O⁃GlcNAcylation in Regulating Inflammatory Signaling Pathways / 中国生物化学与分子生物学报

O⁃GlcNAcylation is an O⁃linked⁃β⁃N⁃acetylglucosamine modification attached to the hydroxyl group of serine or threonine residue within the nuclear or cytoplasmic proteins. O⁃GlcNAcylation profoundly influences important biological events, including kinase activity, transcription and translation, and protein degradation. However, there are few summarized reviews on how O⁃GlcNAcylation modulates signaling pathways associated with inflammatory responses. Due to the attachment and removal of the sugar group catalyzed by O⁃GlcNAc transferase and O⁃GlcNAcase, O⁃GlcNAcylation cycles rapidly with a short half⁃life time (within minutes). Therefore, O⁃GlcNAcylation plays a crucial role in various signaling pathways via intricate cross⁃talking with other post⁃translational modifications of protein, such as phosphorylation, acetylation, ubiquitylation, and methylation. Currently, most researchers focused on the Toll⁃like receptor (TLR)⁃initiated NF⁃κB signaling when it comes to the relationship between O⁃GlcNAcylation and inflammation. Evidence has shown that O⁃GlcNAcylation at T352 or at T305 on p65 promotes its nuclear translocation activity, while O⁃GlcNAcylation at S536 blocks the activation of p65 by competing with phosphorylation. Meanwhile, O⁃GlcNAcylation modulates upstream and downstream regulators of NF⁃κB and then governs the polarization of M1/ M2 macrophage and the progress of inflammation reactions. Furthermore, O⁃GlcNAcylation indirectly participates in the kinase activation of MAPKs by interfering with the proteins at the upper reaches (i. e. MEK2 and Ras proteins). Besides, O⁃GlcNAcylation has a profound influence on multiple kinases of PI3K/ AKT signaling. Nevertheless, O⁃GlcNAcylation manipulates inflammation⁃associated transcriptional factors on the JAK/ STAT pathway. Comparatively, the involved signaling transduction for the inflammatory response in vivo is far more complicated and multidimensional than that in vitro. And O⁃GlcNAcylation is widely involved with the onset and development of inflammatory diseases located at the pancreas, liver, lung, gut, and adipose tissues. Novel research has firstly found that gut bacteria expressing O⁃GlcNAcase⁃like hydrolases exert potent prevention on mouse colitis induced by different chemical drugs, which indicates the mediating role of O⁃GlcNAcylation in mutual interactions between gut microbiota and host inflammation. In summary, recent findings provided a novel strategy for preventing and treating inflammatory diseases by targeting O⁃GlcNAcylation.

Loss of O-GlcNAcylation on MeCP2 at Threonine 203 Leads to Neurodevelopmental Disorders / 神经科学通报·英文版

Mutations of the X-linked methyl-CpG-binding protein 2 (MECP2) gene in humans are responsible for most cases of Rett syndrome (RTT), an X-linked progressive neurological disorder. While genome-wide screens in clinical trials have revealed several putative RTT-associated mutations in MECP2, their causal relevance regarding the functional regulation of MeCP2 at the etiologic sites at the protein level requires more evidence. In this study, we demonstrated that MeCP2 was dynamically modified by O-linked-β-N-acetylglucosamine (O-GlcNAc) at threonine 203 (T203), an etiologic site in RTT patients. Disruption of the O-GlcNAcylation of MeCP2 specifically at T203 impaired dendrite development and spine maturation in cultured hippocampal neurons, and disrupted neuronal migration, dendritic spine morphogenesis, and caused dysfunction of synaptic transmission in the developing and juvenile mouse cerebral cortex. Mechanistically, genetic disruption of O-GlcNAcylation at T203 on MeCP2 decreased the neuronal activity-induced induction of Bdnf transcription. Our study highlights the critical role of MeCP2 T203 O-GlcNAcylation in neural development and synaptic transmission potentially via brain-derived neurotrophic factor.

O-GlcNAcylation in Ventral Tegmental Area Dopaminergic Neurons Regulates Motor Learning and the Response to Natural Reward / 神经科学通报·英文版

Protein O-GlcNAcylation is a post-translational modification that links environmental stimuli with changes in intracellular signal pathways, and its disturbance has been found in neurodegenerative diseases and metabolic disorders. However, its role in the mesolimbic dopamine (DA) system, especially in the ventral tegmental area (VTA), needs to be elucidated. Here, we found that injection of Thiamet G, an O-GlcNAcase (OGA) inhibitor, in the VTA and nucleus accumbens (NAc) of mice, facilitated neuronal O-GlcNAcylation and decreased the operant response to sucrose as well as the latency to fall in rotarod test. Mice with DAergic neuron-specific knockout of O-GlcNAc transferase (OGT) displayed severe metabolic abnormalities and died within 4-8 weeks after birth. Furthermore, mice specifically overexpressing OGT in DAergic neurons in the VTA had learning defects in the operant response to sucrose, and impaired motor learning in the rotarod test. Instead, overexpression of OGT in GABAergic neurons in the VTA had no effect on these behaviors. These results suggest that protein O-GlcNAcylation of DAergic neurons in the VTA plays an important role in regulating the response to natural reward and motor learning in mice.

Exercise and Alzheimer's Disease: A Review of Research Based on Post￣translational Modification of Tau Protein / 中国生物化学与分子生物学报

Alzheimer' s disease (AD) is an age-related neurodegenerative disease which seriously damages the physical and mental health of the elderly and causes huge economic pressure to the society. However, the pathogenesis of AD is not completely elucidated. There is still no effective drug to cure AD in clinical practice. Tau protein is a soluble and non-aggregating microtubule-related protein, which can stabilize microtubule structure. The structure and function of Tau protein are abnormal in AD' s brain while under pathological conditions, and the abnormal Tau protein aggregates to insoluble neurofibrillary tangles which damages microtubules and leads to cognitive dysfunction. These changes of Tau protein are regulated by a variety of post-translational modifications, which directly change the properties and functions of proteins by attaching specific chemical moieties to Tau protein's C-terminus or N-terminus. It's confirmed that a variety of Tau post-translational modifications, like phosphorylation, glycosylation, acetylation and sumoylation is abnormal in AD's brain, which is closely related to Tau degradation and the accumulation of toxic substances. In this review, we summarized the latest progress supporting the role of exercise regulated Tau post-translational modification in the prevention and treatment of Alzheimer's disease. Firstly, exercise inhibits tau protein hyperphosphorylation by suppressing the activity of GSK-3β and MAPKs and possibly by up-regulating the activity of PP2A. Secondly, exercise increases tau protein O-GlcNAcylation by up-regulating the expression of GLUT1 and GLUT3, also possibly by regulating the balance of activity of OGT and OGA. Thirdly, exercise decreases tau protein acetylation possibly by inhibiting p300 and activating SIRT1; exercise regulates the acetylation of Tau KXGS possibly by inhibiting HDAC6. Lastly, exercise inhibits abnormal Tau sumoylation possibly by regulating the co-location sites of phosphorylation and sumoylation.

Advances of relationship between protein O-GlcNAcylation and glucose metabolism in tumors / 中国药科大学学报

@#O-GlcNAcylation is the addition of a single N-acetylglucosamine(GlcNAc)moiety to the hydroxyl groups of serine or threonine residues of nuclear and cytoplasmic proteins. The transcription factors, kinases of the metabolic pathways and some cytoplasmic enzymes can be O-GlcNAcylated to affect cell transcription, signal transduction, cell metabolism and other biological functions. Abnormal glucose metabolism of tumors has been a hotspot in the research field of tumor pathogenesis and therapeutic targets recently. O-GlcNAclation regulates the glucose metabolism of tumor by affecting the activity of kinases in the metabolic pathway, which is closely associated with the abnormal glucose metabolism of tumor. The abnormal O-GlcNAcylation is one of the potential reasons of cancer. In this review, in order to provide a theoretical reference for developing anti-tumor targets and drugs targeting O-GlcNAc modification, we briefly summarized how O-GlcNAcylation regulated glucose metabolism on glucose metabolism, glucose uptake, glycolysis, pentose phosphate pathway and tricarboxylic acid cycle in cancer cell.

O-GlcNAcylation, a sweet link to the pathology of diseases / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

O-linked N-acetylglucosamine (O-GlcNAc) is a dynamic post-translational modification occurring on myriad proteins in the cell nucleus, cytoplasm, and mitochondria. The donor sugar for O-GlcNAcylation, uridine-diphosphate N-acetylglucosamine (UDP-GlcNAc), is synthesized from glucose through the hexosamine biosynthetic pathway (HBP). The recycling of O-GlcNAc on proteins is mediated by two enzymes in cells—O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and removal of O-GlcNAc, respectively. O-GlcNAcylation is involved in a number of important cell processes including transcription, translation, metabolism, signal transduction, and apoptosis. Deregulation of O-GlcNAcylation has been reported to be associated with various human diseases such as cancer, diabetes, neurodegenerative diseases, and cardiovascular diseases. A better understanding of the roles of O-GlcNAcylation in physiopathological processes would help to uncover novel avenues for therapeutic intervention. The aim of this review is to discuss the recent updates on the mechanisms and impacts of O-GlcNAcylation on these diseases, and its potential as a new clinical target.

O-GlcNAcylation, a sweet link to the pathology of diseases / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

O-linked N-acetylglucosamine (O-GlcNAc) is a dynamic post-translational modification occurring on myriad proteins in the cell nucleus, cytoplasm, and mitochondria. The donor sugar for O-GlcNAcylation, uridine-diphosphate N-acetylglucosamine (UDP-GlcNAc), is synthesized from glucose through the hexosamine biosynthetic pathway (HBP). The recycling of O-GlcNAc on proteins is mediated by two enzymes in cells-O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and removal of O-GlcNAc, respectively. O-GlcNAcylation is involved in a number of important cell processes including transcription, translation, metabolism, signal transduction, and apoptosis. Deregulation of O-GlcNAcylation has been reported to be associated with various human diseases such as cancer, diabetes, neurodegenerative diseases, and cardiovascular diseases. A better understanding of the roles of O-GlcNAcylation in physiopathological processes would help to uncover novel avenues for therapeutic intervention. The aim of this review is to discuss the recent updates on the mechanisms and impacts of O-GlcNAcylation on these diseases, and its potential as a new clinical target.

Quercetin induces cell death in cervical cancer by reducing O-GlcNAcylation of adenosine monophosphate-activated protein kinase / 대한해부학회지

Hyper-O-GlcNAcylation is a general feature of cancer which contributes to various cancer phenotypes, including cell proliferation and cell growth. Quercetin, a naturally occurring dietary flavonoid, has been reported to reduce the proliferation and growth of cancer. Several reports of the anticancer effect of quercetin have been published, but there is no study regarding its effect on O-GlcNAcylation. The aim of this study was to investigate the anticancer effect of quercetin on HeLa cells and compare this with its effect on HaCaT cells. Cell viability and cell death were determined by MTT and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling assays. O-GlcNAcylation of AMP-activated protein kinase (AMPK) was examined by succinylated wheat germ agglutinin pulldown and immunoprecipitation. Immunofluorescence staining was used to detect the immunoreactivitiy of O-linked N-acetylglucosamine transferase (OGT) and sterol regulatory element binding protein 1 (SREBP-1). Quercetin decreased cell proliferation and induced cell death, but its effect on HaCaT cells was lower than that on HeLa cells. O-GlcNAcylation level was higher in HeLa cells than in HaCaT cells. Quercetin decreased the expression of global O-GlcNAcylation and increased AMPK activation by reducing the O-GlcNAcylation of AMPK. AMPK activation due to reduced O-GlcNAcylation of AMPK was confirmed by treatment with 6-diazo-5-oxo-L-norleucine. Our results also demonstrated that quercetin regulated SREBP-1 and its transcriptional targets. Furthermore, immunofluorescence staining showed that quercetin treatment decreased the immunoreactivities of OGT and SREBP-1 in HeLa cells. Our findings demonstrate that quercetin exhibited its anticancer effect by decreasing the O-GlcNAcylation of AMPK. Further studies are needed to explore how quercetin regulates O-GlcNAcylation in cancer.

PPP2R2A binds and dephosphorylates GFPT2 in breast cancer cells / 生物工程学报

PPP2R2A is one of the regulatory subunits of the PP2A phosphatase complexes, and previous studies showed that its upregulation promotes cancer cell survival and growth. In this research, we used the tandem affinity purification and the HPLC-Chip-ESI/MS/MS mass spectrometry to screen the PPP2R2A-binding proteins and the results indicated that the GFPT-1/-2 were the potential partners of PPP2R2A. We further validated the interaction between PPP2R2A and GFPT-1/-2 through GST Pull-down, co-immunoprecipitation and immunofluorescence assays. And we found that knockdown of PPP2R2A by lentivirus-mediated shRNA enhanced the phosphorylation of GFPT2, whereas the phosphorylation of GFPT1 had no significant change. GFPT2 is a rate-limiting enzyme in the hexosamine pathway. Our results showed that the knockdown of PPP2R2A promoted the total cellular O-GlcNAcylation in MDA-MB-231 breast cancer cells. These results suggest that PPP2R2A interacts with GFPT1/2, and leads to the phosphorylation of GFPT2, which can regulate the cellular O-GlcNAcylation.

Potential coordination role between O-GlcNAcylation and epigenetics

Dynamic changes of the post-translational O-GlcNAc modification (O-GlcNAcylation) are controlled by O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) and the glycoside hydrolase O-GlcNAcase (OGA) in cells. O-GlcNAcylation often occurs on serine (Ser) and threonine (Thr) residues of the specific substrate proteins via the addition of O-GlcNAc group by OGT. It has been known that O-GlcNAcylation is not only involved in many fundamental cellular processes, but also plays an important role in cancer development through various mechanisms. Recently, accumulating data reveal that O-GlcNAcylation at histones or non-histone proteins can lead to the start of the subsequent biological processes, suggesting that O-GlcNAcylation as 'protein code' or 'histone code' may provide recognition platforms or executive instructions for subsequent recruitment of proteins to carry out the specific functions. In this review, we summarize the interaction of O-GlcNAcylation and epigenetic changes, introduce recent research findings that link crosstalk between O-GlcNAcylation and epigenetic changes, and speculate on the potential coordination role of O-GlcNAcylation with epigenetic changes in intracellular biological processes.

Effects of O-GlcNAcylation modification and Akt1 on proliferation and invasion of gastric cancer cells / 重庆医学

Objective To study the influence of O-GlcNAcylation on on proliferation and invasion of gastric cancer cells and evaluate the role of Aktl on O-GlcNAcylation promotting cells proliferation and invasion in gastric cancer.Methods Build the cell model:O-GlcNAc glycosylation levels rise or fall.The cell viability was determine by MTT.To investigate whether O-GlcNAcylation affected colony formation ability of gastric cancer cells,soft agar colony assays were carried out.Cell migration or invasion was using transwell chambers.The expression of Akt1 was detected through Western blot.Thiamet-G was used to eualuate the role of Akt1 on O-Gcnac cylation regulating invasion in gastric Cancei.Results O-GlcNAcylation was increased the gastric cancer cells proliferation ability,colony formation ability,migration and invasion ability in vitro.Akt1 was activated by Ser473 phosphorylation upregulation though O-GlcNAcylation.Akt1 shRNA was inhibition the cell invasive which induced by Thiamet-G.Akt1 overexpression was promoted by Thiamet-G-induced cell invasion.Conclusion O-GlcNAcylation enhanced oncogenic phenotypes possibly partially involving Akt1.

Vascular O-GlcNAcylation augments reactivity to constrictor stimuli by prolonging phosphorylated levels of the myosin light chain

O-GlcNAcylation is a modification that alters the function of numerous proteins. We hypothesized that augmented O-GlcNAcylation levels enhance myosin light chain kinase (MLCK) and reduce myosin light chain phosphatase (MLCP) activity, leading to increased vascular contractile responsiveness. The vascular responses were measured by isometric force displacement. Thoracic aorta and vascular smooth muscle cells (VSMCs) from rats were incubated with vehicle or with PugNAc, which increases O-GlcNAcylation. In addition, we determined whether proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation. PugNAc enhanced phenylephrine (PE) responses in rat aortas (maximal effect, 14.2±2 vs 7.9±1 mN for vehicle, n=7). Treatment with an MLCP inhibitor (calyculin A) augmented vascular responses to PE (13.4±2 mN) and abolished the differences in PE-response between the groups. The effect of PugNAc was not observed when vessels were preincubated with ML-9, an MLCK inhibitor (7.3±2 vs 7.5±2 mN for vehicle, n=5). Furthermore, our data showed that differences in the PE-induced contractile response between the groups were abolished by the activator of AMP-activated protein kinase (AICAR; 6.1±2 vs 7.4±2 mN for vehicle, n=5). PugNAc increased phosphorylation of myosin phosphatase target subunit 1 (MYPT-1) and protein kinase C-potentiated inhibitor protein of 17 kDa (CPI-17), which are involved in RhoA/Rho-kinase-mediated inhibition of myosin phosphatase activity. PugNAc incubation produced a time-dependent increase in vascular phosphorylation of myosin light chain and decreased phosphorylation levels of AMP-activated protein kinase, which decreased the affinity of MLCK for Ca2+/calmodulin. Our data suggest that proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation, favoring vascular contraction.

A Role for Timely Nuclear Translocation of Clock Repressor Proteins in Setting Circadian Clock Speed

By means of a circadian clock system, all the living organisms on earth including human beings can anticipate the environmental rhythmic changes such as light/dark and warm/cold periods in a daily as well as in a yearly manner. Anticipating such environmental changes provide organisms with survival benefits via manifesting behavior and physiology at an advantageous time of the day and year. Cell-autonomous circadian oscillators, governed by transcriptional feedback loop composed of positive and negative elements, are organized into a hierarchical system throughout the organisms and generate an oscillatory expression of a clock gene by itself as well as clock controlled genes (ccgs) with a 24 hr periodicity. In the feedback loop, hetero-dimeric transcription factor complex induces the expression of negative regulatory proteins, which in turn represses the activity of transcription factors to inhibit their own transcription. Thus, for robust oscillatory rhythms of the expression of clock genes as well as ccgs, the precise control of subcellular localization and/or timely translocation of core clock protein are crucial. Here, we discuss how sub-cellular localization and nuclear translocation are controlled in a time-specific manner focusing on the negative regulatory clock proteins.

Synapsin-1 and tau reciprocal O-GlcNAcylation and phosphorylation sites in mouse brain synaptosomes

O-linked N-acetylglucosamine (O-GlcNAc) represents a key regulatory post-translational modification (PTM) that is reversible and often reciprocal with phosphorylation of serine and threonine at the same or nearby residues. Although recent technical advances in O-GlcNAc site-mapping methods combined with mass spectrometry (MS) techniques have facilitated study of the fundamental roles of O-GlcNAcylation in cellular processes, an efficient technique for examining the dynamic, reciprocal relationships between O-GlcNAcylation and phosphorylation is needed to provide greater insights into the regulatory functions of O-GlcNAcylation. Here, we describe a strategy for selectively identifying both O-GlcNAc- and phospho-modified sites. This strategy involves metal affinity separation of O-GlcNAcylated and phosphorylated peptides, beta-elimination of O-GlcNAcyl or phosphoryl functional groups from the separated peptides followed by dithiothreitol (DTT) conjugation (BEMAD), affinity purification of DTT-conjugated peptides using thiol affinity chromatography, and identification of formerly O-GlcNAcylated or phosphorylated peptides by MS. The combined metal affinity separation and BEMAD approach allows selective enrichment of O-GlcNAcylated peptides over phosphorylated counterparts. Using this approach with mouse brain synaptosomes, we identified the serine residue at 605 of the synapsin-1 peptide, 603QASQAGPGPR612, and the serine residue at 692 of the tau peptide, 688SPVVSGDTSPR698, which were found to be potential reciprocal O-GlcNAcylation and phosphorylation sites. These results demonstrate that our strategy enables mapping of the reciprocal site occupancy of O-GlcNAcylation and phosphorylation of proteins, which permits the assessment of cross-talk between these two PTMs and their regulatory roles.