Characterization of the structural determinants required for the high affinity interaction of asparagine-linked oligosaccharides with immobilized Phaseolus vulgaris leukoagglutinating and erythroagglutinating lectins

Characterization of glycoproteins in the epithelial cells of human and other mammalian gallbladder. A review

The mammalian gallbladder mucosa is lined by a simple columnar epithelium. Typical surface epithelial cells (principal cells) contain short microvilli, secretory granules, dense bodies, mitochondria and Golgi apparatus. Dense bodies are thought to be lysosomes. Secretory granules contain mucous glycoproteins which are released to the lumen by exocytosis. Oligosaccharide side chains of mucous glycoproteins may provide a favorable environment for nucleation of cholesterol in gallstone formation; therefore they have been studied during the past decades. Histochemical techniques allow the in situ identification of carbohydrates at both the cellular and subcellular levels. The oligosaccharide chains of principal cell mucous glycoproteins have been studied by classical histochemical techniques (PAS, alcian blue, HID, etc). These techniques indicate that mammalian gallbladder mucous glycoproteins are heavily sulphated, whereas sialic acid residues are scarce. Neutral mucins have not been described in the mammalian gallbladder. Electron microscopic studies have located the oligosaccharide chains in secretory granules and Golgi apparatus. More recently, lectins (molecules which specifically recognize and bind with different saccharides or saccharide sequences) have been applied for the intracellular localization of carbohydrate residues. Lectin histochemistry has detected fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-acetylneuraminic acid residues in mucous granules, Golgi apparatus and apical membrane of human principal cells. Mannose residues were observed only in dense bodies. The combined use of deglycosylation procedures and lectin histochemistry has revealed a variety of terminal sequences in oligosaccharide chains of gallbladder mucous glycoproteins: Neu5Ac(alpha 2-3)Gal(beta 1-3)GalNAc, Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc and Gal(beta 1-4)GlcNAc. This technology also suggested the occurrence of N-linked oligosaccharides in the dense bodies of principal cells. Mucous granules mainly contained mucin-type O-linked oligosaccharides although some N-linked chains have also been detected. Gallstone formation is probably a complex process depending on multiple factors. Mucous glycoproteins are one of the factors involved in this process. Histochemical methods offer an excellent research tool for the characterization of glycoproteins in the epithelial cells of the gallbladder, thus contributing to the elucidation of the pathophysiology of gallstone formation.

Expression of beta 1,6 branched asparagine-linked oligosaccharides in non-mitotic and non-migratory cells of normal human and rat tissues

Malignant transformation of cells leads to the synthesis of large asparagine-linked oligosaccharides that exhibit a higher degree of beta 1,6 branching. In rodent and human tumor cell lines and certain human tumors, increased beta 1,6 branching of oligosaccharides has been shown to be associated with metastasis. In addition, this structural change occurs in glycoproteins of stimulated normal human lymphocytes. The leukoagglutinating Phaseolus vulgaris lectin (L-PHA) has a high affinity for tri- and tetraantennary beta 1,6 branches carrying oligosaccharides and has been widely used for the detection of such structures by histochemistry and blotting. We have analyzed a spectrum of normal human and rat tissues using a sensitive silver-intensified lectin-gold technique. Staining by L-PHA was detected in undifferentiated cells of germinative layers of the gastrointestinal and respiratory tract as well as testis. However, differentiated and non-mitotic epithelia in most organs showed strong lectin staining as well. Notable exceptions were the epithelium of the colon and resting mammary gland, which were unreactive with L-PHA. The histochemical studies were supplemented by lectin blotting, which showed the presence of diverse L-PHA-reactive glycoproteins in rat tissues. Our data may be of importance for the use of L-PHA in studies on human malignant tumors.

Elongation of N-acetyllactosamine repeats in diantennary oligosaccharides

Glycosylated [Asn22]lysozyme has been shown to contain N-acetyllactosamine repeats when expressed in chinese hamster ovary (CHO) cells. We find that the major portion of N-acetyllactosamine repeats are associated with diantennary oligosaccharides. In Lec2 CHO cells, which are deficient in sialylation, glycosylated lysozyme is synthesized with increased contents of N-acetyllactosamine repeats terminating in beta-galactosyl residues. In the Lec2 cells and the parental CHO cell line, Pro 5, only a minor portion of the oligosaccharides in lysozyme are of the triantennary type. Previously, it has been shown that the synthesis of N-acetyllactosamine repeats in Asn-linked oligosaccharides is enhanced by an increase in the activity of the elongating beta-N-acetylglucosaminyl transferase and by the synthesis of beta-1,6-linked antennae. The results with glycosylated lysozyme suggest that glycoproteins bearing diantennary oligosaccharides can contain several N-acetyllactosamine repeats and that the number of the latter can be increased by decreasing the activity of the capping sialyl transferases.

Overexpression of N-acetylglucosaminyltransferase III disrupts the tyrosine phosphorylation of Trk with resultant signaling dysfunction in PC12 cells treated with nerve growth factor

beta-1,4-N-Acetylglucosaminyltransferase III (GnT-III: EC 2.4.1.144) is a pivotal glycosyltransferase which participates in branch formation by catalysis of the synthesis of a bisecting GlcNAc structure in N-glycans. These structures are thought to be one of the unique features of the N-glycans of neural tissues. To examine the intracellullar role of GnT-III expression and its product in neural cells, its gene was overexpressed in rat pheochromocytoma PC12 cells which normally express a low level of GnT-III. In the GnT-III gene-transfected cells, lectin blot analysis showed that some glycoproteins showed increased levels of bisecting GlcNAc structures. Following treatment with nerve growth factor (NGF) the control cells showed neurite outgrowth for differentiation whereas the transfectants showed no morphological response or change in the rate of cell growth. Transient tyrosine phosphorylation of the Trk/NGF receptor was detected at 5-15 min after NGF treatment in control cells, but not detected in the GnT-III gene-transfected cells despite the intact binding of NGF to the cells. Moreover the dimerization of Trk with NGF treatment was not induced in the GnT-III transfectant as compared with the dimerization seen in control cells. These results indicate that overexpression of GnT-III gene in PC12 cells affects some functions of glycoprotein receptors such as Trk by alteration of N-glycan structures, and results in changes in the intracellular signaling pathway of tyrosine phosphorylation modified by NGF.

Modification of blood group A expression in human pancreatic tumor cell lines by inhibitors of N-glycan processing

Pancreatic adenocarcinomas induced in Syrian hamsters by N-nitrosobis (2-oxopropyl)amine (BOP) treatment express blood group A (BGA) antigen, which was previously shown by this lab to be expressed on multiantennary asparagine (Asn)-linked glycans attached to membrane glycoproteins. To determine if a similar expression pattern was found in humans, three human pancreatic ductal adenocarcinoma cell lines (CD18, CD11, and Capan 1) from individuals of blood type A were analyzed and shown to express BGA antigen on membrane glycoproteins similar in molecular mass to those found in hamster tumor cells. The BGA antigen was located on Asn-linked oligosaccharides in all three human cell lines, as indicated by loss of activity after peptide:N-glycosidase F (PNGase F) treatment. Also, as shown previously in hamster pancreatic tumor cells, BGA expression at the surface of the human cell lines was blocked by growth of the cells in media containing deoxymannojirimycin (dMM), an inhibitor of mannosidase I. These results demonstrate that the BGA antigen is on Asn-linked glycans in human pancreatic adenocarcinoma cells and that these glycoproteins are processed similarly to the BGA glycoproteins in hamster pancreatic adenocarcinoma.

Phytohemagglutinin-L (PHA-L) lectin surface binding of N-linked beta 1-6 carbohydrate and its relationship to activated mutant ras in human pancreatic cancer cell lines

Alterations of the N-linked carbohydrate core structure of cell surface glycoproteins (beta 1-6 branching) can be detected by phytohemagglutinin (PHA-L) lectin binding and has been linked to tumor progression and K-ras activation in colon cancer. The purpose of this study was to determine the prevalence of this carbohydrate alteration and its relationship to K-ras activation in pancreatic cancer. Nine human pancreatic cancer cell lines and 4 colon lines as controls were grown under standard tissue culture conditions. K-ras genome analysis was performed by polymerase chain reaction amplification and sequencing. The proportion of cellular p21-ras bound to GTP (ras-GTP level) was determined using immunoprecipitation of 32P-labeled cell lysates followed by thin layer chromatography and phosphoimaging analysis. Lectin blot analysis was performed on crude membrane preparations. Sensitivity to lectins was assessed with cell culture thymidine incorporation. Of 9 pancreatic cancer lines tested, 3 had wild type K-ras, 2 had heterozygous and 4 had homozygous mutations in codon 12 of K-ras. These genotypes correlated strongly with the level of ras-GTP measured. K-ras mutants had increased levels of ras-GTP compared to wild-type cell lines. PHA-L binding to cell membranes correlated positively with ras-GTP levels in 7 out of 9 cell lines. PHA-L toxicity was greatest in cells with positive PHA-L reactivity on Western blotting. A positive correlation between the presence of K-ras mutation, increased ras-GTP level, and increased cell surface beta 1-6 N-linked carbohydrate exists in pancreatic cancer cell lines.

Expression of L-PHA-binding proteins in breast cancer: reconstitution and molecular characterization of beta 1-6 branched oligosaccharides in three-dimensional cell culture

Expression of beta 1-6 branched oligosaccharides in human breast cancer cells was investigated in vivo and in vitro. Lectin histochemical and lectin blotting analyses of surgically resected specimens were performed using L-PHA (phaseolus vulgaris leukoagglutinin) lectin, which binds to beta 1-6 oligosaccharides. The glycoproteins bearing beta 1-6 oligosaccharides of breast cancer tissues were found to be 170 kD and 120 kD in molecular weight, and the former appeared to be an epitope of carcinoembryonic antigen (CEA). The beta 1-6 oligosaccharides were expressed in both cancer cell lines at the outer layer of the colonies when cultured in type I collagen, but not in agarose gel. No correlation was observed between beta 1-6 expression and cell cycle. The beta 1-6 oligosaccharides did not coincide with breast cancer-associated antigens, such as CEA, MUC1, and cathepsin D. The beta 1-6 oligosaccharides of these cell lines were markedly inhibited when swainsonine, a mannosidase II inhibitor, was added to the culture medium. The 120 kD molecule, which was obtained from MCF-7 cells cultured in type I collagen gel, was consistent with that of breast cancer tissues and was similar to lysosome-associated membrane glycoproteins (LAMPs). The results suggest that the glycoproteins bearing beta 1-6 branched oligosaccharides in human breast cancer incorporate an epitope of CEA and human LAMPs and that the expression of LAMPs may depend on their surrounding matrices and may play an important role in cancer invasion or metastasis.

Glycans of the trabecular meshwork in primary open angle glaucoma

AIMS

Glycan expression was compared in glaucomatous trabecular meshwork (TM) and normal TM in order to determine any differences which may reflect pathological changes underlying primary open angle glaucoma (POAG).

METHODS

Resin embedded TM from trabeculectomy specimens from 15 eyes with POAG and from 12 eyes with normal anterior segments were probed with a panel of biotinylated lectins and an avidin-peroxidase revealing system at the light microscope level. Statistical analyses were performed on the comparative staining results.

RESULTS

The lectins ConA and ePHA showed strong staining in all areas of both glaucomatous and normal TM; ePHA staining of Schlemm's canal (SC) from POAG TM was significantly less than that from normal TM (ePHA-SC p = 0.04). The lectins PSA, LCA, and SNA bound moderately strongly to SC endothelium and weakly to the endothelium of the corneoscleral meshwork (CSM); glaucomatous SC endothelial binding was significantly less than that of normal SC endothelium for PSA and LCA (PSA-SC p = 0.002, LCA-SC p = 0.002). STA and DSA showed moderately strong binding while WGA, ECA, AHA, and MPA bound weakly throughout the TM; for DSA and MPA this staining was significantly greater in POAG than in normal TM (DSA-SC p = 0.001, DSA-CSM p = 0.002, MPA-SC p = 0.01, MPA-CSM p = 0.02). Jac stained strongly throughout the TM and showed no significant difference in POAG compared with normal TM (Jac-SC p = 0.6, Jac-CSM p = 1). 1PHA, SBA, DBA, CTA, UEA-1 and LTA did not bind to glaucomatous TM or normal TM. There were no age-related changes seen.

CONCLUSIONS

The expression of some complex and hybrid, bisected and non-bisected N-linked glycans is significantly diminished in glaucomatous TM compared with normal TM. Some glycans with multiple N-acetylglucosamine residues and O-linked glycans with terminal and subterminal galactosyl groups are significantly increased in POAG TM. Glycan expression does not change significantly with age in POAG or normal TM.

The macrophage cell surface glycoprotein F4/80 is a highly glycosylated proteoglycan

Molecules whose expression is limited to particular leukocyte populations are of interest since they may perform unique functions for these cells. We therefore examined the biochemical nature of the F4/80 molecule, which is expressed solely on macrophage and dendritic cell subpopulations. Our study clearly indicates that post-translational modifications, which can influence both a protein's structural and functional features, constitute a major component of the 160-kDa cell-surface F4/80 molecule. The F4/80 molecule is synthesized as a single polypeptide chain which acquires numerous intramolecular disulfide bonds and requires an extended time period (T1/2 = 60 min) for transport to an endoglycosidase H-resistant form. The F4/80 molecule contains extensive N-linked glycosylation which contributes approximately 40 kDa to the mature molecule. The N-linked carbohydrates are of the branched, complex type, containing repeating N-acetylglycosamine or N-acetyllactosamine units which mediate the reactivity of the F4/80 molecule with Datura stramonium lectin. O-linked glycosylation is also present and contributes approximately 10 kDa to the F4/80 molecule. Furthermore, the sialic acid modifications of the F4/80 molecule are primarily through alpha 2-6 linkages to galactose. Finally, we demonstrate that the F4/80 molecule is a proteoglycan modified by chondroitin sulfate glycosaminoglycans. In addition to clarifying the nature of the F4/80 molecule biochemically, these post-translational modifications have specific implications for molecular recognition processes. We conclude that the modifications of the F4/80 molecule may mediate cell-cell recognition, cell adhesion, or ligand binding independently of the F4/80 molecule protein core.

Purification and characterization of a pod lectin from Great Northern bean, Phaseolus vulgaris L

The pods of the Great Northern bean plant contain a lectin (GNpL) that highly resembles seed lectins (GNLs) of the same plant. Purification of GNpL from pod extracts was achieved by ion-exchange chromatographies on CM- and DEAE-celluloses and gel filtration chromatography on Sephacryl S-300 HR. GNpL has a similar SDS-PAGE pattern to that of GNLs. GNpL and GNLs yield three subunits though each GNpL subunit is 0.5 kDa smaller than the corresponding GNLs subunit (GNpL; pod-alpha-subunit of 34.0 kDa, pod-beta-subunit of 36.5 kDa, and pod-gamma-subunit of 38.5 kDa). GNpL and GNLs display indistinguishable carbohydrate specificities and have similar amino acid compositions. Pod-alpha-subunit cross-reacts with antibodies against GNLs on western blotting. On the other hand, the N-terminal amino acid sequence of pod-alpha-subunit suggests that GNpL is a distinct gene product from those of GNLs genes although they are shown to be homologous proteins.

Fractionation of glycoprotein-derived oligosaccharides by affinity chromatography using immobilized lectin columns

Lectin affinity column chromatography is becoming a method of choice for the fractionation and purification of oligosaccharides, especially N-linked oligosaccharides. Using lectin affinity, it is easy to separate structural isomers and to isolate oligosaccharides based on specific features. Further, serial lectin column chromatography, when various lectin columns are used at the same time, can afford a very sensitive method for the fractionation and characterization of extremely small amounts of oligosaccharides. Thus, when used in conjunction with other separation techniques, lectin affinity chromatography can help to purify rapidly oligosaccharides and provide substantial information about their structural features.

A systematic histochemical investigation in mammals of the dense glycocalyx glycosylations common to all cells bordering the interstitial fluid compartment of the brain

Microanatomical evidence is presented that the intercellular fluid (ICF) compartment of the central nervous tissue is lined entirely and exclusively by heavily glycosylated cells, with glycoconjugates exposed primarily at the apical cell surface, fronting the CSF or blood. On both common ependymal cells and on those specialised to form the choroid plexus epithelium, oligosaccharides coat the cilia and microvilli at the apical surface, and also the smoother lateral and basal cell surfaces. In the ependyma, folded and wrinkled structures seem especially associated with freely exposed carbohydrates. On cerebral endothelial cells, oligosaccharides coat the luminal surface densely and the basal surface lightly. The patterns of carbohydrate distribution thus vary from one cell type to another, but the different cell types all bear essentially the same set of oligosaccharides, variations being due largely to degree of terminal sialylation. Furthermore, the same set of oligosaccharides borders the brain in a broad spectrum of mammals, including pouched and placental mammals. In both epithelia and endothelia, the lectin binding sites visualised in fixed and embedded preparations were shown to be exposed likewise at the cell surfaces in unfixed tissues and so able to bind molecules present in the fluid (CSF or blood) bathing the cells in vivo. This phylogenetically ancient enclosure of the ICF compartment in a "ring of sugars" is suggested to relate to regulation of the central neuronal microenvironment.

Glycoproteins in human parotid saliva assessed by lectin probes after resolution by sodium dodecyl sulphate-polyacrylamide gel electrophoresis

Human parotid salivary glycoproteins separated by gradient sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroblotted onto nitrocellulose have been investigated using a battery of biotinylated lectin probes of characterized sugar specificity. Lectin binding, detected on blots using avidin-biotin complex (ABC) and a chemiluminescence generating substrate, was recorded on photographic film and compared with the original fluorescein isothiocyanate (FITC) stained blots or with Coomassie Brilliant Blue R-250-stained gels run in parallel. A number of glycoprotein bands which were undetected by protein stains or the periodic acid Schiff reaction were revealed by lectins. Binding by lectins from Concanavalia ensiformis, Lens culinaris, Limax flavus, Phaseolus vulgaris, Ricinus communis, Triticum vulgaris, Lotus tetragonobulus and Ulex europaeus indicated that sialylated and fucosylated triantennary and bisected, N-linked complex sugar chains were present on many glycoproteins in addition to the major glycosylated proline-rich glycoprotein (GI). Binding with lectins from Arachis hypogaea and Dolichos biflorus indicated that the O-linked sugar chains were confined to the alpha-heavy chain of Ig A. Comparison of lectin binding in samples from five healthy individuals revealed differences in a number of glycoproteins in addition to the previously characterized G1 and CON 1/CON 2 polymorphisms and demonstrated that the H blood group antigen was expressed mainly on G1 in parotid saliva. This study will be used as a basis upon which to study salivary glycoproteins in diseases affecting parotid glands.

Recent progress in the molecular biology of the cloned N-acetylglucosaminyltransferases

Several genes which code for the N-acetylglucosaminyltransferases have been cloned and characterized. Physiological and pathophysiological roles of the genes still remain to be elucidated but accumulated evidence suggests that the N-acetylglucosaminyltransferase genes are implicated in differentiation, morphogenesis and cancer metastasis.

Effects of N-3554S, a polyprenyl phosphate, on B16-F10 mouse melanoma cells

N-3554S, an optically active S-isomer of alpha-dihydrodecaprenyl phosphate, reduced the tumorigenicity of cultured B16-F10 mouse melanoma cells probably by affecting protein N-glycosylation. Accordingly, membrane glycoprotein samples were prepared from the melanoma cells cultured with or without N-3554S, and amounts and structures of N-linked sugar chains were determined. Analyses of the N-linked oligosaccharides released by hydrazinolysis from these samples and reduced with NaB3H4 revealed that the N-3554S-treated cells contain 1.5-1.8 times as much oligosaccharides as the control cells, and the relative amounts of high-mannose-type and bi-, tri- and tetra-antennary complex-type sugar chains are almost the same between two samples. Western blot analysis, however, showed that binding of L-PHA, which binds to oligosaccharides with the GlcNAc beta 1-->6(GlcNAc beta 1-->2)Man structure, is significantly reduced in 90 K, 96 K, 140 K, 155 K and 180 K glycoproteins in N-3554S-treated cells. Immunoblot analysis showed that the 140 K glycoprotein could be a fibronectin receptor. It was also shown that N-3554S treatment enhances the adhesiveness of the cells to fibronectin. These results indicate that N-3554S affects N-glycosylation of membrane glycoproteins and alters the cell surface properties of B16-F10 cells.

Alpha-lactalbumin induces bovine milk beta 1,4-galactosyltransferase to utilize UDP-GalNAc

We now report that alpha-lactalbumin (alpha-LA) has a novel effect on bovine milk UDP-Gal:GlcNAc-beta 1,4-galactosyltransferase (beta 1,4-GT) and induces the enzyme to efficiently utilize UDP-GalNAc as a donor. In the presence of alpha-LA the enzyme transfers GalNAc to free GlcNAc to produce GalNAc beta 1-4GlcNAc at a rate 55% of that compared to the rate when UDP-Gal is the donor in the absence of alpha-LA. The stimulation by alpha-LA is dependent on the concentrations of alpha-LA, acceptor, and sugar nucleotide. Interestingly, beta 1,4-GT is unable to transfer Gal-NAc to Glc with or without alpha-LA. alpha-LA also stimulates the transfer of GalNAc from UDP-GalNAc to various chitin oligomers, although the degree of stimulation decreases as the acceptor size increases. Thus, bovine milk beta 1,4-GT has an inherent ability to utilize two different sugar nucleotides and the sugar nucleotide preference is regulatable by alpha-LA.

Retinoic acid and methotrexate specifically increase PHA-E-lectin binding to a 67-kDa glycoprotein in LA-N-1 human neuroblastoma cells

Retinoic acid (RA) decreased growth and increased morphologic differentiation of human neuroblastoma LA-N-1 cells. These phenomena correlated with a specific enhancement of PHA-E lectin binding to a glycoprotein of MW 67 kDa (gp67). Gp67 was found susceptible to N-glycanase and displayed BSA binding by affinity chromatography analysis. The chemotherapeutic agent methotrexate (MTX) also reduced growth and induced differentiation of LA-N-1 cells. In addition, the cells responded to MTX as well as to doxorubicin by a marked increase in PHA-E binding to gp67. We conclude that reduced growth and induction of morphological differentiation of LA-N-1 cells correlates with increased binding of PHA-E to gp67.

Estrous cycle-related alterations in the expression of glycoconjugates and lectins in the mouse endometrium shown histochemically

Alterations of the hormonal status may influence diverse cell features relevant to intra- and intercellular communication. We studied histochemically the expression of glycans and endogenous sugar-binding proteins (endolectins) in the mouse endometrium during the estrous cycle. The avidin-biotin-peroxidase complex (ABC) technique was used on paraffin sections with a panel of biotinylated lectins and neoglycoproteins. Stage-specific changes were observed with Galanthus nivalis agglutinin (GNA), Ulex europaeus-I agglutinin (UEA-1), Sambucus nigra agglutinin (SNA), Ricinus communis agglutinin (RCA-I) and Glycine max agglutinin (SBA) in both the luminal and the glandular epithelium, but to a lesser extent in the latter. The stromal constituents also exhibited modifications in lectin-binding profiles in cyclic mice. In addition to the analysis of cell glycans endogenous carbohydrate-binding sites were studied using synthetic probes, biotinylated neoglycoproteins. These tools made it possible to conclude that hormonal status can affect the expression of endolectins. We have attempted to correlate the glycohistochemical findings with recently published data obtained biochemically. The results indicate that phase-specific alterations in lectin-binding glycoproteins and endolectins occur in the endometrium of mice associated with their short reproductive cycle.

Transforming growth factor beta up-regulates expression of the N-acetylglucosaminyltransferase V gene in mouse melanoma cells

beta-1,6-N-acetylglucosaminyltransferase V (GnT-V) (EC 2.4.1.155) that catalyzes beta-1,6 branching in asparagine-linked oligosaccharides is activated on viral or oncogenic transformation and is associated with tumor metastasis. To study the molecular mechanisms involved in regulation of expression of the GnT-V gene, we cloned cDNA and genomic DNA for the enzyme (Saito, H., Nishikawa, A., Gu, J., Ihara, Y., Soejima, Y., Sekiya, C., Niikawa, N., and Taniguchi, N. (1994) Biochem. Biophys. Res. Commun. 198, 318-327). We found that transforming growth factor beta (TGF beta) specifically induced GnT-V expression in mouse melanoma cells. The activity of GnT-V was increased 24 h after the addition of TGF beta and remained at high levels up to 72 h. Northern blot analysis showed that the mRNA levels of GnT-V were consistent with the increased activity. To further investigate the nature of the induction, mRNA stability and transcriptional activity were assayed. The enhancement of the GnT-V mRNA expression resulted from prolonged mRNA stability, not from increased transcription. Consequently, elevated mRNA levels were observed even 72 h after the addition of TGF beta. Lectin blot analysis involving leukoagglutinin showed newly synthesized beta-1,6 branching structures in the sugar chains of a protein of approximately 130 kDa at 48 h after TGF beta treatment. These results suggested that TGF beta caused changes in the sugar chains of proteins in melanoma cells by up-regulating GnT-V expression.

Use of lectins as diagnostic and therapeutic tools for cancer

Within the past few years, lectins have become a well-established means for understanding varied aspects of cancer and metastasis. Evidence is now emerging that lectins are dynamic contributors to tumor cell recognition (surface markers), cell adhesion and localization, signal transduction across membranes, mitogenic stimulation, augmentation of host immune defense, cytotoxicity, and apoptosis. To advance understanding of these lectin-dependent processes, attempts are being made to discover new lectins that have one or more of these functions and to develop lectin- (or glycoconjugate-) based tools that could be used to home in on tumor cells. This review will summarize current research on the lectins and recent advances in the development of lectin-based diagnostic and therapeutic tools for cancer. Additionally, the future potential of lectin-based diagnosis and therapy is discussed.

Analysis of asparagine-linked oligosaccharides by sequential lectin affinity chromatography

Lectins are proteins that specifically bind to a particular carbohydrate structure. Affinity chromatography with immobilized lectins is a quite effective technique not only for the fractionation of glycoproteins or oligosaccharides but also their structural assessment. In this article, we focus on the separation of glycopeptides and oligosaccharides derived from glycoproteins by affinity chromatography on immobilized lectin columns.

Fine sugar specificity of the mistletoe (Viscum album) lectin I

The behaviour of N-acetyllactosamine-type oligosaccharides and glycopeptides on a column of mistletoe lectin I (MLI) immobilized on Sepharose 4B was examined. The immobilized lectin does not show any affinity for asialo-N-glycosylpeptides and related oligosaccharides, which possess one to four unmasked N-acetyllactosamine sequences. However, substitution of at least one of the N-acetyllactosamine sequences by sialic acid residues, either at O-3 or O-6 of galactose, slightly enhances the affinity of the lectin. Such sialylated N-glycosylpeptides or oligosaccharides are eluted from the lectin column by the starting buffer as retarded fractions. Surprisingly, the affinity of the immobilized MLI is higher for P1 antigen-containing glycopeptide isolated from turtle-dove ovomucoid and for glycopeptides from bovine thyroglobulin containing terminal non-reducing Gal alpha 1-3Gal sequences. These structures are strongly bound on the lectin column and their elution is obtained with 0.15 M galactose in the starting buffer.

Distribution patterns in glycoconjugate expression during the development of the rat palate

The distribution of complex carbohydrate structures during the embryonic development of the rat palate was analysed by examining lectin-binding patterns in serial paraffin and cryostat sections. With few exceptions, the binding patterns showed a general increase in lectin receptors in the more developed stages of palatogenesis. High mannose oligosaccharides were especially amplified during development. Terminal fucose molecules were not expressed. In contrast, terminal sialic acid molecules were ubiquitously distributed in epithelial and mesenchymal tissues. Non-sialylated terminal N-acetylglucosamine was specifically restricted to evolving bone matrix. Before palatal fusion, quantitative but not qualitative differences were detected between oral, nasal, and medial-edge epithelial surfaces. The only exception was LCA, which specifically marked epithelial cells at the tip of palatal shelves. A very selective affinity for Jacalin was demonstrated in the oral epithelium of the palate after day 16, suggesting the presence of sialylated terminal galactose-(beta-1,3)-N-acetylgalactosamine. PNA specifically marked the basal lamina of the oral side of palatal processes. The binding patterns of DBA, GSL IA, SBA, and VVA indicated that the epithelium of the tongue is characterized by terminal alpha- and beta-galactose residues, whereas palatine cells possess only molecules with beta-anomery. During palatogenesis, glycosaminoglycans patterns were significantly modified. Our data suggest that alteration of complex carbohydrate structures may play a central role in modulating cell-cell and cell-matrix interactions. The significance of these findings, however, remains to be elucidated.

Interaction of immobilized recombinant mouse C-type macrophage lectin with glycopeptides and oligosaccharides

Inflammatory and tumoricidal macrophages express galactose- and N-acetylgalactosamine-specific Ca(2+)-dependent lectins on their surfaces. This lectin is a family member of membrane-bound C-type animal lectins and consists of 304 amino acid residues (molecular weight 34,595). In the present study, expression vectors containing a nucleotide sequence corresponding to the carbohydrate-binding domain of mouse macrophage lectin cDNA have been prepared. The carbohydrate-binding specificity of the recombinant macrophage lectin expressed in Escherichia coli was investigated by comparing elution profiles of various glycopeptides having defined carbohydrate structures on immobilized lectins. When elution profiles of high mannose-type and complex-type Asn-linked carbohydrate chains were compared, the degree of retardation from immobilized macrophage lectin column was in the order tetraantennary complex-type with terminal galactosyl residues > triantennary complex-type with terminal galactosyl residues > biantennary complex-type with terminal galactosyl residues > high mannose-type glycopeptides. N-Terminal octapeptides from human glycophorin A that bore three NeuAc alpha 2-3Gal beta 1-3(NeuAc alpha 2-6)GalNAc serine/threonine-linked tetrasaccharide chains and their sequentially deglycosylated derivatives were also applied to this column. Glycopeptides carrying three constitutive GalNAc-Ser/Thr(Tn-antigen) had the strongest affinity, whereas those with fully sialylated carbohydrate tetrasaccharide chains showed weak interaction. The association kinetics of Asn-linked glycopeptides from bovine asialofetuin to recombinant macrophage lectin was determined by surface plasmon resonance spectroscopy. The results indicate k(assoc) value of 1.63 x 10(4) M-1 s-1. The calculated value for Ka was 6.20 x 10(7) M.

Serological and biochemical characterization of recombinant baculovirus carcinoembryonic antigen

Carcinoembryonic antigen (CEA), a glycosylated protein of M(r) 180 kDa, is one of the most widely used human tumor markers. A majority of gastrointestinal cancers as well as breast and nonsmall cell lung carcinomas express CEA. We have previously described a recombinant baculovirus BVCEA-140 expressing the full-length human CEA and a variant, BVCEA-16, that encodes only the NH2-terminal domain, as well as a recombinant (BVNCA) expressing the closely related molecule nonspecific cross-reactive antigen (NCA). We have now compared a panel of 24 anti-CEA and anti-NCA monoclonal antibodies (MAbs) for their ability to bind to these recombinant CEA and NCA proteins, as well as with a new 60 kDa subgenomic form designated BVCEA-60. The epitope mapping studies indicate that all the CEA specific MAbs can recognize BVCEA-140. We also compared the sugar composition of BVCEA-140 to native CEA, using a lectin-linked immunoradiometric assay. The results demonstrated that both the native and recombinant baculovirus CEA contain simple high-mannose carbohydrates as well as biantennary and biantennary hybrid complexes. However, native CEA also contains triantennary and tetraantennary complex sugars, while the recombinant CEA molecule does not. Immunogenicity of the recombinant CEA molecules was demonstrated in mice. ELISA and Western blot analyses were used to determine the cross-reactivity of the anti-CEA sera. Mice immunized with BVCEA-140 elicit antibodies that are reactive to native CEA. When the BVCEA-16 was used as an immunogen, the antisera failed to detect native CEA or BVCEA-140. These studies demonstrate that minor sugar differences exist between native and baculovirus-derived CEA. However, epitope mapping with a panel of 24 anti-CEA MAbs (recognizing at least 10 CEA epitopes) stowed virtual immunologic identity between these two molecules. Moreover, BVCEA-140 appears to be a more potent humoral immunogen in mice than native CEA. These purified recombinant proteins can thus serve as standards in CEA serum assays for the possible detection and characterization of cell-mediated immune responses to CEA and as a potential source of immunogen (primary or for boosting) for active specific immunotherapy protocols of human carcinomas.

Purification and characterization of the ecto-Mg-ATPase of chicken gizzard smooth muscle

The ecto-Mg-ATPase isolated from chicken gizzard smooth muscle was solubilized, purified and characterized. The purification did not require the use of expensive or specialized apparatus. The chromatographic and electrophoretic characteristics of the ecto-Mg-ATPase from chicken are similar to those reported earlier for the ecto-Mg-ATPase isolated from rabbit skeletal muscle transverse tubule membranes [1992, J. Biol. Chem. 267, 11777-11782]. One obvious difference found was that the solubilized chicken ecto-Mg-ATPase can be stimulated approximately 1900% by the lectin Concanavalin A (Con A) under the same conditions that the rabbit enzyme is inhibited by approximately 50%. This stimulatory effect of Con A is useful for following the purification, and also increases the specific activity of the chicken enzyme to a very high level similar to that observed for the rabbit enzyme. After purification of the solubilized chicken ecto-Mg-ATPase by three steps of anion exchange chromatography, as well as Con A and erythroagglutinating Phaseolus vulgaris (PHA-E) lectin affinity chromatographies, a single diffuse glycoprotein band at approximately 66 kDa is observed after SDS-PAGE. This protein could be deglycosylated to a core protein of 53 kDa. Thus, the chicken gizzard protein is very similar in molecular size to the rabbit skeletal muscle ecto-Mg-ATPase both before and after deglycosylation [1992, J. Biol. Chem. 267, 11777-11782]. The N-terminal sequence of the 66 kDa chicken gizzard protein was found to be: Ala-Arg-Arg-Ala-Ala-Ala-Val-Leu-Leu-Leu-Leu-Ala. This is a unique sequence which, while very different from the rabbit ecto-Mg-ATPase N-terminus, exhibits some of the same characteristics, since it contains basic residues as the second and third amino acids, with the remainder of the N-terminus being very hydrophobic in nature. Furthermore, the chicken gizzard ecto-Mg-ATPase can be separated from the adhesion molecule, truncated cadherin (T-cadherin) by anion exchange chromatography, and is therefore not identical to that protein, as had been recently proposed [1993, Arch. Biochem. Biophys. 303, 32-43].

Purification and characterization of N-acetylglucosamine-6-sulfate sulfatase from bovine kidney: evidence for the presence of a novel endosulfatase activity

N-Acetylglucosamine-6-sulfate sulfatase (NG6SS) is an enzyme that catalyzes the hydrolysis of sulfate esters from the C-6 hydroxyl of N-acetylglucosamine. We report our purification and characterization of the enzyme and the discovery that it can remove sulfate from internally sulfated GlcNAc on glycopeptides and glycoproteins. The enzyme was purified from bovine kidney over 200,000-fold using a combination of ion-exchange and size-exclusion chromatography. NG6SS is soluble and occurs as a single subunit with apparent solution molecular weight of 60.2 kDa on gel filtration chromatography and approximately 52.5 and 57.8 kDa on reducing and nonreducing SDS/PAGE, respectively. The enzyme is highly basic and exhibits a broad pH range with an optimum at pH 6.5 and a temperature optimum of 37 degrees C. Among the mono- and disaccharide sulfates tested, only GlcNAc-6-SO4 is an effective substrate with a Km of 4.7 mM, and either free sulfate or phosphate inhibits the activity. Unexpectedly, we found that the enzyme displays endosulfatase activity and quantitatively releases 35SO4 from 35SO4-labeled glycopeptides and intact glycoproteins isolated from human Molt-3 cells, which we have previously shown to synthesize glycoproteins containing GlcNAc-6-SO4 residues within the sequence Gal beta 1-4[SO-3-6]-GlcNAc beta 1-R of complex-type N-linked oligosaccharides. The N-terminal sequence of the bovine NG6SS was homologous to a human-liver-derived N-acetylglucosamine-6-sulfatase. The endosulfatase activity of bovine kidney NG6SS may be important in its potential role in the degradation of sulfated glycans and may make this enzyme a valuable reagent to study the biological functions of sulfated glycoproteins.

Glycosylation of gamma-glutamyltransferase is modified by ethanol in H5-6 hepatoma cell line

The H5-6 cultured rat hepatoma cell line was used to investigate the post-translational maturation of gamma-glutamyltransferase (GGT) and the effects of acute ethanol administration on the expression and glycosylation of this membrane-bound glycoprotein. We found that the two subunits of H5-6 GGT with molecular masses of 55 and 33 kDa were derived from a single glycosylated precursor of 80 kDa. In addition, signals of high molecular mass (more than 90 kDa) were detected. In vitro deglycosylation experiments indicated that N-linked sugars represented about 25% of the molecular weight of the H5-6 enzyme. By use of serial lectin affinity technique, we showed that N-linked sugar chains were mainly of the biantennary complex and hybrid-type, without fucose linkage to the innermost N-acetyl-glucosamine. Ethanol treatment did not seem to affect the expression of GGT and the sialic acid content of the enzyme, but altered its oligosaccharide chain composition both quantitatively and qualitatively.

Exposure of the rat small intestine to raw kidney beans results in reorganization of absorptive cell microvilli

BACKGROUND/AIMS

A single exposure to raw kidney beans (RKB) results in vesiculation, shortening, and then regrowth of microvilli in the rat small intestine. This study investigated changes that occur in the structure of microvilli 2-10 hours after RKB exposure.

METHODS

Circumferences of microvilli from absorptive cells obtained sequentially after challenge with RKB or chow were assigned to one of three groups: small, intermediate, or large. The distribution and concentration of actin in intact mucosae or isolated epithelial sheets were determined by confocal laser scanning microscopy, immunocytochemistry, and immunoblot analysis with specific probes.

RESULTS

Six hours after exposure to RKB, most microvilli were large, abnormal in shape, and contained significantly more actin filaments than large microvilli from control rats. In addition, the fluorescence intensity of F-actin increased within injured microvilli without changes in the total intracellular actin concentration. By 8-10 hours after challenge with RKB, some microvilli remained larger than those of control rats but had resumed their normal shape and contained fewer actin filaments than at 6 hours.

CONCLUSIONS

Exposure of the rat small intestine to RKB results in enlargement of absorptive cell microvilli and reorganization of membrane and core actin filaments without changes in intracellular actin concentration. Enlarged microvilli are rapidly repaired.

Branching N-linked oligosaccharides in breast cancer

Tumor progression in rodent and human tumors is commonly associated with changes in glycoprotein glycosylation, in particular increased beta 1-6GlcNAc-branching, a regulatory step in expression of polylactosamine and extended-chain Lewis antigens. Loss of the branched oligosaccharides in murine tumor cells either due to somatic mutation, or treatment of the cells with the oligosaccharide processing inhibitor swainsonine, blocks tumor cells invasion in vitro and reduces solid tumor growth in vivo. Swainsonine and other inhibitors of N-linked oligosaccharide processing may be useful anti-cancer drugs, a premise which has begun to be tested in humans.

Use of Phaseolus vulgaris leukoagglutinating lectin in histochemical and blotting techniques: a comparison of digoxigenin- and biotin-labelled lectins

An increase in the number of beta 1,6 branches of the trimannosyl core of asparagine-linked oligosaccharides has been shown to be directly correlated with the metastatic potential of cultured tumour cells. The Phaseolus vulgaris leukoagglutinating lectin (PHA-L) binds to beta 1,6 branches of tri- and tetra-antennary oligosaccharides. We have applied digoxigenin- and biotin-conjugated PHA-L to establish a non-radioactive detection system for beta 1,6 branches, which can be used in lectin blotting as well as light and electron microscopic cytochemistry. For this purpose the HCT116 human colon carcinoma cell line and colon carcinoma tissue were investigated. Digoxigenin-conjugated PHA-L in conjunction with alkaline phosphatase-conjugated anti-digoxigenin antibodies was superior to biotin-conjugated PHA-L in lectin blotting with respect to sensitivity and specificity. Similarly, the digoxigenin conjugated PHA-L in conjunction with gold-labelled anti-digoxigenin antibodies resulted in more intense specific staining and lower background compared to biotin-conjugated PHA-L visualized with a streptavidin immunogold complex. The specificity of lectin binding in blotting and cytochemical studies was demonstrated by the absence of staining when the lectin was omitted or preabsorbed with glycoprotein, and following pretreatment of the cellular homogenates or tissue sections by N-glycosidase F. Our results demonstrate that digoxigenin-conjugated PHA-L provides high sensitivity and specificity for histochemical and blotting techniques and is amenable for quantification. The technique should have applications in tumour research.

Isolation of an immunosuppressive lectin from Phaseolus vulgaris L. cv Cacahuate using stroma

An immunosuppressive lectin was isolated from seed of Phaseolus vulgaris cv Cacahuate using physically entrapped stroma. The lectin was found to be a 94 kDa tetrameric protein. When 50 micrograms, of this lectin were administered intraperitoneally 2 days before the immunization with sheep red blood cells, humoral response against the immunogen was completely inhibited. Other properties of the protein are discussed.

Carbonoyloxy analogs of the anti-metastatic drug swainsonine. Activation in tumor cells by esterases

Swainsonine (SW), a plant alkaloid and inhibitor of alpha-mannosidases, has been shown to inhibit N-linked oligosaccharide processing and to block tumor cell metastasis in mice. In this study, a series of SW analogs were chemically synthesized and compared for inhibition of complex-type N-linked oligosaccharide processing in cultured MDAY-D2 tumor cells, for inhibition of alpha-mannosidases in vitro, and for stimulation of bone marrow proliferation in vivo. Carbonoyloxy substitutions at the 2 and 8 carbons of SW reduced inhibitor activity by 2-3 orders of magnitude for Jack Bean and MDAY-D2 tumor cell lysosomal alpha-mannosidases in vitro. However, 2-p-nitrobenzoyloxy-, 2-octanoyloxy- and 2-butanoyloxy-derivatives of SW retained full activity as inhibitors of Golgi oligosaccharide processing in viable MDAY-D2 tumor cells. Inhibition of oligosaccharide processing was reduced by the esterase inhibitor diethyl p-nitrophenyl phosphate, suggesting that although 2-p-nitrobenzoyloxy-SW, 2-octanoyloxy-SW and 2-butanoyloxy-SW are relatively poor inhibitors of alpha-mannosidases in vitro, the compounds enter cells at a rate comparable to that of SW, and are converted to SW by cellular esterases. The more lipophilic esters, 2-benzoyloxy-SW, 2-toluoyloxy-SW, 8-palmitoyloxy-SW and 8-myristinoyloxy-SW, showed IC50 values at least 10 times higher for inhibition of Golgi oligosaccharide processing, probably due to less efficient entry of the compounds into tumor cells. The anti-metastatic activities of SW and two analogs were tested and shown to correlate with the IC50 values for inhibition of Golgi oligosaccharide processing in cultured tumor cells. In vivo, SW and the analogs were administered intraperitoneally to mice and found to have comparable activities as stimulators of bone marrow cell proliferation. Carbonoyloxy substitutions at the 2- or 8-position of SW with other chemical groups may lead to new drugs with improved pharmacokinetics and anti-cancer activity.

Monoclonal antibodies that recognize the trisaccharide epitope Gal alpha 1-3Gal beta 1-4GlcNAc present on Ehrlich tumor cell membrane glycoproteins

Monoclonal antibodies were prepared against the trisaccharide Gal alpha 1-3Gal beta 1-4GlcNAc, a sequence which occurs on the surface of Ehrlich ascites tumor cells as well as in thyroglobulin, laminin and a variety of other proteins. This was accomplished by immunizing BALB/c mice with the fraction of Ehrlich cell membrane glycoproteins obtained by affinity chromatography on a Griffonia simplicifolia I (GS I) column which selectively binds alpha-D-galactosyl-terminated structures. Detection of Gal alpha 1-3Gal beta 1-4GlcNAc-specific antibodies was accomplished by employing glycoproteins containing the trisaccharide sequence; fusion with spleen cells from an immunized mouse was accomplished in the presence of polyethylene glycol (PEG1500). An enzyme-linked immunosorbent assay (ELISA) system was used to identify two clones (2.10G and 6.8E), which recognized the desired trisaccharide conjugate. These clones also recognized a thyroglobulin fraction isolated by GS I affinity chromatography and murine laminin, both of which possess the Gal alpha 1-3Gal beta 1-4GlcNAc sequence. Inhibition of antibody-trisaccharide reactivity, examined employing an ELISA assay, revealed that two trisaccharides, Gal alpha 1-3Gal beta 1-4GlcNAc/Glc, were the best inhibitory haptens; Gal beta 1-4GlcNAc (LacNAc), Gal alpha 1-3Gal and Gal beta 1-4Glc (lactose) were poor inhibitors. Indirect immunofluorescence staining of unfixed Ehrlich cells using the monoclonal antibody at 4 degrees C revealed fluorescence over the entire cell surface. Indirect immunogold labeling of semithin and ultrathin sections of aldehyde fixed and Lowicryl K4M-embedded Ehrlich cells resulted in specific labeling of the cell surface and internal structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of feline and canine platelet glycoproteins by immuno- and lectin histochemistry

Canine and feline platelet cytocentrifuge preparations (CCPs), cryostat and paraffin-embedded bone marrow sections were used in this study. We evaluated whether platelets, megakaryocytes and megakaryocyte precursor cells could be labelled by monoclonal antibodies (Y2/51, CLB-thromb/1, HPL1) against human platelet membrane glycoprotein GP IIIa and the GP IIb/IIIa complex or by the following 10 biotinylated lectins: concanavalin A (Con A), Lens culinaris agglutinin (LCA), Pisum sativum agglutinin (PsA), wheat germ agglutinin (WGA), peanut agglutinin (PNA), Phaseolus vulgaris lectin (PHA-L), Ricinus communis agglutinin 120 (RCA120), Ulex europaeus agglutinin-I(UEA-1), soybean agglutinin (SBA) and Dolichos biflorus agglutinin (DBA). Monoclonal antibodies Y2/51 and HPL1 cross reacted with platelets and megakaryocytic cells from both species, whereas CLB-thromb/1 was unreactive with canine preparations. Only Y2/51 labelled megakaryocytic cells in paraffin-embedded samples. LCA, PSA, WGA and PHA-L labelled feline and canine platelets and different numbers of morphologically identifiable megakaryocytes and numerous other, mostly myeloid, cells. Immunoblots of dog and cat platelet lysates using Y2/51 visualized a single protein of 95 kDa (unreduced), a mol.wt value within the range of those reported for GP IIIa. Some of the platelet (but not necessarily megakaryocyte) glycoproteins reacting with LCA, PSA and WGA could be identified in lectin blots following one- or two (nonreduced/reduced)-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Thus in dogs and cats, the immunohistochemical detection of GP IIIa (and eventually GP IIb/IIIa) rather than lectin binding patterns could be important for the diagnosis of megakaryoblastic leukaemias.

Induction of N-acetylglucosaminyltransferase V by elevated expression of activated or proto-Ha-ras oncogenes

Viral infection of cultured cells with transforming viruses causes an increase in cell-surface N-linked beta 1-6 (GlcNAc beta 1-6Man) branching of complex-type oligosaccharides. Similar observations have been made after transfection of cells with activated oncogenes, which is associated with an induction of tumorigenic and metastatic properties. In this study, the effects of transfection of both activated and proto-Ha-ras oncogenes into NIH3T3 cells were analyzed. The results showed that, in comparison with NIH3T3 cells, both ras transfectants have increased sensitivity to the cytotoxic action of L-PHA. An increase in beta 1-6 branching and an increased level of N-acetylglucosaminyltransferase V (GlcNAc-T V), the enzyme which initiates the beta 1-6 branching were also observed. The levels of GlcNAc-T I and beta 1-4 Gal-T remained unchanged in activated Ha-ras transfected NIH3T3 cells. These data suggest that a specific induction of GlcNAc-T V occurs after transfection with either the proto- or activated Ha-ras oncogenes, which is responsible for the increased beta 1-6 branching previously observed.

Differential glycosylation of the 5A11/HT7 antigen by neural retina and epithelial tissues in the chicken

The 5A11/HT7 antigen, a member of the immunoglobulin supergene family, has been implicated in heterotypic cell-cell interactions during retina development. Immunopurified 5A11 antigen isolated from Nonidet P-40-solubilized retina membranes had two components as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a 45.5-kDa doublet and a 69-kDa polypeptide. Immunoreactive bands of 46-50 kDa were recognized following SDS-PAGE of detergent-solubilized membrane proteins from liver, kidney, and erythrocytes. Treatment with N-glycosidase F (EC 3.2.2.18) converted the 45.5-50-kDa immunoreactive polypeptides from all tissues to 32 kDa, indicating that the observed differences in molecular mass were due to differences in glycosylation. N-Glycosidase F treatment also converted the 69-kDa form from retina to 46 kDa, indicating a different polypeptide core than the 32-kDa species. Treatment with endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96) resulted in modest increases in electrophoretic mobility due to hydrolysis of high mannose or hybrid oligosaccharides and lack of hydrolysis of complex oligosaccharides resistant to endo-beta-N-acetylglucosaminidase H digestion. Immunoreactivity was retained after deglycosylation. Much of the difference in molecular weight could be attributed to variations in sialylation. The higher molecular mass species of the 45.5-kDa doublet from retina and the polypeptides from other tissues were susceptible to neuraminidase (EC 3.2.1.18) and O-glycosidase (endo-alpha-N-acetylgalactosaminidase; EC 3.2.1.97) digestion. Labeling with elderberry bark lectin (specific for alpha 2,6-linked sialic acid) was confined to the higher molecular mass species of the 45.5-kDa doublet and was considerably greater in antigen derived from epithelia rather than neural retina. In paraffin sections of chick retina, elderberry bark lectin staining was confined to the retinal pigmented epithelium, photoreceptor cells, and bipolar cells with no staining of the Müller cells, which bear the bulk of the 5A11 antigen. These results indicate tissue-specific posttranslational modifications, particularly differences in sialylation of antigen-bearing polypeptides.