Swainsonine reduces 5-fluorouracil tolerance in the multistage resistance of colorectal cancer cell lines

<p>Abstract</p> <p>Background</p> <p>Drug resistance is a major problem in cancer chemotherapy. Acquisition of chemo-resistance not only reduces the effectiveness of drugs, but also promotes side effects and markedly reduces the patient's quality of life. However, a number of resistance mechanisms have been reported and are thought to be the reason for the difficulties in solving drug-resistance problems.</p> <p>Result</p> <p>To investigate the mechanisms of drug resistance, a set of cell lines with different levels of sensitivity and possessing different mechanisms of resistance to 5-fluorouracil (5-FU) was established from a colorectal cancer cell line. The expression of thymidylate synthase, orotic acid phosphoribosyltransferase and dihydropyrimidine dehydrogenase, which are well known to be related to drug resistance, differed among these cell lines, indicating that these cell lines acquired different resistance mechanisms. However, swainsonine, an inhibitor of N-glycan biosynthesis, reduced 5-FU-tolerance in all resistant cells, whereas the sensitivity of the parental cells was unchanged. Further analysis of the N-glycan profiles of all cell lines showed partial inhibition of biosynthesis and no cytotoxicity at the swainsonine dosage tested.</p> <p>Conclusion</p> <p>These observations suggest that N-linked oligosaccharides affect 5-FU resistance more widely than do drug-resistance related enzymes in colorectal cancer cells, and that the N-glycan could be a universal target for chemotherapy. Further, swainsonine may enhance the performance of chemotherapy by reducing tolerance.</p

Vascular RAGE transports oxytocin into the brain to elicit its maternal bonding behaviour in mice

金沢大学医薬保健研究域医学系Oxytocin sets the stage for childbirth by initiating uterine contractions, lactation and maternal bonding behaviours. Mice lacking secreted oxcytocin (Oxt -/-, Cd38 -/-) or its receptor (Oxtr -/-) fail to nurture. Normal maternal behaviour is restored by peripheral oxcytocin replacement in Oxt -/- and Cd38 -/-, but not Oxtr -/- mice, implying that circulating oxcytocin crosses the blood-brain barrier. Exogenous oxcytocin also has behavioural effects in humans. However, circulating polypeptides are typically excluded from the brain. We show that oxcytocin is transported into the brain by receptor for advanced glycation end-products (RAGE) on brain capillary endothelial cells. The increases in oxcytocin in the brain which follow exogenous administration are lost in Ager -/- male mice lacking RAGE, and behaviours characteristic to abnormalities in oxcytocin signalling are recapitulated in Ager -/- mice, including deficits in maternal bonding and hyperactivity. Our findings show that RAGE-mediated transport is critical to the behavioural actions of oxcytocin associated with parenting and social bonding.3082047

Separation of isomeric 2-aminopyridine derivatized N-glycans and N-glycopeptides of human serum immunoglobulin G by using a zwitterionic type of hydrophilic-interaction chromatography

Isomeric oligosaccharides and isomeric glycopeptides are sometimes difficult to separate on normal-phase (NP) and reversed-phase (RP) columns. A zwitterionic type of hydrophilic-interaction chromatography column with sulfobetaine groups (called ZIC-HILIC column) was first applied to the separation of 2-aminopyridine derivatized (PA) N-glycans and tryptic peptides of human serum immunoglobulin G (IgG). It is shown that the ZIC-HILIC column has high capability for structural recognition of isomeric N-glycans as well as high selectivity for glycopeptides. The former feature (i.e., structural recognition) was proven by sufficient separation of neutral PA N-glycan isomers, which are usually difficult to separate on NP and RP columns. In addition, it is noteworthy that IgG glycopeptides consisting of isomeric N-glycans and the same peptide sequences can be sufficiently separated on a ZIC-HILIC column. The latter feature (i.e., selectivity) was also demonstrated by easily separating two peptide groups with/without N-glycans. Thus, we note that the ZIC-HILIC column is highly promising for a simple analysis of N-glycans and N-glycopeptide samples. (c) 2006 Elsevier B.V. All rights reserved

Direct structural assignment of neutral and sialylated N-glycans of glycopeptides using collision-induced dissociation MSⁿ spectral matching.

Mass spectrometric analyses of various N-glycans binding to proteins and peptides are highly desirable for elucidating their biological roles. An approach based on collision-induced dissociation (CID) MSⁿ spectra acquired by electrospray ionization linear ion trap time-of-flight mass spectrometry (ESI-LIT-TOFMS) in the positive- and negative-ion modes has been proposed as a direct method of assigning N-glycans without releasing them from N-glycopeptides. In the positive-ion mode of this approach, the MS² spectrum of N-glycopeptide was acquired so that a glycoside-bond cleavage occurs in the chitobiose residue (i.e., GlcNAcβ1-4GlcNAc, GlcNAc: N-acetylglucosamine) attached to asparagine (N), and two charges on the [M+H+Na]²+ precursor ion are shared with both of the resulting fragments. These fragments are sodiated Bn-type fragment ions of oligosaccharide (N-glycan) and a protonated peptide ion retaining one GlcNAc residue on the asparagine (N) residue. The structure of N-glycan was assigned by comparing MS³ spectra derived from both the sodiated Bn-type fragment ions of N-glycopeptide and the PA (2-aminopyridine) N-glycan standard (i.e., MSⁿ spectral matching). In a similar manner, the structural assignment of sialylated N-glycan was performed by employing the negative-ion CID MSⁿ spectra of deprotonated Bn-type fragment ions of N-glycopeptide and the PA N-glycan standard. The efficacy of this approach was tested with chicken egg yolk glycopeptides with a neutral and a sialylated N-glycan, and human serum IgG glycopeptides with neutral N-glycan isomers. These results suggest that the approach based on MSⁿ spectral matching is useful for the direct and simple structural assignment of neutral and sialylated N-glycans of glycopeptides. Copyright © 2006 John Wiley & Sons, Ltd

High Throughput Quantitative Glycomics and Glycoform-focused Proteomics of Murine Dermis and Epidermis

Despite recent advances in our understanding of the significance of the protein glycosylation, the throughput of protein glycosylation analysis is still too low to be applied to the exhaustive glycoproteomic analysis. Aiming to elucidate the N-glycosylation of murine epidermis and dermis glycoproteins, here we used a novel approach for focused proteomics. A gross N-glycan profiling (glycomics) of epidermis and dermis was first elucidated both qualitatively and quantitatively upon N-glycan derivatization with novel, stable isotope-coded derivatization reagents followed by MALDI-TOF(/TOF) analysis. This analysis revealed distinct features of the N-glycosylation profile of epidermis and dermis for the first time. A high abundance of high mannose type oligosaccharides was found to be characteristic of murine epidermis glycoproteins. Based on this observation, we performed high mannose type glycoform-focused proteomics by direct tryptic digestion of protein mixtures and affinity enrichment. We identified 15 glycoproteins with 19 N-glycosylation sites that carry high mannose type glycans by off-line LC-MALDI-TOF/TOF mass spectrometry. Moreover the relative quantity of microheterogeneity of different glycoforms present at each N-glycan binding site was determined. Glycoproteins identified were often contained in lysosomes (e.g. cathepsin L and gamma-glutamyl hydrolase), lamellar granules (e.g. glucosylceramidase and cathepsin D), and desmosomes (e g. desmocollin 1, desmocollin 3, and desmoglein). Lamellar granules are organelles found in the terminally differentiating cells of keratinizing epithelia, and desmosomes are intercellular junctions in vertebrate epithelial cells, thus indicating that N-glycosylation of tissue-specific glycoproteins may contribute to increase the relative proportion of high mannose glycans. The striking roles of lysosomal enzymes in epidermis during lipid remodeling and desquamation may also reflect the observed high abundance of high mannose glycans

Structural assignment of isomeric 2-aminopyridine derivatized monosialylated biantennary N-linked oligosaccharides using negative-ion MSn spectral matching

To investigate the possibility of structural assignment based on negative-ion MSn spectral matching, four isomers of 2-aminopyridine-derivatized (PA) monosialylated oligosaccharides (i.e., complex type N-glycans with an α2-3 or α2-6 linked sialic acid on α1-6 or α1-3 antennae) were analyzed by using high-performance liquid chromatography/electrospray ion trap time-of-flight mass spectrometry(HPLC/ESI-IT-TOF MS). The negative ion [M-2H]2- is observed dominantly in the MS1 spectra without the loss of a sialic acid. The MS2 spectra derived from it are sufficiently reproducible that MS2 spectral matching based on correlation coefficients can be applied to the assignment of these isomers. The isomers containing a sialic acid on α1-6 or α1-3 antennae can be distinguished by MS2 spectral matching, but the α2-3 and α2-6 linkage types of sialic acid cannot be distinguished by their MS2 spectra. However, MS3 spectra derived from fragment ions containing a sialic acid (i.e., C4- and D-type ions) clearly differentiate the α2-3 and α2-6 linkage types of sialic acid in their MS3 spectral patterns. This difference might be rationalized in terms of a proton transfer from the reducing-end mannose to the negatively-charged sialic acid. These two moieties are very close in the structural conformations of the precursor C4-type fragment ions, as predicted by molecular mechanics calculations. Thus, negative-ion MSn (n=2, 3) spectral matching was proven to be useful for the structural assignment of these four monosialylated PA N-glycan isomers