Biomedical subjects

D Kitamura

Publications and source records attributed to D Kitamura.

At least 19 recordsLinked to original sources

PubMed2007

Stage-specific expression of DNasegamma during B-cell development and its role in B-cell receptor-mediated apoptosis in WEHI-231 cells.

Here, we describe the non-redundant roles of caspase-activated DNase (CAD) and DNasegamma during apoptosis in the immature B-cell line WEHI-231. These cells induce DNA-ladder formation and nuclear fragmentation by activating CAD during cytotoxic drug-induced apoptosis. Moreover, these apoptotic manifestations are accompanied by inhibitor of CAD (ICAD) cleavage and are abrogated by the constitutive expression of a caspase-resistant ICAD mutant. No such nuclear changes occur during oxidative stress-induced necrosis, indicating that neither CAD nor DNasegamma functions under necrotic conditions. Interestingly, the DNA-ladder formation and nuclear fragmentation induced by B-cell receptor ligation occur in the absence of ICAD cleavage and are not significantly affected by the ICAD mutant. Both types of nuclear changes are preceded by the upregulation of DNasegamma expression and are strongly suppressed by 4-(4,6-dichloro-[1, 3, 5]-triazin-2-ylamino)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid (DR396), which is a specific inhibitor of DNasegamma. Our results suggest that DNasegamma provides an alternative mechanism for inducing nuclear changes when the working apoptotic cascade is unsuitable for CAD activation.

Animals↗

PubMed2001

B cell adaptor containing src homology 2 domain (BASH) links B cell receptor signaling to the activation of hematopoietic progenitor kinase 1.

The B cell adaptor containing src homology 2 domain (BASH; also termed BLNK or SLP-65), is crucial for B cell antigen receptor (BCR)-mediated activation, proliferation, and differentiation of B cells. BCR-mediated tyrosine-phosphorylation of BASH creates binding sites for signaling effectors such as phospholipase Cgamma (PLCgamma)2 and Vav, while the function of its COOH-terminal src homology 2 domain is unknown. We have now identified hematopoietic progenitor kinase (HPK)1, a STE20-related serine/threonine kinase, as a protein that inducibly interacts with the BASH SH2 domain. BCR ligation induced rapid tyrosine-phosphorylation of HPK1 mainly by Syk and Lyn, resulting in its association with BASH and catalytic activation. BCR-mediated activation of HPK1 was impaired in Syk- or BASH-deficient B cells. The functional SH2 domain of BASH and Tyr-379 within HPK1 which we identified as a Syk-phosphorylation site were both necessary for interaction of both proteins and efficient HPK1 activation after BCR stimulation. Furthermore, HPK1 augmented, whereas its kinase-dead mutant inhibited IkappaB kinase beta (IKKbeta) activation by BCR engagement. These results reveal a novel BCR signaling pathway leading to the activation of HPK1 and subsequently IKKbeta, in which BASH recruits tyrosine-phosphorylated HPK1 into the BCR signaling complex.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Genomic structure and transcriptional regulation of the early B cell gene chB1.

The avian B cell differentiation Ag chB1 is a membrane glycoprotein relative of the mammalian B cell differentiation Ag CD72. Unlike CD72, this C-type lectin is expressed in relatively high levels on immature B cells in the bursa of Fabricius and is down-regulated on mature B cells in the periphery. An immunoreceptor tyrosine-based inhibitory motif in the chB1 cytoplasmic tail suggests a potential regulatory role in intrabursal B cell development. To gain further insight into the selective expression and function of chB1, we determined the genomic organization of chB1 and examined the mechanism of its transcriptional regulation. The 8-exon chB1 gene proved to have very similar organization to that of mouse CD72, further supporting the idea that chB1 is a CD72 relative. As for mouse CD72, the chB1 promoter region lacks a TATA box but contains a conserved initiator element. The 131-bp region (-161 to -30) proximal to the transcriptional start site, which contains a potential early B cell factor binding site, is essential for the B lineage stage-specific transcription of chB1, whereas PU.1 and B cell-specific activator protein/Pax5 have been shown to play important roles in CD72 promoter activity and cell-type specificity. This analysis suggests that differences in transcriptional regulation of these phylogenetically related genes may determine the differences in expression pattern and, therefore, the function of avian chB1 and mammalian CD72 during B cell development.

5' Untranslated Regions↗

PubMed2001

MIST functions through distinct domains in immunoreceptor signaling in the presence and absence of LAT.

MIST (also termed Clnk) is an adaptor protein structurally related to SLP-76 and BLNK/BASH/SLP-65 hematopoietic cell-specific adaptor proteins. By using the BLNK-deficient DT40 chicken B cell system, we demonstrated MIST functions through distinct intramolecular domains in immunoreceptor signaling depending on the availability of linker for activation of T cells (LAT). MIST can partially restore the B cell antigen receptor (BCR) signaling in the BLNK-deficient cells, which requires phosphorylation of the two N-terminal tyrosine residues. Co-expression of LAT with MIST fully restored the BCR signaling and dispenses with the requirement of the two tyrosines in MIST for BCR signaling. However, some other tyrosine(s), as well as the Src homology (SH) 2 domain and the two proline-rich regions in MIST, is still required for full reconstitution of the BCR signaling, in cooperation with LAT. The C-terminal proline-rich region of MIST is dispensable for the LAT-aided full restoration of MAP kinase activation, although it is responsible for the interaction with LAT and for the localization in glycolipid-enriched microdomains. On the other hand, the N-terminal proline-rich region, which is a binding site of the SH3 domain of phospholipase Cgamma, is essential for BCR signaling. These results revealed a marked plasticity of MIST function as an adaptor in the cell contexts with or without LAT.

Adaptor Proteins, Signal Transducing↗

PubMed2001

A pivotal role for DNase I-sensitive regions 3b and/or 4 in the induction of somatic hypermutation of IgH genes.

Chimeric mice were prepared from embryonic stem cells transfected with IgH genes as transgenes and RAG-2-deficient blastocysts for the purpose of identifying the cis-acting elements responsible for the induction of somatic hypermutation. Among the three transgene constructs used, the V(H) promoter, the rearranged V(H)-D-J(H), an intron enhancer/matrix attachment region, and human Cmu were common to all, but the 3'-untranslated region in each construct was different. After immunization of mice with a T cell-dependent Ag, the distribution and frequency of hypermutation in transgenes were analyzed. The transgene lacking the 3' untranslated region showed a marginal degree of hypermutation. Addition of the 3' enhancer resulted in a slight increase in the number of mutations. However, the transgene containing DNase I-sensitive regions 3b and 4 in addition to the 3' enhancer showed more than a 10-fold increase in hypermutation, reaching levels comparable to those observed in endogenous V(H)186.2 genes of C57BL/6 mice.

Animals↗

PubMed2001

Notch signaling suppresses IgH gene expression in chicken B cells: implication in spatially restricted expression of Serrate2/Notch1 in the bursa of Fabricius.

The bursa of Fabricius is a central organ for chicken B cell development and provides an essential microenvironment for expansion of the B cell pool and for generation of a diversified B cell repertoire. We report here that genes encoding the Notch family of transmembrane proteins, key regulators of cell fate determination in development, are differentially expressed in the bursa of Fabricius: Notch1 is expressed in medullary B cells located close to the basement membrane-associated epithelium (BMAE). In contrast, a Notch ligand, Serrate2, is expressed exclusively in the BMAE, which surrounds bursal medulla. A basic helix-loop-helix-type transcription factor, Hairy1, a downstream target of Notch signaling, is expressed in the bursa coordinately with Notch1 and Serrate2 and an immature B cell line, TLT1, which expresses both Notch1 and Serrate2. Furthermore, stable expression of a constitutively active form of chicken Notch1 or Notch2 in a B cell line results in a down-regulation of surface IgM expression, which is accompanied by the reduction of IgH gene transcripts. Transient reporter assay with the human IgH gene intronic enhancer reveals that an active form of Notch1 inhibits the IgH enhancer activity in chicken B cells, suggesting that Notch-mediated signals suppress the IgH gene expression via influencing the IgH intronic enhancer. These findings raise the possibility that the local activation of Notch1 in a subset of B cells by Serrate2 expressed in BMAE may influence the cell fate decision that is involved in B cell differentiation and selection inside the bursa.

Amino Acid Sequence↗

PubMed2000

Cell cycle arrest and apoptosis induced by Notch1 in B cells.

Notch receptors play various roles for cell fate decisions in developing organs, although their functions at the cell level are poorly understood. Recently, we found that Notch1 and its ligand are each expressed in juxtaposed cell compartments in the follicles of the bursa of Fabricius, the central organ for chicken B cell development. To examine the function of Notch1 in B cells, a constitutively active form of chicken Notch1 was expressed in a chicken B cell line, DT40, by a Cre/loxP-mediated inducible expression system. Remarkably, the active Notch1 caused growth suppression of the cells, accompanied by a cell cycle inhibition at the G(1) phase and apoptosis. The expression of Hairy1, a gene product up-regulated by the Notch1 signaling, also induced the apoptosis, but no cell cycle inhibition. Thus, Notch1 signaling induces apoptosis of the B cells through Hairy1, and the G(1) cell cycle arrest through other pathways. This novel function of Notch1 may account for the recent observations indicating the selective inhibition of early B cell development in mice by Notch1.

Animals↗

PubMed2000

The B cell-restricted adaptor BASH is required for normal development and antigen receptor-mediated activation of B cells.

B cell antigen receptor signals development, activation, proliferation, or apoptosis of B cells depending on their condition, and its proper signaling is critical for activation and homeostasis of the immune system. The B cell-restricted adaptor protein BASH (also termed BLNK/SLP-65) is rapidly phosphorylated by the tyrosine kinase Syk after BCR ligation and binds to various signaling proteins. BASH structurally resembles SLP-76, which is essential for T cell development and T cell receptor signaling. To evaluate the role for BASH in B cell development and function in vivo, we disrupted BASH alleles in embryonic stem cells by means of homologous recombination and used these cells to complement lymphocyte-incompetent blastocysts from RAG2-deficient mice. In the resultant chimeric mice, T cell development was apparently normal, but B cell development was impaired, and a normally rare population of large preB cells expressing preB cell receptor dominated in the bone marrow in place of small preB cells, although they were mostly noncycling. In addition, the mature B cell populations in the periphery and the bone marrow profoundly decreased in size, as did B-1 cells in the peritoneal cavity, and serum Ig was severely reduced. The BASH-deficient B cells scarcely proliferated or up-regulated B7-2 in response to BCR ligation and poorly proliferated upon CD40 ligation or lipopolysaccharide stimulation. This phenotype indicates that BASH is critical for preB cell receptor signaling inducing proliferation of large preB cells and the following differentiation, for peripheral B cell maturation, and for BCR signaling inducing activation/proliferation of B cells.

Adaptor Proteins, Signal Transducing↗

PubMed2000

BLNK is associated with the CD72/SHP-1/Grb2 complex in the WEHI231 cell line after membrane IgM cross-linking.

Tyrosine phosphorylation of CD72 strongly correlates with B cell antigen receptor signals leading to apoptosis. We have previously shown that CD72 carrying two immunoreceptor tyrosine-based inhibition motifs (ITIM) is an in vivo substrate of SHP-1. CD72 forms a complex with SHP-1 and Grb2 via its tyrosine-phosphorylated ITIM when the WEHI231 cell line, which is representative of immature B cells, undergoes apoptosis. The CD72 complex formation was also demonstrated in normal primary B cells, suggesting that the complex formation in apoptotic B cells is a universal mechanism. In this study, we further investigated the molecular components of the CD72 complex in WEHI231 cells in order to understand the molecular mechanism involved in the signaling pathway mediated through the complex. Our experiments demonstrate that BLNK, a recently identified adaptor molecule predominantly expressed in B cells, is associated with the CD72 complex via the Src homology 3 domain(s) of Grb2 in the cell line after membrane IgM (mIgM) engagement. The results suggest that the mIgM-mediated signal strongly correlates with the formation of the CD72 / SHP-1 / Grb2 / BLNK complex.

Adaptor Proteins, Signal Transducing↗

PubMed2000

A BASH/SLP-76-related adaptor protein MIST/Clnk involved in IgE receptor-mediated mast cell degranulation.

Cross-linking of the high-affinity IgE receptor (FcepsilonRI) on mast cells by IgE-antigen complex triggers signal transduction cascades leading to the release of inflammatory mediators and production of cytokines, which are critical for the development of allergic reactions. We have identified a novel member of the BASH/SLP-76 immunoreceptor-coupled adaptor family expressed in mast cells, termed MIST (for mast cell immunoreceptor signal transducer), which has later been found to be identical to a recently reported cytokine-dependent hemopoietic cell linker, Clnk. Upon FcepsilonRI cross-linking, MIST/Clnk is tyrosine phosphorylated and associates with signaling proteins, phospholipase Cgamma, Vav, Grb2 and linker for activation of T cells (LAT). Overexpression of a mutant form of MIST/Clnk inhibited FcepsilonRI-mediated degranulation, increase in intracellular Ca(2+), NF-AT activation and phosphorylation of LAT. As a crucial signaling component for FcepsilonRI-induced mast cell degranulation, MIST/Clnk might serve as a target for anti-allergic therapy.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Establishment of an embryonic stem (ES) cell line derived from a non-obese diabetic (NOD) mouse: in vivo differentiation into lymphocytes and potential for germ line transmission.

A non-obese diabetic (NOD) mouse-derived embryonic stem (ES) cell line has been stably maintained in an undifferentiated state with a characteristic ES cell-like morphology, expressing the stem cell marker alkaline phosphatase, and displaying a normal diploid karyotype. After injecting the NOD-ES cells into blastocysts, chimeric mice were obtained. Small but significant numbers of lymphocytes expressed the NOD-derived MHC allele. When a chimeric mouse was mated with C57BL/6 mice, an agouti mouse was obtained, having the NOD-derived H-2 I-A(beta)g7 haplotype. Thus, an NOD-ES cell line which can differentiate into lymphocytes with potential for germ line transmission was successfully established.

Animals↗

PubMed1998

BASH, a novel signaling molecule preferentially expressed in B cells of the bursa of Fabricius.

The bursa of Fabricius is a gut-associated lymphoid organ that is essential for the generation of a diversified B cell repertoire in the chicken. We describe here a novel gene preferentially expressed in bursal B cells. The gene encodes an 85-kDa protein, designated BASH (B cell adaptor containing SH2 domain), that contains N-terminal acidic domains with SH2 domain-binding phosphotyrosine-based motifs, a proline-rich domain, and a C-terminal SH2 domain. BASH shows a substantial sequence similarity to SLP-76, an adaptor protein functioning in TCR-signal transduction. BASH becomes tyrosine-phosphorylated with the B cell Ag receptor (BCR) cross-link or by coexpression with Syk and Lyn and associates with signaling molecules including Syk and a putative chicken Shc homologue. Overexpression of BASH results in suppression of the NF-AT activation induced by BCR-cross-linking. These findings suggest that BASH is involved in BCR-mediated signal transduction and could play a critical role in B cell development in the bursa.

Adaptor Proteins, Signal Transducing↗

PubMed1998

T and B cell development in BP-1/6C3/aminopeptidase A-deficient mice.

Stage-restricted expression of cell surface molecules serves to delineate B lineage cells during their progressive differentiation within the bone marrow. The BP-1/6C3 Ag, aminopeptidase A (APA), is selectively expressed by the pre-B and immature B cells. This ectoenzyme, which is also present on bone marrow-derived stromal cells, thymic cortical epithelial cells, renal proximal tubular cells, intestinal enterocytes, and endothelial cells, cleaves acidic glutamyl and aspartyl residues from the N-terminus of angiotensin and other biologically active peptides to quench their functional activity. BP-1/6C3/APA expression by early B lineage cells is up-regulated by IL-7, an important growth factor for pre-B cells and T cells. To explore the physiologic role of this peptidase, we generated a mouse model of BP-1 deficiency by gene targeting in embryonal stem cells. While mice homozygous for the BP-1 mutation did not express detectable BP-1 protein or enzyme activity, they developed normally, generated normal numbers of T and B cells, exhibited integrity of Ab responses to both thymus-dependent and -independent Ags, and produced normal serum Ig levels. Phenotypic analysis of bone marrow and thymic lymphocytes indicated a normal pattern of B and T lineage differentiation. B lymphopoiesis in fetal liver cultures and the proliferative responses of bone marrow cells to IL-7 and LPS were also unimpaired. These findings indicate that BP-1 ectoenzyme activity is not essential for normal B and T cell development.

Aminopeptidases↗

PubMed1998

Deficiency in protein L-isoaspartyl methyltransferase results in a fatal progressive epilepsy.

Protein L-isoaspartyl methyltransferase (PIMT) is suggested to play a role in the repair of aged protein spontaneously incorporated with isoaspartyl residues. We generated PIMT-deficient mice by targeted disruption of the PIMT gene to elucidate the biological role of the gene in vivo. PIMT-deficient mice died from progressive epileptic seizures with grand mal and myoclonus between 4 and 12 weeks of age. An anticonvulsive drug, dipropylacetic acid (DPA), improved their survival but failed to cure the fatal outcome. L-Isoaspartatate, the putative substrate for PIMT, was increased ninefold in the brains of PIMT-deficient mice. The brains of PIMT-deficient mice started to enlarge after 4 weeks of age when the apical dendrites of pyramidal neurons in cerebral cortices showed aberrant arborizations with disorganized microtubules. We conclude that methylation of modified proteins with isoaspartyl residues is essential for the maintenance of a mature CNS and that a deficiency in PIMT results in fatal progressive epilepsy in mice.

Animals↗

PubMed1998

Lyn-mediated down-regulation of B cell antigen receptor signaling: inhibition of protein kinase C activation by Lyn in a kinase-independent fashion.

Stimulation of the B cell Ag receptor (BCR) induces activation of tyrosine kinases such as Lyn and Syk, phosphorylation and activation of multiple signaling components, and eventually, the expression of several genes including c-myc. Syk is required for activation of phospholipase C-gamma 2 and the subsequent phosphatidylinositol hydrolysis, leading to protein kinase C (PKC) activation and intracellular Ca2+ increase. In contrast, the function of Lyn remains obscure. Here, we report that BCR-mediated induction of c-myc promoter activity and of PKC activity, but not the expression level of functional PKC, was markedly augmented in Lyn-deficient chicken B cells. This enhancement was reversed to the level of wild-type cells by the expression of exogenous Lyn of kinase-inactive form. These results indicate that Lyn inhibits BCR-mediated activation of a large portion of PKC isozymes in a kinase-independent fashion. This finding reveals a novel role of Lyn in negative regulation of BCR signaling.

Animals↗

PubMed1998

Proliferation of CD3+ B220- single-positive normal T cells was suppressed in B-cell-deficient lpr mice.

It is known that lpr mice develop systemic lymphadenopathy and lupus erythematosus-like autoimmune disease that are associated with the accumulation of CD4- CD8- (double-negative; DN) CD3+ B220+ abnormal T cells as well as normal mature CD4+ or CD8+ single-positive (SP) CD3+ T cells. In order to clarify the role of B cells in the lymphoproliferation and autoimmunity of lpr mice, we created B-cell-deficient C57BL/6 (B6) lpr mice (B6lpr/lpr microMT/microMT) by crossing B6lpr/lpr mice with B6 microMT/microMT mice in which the B-cell development was arrested at pre-B stage owing to a targeted disruption of the immunoglobulin mu heavy-chain gene locus. In the B-cell-deficient B6-lpr mice, both lymphadenopathy and splenomegaly were markedly suppressed. Although the accumulation of both CD3+ B220- SP normal T cells and CD3+ B220+ DN abnormal T cells was inhibited in the B-cell-deficient lpr mice, the decrease in numbers of CD3+ B220- SP normal T cells occurred more strikingly than that of the CD3+ B220+ DN abnormal T cells. Glomerulonephritis did not develop in the B-cell-deficient lpr mice over 40 weeks. The present results indicate that the B cells thus play a crucial role in the extensive proliferation of normal CD3+ B220- mature SP T cells rather than the accumulation of abnormal DN T cells.

Animals↗

PubMed1997

Role of tyrosine phosphorylation of HS1 in B cell antigen receptor-mediated apoptosis.

The 75-kD HS1 protein is highly tyrosine-phosphorylated during B cell antigen receptor (BCR)-mediated signaling. Owing to low expression of HS1, WEHI-231-derived M1 cells, unlike the parental cells, are insensitive to BCR-mediated apoptosis. Here, we show that BCR-associated tyrosine kinases Lyn and Syk synergistically phosphorylate HS1, and that Tyr-378 and Tyr-397 of HS1 are the critical residues for its BCR-induced phosphorylation. In addition, unlike wild-type HS1, a mutant HS1 carrying the mutations Phe-378 and Phe-397 was unable to render M1 cells sensitive to apoptosis. Wild-type HS1, but not the mutant, localized to the nucleus under the synergy of Lyn and Syk. Thus, tyrosine phosphorylation of HS1 is required for BCR-induced apoptosis and nuclear translocation of HS1 may be a prerequisite for B cell apoptosis.

Adaptor Proteins, Signal Transducing↗

PubMed1997

HAX-1, a novel intracellular protein, localized on mitochondria, directly associates with HS1, a substrate of Src family tyrosine kinases.

Cross-linking of the Ag receptors on lymphocytes initiates activation of the receptor-coupled tyrosine kinases. HS1 is one of the substrates of these kinases and has been shown to transduce the signals for both clonal expansion and deletion in lymphoid cells. To gain further insight into the mechanism of action of HS1, we have tried to identify a protein that interacts with HS1 by yeast two-hybrid screening. The isolated cDNA, designated HAX-1, encodes a novel 35-kDa protein. The HAX-1 gene is expressed ubiquitously among tissues, and its protein is localized mainly in mitochondria, but also in endoplasmic reticulum and nuclear envelope in the cell. HS1/HAX-1 association is confirmed by coimmunoprecipitation of these proteins in the lysates of B lymphoma cells and COS-7 cells transfected with the corresponding cDNA expression vectors. Colocalization of these proteins in the cell is evident under confocal laser scanning microscope. Deletion mutant analysis of these proteins reveals that the association is mediated by the amino terminal region of HS1 and the carboxyl-terminal half of HAX-1. The potential role of the HAX-1/HS1 complex is discussed.

Adaptor Proteins, Signal Transducing↗