Endoplasmic reticulum (ER) stress and autophagy are regulated by shared signaling pathways, and their dysfunction is directly related to pathological conditions. This study investigated the function of the
unc-51 like autophagy activating kinase 1 (ULK1)-autophagy related 13 (ATG13) complex in ER stress conditions through a knockout (KO) approach. Unlike other autophagy genes, KO of ULK1 or ATG13 attenuated ER stress and promoted
mammalian target of rapamycin complex 1 (
mTORC1) activation. Compared with wild type (WT) cells, ULK1 and ATG13 KO cells displayed increased viability, while
beclin 1, ATG14, and ULK1/2 KO cells did not.
Tunicamycin treatment upregulated the expression of ER stress
markers (DNA damage inducible transcript 3,
heat shock protein family A (Hsp70) member 5, and phosphorylated eukaryotic translation
initiation factor 2 alpha
kinase 3, eukaryotic translation
initiation factor 2 subunit alpha, and endoplasmic reticulum to nucleus signaling 1); however, these were decreased in ULK1 and ATG13 KO cells.
Insulin treatment upregulates the phosphorylation of
ribosomal protein S6 kinase B1 (RPS6KB1) and AKT
serine/threonine kinase 1 (AKT1), which was suppressed by
tunicamycin. Notably, ATG13 and ULK1 deficiency ameliorated
tunicamycin-induced
insulin resistance, with enhanced RPS6KB1 and AKT1 phosphorylation in KO cells compared to WT cells. Although ULK1 and ATG13 are necessary for autophagy induction after
tunicamycin-induced ER stress, autophagy does not seem to directly affect
tunicamycin-induced cell death, ER stress, or
insulin resistance. Our results indicate that loss of the ULK1-ATG13 complex attenuates ER stress and cell death and increases
mTORC1 signaling.