Polypyrimidine Tract-Binding Protein Is Involved in Regulation of Albumin Synthesis in Response to Food Intake

  • KUWAHATA Masashi
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School Department of Food Sciences and Nutritional Health, Faculty of Human Environment, Kyoto Prefectural University
  • KURAMOTO Yasuko
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • SAWAI Yukiko
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • AMANO Saki
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • TOMOE Yuka
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • SEGAWA Hiroko
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • TATSUMI Sawako
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • ITO Mikiko
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School
  • KOBAYASHI Yukiko
    Department of Food Sciences and Nutritional Health, Faculty of Human Environment, Kyoto Prefectural University
  • KIDO Yasuhiro
    Department of Food Sciences and Nutritional Health, Faculty of Human Environment, Kyoto Prefectural University
  • OKA Tatsuzo
    Department of Veterinary Medicine, Faculty of Agriculture, Kagoshima University
  • MIYAMOTO Ken-ichi
    Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School

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Abstract

Our recent study demonstrates that polypyrimidine tract-binding protein (PTB), which is a sequence specific RNA-binding protein, attenuates albumin synthesis in a cell-free translation system. In this study, the effects of food intake on regulation of albumin synthesis through binding of PTB to albumin messenger RNA (mRNA) were investigated. Rats were divided into 1 of 3 groups: fed; fasted for 36 h; or fasted for 36 h and then refed for 24 h. No significant differences in albumin mRNA levels were found among fed, fasted and refed rats. However, a decrease in the proportion of albumin mRNA associated with polysomes was identified in fasted rats. Furthermore, UV-cross linking analysis demonstrated that levels of albumin mRNA-PTB complex were increased in liver extracts from fasted rats. No significant differences in PTB levels in liver homogenate were found among the experimental groups. However, PTB level in the cytoplasmic fraction was higher in fasted rats than in fed rats. In refed rats, PTB level in the cytoplasmic fraction returned to a level comparable to that in fed rats, but was inhibited by treatment with rapamycin, a mammalian target of rapamycin (mTOR) inhibitor. These results suggest that localization of PTB is regulated by food intake through mTOR signaling, and alterations in level of albumin mRNA-PTB complex play a role in mediating the effects of food intake on albumin synthesis in the rat liver.

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