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Aberrant sugar metabolism is linked to an increased risk of pancreatic cancer. Previously, we found that high glucose induces genome instability and de novo oncogenic KRAS mutation preferentially in pancreatic cells through dysregulation of O-GlcNAcylation. Increasing O-GlcNAcylation by extrinsically supplying N-acetyl-D-glucosamine (GlcNAc) causes genome instability in all kinds of cell types regardless of pancreatic origin. Since many people consume excessive amount of sugar (glucose, fructose, and sucrose) in daily life, whether high sugar consumption directly causes genome instability in animals remains to be elucidated. In this communication, we show that excess sugar in the daily drink increases DNA damage and protein O-GlcNAcylation preferentially in pancreatic tissue but not in other kinds of tissue of mice. The effect of high sugar on the pancreatic tissue may be attributed to the intrinsic ratio of GFAT and PFK activity, a limiting factor that dictates UDP-GlcNAc levels. On the other hand, GlcNAc universally induces DNA damage in all six organs examined. Either inhibiting O-GlcNAcylation or supplementing dNTP pool diminishes the induced DNA damage in these organs, indicating that the mechanism of action is similar to that of high glucose treatment in pancreatic cells. Taken together, these results suggest the potential hazards of high sugar drinks and high glucosamine intake to genomic instability and possibly cancer initiation.

SUMMARY: As an essential enzyme in the uridine diphosphate (UDP)‐GlcNAc biosynthesis pathway, the significant role of N‐acetylglucosamine phosphate mutase (AGM) remains unknown in plants. In the present study, a functional plant AGM (AtAGM) was identified from Arabidopsis thaliana. AtAGM catalyzes the isomerization of GlcNAc‐1‐P and GlcNAc‐6‐P, and has broad catalytic activity on different phosphohexoses. UDP‐GlcNAc contents were significantly decreased in AtAGM T‐DNA insertional mutants, which caused temperature‐dependent growth defects in seedlings and vigorous growth in adult plants. Further analysis revealed that protein O‐GlcNAcylation but not N‐glycosylation was dramatically impaired in Atagm mutants due to UDP‐GlcNAc shortage. Combined with the results from O‐GlcNAcylation or N‐glycosylation deficient mutants, and O‐GlcNAcase inhibitor all suggested that protein O‐GlcNAcylation impairment mainly leads to the phenotypic variations of Atagm plants. In conclusion, based on the essential role in UDP‐GlcNAc biosynthesis, AtAGM is important for plant growth mainly via protein O‐GlcNAcylation‐level regulation. [ABSTRACT FROM AUTHOR]

Abstract Altered metabolism and deregulated cellular energetics are now considered a hallmark of all cancers. Glucose, glutamine, fatty acids, and amino acids are the primary drivers of tumor growth and act as substrates for the hexosamine biosynthetic pathway (HBP). The HBP culminates in the production of an amino sugar uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) that, along with other charged nucleotide sugars, serves as the basis for biosynthesis of glycoproteins and other glycoconjugates. These nutrient-driven post-translational modifications are highly altered in cancer and regulate protein functions in various cancer-associated processes. In this review, we discuss recent progress in understanding the mechanistic relationship between the HBP and cancer.

The hexosamine biosynthetic pathway (HBP) is a glucose metabolism pathway that results in the synthesis of a nucleotide sugar UDP-GlcNAc, which is subsequently used for the post-translational modification (O-GlcNAcylation) of intracellular proteins that regulate nutrient sensing and stress response. The HBP is carried out by a series of enzymes, many of which have been extensively implicated in cancer pathophysiology. Increasing evidence suggests that elevated activation of the HBP may act as a cancer biomarker. Inhibition of HBP enzymes could suppress tumor cell growth, modulate the immune response, reduce resistance, and sensitize tumor cells to conventional cancer therapy. Therefore, targeting the HBP may serve as a novel strategy for treating cancer patients. Here, we review the current findings on the significance of HBP enzymes in various cancers and discuss future approaches for exploiting HBP inhibition for cancer treatment. [ABSTRACT FROM AUTHOR]

Our previous studies identified that retinal endothelial damage caused by hyperglycemia or nucleoside diphosphate kinase-B (NDPK-B) deficiency is linked to elevation of angiopoietin-2 (Ang-2) and the activation of the hexosamine biosynthesis pathway (HBP). Herein, we investigated how NDPK-B is involved in the HBP in endothelial cells (ECs). The activities of NDPK-B and O-GlcNAcase (OGA) were measured by in vitro assays. Nucleotide metabolism and O-GlcNAcylated proteins were assessed by UPLC-PDA (Ultra-performance liquid chromatography with Photodiode array detection) and immunoblot, respectively. Re-expression of NDPK-B was achieved with recombinant adenoviruses. Our results show that NDPK-B depletion in ECs elevated UDP-GlcNAc levels and reduced NDPK activity, similar to high glucose (HG) treatment. Moreover, the expression and phosphorylation of glutamine:fructose-6-phosphate amidotransferase (GFAT) were induced, whereas OGA activity was suppressed. Furthermore, overall protein O-GlcNAcylation, along with O-GlcNAcylated Ang-2, was increased in NDPK-B depleted ECs. Pharmacological elevation of protein O-GlcNAcylation using Thiamet G (TMG) or OGA siRNA increased Ang-2 levels. However, the nucleoside triphosphate to diphosphate (NTP/NDP) transphosphorylase and histidine kinase activity of NDPK-B were dispensable for protein O-GlcNAcylation. NDPK-B deficiency hence results in the activation of HBP and the suppression of OGA activity, leading to increased protein O-GlcNAcylation and further upregulation of Ang-2. The data indicate a critical role of NDPK-B in endothelial damage via the modulation of the HBP.

Abstract: Hyaluronan (HA) is a glycosaminoglycan composed by repeating units of D-glucuronic acid (GlcUA) and N-acetylglucosamine (GlcNAc) that is ubiquitously present in the extracellular matrix (ECM) where it has a critical role in the physiology and pathology of several mammalian tissues. HA represents a perfect environment in which cells can migrate and proliferate. Moreover, several receptors can interact with HA at cellular level triggering multiple signal transduction responses. The control of the HA synthesis is therefore critical in ECM assembly and cell biology; in this review we address the metabolic regulation of HA synthesis. In contrast with other glycosaminoglycans, which are synthesized in the Golgi apparatus, HA is produced at the plasma membrane by HA synthases (HAS1-3), which use cytoplasmic UDP-glucuronic acid and UDP-N-acetylglucosamine as substrates. UDP-GlcUA and UDP-hexosamine availability is critical for the synthesis of GAGs, which is an energy consuming process. AMP activated protein kinase (AMPK), which is considered a sensor of the energy status of the cell and is activated by low ATP:AMP ratio, leads to the inhibition of HA secretion by HAS2 phosphorylation at threonine 110. However, the most general sensor of cellular nutritional status is the hexosamine biosynthetic pathway that brings to the formation of UDP-GlcNAc and intracellular protein glycosylation by O-linked attachment of the monosaccharide β-N-acetylglucosamine (O-GlcNAcylation) to specific aminoacid residues. Such highly dynamic and ubiquitous protein modification affects serine 221 residue of HAS2 that lead to a dramatic stabilization of the enzyme in the membranes. [Copyright &y& Elsevier]

Our previous studies identified that retinal endothelial damage caused by hyperglycemia or nucleoside diphosphate kinase-B (NDPK-B) deficiency is linked to elevation of angiopoietin-2 (Ang-2) and the activation of the hexosamine biosynthesis pathway (HBP). Herein, we investigated how NDPK-B is involved in the HBP in endothelial cells (ECs). The activities of NDPK-B and O-GlcNAcase (OGA) were measured by in vitro assays. Nucleotide metabolism and O-GlcNAcylated proteins were assessed by UPLC-PDA (Ultra-performance liquid chromatography with Photodiode array detection) and immunoblot, respectively. Re-expression of NDPK-B was achieved with recombinant adenoviruses. Our results show that NDPK-B depletion in ECs elevated UDP-GlcNAc levels and reduced NDPK activity, similar to high glucose (HG) treatment. Moreover, the expression and phosphorylation of glutamine:fructose-6-phosphate amidotransferase (GFAT) were induced, whereas OGA activity was suppressed. Furthermore, overall protein O-GlcNAcylation, along with O-GlcNAcylated Ang-2, was increased in NDPK-B depleted ECs. Pharmacological elevation of protein O-GlcNAcylation using Thiamet G (TMG) or OGA siRNA increased Ang-2 levels. However, the nucleoside triphosphate to diphosphate (NTP/NDP) transphosphorylase and histidine kinase activity of NDPK-B were dispensable for protein O-GlcNAcylation. NDPK-B deficiency hence results in the activation of HBP and the suppression of OGA activity, leading to increased protein O-GlcNAcylation and further upregulation of Ang-2. The data indicate a critical role of NDPK-B in endothelial damage via the modulation of the HBP. [ABSTRACT FROM AUTHOR]