title: Up-regulation of O-GlcNAc transferase with glucose deprivation in HepG2 cells is mediated by decreased hexosamine pathway flux.
abstract: O-Linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification of proteins that functions as a nutrient sensing mechanism. We have previously shown a significant induction of O-GlcNAc modification under conditions of glucose deprivation. Increased O-GlcNAc modification was mediated by increased mRNA for nucleocytoplasmic O-linked N-acetylglucosaminyltransferase (ncOGT). We have investigated the mechanism mediating ncOGT induction with glucose deprivation. The signal does not appear to be general energy depletion because no differences in AMP-dependent kinase protein levels or phosphorylation were observed between glucose-deprived and normal glucose-treated cells. However, treatment of glucose-deprived cells with a small dose (1 mm) of glucosamine blocked the induction of ncOGT mRNA and subsequent increase in O-GlcNAc protein modification, suggesting that decreased hexosamine flux is the signal for ncOGT up-regulation. Consistent with this, treatment of glucose-deprived cells with an inhibitor of O-GlcNAcase (O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenyl carbamat) completely prevented the subsequent up-regulation of ncOGT. Glucosamine treatment also resulted in a 40% rescue of the down-regulation of glycogen synthase activity normally seen after glucose deprivation. We conclude that deglycosylation of proteins within the first few hours of glucose deprivation promotes ncOGT induction. These findings suggest a novel negative feedback regulatory loop for OGT and O-GlcNAc regulation.
authors.affiliation: Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84132, USA.
authors.forename: Rodrick P
authors.initials: RP
authors.lastname: Taylor
authors.forename: Taylor S
authors.initials: TS
authors.lastname: Geisler
authors.forename: Jefferson H
authors.initials: JH
authors.lastname: Chambers
authors.forename: Donald A
authors.initials: DA
authors.lastname: McClain
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000117:Acetylglucosamine / Q000378:metabolism* / Q000494:pharmacology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology; D003593:Cytoplasm / Q000201:enzymology; D004790:Enzyme Induction / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D006006:Glycogen Synthase / Q000096:biosynthesis; D006801:Humans; D017351:N-Acetylglucosaminyltransferases / Q000096:biosynthesis*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D012333:RNA, Messenger; D017351:N-Acetylglucosaminyltransferases; C063057:UDP-N-acetylglucosamine-peptide beta-N-acetylglucosaminyltransferase; D006006:Glycogen Synthase; D055372:AMP-Activated Protein Kinases; D005947:Glucose; D000117:Acetylglucosamine