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Articles by T Imamura
Total Records ( 4 ) for T Imamura
  M Saberi , D Bjelica , S Schenk , T Imamura , G Bandyopadhyay , P Li , V Jadhar , C Vargeese , W Wang , K Bowman , Y Zhang , B Polisky and J. M. Olefsky

The transcription factor TORC2 [transducer of regulated cAMP-responsive element-binding protein (CREB) activity 2] is a major regulator of hepatic gluconeogenesis and is increased in hyperglycemic rodent models. Because chronic hyperglycemia and increased hepatic glucose production, via increased gluconeogenesis, is a key feature of type 2 diabetes, an effective in vivo method to efficiently knock down TORC2 could provide a potential therapy for treating hyperglycemia and type 2 diabetes. To assess this, primary mouse hepatocytes, high-fat diet (HFD)-fed mice, and Zucker diabetic fatty (ZDF) rats were treated with a siRNA against TORC2 (siTORC2), which was delivered via a novel lipid nanoparticle system, or control siRNA (siCON). Compared with siCON, administration of siTORC2 resulted in highly efficient, sustained (1–3 wk) knockdown of TORC2 and its gluconeogenic target genes phosphoenolpyruvate carboxykinase and glucose-6-phophatase in primary mouse hepatocytes and in the livers of HFD-fed mice. In mice, this knockdown was specific to the liver and did not occur in kidney, skeletal muscle, or adipose tissue. In HFD-fed mice, siTORC2 reduced in vivo gluconeogenic capacity, fasting hepatic glucose production, and hyperglycemia, and led to improved hepatic and skeletal muscle insulin sensitivity. siTORC2 treatment also improved systemic hyperglycemia in ZDF rats. In conclusion, these results demonstrate the importance of TORC2 in modulating HGP in vivo and highlight a novel, liver-specific siRNA approach for the potential treatment of hyperglycemia and type 2 diabetes.

  T Yoshizaki , S Schenk , T Imamura , J. L Babendure , N Sonoda , E. J Bae , D. Y Oh , M Lu , J. C Milne , C Westphal , G Bandyopadhyay and J. M. Olefsky

Chronic inflammation is an important etiology underlying obesity-related disorders such as insulin resistance and type 2 diabetes, and recent findings indicate that the macrophage can be the initiating cell type responsible for this chronic inflammatory state. The mammalian silent information regulator 2 homolog SIRT1 modulates several physiological processes important for life span, and a potential role of SIRT1 in the regulation of insulin sensitivity has been shown. However, with respect to inflammation, the role of SIRT1 in regulating the proinflammatory pathway within macrophages is poorly understood. Here, we show that knockdown of SIRT1 in the mouse macrophage RAW264.7 cell line and in intraperitoneal macrophages broadly activates the JNK and IKK inflammatory pathways and increases LPS-stimulated TNF secretion. Moreover, gene expression profiles reveal that SIRT1 knockdown leads to an increase in inflammatory gene expression. We also demonstrate that SIRT1 activators inhibit LPS-stimulated inflammatory pathways, as well as secretion of TNF, in a SIRT1-dependent manner in RAW264.7 cells and in primary intraperitoneal macrophages. Treatment of Zucker fatty rats with a SIRT1 activator leads to greatly improved glucose tolerance, reduced hyperinsulinemia, and enhanced systemic insulin sensitivity during glucose clamp studies. These in vivo insulin-sensitizing effects were accompanied by a reduction in tissue inflammation markers and a decrease in the adipose tissue macrophage proinflammatory state, fully consistent with the in vitro effects of SIRT1 in macrophages. In conclusion, these results define a novel role for SIRT1 as an important regulator of macrophage inflammatory responses in the context of insulin resistance and raise the possibility that targeting of SIRT1 might be a useful strategy for treating the inflammatory component of metabolic diseases.

  H Ide , Y Terado , S Tokiwa , K Nishio , K Saito , S Isotani , Y Kamiyama , S Muto , T Imamura and S. Horie

Adrenocortical cancer (ACC) is a rare and aggressive endocrine tumor. The patient presented with a large retroperitoneum tumor and lung metastases. Removal of the adrenocortical tumor with part of the transverse colon and tail of the pancreas, spleen and kidney was successfully performed following chemotherapy. Levels of serum neuron-specific enolase (NSE) were found to be markedly high before surgery and may be clinically useful markers for monitoring tumor status during management. Immunohistochemical studies showed that the cancer cells were positive for NSE and overexpression of p53. We identified a novel germ line variant of the 177 mutant (Pro to Arg; P177R) of p53 by genomic sequencing. The genetic and biochemical data presented in this case confirm the importance of screening for p53 status in ACC with inherited cancer syndrome.

  A Mizutani , M Saitoh , T Imamura , K Miyazawa and K. Miyazono

Arkadia is a positive regulator of transforming growth factor (TGF)-β signalling that induces ubiquitin-dependent degradation of several inhibitory proteins of TGF-β signalling through its C-terminal RING domain. We report here that, through yeast-two-hybrid screening for Arkadia-binding proteins, the µ2 subunit of clathrin-adaptor 2 (AP2) complex was identified as an interacting partner of Arkadia. Arkadia was located in both the nucleus and the cytosol in mammalian cells. The C-terminal YXX-binding domain of the µ2 subunit associated with the N-terminal YALL motif of Arkadia. Arkadia ubiquitylated the µ2 subunit at Lys130. In addition, Arkadia interacted with the AP2 complex, and modified endocytosis of epidermal growth factor receptor (EGFR) induced by EGF. Arkadia thus appears to regulate EGF signalling by modulating endocytosis of EGFR through interaction with AP2 complex.

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