Pathogenesis of ELANE-mutant severe neutropenia revealed by induced pluripotent stem cells.

Severe congenital neutropenia (SCN) is often associated with inherited heterozygous point mutations in ELANE, which encodes neutrophil elastase (NE). However, a lack of appropriate models to recapitulate SCN has substantially hampered the understanding of the genetic etiology and pathobiology of this disease. To this end, we generated both normal and SCN patient-derived induced pluripotent stem cells (iPSCs), and performed genome editing and differentiation protocols that recapitulate the major features of granulopoiesis. Pathogenesis of ELANE point mutations was the result of promyelocyte death and differentiation arrest, and was associated with NE mislocalization and activation of the unfolded protein response/ER stress (UPR/ER stress). Similarly, high-dose G-CSF (or downstream signaling through AKT/BCL2) rescues the dysgranulopoietic defect in SCN patient-derived iPSCs through C/EBPß-dependent emergency granulopoiesis. In contrast, sivelestat, an NE-specific small-molecule inhibitor, corrected dysgranulopoiesis by restoring normal intracellular NE localization in primary granules; ameliorating UPR/ER stress; increasing expression of CEBPA, but not CEBPB; and promoting promyelocyte survival and differentiation. Together, these data suggest that SCN disease pathogenesis includes NE mislocalization, which in turn triggers dysfunctional survival signaling and UPR/ER stress. This paradigm has the potential to be clinically exploited to achieve therapeutic responses using lower doses of G-CSF combined with targeting to correct NE mislocalization.

Efficacy of a Mer and Flt3 tyrosine kinase small molecule inhibitor, UNC1666, in acute myeloid leukemia.

Mer and Flt3 receptor tyrosine kinases have been implicated as therapeutic targets in acute myeloid leukemia (AML). In this manuscript we describe UNC1666, a novel ATP-competitive small molecule tyrosine kinase inhibitor, which potently diminishes Mer and Flt3 phosphorylation in AML. Treatment with UNC1666 mediated biochemical and functional effects in AML cell lines expressing Mer or Flt3 internal tandem duplication (ITD), including decreased phosphorylation of Mer, Flt3 and downstream effectors Stat, Akt and Erk, induction of apoptosis in up to 98% of cells, and reduction of colony formation by greater than 90%, compared to treatment with vehicle. These effects were dose-dependent, with inhibition of downstream signaling and functional effects correlating with the degree of Mer or Flt3 kinase inhibition. Treatment of primary AML patient samples expressing Mer and/or Flt3-ITD with UNC1666 also inhibited Mer and Flt3 intracellular signaling, induced apoptosis, and inhibited colony formation. In summary, UNC1666 is a novel potent small molecule tyrosine kinase inhibitor that decreases oncogenic signaling and myeloblast survival, thereby validating dual Mer/Flt3 inhibition as an attractive treatment strategy for AML.

Angiotensin-converting enzyme overexpression in myelocytes enhances the immune response.

Angiotensin-converting enzyme (ACE) plays an important role in blood pressure control. ACE also has effects on renal function, reproduction, hematopoiesis, and several aspects of the immune response. ACE 10/10 mice overexpress ACE in monocytic cells; macrophages from ACE 10/10 mice demonstrate increased polarization toward a proinflammatory phenotype. As a result, ACE 10/10 mice have a highly effective immune response following challenge with melanoma, bacterial infection, or Alzheimer disease. As shown in ACE 10/10 mice, enhanced monocytic function greatly contributes to the ability of the immune response to defend against a wide variety of antigenic and non-antigenic challenges.

Recurrent DNMT3A mutations in patients with myelodysplastic syndromes.

Alterations in DNA methylation have been implicated in the pathogenesis of myelodysplastic syndromes (MDS), although the underlying mechanism remains largely unknown. Methylation of CpG dinucleotides is mediated by DNA methyltransferases, including DNMT1, DNMT3A and DNMT3B. DNMT3A mutations have recently been reported in patients with de novo acute myeloid leukemia (AML), providing a rationale for examining the status of DNMT3A in MDS samples. In this study, we report the frequency of DNMT3A mutations in patients with de novo MDS, and their association with secondary AML. We sequenced all coding exons of DNMT3A using DNA from bone marrow and paired normal cells from 150 patients with MDS and identified 13 heterozygous mutations with predicted translational consequences in 12/150 patients (8.0%). Amino acid R882, located in the methyltransferase domain of DNMT3A, was the most common mutation site, accounting for 4/13 mutations. DNMT3A mutations were expressed in the majority of cells in all tested mutant samples regardless of myeloblast counts, suggesting that DNMT3A mutations occur early in the course of MDS. Patients with DNMT3A mutations had worse overall survival compared with patients without DNMT3A mutations (P=0.005) and more rapid progression to AML (P=0.007), suggesting that DNMT3A mutation status may have prognostic value in de novo MDS.

A novel effect of DNA methyltransferase and histone deacetylase inhibitors: NFkappaB inhibition in malignant myeloblasts.

Malignant myeloblasts arising in high-risk myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are characterized by the constitutive activation of the anti-apoptotic transcription factor NFkappaB. We found that DNA methyltransferase (DNMT) inhibitors (such as azacytidine and 5-aza-2'-deoxycytidine) and histone deacetylase (HDAC) inhibitors (such as trichostatin and valproic acid) efficiently induced apoptosis in the P39 MDS/AML cell line, correlating with an inhibition of NFkappaB (which translocated from the nucleus to the cytoplasm). This effect was obtained rapidly, within a few hours, suggesting that it was not due to epigenetic reprogramming. Indeed, DNMT and HDAC inhibitors reduced the phosphorylation of the NFkappaB-activating kinase IKKalpha/beta, and this effect was also observed in enucleated cells. Finally, circulating myeloblasts from AML patients treated with the DNMT inhibitor 5-aza-2'-deoxycytidine manifested a rapid (2 hours post-treatment) inhibition of NFkappaB and IKKalpha/beta. Altogether, these results indicate that DNMT and HDAC inhibitors can inhibit the constitutive activation of NFkappaB in malignant myeloblasts in vitro and in vivo through a novel mechanism.

Human Flt3 is expressed at the hematopoietic stem cell and the granulocyte/macrophage progenitor stages to maintain cell survival.

FLT3/FLK2, a member of the receptor tyrosine kinase family, plays a critical role in maintenance of hematopoietic homeostasis, and the constitutively active form of the FLT3 mutation is one of the most common genetic abnormalities in acute myelogenous leukemia. In murine hematopoiesis, Flt3 is not expressed in self-renewing hematopoietic stem cells, but its expression is restricted to the multipotent and the lymphoid progenitor stages at which cells are incapable of self-renewal. We extensively analyzed the expression of Flt3 in human (h) hematopoiesis. Strikingly, in both the bone marrow and the cord blood, the human hematopoietic stem cell population capable of long-term reconstitution in xenogeneic hosts uniformly expressed Flt3. Furthermore, human Flt3 is expressed not only in early lymphoid progenitors, but also in progenitors continuously along the granulocyte/macrophage pathway, including the common myeloid progenitor and the granulocyte/macrophage progenitor. We further found that human Flt3 signaling prevents stem and progenitors from spontaneous apoptotic cell death at least through up-regulating Mcl-1, an indispensable survival factor for hematopoiesis. Thus, the distribution of Flt3 expression is considerably different in human and mouse hematopoiesis, and human FLT3 signaling might play an important role in cell survival, especially at stem and progenitor cells that are critical cellular targets for acute myelogenous leukemia transformation.

PLC-beta2 activity on actin-associated polyphosphoinositides promotes migration of differentiating tumoral myeloid precursors.

During both maturation and function, neutrophils are subjected to reorganization of the actin cytoskeleton. Among the molecules that influence cytoskeletal architecture, the amount and subcellular localization of phosphoinositides, regulated by specific kinases and phosphatases, may play a crucial role. In neutrophils, PLC-beta2 is a major phosphoinositide-dependent phospholipase C isoform activated in response to chemoattractants, even though its role in the modifications of cell morphology and motility that occur during the inflammatory process has not been fully elucidated. In APL-derived promyelocytes induced to complete their maturation program, we have found that the expression levels of PLC-beta2 positively correlate with the degree of the reached neutrophil differentiation. Here, we demonstrate that PLC-beta2 modulates the migration capability of promyelocytes induced to differentiate with ATRA. In differentiating cells, the association of PLC-beta2 with actin, mediated by the PH domain, seems crucial for catalytic activity. We conclude that phosphodiesterase activity of PLC-beta2 on the actin-associated PIP2 may be responsible, by modifying the phosphoinositide pools, for the modifications of cytoskeleton architecture that take place during motility of differentiating promyelocytes.

2,2',4,4'-Tetrachlorobiphenyl upregulates cyclooxygenase-2 in HL-60 cells via p38 mitogen-activated protein kinase and NF-kappaB.

Polychlorinated biphenyls (PCBs) are ubiquitous, persistent environmental contaminants that affect a number of cellular systems, including neutrophils. Among the effects caused by the noncoplanar PCB 2,2',4,4'-tetrachlorobiphenyl (2244-TCB) in granulocytic HL-60 cells are increases in superoxide anion production, activation of phospholipase A(2) with subsequent release of arachidonic acid (AA) and upregulation of the inflammatory gene cyclooxygenase-2 (COX-2). The objective of this study was to determine the signal transduction pathways involved in the upregulation of COX-2 by 2244-TCB. Treatment of HL-60 cells with 2244-TCB led to increased expression of COX-2 mRNA. This increase was prevented by the transcriptional inhibitor actinomycin D in cells pretreated with 2244-TCB for 10 min. The increase in COX-2 mRNA was associated with release of (3)H-AA, phosphorylation of p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinases, increased levels of nuclear NF-kappaB and increased superoxide anion production. Bromoenol lactone, an inhibitor of the calcium-independent phospholipase A(2), reduced (3)H-AA release but had no effect on COX-2 mRNA, protein or activity. Pretreatment with SB-202190 or SB-203580, inhibitors of the p38 MAP kinase pathway, prevented the 2244-TCB-mediated induction of COX-2 and phosphorylation of p38 and ERK MAP kinases. These inhibitors did not alter (3)H-AA release. Treatment with PD 98059 or U 0126, inhibitors of the MAP/ERK (MEK) pathway, prevented the 2244-TCB-mediated activation of ERK but had no effect on COX-2 induction or p38 phosphorylation. 2244-TCB treatment did not affect c-Jun N-terminal kinase (JNK) phosphorylation. 2244-TCB exposure increased the amount of nuclear NF-kappaB. This increase was prevented by pretreatment with p38 MAP kinase inhibitors, but not by pretreatment with MEK inhibitors. Pretreatment with inhibitors of NF-kappaB prevented the 2244-TCB-mediated induction of COX-2 mRNA. 2244-TCB-mediated increases in superoxide anion were prevented by the NADPH oxidase inhibitor apocynin or the free radical scavenger 4-hydroxy TEMPO, but neither of these inhibitors affected the 2244-TCB-induced changes in COX-2 mRNA levels or (3)H-AA release. Taken together these data suggest that p38 MAP kinase-dependent activation of NF-kappaB is critical for the 2244-TCB-mediated upregulation of COX-2 mRNA.

Arginase 1 is expressed in myelocytes/metamyelocytes and localized in gelatinase granules of human neutrophils.

Arginase 1 (ARG1) metabolizes arginine, thus reducing the availability of arginine as a substrate for nitric oxide synthase (NOS). The decreased production of nitric oxide (NO) by NOS and the production of ornithine by ARG1 affect immune responses and tissue regeneration at sites of infection, respectively. We here demonstrate that ARG1 is synthesized in myelocytes/metamyelocytes and is stored in gelatinase granules. In accordance with this, activated neutrophils coreleased ARG1 and gelatinase to the extracellular environment on stimulation with phorbol-12-myristate 13-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP), or tumor necrosis factor alpha (TNF-alpha). Overall, these findings define ARG1 as a genuine gelatinase granule protein and support a model in which activated neutrophils release ARG1 at sites of infection to modulate immune responses and promote tissue regeneration.

Src homology 2 domain of overexpressed Lyn kinase is responsible for the acceleration of granulocyte colony-stimulating factor-induced neutrophilic nuclear lobulation.

We have previously shown that the overexpression of a Src family kinase, Lyn, and its kinase-negative form, LynKN, in a granulocyte progenitor cell line, GM-I62M, accelerates neutrophilic nuclear lobulation when the cells are cultured in the presence of granulocyte colony-stimulating factor. In this study, we investigated the role of the Src homology 2 (SH2) and SH3 domains of Lyn in the accelerated induction of nuclear lobulation. In contrast to wild-type Lyn, the overexpression of its SH2 domain mutant did not induce the accelerated nuclear morphological changes, but the overexpressed SH3 domain mutant had the same effects as wild-type Lyn. Therefore, the SH2 domain of Lyn is responsible for the accelerated induction of neutrophilic nuclear lobulation upon G-CSF stimulation.

CD44 and TGFbeta1 synergise to induce expression of a functional NADPH oxidase in promyelocytic cells.

Bone marrow stromal cells produce large amounts of extracellular matrix and cytokines. Amongst them, hyaluronan, a glycosaminoglycan and ligand for the cell surface molecule CD44, and TGFbeta1, a cytokine particularly important in monocyte differentiation. We have studied in vitro the role of hyaluronan and TGFbeta1 in the differentiation process of U937 monocytic progenitor cells. We provide evidence that, in the presence of whole blood-derived serum, the addition of hyaluronan is sufficient to induce the expression of NADPH-oxidase components but not of other monocytic markers (CD14, CD11b, and VLA-4). In the presence of plasma-derived serum, besides hyaluronan, the additional presence of TGFbeta1 was required for the expression of all of the components of the NADPH oxidase. We further show that hyaluronan mediates its effect through CD44. We conclude that cell matrix factors act cooperatively with cytokines to induce the expression of the components of the NADPH-oxidase in monocytic progenitor cells.

EFA (9-beta-D-erythrofuranosyladenine) is an effective salvage agent for methylthioadenosine phosphorylase-selective therapy of T-cell acute lymphoblastic leukemia with L-alanosine.

The deficiency of methylthioadenosine phosphorylase (MTAP) in T-cell acute lymphoblastic leukemia (T-ALL) and other cancers, while constitutively expressed in normal cells, allows for selective therapy using L-alanosine, an inhibitor of de novo AMP synthesis. We demonstrate that MTAP- T-ALL cells obtained at relapse are as sensitive to L-alanosine toxicity as diagnosis samples. The therapeutic index of L-alanosine can be increased by the use of a MTAP substrate, which protects MTAP+ normal cells. Since MTAP substrates MTA and 5'deoxyadenosine are prone to toxicities associated with adenosine, we synthesized and evaluated a potentially nontoxic MTAP substrate, 9-beta-D-erythrofuranosyladenine (EFA). The cytotoxicity of EFA to hematopoietic progenitors erythroid burst-forming units (BFU-Es) and granulocyte-macrophage colony-forming units (CFU-GMs) was at least 26- to 41-fold less than that of MTA. In addition, EFA selectively rescued MTAP+ MOLT-4 cells from L-alanosine toxicity at 25 microM with negligible toxicity even at 100 microM. As for MTA, significant, albeit incomplete, rescue was achieved at 12.5 microM, but higher concentrations were toxic. EFA at 20 microM or less rescued primary MTAP+ T-ALL cells and normal lymphocytes from L-alanosine toxicity. Collectively, these data indicate that EFA is an effective agent for salvaging MTAP+ cells from L-alanosine toxicity and is superior to MTA due to lower cytotoxicity.

The ultrastructure of hybrid acute leukemia: a study of 15 cases.

The objective of this study was to investigate the ultrastructural characteristics of hybrid acute leukemia (HAL). Fifteen cases of HAL were studied by transmission electron microscopy (TEM), focusing on organelles and myeloperoxidase (MPO) reaction of leukemic cells. By TEM, 5 out 15 cases of HAL were consistent with immunophenotyping (3 cases of biphenotypic type, and 2 cases of biclonal type with granulocytes and lymphocytes); 2 cases were suspected as HAL. On other hand, 5 cases of HAL were assigned to ALL, and 2 cases were misinterpreted as M5a and 1 as M4b. Most of the blast cells of biphenotypic HAL showed lymphoid features, except some cases containing MPO positive granules in blasts, while a few cases exhibited monocytic or nonspecific features. TEM offers advantages in the diagnosis of biclonal type HAL and biphenotypic HAL positive for MPO. However, it is difficult to differentiate MPO-negative cases of biphenotypic HAL from ALL and a few cases may be misinterpreted as M5 by TEM.

The value of dot plot patterns and leukemia-associated phenotypes in AML diagnosis by multiparameter flow cytometry.

The immunophenotypic features in patients with acute myeloid leukemia (AML) were investigated at diagnosis using a wide antibody panel including progenitor-associated, myeloid and lymphoid markers in quadruple combinations. Analyzed were bone marrow samples from 37 adult and pediatric patients for exact identification of AML blasts according their localization on CD45/SSC dot plots and aberrant immunophenotypes in various subtype of AML. We found the localization of AML blasts on CD45/SSC dot plots, which in combination with immunophenotype profile of blasts allow discrimination of several AML subtypes (M0-M2, M3, M4/M5 and other types). In 27/37 AML patients (73%) at least one leukemia-associated phenotype (LAP) was found, two or more aberrancies coexisted in more than a half of them (78%). Asynchronous expression was the most frequent type of LAP (77.8%, 21/27) followed by coexpression of lymphoid-associated antigens, which occurred in 18/27 (66.7%) patients. Presented study showed that leukemic cells of each AML patient had a unique antigenic profile and could be discriminated from their normal counterparts based on typical light scatter profiles and aberrant antigen expression that could further be used for detection of minimal residual disease.

Myeloid enzymes profile related to the immunophenotypic characteristics of blast cells from patients with acute myeloid leukemia (AML) at diagnosis.

The purpose of this study was to assess the possible relationship between the cytochemical enzyme profile and immunophenotypic characteristics of distinct acute myeloid leukemia (AML) subtypes in discrete stages of leukemic cells maturation. As the proportion of leukemic blast cells is critical for exact cytochemical analysis, study was restricted to the evaluation of 48 adult and pediatric patients with newly diagnosed AMLs with 80% or more blasts in analyzed samples. The cytochemical investigation of myeloperoxidase (MPO), Sudan black B (SBB), chloroacetate esterase (CAE), alpha-naphthyl butyrate esterase (ANBE), alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP) in peripheral blood and/or bone marrow was performed. The immunophenotype was examined for the maturation dependent myeloid antigens CD13, CD33, CD11b, CD14, CD15, CD65, CD36, cytoplasmic MPO, non-lineage associated CD34 and HLA-DR antigens, lymphoid- associated antigens CD7, CD4, CD38 as well as natural killer cell associated marker CD56. Flow cytometry by double marker staining and visualization of pathologic cells in dot plots reflected immunophenotypic aberrancy and degree of cell maturation. The patients were classified into AML subtypes M0- M2, M3, M4 and M5 according to the main morphological, cytochemical and immunophenotypical features. The variable combinations of MPO, SBB, CAE and ANBE were identified in relation to immunophenotype. The cytochemical profile of blasts was in concordance with immunophenotype, particularly in more differentiated AML subtypes, M3, M4 and M5. The findings of myeloid antigens expression and cytochemical features in poorly differentiated AML subtypes showed no practical relevance of cytochemical analysis. Notwithstanding that the cytochemical analysis of AML subtypes not sufficiently identifies the distinct aberrancies in heterogeneous leukemic blast cell populations, evaluation of the cytochemical profile in connection with immunophenotyping may help to classify the AML patients to relevant subtypes with more accuracy.

[Retrospective analysis of the morphological, cytochemical, cytogenetic, electron microscopic, and biochemical features of blast cells in acute promyelocytic leukemia]. / Retrospektivnyi analiz morfologicheskikh, tsitokhimicheskikh, tsitogeneticheskikh, élektronno-mikroskopicheskikh, biokhimicheskikh osobennostei blastnykh kletok pri ostrom promielotsitarnom leikoze.

The paper presents a retrospective analysis of long-term follow-ups (from 1959 to 2000) of 86 patients with acute pro-myelocytic leukemia, a rare type of hemoblastoses. The specific features of this form of leukemia is that blast cells of the bone marrow and peripheral blood have a specific granularity that plays a decisive role in the development of the severe hemorrhagic syndrome leading to patients' death. The morphological, cytochemical, cytogenetic, electron microscopic, and biochemical features of blast cells in this disease and its pathogenesis, clinical presentation, and treatment are considered. An extract from the records of a female patient who has had a complete clinical and hematological remission for 22 years is given. The follow-up of such a prolonged remission has not been covered in the Russian literature.