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Articles by T Oka
Total Records ( 2 ) for T Oka
  J Xue , F Mraiche , D Zhou , M Karmazyn , T Oka , L Fliegel and G. G. Haddad

In myocardial disease, elevated expression and activity of Na+/H+ exchanger isoform 1 (NHE1) are detrimental. To better understand the involvement of NHE1, transgenic mice with elevated heart-specific NHE1 expression were studied. N-line mice expressed wild-type NHE1, and K-line mice expressed activated NHE1. Cardiac morphology, interstitial fibrosis, and cardiac function were examined by histological staining and echocardiography. Differences in gene expression between the N-line or K-line and nontransgenic littermates were probed with genechip analysis. We found that NHE1 K-line (but not N-line) hearts developed hypertrophy, including elevated heart weight-to-body weight ratio and increased cross-sectional area of the cardiomyocytes, interstitial fibrosis, as well as depressed cardiac function. N-line hearts had modest changes in gene expression (50 upregulations and 99 downregulations, P < 0.05), whereas K-line hearts had a very strong transcriptional response (640 upregulations and 677 downregulations, P < 0.05). In addition, the magnitude of expression alterations was much higher in K-line than N-line mice. The most significant changes in gene expression were involved in cardiac hypertrophy, cardiac necrosis/cell death, and cardiac infarction. Secreted phosphoprotein 1 and its signaling pathways were upregulated while peroxisome proliferator-activated receptor signaling was downregulated in K-line mice. Our study shows that expression of activated NHE1 elicits specific pathways of gene activation in the myocardium that lead to cardiac hypertrophy, cell death, and infarction.

  T Kanzaki , S Ushioku , A Nakagawa , T Oka , K Takahashi , T Nakamura , K Kuwajima , A Yamagishi and M. Yohda

Group II chaperonins exist in archaea and the eukaryotic cytosol, and mediate protein folding in an ATP-dependent manner. We have been studying the reaction mechanism of group II chaperonins using chaperonin, the recombinant chaperonin subunit homo-oligomer from a hyperthermophilic archaeon, Thermococcus sp. strain KS-1 (T. KS-1). Although the high stability and activity of T. KS-1 chaperonin provided advantages for our study, its high thermophilicity caused the difficulty in using various analytical methods. To resolve this problem, we tried to adapt T. KS-1 chaperonin to moderate temperatures by mutations. The comparison of amino acid sequences between 26 thermophilic and 17 mesophilic chaperonins showed that three amino acid replacements are likely responsible for the difference of their optimal temperatures. We introduced three single mutations and also their double combinations into T. KS-1 chaperonin. Among them, K323R single mutant exhibited the improvements of the folding activity and the ATP-dependent conformational change ability at lower temperatures, such as 50°C and 40°C. Since K323 may secure helix 12 in the closed conformation by interacting with D198, the replacement of Lys to Arg likely induced the higher mobility of the built-in lid, resulting in the higher activity at relatively low temperatures.

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