The role of protein glycosylation inhibitors in the prevention of metastasis and therapy of cancer

GRASP depletion-mediated Golgi destruction decreases cell adhesion and migration via the reduction of α5β1 integrin

The Golgi apparatus is a membrane-bound organelle that serves as the center for trafficking and processing of proteins and lipids. To perform these functions, the Golgi forms a multilayer stacked structure held by GRASP55 and GRASP65 trans-oligomers and perhaps their binding partners. Depletion of GRASP proteins disrupts Golgi stack formation and impairs critical functions of the Golgi, such as accurate protein glycosylation and sorting. However, how Golgi destruction affects other cellular activities is so far unknown. Here, we report that depletion of GRASP proteins reduces cell attachment and migration. Interestingly, GRASP depletion reduces the protein level of α5β1 integrin, the major cell adhesion molecule at the surface of HeLa and MDA-MB-231 cells, due to decreased integrin protein synthesis. GRASP depletion also increases cell growth and total protein synthesis. These new findings enrich our understanding on the role of the Golgi in cell physiology and provide a potential target for treating protein-trafficking disorders.

Positive-unlabelled learning of glycosylation sites in the human proteome

BACKGROUND

As an important type of post-translational modification (PTM), protein glycosylation plays a crucial role in protein stability and protein function. The abundance and ubiquity of protein glycosylation across three domains of life involving Eukarya, Bacteria and Archaea demonstrate its roles in regulating a variety of signalling and metabolic pathways. Mutations on and in the proximity of glycosylation sites are highly associated with human diseases. Accordingly, accurate prediction of glycosylation can complement laboratory-based methods and greatly benefit experimental efforts for characterization and understanding of functional roles of glycosylation. For this purpose, a number of supervised-learning approaches have been proposed to identify glycosylation sites, demonstrating a promising predictive performance. To train a conventional supervised-learning model, both reliable positive and negative samples are required. However, in practice, a large portion of negative samples (i.e. non-glycosylation sites) are mislabelled due to the limitation of current experimental technologies. Moreover, supervised algorithms often fail to take advantage of large volumes of unlabelled data, which can aid in model learning in conjunction with positive samples (i.e. experimentally verified glycosylation sites).

RESULTS

In this study, we propose a positive unlabelled (PU) learning-based method, PA2DE (V2.0), based on the AlphaMax algorithm for protein glycosylation site prediction. The predictive performance of this proposed method was evaluated by a range of glycosylation data collected over a ten-year period based on an interval of three years. Experiments using both benchmarking and independent tests show that our method outperformed the representative supervised-learning algorithms (including support vector machines and random forests) and one-class learners, as well as currently available prediction methods in terms of F1 score, accuracy and AUC measures. In addition, we developed an online web server as an implementation of the optimized model (available at http://glycomine.erc.monash.edu/Lab/GlycoMine_PU/ ) to facilitate community-wide efforts for accurate prediction of protein glycosylation sites.

CONCLUSION

The proposed PU learning approach achieved a competitive predictive performance compared with currently available methods. This PU learning schema may also be effectively employed and applied to address the prediction problems of other important types of protein PTM site and functional sites.

Prognostic relevance of glycosylation-associated genes in breast cancer

Glycosylation of cellular proteins has important impact on their stability and functional properties, and glycan structures strongly influence cell adhesion. Many enzymes are involved in glycoconjugate synthesis and degradation, but there is only limited information about their role in breast cancer progression. Therefore, we retrieved RNA expression data of 202 glycosylation genes generated by microarray analysis (Affymetrix HG-U133A) in a cohort of 194 mammary carcinomas with long-term follow-up information. After univariate and multivariate Cox regression analysis, genes with independent prognostic value were identified. These were further analysed by Kaplan-Meier analysis and log-rank tests, and their prognostic value was validated in a second cohort of 200 tumour samples from patients without systemic therapy. In our first cohort, we identified 24 genes with independent prognostic value, coding for sixteen anabolic and eight catabolic enzymes. Functionally, these genes are involved in all important glycosylation pathways, namely O-glycosylation, N-glycosylation, O-fucosylation, synthesis of glycosaminoglycans and glycolipids. Eighteen genes also showed prognostic significance in chemotherapy-treated patients. In the second cohort, six of the 24 relevant genes were of prognostic significance (FUT1, FUCA1, POFUT1, MAN1A1, RPN1 and DPM1), whereas a trend was observed for three additional probesets (GCNT4, ST3GAL6 and UGCG). In a stratified analysis of molecular subtypes combining both cohorts, great differences appeared suggesting a predominant role of N-glycosylation in luminal cancers and O-glycosylation in triple-negative ones. Correlations of gene expression with metastases of various localizations point to a role of glycan structures in organ-specific metastatic spread. Our results indicate that various glycosylation reactions influence progression and metastasis of breast cancer and might thus represent potential therapeutic targets.

The ubiquitin ligase HACE1 regulates Golgi membrane dynamics during the cell cycle

Partitioning of the Golgi membrane into daughter cells during mammalian cell division occurs through a unique disassembly and reassembly process that is regulated by ubiquitination. However, the identity of the ubiquitin ligase is unknown. Here we show that the Homologous to the E6-AP Carboxyl Terminus (HECT) domain containing ubiquitin ligase HACE1 is targeted to the Golgi membrane through interactions with Rab proteins. The ubiquitin ligase activity of HACE1 in mitotic Golgi disassembly is required for subsequent postmitotic Golgi membrane fusion. Depletion of HACE1 using small interfering RNAs or expression of an inactive HACE1 mutant protein in cells impaired postmitotic Golgi membrane fusion. The identification of HACE1 as a Golgi-localized ubiquitin ligase provides evidence that ubiquitin has a critical role in Golgi biogenesis during the cell cycle.

The need for a multi-level biochemical approach to defeat cancer that will also support the host

Cited research papers support the main hypothesis that selected publications supply sufficient information for a combined multi-level treatment strategy against cancer that will also strengthen the host. The three major elements of the proposal are: (A) metastasis being separate from tumor growth requires specific antimetastatic treatments. For this, manipulation of the composition of phospholipids will alter cellular charge characteristics which are instrumental in adhesion. (B) Formate metabolism is at the center of many activities that are controlling tumor growth. The rational and consequences of this are as follows. Supply of formate depends mainly on serine, and consumption on conversion to CO2 yielding needed NADPH. The remainder is used to complete IMP configuration with 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP). At homeostasis residual ZMP activates AMP-activated protein kinase (AMPK) to curb growth promoting phosphatidylinositol-3-kinase (PI3PK). Residual ZMP also activates the oxidation of choline to betaine supplying methyl groups needed for global methylation of DNA while increased oxidation of choline also alters cellular phospholipid composition (refer to metastasis). At low formate level, increased accumulated ZMP becomes pyrophosporylated to ZTP. AMPK activation shifts to PI3PK activity for insulin action restoring formate supplied by serine derived from glycolysis. Increased NADPH-generating glucose-6-phosphate dehydrogenase is diminishing NADP+ required for dehydrogenation of formate. This is restoring the formate balance while lowering ZMP levels to that of homeostasis. Evidence suggests that transformed cells exceed up-regulation of formate thus suppressing all ZMP accumulations resulting in limited AMPK activation, cessation of choline oxidation to betaine and loss of global methylation of DNA. This scenario appears to be tied to tumor survival, a state that could be altered by metabolic interventions using mild agents as described in the research reports cited. (C) Because of a preponderance of pyrimidines in cancer supporting UTP requiring immune evasion, exogenous IMP may offset this imbalance and thus hinder tumor anti-immune activities while strengthen host immune functions. For studies to confirm the proposal, the overall expected result is that a combined administration of all these agents cited here will outperform any single agent considered so far for anticancer treatment.

Combination of tunicamycin with anticancer drugs synergistically enhances their toxicity in multidrug-resistant human ovarian cystadenocarcinoma cells

BACKGROUND

The pharmacologic modulatory effects of the antibiotic, tunicamycin (TM), on multidrug-resistant human UWOV2 ovarian cancer cells are reported. The UWOV2 cell line was derived from a cystadenocarcinoma in a patient refractory to combination chemotherapy with actinomycin D, vincristine (VCR), cis-diaminedichloroplatinum (II) (CDDP) and doxorubicin (DXR). In an attempt to explain drug resistance in this cell line, we examined the effects of TM on their sensitivity to various anticancer drugs, the uptake, efflux and retention of [3H]VCR, and their ability to bind [14C]DXR and [3H]azidopine (AZD), a photoaffinity label of the multidrug transporter, P-glycoprotein (Pgp).

RESULTS

TM effectively decreased the EC50 for DXR, EXR, VCR and CDDP, thus enhancing their cytotoxicity. The antibiotic also prolonged the intracellular retention time of [3H]VCR and increased the binding of both [14C]DXR and [3H]AZD to the cells.

CONCLUSION

It is concluded that the pharmacomodulatory effects of TM in these cells are mediated by global inhibition of protein and glycoprotein synthesis and synergistic interaction with antineoplastic drugs. The ability of TM to enhance the sensitivity of drug resistant tumour cells may have impact on the design and optimization of novel resistance modifiers to improve the efficacy of combination treatment of intractable neoplasms.

Association of Ipomoea carnea and BCG reduces birth defects caused by cyclophosphamide in rats

Immunosuppressive drugs can induce the development of malformations in fetuses of mothers exposed to them, possibly affecting the placental function directly or by crossing the placenta to enter fetal circulation. However, activation of the maternal immune system with well-known immunomodulator substances has been shown to produce a significant decrease in morphological defects caused by diverse teratogenic agents. All of these studies were performed on mice only, whereas the rat is the chosen species for developing teratological studies. Thus, the purpose of the present study was to investigate the possible protective effect of Bacillus Calmette Guérin (BCG) and/or the aqueous fraction (AF) of the plant Ipomoea carnea on the decrease of the teratogenic effect resulting from cyclophosphamide (CP), an antineoplastic and immunosuppressive drug, exposure in pregnant rats. It was verified that both BCG and/or AF attenuated the embryotoxic effects of CP in rats. All immune stimulated dams demonstrated an increase in placenta and fetus body weight. In conclusion, the present work showed that the rat is a good model for performing studies which aim for a clearer understanding of the mechanism by which maternal stimulation reduces malformations and how the association of I. carnea AF and BCG provided improved immunostimulation compared to BCG alone; however, additional studies are required to determine the specific mechanisms by which immune stimulant substances decrease malformation.

Man2C1, an alpha-mannosidase, is involved in the trimming of free oligosaccharides in the cytosol

The endoplasmic-reticulum-associated degradation of misfolded (glyco)proteins ensures that only functional, correctly folded proteins exit from the endoplasmic reticulum and that misfolded ones are degraded by the ubiquitin-proteasome system. During the degradation of misfolded glycoproteins, they are deglycosylated by the PNGase (peptide:N-glycanase). The free oligosaccharides released by PNGase are known to be further catabolized by a cytosolic alpha-mannosidase, although the gene encoding this enzyme has not been identified unequivocally. The findings in the present study demonstrate that an alpha-mannosidase, Man2C1, is involved in the processing of free oligosaccharides that are formed in the cytosol. When the human Man2C1 orthologue was expressed in HEK-293 cells, most of the enzyme was localized in the cytosol. Its activity was enhanced by Co2+, typical of other known cytosolic alpha-mannosidases so far characterized from animal cells. The down-regulation of Man2C1 activity by a small interfering RNA drastically changed the amount and structure of oligosaccharides accumulating in the cytosol, demonstrating that Man2C1 indeed is involved in free oligosaccharide processing in the cytosol. The oligosaccharide processing in the cytosol by PNGase, endo-beta-N-acetylglucosaminidase and alpha-mannosidase may represent the common 'non-lysosomal' catabolic pathway for N-glycans in animal cells, although the molecular mechanism as well as the functional importance of such processes remains to be determined.

Interference with O-glycosylation in RMA lymphoma cells leads to a reduced in vivo growth of the tumor

Carbohydrate processing in cancer cells can influence the growth, metastatic potential, vascularization and immune recognition of such cells. Interference with N-glycosylation has been shown both to reduce the membrane expression of MHC class I and to increase the in vitro sensitivity of tumor cells to NK cell killing. We investigated the effect of O-glycosylation inhibition on the in vivo growth, phenotype and NK sensitivity of RMA lymphoma cells using benzyl N-acetyl-alpha-D-galactosamide (BAG). BAG-treated cells were found to have a strongly reduced local growth potential in vivo. However, inhibition of O-glycosylation caused this effect without any significant downregulation of MHC-I and increase in sensitivity to NK killing as seen after inhibition of N-glycosylation using Castanospermine. BAG treatment of RMA cells resulted in the removal of larger O-linked glycans and a high expression of the T-antigen (GalGalNAc), a target for natural antibodies (NAs) induced by the gastrointestinal bacterial flora. Whether the loss of larger O-linked glycans, and associated functions, or of biological effects of NA contributed to the antitumor effect remains to be established. The results support the idea that inhibitors of O- as well as N-linked glycosylation may be useful for the treatment of cancer, given that they can be specifically targeted to the tumor tissue.

Different adhesion and migration properties of human HCV29 non-malignant urothelial and T24 bladder cancer cells: role of glycosylation

In tumour cells, alterations in cellular glycosylation may play a key role in their metastatic behaviour. This study used cell lines having very different behaviour in vivo: HCV29 non-malignant transitional epithelium and T24 bladder transitional cell carcinoma. These differences in behaviour might be due in part to differences in cellular glycosylation patterns. Glycan chain analysis of their glycoproteins was performed with the use of specific lectins. The functional role of carbohydrates was studied by treating these cells with swainsonine, an inhibitor of Golgi alpha-mannosidase II, and in vitro adhesion and migration assays. The adhesion of swainsonine-treated HCV29 and T24 cells was increased on fibronectin and type IV collagen by 1.5- and 2-fold, respectively, whereas adhesion on laminin was virtually unchanged after swainsonine-treatment in HCV29 cells and was increased in T24 cells. Swainsonine treatment reduced the rate of T24 cell migration by 20%. We concluded that beta1-6 branched tri- and tetraantennary complex-type glycans have an important function in adhesion and migration in the studied cell lines. These data support the view that oligosaccharides are involved in several steps of the metastatic process.

Biomedical applications of poisonous plant research

Research designed to isolate and identify the bioactive compounds responsible for the toxicity of plants to livestock that graze them has been extremely successful. The knowledge gained has been used to design management techniques to prevent economic losses, predict potential outbreaks of poisoning, and treat affected animals. The availability of these compounds in pure form has now provided scientists with tools to develop animal models for human diseases, study modes of action at the molecular level, and apply such knowledge to the development of potential drug candidates for the treatment of a number of genetic and infectious conditions. These advances are illustrated by specific examples of biomedical applications of the toxins of Veratrum californicum (western false hellebore), Lupinus species (lupines), and Astragalus and Oxytropis species (locoweeds).

Synthesis of the New Mannosidase Inhibitors, Diversity-Oriented 5-Substituted Swainsonine Analogues, via Stereoselective Mannich Reaction

5alpha-substituted swainsonine analogues were synthesized by Mannich reaction of an in situ generated (-)-swainsonine iminium ion intermediate. 5alpha-substituted swainsonine analogues were epimerized to their 5beta-isomers in protic solvent. [reaction: see text]

Suppression of 6A8 ?-mannosidase gene expression reduced the potentiality of growth and metastasis of human nasopharyngeal carcinoma

Suppression of alpha-mannosidases by chemicals has been shown to reduce the potentiality of growth and metastasis of various tumors. In our study, the effect of 6A8 alpha-mannosidase (MAN 6A8), recently discovered in our laboratory, on malignant behaviors of tumor cells was examined. Since the suppressive effect of chemicals on alpha-mannosidase is not specific, antisense technique was used to specifically inhibit expression of the MAN 6A8 in human nasopharyngeal carcinoma cells, CNE-2L2. Two cell clones, AS1 and AS2, with pronounced suppression of MAN 6A8 expression were developed. Wild-type (W), mock-transduced (M) and irrelevant DNA-transduced (IR) CNE-2L2 cells with normal expression of the enzyme were used as controls. Malignant behaviors of the cells were examined. Significant inhibition of growth of AS cells in vitro measured by MTT assay, colony formation and anchorage-independent colony formation was found. Pronounced inhibition of formation of tumors from AS cells inoculated into nude mice and metastasis was also observed. W, M and IR cells cultured in plate wells appeared dispersed with a fibroblastic or epithelial morphology, whereas AS cells were in compact sheets with an epithelioid organization. Since E-cadherin is the key factor in homophilic adhesion of epithelial cells, its expression on the surface of CNE-2L2 cells was determined. E-cadherin expression on AS cells was enhanced, whereas it was markedly diminished on W, M and IR cells. In addition, lamellipodia, which play an important role in cell spreading and mobility, almost disappeared on AS cells. The results demonstrate a significant suppressive effect of reduced expression of MAN 6A8 on malignant behaviors of CNE-2L2 cells.

Synthesis of conjugates ofL-fucose andortho-carborane as potential agents for boron neutron capture therapy

The synthesis of three potential boron neutron capture therapy agents (6–8) is reported. The compounds synthesized are comprised of ortho-carborane covalently attached to L-fucose via C-6. Incorporation of the carborane moiety was achieved either through the reaction of an L-fucose-derived alkyne with decaborane or by the coupling of a 6-amino-L-galactopyranose derivative with carborane carboxylic acid chloride (18).Key words: L-fucose, fucosyltransferase, boron neutron capture therapy, ortho-carborane.

Suppressive effects of swainsonine and N-butyldeoxynojirimycin on human bone marrow neutrophil maturation

The effects of the N-linked oligosaccharide inhibitors swainsonine and N-butyldeoxynojirimycin (NB-DNJ) on granulopoiesis was investigated using human bone marrow cells in in vitro liquid and agar cultures. The addition of the inhibitors into cultures containing granulocyte colony-stimulating factor (G-CSF) suppressed maturation from myelocytes into mature neutrophils. Swainsonine did not induce apoptosis, but NB-DNJ induced considerable apoptosis, especially in the presence of G-CSF. This result indicated that the decrease of mature neutrophils by swainsonine was not because of cell degeneration. In the case of NB-DNJ, it was thought to be because of both maturation suppression and apoptosis. In a colony-forming unit-granuloid (CFU-G) colony assay, the number of colonies was increased in the presence of the inhibitors, but the morphology of colonies was predominantly compact, or immature. The inhibitors also suppressed the expressions of mRNAs of CCAAT/enhancer binding protein epsilon (C/EBPepsilon) and G-CSF receptor as markers of terminal neutrophil maturation. These findings suggested that the incompleteness of N-linked oligosaccharide leads to the suppression of terminal neutrophil maturation.