Polypyrimidine tract-binding protein is involved in regulation of albumin synthesis in response to food intake.
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.
Kuwahata
Masashi
M
Department of Molecular Nutrition, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan. kuwahata@kpu.ac.jp
Kuramoto
Yasuko
Y
Sawai
Yukiko
Y
Amano
Saki
S
Tomoe
Yuka
Y
Segawa
Hiroko
H
Tatsumi
Sawako
S
Ito
Mikiko
M
Kobayashi
Yukiko
Y
Kido
Yasuhiro
Y
Oka
Tatsuzo
T
Miyamoto
Ken-Ichi
K
D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D003593:Cytoplasm / Q000378:metabolism; D004032:Diet; D004435:Eating; D005215:Fasting; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D007328:Insulin / Q000097:blood; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D038601:Ribosomal Protein S6 / Q000187:drug effects / Q000378:metabolism; D012709:Serum Albumin / Q000096:biosynthesis / Q000235:genetics*; D020123:Sirolimus / Q000494:pharmacology
D007328:Insulin; D012333:RNA, Messenger; D038601:Ribosomal Protein S6; D012709:Serum Albumin; D038941:Polypyrimidine Tract-Binding Protein; D020123:Sirolimus