> 10(6)-fold at 4 weeks) ex vivo expansion of progenitor cell populations capable of differentiating into multilineages. Gene expression analysis revealed that AML1a expression was associated with up-regulation of genes, including Hoxa9, Meis1, Stat1, and Ski. shRNA-mediated silencing of these genes attenuated AML1a-mediated activities. Overall, these findings establish AML1a as an isoform-specific molecule that can influence several transcriptional regulators associated with HSCs, leading to enhanced self-renewal activity and hematopoietic stem/progenitor cell expansion ex vivo and in vivo. Therefore, the abilities of AML1a may have implications for HSC transplantation and transfusion medicine, given that the effects also can be obtained by cell-penetrating AML1a protein.

NF-Y is necessary for hematopoietic stem cell proliferation and survival

HSC function depends on the tight control of proliferation and the balance between self-renewal and differentiation. Here, we report that the trimeric transcription factor NF-Y is critical for the survival of cycling, but not quiescent HSCs. With the use of a conditional knockout mouse model, we demonstrate that NF-Ya deletion creates an accumulation of HSCs in G(2)/M and prompts apoptosis, causing hematopoietic failure and death of the animal. These defects are accompanied by the dysregulation of multiple genes that influence cell cycle control (cyclin b1 and p21), apoptosis (Bcl-2), and self-renewal (HoxB4, Notch1, Bmi-1) and are independent of p53. Our results identify NF-Y as a pivotal upstream participant in a regulatory network necessary for the preservation of cycling HSCs.

A new chapter: hematopoietic stem cells are direct players in immunity

Several lines of evidence support the hypothesis that hematopoietic stem cells (HSCs) directly interact with the immune system and have potential for immune privilege. Although the microenvironment or niche provides protection for HSCs from immune attack, HSCs are also capable of interacting with the immune system as signal "providers" and signal "receivers". On the one hand, HSCs display surface immune inhibitory molecules to evade the attack from the innate and adaptive immune systems; on the other hand, HSCs are capable of directly sensing the signals from the immune system through their surface receptors. Thus, HSCs are important direct players in the immune system.

Inflammatory modulation of HSCs: viewing the HSC as a foundation for the immune response

Cells of the innate and adaptive immune systems are the progeny of a variety of haematopoietic precursors, the most primitive of which is the haematopoietic stem cell. Haematopoietic stem cells have been thought of generally as dormant cells that are only called upon to divide under extreme conditions, such as bone marrow ablation through radiation or chemotherapy. However, recent studies suggest that haematopoietic stem cells respond directly and immediately to infections and inflammatory signals. In this Review, we summarize the current literature regarding the effects of infection on haematopoietic stem cell function and how these effects may have a pivotal role in directing the immune response from the bone marrow.

The role of stat1b in zebrafish hematopoiesis

STAT1 mediates response to interferons and regulates immunity, cell proliferation, apoptosis, and sensitivity of Fanconi Anemia cells to apoptosis after interferon signaling; the roles of STAT1 in embryos, however, are not understood. To explore embryonic functions of STAT1, we investigated stat1b, an unstudied zebrafish co-ortholog of human STAT1. Zebrafish stat1a encodes all five domains of the human STAT1-alpha splice form but, like the human STAT1-beta splice variant, stat1b lacks a complete transactivation domain; thus, two unlinked zebrafish paralogs encode protein forms translated from two splice variants of a single human gene, as expected by sub-functionalization after genome duplication. Phylogenetic and conserved synteny studies showed that stat1b and stat1a arose as duplicates in the teleost genome duplication (TGD) and clarified the evolutionary origin of STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B and STAT6 by tandem and genome duplication. RT-PCR revealed maternal expression of stat1a and stat1b. In situ hybridization detected stat1b but not stat1a expression in embryonic hematopoietic tissues. Morpholino knockdown of stat1b, but not stat1a, decreased expression of the myeloid and granulocyte markers spi and mpo and increased expression of the hematopoietic progenitor marker scl, the erythrocyte marker gata1, and hemoglobin. These results suggest that zebrafish Stat1b promotes myeloid development at the expense of erythroid development.

Interferon regulatory factor-2 regulates exocytosis mechanisms mediated by SNAREs in pancreatic acinar cells

BACKGROUND & AIMS

Pancreatic acinar cells are used to study regulated exocytosis. We investigated the role of interferon regulatory factor-2 (IRF2) in exocytosis in pancreatic acinar cells.

METHODS

Pancreas tissues from Irf2⁺/⁺, Irf2⁺/⁻), and Irf2⁻/⁻ mice were examined by microscopy, immunohistochemical, and immunoblot analyses; amylase secretion was quantified. We also compared salivary glands and pancreatic islets of Irf2⁻/⁻ mice with those of Irf2⁺/⁻ mice. To examine the effects of increased signaling by type I interferons, we studied pancreatic acini from Irf2⁻/⁻Ifnar1⁻/⁻ mice. The effect of IRF2 on amylase secretion was studied using an acinar cell line and a retroviral system. We studied expression of IRF2 in wild-type mice with cerulein-induced pancreatitis and changes in pancreatic tissue of Irf2⁻/⁻ mice, compared with those of Irf2⁺/⁻ mice.

RESULTS

Irf2⁻/⁻ pancreas was white and opaque; numerous and wide-spread zymogen granules were observed throughout the cytoplasm, along with lack of fusion between zymogen granules and the apical membrane, lack of secretagogue-stimulated amylase secretion, and low serum levels of amylase and elastase-1, indicating altered regulation of exocytosis. The expression pattern of soluble N-ethylmaleimide-sensitive factor attachment protein receptors changed significantly, specifically in pancreatic acini, and was not rescued by disruption of type I interferon signaling. Down-regulation of IRF2 decreased amylase secretion in an acinar cell line. In mice with pancreatitis, levels of IRF2 were reduced. Irf2⁻/⁻ acini were partially resistant to induction of pancreatitis.

CONCLUSIONS

IRF2 regulates exocytosis in pancreatic acinar cells; defects in this process might be involved in the early phases of acute pancreatitis.

Integrative nucleophosmin mutation-associated microRNA and gene expression pattern analysis identifies novel microRNA - target gene interactions in acute myeloid leukemia

BACKGROUND

MicroRNAs are regulators of gene expression, which act mainly by decreasing mRNA levels of their multiple targets. Deregulated microRNA expression has been shown for acute myeloid leukemia, a disease also characterized by altered gene expression associated with distinct genomic aberrations such as nucleophosmin (NPM1) mutations. To shed further light on the role of deregulated microRNA and gene expression in cytogenetically normal acute myeloid leukemia with NPM1 mutation we performed an integrative analysis of microRNA and mRNA expression data sets.

DESIGN AND METHODS

Both microRNA and gene expression profiles were investigated in samples from a cohort of adult cytogenetically normal acute myeloid leukemia patients (n=43; median age 46 years, range 23-60 years) with known NPM1 mutation status (n=23 mutated, n=20 wild-type) and the data were integratively analyzed. Putative microRNA-mRNA interactions were validated by quantitative reverse transcriptase polymerase chain reaction, western blotting and luciferase reporter assays. For selected microRNAs, sensitivity of microRNA-overexpressing cells to cytarabine treatment was tested by FACS viability and cell proliferation assays.

RESULTS

Our integrative approach of analyzing both microRNA- and gene expression profiles in parallel resulted in a refined list of putative target genes affected by NPM1 mutation-associated microRNA deregulation. Of 177 putative microRNA - target mRNA interactions we identified and validated 77 novel candidates with known or potential involvement in leukemogenesis, such as IRF2-miR-20a, KIT-miR-20a and MN1-miR-15a. Furthermore, our data showed that deregulated expression of tumor suppressor microRNAs, such as miR-29a and miR-30c, might contribute to sensitivity to cytarabine, which is observed in NPM1 mutated acute myeloid leukemia.

CONCLUSIONS

Overall, our observations highlight that integrative data analysis approaches can improve insights into leukemia biology, and lead to the identification of novel microRNA - target gene interactions of potential relevance for acute myeloid leukemia treatment.

Integrating physiological regulation with stem cell and tissue homeostasis

Stem cells are uniquely able to self-renew, to undergo multilineage differentiation, and to persist throughout life in a number of tissues. Stem cells are regulated by a combination of shared and tissue-specific mechanisms and are distinguished from restricted progenitors by differences in transcriptional and epigenetic regulation. Emerging evidence suggests that other aspects of cellular physiology, including mitosis, signal transduction, and metabolic regulation, also differ between stem cells and their progeny. These differences may allow stem cells to be regulated independently of differentiated cells in response to circadian rhythms, changes in metabolism, diet, exercise, mating, aging, infection, and disease. This allows stem cells to sustain homeostasis or to remodel relevant tissues in response to physiological change. Stem cells are therefore not only regulated by short-range signals that maintain homeostasis within their tissue of origin, but also by long-range signals that integrate stem cell function with systemic physiology.

Systemic responses during local viral infections: type I IFNs sound the alarm

Type I IFNs are well known for their role in controlling virus replication and spread. Type I IFNs produced by the infected tissue also signal beyond the boundaries of the infection to regulate different elements of the anti-viral immune response. Recent reports show that type I IFNs directly condition naive monocytes residing in the distal bone marrow (BM) and induce the expression of effector molecules in memory T cells, before their recruitment to the infected site. In addition, hematopoietic stem cells (HSCs) were shown to enter the cell cycle in response to systemically distributed type I IFNs. These discoveries expand our understanding of the pleiotropic effects of type I IFNs during infection and highlight the critical role of systemic signals in the development of an effective response to a localized viral infection.

Posttranscriptional control of type I interferon genes by KSRP in the innate immune response against viral infection

Inherently unstable mRNAs contain AU-rich elements (AREs) in the 3' untranslated regions. Expression of ARE-containing type I interferon transcripts is robustly induced upon viral infection and rapidly shut off thereafter. Their transient accumulation is partly mediated through posttranscriptional regulation. Here we show that mouse embryonic fibroblasts derived from knockout mice deficient in KH-type splicing regulatory protein (KSRP), an RNA-binding protein required for ARE-mediated mRNA decay, produce higher levels of Ifna and Ifnb mRNAs in response to viral infection as a result of decreased mRNA decay. Functional analysis showed that KSRP is required for the decay of Ifna4 and Ifnb mRNAs by interaction with AREs. The increased IFN expression renders Ksrp(-)(/)(-) cells refractory to herpes simplex virus type 1 and vesicular stomatitis virus infection. These findings support a role of a posttranscriptional mechanism in the control of type I IFN expression and highlight the function of KSRP in innate immunity by negatively regulating IFN production.

Mathematical study on kinetics of hematopoietic stem cells--theoretical conditions for successful transplantation

Numerous haematological diseases occur due to dysfunctions during homeostasis processes of blood cell production. Haematopoietic stem cell transplantation (HSCT) is a therapeutic option for the treatment of haematological malignancy and congenital immunodeficiency. Today, HSCT is widely applied as an alternative method to bone marrow transplantation; however, HSCT can be a risky procedure because of potential side effects and complications after transplantations. Although an optimal regimen to achieve successful HSCT while maintaining quality of life is to be developed, even theoretical considerations such as the evaluations of successful engraftments and proposals of clinical management strategies have not been fully discussed yet. In this paper, we construct and investigate mathematical models that describe the kinetics of hematopoietic stem cell self-renewal and granulopoiesis under the influence of growth factors. Moreover, we derive theoretical conditions for successful HSCT, primarily on the basis of the idea that the basic reproduction number R (0) represents a threshold condition for a population to successfully grow in a given steady-state environment. Successful engraftment of transplanted haematopoietic stem cells (HSCs) is subsequently ensured by employing a concept of dynamical systems theory known as 'persistence'. On the basis of the implications from the modelling study, we discuss how the conditions derived for a successful HSCT are used to link to experimental studies.

Stem cell quiescence

Adult stem cells are maintained in a quiescent state but are able to exit quiescence and rapidly expand and differentiate in response to stress. The quiescent state appears to be necessary for preserving the self-renewal of stem cells and is a critical factor in the resistance of cancer stem cells (CSCs) to chemotherapy and targeted therapies. Limited knowledge about quiescence mechanisms has prevented significant advances in targeting of drug-resistant quiescent CSCs populations in the clinic. Thus, an improved understanding of the molecular mechanisms of quiescence in adult stem cells is critical for the development of molecularly targeted therapies against quiescent CSCs in different cancers. Recent studies have provided a better understanding of the intrinsic and extrinsic regulatory mechanisms that control stem cell quiescence. It is now appreciated that the p53 gene plays a critical role in regulating stem cell quiescence. Other intrinsic regulatory mechanisms include the FoxO, HIF-1α, and NFATc1 transcription factors and signaling through ATM and mTOR. Extrinsic microenvironmental regulatory mechanisms include angiopoietin-1, TGF-β, bone morphogenic protein, thrombopoietin, N-cadherin, and integrin adhesion receptors; Wnt/β-catenin signaling; and osteopontin. In this article, we review current advances in understanding normal stem cell quiescence, their significance for CSC quiescence and drug resistance, and the potential clinical applications of these findings.

CD48 on hematopoietic progenitors regulates stem cells and suppresses tumor formation

The proliferation and differentiation of adult stem cells is balanced to ensure adequate generation of differentiated cells, stem cell homeostasis, and guard against malignant transformation. CD48 is broadly expressed on hematopoietic cells but excluded from quiescent long-term murine HSCs. Through its interactions with CD244 on progenitor cells, it influences HSC function by altering the BM cytokine milieu, particularly IFNγ. In CD48-null mice, the resultant misregulation of cytokine signaling produces a more quiescent HSC, a disproportionate number of short-term progenitors, and hyperactivation of Pak1, leading to hematologic malignancies similar to those found in patients with X-linked lymphoproliferative disease. CD48 plays a vital role as an environmental sensor for regulating HSC and progenitor cell numbers and inhibiting tumor development.

Chronic exposure to a TLR ligand injures hematopoietic stem cells

Hematopoietic stem cells (HSC) can be harmed by disease, chemotherapy, radiation, and normal aging. We show in this study that damage also occurs in mice repeatedly treated with very low doses of LPS. Overall health of the animals was good, and there were relatively minor changes in marrow hematopoietic progenitors. However, HSC were unable to maintain quiescence, and transplantation revealed them to be myeloid skewed. Moreover, HSC from treated mice were not sustained in serial transplants and produced lymphoid progenitors with low levels of the E47 transcription factor. This phenomenon was previously seen in normal aging. Screening identified mAbs that resolve HSC subsets, and relative proportions of these HSC changed with age and/or chronic LPS treatment. For example, minor CD150(Hi)CD48(-) populations lacking CD86 or CD18 expanded. Simultaneous loss of CD150(Lo/-)CD48(-) HSC and gain of the normally rare subsets, in parallel with diminished transplantation potential, would be consistent with age- or TLR-related injury. In contrast, HSC in old mice differed from those in LPS-treated animals with respect to VCAM-1 or CD41 expression and lacked proliferation abnormalities. HSC can be exposed to endogenous and pathogen-derived TLR ligands during persistent low-grade infections. This stimulation might contribute in part to HSC senescence and ultimately compromise immunity.

The renaissance of interferon therapy for the treatment of myeloid malignancies

IFNα has been used to treat malignant and viral disorders for more than 25 years. Its efficacy is likely the consequence of its broad range of biologic activities, including direct effects on malignant cells, enhancement of anti-tumor immune responses, induction of proapoptotic genes, inhibition of angiogenesis, and promotion of the cycling of dormant malignant stem cells. Because of the recent development of "targeted" therapies, the use of IFN has been dramatically reduced over the last decade. The increasing awareness of the multistep pathogenesis of many malignancies has suggested, however, that such an approach using target-specific agents is not universally effective. These observations have resulted in a number of recent clinical trials utilizing IFNα in patients with chronic myeloid leukemia (CML), systemic mast cell disease, hypereosinophilic syndrome and the Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) with promising outcomes. These reports provide evidence that IFNα, alone or in combination with other agents, can induce surprisingly robust molecular response rates and possibly improve survival. Although IFNα at present remains an experimental form of therapy for patients with myeloid malignancies, these promising results suggest that it may become again an important component of the therapeutic arsenal for this group of hematologic malignancies.

Type I interferon signaling regulates Ly6C(hi) monocytes and neutrophils during acute viral pneumonia in mice

Type I interferon (IFN-I) plays a critical role in the homeostasis of hematopoietic stem cells and influences neutrophil influx to the site of inflammation. IFN-I receptor knockout (Ifnar1^−/−) mice develop significant defects in the infiltration of Ly6C^hi monocytes in the lung after influenza infection (A/PR/8/34, H1N1). Ly6C^hi monocytes of wild-type (WT) mice are the main producers of MCP-1 while the alternatively generated Ly6C^int monocytes of Ifnar1^−/− mice mainly produce KC for neutrophil influx. As a consequence, Ifnar1^−/− mice recruit more neutrophils after influenza infection than do WT mice. Treatment of IFNAR1 blocking antibody on the WT bone marrow (BM) cells in vitro failed to differentiate into Ly6C^hi monocytes. By using BM chimeric mice (WT BM into Ifnar1^−/− and vice versa), we confirmed that IFN-I signaling in hematopoietic cells is required for the generation of Ly6C^hi monocytes. Of note, WT BM reconstituted Ifnar1^−/− chimeric mice with increased numbers of Ly6C^hi monocytes survived longer than influenza-infected Ifnar1^−/− mice. In contrast, WT mice that received Ifnar1^−/− BM cells with alternative Ly6C^int monocytes and increased numbers of neutrophils exhibited higher mortality rates than WT mice given WT BM cells. Collectively, these data suggest that IFN-I contributes to resistance of influenza infection by control of monocytes and neutrophils in the lung.

Type I interferon (IFN-I) was originally reported as a molecule that interferes with influenza virus replication. Various IFN-I inducible antiviral proteins contribute to dampening virus replication and dissemination. Thus, loss of IFN-I signaling attenuates antiviral response and aggravates disease. Recent studies suggest the possible role of IFN-I in hematopoiesis, which subsequently might have an effect on the immune cell response at the site of infection. Indeed, IFN-I signaling-defective mice have been shown to develop aberrant cell populations. The aim of this current study was to clarify the mechanisms of IFN-I signaling in the regulation of monocytes and neutrophils. We show that IFN-I is directly involved in monocyte differentiation and that loss of IFN-I signaling allows mice to generate monocytes whose gene profile is significantly different. We found that monocytes are an important source of chemokines for further monocyte recruitment, but IFN-I-defective monocytes produce chemokines for neutrophil recruitment. As a result, mice lacking IFN-I signaling recruit more neutrophils and a reduced number of alternatively generated monocytes. Thus, our findings indicate that authentic monocyte differentiation, which requires IFN-I signaling, is critical in controlling neutrophils and protecting mice against influenza virus infection.

Dynamic variation in cycling of hematopoietic stem cells in steady state and inflammation

Both fast-cycling and quiescent mouse hematopoietic stem cells (HSCs) can reconstitute lifelong hematopoiesis, and HSC cycling status can fluctuate over time in steady state and accelerate upon inflammation.

Hematopoietic stem cells (HSCs) maintain blood production. How often mouse HSCs divide and whether each HSC contributes simultaneously, sequentially, or repetitively to hematopoiesis remains to be determined. We track division of 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFSE)–labeled HSC in vivo. We found that, in steady-state mice, bone marrow cells capable of reconstituting lifelong hematopoiesis are found within both fast-cycling (undergoing five or more divisions in 7 wk) and quiescent (undergoing zero divisions in 12–14 wk) lineage marker–negative c-Kit⁺ Sca-1⁺ populations. The contribution of each population to hematopoiesis can fluctuate with time, and cells with extensive proliferative history are prone to return to quiescence. Furthermore, injection of the bacterial component lipopolysaccharide increased the proliferation and self-renewal capacity of HSCs. These findings suggest a model in which all HSCs undergo dynamic and demand-adapted entry into and exit out of the cell cycle over time. This may facilitate a similar degree of turnover of the entire HSC pool at the end of life.

Quiescence regulators for hematopoietic stem cell

Hematopoietic stem cell (HSC) either stays in quiescence or proliferates toward differentiation for the production of mature blood cells, or toward self-renewal for giving rise to itself. In order to both maintain a supply of mature blood cells and not exhaust HSCs throughout the lifetime of an individual, under steady state, most HSCs remain quiescent and only a small number enter the cell cycle. Quiescence of HSCs is not only critical for protecting the stem cell compartment and sustaining stem cell pools over long periods, but it is also critical for protecting stem cells by minimizing their accumulation of replication-associated mutations. The balance between quiescence and proliferation is tightly controlled by both HSC-intrinsic and -extrinsic mechanisms. In recent years, through reductionistic strategies, a wide variety of molecules or pathways critical for HSC quiescence regulation have been identified. This regulation network involves both positive and negative regulators. Understanding quiescence regulation in HSC is of great importance not only for understanding the physiological foundation of HSCs, but also for understanding the pathophysiological origins of many related disorders. In this article, I will briefly review the current advance in the quiescence regulators for the HSCs.

CD4 and CD8 T cell immune activation during chronic HIV infection: roles of homeostasis, HIV, type I IFN, and IL-7

Immune activation plays an important role in the pathogenesis of HIV disease. Although the causes are not fully understood, the forces that lead to immune dysfunction differ for CD4 and CD8 T cells. In this study, we report that the molecular pathways that drive immune activation during chronic HIV infection are influenced by differences in the homeostatic regulation of the CD4 and CD8 T cell pools. Proliferation of CD4 T cells is controlled more tightly by CD4 T cell numbers than is CD8 T cell proliferation. This difference reflects the importance of maintaining a polyclonal CD4 T cell pool in host surveillance. Both pools of T cells were found to be driven by viral load and its associated state of inflammation. In the setting of HIV-induced lymphopenia, naive CD4 T cells were recruited mainly into the proliferating pool in response to CD4 T cell depletion, whereas naive CD8 T cell proliferation was driven mainly by levels of HIV RNA. RNA analysis revealed increased expression of genes associated with type I IFN and common γ chain cytokine signaling in CD4 T cell subsets and only type I IFN-associated genes in CD8 T cell subsets. In vitro studies demonstrated enhanced STAT1 phosphorylation in response to IFN-α and increased expression of the IFNAR1 transcripts in naive and memory CD4 T cells compared with that observed in CD8 T cells. CD4 T cell subsets also showed enhanced STAT1 phosphorylation in response to exogenous IL-7.

Inducible gene and shRNA expression in resident hematopoietic stem cells in vivo

Hematopoietic stem cells (HSC) are probably the best understood somatic stem cells and often serve as a paradigm for other stem cells. Nevertheless, most current techniques to genetically manipulate them in vivo are either constitutive and/or induced in settings of hematopoietic stress such as after irradiation. Here, we present a conditional expression system that allows for externally controllable transgenesis and knockdown in resident HSCs, based on a lentiviral vector containing a tet-O sequence and a transgenic mouse line expressing a doxycyclin-regulated tTR-KRAB repressor protein. HSCs harvested from tTR-KRAB mice are transduced with the lentiviral vector containing a cDNA (i.e., Green Fluorescent Protein (GFP)) and/or shRNA (i.e., p53) of interest and then transplanted into lethally irradiated recipients. While the vector is effectively repressed by tTR-KRAB during homing and engraftment, robust GFP/shp53 expression is induced on doxycyclin treatment in HSCs and their progeny. Doxycylin-controllable transcription is maintained on serial transplantation, indicating that repopulating HSCs are stably modified by this approach. In summary, this easy to implement conditional system provides inducible and reversible overexpression or knock down of genes in resident HSCs in vivo using a drug devoid of toxic or activating effects.

Inflammatory signals regulate hematopoietic stem cells

Hematopoietic stem cells (HSCs) are the progenitors of all blood and immune cells, yet their role in immunity is not well understood. Most studies have focused on the ability of committed lymphoid and myeloid precursors to replenish immune cells during infection. Recent studies, however, have indicated that HSCs also proliferate in response to systemic infection and replenish effector immune cells. Inflammatory signaling molecules including interferons, tumor necrosis factor-α and Toll-like receptors are essential to the HSC response. Observing the biology of HSCs through the lens of infection and inflammation has led to the discovery of an array of immune-mediators that serve crucial roles in HSC regulation and function.

["Creation of mouse models for human diseases"]

To translate research findings into medicine and drug development, we have been performing in vivo research using primary human samples. Development of mouse models with reconstituted human immunity would be critical to overcome technical and ethical constraints associated with in vivo human research. To this end, we have created humanized mice by intravenously injecting purified human hematopoietic stem cells (HSCs) into immune-compromised NOD/SCID/IL2rgKO newborns. This xenogeneic transplantation system allows long-term engraftment and multi-lineage differentiation of human HSCs. The humanized mouse fully reconstituted with human myeloid and lymphoid subsets is expected to serve as an in vivo platform for the investigation of human immune function. In addition to understanding normal human hematopoiesis and immunity, the use of humanized mice is expected to allow investigators to translate their research findings into therapeutic and pharmaceutical development. As a possibility for such translation, we developed an in vivo model of human acute myeloid leukemia (AML), a disease in which the majority of patients succumb to relapse. Using the model, we examined the pathogenesis of AML and tried to clarify the role of AML stem cells in chemotherapy resistance and relapse. Humanized mouse model for both normal and diseased immuno-hematopoietic system is opening a new era in translational medicine.

Histone acetyltransferases as regulators of nonhistone proteins: the role of interferon regulatory factor acetylation on gene transcription

When studying transcription factors, it is necessary to investigate posttranslational modifications. Histone acetyltransferases (HATs) are typical of the modification enzymes involved in chromatin regulation. HATs acetylate the transcription factors (nonhistone proteins) as well as histones. Interferon regulatory factors (IRFs) are transcription factors that bind to the interferon regulatory element (IRF-E) and are involved in regulating cell growth, differentiation, and the immune and hematopoietic systems. During the process of binding to a specific DNA element, IRFs also bind to coactivators such as HATs and become modified. This review looks at how IRFs associate with HATs, p300, and PCAF, and thereby contribute to transcriptional activation.

Imatinib plus peginterferon alfa-2a in chronic myeloid leukemia

BACKGROUND

Imatinib (400 mg daily) is considered the best initial therapy for patients with newly diagnosed chronic myeloid leukemia (CML) in the chronic phase. However, only a minority of patients treated with imatinib have a complete molecular remission.

METHODS

We randomly assigned 636 patients with untreated chronic-phase CML to receive imatinib alone at a dose of 400 mg daily, imatinib (400 mg daily) plus cytarabine (20 mg per square meter of body-surface area per day on days 15 through 28 of each 28-day cycle) or pegylated interferon (peginterferon) alfa-2a (90 μg weekly), or imatinib alone at a dose of 600 mg daily. Molecular and cytogenetic responses, time to treatment failure, overall and event-free survival, and adverse events were assessed. An analysis of molecular response at 12 months was planned. A superior molecular response was defined as a decrease in the ratio of transcripts of the tyrosine kinase gene BCR-ABL to transcripts of ABL of 0.01% or less, corresponding to a reduction of 4 log(10) units or more from the baseline level, as assessed by means of a real-time quantitative polymerase-chain-reaction assay.

RESULTS

At 12 months, the rates of cytogenetic response were similar among the four groups. The rate of a superior molecular response was significantly higher among patients receiving imatinib and peginterferon alfa-2a (30%) than among patients receiving 400 mg of imatinib alone (14%) (P=0.001). The rate was significantly higher among patients treated for more than 12 months than among those treated for 12 months or less. Gastrointestinal events were more frequent among patients receiving cytarabine, whereas rash and depression were more frequent among patients receiving peginterferon alfa-2a.

CONCLUSIONS

As compared with other treatments, the addition of peginterferon alfa-2a to imatinib therapy resulted in significantly higher rates of molecular response in patients with chronic-phase CML. (Funded by the French Ministry of Health and others; ClinicalTrials.gov number, NCT00219739.).

Cyclophosphamide synergizes with type I interferons through systemic dendritic cell reactivation and induction of immunogenic tumor apoptosis

Successful chemotherapy accounts for both tumor-related factors and host immune response. Compelling evidence suggests that some chemotherapeutic agents can induce an immunogenic type of cell death stimulating tumor-specific immunity. Here, we show that cyclophosphamide (CTX) exerts two types of actions relevant for the induction of antitumor immunity in vivo: (i) effect on dendritic cell (DC) homeostasis, mediated by endogenous type I interferons (IFN-I), leading to the preferential expansion of CD8α(+) DC, the main subset involved in the cross-presentation of cell-derived antigens; and (ii) induction of tumor cell death with clear-cut immunogenic features capable of stimulating tumor infiltration, engulfment of tumor apoptotic material, and CD8 T-cell cross-priming by CD8α(+) DC. Notably, the antitumor effects of CTX were efficiently amplified by IFN-I, the former providing a source of antigen and a "resetting" of the DC compartment and the latter supplying optimal costimulation for T-cell cross-priming, resulting in the induction of a strong antitumor response and tumor rejection. These results disclose new perspectives for the development of targeted and more effective chemoimmunotherapy treatments of cancer patients.

Infection-induced myelopoiesis during intracellular bacterial infection is critically dependent upon IFN-γ signaling

Although microbial infections can alter steady-state hematopoiesis, the mechanisms that drive such changes are not well understood. We addressed a role for IFN-γ signaling in infection-induced bone marrow suppression and anemia in a murine model of human monocytic ehrlichiosis, an emerging tick-borne disease. Within the bone marrow of Ehrlichia muris-infected C57BL/6 mice, we observed a reduction in myeloid progenitor cells, as defined both phenotypically and functionally. Infected mice exhibited a concomitant increase in developing myeloid cells within the bone marrow, an increase in the frequency of circulating monocytes, and an increase in splenic myeloid cells. The infection-induced changes in progenitor cell phenotype were critically dependent on IFN-γ, but not IFN-α, signaling. In mice deficient in the IFN-γ signaling pathway, we observed an increase in myeloid progenitor cells and CDllb(lo)Gr1(lo) promyelocytic cells within the bone marrow, as well as reduced frequencies of mature granulocytes and monocytes. Furthermore, E. muris-infected IFN-γR-deficient mice did not exhibit anemia or an increase in circulating monocytes, and they succumbed to infection. Gene transcription studies revealed that IFN-γR-deficient CDllb(lo)Gr1(lo) promyelocytes from E. muris-infected mice exhibited significantly reduced expression of irf-1 and irf-8, both key transcription factors that regulate the differentiation of granulocytes and monocytes. Finally, using mixed bone marrow chimeric mice, we show that IFN-γ-dependent infection-induced myelopoiesis occurs via the direct effect of the cytokine on developing myeloid cells. We propose that, in addition to its many other known roles, IFN-γ acts to control infection by directly promoting the differentiation of myeloid cells that contribute to host defense.

Persistent malignant stem cells in del(5q) myelodysplasia in remission

BACKGROUND

The in vivo clinical significance of malignant stem cells remains unclear.

METHODS

Patients who have the 5q deletion (del[5q]) myelodysplastic syndrome (interstitial deletions involving the long arm of chromosome 5) have complete clinical and cytogenetic remissions in response to lenalidomide treatment, but they often have relapse. To determine whether the persistence of rare but distinct malignant stem cells accounts for such relapses, we examined bone marrow specimens obtained from seven patients with the del(5q) myelodysplastic syndrome who became transfusion-independent while receiving lenalidomide treatment and entered cytogenetic remission.

RESULTS

Virtually all CD34+, CD38+ progenitor cells and stem cells that were positive for CD34 and CD90, with undetectable or low CD38 (CD38−/low), had the 5q deletion before treatment. Although lenalidomide efficiently reduced these progenitors in patients in complete remission, a larger fraction of the minor, quiescent, CD34+,CD38-/low, CD90+ del(5q) stem cells as well as functionally defined del(5q) stem cells remained distinctly resistant to lenalidomide. Over time, lenalidomide resistance developed in most of the patients in partial and complete remission, with recurrence or expansion of the del(5q) clone and clinical and cytogenetic progression.

CONCLUSIONS

In these patients with the del(5q) myelodysplastic syndrome, we identified rare and phenotypically distinct del(5q) myelodysplastic syndrome stem cells that were also selectively resistant to therapeutic targeting at the time of complete clinical and cytogenetic remission. (Funded by the EuroCancerStemCell Consortium and others.)

Cell-autonomous regulation of hematopoietic stem cell cycling activity by ATP

Extracellular nucleotides regulate many cellular functions through activation of purinergic receptors in the plasma membrane. Here, we show that in hematopoietic stem cell (HSC), ATP is stored in vesicles and released in a calcium-sensitive manner. HSC expresses ATP responsive P2X receptors and in vitro pharmacological P2X antagonism restrained hematopoietic progenitors proliferation, but not myeloid differentiation. In mice suffering from chronic inflammation, HSCs were significantly expanded and their cycling activity was sensitive to treatment with the P2X antagonist periodate-oxidized 2,3-dialdehyde ATP. Our results indicate that ATP acts as an autocrine stimulus in regulating HSCs pool size.