O-GlcNAcylation promotes fatty acid synthase activity under nutritional stress as a pro-survival mechanism in cancer cells

Protein O-GlcNAcylation is a specific form of protein glycosylation that targets a wide range of proteins with important functions. O-GlcNAcylation is known to be deregulated in cancer and has been linked to multiple aspects of cancer pathology. Despite its ubiquity and importance, the current understanding of the role of O-GlcNAcylation in the stress response remains limited. In this study, we performed a quantitative chemical proteomics-based open study of the O-GlcNAcome in HeLa cells, and identified 163 differentially-glycosylated proteins under starvation, involving multiple metabolic pathways. Among them, fatty acid metabolism was found to be targeted and subsequent analysis confirmed that fatty acid synthase (FASN) is O-GlcNAcylated. O-GlcNAcylation led to enhanced de novo fatty acid synthesis (FAS) activity, and fatty acids contributed to the cytoprotective effects of O-GlcNAcylation under starvation. Moreover, dual inhibition of O-GlcNAcylation and FASN displayed a strong synergistic effect in vitro in inducing cell death in cancer cells. Together, the results from this study provide novel insights into the role of O-GlcNAcylation in the nutritional stress response and suggest the potential of combining inhibition of O-GlcNAcylation and FAS in cancer therapy.     

Hyperglycemia and aberrant <Emphasis Type="Italic">O-GlcNAc</Emphasis>ylation: contributions to tumor progression

A number of cancer types have shown an increased prevalence and a higher mortality rate in patients with hyperglycemic associated pathologies. Although the correlation between diabetes and cancer incidence has been increasingly reported, the underlying molecular mechanisms beyond this association are not yet fully understood. Recent studies have suggested that high glucose levels support tumor progression through multiple mechanisms that are hallmarks of cancer, including cell proliferation, resistance to apoptosis, increased cell migration and invasiveness, epigenetic regulation (hyperglycemic memory), resistance to chemotherapy and altered metabolism. Most of the above occur because hyperglycemia through hexosamine biosynthetic pathway leads to aberrant O-GlcNAcylation of many intracellular proteins that are involved in those mechanisms. Deregulated O-GlcNAcylation is emerging as a general feature of cancer. Despite strong evidence suggesting that aberrant O-GlcNAcylation is or may be involved in the acquisition of all cancer hallmarks, it remains out of the list of the next generation of emerging hallmarks. Here, we discuss some of the current understanding on how hyperglycemia affects cancer cell biology and how aberrant O-GlcNAcylation stands in this context.     

O-GlcNAcylation is a novel regulator of lung and colon cancer malignancy

O-GlcNAc is a monosaccharide attached to serine or threonine hydroxyl moieties on numerous nuclear and cytoplasmic proteins; O-GlcNAcylation is dynamically regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Although recent studies have shown that O-GlcNAcylation plays essential roles in breast cancer progression, it is also necessary to know whether O-GlcNAcylation is involved in other types of human cancer. In this study, O-GlcNAcylation levels and the expressions of OGT and OGA in human lung and colon cancer tissues were examined by immunohistochemistry analysis. We found that O-GlcNAcylation as well as OGT expression was significantly elevated in the cancer tissues compared with that in the corresponding adjacent tissues. Additionally, the roles of O-GlcNAcylation in the malignancy of lung and colon cancer were investigated in vitro. The results showed that O-GlcNAcylation markedly enhanced the anchorage-independent growth of lung and colon cancer cells; O-GlcNAcylation could also enhance lung and colon cancer invasion in a context-dependent manner. All together, this study suggests that O-GlcNAcylation might play important roles in lung and colon cancer formation and progression, and may be a valuable target for diagnosis and therapy of cancer.     

O-GlcNAc修饰调控软骨及成骨分化的研究进展

O-GlcNAc糖基化属于蛋白质的翻译后修饰,参与了基因转录、信号转导、细胞分化等重要的细胞生命活动。软骨细胞与成骨细胞是骨骼系统中两种重要的细胞,它们的分化对骨的形成有重要意义。近年来研究表明O-GlcNAc糖基化通过调节多个信号通路中关键分子的活性影响软骨及成骨细胞的分化。为了更好的阐明O-GlcNAc糖基化调控软骨及成骨分化的分子机制,以期为骨关节炎、骨质疏松治疗提供新的干预靶点,我们对O-GlcNAc糖基化调控软骨及成骨分化的研究现状做如下综述。     

O-乙酰氨基葡萄糖(O-GlcNAc)修饰及其生物学功能研究进展

O-GlcNAc修饰系发生在蛋白质丝氨酸、苏氨酸羟基末端连接的乙酰氨基葡萄糖上的单糖基修饰。自1984年以来,针对O-GlcNAc糖基化修饰的研究日益升温。O-GlcNAc修饰是动态变化、可调控的,满足蛋白质翻译后修饰参与信号通路的必要条件。在多数情况下,O-GlcNAc修饰与磷酸化修饰发生在蛋白质的相同氨基酸残基上,故两种修饰之间常存在竞争性抑制,亦被称之为"阴阳"制衡。O-GlcNAc修饰参与细胞内多种信号通路的调控,调节着生长、增殖、激素响应等过程,在糖尿病、神经退行性疾病和肿瘤等代谢性疾病中扮演重要角色。探究O-GlcNAc修饰及其在生理、病理状态中的作用具有极为重要的意义。     

O-GlcNAcase is essential for embryonic development and maintenance of genomic stability

Dysregulation of O-GlcNAc modification catalyzed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) contributes to the etiology of chronic diseases of aging, including cancer, cardiovascular disease, type 2 diabetes, and Alzheimer's disease. Here we found that natural aging in wild-type mice was marked by a decrease in OGA and OGT protein levels and an increase in O-GlcNAcylation in various tissues. Genetic disruption of OGA resulted in constitutively elevated O-GlcNAcylation in embryos and led to neonatal lethality with developmental delay. Importantly, we observed that serum-stimulated cell cycle entry induced increased O-GlcNAcylation and decreased its level after release from G2/M arrest, indicating that O-GlcNAc cycling by OGT and OGA is required for precise cell cycle control. Constitutively, elevated O-GlcNAcylation by OGA disruption impaired cell proliferation and resulted in mitotic defects with downregulation of mitotic regulators. OGA loss led to mitotic defects including cytokinesis failure and binucleation, increased lagging chromosomes, and micronuclei formation. These findings suggest an important role for O-GlcNAc cycling by OGA in embryonic development and the regulation of the maintenance of genomic stability linked to the aging process.     

O-GlcNAcylation-Inducing Treatments Inhibit Estrogen Receptor α Expression and Confer Resistance to 4-OH-Tamoxifen in Human Breast Cancer-Derived MCF-7 Cells

O-GlcNAcylation (addition of N-acetyl-glucosamine on serine or threonine residues) is a post-translational modification that regulates stability, activity or localization of cytosolic and nuclear proteins. O-linked N-acetylgluocosmaine transferase (OGT) uses UDP-GlcNAc, produced in the hexosamine biosynthetic pathway to O-GlcNacylate proteins. Removal of O-GlcNAc from proteins is catalyzed by the β-N-Acetylglucosaminidase (OGA). Recent evidences suggest that O-GlcNAcylation may affect the growth of cancer cells. However, the consequences of O-GlcNAcylation on anti-cancer therapy have not been evaluated. In this work, we studied the effects of O-GlcNAcylation on tamoxifen-induced cell death in the breast cancer-derived MCF-7 cells. Treatments that increase O-GlcNAcylation (PUGNAc and/or glucosoamine) protected MCF-7 cells from death induced by tamoxifen. In contrast, inhibition of OGT expression by siRNA potentiated the effect of tamoxifen on cell death. Since the PI-3 kinase/Akt pathway is a major regulator of cell survival, we used BRET to evaluate the effect of PUGNAc+glucosamine on PIP₃ production. We observed that these treatments stimulated PIP₃ production in MCF-7 cells. This effect was associated with an increase in Akt phosphorylation. However, the PI-3 kinase inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, which abolished the effect of PUGNAc+glucosamine on Akt phosphorylation, did not impair the protective effects of PUGNAc+glucosamine against tamoxifen-induced cell death. These results suggest that the protective effects of O-GlcNAcylation are independent of the PI-3 kinase/Akt pathway. As tamoxifen sensitivity depends on the estrogen receptor (ERα) expression level, we evaluated the effect of PUGNAc+glucosamine on the expression of this receptor. We observed that O-GlcNAcylation-inducing treatment significantly reduced the expression of ERα mRNA and protein, suggesting a potential mechanism for the decreased tamoxifen sensitivity induced by these treatments. Therefore, our results suggest that inhibition of O-GlcNAcylation may constitute an interesting approach to improve the sensitivity of breast cancer to anti-estrogen therapy.     

蛋白分子O-糖基化的研究进展

蛋白分子的氧连接糖基化（O-糖基化）修饰是生物体内必不可少的转录后化学修饰之一,其作用方式类似磷酸化,并且两者之间相互作用,共同调节生物大分子的活性。O-糖基化修饰在生物体的转录、翻译、核运输、细胞骨架的形成以及调节细胞器的功能中发挥着重要的作用。通过影响细胞信号的传导,在细胞吞噬、炎性细胞的迁移以及细胞内大分子物质的循环中也起着重要作用。该文主要通过介绍蛋白分子O-糖基化修饰的基础理论以及。一糖基化修饰作用的几个方面,来简要阐述O-糖基化修饰在生物体内发挥的作用。     

O-GlcNAc修饰对蛋白质泛素化降解途径的影响

O-GlcNAc修饰是一种特殊的糖基化修饰,几乎参与生物体内所有细胞过程的调控。该修饰与泛素化作为两种重要的蛋白质翻译后修饰形式,都与2型糖尿病、神经退行性疾病、癌症等疾病密切相关。O-GlcNAc修饰对蛋白质泛素化降解途径的影响主要体现在4个方面:(1)O-GlcNAc修饰能够抑制26S蛋白酶体的ATPase活性;(2)O-GlcNAc修饰会减少某些底物蛋白的泛素化降解;(3)O-GlcNAc修饰泛素化相关酶并调节其功能;(4)某些蛋白质(包括调控因子)发生O-GlcNAc修饰后间接影响蛋白质泛素化。     

Nutrient-sensitive protein O-GlcNAcylation shapes daily biological rhythms

O-linked-N-acetylglucosaminylation (O-GlcNAcylation) is a nutrient-sensitive protein modification that alters the structure and function of a wide range of proteins involved in diverse cellular processes. Similar to phosphorylation, another protein modification that targets serine and threonine residues, O-GlcNAcylation occupancy on cellular proteins exhibits daily rhythmicity and has been shown to play critical roles in regulating daily rhythms in biology by modifying circadian clock proteins and downstream effectors. We recently reported that daily rhythm in global O-GlcNAcylation observed in Drosophila tissues is regulated via the integration of circadian and metabolic signals. Significantly, mistimed feeding, which disrupts coordination of these signals, is sufficient to dampen daily O-GlcNAcylation rhythm and is predicted to negatively impact animal biological rhythms and health span. In this review, we provide an overview of published and potential mechanisms by which metabolic and circadian signals regulate hexosamine biosynthetic pathway metabolites and enzymes, as well as O-GlcNAc processing enzymes to shape daily O-GlcNAcylation rhythms. We also discuss the significance of functional interactions between O-GlcNAcylation and other post-translational modifications in regulating biological rhythms. Finally, we highlight organ/tissue-specific cellular processes and molecular pathways that could be modulated by rhythmic O-GlcNAcylation to regulate time-of-day-specific biology.