Autophagy under glucose starvation enhances protein translation initiation in response to re-addition of glucose in C2C12 myotubes

Proteolysis is known to play a crucial role in maintaining skeletal muscle mass and function. Autophagy is a conserved intracellular process for the bulk degradation of proteins in lysosomes. Although nutrient starvation is known to induce autophagy, the effect of nutrient repletion following starvation on the mTOR pathway-mediated protein translation remains unclear. In the present study, we examined the effect of glucose starvation on the initiation of protein translation in response to glucose re-addition in C2C12 myotubes. Glucose starvation decreased the phosphorylation of p70 S6 kinase (p70S6K), a bonafide marker for protein translation initiation. Following re-addition of glucose, phosphorylation of p70S6K markedly increased only in glucose-starved cells. Inhibiting autophagy using pharmacological inhibitors diminished the effect of glucose re-addition on the phosphorylation of p70S6K, whereas inhibition of the ubiquitin-proteasome system did not exert any effect. In conclusion, autophagy under glucose starvation partially accounts for the activation of translation initiation by re-addition of glucose.