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Toshinobu Yamamoto

Publications and source records attributed to Toshinobu Yamamoto.

9 recordsLinked to original sources
PubMed2005

Down-regulation of survival signaling through MAPK and Akt in occludin-deficient mouse hepatocytes in vitro.

The tight junction (TJ) regulates epithelial cell polarity and barrier including permeability of the paracellular pathway. Occludin was the first integral membrane protein to be discovered, but it is not indispensable for the formation of TJ strands. The physiological function of occludin is still unclear, although occludin-deficient mice show very complex abnormalities in various organs without overt dysfunction of the TJ. To investigate the role of occludin in TJ expression and apoptosis regulated by survival signal transduction pathways such as MAPK and Akt, we performed primary culture of hepatocytes and established hepatic cell lines from occludin-deficient mice. In primary cultures of occludin-deficient mouse hepatocytes, claudin-2 expression and apoptosis were induced by down-regulation of the activation of MAPK and Akt. In the hepatic cell lines derived from occludin-deficient mice, claudin-2 expression and serum-free induced apoptosis were also increased by down-regulation of the activation of MAPK and Akt. Furthermore, in the hepatic cell lines transiently transfected with mouse and rat occludin genes, induction of claudin-2 expression and the apoptosis were inhibited with increases in activation of MAPK and Akt. These findings show that occludin plays a crucial role in claudin-2-dependent TJ function and the apoptosis involving MAPK and Akt signaling pathways in hepatocytes.

Animals↗
PubMed2005

p38 MAP-kinase regulates function of gap and tight junctions during regeneration of rat hepatocytes.

BACKGROUND/AIMS: Hepatocyte regeneration is considered to be associated with adaptive changes in expression of gap and tight junctions through multiple signal transduction pathways including p38 MAP-kinase. The role of the stress responsitive MAP-kinase, p38 MAP-kinase, signaling pathway in function of gap and tight junctions was examined during regeneration of rat hepatocytes in vivo and in vitro. METHODS: We examined changes in formation, expression and function of gap and tight junctions in rat livers after 70% partial hepatectomy and in primary cultures of rat hepatocytes, by using a p38 MAP-kinase inhibitor, SB203580. RESULTS: When p38 MAP-kinase was activated during partial hepatectomy, down-regulation of Cx32 and up-regulation of claudin-1 were observed. By SB203580 treatment, the down-regulation of Cx32 was inhibited and the up-regulation of claudin-1 was enhanced, well maintaining the structures of gap and tight junctions. SB203580 treatment did not affect the increase of hepatocyte proliferation. In EGF induced proliferative rat hepatocytes treated with SB203580, the expression and function of Cx32 and claudin-1 were increased. CONCLUSIONS: Dynamic changes of formation of gap and tight junctions during regeneration of rat hepatocytes in vivo and in vitro are in part controlled via a p38 MAP-kinase signaling pathway, and are independent of cell growth.

Animals↗
PubMed2004

Tight junction protein MAGI-1 is up-regulated by transfection with connexin 32 in an immortalized mouse hepatic cell line: cDNA microarray analysis.

Gap junctions are considered to play a crucial role in differentiation of epithelial cells, including hepatocytes. Recently, we found that Cx32 but not Cx26 was closely related to tight junctional proteins in primary cultured rat hepatocytes (Kojima et al., Exp Cell Res 263:193-201, 2001) and that Cx32 formation and/or Cx32-mediated intercellular communication could induce expression and function of tight junctions in a mouse hepatic cell line (Kojima et al., Exp Cell Res 276:40-51, 2002). In this study, to investigate the mechanisms of induction of tight junctions by transfection with Cx32, we performed cDNA microarray analysis of Cx32 transfectants, compared with parental cells derived from Cx32-deficient hepatocytes. In cDNA microarray analysis, a 2.5-fold increase in expression of membrane-associated guanylate kinase with inverted orientation-1 (MAGI-1), which is known to be localized at adherens and tight junction regions, was observed. High expression of MAGI-1 in Cx32 transfectants was confirmed by Western blotting and RT-PCR. MAGI-1 was colocalized with occludin, claudin-2, ZO-1, and F-actin, but not with E-cadherin in the apical-most regions at cell borders of Cx32 transfectants, similar to junctional adhesion molecule-1 (JAM-1), which may play a crucial role in formation and assembly of tight junctions. Treatment with the gap junction blocker 18beta-glycyrrhetinic acid did not affect expression of MAGI-1 and JAM-1 in Cx32 transfectants. These results suggest that Cx32 expression is in part related to induction of tight junctions through modulation of MAGI-1 expression in an immortalized mouse hepatic cell line.

Actins↗
PubMed2004

IL-1beta regulates expression of Cx32, occludin, and claudin-2 of rat hepatocytes via distinct signal transduction pathways.

The functions of gap and tight junctions are perturbed during the acute-phase response to liver injury. To elucidate the mechanism of pro-inflammatory cytokine IL-1beta responsible for regulation of hepatic gap and tight junctions, we analyzed expression and function of gap and tight junctions using a rat liver injury model and primary cultures of rat hepatocyte. In rat liver lobules at 24 h after thioacetamide (TAA) treatment, where some IL-1beta-positive non-parenchymal cells existed, disappearance of connexin32-positive spots at cell borders of the hepatocytes and increases of claudin-2 and occludin immunoreactivities in bile canalicular regions were observed. In primary cultures of rat hepatocytes, IL-1beta caused the disappearance of connexin32, which was reciprocal to the induction and localization of claudin-2 to cell membranes. The downregulated connexin32 expression was inhibited by treatment with a MAP-kinase inhibitor (PD98059), whereas the upregulated claudin-2 expression was blocked by p38 MAP and PI3-kinase inhibitors (SB203580 and LY294002). The changes of connexin32 and claudin-2 may be controlled at the transcriptional level via NF-kappaB, HNF-1alpha, and CDX2. Occludin was hyperphosphorylated by IL-1beta treatment and was inhibited by treatment with a PI3-kinase inhibitor. These results demonstrate that MAP-kinase, p38 MAP-kinase, and PI3-kinase are distinctly involved in the regulation of hepatic gap and tight junctions during the acute-phase response to IL-1beta.

Animals↗
PubMed2004

Inhibition of MAP kinase activity moderates changes in expression and function of Cx32 but not claudin-1 during DNA synthesis in primary cultures of rat hepatocytes.

The signal transduction pathways and activation of the MAP kinase or PI3 kinase signaling cascade regulate a variety of cellular processes, including proliferation and differentiation in hepatocytes. To elucidate the mechanisms of signal transmission required for the regulation of gap and tight junctions during DNA synthesis in rat hepatocytes, we determined changes of expression and function of gap and tight junctions of cells grown in primary culture, using inhibitors of signaling pathways for MAP kinase (PD98059) and PI3 kinase (LY294002). During the stimulation of DNA synthesis induced by epidermal growth factor (EGF), immunoreactivity and mRNAs of gap junction protein Cx32 and of tight junction protein claudin-1 markedly decreased with reduction of gap junctional intercellular communication (GJIC) and the fence function of tight junctions. In Western blots, whole-cell lysate of claudin-1 protein decreased and phosphorylated Cx32 protein in the insoluble fraction of Triton X-100 increased during the stimulation of DNA synthesis. During reinhibition of DNA synthesis, the changes of Cx32 and claudin-1 returned to control levels, as did both functions. In treatment with the inhibitors before DNA synthesis, PD98059 inhibited the changes of expression and function of Cx32, but not claudin-1, without inhibition of cell growth, whereas LY294002 completely inhibited cell growth. These findings indicate that the PI3 kinase pathway rather than the MAP kinase pathway plays an important role for EGF-induced proliferation of rat hepatocytes, and that changes of Cx32 in hepatocytes during the stimulation of DNA synthesis may be in part controlled through MAP kinase. Furthermore, Cx32, but not claudin-1, protein may be a target of activated MAP kinase in hepatocytes.

Animals↗
PubMed2003

Regulation of the blood-biliary barrier: interaction between gap and tight junctions in hepatocytes.

Hepatocytes tightly connect with each other by intercellular junctions to form liver cell plates. The junctions composed of gap, tight, and adherens junctions and desmosomes concentrate around bile canaliculi. In particular, tight junctions serve as a barrier to keep bile in bile canaliculi away from the blood circulation. Thus, it is very reasonable to call tight junctions of hepatocytes the blood-biliary barrier. On the other hand, gap junctions of hepatocytes are considered to enable ordered contraction of bile canaculi from centrizonal to periportal hepatocytes by their function of intercellular communication. Gap and tight junctions may thus play a crucial role in bile secretion, one of the most differentiated functions of the liver. In intrahepatic cholestasis, a common pathological condition of the liver, downregulation of gap and tight junctional functions is seen, which results in impaired intercellular communication and in leaky tight junctions. Although the changes in gap and tight junctions had been considered to be independent of each other, recent findings that the tight junction-associated proteins ZO-1 and occludin bind to connexins indicate the possibility of either coordinate or reciprocal regulation of macromolecular complexes containing gap- and tight-junction proteins. In this review, we introduce the interaction and regulation between gap and tight junctions of hepatocytes in vitro and discuss the regulatory mechanisms of the "blood-biliary barrier" to study the molecular pathogenesis of cholestasis.

Actins↗
PubMed2002

[Influenza virus].

Influenza virus is highly infectious and transmitted from human to human by droplet infection. Therefore, once the virus is brought into a hospital, this can lead to a severe outbreak of influenza among medical workers and inpatients, resulting in the failure of hospital functions. The fundamental protective measures against in-hospital infection include stopping the outbreak of influenza and minimizing the spread of infection when mass infection of influenza occurs in a hospital. Thus, it is vital that the infection control committee in each hospital prepares specific countermeasures against influenza infection reflecting the realities. As one such countermeasure, it is recommended is to give influenza vaccination to medical workers and patients before the illness becomes epidemic. Further, once an outbreak of influenza occurs in a hospital, administration of anti-influenza drugs to high-risk patients also needs to be considered.

Amantadine↗
PubMedDate not supplied

Role of the p38 MAP-kinase signaling pathway for Cx32 and claudin-1 in the rat liver.

Liver regeneration and cholestasis are associated with adaptive changes in expression of gap and tight junctions through signal transduction. The roles of stress responsitive MAP-kinase, p38 MAP-kinase, in the signaling pathway for gap junction protein, Cx32, and tight junction protein, claudin-1, were examined in rat liver in vivo and in vitro, including regeneration following partial hepatectomy and cholestasis after common bile duct ligation. Changes in the expression and function of Cx32 and claudin-1 in hepatocytes in vivo were studied using the p38 MAP-kinase inhibitor SB203580. Following partial hepatectomy and common bile duct ligation, down-regulation of Cx32 protein was inhibited by SB203580 treatment. Up-regulation of claudin-1 protein was enhanced by SB203580 treatment after partial hepatectomy but not common bile duct ligation. However, no change of the Ki-67 labeling index (which is a marker for cell proliferation) in the livers treated with SB203580, was observed compared to that without SB203580 treatment. In primary cultures of rat hepatocytes, however, treatment with a p38 MAP-kinase activator, anisomycin, decreased Cx32 and claudin-1 protein levels. p38 MAP-kinase may be an important signaling pathway for regulation of gap and tight junctions in hepatocytes. Changes of gap and tight junctions during liver regeneration and cholestasis are shown to be in part controlled via the p38 MAP-kinase signaling pathway and are independent of cell growth.

Animals↗