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Biochemical and Molecular Actions of Nutrients

Meal Feeding Alters Translational Control of Gene Expression in Rat Liver¹

Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033

²To whom correspondence should be addressed. E-mail: jjefferson{at}psu.edu.

Meal feeding after a period of food deprivation results in a subsequent increase in the protein and RNA content of the liver. To gain insight into the mechanisms involved in the response to food intake, changes in the association of selected mRNAs with polysomes were examined. On the day of the study, rat livers were collected at 0, 15, 60, and 180 min after the start of feeding and analyzed for biomarkers of the translational control of protein synthesis. Protein synthesis was increased within 60 min and was sustained for 180 min. Assembly of the active eukaryotic initiation factor (eIF) 4F complex was elevated within 15 min, as indicated by the relative association of eIF4E · eIF4G, but returned to the basal value within 180 min. Phosphorylation of the ribosomal protein (rp) S6 kinase S6K1 and its substrate rpS6 was increased within 15 min and was sustained for at least 180 min. Both eIF4F assembly and activation of S6K1 have been linked to upregulated translation of a subset of mRNAs. To identify translationally regulated mRNAs, polysomal (i.e., actively translated) and nonpolysomal (nontranslated) fractions were isolated and subjected to microarray analysis. The mRNAs encoding 78 proteins, including 42 proteins involved in protein synthesis, exhibited increased abundance in polysomes in response to feeding. Overall, the results demonstrate that protein synthesis as well as ribosomal protein mRNA translation undergo rapid and sustained stimulation in the liver after meal feeding and thus contribute to the previously observed increases in protein and RNA content.

KEY WORDS: • translation initiation • eukaryotic initiation factors 4E and 4G • mTOR • microarray analysis

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