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Articles by Y Takamura
Total Records ( 2 ) for Y Takamura
  Y Soeda , H Tsuneki , H Muranaka , N Mori , S Hosoh , Y Ichihara , S Kagawa , X Wang , N Toyooka , Y Takamura , T Uwano , H Nishijo , T Wada and T. Sasaoka

Impairment of insulin and IGF-I signaling in the brain is one of the causes of dementia associated with diabetes mellitus and Alzheimer’s disease. However, the precise pathological processes are largely unknown. In the present study, we found that SH2-containing inositol 5'-phosphatase 2 (SHIP2), a negative regulator of phosphatidylinositol 3,4,5-trisphosphate-mediated signals, is widely expressed in adult mouse brain. When a dominant-negative mutant of SHIP2 was expressed in cultured neurons, insulin signaling was augmented, indicating physiological significance of endogenous SHIP2 in neurons. Interestingly, SHIP2 mRNA and protein expression levels were significantly increased in the brain of type 2 diabetic db/db mice. To investigate the impact of increased expression of SHIP2 in the brain, we further employed transgenic mice overexpressing SHIP2 and found that increased amounts of SHIP2 induced the disruption of insulin/IGF-I signaling through Akt. Neuroprotective effects of insulin and IGF-I were significantly attenuated in cultured cerebellar granule neurons from SHIP2 transgenic mice. Consistently, terminal deoxynucleotide transferase-mediated dUTP nick end labeling assay demonstrated that the number of apoptosis-positive cells was increased in cerebral cortex of the transgenic mice at an elderly age. Furthermore, SHIP2 transgenic mice exhibited impaired memory performance in the Morris water maze, step-through passive avoidance, and novel-object-recognition tests. Importantly, inhibition of SHIP2 ameliorated the impairment of hippocampal synaptic plasticity and memory formation in db/db mice. These results suggest that SHIP2 is a potent negative regulator of insulin/IGF-I actions in the brain, and excess amounts of SHIP2 may be related, at least in part, to brain dysfunction in insulin resistance with type 2 diabetes.

  S Okada , M Nagabuchi , Y Takamura , T Nakagawa , K Shinmyozu , J. i Nakayama and K. Tanaka

Recent studies have revealed various functions for the small ubiquitin-related modifier (SUMO) in diverse biological phenomena, such as regulation of cell division, DNA repair and transcription, in yeast and animals. In contrast, only a limited number of proteins have been characterized in plants, although plant SUMO proteins are involved in many physiological processes, such as stress responses, regulation of flowering time and defense reactions to pathogen attack. Here, we reconstituted the Arabidopsis thaliana SUMOylation cascade in Escherichia coli. This system is rapid and effective for the evaluation of the SUMOylation of potential SUMO target proteins. We tested the ability of this system to conjugate the Arabidopsis SUMO isoforms, AtSUMO1, 2, 3 and 5, to a model substrate, AtMYB30, which is an Arabidopsis transcription factor. All four SUMO isoforms tested were able to SUMOylate AtMYB30. Furthermore, SUMOy-lation sites of AtMYB30 were characterized by liquid chromatography–tandem mass spectrometry (LC-MS/MS) followed by mutational analysis in combination with this system. Using this reconstituted SUMOylation system, comparisons of SUMOylation patterns among SUMO isoforms can be made, and will provide insights into the SUMO isoform specificity of target modification. The identification of SUMOylation sites enables us to investigate the direct effects of SUMOylation using SUMOylation-defective mutants. This system will be a powerful tool for elucidation of the role of SUMOylation and of the biochemical and structural features of SUMOylated proteins in plants.

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