O-Linked N-acetyl-β-d-glucosamine (O-GlcNAc) is a dynamic post-translational modification that modifies and regulates over 3000 nuclear, cytoplasmic, and mitochondrial proteins. Upon exposure to stress and injury, cells and tissues increase the O-GlcNAc modification, or O-GlcNAcylation, of numerous proteins promoting the cellular stress response and thus survival. The aim of this study was to identify proteins that are differentially O-GlcNAcylated upon acute oxidative stress (HO) to provide insight into the mechanisms by which O-GlcNAc promotes survival. We achieved this goal by employing Stable Isotope Labeling of Amino Acids in Cell Culture (SILAC) and a novel "G5-lectibody" immunoprecipitation strategy that combines four O-GlcNAc-specific antibodies (CTD110.6, RL2, HGAC39, and HGAC85) and the lectin WGA. Using the G5-lectibody column in combination with basic reversed phase chromatography and C RPLC-MS/MS, 990 proteins were identified and quantified. Hundreds of proteins that were identified demonstrated increased (>250) or decreased (>110) association with the G5-lectibody column upon oxidative stress, of which we validated the O-GlcNAcylation status of 24 proteins. Analysis of proteins with altered glycosylation suggests that stress-induced changes in O-GlcNAcylation cluster into pathways known to regulate the cell's response to injury and include protein folding, transcriptional regulation, epigenetics, and proteins involved in RNA biogenesis. Together, these data suggest that stress-induced O-GlcNAcylation regulates numerous and diverse cellular pathways to promote cell and tissue survival.

Mutant KRAS drives glycolytic flux in lung cancer, potentially impacting aberrant protein glycosylation. Recent evidence suggests aberrant KRAS drives flux of glucose into the hexosamine biosynthetic pathway (HBP). HBP is required for various glycosylation processes, such as protein N- or O-glycosylation and glycolipid synthesis. However, its function during tumorigenesis is poorly understood. One contributor and proposed target of KRAS-driven cancers is a developmentally conserved epithelial plasticity program called epithelial-mesenchymal transition (EMT). Here we showed in novel autochthonous mouse models that EMT accelerated KrasG12D lung tumorigenesis by upregulating expression of key enzymes of the HBP pathway. We demonstrated that HBP was required for suppressing KrasG12D-induced senescence, and targeting HBP significantly delayed KrasG12D lung tumorigenesis. To explore the mechanism, we investigated protein glycosylation downstream of HBP and found elevated levels of O-linked β-N-acetylglucosamine (O-GlcNAcylation) posttranslational modification on intracellular proteins. O-GlcNAcylation suppressed KrasG12D oncogene-induced senescence (OIS) and accelerated lung tumorigenesis. Conversely, loss of O-GlcNAcylation delayed lung tumorigenesis. O-GlcNAcylation of proteins SNAI1 and c-MYC correlated with the EMT-HBP axis and accelerated lung tumorigenesis. Our results demonstrated that O-GlcNAcylation was sufficient and required to accelerate KrasG12D lung tumorigenesis in vivo, which was reinforced by epithelial plasticity programs.

The dynamic modification of nuclear, cytoplasmic, and mitochondrial proteins by O-linked β-N-acetyl-D-Glucosamine (O-GlcNAc) has been shown to regulate over 3,000 proteins in a manner analogous to protein phosphorylation. O-GlcNAcylation regulates the cellular stress response, the cell cycle, and is implicated in the etiology of neurodegeneration, type II diabetes, and cancer. The antibody CTD110.6 is often used to detect changes in the O-GlcNAc modification. Recently, it has been demonstrated that CTD110.6 recognizes N-linked N,N’-diacetylchitobiose, which is thought to accumulate in cells experiencing severe glucose deprivation. In this study, we have addressed two questions: 1) Which other antibodies used to detect O-GlcNAc cross-react with N-linked N,N’-diacetylchitobiose? 2) Does N-linked N,N’-diacetylchitobiose accumulate in response to other cellular stressors? To delineate between O-GlcNAc and N-linked N,N’-diacetylchitobiose, we developed a workflow that has been used to confirm the specificity of a variety of O-GlcNAc specific antibodies. Using this workflow we demonstrated that heat shock, osmotic stress, endoplasmic reticulum stress, oxidative stress, DNA damage, proteasomal inhibition, and ATP depletion induce O-GlcNAcylation but not N-linked N,N’-diacetylchitobiose. Moreover, we demonstrated that while glucose deprivation results in an induction in both O-GlcNAc and N-linked N,N’-diacetylchitobiose, the induction of N-linked N,N’-diacetylchitobiose is exacerbated by the removal of fetal bovine serum.

Objective/Hypothesis Frailty has emerged as a powerful risk stratification tool across surgical specialties; however, an analysis of the impact of frailty on outcomes following skull base surgery has not been published. The aim of this study was to assess the validity of the 5‐factor modified frailty index (mFI‐5) as a predictor of perioperative morbidity and mortality in patients undergoing skull base surgery. Methods A mFI‐5 score was calculated for patients undergoing skull base surgeries using the National Surgical Quality Improvement Program (NSQIP) database from 2005 to 2018. Multivariate logistic regression analysis was used to evaluate the association of increasing frailty with complications in the 30‐day postoperative period, with a subanalysis by operative location. Results A total of 17,912 patients who underwent skull base procedures were identified, with 45.5% of patients having a frailty score of one or greater; 44.9% were male and the mean age was 52.0 (±16.1 SD) years. Multivariable regression analysis revealed frailty to be an independent predictor of overall complications (odds ratio [OR]: 1.325, P < .001), life‐threatening complications (OR: 1.428, P < .001), and mortality (OR: 1.453, P < .001). Higher frailty also correlated with increased length of stay. When procedures were stratified by operative location, frailty correlated significantly with overall complications for middle, posterior, and multiple‐fossae operations but not the anterior fossa. Conclusions Frailty demonstrates a significant and stepwise association with life‐threatening postoperative morbidity, mortality, and length of stay following skull base surgeries. mFI‐5 is an objective and easily calculable measure of preoperative risk, which may facilitate perioperative planning and counseling regarding outcomes prior to surgery. Level of Evidence 3 Laryngoscope, 131:1977–1984, 2021