Down-regulation of Sp1 Activity through Modulation of O-Glycosylation by Treatment with a Low Glucose Mimetic, 2-Deoxyglucose

2-Deoxy-D-Glucose Downregulates Fatty Acid Synthase Gene Expression Via an Endoplasmic Reticulum Stress-Dependent Pathway in HeLa Cells

Fatty acid synthase (FASN) catalyzes the rate-limiting step of cellular lipogenesis. FASN expression is upregulated in various types of cancer cells, implying that FASN is a potential target for cancer therapy. 2-Deoxy-D-glucose (2-DG) specifically targets cancer cells by inhibiting glycolysis and glucose metabolism, resulting in multiple anticancer effects. However, whether the effects of 2-DG involve lipogenic metabolism remains to be elucidated. We investigated the effect of 2-DG administration on FASN expression in HeLa human cervical cancer cells. 2-DG treatment for 24 h decreased FASN mRNA and protein levels and suppressed the activity of an exogenous rat Fasn promoter. The use of a chemical activator or inhibitors or of a mammalian expression plasmid showed that neither AMPK nor the Sp1 transcription factor is responsible for the inhibitory effect of 2-DG on FASN expression. Administration of thapsigargin, an endoplasmic reticulum (ER) stress inducer, or 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF), a site 1 protease inhibitor, mimicked the inhibitory effect of 2-DG on FASN expression. 2-DG did not further decrease FASN expression in the presence of thapsigargin or AEBSF. Site 1 protease mediates activation of ATF6, an ER stress mediator, as well as sterol regulatory element-binding protein 1 (SREBP1), a robust transcription factor for FASN. Administration of 2-DG or thapsigargin for 24 h suppressed activation of ATF6 and SREBP1, as did AEBSF. We speculated that these effects of 2-DG or thapsigargin are due to feedback inhibition via increased GRP78 expression following ER stress. Supporting this, exogenous overexpression of GRP78 in HeLa cells suppressed SREBP1 activation and Fasn promoter activity. These results suggest that 2-DG suppresses FASN expression via an ER stress-dependent pathway, providing new insight into the molecular basis of FASN regulation in cancer.

What matters in aging is signaling for responsiveness

Biological responsiveness refers to the capacity of living organisms to adapt to changes in both their internal and external environments through physiological and behavioral mechanisms. One of the prominent aspects of aging is the decline in this responsiveness, which can lead to a deterioration in the processes required for maintenance, survival, and growth. The vital link between physiological responsiveness and the essential life processes lies within the signaling systems. To devise effective strategies for controlling the aging process, a comprehensive reevaluation of this connecting loop is imperative. This review aims to explore the impact of aging on signaling systems responsible for responsiveness and introduce a novel perspective on intervening in the aging process by restoring the compromised responsiveness. These innovative mechanistic approaches for modulating altered responsiveness hold the potential to illuminate the development of action plans aimed at controlling the aging process and treating age-related disorders.

Vanguard is a Glucose Deprivation-Responsive Long Non-Coding RNA Essential for Chromatin Remodeling-Reliant DNA Repair

Glucose metabolism contributes to DNA damage response pathways by regulating chromatin remodeling, double-strand break (DSB) repair, and redox homeostasis, although the underlying mechanisms are not fully established. Here, a previously uncharacterized long non-coding RNA is revealed that is call Vanguard which acts to promote HMGB1-dependent DNA repair in association with changes in global chromatin accessibility. Vanguard expression is maintained in cancer cells by SP1-dependent transcription according to glucose availability and cellular adenosine triphosphate (ATP) levels. Vanguard promotes complex formation between HMGB1 and HDAC1, with the resulting deacetylation of HMGB1 serving to maintain its nuclear localization and DSB repair function. However, Vanguard downregulation under glucose limiting conditions promotes HMGB1 translocation from the nucleus, increasing DNA damage, and compromising cancer cell growth and viability. Moreover, Vanguard silencing increases the effectiveness of poly (ADP-ribose) polymerase inhibitors against breast cancer cells with wild-type breast cancer gene-1 status, suggesting Vanguard as a potential therapeutic target.

A relatively low glucose promotes the proliferation of vascular endothelial cells by suppressing VEGFR2 O-GlcNAcylation and its proteasome degradation

PURPOSE

Vascular endothelial growth factor receptors (VEGFRs) have been demonstrated to play a critical role in ischemic retinal diseases, as VEGFRs mediate hypoxia-induced neovascularization. Not only hypoxia, ischemia also induces the deficiency of glucose, yet its effects on VEGFR signal and neovascularization have seldom been studied. Bioinformatics analysis predicted that VEGFRs may be regulated by O-GlcNAcylation, while glucose deficiency influences the O-GlcNAcylation.

METHODS

In this study, we treated human retinal microvascular endothelial cells with low glucose (LG) alone or in combination with low oxygen (oxygen and glucose deprivation, OGD). Cell viability and apoptosis rate were used to evaluate cell growth characters.

RESULTS

LG (2.8 mmol/L) treatment induced mRNA and protein levels of VEGFR1, 2, 3 even in the presence of the protein synthesis inhibitor, cycloheximide (CHX), suggesting that the increase in VEGFR proteins is partially associated with post-translational modifications. Immunoprecipitation analysis showed that O-GlcNAc level was decreased by LG in both VEGFR1, 2, but a de-O-GlcNAc glycosylase inhibitor restored the O-GlcNAc levels. This inhibitor also abolished the LG-induced increase in VEGFR2 protein, whereas this effect was not disappeared in the presence of the proteasome inhibitor, MG132. Similar results were also observed under OGD condition. VEGFR2 knockdown more significantly retarded the growth of hRMECs and HUVECs than VEGFR1, 3 knockdown under LG and OGD conditions.

CONCLUSIONS

A relatively low glucose suppressed O-GlcNAcylation in VEGFR2, whereby inhibiting its proteasome degradation; up-regulated VEGFR2 promoted the proliferation of vascular endothelial cells under ischemic condition.

The Antiviral Effects of 2-Deoxy-D-glucose (2-DG), a Dual D-Glucose and D-Mannose Mimetic, against SARS-CoV-2 and Other Highly Pathogenic Viruses

Viral infection almost invariably causes metabolic changes in the infected cell and several types of host cells that respond to the infection. Among metabolic changes, the most prominent is the upregulated glycolysis process as the main pathway of glucose utilization. Glycolysis activation is a common mechanism of cell adaptation to several viral infections, including noroviruses, rhinoviruses, influenza virus, Zika virus, cytomegalovirus, coronaviruses and others. Such metabolic changes provide potential targets for therapeutic approaches that could reduce the impact of infection. Glycolysis inhibitors, especially 2-deoxy-D-glucose (2-DG), have been intensively studied as antiviral agents. However, 2-DG’s poor pharmacokinetic properties limit its wide clinical application. Herein, we discuss the potential of 2-DG and its novel analogs as potent promising antiviral drugs with special emphasis on targeted intracellular processes.

Targeting on glycosylation of mutant FLT3 in acute myeloid leukemia

Objective: To summarize the abnormal location of FLT3 caused by different glycosylation status which further leads to the distinguishing signaling pathways and discuss targeting on FLT3 glycosylation by drugs reported in recent literatures. Methods: We review FLT3 glycosylation in endoplasmic reticulum. The abnormal signal of mutant FLT3 with different glycosylation status is discussed. We also address potential FLT3 glycosylation-targeting strategies for the treatment. Results: Inhibition of FLT3 mutant cells by drugs reported in recent literatures involves the influence of glycosylation of FLT3: 2-deoxy-D-glucose, Tunicamycin and Fluvastatin are reported to inhibit N-glycosylation of FLT3; Pim-1 inhibitors are proved to block the inhibition of Pim-1 on FLT3 Oglycosylation; HSP90 inhibitors and Tyrosine Kinase Inhibitors are shown to increase fully glycosylated form of FLT3. Discussion: The FMS-like tyrosine kinase 3 (FLT3) gene expressed only in CD34+ progenitor cells in bone marrow is located on chromosome 13q12 encoding FLT3 protein. FLT3 is initially synthesized as a 110 KD protein, which glycosylated in the endoplasmic reticulum to a 130 KD immature protein rich in mannose, and further processed into a mature 160 KD protein in the Golgi apparatus, which could be transferred to the cell surface. Therapy targeting on FLT3 glycosylation is a promising direction for AML treatment. Conclusions: The abnormal location of FLT3 caused by different glycosylation status leads to the distinguishing signaling pathways. Targeting on FLT3 glycosylation may provide a new perspective for therapeutic strategies. Abbreviations: ABCG2: ATP-binding cassette transporter breast cancer resistance protein; ATF: activating transcription factor; AML: acute myeloid leukemia; CHOP: CCAAT-enhancer-binding protein homologous protein; 2-DG: 2-deoxy-D-glucose; EFS: event free survival; EPO: erythropoietin; EPOR: erythropoietin receptor; ERS: endoplasmic reticulum stress; FLT3: FMS-like tyrosine kinase 3; GPI: glycosylphosphatidylinositol; HSP: heat shock protein; ITD: internal tandem duplication; IRE1a: inositol-requiring enzyme 1 alpha; JNK: c-Jun N-terminal kinase; JMD: juxtamembrane domain; JAK: janus kinase; MAPK/ERK: mitogen activated protein kinase/extracellular signal-regulated protein kinase; OS: overall survival; PI3K/AKT: phosphatidylinositide 3-kinases/protein kinase B; PERK: RNA-activated protein kinase-like endoplasmic reticulum kinase; Pgp: P-glycoprotein; PTX3: human pentraxin-3; STAT: signal transducer and activator of transcriptions; TKD: tyrosine-kinase domain; TKI: tyrosine kinase inhibitor; TM: Tunicamycin; UPR: unfolded protein reaction.

Robust effect of metabolic syndrome on major metabolic pathways in the myocardium

Although the high-fat-diet-induced metabolic syndrome (MetS) is a precursor of human cardiac pathology, the myocardial metabolic state in MetS is far from clear. The discrepancies in metabolite handling between human and small animal models and the difficulties inherent in obtaining human tissue complicate the identification of the myocardium-specific metabolic response in patients. Here we use the large animal model of swine that develops the hallmark criteria of human MetS. Our comparative metabolomics together with transcriptomics and computational nonnegative matrix factorization (NMF) interpretation of the data exposes significant decline in metabolites related to the fatty acid oxidation, glycolysis, and pentose phosphate pathway. Behind the reversal lies decreased expression of enzymes that operate in the pathways. We showed that diminished glycogen deposition is a metabolic signature of MetS in the pig myocardium. The depletion of glycogen arises from disbalance in expression of genes that break down and synthesize glycogen. We show robust acetoacetate accumulation and activated expression of key enzymes in ketone body formation, catabolism and transporters, suggesting a shift in fuel utilization in MetS. A contrasting enrichment in O-GlcNAcylated proteins uncovers hexosamine pathway and O-GlcNAcase (OGA) expression involvement in the myocardial response to MetS. Although the hexosamine biosynthetic pathway (HBP) activity and the availability of the UDP-GlcNAc substrate in the MetS myocardium is low, the level of O-GlcNacylated proteins is high as the O-GlcNacase is significantly diminished. Our data support the perception of transcriptionally driven myocardial alterations in expression of standard fatty acids, glucose metabolism, glycogen, and ketone body related enzymes and subsequent paucity of their metabolite products in MetS. This aberrant energy metabolism in the MetS myocardium provide insight into the pathogenesis of CVD in MetS.

DR4-Ser424 O-GlcNAcylation Promotes Sensitization of TRAIL-Tolerant Persisters and TRAIL-Resistant Cancer Cells to Death

TNF-related apoptosis-inducing ligand (TRAIL) resistance, including nongenetically acquired tolerance in cancer persister cells, is a major obstacle to translating TRAIL therapy into patients with cancer. However, the underlying mechanisms remain to be elucidated. Here, we show that DR4/TRAIL-R1 is O-GlcNAcylated at Ser424 in its death domain to mediate both apoptosis and necrosis upon TRAIL ligation. We found that DR4-Ser424 mutations, identified from our cell-based functional screen using a cancer patient-derived cDNA expression library and from The Cancer Genome Atlas, caused TRAIL resistance in various human cancer cell lines. Using O-GlcNAc transferase knockdown cells, DR4-preferred versus DR5-preferred cancer cells, and a DR5-neutralizing antibody, we evaluated the essential role of DR4-specific O-GlcNAc modification in TRAIL cytotoxicity. In contrast to DR4, DR5 was not O-GlcNAcylated by TRAIL treatment, discriminating DR4 from DR5-mediated signaling. Apart from genetic changes in DR4-Ser424, we further classified various cancer cell lines originated from stomach, colon, lung, and glioblastoma according to their sensitivity to and receptor preference upon TRAIL death signaling and generated TRAIL-tolerant persister-derived DLD-1^PER cells. Among these, we discovered that DR4 was not modified by O-GlcNAc in most of the TRAIL-resistant cancer cells and DLD-1^PER cells. Interestingly, promoting DR4 O-GlcNAcylation intentionally using 2-deoxy-d-glucose or a high concentration of glucose sensitized those resistant cancer cells to TRAIL. The O-GlcNAcylation-defective DR4 failed to form DISC/necrosome and could not translocate to aggregated platforms for receptor clustering. Our findings demonstrate that DR4 O-GlcNAcylation is crucial for TRAIL death signaling, providing new opportunities for TRAIL therapy overcoming TRAIL resistance in cancers. SIGNIFICANCE: This study reports that a novel posttranslational modification by O-GlcNAcylation of one of the two human TRAIL receptors with a death domain, TRAIL-R1 (DR4), plays a crucial role in enabling both apoptotic and necroptotic cell death induction by TRAIL.

Caspase cleavage of transcription factor Sp1 enhances apoptosis

Sp1 is a ubiquitous transcription factor that regulates many genes involved in apoptosis and senescence. Sp1 also has a role in the DNA damage response; at low levels of DNA damage, Sp1 is phosphorylated by ATM and localizes to double-strand break sites where it facilitates DNA double-strand-break repair. Depletion of Sp1 increases the sensitivity of cells to DNA damage, whereas overexpression of Sp1 can drive cells into apoptosis. In response to a variety of stimuli, Sp1 can be regulated through proteolytic cleavage by caspases and/or degradation. Here, we show that activation of apoptosis through DNA damage or TRAIL-mediated activation of the extrinsic apoptotic pathway induces caspase-mediated cleavage of Sp1. Cleavage of Sp1 was coincident with the appearance of cleaved caspase 3, and produced a 70 kDa Sp1 product. In vitro analysis revealed a novel caspase cleavage site at aspartic acid 183. Mutation of aspartic acid 183 to alanine conferred resistance to cleavage, and ectopic expression of the Sp1 D183A rendered cells resistant to apoptotic stimuli, indicating that Sp1 cleavage is involved in the induction of apoptosis. The 70 kDa product resulting from caspase cleavage of Sp1 comprises amino acids 184-785. This truncated form, designated Sp1-70C, which retains transcriptional activity, induced apoptosis when overexpressed in normal epithelial cells, whereas Sp1D183A induced significantly less apoptosis. Together, these data reveal a new caspase cleavage site in Sp1 and demonstrate for the first time that caspase cleavage of Sp1 promotes apoptosis.

Survive or thrive: tradeoff strategy for cellular senescence

Aging-dependent cellular behaviors toward extrinsic stress are characterized by the confined localization of certain molecules to either nuclear or perinuclear regions. Although most growth factors can activate downstream signaling in aging cells, they do not in fact have any impact on the cells because the signals cannot reach their genetic targets in the nucleus. For the same reason, varying apoptotic stress factors cannot stimulate the apoptotic pathway in senescent cells. Thus, the operation of a functional nuclear barrier in an aging-dependent manner has been investigated. To elucidate the mechanism for this process, the housekeeping transcription factor Sp1 was identified as a general regulator of nucleocytoplasmic trafficking (NCT) genes, including various nucleoporins, importins, exportins and Ran GTPase cycle-related genes. Interestingly, the posttranslational modification of Sp1 is readily influenced by extrinsic stress, including oxidative and metabolic stress. The decrease in SP1 O-GlcNAcylation under oxidative stress or during replicative senescence makes it susceptible to proteosomal degradation, resulting in defective NCT functions and leading to nuclear barrier formation. The operation of the nuclear barrier in aging provides a fundamental mechanism for cellular protection against stress and promotes survival at the expense of growth via stress-sensitive transcriptional control.

Catalytic Promiscuity of O-GlcNAc Transferase Enables Unexpected Metabolic Engineering of Cytoplasmic Proteins with 2-Azido-2-deoxy-glucose

O-GlcNAc transferase (OGT) catalyzes the installation of N-acetylglucosamine (GlcNAc) O-linked to nucleocytoplasmic proteins (O-GlcNAc) within multicellular eukaryotes. OGT shows surprising tolerance for structural changes in the sugar component of its nucleotide sugar donor substrate, uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). Here, we find that OGT uses UDP-glucose to install O-linked glucose (O-Glc) onto proteins only 25-fold less efficiently than O-GlcNAc. Spurred by this observation, we show that OGT transfers 2-azido-2-deoxy-d-glucose (GlcAz) in vitro from UDP-GlcAz to proteins. Further, feeding cells with per-O-acetyl GlcAz (AcGlcAz), in combination with inhibition or inducible knockout of OGT, shows OGT-dependent modification of nuclear and cytoplasmic proteins with O-GlcAz as detected using microscopy, immunoblot, and proteomics. We find that O-GlcAz is reversible within cells, and an unidentified cellular enzyme exists to cleave O-Glc that can also process O-GlcAz. We anticipate that AcGlcAz will prove to be a useful tool to study the O-GlcNAc modification. We also speculate that, given the high concentration of UDP-Glc within certain mammalian tissues, O-Glc may exist within mammals and serve as a physiologically relevant modification.

Antileukemic Activity of 2-Deoxy-d-Glucose through Inhibition of N-Linked Glycosylation in Acute Myeloid Leukemia with FLT3-ITD or c-KIT Mutations

We assessed the antileukemic activity of 2-deoxy-d-glucose (2-DG) through the modulation of expression of receptor tyrosine kinases (RTK) commonly mutated in acute myeloid leukemia (AML). We used human leukemic cell lines cells, both in vitro and in vivo, as well as leukemic samples from AML patients to demonstrate the role of 2-DG in tumor cell growth inhibition. 2-DG, through N-linked glycosylation inhibition, affected the cell-surface expression and cellular signaling of both FTL3-ITD and mutated c-KIT and induced apoptotic cell death. Leukemic cells harboring these mutated RTKs (MV4-11, MOLM-14, Kasumi-1, and TF-1 c-KIT D816V) were the most sensitive to 2-DG treatment in vitro as compared with nonmutated cells. 2-DG activity was also demonstrated in leukemic cells harboring FLT3-TKD mutations resistant to the tyrosine kinase inhibitor (TKI) quizartinib. Moreover, the antileukemic activity of 2-DG was particularly marked in c-KIT-mutated cell lines and cell samples from core binding factor-AML patients. In these cells, 2-DG inhibited the cell-surface expression of c-KIT, abrogated STAT3 and MAPK-ERK pathways, and strongly downregulated the expression of the receptor resulting in a strong in vivo effect in NOD/SCID mice xenografted with Kasumi-1 cells. Finally, we showed that 2-DG decreases Mcl-1 protein expression in AML cells and induces sensitization to both the BH3 mimetic inhibitor of Bcl-xL, Bcl-2 and Bcl-w, ABT-737, and cytarabine. In conclusion, 2-DG displays a significant antileukemic activity in AML with FLT3-ITD or KIT mutations, opening a new therapeutic window in a subset of AML with mutated RTKs.

Novel actions of 2-deoxy-D-glucose: protection against Shiga toxins and changes in cellular lipids

2-Deoxy-D-glucose (2DG) is a structural analogue of glucose with well-established applications as an inhibitor of glycolysis and N-glycosylation. Importantly, 2DG has been shown to improve the efficacy of several cancer chemotherapeutic agents in vivo and thus it is in clinical studies in combination with chemotherapy and radiotherapy. However, although 2DG has been demonstrated to modulate many cellular functions, including autophagy, apoptosis and cell cycle control, little is known about the effects of 2DG on intracellular transport, which is of great importance when predicting the effects of 2DG on therapeutic agents. In addition to proteins, lipids play important roles in cellular signalling and in controlling cellular trafficking. We have, in the present study, investigated the effects of 2DG on cellular lipid composition and by use of protein toxins we have studied 2DG-mediated changes in intracellular trafficking. By quantifying more than 200 individual lipid species from 17 different lipid classes, we have found that 2DG treatment changes the levels and/or species composition of several lipids, such as phosphatidylinositol (PI), diacylglycerol (DAG), cholesteryl ester (CE), ceramide (Cer) and lysophospho-lipids. Moreover, 2DG becomes incorporated into the carbohydrate moiety of glycosphingolipids (GSLs). In addition, we have discovered that 2DG protects cells against Shiga toxins (Stxs) and inhibits release of the cytotoxic StxA1 moiety in the endoplasmic reticulum (ER). The data indicate that the 2DG-induced protection against Stx is independent of inhibition of glycolysis or N-glycosylation, but rather mediated via the depletion of Ca(2+) from cellular reservoirs by 2DG. In conclusion, our results reveal novel actions of 2DG on cellular lipids and Stx toxicity.

p53-Dependent regulation of metabolic function through transcriptional activation of pantothenate kinase-1 gene

It is well established that the p53 tumor suppressor plays a crucial role in controlling cell proliferation and apoptosis upon various types of stress. There is increasing evidence showing that p53 is also critically involved in various metabolic pathways, both in tumor and normal cells. Here, we have identified a novel p53 metabolic target pantothenate kinase-1 (PANK1) via ChIP-on-chip. PanK1 catalyzes the rate-limiting step for CoA synthesis and, therefore, controls intracellular CoA content; Pank1-knockout mice exhibit defect in β-oxidation and gluconeogenesis in the liver after starvation due to insufficient CoA levels. We demonstrated that PANK1 gene is a direct transcriptional target of p53. Although DNA damage-induced p53 upregulates PanK1 expression, depletion of PanK1 expression does not affect p53-dependent growth arrest or apoptosis. Interestingly, upon glucose starvation, PanK1 expression is significantly reduced in HCT116 p53 (-/-) but not in HCT116 p53 (+/+) cells, suggesting that p53 is required to maintain PanK1 expression under metabolic stress conditions. Moreover, by using p53-mutant mice, we observed that, similar to the case in Pank1-knockout mice, gluconeogenesis is partially impaired in p53-null mice. Together, our findings show that p53 plays an important role in regulating energy homeostasis through transcriptional control of PANK1, independent of its canonical functions in apoptosis and cell cycle arrest.

Gene expression of the tumour suppressor LKB1 is mediated by Sp1, NF-Y and FOXO transcription factors

The serine/threonine kinase LKB1 is a tumour suppressor that regulates multiple biological pathways, including cell cycle control, cell polarity and energy metabolism by direct phosphorylation of 14 different AMP-activated protein kinase (AMPK) family members. Although many downstream targets have been described, the regulation of LKB1 gene expression is still poorly understood. In this study, we performed a functional analysis of the human LKB1 upstream regulatory region. We used 200 base pair deletion constructs of the 5'-flanking region fused to a luciferase reporter to identify the core promoter. It encompasses nucleotides -345 to +52 relative to the transcription start site and coincides with a DNase I hypersensitive site. Based on extensive deletion and substitution mutant analysis of the LKB1 promoter, we identified four cis-acting elements which are critical for transcriptional activation. Using electrophoretic mobility shift assays as well as chromatin immunoprecipitations, we demonstrate that the transcription factors Sp1, NF-Y and two forkhead box O (FOXO) family members FOXO3 and FOXO4 bind to these elements. Overexpression of these factors significantly increased the LKB1 promoter activity. Conversely, small interfering RNAs directed against NF-Y alpha and the two FOXO proteins greatly reduced endogenous LKB1 expression and phosphorylation of LKB1's main substrate AMPK in three different cell lines. Taken together, these results demonstrate that Sp1, NF-Y and FOXO transcription factors are involved in the regulation of LKB1 transcription.

Suppressive regulation of KSHV RTA with O-GlcNAcylation

BACKGROUND

The replication and transcription activator (RTA) of Kaposi's sarcoma-associated herpesvirus (KSHV) is a molecular switch that initiates a productive replication of latent KSHV genomes. KSHV RTA (K-RTA) is composed of 691 amino acids with high Ser and Thr content (17.7%), but to what extent these Ser and Thr are modified in vivo has not been explored.

METHODS

By using tandem mass spectrometric analysis of affinity-purified FLAG tagged K-RTA, we sought to identify Ser and Thr residues that are post-translationally modified in K-RTA.

RESULTS

We found that K-RTA is an O-GlcNAcylated protein and Thr-366/Thr-367 is the primary motif with O-GlcNAcylation in vivo. The biological significance of O-GlcNAc modified Thr-366 and Thr-367 was assessed by site-specific amino acid substitution. Replacement of Thr with Ala at amino acid 366 or 367 caused a modest enhancement of K-RTA transactivation activity in a luciferase reporter assay and a cell model for KSHV reactivation. By using co-immunoprecipitation coupled with western blot analysis, we showed that the capacity of K-RTA in associating with endogenous PARP1 was significantly reduced in the Thr-366/Thr-367 O-GlcNAc mutants. PARP1 is a documented negative regulator of K-RTA that can be ascribed by the attachment of large negatively charged polymer onto K-RTA via PARP1's poly (ADP-ribose) polymerase activity. In agreement, shRNA-mediated depletion of O-GlcNAc transferase (OGT) in KSHV infected cells augmented viral reactivation and virus production that was accompanied by diminished K-RTA and PARP1 complexes.

CONCLUSIONS

KSHV latent-lytic switch K-RTA is modified by cellular O-GlcNAcylation, which imposes a negative effect on K-RTA transactivation activity. This inhibitory effect involves OGT and PARP1, two nutritional sensors recently emerging as chromatin modifiers. Thus, we speculate that the activity of K-RTA on its target genes is continuously checked and modulated by OGT and PARP1 in response to cellular metabolic state.

Expression and role in glycolysis of human ADP-dependent glucokinase

A novel murine enzyme, ADP-dependent glucokinase (ADPGK), has been shown to catalyse glucose phosphorylation using ADP as phosphoryl donor. The ancestral ADPGK gene appears to have been laterally transferred from Archaea early in metazoan evolution, but its biological role has not been established. Here, we undertake an initial investigation of the functional properties of human ADPGK in human tumour cell lines and specifically test the hypothesis that ADPGK might prime glycolysis using ADP under stress conditions such as hypoxia. Recombinant human ADPGK was confirmed to catalyse ADP-dependent glucose phosphorylation in vitro, with an apparent K (M) for glucose of 0.29 mM. Expression databases and western blotting of surgical samples demonstrated high expression in many human tissues, including tumours. Unlike hexokinase-2 (HK2), RNAi studies with exon arrays showed that ADPGK is not a transcriptional target of hypoxia inducible factor-1. Consistent with this, ADPGK protein was not upregulated by hypoxia or anoxia. Surprisingly, stable fivefold overexpression of ADPGK in H460 or HCT116 cells had no apparent effect on proliferation or glycolysis, and did not rescue clonogenicity or glycolysis when HK2 was suppressed by siRNA. Furthermore, suppression of ADPGK by siRNA did not cause detectable inhibition of glycolysis or cell killing by anoxia, although it did induce a statistically significant decrease in plating efficiency of H460 cells under aerobic conditions. Thus, human ADPGK catalyses ADP-dependent phosphorylation of glucose in vitro, but despite its high expression in human tumour cell lines it appears not to make a quantifiable contribution to glycolysis under the conditions evaluated.

Heat shock protein 90 stabilizes nucleolin to increase mRNA stability in mitosis

Most studies on heat shock protein 90 (Hsp90) have focused on the involvement of Hsp90 in the interphase, whereas the role of this protein in the nucleus during mitosis remains largely unclear. In this study, we found that the level of the acetylated form of Hsp90 decreased dramatically during mitosis, which indicates more chaperone activity during mitosis. We thus probed proteins that interacted with Hsp90 by liquid chromatography/mass spectrometry (LC/MS) and found that nucleolin was one of those interacting proteins during mitosis. The nucleolin level decreased upon geldanamycin treatment, and Hsp90 maintained the cyclin-dependent kinase 1 (CDK1) activity to phosphorylate nucleolin at Thr-641/707. Mutation of Thr-641/707 resulted in the destabilization of nucleolin in mitosis. We globally screened the level of mitotic mRNAs and found that 229 mRNAs decreased during mitosis in the presence of geldanamycin. Furthermore, a bioinformatics tool and an RNA immunoprecipitation assay found that 16 mRNAs, including cadherin and Bcl-xl, were stabilized through the recruitment of nucleolin to the 3'-untranslated regions (3'-UTRs) of those genes. Overall, strong correlations exist between the up-regulation of Hsp90, nucleolin, and the mRNAs related to tumorigenesis of the lung. Our findings thus indicate that nucleolin stabilized by Hsp90 contributes to the lung tumorigenesis by increasing the level of many tumor-related mRNAs during mitosis.

Post-translational control of sp-family transcription factors

Sp-family transcription factors are widely expressed in human tissues and involved in the regulation of many cellular processes and response to cellular microenvironment. These responses appear to be mediated by alterations in transcription factor affinity for DNA rather than altered protein level. How might such changes be effected? This review will identify the range of known post-translational modifications (PTMs) of Sp-factors and the sometimes conflicting literature about the roles of PTMs in regulating activity. We will speculate on the interaction between cell environment, chromatin microenvironment and the role of PTM in governing functionality of the proteins and the complexes to which they belong.

Nuclear barrier hypothesis of aging as mechanism for trade-off growth to survival

When the aging-dependent cellular behaviors toward growth factors and toxic stress have been analyzed, the perinuclear accumulation of the activated signals, either mitogenic or apoptotic, has been observed, suggesting the aging-dependent inefficiency of the nucleocytoplasmic trafficking of the signals. Thereby, it would be natural to assume the operation of the functional nuclear barrier in aging-dependent manner, which would be designated as "Park and Lim's Barrier." And for the ultimate transcriptional factor for these aging-dependent changes of the functional nuclear barrier, Sp1 transcriptional factor has been suggested to be the most probable candidate. This novel mechanism of aging-dependent operation of the functional nuclear barrier is proposed as the ultimate checking mechanism for cellular protection against toxic environment and the general mechanism for the trade-off growth to survival in aging.

O-GlcNAc protein modification in cancer cells increases in response to glucose deprivation through glycogen degradation

When cellular glucose concentrations fall below normal levels, in general the extent of protein O-GlcNAc modification (O-GlcNAcylation) decreases. However, recent reports demonstrated increased O-GlcNAcylation by glucose deprivation in HepG2 and Neuro-2a cells. Here, we report increased O-GlcNAcylation in non-small cell lung carcinoma A549 cells and various other cells in response to glucose deprivation. Although the level of O-GlcNAc transferase was unchanged, the enzyme contained less O-GlcNAc, and its activity was increased. Moreover, O-GlcNAcase activity was reduced. The studied cells contain glycogen, and we show that its degradation in response to glucose deprivation provides a source for UDP-GlcNAc required for increased O-GlcNAcylation under this condition. This required active glycogen phosphorylase and resulted in increased glutamine:fructose-6-phosphate amidotransferase, the first and rate-limiting enzyme in the hexosamine biosynthetic pathway. Interestingly, glucose deprivation reduced the amount of phosphofructokinase 1, a regulatory glycolytic enzyme, and blocked ATP synthesis. These findings suggest that glycogen is the source for increased O-GlcNAcylation but not for generating ATP in response to glucose deprivation and that this may be useful for cancer cells to survive.

A novel, promoter-based, target-specific assay identifies 2-deoxy-D-glucose as an inhibitor of globotriaosylceramide biosynthesis

Abnormal biosynthesis of globotriaosylceramide (Gb3) is known to be associated with Gb3-related diseases, such as Fabry disease. The Gb3 synthase gene (Gb3S) codes for alpha1,4-galactosyltransferase, which is a key enzyme involved in Gb3 biosynthesis in vivo. Transcriptional repression of Gb3S is a way to control Gb3 biosynthesis and may be a suitable target for the treatment of Gb3-related diseases. To find a transcriptional inhibitor for Gb3S, we developed a convenient cell-based chemical screening assay system by constructing a fusion gene construct of the human Gb3S promoter and a secreted luciferase as reporter. Using this assay, we identified 2-deoxy-D-glucose as a potent inhibitor for the Gb3S promoter. In cultured cells, 2-deoxy-D-glucose markedly reduced endogenous Gb3S mRNA levels, resulting in a reduction in cellular Gb3 content and a corresponding accumulation of the precursor lactosylceramide. Moreover, cytokine-induced expression of Gb3 on the cell surface of endothelial cells, which is closely related to the onset of hemolytic uremic syndrome in O157-infected patients, was also suppressed by 2-deoxy-D-glucose treatment. These results indicate that 2-deoxy-D-glucose can control Gb3 biosynthesis through the inhibition of Gb3S transcription. Furthermore, we demonstrated the general utility of our novel screening assay for the identification of new inhibitors of glycosphingolipid biosynthesis.

Phosphorylated extracellular signal-regulated protein kinases 1 and 2 phosphorylate Sp1 on serine 59 and regulate cellular senescence via transcription of p21Sdi1/Cip1/Waf1

Expression of p21(Sdi1) downstream of p53 is essential for induction of cellular senescence, although cancer cell senescence can also occur in the p53 null condition. We report herein that senescence-associated phosphorylated extracellular signal-regulated protein kinases 1 and 2 (SA-pErk1/2) enhanced p21(Sdi1) transcription by phosphorylating Sp1 on Ser(59) downstream of protein kinase C (PKC) alpha. Reactive oxygen species (ROS), which was increased in cellular senescence, significantly activated both PKCalpha and PKCbetaI. However, PKCalpha, but not PKCbetaI, regulated ROS generation and cell proliferation in senescent cells along with activation of cdk2, proven by siRNAs. PKCalpha-siRNA also reduced SA-pErk1/2 expression in old human diploid fibroblast cells, accompanied with changes of senescence phenotypes to young cell-like. Regulation of SA-pErk1/2 was also confirmed by using catalytically active PKCalpha and its DN-mutant construct. These findings strongly suggest a new pathway to regulate senescence phenotypes by ROS via Sp1 phosphorylation between PKCalpha and SA-pErk1/2: employing GST-Sp1 mutants and MEK inhibitor analyses, we found that SA-pErk1/2 regulated Sp1 phosphorylation on the Ser(59) residue in vivo, but not threonine, in cellular senescence, which regulated transcription of p21(Sdi1) expression. In summary, PKCalpha, which was activated in senescent cells by ROS strongly activated Erk1/2, and the SA-pErk1/2 in turn phosphorylated Sp1 on Ser(59). Sp1-enhanced transcription of p21(Sdi1) resulted in regulation of cellular senescence in primary human diploid fibroblast cells.

Heat shock protein 90 is important for Sp1 stability during mitosis

Our previous study has revealed that heat shock protein (Hsp) 90 can interact with Sp1 to regulate the transcriptional activity of 12(S)-lipoxygenase. Herein, we further found that the interaction between Hsp90 and Sp1 occurred during mitosis. By geldanamycin (GA) treatment and knockdown of Hsp90, we found that this interaction during mitosis was involved in the maintenance of Sp1 stability, and that the phospho-c-Jun N-terminal kinase (JNK)-1 level also decreased. As the JNK-1 was knocked down by the shRNA of JNK-1, Sp1 was degraded through a ubiquitin-dependent proteasome pathway. In addition, for mutation of the JNK-1 phosphorylated residues of Sp1, namely, Sp1(T278/739A) and Sp1(T278/739D), the effect of GA on Sp1 stability was reversed. Finally, based on the involvement of Hsp90 in Sp1 stability, the transcriptional activities of p21(WAF1/CIP1) and 12(S)-lipoxygenase under GA treatment were observed to have decreased. Taken together, Hsp90 is important for maintaining Sp1 stability during mitosis by the JNK-1-mediated phosphorylation of Sp1 to enable division into daughter cells and to regulate the expression of related genes in the interphase.

O-linked N-acetylglucosaminylation of Sp1 inhibits the human immunodeficiency virus type 1 promoter

Human immunodeficiency virus type 1 (HIV-1) gene expression and replication are regulated by the promoter/enhancer located in the U3 region of the proviral 5' long terminal repeat (LTR). The binding of cellular transcription factors to specific regulatory sites in the 5' LTR is a key event in the replication cycle of HIV-1. Since transcriptional activity is regulated by the posttranslational modification of transcription factors with the monosaccharide O-linked N-acetyl-D-glucosamine (O-GlcNAc), we evaluated whether increased O-GlcNAcylation affects HIV-1 transcription. In the present study we demonstrate that treatment of HIV-1-infected lymphocytes with the O-GlcNAcylation-enhancing agent glucosamine (GlcN) repressed viral transcription in a dose-dependent manner. Overexpression of O-GlcNAc transferase (OGT), the sole known enzyme catalyzing the addition of O-GlcNAc to proteins, specifically inhibited the activity of the HIV-1 LTR promoter in different T-cell lines and in primary CD4(+) T lymphocytes. Inhibition of HIV-1 LTR activity in infected T cells was most efficient (>95%) when OGT was recombinantly overexpressed prior to infection. O-GlcNAcylation of the transcription factor Sp1 and the presence of Sp1-binding sites in the LTR were found to be crucial for this inhibitory effect. From this study, we conclude that O-GlcNAcylation of Sp1 inhibits the activity of the HIV-1 LTR promoter. Modulation of Sp1 O-GlcNAcylation may play a role in the regulation of HIV-1 latency and activation and links viral replication to the glucose metabolism of the host cell. Hence, the establishment of a metabolic treatment might supplement the repertoire of antiretroviral therapies against AIDS.

NFkappaB activation is associated with its O-GlcNAcylation state under hyperglycemic conditions

The transcription factor NFkappaB is activated by phosphorylation and acetylation and plays important roles in inflammatory and immune responses in the cell. Additionally, posttranslational modification of the NFkappaB p65 subunit by O-linked N-acetylglucosamine (O-GlcNAc) has been reported, but the modification site of O-GlcNAc on NFkappaB p65 and its exact function have not been elucidated. In this work, we show that O-GlcNAcylation of NFkappaB p65 decreases binding to IkappaB alpha and increases transcriptional activity under hyperglycemic conditions. Also, we demonstrate that both Thr-322 and Thr-352 of NFkappaB p65 can be modified with O-GlcNAc, but modification on Thr-352, not Thr-322, is important for transcriptional activation. Our findings suggest that site-specific O-GlcNAcylation may be a reason why NFkappaB activity increases continuously under hyperglycemic conditions.

Identification and characterization of the human Gb3/CD77 synthase gene promoter

Hemolytic uremic syndrome (HUS) is triggered by verotoxin (VT) produced by the Escherichia coli O157 strain. Several studies have demonstrated that VT induces endothelial cell (EC) death via the VT receptor globotriaosylceramide (Gb3/CD77) leading to this symptom. Inflammatory mediators which are produced as a result of E. coli O157 infection, increase the expression level of Gb3 in EC. Therefore increased expression of Gb3 is considered as a progression step for HUS. The increased expression of Gb3 is due to the transcriptional upregulation of Gb3/CD77 synthase gene (Gb3S, also known as alpha1,4-galactosyltransferase gene), the mechanism of which still remains unknown. To understand the transcriptional machinery and to elucidate the onset mechanism of HUS, we cloned and characterized the human Gb3S promoter. A modified 5'-RACE was used to determine the transcriptional initiation site, which revealed the presence of a TATA-less GC-rich sequence in the proximal region. Promoter activity measured using a luciferase assay demonstrated that the GC-rich sequence is necessary for the basal transcriptional activity, and two silencer elements located 5'-upstream of this GC-rich region regulated the transcriptional level. Furthermore, we found that the GC-rich sequence contained three potential Sp1 binding sites and that all three Sp1 binding elements acted as positive regulators. Since Sp1 is an inducer of several genes in the presence of the inflammatory cytokines in EC, our results suggest that the transcriptional regulation of the Gb3S gene by Sp1 might affect the VT sensitivity of EC and HUS progression.

Histone deacetylase inhibition and blockade of the glycolytic pathway synergistically induce glioblastoma cell death

PURPOSE

High-grade gliomas are difficult to treat due to their location behind the blood-brain barrier and to inherent radioresistance and chemoresistance.

EXPERIMENTAL DESIGN

Because tumorigenesis is considered a multistep process of accumulating mutations affecting distinct signaling pathways, combinations of compounds, which inhibit nonoverlapping pathways, are being explored to improve treatment of gliomas. Histone deacetylase inhibitors (HDI) have proven antitumor activity by blocking cell proliferation, promoting differentiation, and inducing tumor cell apoptosis.

RESULTS

In this report, we show that the HDIs trichostatin A, sodium butyrate, and low nanomolar doses of LAQ824 combined with the glycolysis inhibitor 2-deoxy-d-glucose induce strong apoptosis in cancer cell lines of brain, breast, and cervix in a p53-independent manner. HDIs up-regulate p21, which is blocked by concomitant administration of 2-deoxy-d-glucose.

CONCLUSIONS

We propose simultaneous blockade of histone deacetylation and glycolysis as a novel therapeutic strategy for several major cancers.

Transient downregulation of protein O-N-acetylglucosaminylation by treatment of high-dose nicotinamide in human cells

Nicotinamide at millimolar concentrations affects cell survival in various conditions, and is being utilized therapeutically in many human diseases. However, the effect of an acute treatment of nicotinamide at such high dose on gene expression and cellular metabolism has rarely been determined previously. In this study, we found that levels of O-N-acetylglucosamin(O-GlcNAc)ylated proteins including Sp1 acutely decreased upon treatment of 10 mM nicotinamide. Concomitantly, Sp1 protein level decreased rapidly through accelerated proteasome-mediated proteolysis. Cotreatment of glucosamine or 2-deoxyglucose, which inhibits protein deGlcNAcylation, effectively blocked the decrease induced by nicotinamide. Interestingly, the decline in the levels of Sp1 and protein O- GlcNAcylation was only transient lasting for two days post treatment, and this pattern matched closely the rapid fluctuation of the cellular [NAD+]. Our results suggest a possible link between cellular nicotinamide metabolism and protein O-GlcNAcylation, and an existence of cellular [NAD+] homeostasis.

Sumoylation of specificity protein 1 augments its degradation by changing the localization and increasing the specificity protein 1 proteolytic process

Although specificity protein 1 (Sp1) accumulation has been found in various tumor strains, its mechanism is still not very clear. Herein, we found that modification of Sp1 by SUMO-1 facilitates Sp1 degradation. Our findings revealed that, although the amounts of Sp1 and Sp1 mutant (K16R) [Sp1(K16R)] mRNA in cells were equal, the protein level of Sp1(K16R) was higher than that of wild-type Sp1. We also proved that this sumoylation site was not the residue at which ubiquitination occurred. Invitro and in vivo pull-down assays revealed that more sumoylated Sp1 was localized in the cytoplasm, and the interaction between SUMO-1-Sp1 and the proteasome subunit rpt6 in HeLa cells was enhanced. In addition, although Sp1 accumulated in the tumorous cervical tissue, it was not prone to sumoylation. Finally, by overexpression of HA (hemagglutinin)-SUMO-1-Sp1-myc, HA-Sp1-myc, and HA-Sp1(K16R), we found that modification of Sp1 by SUMO-1 was important for Sp1 proteolysis. In conclusion, modification of Sp1 by SUMO-1 altered its localization and then increased its interaction with rpt6. This interaction increased the efficiency of Sp1 proteolytic processing and ubiquitination and then resulted in Sp1 degradation. Therefore, sumoylation of Sp1 is attenuated during tumorigenesis in order to increase Sp1 stability.

Metabolic regulation of manganese superoxide dismutase expression via essential amino acid deprivation

Organisms respond to available nutrient levels by rapidly adjusting metabolic flux, in part through changes in gene expression. A consequence of adaptations in metabolic rate is the production of mitochondria-derived reactive oxygen species. Therefore, we hypothesized that nutrient sensing could regulate the synthesis of the primary defense of the cell against superoxide radicals, manganese superoxide dismutase. Our data establish a novel nutrient-sensing pathway for manganese superoxide dismutase expression mediated through essential amino acid depletion concurrent with an increase in cellular viability. Most relevantly, our results are divergent from current mechanisms governing amino acid-dependent gene regulation. This pathway requires the presence of glutamine, signaling via the tricarboxylic acid cycle/electron transport chain, an intact mitochondrial membrane potential, and the activity of both the MEK/ERK and mammalian target of rapamycin kinases. Our results provide evidence for convergence of metabolic cues with nutrient control of antioxidant gene regulation, revealing a potential signaling strategy that impacts free radical-mediated mutations with implications in cancer and aging.

Subtractive hybridisation screen identifies genes regulated by glucose deprivation in human neuroblastoma cells

Glucose is the major source of energy for the brain and inadequate glucose supply causes damage of neuronal cells. In this study we employed the human neuroblastoma cell line SH-SY5Y, as an in vitro model for neuronal cells, to identify genes regulated by glucose deprivation. Using subtractive hybridisation screen, validated by Northern analysis, we identify for the first time specific targets of the glucopenic response. These genes are involved in key cellular process including gene transcription, protein synthesis, mitochondrial metabolism, neuronal development, neuroprotection and neuronal apoptosis. Our findings suggest that the fate of neuronal cells undergoing glucose starvation relies on complex gene interactions. Modulation of the expression of these genes in vivo will enable determination of the precise role of each gene and possibly identify key elements and potential therapeutic targets of the glucopenic response.

High glucose increases angiopoietin-2 transcription in microvascular endothelial cells through methylglyoxal modification of mSin3A

Methylglyoxal is a highly reactive dicarbonyl degradation product formed from triose phosphates during glycolysis. Methylglyoxal forms stable adducts primarily with arginine residues of intracellular proteins. The biologic role of this covalent modification in regulating cell function is not known. Here we report that in mouse kidney endothelial cells, high glucose causes increased methylglyoxal modification of the corepressor mSin3A. Methylglyoxal modification of mSin3A results in increased recruitment of O-GlcNAc-transferase, with consequent increased modification of Sp3 by O-linked N-acetylglucosamine. This modification of Sp3 causes decreased binding to a glucose-responsive GC-box in the angiopoietin-2 (Ang-2) promoter, resulting in increased Ang-2 expression. Increased Ang-2 expression induced by high glucose increased expression of intracellular adhesion molecule 1 and vascular cell adhesion molecule 1 in cells and in kidneys from diabetic mice and sensitized microvascular endothelial cells to the proinflammatory effects of tumor necrosis factor alpha. This novel mechanism for regulating gene expression may play a role in the pathobiology of diabetic vascular disease.

PMA stimulates MUC5B gene expression through an Sp1-based mechanism in airway epithelial cells

We previously showed that the MUC5B gene expression was elevated by phorbol 12-myristate 13-acetate (PMA) through an epidermal growth factor receptor-independent Ras/MEKK1/JNK and P38 signaling-based transcriptional mechanism. In the current study, we elucidated the molecular basis of this transcriptional regulation using promoter-reporter gene expression and chromatin immunoprecipitation (ChIP) assays with primary human bronchial epithelial cells that are cultured at the air-liquid interface. We have observed that PMA-induced MUC5B promoter activity is blocked by the Sp1-binding inhibitor, mithramycin A, in a dose-dependent manner. Deletion analysis with the MUC5B promoter construct demonstrated that both basal and PMA-induced promoter-reporter activities reside within the -222/-78 bp region relative to the transcriptional start site. NoShift transcriptional factor assays demonstrated that PMA stimulated Sp1 binding, but not STAT1 and c-Myc binding. Immunoprecipitation studies also verified the enhanced phosphorylation of Sp1 after PMA treatment. Site-directed mutagenesis and transfection studies demonstrated the involvement of Sp1-1 (-122/-114) and the Sp1-2 (-197/-186) cis elements in the basal and PMA-induced MUC5B promoter activity. The ChIP assay with anti-RNA polymerase II reconfirmed the PMA-induced MUC5B promoter activity by showing enhanced RNA polymerase II-DNA complex containing putative MUC5B Sp1-1, Sp1-2, or Sp1-3 sites. However, the ChIP assay using anti-Sp1 antibody demonstrated that the PMA-stimulated binding is only at Sp1-2. These results suggested an Sp1-based transcriptional mechanism with Sp1-1 as the regulator of basal MUC5B promoter activity and Sp1-2 as the regulator of PMA-induced MUC5B gene expression in the human airway epithelial cells.

Interference with energy metabolism by 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside induces HPV suppression in cervical carcinoma cells and apoptosis in the absence of LKB1

Carcinogenesis is a dynamic and stepwise process, which is accompanied by a variety of somatic and epigenetic alterations in response to a changing microenvironment. Hypoxic conditions will select for cells that have adjusted their metabolic profile and can maintain proliferation by successfully competing for scarce nutritional and oxygen resources. In the present study we have investigated the effects of energy depletion in the context of HPV (human papillomavirus)-induced pathogenesis. We show that cervical carcinoma cell lines are susceptible to undergoing either growth arrest or cell death under conditions of metabolic stress induced by AICAR (5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside), a known activator of the AMPK (AMP-activated protein kinase). Our results reveal that AICAR treatment leads to a reduced binding affinity of the transcription factor AP-1 (activator protein-1) and in turn to a selective suppression of HPV transcription. Moreover, the outcome of AICAR on proliferation and survival was dependent on p53 activation and the presence of LKB1, the major upstream kinase of AMPK. Using non-malignant LKB1-expressing somatic cell hybrids, which lose expression after tumorigenic segregation, as well as small interfering RNA LKB1 knockdown approaches, we could further demonstrate that expression of LKB1 protects cells from cytotoxicity induced by agents which modulate the ATP/AMP ratio. Since simulation of low energy status can selectively eradicate LKB1-negative cervical carcinoma cells, AICAR may represent a novel drug in the treatment of cervical cancer.

Modification of p53 with O-linked N-acetylglucosamine regulates p53 activity and stability

Post-translational addition of O-linked N-acetylglucosamine (O-GlcNAc) to p53 is known to occur, but the site of O-GlcNAcylation and its effects on p53 are not understood. Here, we show that Ser 149 of p53 is O-GlcNAcylated and that this modification is associated with decreased phosphorylation of p53 at Thr 155, which is a site that is targeted by the COP9 signalosome, resulting in decreased p53 ubiquitination. Accordingly, O-GlcNAcylation at Ser 149 stabilizes p53 by blocking ubiquitin-dependent proteolysis. Our results indicate that the dynamic interplay between O-GlcNAc and O-phosphate modifications coordinately regulate p53 stability and activity.

Regulation of the ClC-2 lung epithelial chloride channel by glycosylation of SP1

Chloride channel-2 (ClC-2) is a pH- and voltage-activated chloride channel that is highly expressed in mammalian fetal airway epithelia during the period of maximal fluid secretion. A high level of luminal ClC-2 protein expression is maintained by the SP1 transcription factor until SP1 and ClC-2 decline rapidly at birth. Using fetal (preII-19) and adult (L2) rat lung Type 2 cell lines, we demonstrate that the active higher-molecular-weight 105-kD isoform of SP1 is phosphorylated and glycosylated. Exposure of either cell line to high-dose glutamine is sufficient to induce glycosylation of SP1 and to induce and maintain ClC-2. Exposure to tunicamycin to inhibit SP1 glycosylation reduces ClC-2 expression. We also demonstrate that in vivo ClC-2 expression is similarly regulated. SP1 from 6-wk-old murine lung (high ClC-2 expression) is hyperphosphorylated and hyperglycosylated compared with SP1 from 16-wk-old lung (low ClC-2 expression). Our results support the hypothesis that glycosylation of SP1 produces the 105-kD isoform of SP1 and is involved in regulating ClC-2 gene expression.

2-Deoxyglucose: An anticancer and antiviral therapeutic, but not any more a low glucose mimetic

2-Deoxyglucose (2-DG), a non-metabolizable glucose analogue, blocks glycolysis and inhibits protein glycosylation. It has been tested in multiple studies for possible application as an anticancer or antiviral therapeutic. The inhibitory effect of 2-DG on ATP generation made it a good candidate molecule as a calorie restriction mimetic as well. Furthermore, 2-DG has been utilized in numerous studies to simulate a condition of glucose starvation. Because 2-DG disrupts glucose metabolism, protein glycosylation, and ER quality control at the same time, a cellular or pathologic outcome could be easily misinterpreted without clear understanding of 2-DG's effect on each of these aspects. However, the effect of 2-DG on protein glycosylation has rarely been investigated. A recent study suggested that 2-DG causes hyperGlcNAcylation of proteins, while low glucose supply causes hypoGlcNAcylation. In certain aspects of cellular physiology, this difference could be disregarded, but in others, this may possibly cause totally different outcomes.

Hsp90α Recruited by Sp1 Is Important for Transcription of 12(S)-Lipoxygenase in A431 Cells

Sp1 is a basic transcriptional factor that binds to the GC-rich region in the promoter of the target gene. It is involved in transcription of numerous genes by recruiting transcriptional factors to the promoters of target genes. In this study, we found in vivo and in vitro that Hsp90alpha was recruited to the GC-rich region of the 12(S)-lipoxygenase promoter through interaction with Sp1 in A431 cells by employing DNA affinity immunoprecipitation assay and chromatin immunoprecipitation assay. When Hsp90alpha was inhibited by geldanamycin (GA, a specific inhibitor of the Hsp90 family) or by siRNA of Hsp90alpha (to block its activity or to knockdown protein levels), respectively, luciferase activity (driven by the 12(S)-lipoxygenase promoter) and both mRNA and protein levels of 12(S)-lipoxygenase were reduced significantly in cells. In addition, the effect of GA was abolished when the Sp1 binding sites of 12(S)-lipoxygenase were mutated in A431 cells. Interestingly, binding of Sp1 to the 12(S)-lipoxygenase promoter was also decreased upon GA treatment in cells. In conclusion, our results indicate that Sp1 interacts with Hsp90alpha to recruit it to the promoter of 12(S)-lipoxygenase and then to regulate gene transcription by modulating the binding ability of Sp1 to promoters.

Insulin activates the rat sterol-regulatory-element-binding protein 1c (SREBP-1c) promoter through the combinatorial actions of SREBP, LXR, Sp-1 and NF-Y cis-acting elements

The enhanced synthesis of fatty acids in the liver and adipose tissue in response to insulin is critically dependent on the transcription factor SREBP-1c (sterol-regulatory-element-binding protein 1c). Insulin increases the expression of the SREBP-1c gene in intact liver and in hepatocytes cultured in vitro. To learn the mechanism of this stimulation, we analysed the activation of the rat SREBP-1c promoter and its truncated or mutated congeners driving a luciferase reporter gene in transiently transfected rat hepatocytes. The rat SREBP-1c promoter contains binding sites for LXR (liver X receptor), Sp1, NF-Y (nuclear factor-Y) and SREBP itself. We have found that each of these sites is required for the full stimulatory response of the SREBP-1c promoter to insulin. Mutation of either the putative LXREs (LXR response elements) or the SRE (sterol response element) in the proximal SREBP-1c promoter reduced the stimulatory effect of insulin by about 50%. Insulin and the LXR agonist TO901317 increased the association of SREBP-1 with the SREBP-1c promoter. Ectopic expression of LXRalpha or SREBP-1c increased activity of the SREBP-1c promoter, and this effect is further enhanced by insulin. The Sp1 and NF-Y sites adjacent to the SRE are also required for full activation of the SREBP-1c promoter by insulin. We propose that the combined actions of the SRE, LXREs, Sp1 and NF-Y elements constitute an insulin-responsive cis-acting unit of the SREBP-1c gene in the liver.

An Sp1 response element in the Kaposi's sarcoma-associated herpesvirus open reading frame 50 promoter mediates lytic cycle induction by butyrate

Kaposi's sarcoma-associated herpesvirus (KSHV) can be driven into the lytic cycle in vitro by phorbol esters and sodium butyrate. This report begins to analyze the process by which butyrate activates the promoter of KSHV open reading frame 50 (ORF50), the key viral regulator of the KSHV latency to lytic cycle switch. A short fragment of the promoter, 134 nucleotides upstream of the translational start of ORF50, retained basal uninduced activity and conferred maximal responsiveness to sodium butyrate. The butyrate response element was mapped to a consensus Sp1-binding site. By means of electrophoretic mobility shift assays, both Sp1 and Sp3 were shown to form complexes in vitro with the ORF50 promoter at the Sp1 site. Butyrate induced the formation of a group of novel complexes, including several Sp3-containing complexes, one Sp1-containing complex, and several other complexes that were not identified with antibodies to Sp1 or Sp3. Formation of all butyrate-induced DNA-protein complexes was mediated by the consensus Sp1 site. In insect and mammalian cell lines, Sp1 significantly activated the ORF50 promoter linked to luciferase. Chromatin immunoprecipitation experiments in a PEL cell line showed that butyrate induced Sp1, CBP, and p300 binding to the ORF50 promoter in vivo in an on-off manner. The results suggest that induction of the KSHV lytic cycle by butyrate is mediated through interactions at the Sp1/Sp3 site located 103 to 112 nucleotides upstream of the translational initiation of ORF50 presumably by enhancing the binding of Sp1 to this site.

Hyperglycemia and Inhibition of Glycogen Synthase in Streptozotocin-treated Mice

Glycogen synthase is post-translationally modified by both phosphate and O-linked N-acetylglucosamine (O-GlcNAc). In 3T3-L1 adipocytes exposed to high concentrations of glucose, O-GlcNAc contributes to insulin resistance of glycogen synthase. We sought to determine whether O-GlcNAc also regulates glycogen synthase in vivo. Glycogen synthase activity in fat pad extracts was inhibited in streptozotocin (STZ)-treated diabetic mice. The half-maximal activation concentration for glucose 6-phosphate (A(0.5)) was increased to 830 +/- 120 microm compared with 240 +/- 20 microm in control mice (C, p < 0.01), while the basal glycogen synthase activity (%I-form) was decreased to 2.4 +/- 1.4% compared with 10.1 +/- 1.8% in controls (p < 0.01). Glycogen synthase activity remained inhibited after compensatory insulin treatment. After insulin treatment kinetic parameters of glycogen synthase were more closely correlated with blood glucose (A(0.5), r(2) = 0.70; %I-form, r(2) = 0.59) than insulin levels (A(0.5), r(2) = 0.04; %I-form, r(2) = 0.09). Hyperglycemia also resulted in an increase in the level of O-GlcNAc on glycogen synthase (16.1 +/- 1.8 compared with 7.0 +/- 0.9 arbitrary intensity units for controls, p < 0.01), even though the level of phosphorylation was identical in diabetic and control mice either with (STZ: 2.9 +/- 1.0 and C: 3.2 +/- 0.8) or without (STZ: 12.2 +/- 2.8 and C: 13.8 +/- 3.0 arbitrary intensity units) insulin treatment. In all mice the percent activation of glycogen synthase that could be achieved in vitro by recombinant protein phosphatase 1 (230 +/- 30%) was significantly greater in the presence of beta-d-N-acetylglucosaminidase (410 +/- 60%, p < 0.01). This synergistic stimulation of glycogen synthase due to codigestion by protein phosphatase 1 and beta-d-N-acetylglucosaminidase was more pronounced in STZ-diabetic mice (310 +/- 70%) compared with control mice (100 +/- 10%, p < 0.05). The findings demonstrate that O-GlcNAc has a role in the regulation of glycogen synthase both in normoglycemia and diabetes.

Hypoxia-inducible factor-1-independent regulation of vascular endothelial growth factor by hypoxia in colon cancer

The induction of vascular endothelial growth factor (VEGF) is an essential feature of tumor angiogenesis, and the hypoxia-inducible factor-1 (HIF-1) transcription factor is known to be a key mediator of this process. In colon cancer, the frequently mutated K-ras oncogene also can regulate VEGF expression, but the role that K-ras may play in hypoxia is unknown. Hypoxia induced VEGF promoter activity, mRNA, and protein levels in colon cancer cells. Although HIF-1alpha was induced by hypoxia, VEGF reporter constructs with selectively mutated hypoxia-response elements remained responsive to hypoxia. In addition, "knockdown" of HIF-1alpha by RNA interference only minimally inhibited the hypoxic induction of VEGF. A region of the VEGF promoter between -420 and -90 bp mediated this HIF-independent induction by hypoxia. The introduction of K-ras(Val12) augmented the hypoxic induction of VEGF, and this was observed in wild-type and HIF-1alpha knockdown colon cancer cells. Thus, VEGF may be induced by hypoxia through HIF-dependent and HIF-independent pathways, and K-ras also can induce VEGF in hypoxia independent of HIF-1. These findings suggest the existence of multiple mechanisms regulating the hypoxic induction of VEGF in colon cancer.