Inhibition of mTOR affects protein stability of OGT

• Published in: Biochemical and biophysical research communications Vol. 453; no. 2; pp. 208 - 212
• Main Authors: Park, S, Pak, J, Jang, I, Cho, JW
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 17.10.2014
• Subjects: Acetylglucosamine - metabolism; Animals; Autophagy; Autophagy - drug effects; Autophagy - physiology; beta-N-Acetylhexosaminidases - metabolism; Enzyme Stability; Hep G2 Cells; Humans; Indoles - pharmacology; Mice; mTOR inhibitor; N-Acetylglucosaminyltransferases - chemistry; N-Acetylglucosaminyltransferases - metabolism; Naphthyridines - pharmacology; O-GlcNAc; OGT; Proteasomal degradation; Proteasome Endopeptidase Complex - metabolism; Protein Kinase Inhibitors - pharmacology; Protein stability; Purines - pharmacology; TOR Serine-Threonine Kinases - antagonists & inhibitors; Proteasomal degradation; mTOR inhibitor; Protein stability; O-GlcNAc; OGT; Autophagy
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2014.05.047

•Protein O-GlcNAc modification decreases in PP242 or Torin1 treatment.•Protein level of OGT and OGA changes in opposite directions under mTOR inhibition.•OGT protein increases in Atg knockdown.•Inhibition of autophagy or proteasome restores OGT protein in HepG2 cells. Autophagy regulates cellular homeostasis through degradation of aged or damaged subcellular organelles and components. Interestingly, autophagy-deficient beta cells, for example Atg7-mutant mice, exhibited hypoinsulinemia and hyperglycemia. Also, autophagy response is diminished in heart of diabetic mice. These results implied that autophagy and diabetes are closely connected and affect each other. Although protein O-GlcNAcylation is up-regulated in hyperglycemia and diabetes, and O-GlcNAcylated proteins play an important role in metabolism and nutrient sensing, little is known whether autophagy affects O-GlcNAc modification and vice versa. In this study, we suppressed the action of mTOR by treatment of mTOR catalytic inhibitors (PP242 and Torin1) to induce autophagic flux. Results showed a decrease in global O-GlcNAcylation, which is due to decreased OGT protein and increased OGA protein. Interestingly, knockdown of ATG genes or blocking of lysosomal degradation enhanced protein stability of OGT. In addition, when proteasomal inhibitor was treated together with mTOR inhibitor, protein level of OGT almost recovered to control level. These data suggest that mTOR inhibition is a more efficient way to reduce protein level of OGT rather than that of CHX treatment. We also showed that not only proteasomal degradation regulated OGT stability but autophagic degradation also affected OGT stability in part. We concluded that mTOR signaling regulates protein O-GlcNAc modification through adjustment of OGT stability.