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T Honjo

Publications and source records attributed to T Honjo.

At least 73 records · Page 4Linked to original sources
PubMed1999

Notch signalling controls pancreatic cell differentiation.

The pancreas contains both exocrine and endocrine cells, but the molecular mechanisms controlling the differentiation of these cell types are largely unknown. Despite their endodermal origin, pancreatic endocrine cells share several molecular characteristics with neurons, and, like neurons in the central nervous system, differentiating endocrine cells in the pancreas appear in a scattered fashion within a field of progenitor cells. This indicates that they may be generated by lateral specification through Notch signalling. Here, to test this idea, we analysed pancreas development in mice genetically altered at several steps in the Notch signalling pathway. Mice deficient for Delta-like gene 1 (Dll1) or the intracellular mediator RBP-Jkappa showed accelerated differentiation of pancreatic endocrine cells. A similar phenotype was observed in mice over-expressing neurogenin 3 (ngn 3) or the intracellular form of Notch3 (a repressor of Notch signalling). These data provide evidence that ngn3 acts as proendocrine gene and that Notch signalling is critical for the decision between the endocrine and progenitor/exocrine fates in the developing pancreas.

Animals↗
PubMed1999

Expression levels of B cell surface immunoglobulin regulate efficiency of allelic exclusion and size of autoreactive B-1 cell compartment.

Surface-expressed immunoglobulin (Ig) has been shown to have a critical role in allelic exclusion of Ig heavy (H) and light (L) chains. Although various degrees of suppression of endogenous Ig expression are observed in Ig transgenic (Tg) mice, it was not clear whether this difference is due to different onsets of Tg expression or to different levels of Tg expression, which are obviously affected by integration sites of the transgene. In this study we generated antierythrocyte antibody Tg mice that carry tandem joined H and L chain transgenes (H+L) and confirmed that homozygosity of the transgene loci enhances the level of transgene expression as compared with heterozygosity. Suppression of endogenous H and L chain gene expression was stronger in homozygous than in heterozygous Tg mice. Similar results were obtained in control Tg mice carrying the H chain only. These results suggest that there is a threshold of the B cell receptor expression level that induces allelic exclusion. In addition, despite the same B cell receptor specificity, the size of Tg autoreactive B-1 cell compartment in the peritoneal cavity is larger in homozygous than in heterozygous mice, although the number of the Tg B-2 cell subset decreased in the spleen and bone marrow of homozygous Tg mice as compared with heterozygous Tg mice. By contrast, homozygosity of the H chain alone Tg line, which does not recognize self-antigens, did not increase the size of the peritoneal B-1 subset. These results suggest that the size of the B-1 cell subset in the Tg mice may depend on strength of signals through B cell receptors triggered by self-antigens.

Alleles↗
PubMed1999

DANCE, a novel secreted RGD protein expressed in developing, atherosclerotic, and balloon-injured arteries.

We have identified and characterized mouse, rat, and human cDNAs that encode a novel secreted protein of 448 amino acids named DANCE (developmental arteries and neural crest epidermal growth factor (EGF)-like). DANCE contains six calcium-binding EGF-like domains, one of which includes an RGD motif. Overexpression studies of recombinant DANCE protein document that DANCE is a secreted 66-kDa protein. DANCE and recently described protein S1-5 comprise a new EGF-like protein family. The human DANCE gene was mapped at chromosome 14q32.1. DANCE mRNA is mainly expressed in heart, ovary, and colon in adult human tissues. Expression profile analysis by in situ hybridization revealed prominent DANCE expression in developing arteries. DANCE is also expressed in neural crest cell derivatives, endocardial cushion tissue, and several other mesenchymal tissues. In adult vessels, DANCE expression is largely diminished but is reinduced in balloon-injured vessels and atherosclerotic lesions, notably in intimal vascular smooth muscle cells and endothelial cells that lose their ability to proliferate in late stage of injury. DANCE protein was shown to promote adhesion of endothelial cells through interaction of integrins and the RGD motif of DANCE. DANCE is thus a novel vascular ligand for integrin receptors and may play a role in vascular development and remodeling.

Amino Acid Sequence↗
PubMed1999

Murine leukemia provirus-mediated activation of the Notch1 gene leads to induction of HES-1 in a mouse T lymphoma cell line, DL-3.

Constitutive activation of Notch signaling is known to be associated with tumorigenesis. In a mouse T lymphoma cell line, DL-3, we found that a murine leukemia provirus was inserted in the Notch1 locus, which led to marked expression of a virus-Notch1 fusion mRNA encoding an intracellular portion of the Notch1 protein. Furthermore, expression and nuclear localization of this constitutively active form of Notch1 protein were confirmed. Corresponding to this finding, the transcription of the hairy/enhancer of split (HES-1) gene, a known target of Notch1 signaling, was elevated in this cell line. A potential role for overexpressed HES-1 in the development of the lymphoma was discussed.

Amino Acid Sequence↗
PubMed1999

Signaling through the antigen receptor of B lymphocytes activates a p53-independent pathway of c-Myc-induced apoptosis.

Deregulated expression of c-Myc has been shown to induce or enhance apoptosis in various different cell types. c-Myc requires p53 for apoptosis in some but not all the cell types, indicating heterogeneous mechanisms for c-Myc-induced apoptosis. In B lymphoma line WEHI-231, stable expression of c-Myc has been demonstrated to protect cells from BCR-mediated apoptosis. However, stable expression of c-Myc carrying pro-apoptotic functions may generate variant cells resistant to apoptosis. By utilizing an inducible system for c-Myc, we demonstrated here that deregulated expression of c-Myc induced apoptosis of WEHI-231 by itself, indicating that c-Myc induces apoptosis in WEHI-231 as is the case for other cell types. When transactivation of p53 was inactivated, WEHI-231 cells overexpressing c-Myc no longer underwent apoptosis in the absence of other stimuli, but showed markedly enhanced apoptosis in the presence of BCR ligation. These results indicate that deregulated c-Myc expression enhances apoptosis by a p53-independent pathway in the presence of BCR signaling but requires p53 for apoptosis in the absence of BCR crosslinking in WEHI-231. BCR ligation may thus activate a p53-independent pathway of c-Myc-induced apoptosis.

Apoptosis↗
PubMed1999

Specific expression of activation-induced cytidine deaminase (AID), a novel member of the RNA-editing deaminase family in germinal center B cells.

We have identified a novel gene referred to as activation-induced deaminase (AID) by subtraction of cDNAs derived from switch-induced and uninduced murine B lymphoma CH12F3-2 cells, more than 80% of which switch exclusively to IgA upon stimulation. The amino acid sequence encoded by AID cDNA is homologous to that of apolipoprotein B (apoB) mRNA-editing enzyme, catalytic polypeptide 1 (APOBEC-1), a type of cytidine deaminase that constitutes a catalytic subunit for the apoB mRNA-editing complex. In vitro experiments using a glutathione S-transferase AID fusion protein revealed significant cytidine deaminase activity that is blocked by tetrahydrouridine and by zinc chelation. However, AID alone did neither demonstrate activity in C to U editing of apoB mRNA nor bind to AU-rich RNA targets. AID mRNA expression is induced in splenic B cells that were activated in vitro or by immunizations with sheep red blood cells. In situ hybridization of immunized spleen sections revealed the restricted expression of AID mRNA in developing germinal centers in which modulation of immunoglobulin gene information through somatic hypermutation and class switch recombination takes place. Taken together, these findings suggest that AID is a new member of the RNA-editing deaminase family and may play a role in genetic events in the germinal center B cell.

APOBEC-1 Deaminase↗
PubMed1999

Delta-induced Notch signaling mediated by RBP-J inhibits MyoD expression and myogenesis.

Signaling induced by interaction between the receptor Notch and its ligand Delta plays an important role in cell fate determination in vertebrates as well as invertebrates. Vertebrate Notch signaling has been investigated using its constitutively active form, i.e. the truncated intracellular region which is believed to mimic Notch-Delta signaling by interaction with a DNA-binding protein RBP-J. However, the molecular mechanism for Notch signaling triggered by ligand binding, which leads to inhibition of differentiation, is not clear. We have established a myeloma cell line expressing mouse Delta1 on its cell surface which can block muscle differentiation by co-culture with C2C12 muscle progenitor cells. We showed that Delta-induced Notch signaling stimulated transcriptional activation of RBP-J binding motif, containing promoters including the HES1 promoter. Furthermore, ligand-induced Notch signaling up-regulated HES1 mRNA expression within 1 h and subsequently reduced expression of MyoD mRNA. Since cycloheximide treatment did not inhibit induction of HES1 mRNA, the HES1 promoter appears to be a primary target of activated Notch. In addition, a transcriptionally active form of RBP-J, i.e. VP16-RBP-J, inhibited muscle differentiation of C2C12 cells by blocking the expression of MyoD protein. These results suggest that HES1 induction by the Delta1/Notch signaling is mediated by RBP-J and blocks myogenic differentiation of C2C12 cells by subsequent inhibition of MyoD expression.

Animals↗
PubMed1999

Fractalkine and macrophage-derived chemokine: T cell-attracting chemokines expressed in T cell area dendritic cells.

Dendritic cells (DC) are a system of antigen-presenting cells specialized in interaction with T cells. Recently it has been reported that DC can produce CC (beta) chemokines that attract T cells. In this study we isolated mouse fractalkine and macrophage-derived chemokine (MDC) belonging to CX3C (delta) and CC chemokine families, respectively, from bone marrow-derived mature DC. While expression of fractalkine, which has so far been only examined in the brain and in vitro endothelial cells so far, was rather ubiquitous, MDC, which has been reported to be synthesized by macrophages and DC, was expressed specifically in the thymus and lymph node. This is the first report that indicates fractalkine expression by DC. Expression of fractalkine and MDC mRNA increased with maturation of DC during in vitro culture of bone marrow cells. Spleen- and epidermis-derived mature DC in culture also expressed these chemokines. Furthermore, their expression was detected selectively by Northern hybridization in CD11c+ B220- DC freshly purified from lymph nodes, and in large stellate cells in the lymph node T cell areas by in situ hybridization. Conditioned media of 293T cells transfected with these chemokine cDNA were chemotactic to Con A-activated splenic T cells as well as the mouse T cell line EL4. In conclusion, while fractalkine and MDC belong to different families of chemokines, both may be involved in recruitment of T cells for interaction with mature DC in the immune response.

Animals↗
PubMed1999

Chromosomal mapping of two RBP-J-related genes: Kyo-T and RBP-L.

We have recently isolated two genes encoding proteins which have either homology or affinity to RBP-J, a transcription factor involved in Notch signaling. Kyo-T interacts with RBP-J and possibly regulates the function of RBP-J. RBP-L has a highly homologous region with RBP-J but the function of RBP-L is unknown. Fluorescence in situ hybridization analysis of human metaphase chromosomes localized Kyo-T and RBP-L to Xq26 and 20q12-13.1, respectively.

Base Sequence↗
PubMed1999

Characterization of mutated protein encoded by partially duplicated fibrillin-1 gene in tight skin (TSK) mice.

Fibrillin-1 (Fbn-1) is a ubiquitous protein present in the extracellular matrix of various organs and it is a major component of microfibrils embedded in the core of elastic fibers. In humans, mutations or deletions of the Fbn-1 gene are associated with several genetic diseases. In addition, several microsatellite alleles near Fbn-1 gene were found associated with diffuse scleroderma. In TSK/+ mice, which develop a scleroderma-like syndrome, the Fbn-1 gene exhibits an inframe duplication of exons 17-40. In this study, we report that the synthesis and secretion of wild-type Fbn-1 in TSK/+ is higher than that of the mutated Fbn-1 protein excluding the possibility that TSK genetic defect is due to a loss of the wild allele. We also demonstrate for the first time that TGF-beta, which plays a crucial role in skin fibrosis, binds to both wild-type and mutated Fbn-1. The amount of bound TGF-beta was higher in mutated than wild-type Fbn-1 and appears related to the number of TGF-beta binding motifs.

Animals↗
PubMed1999

Development of lupus-like autoimmune diseases by disruption of the PD-1 gene encoding an ITIM motif-carrying immunoreceptor.

PD-1, a 55 kDa transmembrane protein containing an immunoreceptor tyrosine-based inhibitory motif, is induced in lymphocytes and monocytic cells following activation. Aged C57BL/6(B6)-PD-1(-/-) congenic mice spontaneously developed characteristic lupus-like proliferative arthritis and glomerulonephritis with predominant IgG3 deposition, which were markedly accelerated by introduction of a Fas mutation (lpr). Introduction of a PD-1 null mutation into the 2C-TCR (anti-H-2Ld) transgenic mice of the H-2(b/d) background resulted in the chronic and systemic graft-versus-host-like disease. Furthermore, CD8+ 2C-TCR+ PD-1(-/-) T cells exhibited markedly augmented proliferation in vitro in response to H-2d allogenic cells. Collectively, it is suggested that PD-1 is involved in the maintenance of peripheral self-tolerance by serving as a negative regulator of immune responses.

Animals↗
PubMed1999

Induction of germline transcription in the TCRgamma locus by Stat5: implications for accessibility control by the IL-7 receptor.

IL-7 receptor (IL-7R) plays critical roles in lymphocyte development by promoting survival and proliferation and by inducing V(D)J recombination in TCR and Ig loci. Here, we demonstrate that IL-7R-activated Stat5 binds to consensus motifs in the 5' regions of Jgamma segments and induces germline transcripts. We also show that a constitutively active form of Stat5 restores V-J recombination of TCRgamma genes and partially rescues T cell development from IL-7R(-/-) T cell precursors, especially in favor of gammadelta T cells. Therefore, this study reveals a potential role of Stat5 in T cell development and also implies that IL-7R may control the accessibility of the TCRgamma locus through Stat5-induced germline transcription.

Animals↗
PubMed1999

Alymphoplasia is caused by a point mutation in the mouse gene encoding Nf-kappa b-inducing kinase.

The alymphoplasia (aly) mutation of mouse is autosomal recessive and characterized by the systemic absence of lymph nodes (LN) and Peyer's patches (PP) and disorganized splenic and thymic structures with immunodeficiency. Although recent reports have shown that the interaction between lymphotoxin (LT) and the LT beta-receptor (Ltbeta r, encoded by Ltbr) provides a critical signal for LN genesis in mice, the aly locus on chromosome 11 is distinct from those for LT and its receptor. We found that the aly allele carries a point mutation causing an amino acid substitution in the carboxy-terminal interaction domain of Nf-kappa b-inducing kinase (Nik, encoded by the gene Nik). Transgenic complementation with wild-type Nik restored the normal structures of LN, PP, spleen and thymus, and the normal immune response in aly/aly mice. In addition, the aly mutation in a kinase domain-truncated Nik abolished its dominant-negative effect on Nf-kappa b activation induced by an excess of Ltbeta r. Our observations agree with previous reports that Ltbeta r-deficient mice showed defects in LN genesis and that Nik is a common mediator of Nf-kappa b activation by the tumour necrosis factor (TNF) receptor family. Nik is able to interact with members of the TRAF family (Traf1, 2, 3, 5 and 6), suggesting it acts downstream of TRAF-associating receptor signalling pathways, including Tnfr, Cd40, Cd30 and Ltbeta r. The phenotypes of aly/aly mice are more severe than those of Ltbr-/- mice, however, indicating involvement of Nik in signal transduction mediated by other receptors.

Amino Acid Sequence↗
PubMed1999

Regulation of B-1 cell activation and its autoantibody production by Lyn kinase-regulated signallings.

The src-family protein tyrosine kinase, Lyn, has been reported to play a crucial role in the regulation of B-cell antigen receptor (BCR)-mediated signalling. To elucidate the role of Lyn in the maintenance of immunological tolerance and the prevention of B-1 cell activation and its autoantibody production, Lyn-deficient mice were crossed with transgenic mice carrying the immunoglobulin heavy and light chain genes encoding an autoantibody against mouse red blood cells. In the transgenic mice, most peripheral B cells expressed the B-1 cell phenotype. When the transgenic mice were bred in specific pathogen-free (SPF) conditions, B-1 cells were anergic and did not produce any autoantibody. In contrast, Lyn-deficient transgenic mice kept in the same SPF conditions revealed markedly increased numbers of activated B-1 cells and developed severe autoimmune haemolytic anaemia. Moreover, the mice had a huge splenomegaly containing a remarkable accumulation of erythroblasts, resulted from extramedullary erythropoiesis, in addition to the increased numbers of lymphoblast-like cells of the B-1 cell lineages. The present study demonstrates a crucial role of Lyn kinase in the regulation of B-1 cell activation and maintenance of tolerance.

Anemia, Hemolytic, Autoimmune↗
PubMed1999

Requirement of IL-5 for induction of autoimmune hemolytic anemia in anti-red blood cell autoantibody transgenic mice.

IL-5, IL-10 and lipopolysaccharide (LPS) are known to activate B-1 cells in vivo in normal mice and anti-red blood cell autoantibody transgenic mice (HL mice). To assess the exact role of IL-5 in proliferation and activation of peritoneal B-1 cells, we analyzed IL-5 receptor alpha chain-deficient HL (IL-5Ralpha-/- x HL) mice generated by the cross between IL-5Ralpha-/- and HL mice. In IL-5Ralpha-/- x HL mice, Ig-producing B-1 cells in the peritoneal cavity were negligible, although the total number of B-1 cells in the peritoneal cavity were as many as 30% of that in HL mice. Moreover, LPS- or IL-10-induced differentiation of B-1 cells into antibody-producing cells was severely impaired in IL-5Ralpha-/- x HL mice. We also used in vivo 5-bromo-2'-deoxyuridine labeling to estimate the proliferation of B-1 cells in IL-5Ralpha-/- mice. The absence of IL-5Ralpha did not affect spontaneous proliferation of peritoneal B-1 cells. However, induced proliferation of peritoreal B-1 cells by oral administration of LPS was markedly impaired in IL-5Ralpha-/- mice. These results suggest that IL-5 is required for activation-associated proliferation of B-1 cells but not for their spontaneous proliferation and support the idea that IL-5 plays an important role on the induction of autoantibody production from B-1 cells.

Anemia, Hemolytic, Autoimmune↗
PubMed1999

Studies on the cell-type specific expression of RBP-L, a RBP-J family member, by replacement insertion of beta-galactosidase.

The RBP-L gene encodes a DNA binding protein that is structurally related to RBP-J, the mammalian homolog of Drosophila Suppressor of Hairless. Although the RBP-L protein binds the same DNA sequence as RBP-J, the in vivo function of this protein remains largely unknown. In order to investigate the role of this protein, we generated RBP-L mutant mice by targeted disruption involving replacement of the protein-coding sequence in the first exon with an in-frame fusion of the nlacZ cDNA. The homozygous mutant mice appeared morphologically normal and fertile. Unexpectedly, we found the possible existence of additional promoter(s) downstream of the first exon whose activity was not fully disrupted in the mutant mice. The promoter upstream of the first exon is regulated in a cell type-specific manner so that transcription is active in neurons but almost inactive in lung where the downstream promoter is active. The specific expression of the beta-galactosidase fusion protein was detected in layer VI of the cerebral cortex, in the pyramidal cell layer of the hippocampus, and in the granule cell layer of the dentate gyrus. Furthermore, we found that the upstream promoter activity in neurons might be regulated by some neuronal activity.

Amino Acid Sequence↗