Masamichi Isobe

Myelodysplastic syndromes are induced by histone methylation–altering ASXL1 mutations

Recurrent mutations in the gene encoding additional sex combs-like 1 (ASXL1) are found in various hematologic malignancies and associated with poor prognosis. In particular, ASXL1 mutations are common in patients with hematologic malignancies associated with myelodysplasia, including myelodysplastic syndromes (MDSs), and chronic myelomonocytic leukemia. Although loss-of-function ASXL1 mutations promote myeloid transformation, a large subset of ASXL1 mutations is thought to result in stable truncation of ASXL1. Here we demonstrate that C-terminal–truncating Asxl1 mutations (ASXL1-MTs) inhibited myeloid differentiation and induced MDS-like disease in mice. ASXL1-MT mice displayed features of human-associated MDS, including multi-lineage myelodysplasia, pancytopenia, and occasional progression to overt leukemia. ASXL1-MT resulted in derepression of homeobox A9 (Hoxa9) and microRNA-125a (miR-125a) expression through inhibition of polycomb repressive complex 2–mediated (PRC2-mediated) methylation of histone H3K27. miR-125a reduced expression of C-type lectin domain family 5, member a (Clec5a), which is involved in myeloid differentiation. In addition, HOXA9 expression was high in MDS patients with ASXL1-MT, while CLEC5A expression was generally low. Thus, ASXL1-MT–induced MDS-like disease in mice is associated with derepression of Hoxa9 and miR-125a and with Clec5a dysregulation. Our data provide evidence for an axis of MDS pathogenesis that implicates both ASXL1 mutations and miR-125a as therapeutic targets in MDS.

The Receptor LMIR3 Negatively Regulates Mast Cell Activation and Allergic Responses by Binding to Extracellular Ceramide

Mast cells (MCs) are key effector cells in allergic reactions. However, the inhibitory mechanism that prevents excessive activation of MCs remains elusive. Here we show that leukocyte mono-immunoglobulin-like receptor 3 (LMIR3; also called CD300f) is a negative regulator of MC activation in vivo. LMIR3 deficiency exacerbated MC-dependent allergic responses in mice, including anaphylaxis, airway inflammation, and dermatitis. Both physical binding and functional reporter assays via an extracellular domain of LMIR3 showed that several extracellular lipids (including ceramide) and lipoproteins were possible ligands for LMIR3. Importantly, MCs were frequently surrounded by extracellular ceramide in vivo. Upon engagement of high-affinity immunoglobulin E receptor, extracellular ceramide-LMIR3 binding inhibited MC activation via immunoreceptor tyrosine-based inhibitory and switch motifs of LMIR3. Moreover, pretreatment with LMIR3-Fc fusion protein or antibody against either ceramide or LMIR3 interfered with this binding in vivo, thereby exacerbating passive cutaneous anaphylaxis. Thus, the interaction between extracellular ceramide and LMIR3 suppressed MC-dependent allergic responses.

Ceramide-CD300f binding suppresses experimental colitis by inhibiting ATP-mediated mast cell activation

Objective Extracellular ATP mediates mast cell-dependent intestinal inflammation via P2X7 purinoceptors. We have previously shown that CD300f (also called the leucocyte mono-immunoglobulin-like receptor 3 (LMIR3)) suppresses immunoglobulin E-dependent and mast cell-dependent allergic responses by binding to ceramide. The aim of the present study was to clarify the role of ceramide–LMIR3 interaction in the development of IBD. Design The dextran sodium sulfate (DSS)-induced colitis model was used in wild-type (WT), LMIR3−/−, mast cell-deficient KitW-sh/W-sh, KitW-sh/W-shLMIR3−/− or KitW-sh/W-sh mice engrafted with WT or LMIR3−/− bone marrow-derived mast cells (BMMCs). The severity of colitis was determined by clinical and histological criteria. Lamina propria cell populations were assessed by flow cytometry. Production of chemical mediators from lamina propria cells was measured by real-time reverse transcription PCR. Production of chemical mediators from ATP-stimulated BMMCs in the presence or absence of ceramide was measured by ELISA. The severity of DSS-induced colitis was assessed in mice given either an Fc fusion protein containing an extracellular domain of LMIR3, and anticeramide antibody, or ceramide liposomes. Results LMIR3 deficiency exacerbated DSS-induced colitis in mice. KitW-sh/W-sh mice harbouring LMIR3−/− mast cells exhibited more severe colitis than those harbouring WT mast cells. Ceramide–LMIR3 interaction inhibited ATP-stimulated activation of BMMCs. DSS-induced colitis was aggravated by disrupting the ceramide–LMIR3 interaction, whereas it was suppressed by treating with ceramide liposomes. Conclusions LMIR3-deficient colonic mast cells were pivotal in the exacerbation of DSS-induced colitis in LMIR3−/− mice. Ceramide liposomes attenuated DSS-induced colitis by inhibiting ATP-mediated activation of colonic mast cells through ceraimide–LMIR3 binding.

A Soluble Form of LMIR5/CD300b Amplifies Lipopolysaccharide-Induced Lethal Inflammation in Sepsis

Leukocyte mono-Ig–like receptor 5 (LMIR5, also called CD300b) is an activating receptor expressed in myeloid cells. We have previously demonstrated that T cell Ig mucin 1 works as a ligand for LMIR5 in mouse ischemia/reperfusion injury of the kidneys. In this article, we show that LMIR5 is implicated in LPS-induced sepsis in mice. Notably, neutrophils constitutively released a soluble form of LMIR5 (sLMIR5) through proteolytic cleavage of surface LMIR5. Stimulation with TLR agonists augmented the release of sLMIR5. LPS administration or peritonitis induction increased serum levels of sLMIR5 in mice, which was substantially inhibited by neutrophil depletion. Thus, neutrophils were the main source of LPS-induced sLMIR5 in vivo. On the other hand, i.p. administration of LMIR5-Fc, a surrogate of sLMIR5, bound to resident macrophages (Mϕ) and stimulated transient inflammation in mice. Consistently, LMIR5-Fc induced in vitro cytokine production of peritoneal Mϕ via its unknown ligand. Interestingly, LMIR5 deficiency profoundly reduced systemic cytokine production and septic mortality in LPS-administered mice, although it did not affect in vitro cytokine production of LPS-stimulated peritoneal Mϕ. Importantly, the resistance of LMIR5-deficient mice to LPS- or peritonitis-induced septic death was decreased by LMIR5-Fc administration, implicating sLMIR5 in LPS responses in vivo. Collectively, neutrophil-derived sLMIR5 amplifies LPS-induced lethal inflammation.

Leukemic T cells are specifically enriched in a unique CD3dimCD7low subpopulation of CD4+ T cells in acute-type adult T-cell leukemia

The morphological discrimination of leukemic from non‐leukemic T cells is often difficult in adult T‐cell leukemia (ATL) as ATL cells show morphological diversity, with the exception of typical “flower cells.” Because defects in the expression of CD3 as well as CD7 are common in ATL cells, we applied multi‐color flow cytometry to detect a putative leukemia‐specific cell population in the peripheral blood from ATL patients. CD4+CD14− cells subjected to two‐color analysis based on a CD3 vs CD7 plot clearly demonstrated the presence of a CD3dimCD7low subpopulation in each of nine patients with acute‐type ATL. The majority of sorted cells from this fraction showed a flower cell‐like morphology and carried a high proviral load for the human T‐cell leukemia virus type 1 (HTLV‐I). Genomic integration site analysis (inverse long‐range PCR) and analysis of the T cell receptor Vβ repertoire by flow cytometry indicated that the majority of leukemia cells were included in the CD3dimCD7low subpopulation. These results suggest that leukemic T cells are specifically enriched in a unique CD3dimCD7low subpopulation of CD4+ T cells in acute‐type ATL. (Cancer Sci 2011; 102: 569–577)

Human CD300C delivers an Fc receptor-γ-dependent activating signal in mast cells and monocytes and differs from CD300A in ligand recognition.

Background: Human CD300C is not fully characterized because of the unavailability of its specific antibody. Results: Stimulation with a specific CD300C antibody activates human monocytes and mast cells that express high levels of CD300C. Conclusion: Specific engagement of CD300C, but not its co-engagement with CD300A, delivers an Fc receptor-γ-dependent activating signal. Significance: The activating function of CD300C is associated with its ligand specificity. CD300C is highly homologous with an inhibitory receptor CD300A in an immunoglobulin-like domain among the human CD300 family of paired immune receptors. To clarify the precise expression and function of CD300C, we generated antibodies discriminating between CD300A and CD300C, which recognized a unique epitope involving amino acid residues CD300A(F56-L57) and CD300C(L63-R64). Notably, CD300C was highly expressed in human monocytes and mast cells. Cross-linking of CD300C by its specific antibody caused cytokine/chemokine production of human monocytes and mast cells. Fc receptor γ was indispensable for both efficient surface expression and activating functions of CD300C. To identify a ligand for CD300A or CD300C, we used reporter cell lines expressing a chimera receptor harboring extracellular CD300A or CD300C and intracellular CD3ζ, in which its unknown ligand induced GFP expression. Our results indicated that phosphatidylethanolamine (PE) among the lipids tested and apoptotic cells were possible ligands for both CD300C and CD300A. PE and apoptotic cells more strongly induced GFP expression in the reporter cells through binding to extracellular CD300A as compared with CD300C. Differential recognition of PE by extracellular CD300A and CD300C depended on different amino acid residues CD300A(F56-L57) and CD300C(L63-R64). Interestingly, GFP expression induced by extracellular CD300C-PE binding in the reporter cells was dampened by co-expression of full-length CD300A, indicating the predominance of CD300A over CD300C in PE recognition/signaling. PE consistently failed to stimulate cytokine production in monocytes expressing CD300C with CD300A. In conclusion, specific engagement of CD300C led to Fc receptor γ-dependent activation of mast cells and monocytes.

Transforming growth factor-β-stimulated clone-22 is a negative-feedback regulator of Ras / Raf signaling: Implications for tumorigenesis.

Transforming growth factor‐β (TGF‐β)‐stimulated clone‐22 (TSC‐22), also called TSC22D1‐2, is a putative tumor suppressor. We previously identified TSC‐22 downstream of an active mutant of fms‐like tyrosine kinase‐3 (Flt3). Here, we show that TSC‐22 works as a tumor suppressor through inhibiting Ras/Raf signaling. Notably, TSC‐22 was upregulated by Ras/Raf activation, whereas its upregulation was inhibited by concurrent STAT5 activation. Although TSC‐22 was normally retained in the cytoplasm by its nuclear export signal (NES), Ras/Raf activation caused nuclear translocation of TSC‐22, but not TSC22D1‐1. Unlike glucocorticoid‐induced leucine zipper (GILZ/TSC22D3‐2) previously characterized as a negative regulator of Ras/Raf signaling, TSC‐22 failed to interact physically with Ras/Raf. Importantly, transduction with TSC‐22, but not TSC22D1‐1, suppressed the growth, transformation and tumorigenesis of NIH3T3 cells expressing oncogenic H‐Ras: this suppression was enhanced by transduction with a TSC‐22 mutant lacking NES that had accumulated in the nucleus. Collectively, upregulation and nuclear translocation of TSC‐22 played an important role in the feedback suppression of Ras/Raf signaling. Consistently, TSC22D1‐deficient mice were susceptible to tumorigenesis in a mouse model of chemically‐induced liver tumors bearing active mutations of Ras/Raf. Thus, TSC‐22 negatively regulated Ras/Raf signaling through a mechanism different from GILZ, implicating TSC‐22 as a novel suppressor of oncogenic Ras/Raf‐induced tumors. (Cancer Sci 2012; 103: 26–33)

The CD3 versus CD7 plot in multicolor flow cytometry reflects progression of disease stage in patients infected with HTLV-I.

Purpose In a recent study to purify adult T-cell leukemia-lymphoma (ATL) cells from acute-type patients by flow cytometry, three subpopulations were observed in a CD3 versus CD7 plot (H: CD3highCD7high; D: CD3dimCD7dim; L: CD3dimCD7low). The majority of leukemia cells were enriched in the L subpopulation and the same clone was included in the D and L subpopulations, suggesting clonal evolution. In this study, we analyzed patients with indolent-type ATL and human T-cell leukemia virus type I (HTLV-I) asymptomatic carriers (ACs) to see whether the CD3 versus CD7 profile reflected progression in the properties of HTLV-I-infected cells. Experimental Design Using peripheral blood mononuclear cells from patient samples, we performed multi-color flow cytometry. Cells that underwent fluorescence-activated cell sorting were subjected to molecular analyses, including inverse long PCR. Results In the D(%) versus L(%) plot, patient data could largely be categorized into three groups (Group 1: AC; Group 2: smoldering- and chronic-type ATL; and Group 3: acute-type ATL). Some exceptions, however, were noted (e.g., ACs in Group 2). In the follow-up of some patients, clinical disease progression correlated well with the CD3 versus CD7 profile. In clonality analysis, we clearly detected a major clone in the D and L subpopulations in ATL cases and, intriguingly, in some ACs in Group 2. Conclusion We propose that the CD3 versus CD7 plot reflects progression of disease stage in patients infected with HTLV-I. The CD3 versus CD7 profile will be a new indicator, along with high proviral load, for HTLV-I ACs in forecasting disease progression.

Ceramide-CD300f binding inhibits lipopolysaccharide-induced skin inflammation

LPS triggers inflammatory responses; however, the negative regulation of LPS responses in vivo remains poorly understood. CD300f is an inhibitory receptor among the CD300 family of paired activating and inhibitory receptors. We have previously identified ceramide as a ligand for CD300f and shown that the binding of ceramide to CD300f inhibits IgE-mediated mast cell activation and allergic responses in mouse models. Here we identify the critical role of CD300f in inhibiting LPS-induced skin inflammation. CD300f deficiency remarkably enhanced LPS-induced skin edema and neutrophil recruitment in mice. Higher levels of factors that increase vascular permeability and of factors that induce neutrophil recruitment were detected in LPS-injected skin pouch exudates of CD300f−/− mice as compared with wild-type mice. CD300f was highly expressed in mast cells and recruited neutrophils, but not in macrophages, among skin myeloid cells. CD300f deficiency failed to influence the intrinsic migratory ability of neutrophils. Ceramide-CD300f binding suppressed the release of chemical mediators from mast cells and from neutrophils in response to LPS. Adoptive transfer experiments indicated that mast cells mediated enhanced edema in LPS-stimulated skin of CD300f−/− mice, whereas mast cells together with recruited neutrophils mediated robust neutrophil accumulation. Importantly, administering a ceramide antibody or ceramide-containing vesicles enhanced or suppressed LPS-induced skin inflammation of wild-type mice, respectively. Thus, ceramide-CD300f binding inhibits LPS-induced skin inflammation, implicating CD300f as a negative regulator of Toll-like receptor 4 (TLR4) signaling in vivo.

Cryopreserved CD34+ Cell Dose, but Not Total Nucleated Cell Dose, Influences Hematopoietic Recovery and Extensive Chronic Graft-versus-Host Disease after Single-Unit Cord Blood Transplantation in Adult Patients

Low cryopreserved total nucleated cell (TNC) dose in a cord blood (CB) unit has been shown to be associated with engraftment failure and mortality after single-unit cord blood transplantation (CBT) in adults. Although CB banks offer specific characteristics of cryopreserved cell dose, such as TNC, CD34+ cells, and colony-forming unit for granulocyte/macrophage (CFU-GM), the impact of each cell dose on engraftment and outcomes after single-unit CBT in adults remains unclear. We retrospectively analyzed the results of 306 CBTs for 261 adult patients in our institution between 1998 and 2016. The median age was 43 years (range, 16 to 68), the median actual body weight (ABW) was 56.2 kg (range, 36.2 to 104.0), the median ideal body weight (IBW) was 62.3 kg (range, 39.7 to 81.3), the median TNC dose was 2.46 × 107/ABW kg (range, 1.07 to 5.69), the median CD34+ cell dose was .91 × 105/ABW kg (range, .15 to 7.75), and the median CFU-GM dose was 24.46 × 103/ABW kg (range, .04 to 121.81). Among patients who achieved engraftment, the speed of neutrophil, platelet, and red blood cell engraftment significantly correlated with CD34+ cell dose, but not with TNC and CFU-GM dose, based on both ABW and IBW. In multivariate analysis, the incidence of extensive chronic graft-versus-host disease (GVHD) was significantly higher in patients receiving the highest CD34+ cell dose, based on both ABW and IBW. Nevertheless, no cell dose was associated with survival, transplantation-related mortality, and relapse. In conclusion, cryopreserved CD34+ cell dose was the best predictor for hematopoietic recovery and extensive chronic GVHD after CBT. The cryopreserved CD34+ cell dose should be used for unit selection criteria in single-unit CBT for adults.