Zihao Wang

Dynamic posttranslational modification of serine and threonine residues of nucleocytoplasmic proteins by β-N-acetylglucosamine (O-GlcNAc) is a regulator of cellular processes such as transcription, signaling, and protein-protein interactions. Like phosphorylation, O-GlcNAc cycles in response to a wide variety of stimuli. Although cycling of O-GlcNAc is catalyzed by only two highly conserved enzymes, O-GlcNAc transferase (OGT), which adds the sugar, and β-N-acetylglucosaminidase (O-GlcNAcase), which hydrolyzes it, the targeting of these enzymes is highly specific and is controlled by myriad interacting subunits. Here, we demonstrate by multiple specific immunological and enzymatic approaches that histones, the proteins that package DNA within the nucleus, are O-GlcNAcylated in vivo. Histones also are substrates for OGT in vitro. We identify O-GlcNAc sites on histones H2A, H2B, and H4 using mass spectrometry. Finally, we show that histone O-GlcNAcylation changes during mitosis and with heat shock. Taken together, these data show that O-GlcNAc cycles dynamically on histones and can be considered part of the histone code.

O -linked N -acetylglucosamine ( O -GlcNAc) is a reversible posttranslational modification of Ser and Thr residues on cytosolic and nuclear proteins of higher eukaryotes catalyzed by O -GlcNAc transferase (OGT). O -GlcNAc has recently been found on Notch1 extracellular domain catalyzed by EGF domain-specific OGT. Aberrant O -GlcNAc modification of brain proteins has been linked to Alzheimer's disease (AD). However, understanding specific functions of O -GlcNAcylation in AD has been impeded by the difficulty in characterization of O -GlcNAc sites on proteins. In this study, we modified a chemical/enzymatic photochemical cleavage approach for enriching O -GlcNAcylated peptides in samples containing ∼100 μg of tryptic peptides from mouse cerebrocortical brain tissue. A total of 274 O -GlcNAcylated proteins were identified. Of these, 168 were not previously known to be modified by O -GlcNAc. Overall, 458 O -GlcNAc sites in 195 proteins were identified. Many of the modified residues are either known phosphorylation sites or located proximal to known phosphorylation sites. These findings support the proposed regulatory cross-talk between O -GlcNAcylation and phosphorylation. This study produced the most comprehensive O -GlcNAc proteome of mammalian brain tissue with both protein identification and O -GlcNAc site assignment. Interestingly, we observed O -β-GlcNAc on EGF-like repeats in the extracellular domains of five membrane proteins, expanding the evidence for extracellular O -GlcNAcylation by the EGF domain-specific OGT. We also report a GlcNAc-β-1,3-Fuc-α-1- O -Thr modification on the EGF-like repeat of the versican core protein, a proposed substrate of Fringe β-1,3- N -acetylglucosaminyltransferases.

O-GlcNAcylation on serine and threonine side chains of nuclear and cytoplasmic proteins is dynamically regulated in response to various environmental and biological stimuli. O-GlcNAcylation is remarkably similar to O-phosphorylation and appears to have a dynamic interplay with O-phosphate in cellular regulation. A systematic glycoproteomics analysis of the affects of inhibiting specific kinases on O-GlcNAcylation should help reveal both the global and specific dynamic relationships between these two abundant post-translational modifications. Here we report the O-GlcNAc perturbations in response to inhibition of glycogen synthase kinase-3 (GSK-3), a pivotal kinase involved in many signaling pathways. By combining immunoaffinity chromatography and SILAC (stable isotope labeling with amino acids in cell culture)-based quantitative mass spectrometry, we identified 45 potentially O-GlcNAcylated proteins. Quantitative measurements indicated that at least 10 proteins had an apparent increase of O-GlcNAcylation upon GSK-3 inhibition by lithium, whereas surprisingly 19 other proteins showed decreases. O-GlcNAcylation changes on a subset of the proteins were confirmed by follow-up experiments. By combining a new O-GlcNAc peptide enrichment method and beta-elimination followed by Michael addition with DTT, we also mapped the O-GlcNAc site (Ser-55) of vimentin, which showed an apparent increase of O-GlcNAcylation upon GSK-3 inhibition. Based on the MS data, we further investigated potential roles of O-GlcNAc on host cell factor-1, a transcription co-activator, and showed that dynamic regulation of O-GlcNAcylation on host cell factor-1 influenced its subcellular distribution. Taken together, these data indicated the complex interplay between phosphorylation and O-GlcNAcylation that occurs within signaling networks.

Glioblastoma (GBM) is the most malignant and lethal intracranial tumor, with extremely limited treatment options. Immunotherapy has been widely studied in GBM, but none can significantly prolong the overall survival (OS) of patients without selection. Considering that GBM cancer stem cells (CSCs) play a non-negligible role in tumorigenesis and chemoradiotherapy resistance, we proposed a novel stemness-based classification of GBM and screened out certain population more responsive to immunotherapy. The one-class logistic regression algorithm was used to calculate the stemness index (mRNAsi) of 518 GBM patients from The Cancer Genome Atlas (TCGA) database based on transcriptomics of GBM and pluripotent stem cells. Based on their stemness signature, GBM patients were divided into two subtypes via consensus clustering, and patients in Stemness Subtype I presented significantly better OS but poorer progression-free survival than Stemness Subtype II. Genomic variations revealed patients in Stemness Subtype I had higher somatic mutation loads and copy number alteration burdens. Additionally, two stemness subtypes had distinct tumor immune microenvironment patterns. Tumor Immune Dysfunction and Exclusion and subclass mapping analysis further demonstrated patients in Stemness Subtype I were more likely to respond to immunotherapy, especially anti-PD1 treatment. The pRRophetic algorithm also indicated patients in Stemness Subtype I were more resistant to temozolomide therapy. Finally, multiple machine learning algorithms were used to develop a 7-gene Stemness Subtype Predictor, which were further validated in two external independent GBM cohorts. This novel stemness-based classification could provide a promising prognostic predictor for GBM and may guide physicians in selecting potential responders for preferential use of immunotherapy.

Parkinson’s disease (PD) is the second-most common neurodegenerative disease after Alzheimer’s disease. The most important pathological feature of PD is the irreversible damage of dopamine neurons, which is related to autophagy and neuroinflammation in the substantia nigra. Previous studies found that the activation of NAcht Leucine-rich repeat Protein 3 (NLRP3) inflammasome/pyroptosis and cell division protein kinase 5 (CDK5)-mediated autophagy played an important role in PD. Bioinformatics analyses further predicted that microRNA (miR)-188-3p potentially targets NLRP3 and CDK5. Adipose-derived stem cell (ADSC)-derived exosomes were found to be excellent vectors for genetic therapy. We assessed the levels of injury, autophagy, and inflammasomes in 1-methyl-4-phenyl-1,2,4,5-tetrahydropyridine (MPTP)-induced PD mice models and neurotoxin 1-methyl-4-phenylpyridinium (MPP+)-induced cell models after treating them with miR-188-3p-enriched exosomes. miR-188-3p-enriched exosome treatment suppressed autophagy and pyroptosis, whereas increased proliferation via targeting CDK5 and NLRP3 in mice and MN9D cells. It was revealed that mir-188-3p could be a new therapeutic target for curing PD patients. Parkinson’s disease (PD) is the second-most common neurodegenerative disease after Alzheimer’s disease. The most important pathological feature of PD is the irreversible damage of dopamine neurons, which is related to autophagy and neuroinflammation in the substantia nigra. Previous studies found that the activation of NAcht Leucine-rich repeat Protein 3 (NLRP3) inflammasome/pyroptosis and cell division protein kinase 5 (CDK5)-mediated autophagy played an important role in PD. Bioinformatics analyses further predicted that microRNA (miR)-188-3p potentially targets NLRP3 and CDK5. Adipose-derived stem cell (ADSC)-derived exosomes were found to be excellent vectors for genetic therapy. We assessed the levels of injury, autophagy, and inflammasomes in 1-methyl-4-phenyl-1,2,4,5-tetrahydropyridine (MPTP)-induced PD mice models and neurotoxin 1-methyl-4-phenylpyridinium (MPP+)-induced cell models after treating them with miR-188-3p-enriched exosomes. miR-188-3p-enriched exosome treatment suppressed autophagy and pyroptosis, whereas increased proliferation via targeting CDK5 and NLRP3 in mice and MN9D cells. It was revealed that mir-188-3p could be a new therapeutic target for curing PD patients.