Mamiko Sakata-Yanagimoto

Gain-of-function of mutated C-CBL tumour suppressor in myeloid neoplasms

Acquired uniparental disomy (aUPD) is a common feature of cancer genomes, leading to loss of heterozygosity. aUPD is associated not only with loss-of-function mutations of tumour suppressor genes, but also with gain-of-function mutations of proto-oncogenes. Here we show unique gain-of-function mutations of the C-CBL (also known as CBL) tumour suppressor that are tightly associated with aUPD of the 11q arm in myeloid neoplasms showing myeloproliferative features. The C-CBL proto-oncogene, a cellular homologue of v-Cbl, encodes an E3 ubiquitin ligase and negatively regulates signal transduction of tyrosine kinases. Homozygous C-CBL mutations were found in most 11q-aUPD-positive myeloid malignancies. Although the C-CBL mutations were oncogenic in NIH3T3 cells, c-Cbl was shown to functionally and genetically act as a tumour suppressor. C-CBL mutants did not have E3 ubiquitin ligase activity, but inhibited that of wild-type C-CBL and CBL-B (also known as CBLB), leading to prolonged activation of tyrosine kinases after cytokine stimulation. c-Cbl-/- haematopoietic stem/progenitor cells (HSPCs) showed enhanced sensitivity to a variety of cytokines compared to c-Cbl+/+ HSPCs, and transduction of C-CBL mutants into c-Cbl-/- HSPCs further augmented their sensitivities to a broader spectrum of cytokines, including stem-cell factor (SCF, also known as KITLG), thrombopoietin (TPO, also known as THPO), IL3 and FLT3 ligand (FLT3LG), indicating the presence of a gain-of-function that could not be attributed to a simple loss-of-function. The gain-of-function effects of C-CBL mutants on cytokine sensitivity of HSPCs largely disappeared in a c-Cbl+/+ background or by co-transduction of wild-type C-CBL, which suggests the pathogenic importance of loss of wild-type C-CBL alleles found in most cases of C-CBL-mutated myeloid neoplasms. Our findings provide a new insight into a role of gain-of-function mutations of a tumour suppressor associated with aUPD in the pathogenesis of some myeloid cancer subsets.

Gain‐of‐function mutations and copy number increases of Notch2 in diffuse large B‐cell lymphoma

Signaling through the Notch1 receptor has a pivotal role in early thymocyte development. Gain of Notch1 function results in the development of T‐cell acute lymphoblastic leukemia in a number of mouse experimental models, and activating Notch1 mutations deregulate Notch1 signaling in the majority of human T‐cell acute lymphoblastic leukemias. Notch2, another member of the Notch gene family, is preferentially expressed in mature B cells and is essential for marginal zone B‐cell generation. Here, we report that 5 of 63 (~8%) diffuse large B‐cell lymphomas, a subtype of mature B‐cell lymphomas, have Notch2 mutations. These mutations lead to partial or complete deletion of the proline‐, glutamic acid‐, serine‐ and threonine‐rich (PEST) domain, or a single amino acid substitution at the C‐terminus of Notch2 protein. Furthermore, high‐density oligonucleotide microarray analysis revealed that some diffuse large B‐cell lymphoma cases also have increased copies of the mutated Notch2 allele. In the Notch activation‐sensitive luciferase reporter assay in vitro, mutant Notch2 receptors show increased activity compared with wild‐type Notch2. These findings implicate Notch2 gain‐of‐function mutations in the pathogenesis of a subset of B‐cell lymphomas, and suggest broader roles for Notch gene mutations in human cancers. (Cancer Sci 2009; 100: 920–926)

Hes1 immortalizes committed progenitors and plays a role in blast crisis transition in chronic myelogenous leukemia

Hairy enhancer of split 1 (Hes1) is a basic helix-loop-helix transcriptional repressor that affects differentiation and often helps maintain cells in an immature state in various tissues. Here we show that retroviral expression of Hes1 immortalizes common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) in the presence of interleukin-3, conferring permanent replating capability on these cells. Whereas these cells did not develop myeloproliferative neoplasms when intravenously administered to irradiated mice, the combination of Hes1 and BCR-ABL in CMPs and GMPs caused acute leukemia resembling blast crisis of chronic myelogenous leukemia (CML), resulting in rapid death of the recipient mice. On the other hand, BCR-ABL alone caused CML-like disease when expressed in c-Kit-positive, Sca-1-positive, and lineage-negative hematopoietic stem cells (KSLs), but not committed progenitors CMPs or GMPs, as previously reported. Leukemic cells derived from Hes1 and BCR-ABL-expressing CMPs and GMPs were more immature than those derived from BCR-ABL-expressing KSLs. Intriguingly, Hes1 was highly expressed in 8 of 20 patients with CML in blast crisis, but not in the chronic phase, and dominant negative Hes1 retarded the growth of some CML cell lines expressing Hes1. These results suggest that Hes1 is a key molecule in blast crisis transition in CML.

Both Notch1 and Notch2 contribute to the regulation of melanocyte homeostasis.

Notch signaling affects a variety of mammalian stem cells, but there has been limited evidence that a specific Notch molecule regulates adult stem cells. Recently, it was reported that the reduced Notch signaling initiated at the embryonic stage results in a gradual hair graying phenotype after birth. Here we demonstrate that the oral administration of a γ‐secretase inhibitor (GSI) to wild‐type adult C57/Bl6 mice led to a gradual increase in gray spots, which remained unchanged for at least 20u2003weeks after discontinuing the GSI. In GSI‐treated mice, there was a severe decrease in unpigmented melanocytes in the bulge/subbulge region where melanocyte stem cells are located. While we confirmed that Notch1+/−Notch2+/− double heterozygous mice with a C57/Bl6 background were born with a normal hair color phenotype and gradually turned gray after the second hair cycle, in the c‐kit mutant Wv background, Notch1+/− and Notch2+/− mice had larger white spots on the first appearance of hair than did the Wv/+ mice, which did not change throughout life. Notch1+/−Notch2+/−Wv/+ mice had white hair virtually all over the body at the first appearance of hair and the depigmentation continued to progress thereafter. Using a neural crest organ culture system, GSI blocked the generation of pigmented melanocytes when added to the culture during the period of melanoblast proliferation, but not during the period of differentiation. These observations imply roles of Notch signaling in both development of melanocyte during embryogenesis and maintenance of melanocyte stem cells in adulthood, while the degree of requirement is distinct in these settings: the latter is more sensitive than the former to the reduced Notch signaling. Furthermore, Notch1 and Notch2 cooperates with c‐kit signaling during embryogenesis, and they cooperate with each other to regulate melanocyte homeostasis after birth.

Derivation of functional mature neutrophils from human embryonic stem cells

Human embryonic stem cells (hESCs) proliferate infinitely and are pluripotent. Only a few reports, however, describe specific and efficient methods to induce hESCs to differentiate into mature blood cells. It is important to determine whether and how these cells, once generated, behave similarly with their in vivo-produced counterparts. We developed a method to induce hESCs to differentiate into mature neutrophils. Embryoid bodies were formed with bone morphogenic protein-4, stem cell factor (SCF), Flt-3 ligand (FL), interleukin-6 (IL-6)/IL-6 receptor fusion protein (FP6), and thrombopoietin (TPO). Cells derived from the embryoid bodies were cultured on a layer of irradiated OP9 cells with a combination of SCF, FL, FP6, IL-3, and TPO, which was later changed to granulocyte-colony-stimulating factor. Morphologically mature neutrophils were obtained in approximately 2 weeks with a purity and efficiency sufficient for functional analyses. The population of predominantly mature neutrophils (hESC-Neus) showed superoxide production, phagocytosis, bactericidal activity, and chemotaxis similar to peripheral blood neutrophils from healthy subjects, although there were differences in the surface antigen expression patterns, such as decreased CD16 expression and aberrant CD64 and CD14 expression in hESC-Neus. Thus, this is the first description of a detailed functional analysis of mature hESC-derived neutrophils.

Coordinated regulation of transcription factors through Notch2 is an important mediator of mast cell fate

Mast cells are thought to participate in a wide variety of pathophysiological conditions. Mechanisms of regulation, however, of mast cell production and maturation are still to be elucidated. Mast cell developmental process is likely to be profoundly affected by cell-autonomous transcriptional regulators such as the GATA family and CCAAT/enhancer binding protein (C/EBP) family members. Extracellular regulators such as stem cell factor and IL-3 have essential roles in basal and inducible mast cell generation, respectively. The relationship, however, between the extracellular signaling and cellular transcriptional control is unclear, and the trigger of the mast cell development remains elusive. Notch signaling plays a fundamental role in the lymphopoietic compartment, but its role in myeloid differentiation is less clear. Here, we demonstrate that Notch signaling connects environmental cues and transcriptional control for mast cell fate decision. Delta1, an established Notch ligand, instructs bone marrow common myeloid progenitors and granulocyte-macrophage progenitors toward mast cell lineage at the expense of other granulocyte-macrophage lineages, depending on the function of the Notch2 gene. Notch2 signaling results in the up-regulation of Hes-1 and GATA3, whereas simultaneous overexpression of these transcription factors remarkably biases the progenitor fate toward the mast cell-containing colony-forming cells. C/EBPα mRNA was down-regulated in myeloid progenitors as a consequence of Hes-1 overexpression, in agreement with the recent proposal that the down-regulation of C/EBPα is necessary for mast cell fate determination. Taken together, signaling through Notch2 determines the fate of myeloid progenitors toward mast cell-producing progenitors, via coordinately up-regulating Hes-1 and GATA3.

Notch Activation Induces the Generation of Functional NK Cells from Human Cord Blood CD34-Positive Cells Devoid of IL-15

The development of NK cells from hematopoietic stem cells is thought to be dependent on IL-15. In this study, we demonstrate that stimulation of human cord blood CD34+ cells by a Notch ligand, Delta4, along with IL-7, stem cell factor, and Fms-like tyrosine kinase 3 ligand, but no IL-15, in a stroma-free culture induced the generation of cells with characteristics of functional NK cells, including CD56 and CD161 Ag expression, IFN-γ secretion, and cytotoxic activity against K562 and Jurkat cells. Addition of γ-secretase inhibitor and anti-human Notch1 Ab to the culture medium almost completely blocked NK cell emergence. Addition of anti-human IL-15-neutralizing Ab did not affect NK cell development in these culture conditions. The presence of IL-15, however, augmented cytotoxicity and was required for a more mature NK cell phenotype. CD56+ cells generated by culture with IL-15, but without Notch stimulation, were negative for CD7 and cytoplasmic CD3, whereas CD56+ cells generated by culture with both Delta4 and IL-15 were CD7+ and cytoplasmic CD3+ from the beginning and therefore more similar to in vivo human NK cell progenitors. Together, these results suggest that Notch signaling is important for the physiologic development of NK cells at differentiation stages beyond those previously postulated.

Notch2 signaling is required for proper mast cell distribution and mucosal immunity in the intestine.

Notch receptor-mediated signaling is involved in the developmental process and functional modulation of lymphocytes, as well as in mast cell differentiation. Here, we investigated whether Notch signaling is required for antipathogen host defense regulated by mast cells. Mast cells were rarely found in the small intestine of wild-type C57BL/6 mice but accumulated abnormally in the lamina propria of the small-intestinal mucosa of the Notch2-conditional knockout mice in naive status. When transplanted into mast cell-deficient W(sh)/W(sh) mice, Notch2-null bone marrow-derived mast cells were rarely found within the epithelial layer but abnormally localized to the lamina propria, whereas control bone marrow-derived mast cells were mainly found within the epithelial layer. After the infection of Notch2 knockout and control mice with L3 larvae of Strongyloides venezuelensis, the abundant number of mast cells was rapidly mobilized to the epithelial layer in the control mice. In contrast, mast cells were massively accumulated in the lamina propria of the small intestinal mucosa in Notch2-conditional knockout mice, accompanied by impaired eradication of Strongyloides venezuelensis. These findings indicate that cell-autonomous Notch2 signaling in mast cells is required for proper localization of intestinal mast cells and further imply a critical role of Notch signaling in the host-pathogen interface in the small intestine.

Clinical significance of peripheral blood erythroblastosis after hematopoietic stem cell transplantation.

Erythroblasts (EBL) are normally not observed in peripheral blood, but may be found in patients suffering from a variety of severe diseases. The detection of EBL in peripheral blood has been shown to be associated with a poor prognosis. However, the clinical significance of peripheral erythroblastosis after hematopoietic stem cell transplantation (HSCT) has not been evaluated. We retrospectively analyzed the records of 161 patients who underwent HSCT at our hospital from June 1995 to October 2001. EBL at any level were detected in 94% of the patients. Forty-four and 11 patients experienced erythroblastosis exceeding 200 and 1,000/ul, respectively. The erythroblast count was higher in patients who died than in the survivors (geometric mean value 184 vs. 100/ul, Pu200a=u200a0.01). High-level erythroblastosis (u200a>u200a1,000/ul) within 180 days after HSCT was associated with an extremely poor prognosis (median survival 22.5 days). Among the possible confounding factors, the use of total body irradiation (RR 2.35, 95% CI 1.22u200a-u200a4.54, Pu200a=u200a0.011) and the disease status before transplantation (RR 2.51, 95% CI 1.15u200a-u200a5.49, Pu200a=u200a0.021) were independent significant factors for erythroblastosis after HSCT. As for post-transplant events, a high EBL concentration was frequently preceded by graft-vs.-host disease, thrombotic microangiopathy, hypoxia, and hematological relapse.

A myeloablative conditioning regimen for patients with impaired cardiac function undergoing allogeneic stem cell transplantation: Reduced cyclophosphamide combined with etoposide and total body irradiation

To circumvent the cardiac toxicity of high‐dose cyclophosphamide (CY) in the myeloablative conditioning for those with cardiac comorbidity, we developed a new cardiac sparing conditioning regimen (VP/rCY/TBI) composed of 12 Gy of total body irradiation (TBI), etoposide (VP‐16) (40 mg/kg), and reduced CY (40 mg/kg). We assessed the feasibility of this regimen by retrospectively comparing the outcome of VP/rCY/TBI recipients (n = 18) with that of CY/TBI recipients (n = 140). VP/rCY/TBI recipients had significantly higher cumulative dose of anthracyclines, lower ejection fraction (EF), and poorer Karnofsky performance scales (KPS) than CY/TBI recipients. The cumulative incidences of disease progression were 34.9% in VP/rCY/TBI recipients and 19.0% in CY/TBI recipients (P = 0.33). Despite poorer KPS and more cardiac comorbidity in the VP/rCY/TBI recipients, no difference in the nonprogression mortality rates was observed among recipients of the two regimens (17.5 and 14.3%, respectively, P = 0.96). Severe cardiac toxicity within 28 days after transplantation occurred in 5.9 and 3.6% of VP/rCY/TBI and CY/TBI recipients, respectively (P = 0.64). Graft rejection was not observed in VP/rCY/TBI recipients. There is a possibility that VP/rCY/TBI regimen can be safely administered for patients with pretransplantation cardiac comorbidity while preserving antineoplastic effects. These observations merit further prospective study. Am. J. Hematol., 2008.