• Parasites, Hosts and Diseases
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• 제59권5호
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• pp.501-505
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• 2021

The pathogenic free-living amoeba Naegleria fowleri causes primary amoebic meningoencephalitis, a fatal infection, by penetrating the nasal mucosa and migrating to the brain via the olfactory nerves. N. fowleri can induce host cell death via lytic necrosis. Similar to phosphorylation, O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation (O-GlcNAcylation) is involved in various cell-signaling processes, including apoptosis and proliferation, with O-GlcNAc addition and removal regulated by O-GlcNAc transferase and O-GlcNAcase (OGA), respectively. However, the detailed mechanism of host cell death induced by N. fowleri is unknown. In this study, we investigated whether N. fowleri can induce the modulation of O-GlcNAcylated proteins during cell death in Jurkat T cells. Co-incubation with live N. fowleri trophozoites increased DNA fragmentation. In addition, incubation with N. fowleri induced a dramatic reduction in O-GlcNAcylated protein levels in 30 min. Moreover, pretreatment of Jurkat T cells with the OGA inhibitor PUGNAc prevented N. fowleri-induced O-deGlcNAcylation and DNA fragmentation. These results suggest that O-deGlcNAcylation is an important signaling process that occurs during Jurkat T cell death induced by N. fowleri.

• Anatomy and Cell Biology
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• 제51권4호
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• pp.274-283
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• 2018

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.

• BMB Reports
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• 제40권6호
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• pp.1058-1068
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• 2007

The post-translational modifications of Ser and Thr residues by O-linked $\beta$-N-acetylglucosamine (O-GlcNAc), i.e., O-GlcNAcylation, is considered a key means of regulating signaling, in a manner analogous to protein phosphorylation. Furthermore, it has been suggested that the increased flux of glucose through the hexosamine biosynthetic pathway (HBP) stimulates O-GlcNAcylation, and that this may be responsible for many of the manifestations of type 2 diabetes mellitus. To determine whether excessive O-GlcNAcylation of target proteins results in pancreatic $\beta$ cell dysfunction, we increased nucleocytoplasmic protein O-GlcNAcylation levels in $\beta$ cells by exposing them to streptozotocin and/or glucosamine. Streptozotocin and glucosamine co-treatment increased O-GlcNAcylated proteomic patterns as assessed by immunoblotting, and these increases in nuclear and cytoplasmic protein O-GlcNAcylations were accompanied by impaired insulin secretion and enhanced apoptosis in pancreatic $\beta$ cells. This observed $\beta$cell dysfunction prompted us to examine Akt and Bcl-2 family member proteins to determine which proteins are O-GlcNAcylated under conditions of high HBP throughput, and how these proteins are associated with $\beta$ cell apoptosis. Eventually, we identified ten new O-GlcNAcylated proteins that were expressed during $\beta$ cell apoptosis, and analyzed the functional implications of these proteins in relation to pancreatic $\beta$ cell dysfunction.

• Molecules and Cells
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• 제40권7호
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• pp.476-484
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• 2017

C-X-C chemokine receptor 4 (CXCR4) stimulates cancer metastasis. NF-${\kappa}B$ regulates CXCR4 expression in cancer cells, and O-GlcNAc modification of NF-${\kappa}B$ promotes its transcriptional activity. Here, we determined whether CXCR4 expression is affected by O-GlcNAcylation of NF-${\kappa}B$ in lung metastasis of cervical cancer. We found elevated levels of O-linked-N-actylglucosamine transferase (OGT) and O-GlcNAcylation in cervical cancer cells compared to those in non-malignant epithelial cells and detected increased expression of NF-${\kappa}B$ p65 (p65) and CXCR4 in cervical cancer cells. Knockdown of OGT inhibited the O-GlcNAcylation of p65 and decreased CXCR4 expression levels in HeLa cells. Thiamet G treatment increased O-GlcNAcylated p65, which subsequently enhanced CXCR4 expression levels. Inhibition of O-GlcNAcylation by 6-Diazo-5-oxo-L-norleucine (DON) treatment decreased p65 activation, eventually inhibiting CXCR4 expression in HeLa cells. Lung tissues from mice engrafted with OGT-knockdown HeLa cells (shOGT) exhibited lower expression of Ki-67 and HPV E6 and E7 oncogenes compared to lung tissues from mice engrafted with control HeLa cells (shCTL). In addition, lung tissues from mice engrafted with shOGT cells exhibited lower p65 and CXCR4 immunoreactivity compared to tissues from mice engrafted with shCTL cells. Taken together, our data suggest that p65 O-GlcNAcylation promotes lung metastasis of cervical cancer cells by activating CXCR4 expression.

• 생명과학회지
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• 제23권4호
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• pp.586-594
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• 2013

단백질 번역 후 O-GlcNAc 수식은 단백질 조절의 새로운 기전으로 대두되고 있다. 전통적인 당수식과 달리 O-GlcNAc 수식은 단 한번의 O-GlcNAc 전달로 이루어지며, 핵 및 세포질단백질 모두에 수식될 수 있다. O-GlcNAc은 이 분자를 끝으로 하는 최종수식으로 생각되어 왔으나, 최근의 논문(J Proteome Res. 2011 10:2725-2733)은 AP180 단백질에 O-GlcNAc-P가 존재함을 보고하였다. 이 논문은 O-GlcNAc-P가 일반적인 단백질수식인지에 대한 중요한 질문을 던진다. 이에 답하고자 저자들은 HEK293T 세포에 O-GlcNAc 인산화효소 NAGK를 DsRed2에 연결한 DsRed2-$NAGK_{WT}$ 혹은 효소활성이 없는 돌연변이 NAGK를 표현하는 DsRed2-$NAGK_{D107A}$를 표현시키고, 단백질 추출물을 얻어 2D-PAGE로 분리한 후 인산화 정도를 측정하여, $NAGK_{WT}$에 의하여 인산화가 증가되는 15개의 단백질 스폿을 선별하였다. 이 가운데 7개 스팟을 동정한 결과 2개의 스폿은 O-GlcNAc 수식 단백질인 $HSP90{\beta}$, 다른 2개의 스폿도 O-GlcNAc 수식 단백질인 ENO1로 동정되었으며, 나머지(dUTP nucleotidohydrolase mitochondrial isoform 2, glutathione S-transferase P, grp94)는 O-GlcNAc 수식 여부를 아직 모르는 단백질이였다. NAGK에 의하여 O-GlcNAc 단백질의 인산화가 증가된다는 사실은 O-GlcNAc이 인산화되어 O-GlcNAc-P로 수식됨을 시사하며, 따라서 본 연구의 결과는 O-GlcNAc이 최종 수식이 아님을 지지한다.

• 생명과학회지
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• 제23권2호
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• pp.324-331
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• 2013

O-GlcNAc 화(O-GlcNAcylation)는 단백질의 serine이나 threonine에 N-acetylglucosamine (GlcNAc) 분자가 결합하는 것으로, 기존의 당단백질과 달리 세포질 및 핵단백질 모두에 일어난다. 또한 수정의 속도가 빠르고 가역적으로 일어남이 인산화 수식과 유사하다. 그러나 수많은 인산화효소와 탈인산화효소가 관여하는 것과 달리 O-GlcNAc 수식은 O-GlcNAc transferase (OGT)와 O-GlcNAcase (OGA) 단 두 개의 효소에 의하여 이루어진다. 이러한 단순한 조절기전은 세포가 내외환경에 즉시 적응할 수 있도록 진화한 것으로 해석된다. 즉, O-GlcNAc 수식은 특정한 단백질 하나 하나의 활성을 켜거나 끄는 것이 아니라, 세포의 신호전달과정의 효율을 전반적으로 조절하는 '가변저항기(rheostat)' 역할을 한다. O-GlcNAc 수식은 흔히 같은 아미노산 혹은 그 주변의 아미노산이 인산화되는 것을 수반하는데, 이는 인산화와 함께 서로 조화를 이루어 세포활성을 조절하는 것으로 해석된다. 최근 O-GlcNAc이 더 나아가 O-GlcNAc-P로 인산화될 가능성이 제시되고 있는 바, 본 총설에서는 이의 가능성을 이론적으로 설명하고, 실제 실험결과를 소개한다.

• BMB Reports
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• 제47권10호
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• pp.593-598
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• 2014

RNA polymerase II carboxyl-terminal domain (RNAPII CTD) phosphatases are responsible for the dephosphorylation of the C-terminal domain of the small subunit of RNAPII in eukaryotes. Recently, we demonstrated the identification of several interacting partners with human small CTD phosphatase1 (hSCP1) and the substrate specificity to delineate an appearance of the dephosphorylation catalyzed by SCP1. In this study, using the established cells for inducibly expressing hSCP1 proteins, we monitored the modification of ${\beta}$-O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAcylation is one of the most common post-translational modifications (PTMs). To gain insight into the PTM of hSCP1, we used the Western blot, immunoprecipitation, succinylayed wheat germ agglutinin-precipitation, liquid chromatography-mass spectrometry analyses, and site-directed mutagenesis and identified the $Ser^{41}$ residue of hSCP1 as the O-GlcNAc modification site. These results suggest that hSCP1 may be an O-GlcNAcylated protein in vivo, and its N-terminus may function a possible role in the PTM, providing a scaffold for binding the protein(s).

• BMB Reports
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• 제44권6호
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• pp.415-420
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• 2011

Diabetes is a well-known independent risk factor for vascular disease. However, its underlying mechanism remains unclear. It has been reported that increased influx of the hexosamine biosynthesis pathway (HBP) induces O-GlcNAcylation of proteins, leading to insulin resistance. In this study, we determined whether or not O-GlcNAc modification of proteins could increase vessel contraction. Using an endothelium-denuded aortic ring, we observed that glucosamine induced OGlcNAcylation of proteins and augmented vessel contraction stimulated by U46619, a thromboxane $A_2$ agonist, via augmentation of the phosphorylation of MLC20$MLC_{20}$, MYPT1(Thr855), and CPI17, but not phenylephrine. Pretreatment with OGT inhibitor significantly ameliorated glucosamine-induced vessel constriction. Glucosamine treatment also increased RhoA activity, which was also attenuated by OGT inhibitor. In conclusion, glucosamine, a product of glucose influx via the HBP in a diabetic state, increases vascular contraction, at least in part, through activation of the RhoA/Rho kinase pathway, which may be due to O-GlcNAcylation.

• 한국미생물학회:학술대회논문집
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• 한국미생물학회 2004년도 International Meeting of the Microbiological Society of Korea
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• pp.65-67
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• 2004

O-GlcNAcylation of p53 has been already identified and reported, but the function of O-GlcNAc on p53 has not been studied well. In this report, the general function of O-GlcNAc modification on p53 has been investigated using mouse fibroblast cell, L929. When streptozotocin (STZ), a non-competitive O-GlcNAcase inhibitor was treated to L929, O-GlcNAc modification level was dramatically increased on nucleocytoplasmic proteins, including p53. Because it has been already reported that $TNF\alpha$ induced the production of p53 in L929, $TNF\alpha$ was treated to obtain more p53. Approximately two times more amount of p53 was found from the cells treated STZ and $TNF\alpha$ simultaneously compared to the cell treated $TNF\alpha$ alone. The p53 increment in the presence of STZ was not caused by the induction of p53 gene expression. When new production of p53 induced by the $TNF\alpha$ was inhibited by the treatment of cycloheximide, O-GlcNAc modification decreased and phosphorylation increased on pre-existing p53 after $TNF\alpha$ treatment. But in the presence of STZ and $TNF\alpha$ at the same time, more O-GlcNAcylation occurred on p53, The level of ubiquitination on p53 was also reduced in the presence of STZ. Approximately three times less amount of Mdm2 bound to this hyperglycosylated p53. From this result it might be concluded that treatment of STZ to inhibit O-GlcNAcase increased O-GlcNAc modification level on p53 and the increment of O-GlcNAc modification stabilized p53 from ubiquitin proteolysis system.

• BMB Reports
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• 제57권2호
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• pp.92-97
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• 2024

Elevated blood glucose is associated with an increased risk of atherosclerosis. Data from the current study showed that glucosamine (GlcN), a normal glucose metabolite of the hexosamine biosynthetic pathway (HBP), promoted lipid accumulation in RAW264.7 macrophage cells. Oleic acid- and lipopolysaccharide (LPS)-induced lipid accumulation was further enhanced by GlcN in RAW264.7 cells, although there was no a significant change in the rate of fatty acid uptake. GlcN increased acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), scavenger receptor class A, liver X receptor, and sterol regulatory element-binding protein-1c (SREBP-1c) mRNA expression, and; conversely, suppressed ATP-binding cassette transporter A1 (ABCA-1) and ABCG-1 expression. Additionally, GlcN promoted O-GlcNAcylation of nuclear SREBP-1 but did not affect its DNA binding activity. GlcN stimulated phosphorylation of mammalian target of rapamycin (mTOR) and S6 kinase. Rapamycin, a mTOR-specific inhibitor, suppressed GlcN-induced lipid accumulation in RAW264.7 cells. The GlcN-mediated increase in ACC and FAS mRNA was suppressed, while the decrease in ABCA-1 and ABCG-1 by GlcN was not significantly altered by rapamycin. Together, our results highlight the importance of the mTOR signaling pathway in GlcN-induced macrophage lipid accumulation and further support a potential link between mTOR and HBP signaling in lipogenesis.