Cytotoxicity of plant lectins for mouse embryonal carcinoma cells

Pentacyclic triterpenoid ursolic acid interferes with mast cell activation via a lipid-centric mechanism affecting FcεRI signalosome functions

Pentacyclic triterpenoids, including ursolic acid (UA), are bioactive compounds with multiple biological activities involving anti-inflammatory effects. However, the mode of their action on mast cells, key players in the early stages of allergic inflammation, and underlying molecular mechanisms remain enigmatic. To better understand the effect of UA on mast cell signaling, here we examined the consequences of short-term treatment of mouse bone marrow-derived mast cells with UA. Using IgE-sensitized and antigen- or thapsigargin-activated cells, we found that 15 min exposure to UA inhibited high affinity IgE receptor (FcεRI)–mediated degranulation, calcium response, and extracellular calcium uptake. We also found that UA inhibited migration of mouse bone marrow-derived mast cells toward antigen but not toward prostaglandin E₂ and stem cell factor. Compared to control antigen-activated cells, UA enhanced the production of tumor necrosis factor-α at the mRNA and protein levels. However, secretion of this cytokine was inhibited. Further analysis showed that UA enhanced tyrosine phosphorylation of the SYK kinase and several other proteins involved in the early stages of FcεRI signaling, even in the absence of antigen activation, but inhibited or reduced their further phosphorylation at later stages. In addition, we show that UA induced changes in the properties of detergent-resistant plasma membrane microdomains and reduced antibody-mediated clustering of the FcεRI and glycosylphosphatidylinositol-anchored protein Thy-1. Finally, UA inhibited mobility of the FcεRI and cholesterol. These combined data suggest that UA exerts its effects, at least in part, via lipid-centric plasma membrane perturbations, hence affecting the functions of the FcεRI signalosome.

The 'sweet' spot of cellular pluripotency: protein glycosylation in human pluripotent stem cells and its applications in regenerative medicine

INTRODUCTION

Human pluripotent stem cells (hPSCs) promise for the future of regenerative medicine. The structural and biochemical diversity associated with glycans makes them a unique type of macromolecule modification that is involved in the regulation of a vast array of biochemical events and cellular activities including pluripotency in hPSCs. The primary focus of this review article is to highlight recent advances in stem cell research from a glycobiological perspective. We also discuss how our understanding of glycans and glycosylation may help overcome barriers hindering the clinical application of hPSC-derived cells.

AREAS COVERED

A literature survey using NCBI-PubMed and Google Scholar was performed in 2014.

EXPERT OPINION

Regenerative medicine hopes to provide novel strategies to combat human disease and tissue injury that currently lack effective therapies. Although progress in this field is accelerating, many critical issues remain to be addressed in order for cell-based therapy to become a practical and safe treatment option. Emerging evidence suggests that protein glycosylation may significantly influence the regulation of cellular pluripotency, and that the exploitation of protein glycosylation in hPSCs and their differentiated derivatives may lead to transformative and translational discoveries for regenerative medicine. In addition, hPSCs represent a novel research platform for investigating glycosylation-related disease.

Protein post-translational modifications and regulation of pluripotency in human stem cells

Post-translational modifications (PTMs) are known to be essential mechanisms used by eukaryotic cells to diversify their protein functions and dynamically coordinate their signaling networks. Defects in PTMs have been linked to numerous developmental disorders and human diseases, highlighting the importance of PTMs in maintaining normal cellular states. Human pluripotent stem cells (hPSCs), including embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), are capable of self-renewal and differentiation into a variety of functional somatic cells; these cells hold a great promise for the advancement of biomedical research and clinical therapy. The mechanisms underlying cellular pluripotency in human cells have been extensively explored in the past decade. In addition to the vast amount of knowledge obtained from the genetic and transcriptional research in hPSCs, there is a rapidly growing interest in the stem cell biology field to examine pluripotency at the protein and PTM level. This review addresses recent progress toward understanding the role of PTMs (glycosylation, phosphorylation, acetylation and methylation) in the regulation of cellular pluripotency.

Specific lectin biomarkers for isolation of human pluripotent stem cells identified through array-based glycomic analysis

Rapid and dependable methods for isolating human pluripotent stem cell (hPSC) populations are urgently needed for quality control in basic research and in cell-based therapy applications. Using lectin arrays, we analyzed glycoproteins extracted from 26 hPSC samples and 22 differentiated cell samples, and identified a small group of lectins with distinctive binding signatures that were sufficient to distinguish hPSCs from a variety of non-pluripotent cell types. These specific biomarkers were shared by all the 12 human embryonic stem cell and the 14 human induced pluripotent stem cell samples examined, regardless of the laboratory of origin, the culture conditions, the somatic cell type reprogrammed, or the reprogramming method used. We demonstrated a practical application of specific lectin binding by detecting hPSCs within a differentiated cell population with lectin-mediated staining followed by fluorescence microscopy and flow cytometry, and by enriching and purging viable hPSCs from mixed cell populations using lectin-mediated cell separation. Global gene expression analysis showed pluripotency-associated differential expression of specific fucosyltransferases and sialyltransferases, which may underlie these differences in protein glycosylation and lectin binding. Taken together, our results show that protein glycosylation differs considerably between pluripotent and non-pluripotent cells, and demonstrate that lectins may be used as biomarkers to monitor pluripotency in stem cell populations and for removal of viable hPSCs from mixed cell populations.

A novel lipid raft-associated glycoprotein, TEC-21, activates rat basophilic leukemia cells independently of the type 1 Fc epsilon receptor

Recent data suggest that initiation of signal transduction via type 1 Fc epsilon receptor (Fc epsilon RI) and other immunoreceptors is spatially constrained to lipid rafts. In order to better understand the complexity and function of these structures, we prepared mAb against lipid rafts from the rat basophilic leukemia cell line, RBL-2H3, which is extensively used for analysis of Fc epsilon RI-mediated activation. One of the antibodies was found to recognize a novel glycosylphosphatidylinositol-anchored plasma membrane glycoprotein of 250 amino acids, designated TEC-21, containing a cysteine-rich domain homologous to those found in the urokinase plasminogen activator receptor/Ly-6/snake neurotoxin family. TEC-21 is abundant on the surface of RBL-2H3 cells (>10 (6) molecules/cell), but is absent in numerous rat tissues except for testes. Aggregation of TEC-21 on RBL-2H3 cells induced a rapid increase in tyrosine phosphorylation of several substrates including Syk kinase and LAT adaptor, calcium flux, and release of secretory components. Similar but more profound activation events were observed in cells activated via Fc epsilon RI. However, aggregation of TEC-21 did not induce changes in density of IgE-Fc epsilon RI complexes, tyrosine phosphorylation of Fc epsilon RI beta and gamma subunits, and co-aggregation of Lyn kinase. TEC-21-induced activation events were also observed in Fc epsilon RI(-) mutants of RBL-2H3 cells. Thus, TEC-21 is a novel lipid raft component of RBL-2H3 cells whose aggregation induces activation independently of Fc epsilon RI.

Toxin A of Clostridium difficile is a potent cytotoxin

Clostridium difficile is the cause of antibiotic-associated colitis in humans. The organism produces toxin A, which is generally known as the enterotoxin, and toxin B, which is known as the cytotoxin. Toxin A has been reported to have slight cytotoxic activity; in this study we show that cell lines (F9, OTF9-63, and P19) which express a carbohydrate to which toxin A binds are more sensitive to the toxin. These cell lines can be used as research tools for determining concentrations of biologically active toxin A and should also prove useful for studies of the mechanism of action of the toxin.

Lectin-induced abnormalities of mouse blastocyst hatching and outgrowth in vitro

We have examined the role of cell surface glycoconjugates during mouse blastocyst maturation, hatching, attachment, and outgrowth by monitoring the influence of six lectins on blastocyst development in vitro. Two lectins, concanavalin A and wheat germ agglutinin were toxic to blastocysts at the concentrations used. Bandierea simplicifolia lectin 1 (BSL-1) induced abnormal growth, developmental arrest at the hatching stage, and some disruption of cell contacts. Culture with Lotus tetragonolobus lectin-1 (LTA-1) also disrupted cell contacts and caused developmental arrest. The remaining lectins, Dolichos biflorus agglutinin (DBA) and Ulex europaeus agglutinin (UEA), retarded blastocyst hatching and outgrowth but did not induce any major defects, although differentiation of the inner cell mass was limited by both. This study demonstrates that very low concentrations of lectins can disrupt blastocyst development, suggesting that exposed surface saccharide moieties may be involved in interactions between blastomeres and their environment.

Differential expression of mouse embryonic antigens TEC-1 and TEC-2 in the epididymis of four rodent species

The expression, properties and relationship of two mouse embryonic antigens (TEC-1 and TEC-2), which are defined by monoclonal antibodies, were investigated in the epididymis of four rodent species. Absorption analysis, indirect immunofluorescence microscopy and immunohistochemistry revealed that all the species studied contained in their epididymides, but not in testes, either TEC-1 (Chinese hamster), TEC-2 (guinea pigs, rats) or both TEC-1 and TEC-2 (mice) antigens. In an indirect immunofluorescence assay, the antigens were found on spermatozoa isolated from caudae epididymides of guinea pigs, rats and Chinese hamsters but not mice. On the other hand, the TEC-2 antigen, which is expressed on mouse eggs, was not detected on eggs from the other species studied. Immunolabeling of epididymal extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that both epididymal antigens have apparent molecular weights of greater than 200,000. In guinea pigs, rats and mice, the antigens were detected by a two-site sandwich radioantibody-binding assay in which the antigen is immobilized and detected with the same antibody; this indicates that several antigenic determinants were present on the same carrier. In mice, some carriers seem to express both TEC-1 and TEC-2 epitopes. In Chinese hamsters, TEC-1 antigen was only detected by the solid-phase assay, suggesting that in this species there are markedly fewer antigenic determinants per carrier molecule. Interspecies differences in the activities of epididymal glycosyltransferases and/or glycosidases appear to be the biochemical mechanism of the species-specific expression of these antigens.

Aggregation-deficient embryonal carcinoma cells: defects in peanut agglutinin (PNA) receptors

The components involved in cell adhesion were studied using the H6 line of embryonal carcinoma cells. H6 cells are especially suitable for studies on cell interactions, since genetic mutants can be selected, and various processes of cell adhesion can be controlled by regulating the calcium concentration in the medium. Three aggregation-defective variants of H6 were isolated, all of which showed reduced binding of the lectin, peanut agglutinin (PNA). Quantitation of PNA receptors on the cell surface by immunoprecipitation of iodinated surface proteins indicated that these receptors were reduced on the variants by one-half to one-quarter. The separation of immunoprecipitated PNA receptors on sodium-dodecyl-sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that one type of receptor, with an apparent molecular weight of 94 kilodaltons, was reduced. Parental and variant cells bind similar quantities of concanavalin A and soybean agglutinin, suggesting that there is no generalized effect on major glycoproteins. Thus, the defect in aggregation and the defect in the 94-kilodalton protein may be correlated, and this glycoprotein may have a role in the mediation of H6 cell-cell adhesion.

Developmentally regulated surface structures of teratocarcinoma stem cells studied by mutant cell lines

Monoclonal antibodies TEC-01, TEC-02, and TEC-03, which define three developmentally regulated antigens TEC-1 (SSEA-1-like), TEC-2, and TEC-3, have been used to isolate and characterize teratocarcinoma stem cell mutants with altered expression of surface glycoconjugates. Mutants lacking TEC-1 antigen have been isolated by exposing mutagenized P19S1801A1 cells to TEC-01 antibody, which was conjugated to the toxin from Ricinus communis. None of the mutants exhibits significant changes in the expression of TEC-3 antigen, but some are defective in the expression of TEC-2 antigen. Analysis of the expression of TEC-1,2,3 antigens in different lectin-resistant F9 and OTF9-63 cell lines has shown that all express TEC-1 antigen, but some lectin-resistant phenotypes exhibit reduction in the expression of TEC-2 and/or TEC-3 antigens. Mutational events in genes regulating the expression of specific glycosyltransferases or glycosidases appear to be the biochemical mechanism regulating the expression of TEC-1 and TEC-2 antigens.

Differentiation antigens of mouse teratocarcinoma stem cells defined by monoclonal antibodies

Three differentiation antigens of mouse teratocarcinoma stem cells are defined using a panel of ten IgM-class monoclonal antibodies raised against teratocarcinoma F9 cells. TEC-01 and four other antibodies define an antigen that corresponds to SSEA-1. TEC-02 antibody defines an antigen that is expressed on teratocarcinoma stem cells, parietal yolk sac cells PYS-2, unfertilized eggs including the zona pellucida and blastocysts. It is absent from all mouse adult tissues tested. Three other antibodies exhibit binding properties similar to TEC-02. TEC-03 antibody defines an antigen that is expressed on teratocarcinoma stem cells, PYS-2 cells and mouse blastocysts. It is absent from all mouse adult tissues except for lungs.

Isolation and partial characterization of lectin-resistant F9 cells

Cytotoxic plant lectins have been used for the single-step selection of mouse embryonal carcinoma cell mutants with altered expression of surface glycoconjugates. Following mutagenesis, several F9 and OTF9-63 cell lines resistant to the lectins from Triticum vulgaris or Ricinus communis were obtained. At least five distinct lectin-resistant (LecR) phenotypes have been identified on the basis of their relative sensitivities to four different plant lectins and their altered lectin-binding properties. None of the mutant types exhibits a significant change in the ability to bind a monoclonal antibody against the stage-specific embryonic antigen, SSEA-1. All of the mutants form aggregates when cultured in bacteriological petri dishes and appear to differentiate into endoderm-like cells following exposure to retinoic acid. However, two of the LecR cell lines exhibit an altered morphology when grown on a plastic substratum.