Publications (6)27.34 Total impact
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Article: Downregulation of functional Reelin receptors in projection neurons implies that primary Reelin action occurs at early/premigratory stages.
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ABSTRACT: Reelin signaling is essential for correct development of the mammalian brain. Reelin binds to apolipoprotein E receptor 2 and very low-density lipoprotein receptor and induces phosphorylation of Dab1. However, when and where these reactions occur is essentially unknown, and the primary function(s) of Reelin remain unclear. Here, we used alkaline phosphatase fusion of the receptor-binding region of Reelin to quantitatively investigate the localization of functional Reelin receptors (i.e., those on the plasma membrane as mature forms) in the developing brain. In the wild-type cerebral cortex, they are mainly present in the intermediate and subventricular zones, as well as in radial fibers, but much less in the cell bodies of the cortical plate. Functional Reelin receptors are much more abundant in the Reelin-deficient cortical plate, indicating that Reelin induces their downregulation and that it begins before the neurons migrate out of the intermediate zone. In the wild-type cerebellum, functional Reelin receptors are mainly present in the cerebellar ventricular zone but scarcely expressed by Purkinje cells that have migrated out of it. It is thus strongly suggested that Reelin exerts critical actions on migrating projection neurons at their early/premigratory stages en route to their final destinations, in the developing cerebral cortex and cerebellum.Journal of Neuroscience 09/2009; 29(34):10653-62. · 7.11 Impact Factor -
Article: The N-terminal fragment of Reelin is generated after endocytosis and released through the pathway regulated by Rab11.
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ABSTRACT: Reelin is a large secreted glycoprotein essential for brain formation, but its trafficking and function at the molecular level remain incompletely understood. After binding to its receptor, Reelin is internalized by endocytosis. Here we show that internalized Reelin is subject to specific proteolysis within the cell and its N-terminal fragment is re-secreted. This re-secretion is inhibited by bafilomycin A(1) or by expression of a mutant of Rab11, a regulator of the recycling pathway. As the N-terminal fragment does not bind to Reelin receptor but has homology to F-spondin, its recycling may be involved in the regulation of extracellular matrix.FEBS letters 04/2009; 583(8):1299-303. · 3.54 Impact Factor -
Article: Splicing variations in the ligand-binding domain of ApoER2 results in functional differences in the binding properties to Reelin.
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ABSTRACT: Reelin plays critical roles in brain formation by binding to apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor. Several isoforms and fragments of Reelin are generated by alternative splicing and proteolytic cleavage. In addition, two splice variants of ApoER2 have been recognized, namely, LA1237 and LA12378, that differ in the number of ligand-binding type A (LA) repeats. Here, we quantitatively investigated the affinity between various isoforms/fragments of Reelin and the ApoER2 splice variants. ApoER2-LA1237 bound rather strongly to the Reelin central fragment than to the fragment bearing Reelin repeat 8 (RR8). ApoER2-LA12378 bound comparably to all Reelin fragments without the C-terminal region. These findings suggest that LA8 of ApoER2 and RR8 interfere with the interaction between the Reelin central fragment and ApoER2. Using a monoclonal antibody that only recognizes ApoER2-LA12378, we found that this variant of ApoER2 was expressed in the cerebral cortical wall and in the internal granule cells of the cerebellum during development. Primary-cultured cortical neurons did not express ApoER2-LA12378, and the extent of signal activation by Reelin fragments was well correlated with their affinity for ApoER2-LA1237. Therefore, proteolytic cleavage of Reelin and alternative splicing of ApoER2 may be involved in the fine regulation of Reelin signaling.Neuroscience Research 02/2009; 63(4):251-8. · 2.25 Impact Factor -
Article: The extremely conserved C-terminal region of Reelin is not necessary for secretion but is required for efficient activation of downstream signaling.
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ABSTRACT: Reelin is a very large secreted glycoprotein essential for correct development of the mammalian brain. It is also implicated in higher functions and diseases of human brain. However, whether or not secretion of Reelin is regulated and how Reelin transmits signals remain largely unknown. Reelin protein is composed of an N-terminal F-spondin-like domain, Reelin repeats, and a short and highly basic C-terminal region (CTR). The primary sequence of CTR is almost completely conserved among vertebrates except fishes, indicating its importance. A prevailing idea regarding the function of CTR is that it is required for the secretion of Reelin, although this remains unproven. Here we aimed to clarify the function of Reelin CTR. Neither deleting most of CTR nor replacing CTR with unrelated amino acids affected secretion efficiency, indicating that CTR is not absolutely required for the secretion of Reelin. We also found that Reelin mutants without CTR were less potent in activating the downstream signaling in cortical neurons. Although these mutants were able to bind to the Reelin receptor ectodomain as efficiently as wild-type Reelin, quite interestingly, their ability to bind to the isolated cell membrane bearing Reelin receptors or receptor-expressing cells (including cortical neurons) was much weaker than that of wild-type Reelin. Therefore, it is concluded that the CTR of Reelin is not essential for its secretion but is required for efficient activation of downstream signaling events, presumably via binding to an unidentified "co-receptor" molecule(s) on the cell membrane.Journal of Biological Chemistry 08/2007; 282(28):20544-52. · 4.77 Impact Factor -
Article: Hyperproduction of hyaluronan in neu-induced mammary tumor accelerates angiogenesis through stromal cell recruitment: possible involvement of versican/PG-M.
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ABSTRACT: Elevated concentrations of hyaluronan are often associated with human breast cancer malignancy. Here, we investigated the roles of hyaluronan in carcinogenesis and cancer progression using the mouse mammary tumor virus (MMTV)-Neu transgenic model of spontaneous breast cancer. Conditional transgenic mice that express murine hyaluronan synthase 2 (Has2) by Cre-mediated recombination were generated and crossed with the MMTV-Neu mice. In expressing Cre recombinase under the control of the MMTV promoter, the bigenic mice bearing Has2 and neu transgenes exhibited a deposition of hyaluronan matrix and aggressive growth of Neu-initiated mammary tumors. Notably, forced expression of Has2 impaired intercellular adhesion machinery and elicited cell survival signals in tumor cells. Concurrent with these alterations of tumor cells, intratumoral stroma and microvessels were markedly induced. To reveal the molecular basis of hyaluronan-mediated neovascularization, various hyaluronan samples were examined for their ability to potentiate in vivo angiogenesis. In Matrigel plug assays, basic fibroblast growth factor-induced neovascularization was elevated in the presence of either hyaluronan oligosaccharides or a hyaluronan aggregate containing versican. Administration of hyaluronan-versican aggregates, but not native hyaluronan alone, promoted stromal cell recruitment concurrently with the infiltration of endothelial cells. Taken together, these results suggest that hyaluronan overproduction accelerates tumor angiogenesis through stromal reaction, notably in the presence of versican.American Journal Of Pathology 04/2007; 170(3):1086-99. · 4.89 Impact Factor -
Article: Gamma-glutamyltranspeptidase stimulates receptor activator of nuclear factor-kappaB ligand expression independent of its enzymatic activity and serves as a pathological bone-resorbing factor.
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ABSTRACT: A novel bone-resorbing factor was cloned using an expression cloning technique, which involved a Xenopus oocyte expression system and an assay for osteoclast formation. A candidate clone was isolated from a BW5147 mouse T-lymphoma cell cDNA library. Sequencing analysis identified the factor as gamma-glutamyltranspeptidase (GGT), which is an enzyme involved in glutathione metabolism. The addition of purified GGT protein to mouse bone marrow culture effectively induced formation of osteoclasts. An antibody against GGT inhibited osteoclast formation but not the enzymatic activity. We also demonstrated that an inactive form of GGT, the enzymatic activity of which had been blocked by chemical modification with a specific inhibitor, acivicin, supported osteoclast formation. These results indicate that GGT acts on osteoclast formation independent of its own enzymatic activity. Furthermore, both native GGT and inactive GGT stimulated the expression of the receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA and protein from bone marrow stromal cells. This report is the first demonstration of a novel biological activity of GGT protein in a manner independent of its enzymatic activity.Journal of Biological Chemistry 03/2004; 279(7):5752-6. · 4.77 Impact Factor
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Institutions
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2007–2009
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Nagoya City University
Nagoya-shi, Aichi-ken, Japan
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