Meal feeding stimulates phosphorylation of multiple effector proteins regulating protein synthetic processes in rat hearts.

Feeding promotes protein synthesis in cardiac muscle through a stimulation of the mRNA translation initiation phase of protein synthesis either secondary to nutrient-induced rises in insulin or because of direct effects of nutrients themselves. The present set of experiments establishes the effects of meal feeding on the potential signal transduction pathways that may be important in accelerating mRNA translation initiation. Hearts were obtained from male Sprague Dawley rats that had been trained to consume a meal consisting of nonpurified diet prior to, during, and following the test meal. Meal feeding raised the extent of phosphorylation of eukaryotic initiation factor (eIF)4G (Ser(1108)), which returned to basal levels within 3 h of removal of food. Likewise, meal feeding was associated with an increase in phosphorylation of eIF4E binding protein-1(4EBP1) in the gamma-form during feeding. Phosphorylation of mammalian target of rapamycin (mTOR) on Ser(2448) or Ser(2481) or 70-kDa ribosomal protein S6 kinase (S6K1) on Thr(389) was not affected by meal feeding or following removal of food. Likewise, the extent of phosphorylation of TSC2, a potential upstream regulator of mTOR, was not significantly altered during meal feeding. Phosphorylation of protein kinase B (PKB) (Thr(308)) was elevated at all time points after initiating meal feeding. Similarly, the phosphorylation of protein kinase C(PKC)-epsilon but not PKC-delta was elevated at all time points after initiating meal feeding. We conclude from these studies that meal feeding stimulates at least 2 signal pathways in cardiac muscle that raises phosphorylation of eIF4G and 4EBP1 during meal feeding and results in sustained increases in phosphorylation of PKB and PKC-epsilon.