GCN2 upregulates autophagy in response to short-term deprivation of a single essential amino acid.

The ability to adapt the proteolysis rates based on fluctuations in essential amino acid (EAA) availability is essential for life. The GCN2-eIF2α-ATF4 signaling pathway is involved in the adaptive response to EAA deprivations. Our previous results demonstrated that activation of this pathway is involved in upregulating the expression of many autophagy genes at the transcriptional level thanks to the transcription factor ATF4. In the present study, we investigated whether the kinase GCN2 is also involved in early upregulation of the autophagic process in response to EAA deficiencies, thereby contributing to a rapid increase in the proteolysis rate. We observed that a one-hour leucine deprivation upregulated autophagy in both cultured cells and in vivo in mouse liver, as reflected by an increase in both [S278]-ATG16L1 phosphorylation and LC3B conversion, and decreased p62 protein level. Using cells and mice with genetic ablation of Gcn2 as well as genetic reconstitution experiments in vitro, data showed that GCN2 was required for this upregulation of autophagy. Downstream GCN2, the phosphorylation of eIF2α was necessary, while ATF4 was not. Overall, these findings revealed a major role of GCN2-eIF2α signaling in the regulation of autophagy in response to short-term EAA deprivation.