TATA-Box Binding Protein O-GlcNAcylation at T114 Regulates Formation of the B-TFIID Complex and Is Critical for Metabolic Gene Regulation.

In eukaryotes, gene expression is performed by three RNA polymerases that are targeted to promoters by molecular complexes. A unique common factor, the TATA-box binding protein (TBP), is thought to serve as a platform to assemble pre-initiation complexes competent for transcription. Here, we describe a novel molecular mechanism of nutrient regulation of gene transcription by dynamic O-GlcNAcylation of TBP. We show that O-GlcNAcylation at T114 of TBP blocks its interaction with BTAF1, hence the formation of the B-TFIID complex, and its dynamic cycling on and off of DNA. Transcriptomic and metabolomic analyses of TBPT114A CRISPR/Cas9-edited cells showed that loss of O-GlcNAcylation at T114 increases TBP binding to BTAF1 and directly impacts expression of 408 genes. Lack of O-GlcNAcylation at T114 is associated with a striking reprogramming of cellular metabolism induced by a profound modification of the transcriptome, leading to gross alterations in lipid storage.

Pharmaceutical targeting of the cannabinoid type 1 receptor impacts the crosstalk between immune cells and islets to reduce insulitis in humans.

AIMS/HYPOTHESIS: Insulitis, a hallmark of inflammation preceding autoimmune type 1 diabetes, leads to the eventual loss of functional beta cells. However, functional beta cells can persist even in the face of continuous insulitis. Despite advances in immunosuppressive treatments, maintaining functional beta cells to prevent insulitis progression and hyperglycaemia remains a challenge. The cannabinoid type 1 receptor (CB1R), present in immune cells and beta cells, regulates inflammation and beta cell function. Here, we pioneer an ex vivo model mirroring human insulitis to investigate the role of CB1R in this process. METHODS: CD4+ T lymphocytes were isolated from peripheral blood mononuclear cells (PBMCs) from male and female individuals at the onset of type 1 diabetes and from non-diabetic individuals, RNA was extracted and mRNA expression was analysed by real-time PCR. Single beta cell expression from donors with type 1 diabetes was obtained from data mining. Patient-derived human islets from male and female cadaveric donors were 3D-cultured in solubilised extracellular matrix gel in co-culture with the same donor PBMCs, and incubated with cytokines (IL-1ß, TNF-α, IFN-γ) for 24-48 h in the presence of vehicle or increasing concentrations of the CB1R blocker JD-5037. Expression of CNR1 (encoding for CB1R) was ablated using CRISPR/Cas9 technology. Viability, intracellular stress and signalling were assayed by live-cell probing and real-time PCR. The islet function measured as glucose-stimulated insulin secretion was determined in a perifusion system. Infiltration of immune cells into the islets was monitored by microscopy. Non-obese diabetic mice aged 7 weeks were treated for 1 week with JD-5037, then euthanised. Profiling of immune cells infiltrated in the islets was performed by flow cytometry. RESULTS: CNR1 expression was upregulated in circulating CD4+ T cells from individuals at type 1 diabetes onset (6.9-fold higher vs healthy individuals) and in sorted islet beta cells from donors with type 1 diabetes (3.6-fold higher vs healthy counterparts). The peripherally restricted CB1R inverse agonist JD-5037 arrested the initiation of insulitis in humans and mice. Mechanistically, CB1R blockade prevented islet NO production and ameliorated the ATF6 arm of the unfolded protein response. Consequently, cyto/chemokine expression decreased in human islets, leading to sustained islet cell viability and function. CONCLUSIONS/INTERPRETATION: These results suggest that CB1R could be an interesting target for type 1 diabetes while highlighting the regulatory mechanisms of insulitis. Moreover, these findings may apply to type 2 diabetes where islet inflammation is also a pathophysiological factor. DATA AVAILABILITY: Transcriptomic analysis of sorted human beta cells are from Gene Expression Omnibus database, accession no. GSE121863, available at https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSM3448161 .

Dual regulation of fatty acid synthase (FASN) expression by O-GlcNAc transferase (OGT) and mTOR pathway in proliferating liver cancer cells.

Fatty acid synthase (FASN) participates in many fundamental biological processes, including energy storage and signal transduction, and is overexpressed in many cancer cells. We previously showed in a context of lipogenesis that FASN is protected from degradation by its interaction with O-GlcNAc transferase (OGT) in a nutrient-dependent manner. We and others also reported that OGT and O-GlcNAcylation up-regulate the PI3K/AKT/mTOR pathway that senses mitogenic signals and nutrient availability to drive cell cycle. Using biochemical and microscopy approaches, we show here that FASN co-localizes with OGT in the cytoplasm and, to a lesser extent, in the membrane fraction. This interaction occurs in a cell cycle-dependent manner, following the pattern of FASN expression. Moreover, we show that FASN expression depends on OGT upon serum stimulation. The level of FASN also correlates with the activation of the PI3K/AKT/mTOR pathway in hepatic cell lines, and in livers of obese mice and in a chronically activated insulin and mTOR signaling mouse model (PTEN-null mice). These results indicate that FASN is under a dual control of O-GlcNAcylation and mTOR pathways. In turn, blocking FASN with the small-molecule inhibitor C75 reduces both OGT and O-GlcNAcylation levels, and mTOR activation, highlighting a novel reciprocal regulation between these actors. In addition to the role of O-GlcNAcylation in tumorigenesis, our findings shed new light on how aberrant activity of FASN and mTOR signaling may promote the emergence of hepatic tumors.

Muscle cannabinoid 1 receptor regulates Il-6 and myostatin expression, governing physical performance and whole-body metabolism.

Sarcopenic obesity, the combination of skeletal muscle mass and function loss with an increase in body fat, is associated with physical limitations, cardiovascular diseases, metabolic stress, and increased risk of mortality. Cannabinoid receptor type 1 (CB1R) plays a critical role in the regulation of whole-body energy metabolism because of its involvement in controlling appetite, fuel distribution, and utilization. Inhibition of CB1R improves insulin secretion and insulin sensitivity in pancreatic ß-cells and hepatocytes. We have now developed a skeletal muscle-specific CB1R-knockout (Skm-CB1R-/-) mouse to study the specific role of CB1R in muscle. Muscle-CB1R ablation prevented diet-induced and age-induced insulin resistance by increasing IR signaling. Moreover, muscle-CB1R ablation enhanced AKT signaling, reducing myostatin expression and increasing IL-6 secretion. Subsequently, muscle-CB1R ablation increased myogenesis through its action on MAPK-mediated myogenic gene expression. Consequently, Skm-CB1R-/- mice had increased muscle mass and whole-body lean/fat ratio in obesity and aging. Muscle-CB1R ablation improved mitochondrial performance, leading to increased whole-body muscle energy expenditure and improved physical endurance, with no change in body weight. These results collectively show that CB1R in muscle is sufficient to regulate whole-body metabolism and physical performance and is a novel target for the treatment of sarcopenic obesity. -González-Mariscal, I., Montoro, R. A., O'Connell, J. F., Kim, Y., Gonzalez-Freire, M., Liu, Q.-R., Alfaras, I., Carlson, O. D., Lehrmann, E., Zhang, Y., Becker, K. G., Hardivillé, S., Ghosh, P., Egan, J. M. Muscle cannabinoid 1 receptor regulates Il-6 and myostatin expression, governing physical performance and whole-body metabolism.

Exploring the Potential of ß-Catenin O-GlcNAcylation by Using Fluorescence-Based Engineering and Imaging.

Monitoring glycosylation changes within cells upon response to stimuli remains challenging because of the complexity of this large family of post-translational modifications (PTMs). We developed an original tool, enabling labeling and visualization of the cell cycle key-regulator ß-catenin in its O-GlcNAcylated form, based on intramolecular Förster resonance energy transfer (FRET) technology in cells. We opted for a bioorthogonal chemical reporter strategy based on the dual-labeling of ß-catenin with a green fluorescent protein (GFP) for protein sequence combined with a chemically-clicked imaging probe for PTM, resulting in a fast and easy to monitor qualitative FRET assay. We validated this technology by imaging the O-GlcNAcylation status of ß-catenin in HeLa cells. The changes in O-GlcNAcylation of ß-catenin were varied by perturbing global cellular O-GlcNAc levels with the inhibitors of O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Finally, we provided a flowchart demonstrating how this technology is transposable to any kind of glycosylation.

O-GlcNAc transferase associates with the MCM2-7 complex and its silencing destabilizes MCM-MCM interactions.

O-GlcNAcylation of proteins is governed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). The homeostasis of O-GlcNAc cycling is regulated during cell cycle progression and is essential for proper cellular division. We previously reported the O-GlcNAcylation of the minichromosome maintenance proteins MCM2, MCM3, MCM6 and MCM7. These proteins belong to the MCM2-7 complex which is crucial for the initiation of DNA replication through its DNA helicase activity. Here we show that the six subunits of MCM2-7 are O-GlcNAcylated and that O-GlcNAcylation of MCM proteins mainly occurs in the chromatin-bound fraction of synchronized human cells. Moreover, we identify stable interaction between OGT and several MCM subunits. We also show that down-regulation of OGT decreases the chromatin binding of MCM2, MCM6 and MCM7 without affecting their steady-state level. Finally, OGT silencing or OGA inhibition destabilizes MCM2/6 and MCM4/7 interactions in the chromatin-enriched fraction. In conclusion, OGT is a new partner of the MCM2-7 complex and O-GlcNAcylation homeostasis might regulate MCM2-7 complex by regulating the chromatin loading of MCM6 and MCM7 and stabilizing MCM/MCM interactions.

Delta-lactoferrin induces cell death via the mitochondrial death signaling pathway by upregulating bax expression.

Delta-lactoferrin (∆Lf) is a transcription factor belonging to the lactoferrin family, the expression of which inhibits cell proliferation and leads to Skp1 and DcpS gene transactivation. In this study, we showed that ∆Lf expression also induces cell death via apoptosis in HEK 293 and MCF7 cells using a cell viability assay and DNA fragmentation. Western blot analyses showed that apoptosis was caspase-9, 7 and 8 dependent. Proteolytic cleavage of the endonuclease PARP was significantly increased. The levels of expression of Bcl family members were detected by immunochemistry and showed that the Bcl-xl/Bax and Bcl-2/Bax protein ratios were decreased. We determined that the pro-apoptotic effects of ∆Lf are mainly mediated by the activation of the mitochondria-dependent death-signaling pathway. Apoptosis induction by ∆Lf is concomitant with increased cellular levels of Bax protein. Analysis of the Bax promoter region detected a ∆Lf response element located at -155 bp from the transcription start site. Both luciferase reporter gene and chromatin immunoprecipitation assays confirmed that ∆Lf interacts in vitro and in vivo specifically with this sequence. Its deletion, realized using directed mutagenesis, totally abolished ∆Lf transcriptional activity, identifying it as a ∆Lf-responsive element. These results indicate that the Bax gene is a novel ∆Lf target. Moreover we also showed that the O-GlcNAc/P interplay, which controls ∆Lf transcriptional activity, modulates Bax transactivation.

Delta-lactoferrin, an intracellular lactoferrin isoform that acts as a transcription factor.

Delta-lactoferrin (ΔLf) is a transcription factor of which the expression is downregulated in cancer. It is a healthy tissue marker and a high expression level of its transcripts was correlated with a good prognosis in breast cancer. ΔLf results from alternative promoter usage of the hLf gene leading to the production of 2 isoforms with alternative N-termini: lactoferrin, which is secreted, and ΔLf, its nucleocytoplasmic counterpart. ΔLf possesses antiproliferative properties and induces cell cycle arrest. It is an efficient transcription factor interacting in vivo via a ΔLf response element found in the Skp1, Bax, DcpS, and SelH promoters. Since ΔLf possesses different target genes, modifications in its activity or concentration may have crucial effects on cell homeostasis. Posttranslational modifications modulate ΔLf transcription factor activity. Our earlier investigations showed that O-GlcNAcylation negatively regulates ΔLf transcriptional activity, whilst inhibiting its ubiquitination and increasing its half-life. On the other hand, phosphorylation potentiates ΔLf transcriptional activity. Recently, we showed that ΔLf is also modified by SUMOylation. Therefore, cooperation and (or) competition among SUMOylation, ubiquitination, phosphorylation, and O-GlcNAcylation may contribute to the establishment of a fine regulation of ΔLf transcriptional activity depending on the type of target gene and cellular homeostasis.

Thymidylate synthase O-GlcNAcylation: a molecular mechanism of 5-FU sensitization in colorectal cancer.

Alteration of O-GlcNAcylation, a dynamic posttranslational modification, is associated with tumorigenesis and tumor progression. Its role in chemotherapy response is poorly investigated. Standard treatment for colorectal cancer (CRC), 5-fluorouracil (5-FU), mainly targets Thymidylate Synthase (TS). TS O-GlcNAcylation was reported but not investigated yet. We hypothesize that O-GlcNAcylation interferes with 5-FU CRC sensitivity by regulating TS. In vivo, we observed that combined 5-FU with Thiamet-G (O-GlcNAcase (OGA) inhibitor) treatment had a synergistic inhibitory effect on grade and tumor progression. 5-FU decreased O-GlcNAcylation and, reciprocally, elevation of O-GlcNAcylation was associated with TS increase. In vitro in non-cancerous and cancerous colon cells, we showed that 5-FU impacts O-GlcNAcylation by decreasing O-GlcNAc Transferase (OGT) expression both at mRNA and protein levels. Reciprocally, OGT knockdown decreased 5-FU-induced cancer cell apoptosis by reducing TS protein level and activity. Mass spectrometry, mutagenesis and structural studies mapped O-GlcNAcylated sites on T251 and T306 residues and deciphered their role in TS proteasomal degradation. We reveal a crosstalk between O-GlcNAcylation and 5-FU metabolism in vitro and in vivo that converges to 5-FU CRC sensitization by stabilizing TS. Overall, our data propose that combining 5-FU-based chemotherapy with Thiamet-G could be a new way to enhance CRC response to 5-FU.

O-GlcNAcylation/phosphorylation cycling at Ser10 controls both transcriptional activity and stability of delta-lactoferrin.

Delta-lactoferrin (DeltaLf) is a transcription factor that up-regulates DcpS, Skp1, and Bax genes, provoking cell cycle arrest and apoptosis. It is post-translationally modified either by O-GlcNAc or phosphate, but the effects of the O-GlcNAc/phosphorylation interplay on DeltaLf function are not yet understood. Here, using a series of glycosylation mutants, we showed that Ser(10) is O-GlcNAcylated and that this modification is associated with increased DeltaLf stability, achieved by blocking ubiquitin-dependent proteolysis, demonstrating that O-GlcNAcylation protects against polyubiquitination. We highlighted the (391)KSQQSSDPDPNCVD(404) sequence as a functional PEST motif responsible for DeltaLf degradation and defined Lys(379) as the main polyubiquitin acceptor site. We next investigated the control of DeltaLf transcriptional activity by the O-GlcNAc/phosphorylation interplay. Reporter gene analyses using the Skp1 promoter fragment containing a DeltaLf response element showed that O-GlcNAcylation at Ser(10) negatively regulates DeltaLf transcriptional activity, whereas phosphorylation activates it. Using a chromatin immunoprecipitation assay, we showed that O-GlcNAcylation inhibits DNA binding. Deglycosylation leads to DNA binding and transactivation of the Skp1 promoter at a basal level. Basal transactivation was markedly enhanced by 2-3-fold when phosphorylation was mimicked at Ser(10) by aspartate. Moreover, using double chromatin immunoprecipitation assays, we showed that the DeltaLf transcriptional complex binds to the DeltaLf response element and is phosphorylated and/or ubiquitinated, suggesting that DeltaLf transcriptional activity and degradation are concomitant events. Collectively, our results indicate that reciprocal occupancy of Ser(10) by either O-phosphate or O-GlcNAc coordinately regulates DeltaLf stability and transcriptional activity.

Discrimination and evaluation of lactoferrin and delta-lactoferrin gene expression levels in cancer cells and under inflammatory stimuli using TaqMan real-time PCR.

The lactoferrin gene is known to be expressed either constitutively or under inducible conditions such as hormonal stimuli or inflammation. Its transcription from alternative promoters leads to two products, lactoferrin (Lf) and delta-lactoferrin (DeltaLf) mRNAs the expressions of which are altered during oncogenesis. The comparison of the two enhancer/promoter regions revealed that the two isoforms might be differentially trans-activated. Nevertheless, concomitant expression of both transcripts has been found in some normal tissues and in a subset of breast cancer cell lines and biopsies. Moreover, we found putative inflammatory response elements in both P1 and P2 promoter regions suggesting that both Lf and DeltaLf might be upregulated under inflammatory stimuli. Therefore, a duplex Taqman gene expression assay has been developed and used to profile mRNA expression of the Lf gene in the case of cancer and under inflammatory conditions. Discrimination between the two transcripts is achieved by using a primer pairs/probe set within exon 1beta for DeltaLf and a primer pairs/probe set within exon 1 and exon 2 for Lf. In this study, we confirmed that Lf/DeltaLf Taqman gene expression assay is a powerful tool to investigate the expression of both Lf and DeltaLf transcripts. We also showed that lymphocytes and leukocytes isolated from fresh human blood expressed an extremely high level of DeltaLf messengers. An extensive series of cancer cell lines has been studied confirming that both P1 and P2 promoter regions of the Lf gene are downregulated or silenced in the case of cancer. Furthermore, using stimulation by bacterial lipopolysaccharides (LPS), we showed that in MDA-MB-231 and HT-29 epithelial cells, Lf expression is strongly increased with a higher expression level in MDA-MB-231 whereas DeltaLf expression is not. These results suggest that the NF-kappaB/cRel response elements present in the P1 promoter region are functional whereas those present in the P2 promoter region are not and show that DeltaLf is not regulated in inflammatory conditions.

Cross-Dysregulation of O-GlcNAcylation and PI3K/AKT/mTOR Axis in Human Chronic Diseases.

The hexosamine biosynthetic pathway (HBP) and the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway are considered as nutrient sensors that regulate several essential biological processes. The hexosamine biosynthetic pathway produces uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), the substrate for O-GlcNAc transferase (OGT), the enzyme that O-GlcNAcylates proteins on serine (Ser) and threonine (Thr) residues. O-linked ß-N-acetylglucosaminylation (O-GlcNAcylation) and phosphorylation are highly dynamic post-translational modifications occurring at the same or adjacent sites that regulate folding, stability, subcellular localization, partner interaction, or activity of target proteins. Here we review recent evidence of a cross-regulation of PI3K/AKT/mTOR signaling pathway and protein O-GlcNAcylation. Furthermore, we discuss their co-dysregulation in pathological conditions, e.g., cancer, type-2 diabetes (T2D), and cardiovascular, and neurodegenerative diseases.

Apart From Rhoptries, Identification of Toxoplasma gondii's O-GlcNAcylated Proteins Reinforces the Universality of the O-GlcNAcome.

O-linked ß-N-acetylglucosaminylation or O-GlcNAcylation is a widespread post-translational modification that belongs to the large and heterogeneous group of glycosylations. The functions managed by O-GlcNAcylation are diverse and include regulation of transcription, replication, protein's fate, trafficking, and signaling. More and more evidences tend to show that deregulations in the homeostasis of O-GlcNAcylation are involved in the etiology of metabolic diseases, cancers and neuropathologies. O-GlcNAc transferase or OGT is the enzyme that transfers the N-acetylglucosamine residue onto target proteins confined within the cytosolic and nuclear compartments. A form of OGT was predicted for Toxoplasma and recently we were the first to show evidence of O-GlcNAcylation in the apicomplexans Toxoplasma gondii and Plasmodium falciparum. Numerous studies have explored the O-GlcNAcome in a wide variety of biological models but very few focus on protists. In the present work, we used enrichment on sWGA-beads and immunopurification to identify putative O-GlcNAcylated proteins in Toxoplasma gondii. Many of the proteins found to be O-GlcNAcylated were originally described in higher eukaryotes and participate in cell shape organization, response to stress, protein synthesis and metabolism. In a more original way, our proteomic analyses, confirmed by sWGA-enrichment and click-chemistry, revealed that rhoptries, proteins necessary for invasion, are glycosylated. Together, these data show that regardless of proteins strictly specific to organisms, O-GlcNAcylated proteins are rather similar among living beings.

Human delta-lactoferrin is a transcription factor that enhances Skp1 (S-phase kinase-associated protein) gene expression.

Delta-lactoferrin is a cytoplasmic lactoferrin isoform that can locate to the nucleus, provoking antiproliferative effects and cell cycle arrest in S phase. Using macroarrays, the expression of genes involved in the G(1)/S transition was examined. Among these, Skp1 showed 2-3-fold increased expression at both the mRNA and protein levels. Skp1 (S-phase kinase-associated protein) belongs to the Skp1/Cullin-1/F-box ubiquitin ligase complex responsible for the ubiquitination of cellular regulators leading to their proteolysis. Skp1 overexpression was also found after delta-lactoferrin transient transfection in other cell lines (HeLa, MDA-MB-231, HEK 293) at comparable levels. Analysis of the Skp1 promoter detected two sequences that were 90% identical to those previously known to interact with lactoferrin, the secretory isoform of delta-lactoferrin (GGCACTGTAC-S1(Skp1), located at - 1067 bp, and TAGAAGTCAA-S2(Skp1), at - 646 bp). Both gel shift and chromatin immunoprecipitation assays demonstrated that delta-lactoferrin interacts in vitro and in vivo specifically with these sequences. Reporter gene analysis confirmed that delta-lactoferrin recognizes both sequences within the Skp1 promoter, with a higher activity on S1(Skp1). Deletion of both sequences totally abolished delta-lactoferrin transcriptional activity, identifying them as delta-lactoferrin-responsive elements. Delta-lactoferrin enters the nucleus via a short bipartite RRSDTSLTWNSVKGKK(417-432) nuclear localization signal sequence, which was demonstrated to be functional using mutants. Our results show that delta-lactoferrin binds to the Skp1 promoter at two different sites, and that these interactions lead to its transcriptional activation. By increasing Skp1 gene expression, delta-lactoferrin may regulate cell cycle progression via control of the proteasomal degradation of S-phase actors.

Nutrient regulation of gene expression by O-GlcNAcylation of chromatin.

O-GlcNAcylation is a dynamic post-translational modification that is responsive to nutrient availably via the hexosamine biosynthetic pathway and its endproduct UDP-GlcNAc. O-GlcNAcylation serves as a nutrient sensor to regulate the activities of many proteins involved in nearly all biological processes. Within the last decade, OGT, OGA and O-GlcNAcylation have been shown to be at the nexus of epigenetic marks controlling gene expression during embryonic development, cell differentiation, in the maintenance of epigenetic states and in the etiology of epigenetic related diseases. OGT O-GlcNAcylates histones and epigenetic writers/erasers, and regulates gene activation, as well as gene repression. Here, we highlight recent work documenting the important roles O-GlcNAcylation and its cycling enzymes play in the nutrient regulation of epigenetic partners controlling gene expression.

Modification by SUMOylation Controls Both the Transcriptional Activity and the Stability of Delta-Lactoferrin.

Delta-lactoferrin is a transcription factor, the expression of which is downregulated or silenced in case of breast cancer. It possesses antitumoral activities and when it is re-introduced in mammary epithelial cancer cell lines, provokes antiproliferative effects. It is posttranslationally modified and our earlier investigations showed that the O-GlcNAcylation/phosphorylation interplay plays a major role in the regulation of both its stability and transcriptional activity. Here, we report the covalent modification of delta-lactoferrin with the small ubiquitin-like modifier SUMO-1. Mutational and reporter gene analyses identified five different lysine residues at K13, K308, K361, K379 and K391 as SUMO acceptor sites. The SUMOylation deficient M5S mutant displayed enhanced transactivation capacity on a delta-lactoferrin responsive promoter, suggesting that SUMO-1 negatively regulates the transactivation function of delta-lactoferrin. K13, K308 and K379 are the main SUMO sites and among them, K308, which is located in a SUMOylation consensus motif of the NDSM-like type, is a key SUMO site involved in repression of delta-lactoferrin transcriptional activity. K13 and K379 are both targeted by other posttranslational modifications. We demonstrated that K13 is the main acetylation site and that favoring acetylation at K13 reduced SUMOylation and increased delta-lactoferrin transcriptional activity. K379, which is either ubiquitinated or SUMOylated, is a pivotal site for the control of delta-lactoferrin stability. We showed that SUMOylation competes with ubiquitination and protects delta-lactoferrin from degradation by positively regulating its stability. Collectively, our results indicate that multi-SUMOylation occurs on delta-lactoferrin to repress its transcriptional activity. Reciprocal occupancy of K13 by either SUMO-1 or an acetyl group may contribute to the establishment of finely regulated mechanisms to control delta-lactoferrin transcriptional activity. Moreover, competition between SUMOylation and ubiquitination at K379 coordinately regulates the stability of delta-lactoferrin toward proteolysis. Therefore SUMOylation of delta-lactoferrin is a novel mechanism controlling both its activity and stability.

Nutrient regulation of signaling, transcription, and cell physiology by O-GlcNAcylation.

The nutrient sensor, O-linked N-acetylglucosamine (O-GlcNAc), cycles on and off nuclear and cytosolic proteins to regulate many cellular processes, including transcription and signaling. Dysregulated O-GlcNAcylation and its interplay with phosphorylation contribute to the etiology of diabetes, cancer, and neurodegeneration. Herein, we review recent findings about O-GlcNAc's regulation of cell physiology.

Proteomic approach to the identification of novel delta-lactoferrin target genes: Characterization of DcpS, an mRNA scavenger decapping enzyme.

The expression of the transcription factor DeltaLf is deregulated in cancer cells. Its overexpression provokes cell cycle arrest along with antiproliferative effects and we recently showed that the Skp1 gene promoter was a target of DeltaLf. Skp1 belongs to the Skp1/Cullin-1/F-box ubiquitin ligase complex responsible for the ubiquitination and the proteosomal degradation of numerous cellular regulators. The transcriptional activity of DeltaLf is highly controlled and negatively regulated by O-GlcNAc, a dynamic post-translational modification known to regulate the functions of many intracellular proteins. We, therefore, constructed a DeltaLf-M4 mutant corresponding to a constitutively active DeltaLf isoform in which all the glycosylation sites were mutated. In order to discover novel targets of DeltaLf transcriptional activity and to investigate the impact of the O-GlcNAc regulation on this activity in situ we compared the proteome profiles of DeltaLf- and DeltaLf-M4-expressing HEK293 cells versus null plasmid transfected cells. A total of 14 differentially expressed proteins were visualized by 2D electrophoresis and silver staining and eight proteins were identified by mass spectrometry analyses (MALDI-TOF; LC-MS/MS), all of which were upregulated. The identified proteins are involved in several processes such as mRNA maturation and stability, cell viability, proteasomal degradation, protein and mRNA quality control. Among these proteins, only DcpS and TCPB were also upregulated at the mRNA level. Analysis of their respective promoters led to the detection of a cis-regulating element in the DcpS promoter. The S1(DcpS) is 80% identical to the S1 sequence previously described by He and Furmanski [Sequence specificity and transcriptional activation in the binding of lactoferrin to DNA, Nature 373 (1995) 721-724]. Reporter gene analyses and ChIP assays demonstrated that DeltaLf interacts specifically with the DcpS promoter in vivo. These data established that DcpS, a key enzyme in mRNA decay, is a new target of DeltaLf transcriptional activity.

Construction of a multi-functional helper-dependent adenovirus based system for cancer gene therapy.

Adenovirus holds great promise as a gene delivery system; it can hold large amounts of exogenous DNA and can be chemically and genetically modified to improve targeting to specific cells and tissues. A recombinant adenovirus construct expressing p53 is currently in clinical use as a cancer therapy in China. However, the use of adenovirus constructs in therapy is limited due to patients' strong immune response against these viruses and their gene products. To overcome this problem helper-dependent adenoviruses which do not express any viral gene products have been developed. Because the helper-dependent viruses do not express any viral gene products, a helper virus is required for their replication and encapsidation into infectious particles. This manuscript describes the construction of a prototype helper-dependent adenovirus system built such that it can be easily modified. The helper-dependent virus described here is built of a series of four cassettes, each with its own function. Furthermore, each individual cassette can be removed and replaced with a cassette with a different function. In this way, different helper-dependent viruses can be readily created. This type of system could be very useful in cancer therapy: For example, libraries of different cassettes could be maintained, allowing rapid assembly of constructs able to provide therapy for individual tumor types.