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Articles by M Nagata
Total Records ( 3 ) for M Nagata
  S Hamada , K Hara , T Hamada , H Yasuda , H Moriyama , R Nakayama , M Nagata and K. Yokono

Components of insulin/IGF-1 receptor–mediated signaling pathways in pancreatic β-cells have been implicated in the development of diabetes, in part through the regulation of β-cell mass in vivo. Studies in vitro have shown that the protein Ras homolog enriched in brain (Rheb) plays a key role as a positive upstream regulator of the mammalian target of rapamycin complex 1 (mTORC1) pathway in integrating inputs from nutrients and growth factors for cell growth. Our objective was to investigate the role of the mTORC1 pathway in the regulation of β-cell mass in vivo.


We generated transgenic mice that overexpress Rheb in β-cells. We examined the activation of the mTORC1 pathway and its effects on β-cell mass, on glucose metabolism, and on protection against hyperglycemia.


Immunoblots of islet extracts revealed that the phosphorylation levels of ribosomal protein S6 and eukaryotic initiation factor 4E binding protein 1, downstream effectors for mTORC1, were upregulated in transgenic β-cells. Immunostaining of the pancreatic sections with anti–phospho-S6 antibody confirmed upregulation of the mTORC1 pathway in β-cells in vivo. The mice showed improved glucose tolerance with higher insulin secretion. This arose from increased β-cell mass accompanied by increased cell size. The mice also exhibited resistance to hyperglycemia induced by streptozotocin and obesity.


Activation of the mTORC1 pathway by Rheb led to increased β-cell mass in this mouse model without producing obvious unfavorable effects, giving a potential approach for the treatment of β-cell failure and diabetes.

  M Li , Y Seki , P. H. L Freitas , M Nagata , T Kojima , S Sultana , S Ubaidus , T Maeda , J Shimomura , J. E Henderson , M Tamura , K Oda , Z Liu , Y Guo , R Suzuki , T Yamamoto , R Takagi and N. Amizuka

The signaling axis comprising the parathyroid hormone (PTH)-related peptide (PTHrP), the PTH/PTHrP receptor and the fibroblast growth factor receptor 3 (FGFR3) plays a central role in chondrocyte proliferation. The Indian hedgehog (IHH) gene is normally expressed in early hypertrophic chondrocytes, and its negative feedback loop was shown to regulate PTH/PTHrP receptor signaling. In this study, we examined the regulation of PTH/PTHrP receptor gene expression in a FGFR3-transfected chondrocytic cell line, CFK2. Expression of IHH could not be verified on these cells, with consequent absence of hypertrophic differentiation. Also, expression of the PTH/PTHrP receptor (75% reduction of total mRNA) and the PTHrP (50% reduction) genes was reduced in CFK2 cells transfected with FGFR3 cDNA. Interestingly, we verified significant reduction in cell growth and increased apoptosis in the transfected cells. STAT1 was detected in the nuclei of the CFK2 cells transfected with FGFR3 cDNA, indicating predominance of the JAK/STAT signaling pathway. The reduction in PTH/PTHrP receptor gene in CFK2 cells overexpressing FGFR3 was partially blocked by treatment with an inhibitor of JAK3 (WHI-P131), but not with an inhibitor of MAPK (SB203580) or JAK2 (AG490). Altogether, these findings suggest that FGFR3 down-regulates PTH/PTHrP receptor gene expression via the JAK/STAT signaling in chondrocytic cells.

  M Nagata , S Nagata , K Yuki , K Isogaya , M Saitoh , K Miyazono and K. Miyazawa

c-Ski has been known to be phosphorylated at serine residue(s), which results in slower migration of c-Ski in SDS–polyacrylamide gel electrophoresis. The position(s) of phosphorylation, however, has not been determined. In the present study, we identified a phosphorylation site of c-Ski which affects its electrophoretic motility as serine 515 using MALDI–TOF mass spectrometry. A phosphorylation-resistant mutant, c-Ski S515A, did not exhibit a phosphatase-sensitive band shift. In addition, we confirmed that endogenous c-Ski is phosphorylated at serine 515, using a specific antibody. The phosphorylation status of c-Ski, however, does not appear to affect its stability or effects on TGF-β signalling. Identification of the phosphorylation site of c-Ski would allow us further examination of physiological significance of c-Ski phosphorylation.

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