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T Honjo

Publications and source records attributed to T Honjo.

At least 127 records · Page 7Linked to original sources
PubMed1997

Involvement of RBP-J in biological functions of mouse Notch1 and its derivatives.

Notch is involved in the cell fate determination of many cell lineages. The intracellular region (RAMIC) of Notch1 transactivates genes by interaction with a DNA binding protein RBP-J. We have compared the activities of mouse RAMIC and its derivatives in transactivation and differentiation suppression of myogenic precursor cells. RAMIC comprises two separate domains, IC for transactivation and RAM for RBP-J binding. Although the physical interaction of IC with RBP-J was much weaker than with RAM, transactivation activity of IC was shown to involve RBP-J by using an RBP-J null mutant cell line. IC showed differentiation suppression activity that was generally comparable to its transactivation activity. The RBP-J-VP16 fusion protein, which has strong transactivation activity, also suppressed myogenesis of C2C12. The RAM domain, which has no other activities than binding to RBP-J, synergistically stimulated transactivation activity of IC to the level of RAMIC. The RAM domain was proposed to compete with a putative co-repressor for binding to RBP-J because the RAM domain can also stimulate the activity of RBP-J-VP16. These results taken together, indicate that differentiation suppression of myogenic precursor cells by Notch signalling is due to transactivation of genes carrying RBP-J binding motifs.

Animals↗
PubMed1997

Conservation of the Notch signalling pathway in mammalian neurogenesis.

The Notch pathway functions in multiple cell fate determination processes in invertebrate embryos, including the decision between the neuroblast and epidermoblast lineages in Drosophila. In the mouse, targeted mutation of the Notch pathway genes Notch1 and RBP-Jk has demonstrated a role for these genes in somite segmentation, but a function in neurogenesis and in cell fate decisions has not been shown. Here we show that these mutations lead to altered expression of the Notch signalling pathway homologues Hes-5, Mash-1 and Dll1, resulting in enhanced neurogenesis. Precocious neuronal differentiation is indicated by the expanded expression domains of Math4A, neuroD and NSCL-1. The RBP-Jk mutation has stronger effects on expression of these genes than does the Notch1 mutation, consistent with functional redundancy of Notch genes in neurogenesis. Our results demonstrate conservation of the Notch pathway and its regulatory mechanisms from fly to mouse, and support a role for the murine Notch signalling pathway in the regulation of neural stem cell differentiation.

Animals↗
PubMed1997

[Transcriptional activity of EBNA2 through RBP-J].

Epstein-Barr virus (EBV) is consistently associated with a variety of B-cell malignancies including Burkitt lymphoma, post-transplant lymphoma, and central nervous system lymphoma in AIDS. EBV infection in vitro leads to the immortalization of B lymphocytes and the outgrowth of continually proliferating lymphoblastoid cell lines, a process that is dependent on a functional EBV nuclear antigen 2 (EBNA2). EBNA2 is essential for transformation of human primary B-lymphocytes by the EB virus. EBNA2 is a pleiotropic activator of viral and cellular genes and is targeted to DNA by interacting with RBP-J. RBP-J is a novel type of DNA binding nuclear protein which is highly conserved in evolution, and originally isolated by its ability to bind to the Jk-type V (D) J recombination signal sequence. Here we would like to show you the mechanism of EBNA2 through RBP-J, and compare to the interaction of the RBP-J protein with Notch.

DNA-Binding Proteins↗
PubMed1997

Involvement of the cyclin-dependent kinase inhibitor p27Kip1 in negative signaling through the antigen-receptor of B lymphocytes.

Several lines of evidence suggest that interaction with antigens generates a negative signal via the antigen receptor of B lymphocytes (cell surface immunoglobulin; sIg), resulting in apoptosis, growth arrest or functional inactivation, and that activation of B cells requires an additional co-stimulatory signal such as a T cell-derived signal through the B cell membrane molecule CD40. In the B cell line WEHI-231, sIg crosslinking induces apoptosis and cell cycle arrest at the late G1 phase, both of which are reversed by CD40 signaling. Crosslinking of sIg reduces the activity of cyclin dependent kinase (Cdk)2 required for cell cycle progression in the late G1 phase by induction of a Cdk inhibitor (CKI) p27Kip1, but the induction of p27Kip1 is abrogated by CD40 signaling. These results strongly suggest that p27Kip1 plays some role in negative signaling via sIg, resulting in growth arrest of antigen-stimulated B cells.

Animals↗
PubMed1997

Development of erythroid cells from mouse embryonic stem cells in culture: potential use for erythroid transcription factor study.

We developed an efficient differentiation induction system from mouse embryonic stem (ES) cells into blood cells by coculture on a novel stromal cell line named OP9, in order to analyze molecular mechanisms of hematopoietic cell development and differentiation. ES cells could give rise to adult type definitive erythrocytes, myeloid and B lineage cells via multipotential hematopoietic precursor cells, when the cells were simply cocultured with the OP9 stromal cells. The temporal pattern of the appearance of erythroid lineage cells during the differentiation induction was very similar to that detected in mouse ontogeny. This differentiation induction method should facilitate to dissect the function of erythroid transcription factors during erythroid lineage cell development.

Animals↗
PubMed1996

Characterization of novel secreted and membrane proteins isolated by the signal sequence trap method.

We recently described a method, called the signal sequence trap (SST) method, to clone cDNAs of secreted proteins and/or type I transmembrane proteins containing N-terminal signal sequences by using an epitope-tagging expression plasmid vector. In this paper we describe the summary of a large-scale screening of approximately 5900 clones of an SST cDNA library constructed from mouse bone marrow stromal cell line ST-2 cells. Of 26 positive clones obtained and sequenced, 11 clones appeared to contain authentic signal sequences. Five of the clones corresponded to the 5' ends of the cDNA of known genes containing N-terminal signal sequences. The full-length cDNA clones of the 6 other unknown clones were isolated and sequenced. One clone, termed SDF3, encoded a mouse counterpart of human pigment epithelium-derived factor. Another clone, termed SDR1, had considerable homology with basigin, a member of the immunoglobulin superfamily. A third clone, termed SDF5, had partial homology with a Drosophila tissue polarity gene frizzled (fz) and its rat homologues, fz-1 and fz-2. The other three clones had no significant homology with sequences in the databases. These results indicate that the SST method is effective and useful for the isolation of secreted and membrane proteins without knowledge of their functions.

Amino Acid Sequence↗
PubMed1996

Functional conservation of mouse Notch receptor family members.

All the known members of the mouse Notch receptor family were examined for their biochemical function by interaction with a DNA binding protein RBP-Jkappa. mNotch2, mNotch3 and int3 (= mNotch4) were shown to interact with RBP-Jkappa by the GST-fusion pull down assay and dominant negative competition with Epstein Barr virus nuclear antigen 2. Furthermore the intracellular region of int3 was shown to transactivate the Epstein Barr virus TP1 promoter. These results indicate that all mouse Notch family members have biochemical functions similar to mNotch1, which transduces proliferative signal by direct interaction with the DNA binding protein RBP-Jkappa.

Amino Acid Sequence↗
PubMed1996

Isolation and characterization of a novel secretory protein, stromal cell-derived factor-2 (SDF-2) using the signal sequence trap method.

With use of the signal sequence trap method, we isolated a cDNA encoding a novel secretory protein, SDF-2, from the mouse stromal cell line, ST2. The human homologue of SDF-2 was also isolated. The amino acid (aa) sequences deduced from both the clones were conserved more than 92%. The chromosomal localization of the human SDF-2 gene was mapped to 17q11.2. The aa sequence of SDF-2 shows similarity to those of yeast dolichyl phosphate-D-mannose:protein mannosyltransferases, Pmt1p [Strahl-Bolsinger et al. (1993) Proc. Natl. Acad. Sci. USA 90, 8164-8168] and Pmt2p [Lussier et al. (1995) J. Biol. Chem. 270, 2770-2775], whose activities have not been detected in higher eukaryotes.

Amino Acid Sequence↗
PubMed1996

Molecular analysis of stimulatory anti-thyrotropin receptor antibodies (TSAbs) involved in Graves' disease. Isolation and reconstruction of antibody genes, and production of monoclonal TSAbs.

Anti-thyrotropin (TSH) receptor autoantibodies (TRAbs) have been known to be involved in Graves' disease. To understand the molecular mechanism for pathogenesis of TSAbs in Graves' disease, we isolated and reconstituted the Ig genes of EBV-transformed B cell clones producing monoclonal thyroid stimulating Ab (TSAb) obtained from patients with Graves' disease. The V region genes of Ig heavy (H) and light (L) chains of two TSAb clones, IgG clone B6B7 and IgM clone 101-2, were isolated by the PCR. Nucleotide sequencing analysis revealed that germ-line VH and VK segments widely used for autoantibodies including the previously isolated TRAbs were utilized in the two clones. A significant number of somatic mutations were found in V regions of both clones, indicating the involvement of somatic mutations for the TSAb specificity. Reconstituted Ig H and L chain genes of the two clones were stably introduced into myeloma cells for IgG1 production. IgGs purified from cultured supernatants of both transfectants exhibited significant TSAb activities, while they did not inhibit TSH binding to the receptor. The successful expression of recombinant TSAbs in eukaryotic cells will provide opportunities to apply them to various pathophysiologic, diagnostic and therapeutic investigations in autoimmune thyroid diseases.

Antibodies, Monoclonal↗
PubMed1996

In vitro development of primitive and definitive erythrocytes from different precursors.

During mouse embryogenesis the production of "primitive" erythrocytes (EryP) precedes the production of "definitive" erythrocytes (EryD) in parallel with the transition of the hematopoietic site from the yolk sac to the fetal liver. On a macrophage colony-stimulating factor-deficient stromal cell line OP9, mouse embryonic stem cells were shown to give rise to EryP and EryD sequentially with a time course similar to that seen in murine ontogeny. Studies of the different growth factor requirements and limiting dilution analysis of precursor frequencies indicate that most EryP and EryD probably developed from different precursors by way of distinct differentiation pathways.

Animals↗
PubMed1996

Epidermal growth factor can replace thymic mesenchyme in induction of embryonic thymus morphogenesis in vitro.

The thymus is surrounded by a thin layer of mesenchyme and the epithelial-mesenchymal interaction is known to be essential for the thymus development. To clarify the roles of mesenchyme in the thymus lobule formation that occurs around embryonic days 14-15 in vivo, we set up a three-dimensional organ culture system. The epithelium of embryonic day 14 thymic primordium was separated from the mesenchyme and cultured in Matrigel (reconstituted basement membrane). Addition of the mesenchyme to a chamber separated by a membrane filter induced the lobule formation of the thymic epithelium in vitro. We found that epidermal growth factor (EGF) can replace the mesenchyme for lobulation of the embryonic thymus in vitro. Among other growth factors tested, only transforming growth factor (TGF)-alpha was as effective as EGF, in agreement with the fact that EGF and TGF-alpha bind to the same receptor. These results suggest that EGF or its family members may be involved in morphogenesis and differentiation of the thymus gland epithelium, although we cannot exclude the possibility that other unknown factors are required in vivo.

Amino Acid Sequence↗
PubMed1996

Differential modulation of cyclin-dependent kinase inhibitor p27Kip1 by negative signaling via the antigen receptor of B cells and positive signaling via CD40.

The cross-linking of surface immunoglobulins (sIg) of B cells can transmit a negative signal, resulting in cell cycle arrest, apoptosis or both. Signaling via the B cell antigen CD40 reverses the sIg-mediated negative signaling and induces activation and proliferation of B cells. We investigated the molecular mechanism for cell cycle regulation by negative and positive signaling via sIg and CD40, respectively, by using the B cell line WEHI-231. Cross-linking of sIg almost completely reduced the activity of cyclin-dependent kinase (Cdk) 2, essential for cell cycle progression in the late G1 phase, although the level of Cdk2 was not reduced. Among the factors that regulate Cdk2 activation, the activity of the Cdk-activating kinase (CAK) appeared intact and cyclin E was reduced only partially in sIg-cross-linked WEHI-231. In contrast, sIg cross-linking induced a significant Cdk inhibitor (CKI) activity. Since a 27-kDa protein was co-precipitated with Cdk2 in anti-Ig-treated, but not untreated WEHI-231, and the CKI activity in anti-Ig-treated WEHI-231 was neutralized by anti-p27Kip1 antibodies, it is most likely that p27Kip1 is responsible for the CKI activity induced by sIg cross-linking. p27Kip1 may thus play a role in growth inhibition of B cells by negative signaling via sIg. In contrast, CD40 signaling enhanced Cdk2 activity and reduced the p27Kip1 level in anti-Ig-treated WEHI-231, suggesting that the reduction of p27Kip1 plays an important role in the abrogation of sIg-mediated growth arrest by CD40 signaling. Taken together, p27Kip1 is likely to be a crucial target molecule of the negative signaling via sIg and the positive signaling via CD40 essential for T cell-dependent immune responses.

B-Lymphocytes↗
PubMed1996

Autoimmune disease of exocrine organs in immunodeficient alymphoplasia mice: a spontaneous model for Sjögren's syndrome.

Mice homozygous for an autosomal recessive mutation aly (alymphoplasia) lack both lymph nodes and Peyer's patches, and show defects in both humoral and cellular immunity. Histopathological analysis revealed chronic inflammatory changes in exocrine organs such as the salivary gland, lacrimal gland, and pancreas of the homozygotes (aly/aly), but not the heterozygotes (aly/+). In these exocrine organs, mononuclear cells consisting mainly of CD4+ T cells infiltrate periductal areas, and, in some cases, the cell infiltration extended to lobules. The inflammatory changes in exocrine organs were transferred by a T cell-enriched fraction of spleen cells from homozygous animals. These results suggest that autoimmune mechanisms mediated by self-reactive T cells may be involved in the inflammatory lesions of various exocrine organs in the homozygous mice, although these mice show immunodeficiency. Inflammatory changes were also observed in the lung of the homozygotes. Since Sjögren's syndrome is characterized by diffuse lymphocyte infiltration in the periductal areas of the lacrimal and salivary glands and is occasionally associated with pulmonary disease, aly/aly mice may serve as a unique spontaneous model of Sjögren's syndrome.

Adoptive Transfer↗
PubMed1996

Anti-red blood cell autoantibody transgenic mice: murine model of autoimmune hemolytic anemia.

We established an anti-red blood cell (RBC) autoantibody transgenic mouse line, in which almost all B cells were deleted in the periphery. A small number of B-1 cells, however, escaped from deletion, survived and expanded in the peritoneal cavity and the gut, because of the absence of RBC. The activation of B-1 cells by enteric bacteria induced autoimmune hemolytic anemia (AIHA). In turn, AIHA was cured by elimination of peritoneal B-1 cells. This Tg mouse line is useful for revealing the generation and activation of B-1 cells, and for clarifying the physiological and pathological roles of B-1 cells.

Anemia, Hemolytic, Autoimmune↗
PubMed1996

The shortest path from the surface to the nucleus: RBP-J kappa/Su(H) transcription factor.

Communication between cell surface receptors and nuclear transcription factors is of primary importance to multicellular organisms. Since there are numerous molecules involved in this process, their mutual interaction forms complex networks of informational regulation, which is still under extensive investigation. The RBP-J kappa transcription factor interacts directly with the Notch receptor involved in cell lineage commitment, implicating the presence of a uniquely simple communication strategy between the surface receptor and the nucleus.

Animals↗