Malignant cell glycoproteins and glycolipids

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

A novel hypothesis for an alkaline phosphatase 'rescue' mechanism in the hepatic acute phase immune response

The liver isoform of the enzyme alkaline phosphatase (AP) has been used classically as a serum biomarker for hepatic disease states such as hepatitis, steatosis, cirrhosis, drug-induced liver injury, and hepatocellular carcinoma. Recent studies have demonstrated a more general anti-inflammatory role for AP, as it is capable of dephosphorylating potentially deleterious molecules such as nucleotide phosphates, the pathogenic endotoxin lipopolysaccharide (LPS), and the contact clotting pathway activator polyphosphate (polyP), thereby reducing inflammation and coagulopathy systemically. Yet the mechanism underlying the observed increase in liver AP levels in circulation during inflammatory insults is largely unknown. This paper hypothesizes an immunological role for AP in the liver and the potential of this system for damping generalized inflammation along with a wide range of ancillary pathologies. Based on the provided framework, a mechanism is proposed in which AP undergoes transcytosis in hepatocytes from the canalicular membrane to the sinusoidal membrane during inflammation and the enzyme's expression is upregulated as a result. Through a tightly controlled, nucleotide-stimulated negative feedback process, AP is transported in this model as an immune complex with immunoglobulin G by the asialoglycoprotein receptor through the cell and secreted into the serum, likely using the receptor's State 1 pathway. The subsequent dephosphorylation of inflammatory stimuli by AP and uptake of the circulating immune complex by endothelial cells and macrophages may lead to decreased inflammation and coagulopathy while providing an early upstream signal for the induction of a number of anti-inflammatory gene products, including AP itself.

Clinical usefulness of alterations in sialic acid, sialyl transferase and sialoproteins in breast cancer

Sialic acid, the end moieties of the carbohydrate chains are biologically important and essential for functions of glycoconjugates and are reported to be altered in cancer patients. Two hundred and twenty five breast cancer (BC) patients, 100 patients with benign breast disease (BBD) and 100 healthy females (controls) were enrolled for the study. Eight hundred and twenty four follow-up samples of 225 breast carcinoma patients were also evaluated. The association of sialic acid forms, sialyltransferase and α-2-6 sialoproteins levels with presence and extent as well as prognosis of breast carcinoma was studied. Serum sialic acid forms and sialyltransferase revealed significantly elevated levels among untreated breast cancer patients as compared to the controls, patients with BBD as well as cancer patients in remission. Non-responders showed comparable levels of the markers with those found in breast cancer patients at the time of diagnosis. Higher levels of sialic acid forms at diagnosis were associated with poor prognosis. A positive correlation between serum levels of different forms of sialic acids and extent of malignant disease was observed. The changes in serum proteins with terminal α-2-6 sialic acid correlated well with alterations in the levels of sialic acid forms and sialyltransferase. Malignant tissues showed elevated levels of sialic acid and sialyltransferase as compared to surrounding normal tissues.The results suggested potential utility of these markers in evaluation of clinical outcome.

Assessment of serum L-fucose in brain tumor cases

BACKGROUND

Glycosylation of altered tumor cell in relation to cellular heterogeneity in human intracranial tumors remains relatively unexposed. Serum protein-bound carbohydrate, L-Fucose is reported to be overexpressed during tumor progression by many investigators. Therefore, there is a need to determine the diagnostic, prognostic, functional significance of glycoprotein elevations in various cases of tumors.

OBJECTIVE

The objective of the present study was to evaluate the clinical utility of serum L-fucose in patients with brain tumor.

MATERIALS AND METHODS

Serum glyco-conjugate levels were estimated in 99 patients with brain tumors. Estimation of L-fucose was carried out colorimetrically by the method of Winzler using cysteine hydrochloride.

RESULTS

There was a significant increase in L-fucose level in most of the patients. In the posttreatment cases, the L-fucose levels were apparently low compared to preoperative values.

CONCLUSION

Our results showed that the rise in serum L-fucose may be used as a general marker for brain tumors in addition to other markers.

Serum fucosylation changes in oral cancer and oral precancerous conditions: alpha-L-fucosidase as a marker

BACKGROUND

The objective of the current study was to investigate the clinical usefulness of serum fucose, fucosylated glycoproteins (fucoproteins), fucosyltransferase (FucT), and alpha-L-fucosidase in oral carcinoma.

METHODS

Blood samples were collected from 130 patients with untreated oral cancer (OC), from 75 patients with oral precancerous conditions (OPC), and from 100 healthy controls. Cancer patients were followed after the initiation of anticancer treatments, and 75 follow-up samples were also collected. Serum levels of fucose and alpha-L-fucosidase were measured spectrophotometrically. Fucoproteins were detected by using lectin-affinity chromatography. FucT activity was analyzed by using radioassay.

RESULTS

Serum levels of fucose and fucoprotein were found to be increased significantly in patients with untreated OC compared with controls, patients with OPC, and complete responders (CR) to treatment; whereas the levels were comparable between untreated patients with OC and nonresponders (NR). A similar trend was observed for serum FucT levels, and changes in enzyme activity correlated well with fucose and fucoprotein alterations. The OPC group had significantly increased fucosylation of serum proteins. Furthermore, serum alpha-L-fucosidase activity was markedly higher in patients with untreated OC and in patients with OPC compared with controls. Using receiver operating characteristic curves, a cutoff for alpha-L-fucosidase was determined at >450.6 U/mL, which showed good sensitivity and specificity in OC and OPC compared with controls. The enzyme activity was declined in the CR group but remained higher in the NR group compared with pretreatment levels. Furthermore, various clinicopathologic characteristics were correlated positively with serum fucosylation changes.

CONCLUSIONS

The findings of the current study suggest that serum fucosylation has clinical usefulness in the detection of early changes and for monitoring treatment response in patients with OC. Among the markers studied, serum alpha-L-fucosidase was identified as a useful marker for close monitoring of patients during post-treatment follow-up.

Expression and enzyme activity of alpha(1,6)fucosyltransferase in human colorectal cancer

Changes in enzyme activity and the expression levels of alpha(1,6)fucosyltransferase [alpha(1,6)FT] have been reported in certain types of malignant transformations. To develop a better understanding of the role of alpha(1,6)FT in human colorectal carcinoma (CRC), we analysed the enzyme activity in healthy and tumour tissues. alpha(1,6)FT activity was considerably higher in tumour tissue than in healthy tissue and was related to gender, lymph node metastasis, type of growth and tumour stage. We also observed a significant increase in the alpha(1,6)FT expression in tumour tissues as compared to healthy and transitional tissues, inflammatory lesions and adenomas. The immunohistochemical expression in tumour tissues was correlated with the degree of infiltration through the intestinal wall. Finally, a statistical correlation was found between enzyme activity and expression obtained by Western blot in colorectal tumours when compared in the same patient. All these findings demonstrate an alteration of alpha(1,6)FT activity and expression in CRC.

Site-specific fucosylation of sialylated polylactosamines by alpha1,3/4-fucosyltransferases-V and -VI Is defined by amino acids near the N terminus of the catalytic domain

Fucose transfer from GDP-fucose to GlcNAc residues of the sialylated polylactosamine acceptor NeuAcalpha2-3Galbeta1-4Glc-NAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-ceramide leads to two isomeric monofucosyl antigens, VIM2 and sialyl-Le(x). Human alpha1,3/4-fucosyltransferase (FucT)-V catalyzes primarily the synthesis of VIM2, whereas human FucT-VI catalyzes primarily the synthesis of sialyl-Le(x). Thus, these two enzymes have distinct "site-specific fucosylation" properties. Amino acid sequence alignment of these enzymes showed that there are 24 amino acid differences in their catalytic domains. Studies were conducted to determine which of the amino acid differences are responsible for the site-specific fucosylation properties of each enzyme. Domain swapping (replacing a portion of the catalytic domain from one enzyme with an analogous portion from the other enzyme) demonstrated that site-specific fucosylation was defined within a 40-amino acid segment containing 8 amino acid differences between the two enzymes. Site-directed mutagenesis studies demonstrated that the site-specific fucosylation properties of these enzymes could be reversed by substituting 4 amino acids from one sequence with the other. These results were observed in both in vitro enzyme assays and flow cytometric analyses of Chinese hamster ovary cells transfected with plasmids containing the various enzyme constructs. Modeling studies of human FucT using a structure of a bacterial fucosyltransferase as a template demonstrated that the amino acids responsible for site-specific fucosylation map near the GDP-fucose-binding site. Additional enzyme studies demonstrated that FucT-VI has approximately 12-fold higher activity compared with FucT-V and that the Trp(124)/Arg(110) site in these enzymes is responsible primarily for this activity difference.

Enzyme linked lectin assay (ELLA) for direct analysis of transferrin sialylation in serum samples

OBJECTIVES

Glycosylation analysis provides many opportunities for diagnostics, but its complexity hampers its routine application. Aiming to alleviate this problem, we developed a simple assay that can measure sialylation of transferrin directly from serum.

DESIGN AND METHODS

Transferrin samples with different levels of sialylation were prepared by desialylation. Enzyme-linked-lectin assay (ELLA) and high-performance anion-exchange chromatography (HPAEC) have been used to analyze transferrin sialylation. Periodate oxidation was used to oxidize carbohydrates on antibodies.

RESULTS

ELLA was developed for the analysis of serum transferrin sialylation. Antibodies oxidized in situ with periodate have been used to capture transferrin from serum samples. Sialic acid on transferrin has been detected with Sambucus nigra agglutinin (SNA) lectin. Transferrin samples with different sialylation levels prepared by differential desialylation have been used as standards. Accuracy of the method has been confirmed by comparison to HPAEC analysis.

CONCLUSIONS

A rapid and simple ELLA that can be routinely used for the analysis of serum transferrin sialylation has been developed.

Tumor suppressor p16INK4a--modulator of glycomic profile and galectin-1 expression to increase susceptibility to carbohydrate-dependent induction of anoikis in pancreatic carcinoma cells

Expression of the tumor suppressor p16(INK4a) after stable transfection can restore the susceptibility of epithelial tumor cells to anoikis. This property is linked to increases in the expression and cell-surface presence of the fibronectin receptor. Considering its glycan chains as pivotal signals, we assumed an effect of p16(INK4a) on glycosylation. To test this hypothesis for human Capan-1 pancreatic carcinoma cells, we combined microarray for selected glycosyltransferase genes with 2D chromatographic glycan profiling and plant lectin binding. Major differences between p16-positive and control cells were detected. They concerned expression of beta1,4-galactosyltransferases (down-regulation of beta1,4-galactosyltransferases-I/V and up-regulation of beta1,4-galactosyltransferase-IV) as well as decreased alpha2,3-sialylation of O-glycans and alpha2,6-sialylation of N-glycans. The changes are compatible with increased beta(1)-integrin maturation, subunit assembly and binding activity of the alpha(5)beta(1)-integrin. Of further functional relevance in line with our hypothesis, we revealed differential reactivity towards endogenous lectins, especially galectin-1. As a result of reduced sialylation, the cells' capacity to bind galectin-1 was enhanced. In parallel, the level of transcription of the galectin-1 gene increased conspicuously in p16(INK4a)-positive cells, and even figured prominently in a microarray on 1996 tumor-associated genes and in proteomic analysis. The cells therefore gain optimal responsiveness. The correlation between genetically modulated galectin-1 levels and anoikis rates in engineered transfectants inferred functional significance. To connect these findings to the fibronectin receptor, galectin-1 was shown to be co-immunoprecipitated. We conclude that p16(INK4a) orchestrates distinct aspects of glycosylation that are relevant for integrin maturation and reactivity to an endogenous effector as well as the effector's expression. This mechanism establishes a new aspect of p16(INK4a) functionality.

A comparative study of serum protein-bound sialic acid in benign and malignant prostatic growth: possible role of oxidative stress in sialic acid homeostasis

Benign and malignant prostatic growths are associated with an increase in sialoconjugates (e.g. prostate-specific antigen (PSA)) in blood. Oxidative stress plays a crucial role in pathogenesis of various malignancies. The objective of this study was to evaluate oxidative stress parameters and protein-bound sialic acid level in sera of prostatic tumor cases and to asses for any association between them. Sera samples were collected and estimated for carbonylation of proteins, lipid peroxidation products, PSA and protein-bound sialic acid from 10 patients in each group with prostatic carcinoma (Ca prostate) and benign prostatic hyperplasia (BPH) along with 10 healthy male subjects of similar age group as control. In carcinoma prostate cases, lipid peroxides, protein carbonyls, protein-bound sialic acid and PSA were significantly increased compared to BPH and controls. There was significant association between oxidative stress parameters (lipid peroxide and protein carbonyl) and sialoconjugates (PSA and protein-bound sialic acid). In BPH cases, serum lipid peroxides and protein-bound sialic acid were significantly higher in comparison to controls and protein carbonyls were correlated with protein-bound sialic acid. ROC curve for sialic acid showed that it can be used as a marker to differentiate carcinoma prostate from benign growth of prostate at a cutoff level of 11.38 mug/mg protein with a sensitivity of 100% and specificity of 80%. We conclude that oxidative stress might be associated with the degree of sialylation of protein and graded changes in these parameters possibly unveil the pathogenic demarcation from benign to malignant condition of prostate.

Tumor galectinology: insights into the complex network of a family of endogenous lectins

Beta-Galactosides of cell surface glycoconjugates are docking sites for endogenous lectins of the galectin family. In cancer cells, primarily galectins-1 and -3 have been studied to date. With the emergence of insights into their role in growth control, resistance to or induction of apoptosis and invasive behavior the notion is supported that they can be considered as functional tumor markers. In principle, the same might hold true for the other members of the galectin family. But their expression in tumors has hitherto been a subject of attention only to a very limited extent. Pursuing our concept to define the complexity of the galectin network in cancer cells and the degree of functional overlap/divergence with diagnostic/therapeutic implications, we have introduced comprehensive RT-PCR monitoring to map their galectin gene expression. The data on so far less appreciated galectins in this context such as galectins-4 and -8 vindicate this approach. They, too, attach value to extend the immunohistochemical panel accordingly. Our initial histopathological and cell biological studies, for example on colon cancer progression, prove the merit of this procedure. Aside from the detection of gene expression profiles by RT-PCR, the detailed molecular biological monitoring yielded further important information. We describe different levels of regulation of galectin production in colon cancer cells in the cases of the tandem-repeat-type galectins-8 and -9. Isoforms for them are present with insertions into the peptide linker sequence attributed to alternative splicing. Furthermore, variants with distinct amino acid substitutions (galectin-8, Po66-CBP, PCTA-1, CocaI/II and galectin-9/ecalectin) and generation of multiple mRNA species, notably those coding for truncated galectin-8 and -9 versions with only one lectin site, justify to portray these two family members not as distinct individuals but as groups. In aggregate, the ongoing work to thoroughly chart the galectin network and to disentangle the individual functional contributions is expected to make its mark on our understanding of the malignant phenotype in certain tumor types.

Evaluation of serum sialic acid, sialyltransferase and sialoproteins in oral cavity cancer

OBJECTIVE

Altered glycosylation of glycoconjugates is among the important molecular changes that accompany malignant transformation. The aim of our study was to investigate clinical usefulness of circulatory levels of sialic acid, sialoproteins and sialyltransferase for early diagnosis and management of oral cavity cancer (OC) patients.

MATERIALS AND METHODS

Blood samples collected from 210 untreated OC patients, 100 patients with oral precancerous conditions (OPC) and 100 healthy males. OC patients were followed after initiation of anticancer treatment and 394 follow-up samples were also collected. Serum sialic acid levels were measured spectrophotometrically. Sialyltransferase activity was analysed using radioassay. Alpha 2-6 sialoproteins were isolated using lectin affinity chromatography.

RESULTS

Serum levels of free, protein bound and total sialic acid as well as their ratio with total proteins were significantly elevated in untreated OC patients compared with healthy individuals, patients with OPC as well as complete responders (CR). Levels of the markers were comparable between untreated OC patients and non-responders. We observed positive correlation between serum levels of the markers and extent of malignant disease. Serum sialyltransferase activity showed significant elevations in OC patients compared with the controls (P<0.001), patients with OPC (P<0.05) and CR (P<0.05). Higher sialic acid levels in OC patients at the time of diagnosis showed poor survival. The changes in serum proteins with terminal alpha 2-6 sialic acid correlated well with the alterations in the levels of sialic acid forms and sialyltransferase activity.

CONCLUSION

Our results confirmed the elevations in sialic acid and sialyltransferase levels in OC patients and suggested potential utility of these parameters in prognostication and treatment monitoring of this neoplasm. The alterations in these parameters in circulation were in accordance with the changes in alpha 2-6 sialylated proteins.

Prognostic values of galectin-3 and the macrophage migration inhibitory factor (MIF) in human colorectal cancers

This study aims to investigate whether the immunohistochemical levels of expression of galectin-3 and the macrophage migration inhibitory factor (MIF) are associated with prognostic values in human colorectal tumors. This was performed on 99 specimens including 69 colorectal tumors (17 Dukes A, 19 Dukes B, 15 Dukes C and 18 metastatic tumors that we labeled as D), 10 hepatic metastases from colorectal cancers and 20 normal specimens (biopsies). The immunohistochemical levels of expression of MIF and galectin-3 were quantified on routine histological slides by means of computer-assisted microscopy. Separate analyses were performed on epithelial and connective tissue. The levels of expression of both MIF and galectin-3 were very significantly higher in epithelial tumor tissue when compared with normal epithelial specimens. A positive and significant correlation between MIF and galectin-3 expression was evidenced in connective tumor tissue, and in particular in the cases associated with short survival periods (less than 5 years). In the case of the Dukes A or B tumors, we established two new prognostic groups (labeled I and II) on the basis of the levels of galectin-3 expression measured in the tumor epithelium. In the case of the Dukes C or D tumors, we established two other prognostic groups (labeled III and IV) on the basis of the levels of MIF expression measured in the connective tissue. Kaplan-Meyer analyses confirmed the additional prognostic values (as compared with conventional clinical staging) given by this new classification (groups I to IV). They show that the Dukes A or B tumors characterized by low levels of galectin-3 expression in the tumor epithelium are associated with significantly better prognoses than those characterized by high levels. In addition, the Dukes C or D tumors characterized by high levels of MIF expression in the connective tumor tissue are associated with significantly better prognoses than those characterized by low levels. In conclusions, MIF and galectin-3 expression levels in colorectal tumors are related to their levels of biological aggressiveness. These markers could be used to identify patients at risk, for whom more aggressive adjuvant therapy seems to be indicated.

Human lung adenocarcinoma alpha1,3/4-L-fucosyltransferase displays two molecular forms, high substrate affinity for clustered sialyl LacNAc type 1 units as well as mucin core 2 sialyl LacNAc type 2 unit and novel alpha1,2-L-fucosylating activity

Human lung tumor alpha1,3/4-L-fucosyltransferase (FT) was purified (2000-fold, 29% recovery) from 290 g of tissue by including a chromatography step on Affinity Gel-GDP. Two molecular forms (FTA, larger size carrying 15% alpha1,4-FT activity; FTB, the major form with 85% activity) were separated by further fractionation on a Sephacryl S-100 HR column. A difference in the electrophoretic mobilities of these two activities was also found on native polyacrylamide gel electrophoresis (PAGE). Both forms were devoid of typical alpha1,2-fucosylating activity but were associated with the novel alpha1,2-fucosylating ability of converting the Lewis a determinant to Lewis b. Based on percentage activity toward 2-O-MeGalbeta1,3GlcNAcbeta-O-Bn, both forms exhibited the same extent of activity toward various acceptors, which included sulfated, sialylated, or methylated LacNAc type 1 or type 2 as well as mucin core 2 acceptors. However, FTA and FTB exhibited a difference in their ability to act on mucin core 2 3'-sialyl LacNAc (activities 24.2% and 40.8%, respectively, as compared to 2-O-MeGalbeta1,3GlcNAcbeta-O-Bn). The unsubstituted LacNAc type 1 acceptors were 15-20 times as active as the corresponding LacNAc type 2 acceptors. The 3-O-substitution on the beta1,4-linked Gal (methyl, sulfate, or sialyl) in mucin core 2 acceptors increased the efficiency of these acceptors five- to eightfold. The most efficient acceptor for FTA and FTB was 3-O-sulfoGalbeta1,3GlcNAcbeta-O-Al (K(m) 100 and 47 microM, respectively). The K(m) (mM) values for 2-O-methyl Galbeta1,3GlcNAcbeta-O-Bn and 3-O-sialyl Galbeta1,3GlcNAcbeta-O-Bn were 0.40 and 2.5 (FTA) and 0.16 and 0.67 (FTB), respectively. The 35-kDa glycoprotein ancrod (from Malayan pit viper venom) containing 36% complex N-glycans with the antennae NeuAcalpha2,3Galbeta1,3GlcNAcbeta- acted as the best macromolecular acceptor substrate (K(m): 45 microM), as examined with FTB. On desialylation the acceptor efficiency dropped to approximately 50% (K(m) for asialo ancrod: 167 microM). Sialylglycoproteins, such as carcinoembryonic antigen, fetuin, and bovine alpha(1)-acid glycoprotein, were better acceptors than asialo fetuin. On the contrary, fetuin triantennary glycopeptide containing predominantly NeuAcalpha2,3Galbeta1,4GlcNAcbeta- was only 55% active as compared to the asialo glycopeptide (K(m): 1.43 and 0.63 mM, respectively). Thus, the human lung tumor alpha1,3/4-L-FT has the potential to generate clustered sialyl Lewis a and Lewis b determinants in N-glycans and sialyl Lewis x determinant in mucin core 2 structures.

A GDP-fucose-protected, pyridoxal-5'-Phosphate/NaBH(4)-sensitive lys residue common to human alpha1-->3Fucosyltransferases corresponds to Lys(300) in FucT-IV

Human alpha1-->3/4fucosyltransferases (FucTs) contain a common essential pyridoxal-5'-phosphate(PLP)/NaBH(4) reactive, GDP-fucose-protectable Lys. For identification, site-directed mutants at lysines of FucT-IV and -VII were prepared and tested. Non conserved lysine mutants K119Y and K394Q were similar to wild-type FucT-IV. However, mutants of conserved lysines K228R and K300R were distinct. The specific activity of K228R was 2- to 3-fold lower but retained K(m) values for donor and acceptor substrates as wild-type FucT-IV. The specific activity of K300R was reduced over 400-fold with an apparent K(m) for GDP-fucose over 200 microM. FucT-VII mutants K169R and K240R (equivalent to K228R and K300R for FucT-IV, respectively) were inactive. No change in PLP/NaBH(4) sensitivity occurred with K119Y, K228R, and K394Q compared to wild-type FucT-IV. These and previous results (A. L. Sherwood, A. T. Nguyen, J. M. Whitaker, B. A. Macher, M. R. Stroud, and E. H. Holmes, J. Biol. Chem. 273, 25256-25260, 1998) demonstrate that of three conserved lysines in FucT-IV, two (Lys(228) and Lys(283)) are not involved in substrate binding but perhaps in catalysis. The third site, Lys(300), is involved in GDP-fucose binding and PLP/NaBH(4) inactivation.

Photoaffinity glycoprobes-a new tool for the identification of lectins

One of the proposed functions for the carbohydrate structures on glycoconjugates is the transfer of information through interaction with specific lectin receptors. However, the number of elucidated functional lectin-carbohydrate interactions is still relatively small, largely due to the lack of adequate methods to identify lectin activity in complex biological samples. Aiming to solve this problem, we have developed a method based on the novel group of compounds we named glycoprobes. The glycoprobe consists of three vital parts: (1) glycan, (2) digoxin tag, and (3) photoreactive crosslinker. When incubated in dark, oligosaccharide part of the glycoprobe forms a complex with lectin. After illumination, covalent link between the probe and the lectin is formed resulting in a digoxin-tagged lectin. Using antibodies against digoxin, this complex can easily be identified immuno/cytochemically, or by Western blots. To demonstrate the applicability of glycoprobes we have used Man(9)-glycoprobe (containing Man(9)oligosaccharide) and YEE(ahGalNAc)(3)-glycoprobe (containing a synthetic neoglycopeptide with three terminal N-acetyl-galactosamine residues; Lee and Lee, Glycoconjugate J., 1987,4, 317) to identify lectins in bovine serum and rat liver membranes. The simplicity of the method enables its application in routine monitoring of changes in lectin activity during various developmental or pathological processes. An example of GalNAc-binding analysis in human serum is shown.

Evaluation of glycoprotein constituents in head and neck cancer patients undergoing radiotherapy

BACKGROUND

Alterations in serum levels of several glycoprotein constituents are reported to be useful for treatment monitoring of cancer patients. The purpose of this study was to determine efficacy of sialic acid and seromucoid fraction as treatment monitors for head and neck (H&N) cancer patients undergoing radiotherapy (RT).

METHODS

Serum levels of total sialic acid (TSA), lipid-bound sialic acid (LSA), and seromucoid fraction (measured as Mucoid protein [MP] and hexose) were studied in age matched controls and in patients with H&N cancer at diagnosis and during/after completion of RT. The markers were estimated by spectrophotometric methods.

RESULTS

Serum levels of sialic acid forms and seromucoid fraction were significantly elevated (p<.001) in untreated H&N cancer patients (n = 32) as compared with controls (n = 50). The marker levels were significantly declined (p<.001) in H&N cancer patients who responded to RT as compared with their levels at diagnosis, whereas the levels were persistently elevated in nonresponders.

CONCLUSION

Evaluation of sialic acid forms and seromucoid fraction could be used for monitoring the treatment of H&N cancer patients undergoing RT.

Total serum sialic acid is a general disease marker rather than a specific tumour marker in dogs

The aim of the present study was to examine the levels of total sialic acid (TSA) in serum of clinically healthy dogs and dogs with various diseases to evaluate the usefulness of TSA as a tumour marker. TSA levels in clinically healthy dogs were not different between sexes, but pregnant and lactating dogs had higher mean (+/- standard deviation (SD)) TSA levels than clinically healthy female dogs (642 +/- 78 vs. 495 +/- 73 mg/l, P < 0.001). Eighty-eight dogs with different tumours (54 malignant and 34 benign tumours of different tissues) had higher mean TSA levels than 148 clinically healthy dogs (675 +/- 143 vs. 498 +/- 75 mg/l, P < 0.01). Fifty dogs with other diseases excluding tumours (skin, urinary system, and gastrointestinal diseases, pyometra, other inflammatory diseases, and Cushing's syndrome) had slightly higher TSA levels than the tumour-bearing dogs (730 +/- 159 mg/l, P = 0.02). TSA levels in dogs with malignant tumours did not differ from dogs with benign tumours (682 +/- 144 vs. 664 +/- 142 mg/l, P = 0.73). A receiver-operating characteristic (ROC) plot revealed a maximum sensitivity and specificity combination of 69% and 91% (TSA cut-off concentration 595 mg/l) in distinguishing between healthy dogs and dogs with tumours. When evaluating TSA measurements to distinguish dogs with other diseases from dogs with tumours, a maximum sensitivity and specificity combination of 50% and 75% was found (cut-off concentration 761 mg/l). WHO staging of mammary tumours revealed an increase in TSA levels with increasing stage (P < 0.0001, rs, = 0.62). In conclusion, the nonspecificity of increases makes TSA determinations unsuitable as a tumour marker. TSA levels seem instead to be a general disease marker. Whether serial TSA measurements could be used in the follow-up of dogs operated for malignant tumours should be further investigated.

Cloning and expression of the catalytic domain from rat hepatoma H35 cell GDP-fucose:GM1 alpha 1-->2fucosyltransferase, an enzyme which is activated during early stages of chemical carcinogenesis in rat liver

A ganglioside GM1-specific alpha 1-->2fucosyltransferase is induced during the early stages of chemical carcinogenesis with N-2-acetylaminofluorene (AAF) in rat liver hepatocytes. The induction of this enzyme gives rise to the expression of a fucose-containing ganglioside with the same determinant structure as blood group B on a GM1 ganglioside core. Fucoganglioside synthesis is not found in normal rat liver but is elevated in premalignant liver and is often highly expressed in derived rat hepatoma cell lines. Based upon the consensus sequence from portions of previously cloned human, rabbit, and rat alpha 1-->2fucosyltransferase enzymes, primers were designed which were used in RT-PCR experiments with rat hepatoma H35 cell total RNA to generate cDNAs encoding the extracellular, catalytic domain of the H35 cell alpha 1-->2fucosyltransferase. Sequencing of these PCR fragments showed them to encode a novel enzyme with high homology to other cloned enzymes, particularly secretor alpha 1-->2fucosyltransferases. The derived sequence indicated that the 3' portion of the gene was virtually identical to the alpha 1-->2fucosyltransferase B (FTB) fragment reported earlier in rat PROb colon-adenocarcinoma cells (J-P. Piau et al. Biochem. J. 300, 623-626, 1994). A PCR product corresponding to the H35 cell alpha 1-->2fucosyltransferase was obtained from total RNA isolated from F344 rat liver after 0.03% N-2-acetylaminofluorene administration. No PCR product was obtained from total RNA isolated from normal F344 liver using PCR primers for the H35 cell alpha 1-->2fucosyltransferase. The H35 cell alpha 1-->2fucosyltransferase was expressed in the pPROTA vector and the derived fusion protein demonstrated the ability to transfer fucose to ganglioside GM1 but not to the neolacto-series acceptor nLcOse4Cer.

Lectin histochemistry of laryngeal squamous cell carcinomas

A panel of five biotinylated lectins was applied to study the presence and distribution of membrane carbohydrate residues in the normal laryngeal epithelium and in laryngeal squamous cell carcinomas (SCCs) of 86 patients with the avidin-biotin peroxidase complex technique. The lectin-binding pattern of well-differentiated SCCs was comparable to that of the spinous cells of the normal laryngeal epithelium. In the less differentiated SCCs, staining of the keratinocyte plasma membrane with lectins was either reduced or absent, indicating a decline in the glycosylation of cell surface glycoconjugates. The lectins applied here could be used in the rapid assessment of less-differentiated areas within a laryngeal SCC, but they cannot be regarded as reliable markers of laryngeal keratinocytes undergoing malignant transformation.

Fucose levels in sera and in tumours of colorectal adenocarcinoma patients

Fucose levels were determined in normal and tumour-derived tissues from patients with colorectal adenocarcinoma. Total, free and bound fucose were significantly higher (P < 0.001) in the tumoral tissue. Comparison of serum fucose levels between patients with colorectal cancer and control subjects indicated no statistically significant differences in total, free and bound fucose expressed as nmol/ml serum. However, when total and bound fucose were normalized to total protein (nmol/mg protein), an elevation in both parameters was found in colorectal cancer patients, although only that for total fucose was statistically significant (P < 0.001). A clear association between fucose content and clinical stage of patients according to the Dukes' classification can not be established, although patients at stage C showed higher levels of fucose both in serum and tissue. The current investigation provides direct evidence of a relationship between the elevation of fucose and the presence of tumour in colorectal cancer patients.

CD44 in inflammation and metastasis

CD44 is a major cell surface receptor for the glycosaminoglycan, hyaluronan (HA). CD44 binds HA specifically, although certain chondroitin-sulfate containing proteoglycans may also be recognized. CD44 binding of HA is regulated by the cells in which it is expressed. Thus, CD44 expression alone does not correlate with HA binding activity. CD44 is subject to a wide array of post-translational carbohydrate modifications, including N-linked, O-linked and glycosaminoglycan side chain additions. These modifications, which differ in different cell types and cell activation states, can have profound effects on HA binding function and are the main mechanism of regulating CD44 function that has been described to date. Some glycosaminoglycan modifications also affect ligand binding specificity, allowing CD44 to interact with proteins of the extracellular matrix, such as fibronectin and collagen, and to sequester heparin binding growth factors. It is not yet established whether the HA binding function of CD44 is responsible for its proposed involvement in inflammation. It has been shown, however, that CD44/HA interactions can mediate leukocyte rolling on endothelial and tissue substrates and that CD44-mediated recognition of HA can contribute to leukocyte activation. Changes in CD44 expression (mainly up-regulation, occasionally down-regulation, and frequently alteration in the pattern of isoforms expressed) are associated with a wide variety of cancers and the degree to which they spread; however, in other cancers, the CD44 pattern remains unchanged. Increased expression of CD44 is associated with increased binding to HA and increased metastatic potential in some experimental tumor systems; however, in other systems increased HA binding and metastatic potential are not correlated. CD44 may contribute to malignancy through changes in the regulation of HA recognition, the recognition of new ligands and/or other new biological functions of CD44 that remain to be discovered.

Alterations of glycosidases in human colonic adenocarcinoma

OBJECTIVES

We have carried out a detailed study of some glycosidases in an attempt to explain the differential profile of enzyme activity between human colonic adenocarcinoma and normal mucosa.

DESIGN AND METHODS

Several glycosidase activities associated with human colonic adenocarcinoma and control tissues were submitted to a detailed structural and functional characterization.

RESULTS

Tumoral and control samples were assayed for beta-D-galactosidase, beta-D-glucuronidase, alpha-D-mannosidase, beta-NAc-D-glucosaminidase and beta-NAc-D-galactosaminidase activities. Tumoral tissue showed higher beta-D-galactosidase, beta-NAc-D-glucosaminidase, and beta-NAc-D-galactosaminidase activities than control tissue. Glycosidases from tumoral and control tissues demonstrated no differences in optimum pH, subcellular distribution, pH and thermal stability. However, the kinetic analysis showed a statistically significant increased Vmax in tumoral colon with respect to the control for beta-D-galactosidase, beta-NAc-D-glucosaminidase, and beta-NAc-D-galactosaminidase activities. The Km remained unaltered.

CONCLUSIONS

The increased Vmax detected for some glycosidase activities in human colonic adenocarcinoma could correspond with a greater presence of enzyme proteins in the tumoral cells, and not to changes in protein and/or active site structure.

Enhancement of glycosylation of cellular glycoconjugates in the squamous carcinoma cell line MDA886Ln by beta-all-trans retinoic acid

Retinoids have been shown to inhibit the growth and modulate the glycosylation of head and neck squamous cell carcinoma (HNSCC) cells including the MDA886Ln cells. To examine the effects of beta-all-trans retinoic acid (RA) on glycoconjugates in HNSCC MDA886Ln cells, the cells were grown in the absence or presence of 1 microM RA and then labeled with tritiated monosaccharides, extracted and analysed by polyacrylamide gel electrophoresis and fluorography. RA increased markedly the incorporation of [3H]-glucosamine, [3H]-galactose, and [3H]-mannose into numerous cellular glycoconjugates, however, the incorportion of [3H]-fucose and [3H]-leucine was almost unaffected by RA. RA increased the incorporation of glucosamine and galactose but not mannose into high molecular weight (HMW) glycoconjugates of about 220 and 500-600 kDa. To analyse the steady state level of glycoconjugates by lectin blotting, extracts of unlabeled cells were separated by gel electrophoresis and the gels were probed with 125I-labeled wheat germ agglutinin (WGA) and Maackia amurensis (MA) agglutinin. Both lectins were found to bind to numerous glycoconjugates including the HMW glycoconjugates, whereas 125I-peanut agglutinin bound only to the HMW glycoconjugates RA treatment increased the binding of all three lectins to the HMW glycoconjugates. These findings demonstrate that RA enhanced the incorporation of specific monosaccharides into a variety of glycoconjugates and in particular into HMW mucin-like glycoconjugates. This effect of RA may be the result of induction of a more normal differentiation state of the HNSCC cells.

Glycobiology in Medicine

Glycoconjugates play important roles in biological reactions (for example sialyl Lewis(x) in 'homing' of leukocytes and mannose-6-phosphate in targeting of lysosomal enzymes) and thus aberration in carbohydrate structures in glycoconjugates can lead to abnormal biological behaviors. In fact, glycoconjugates expressed on the surfaces of tumor and cancer cells are considerably different from those of the normal cells, at least quantitatively. There are many known carbohydrate-deficient glycoprotein syndromes. As recognition of carbohydrate groups is mostly performed by carbohydrate-binding proteins, aberration in these proteins also results in disease status (for example I-cell disease). Many pathogens use carbohydrates as recognition markers for invasion (examples are influenza virus and cholera toxin). The carbohydrate receptors in various organs can be used for targeting drugs, antibodies and even DNAs. Conjugation of polysaccharides derived from pathogenic micro-organisms with appropriate proteins provides effective vaccines against the micro-organisms. Copyright 1996 S. Karger AG, Basel

Elevation of acid glycosidase activities in thyroid and gastric tumors

Numerous investigators have suggested that cell glycoconjugates are modified by the development of cancer and the progression of this to a malignant form. Accordingly, in the present work, beta-D-galactosidase, alpha-L-fucosidase, beta-N-acetyl-D-glucosaminidase and beta-N-acetyl-D-galactosaminidase activities were studied in human thyroid and gastric tumours. Samples were obtained from human gastric mucosa and thyroid gland tumours together with a part of the surrounding normal tissue (control). Enzyme activity was determined spectrophotometrically based on the release of p-nitrophenol from suitable p-nitrophenyl-derivative substrates. Results showed that beta-D-galactosidase, alpha-L-fucosidase, beta-N-acetyl-D-glucosaminidase and beta-N-acetyl-D-galactosaminidase activities were detected in tumour and control samples from thyroid and gastric tissues. The gastric mucosa also showed alpha-L-mannosidase activity. The specific activities of these glycosidases were higher (two- or three-fold) in tumour tissues as compared with their controls. beta-D-galactosidase, beta-N-acetyl-D-glucosaminidase and beta-N-acetyl-D-galactosaminidase activities from thyroid and gastric tumours showed a significant increase in V(max) as compared with their respective controls (P < 0.05 or P < 0.001). Thyroid alpha-L-fucosidase activity showed a statistically and significantly increased affinity (lower K(m)) in tumour samples as compared to normal tissue. In conclusion both gastric and thyroid tumours showed enhanced glycosidase activity as compared with enzyme activity observed in normal tissue. These results are in agreement with the notion of a markedly raised degradation within lysosomes of tumour cells.

Nonradioactive immunoquantification of alpha-L-fucosidase protein in human colon tissues

alpha-L-Fucosidase is a glycosidase involved in the degradation of fucoglycoconjugates and has a diagnostic significance because it has been described to be altered in several known diseases. However, in vitro studies on enzymatic activities may not reflect the real protein levels in tissues. This paper describes a simple method to quantify alpha-L-fucosidase protein levels in human crude extracts, combining the slot-blot technique and a nonradioactive immunoassay. Taking advantage of the similarities in different mammalian fucosidases, a polyclonal antiserum was raised against commercial purified alpha-L-fucosidase from bovine kidney that cross-reacted with the human colon enzyme. The method is able to detect as little as 0.75 ng alpha-L-fucosidase. To illustrate the direct application of this technique, we analysed and quantified alpha-L-fucosidase protein levels in 18 human colon crude samples. This technique could prove useful in clinical pathology, allowing fast and accurate measurement of alpha-L-fucosidase in crude extracts.

Inhibition of experimental metastasis by enzyme inhibitors from microorganisms and plants

Various antibacterial compounds, antitumor compounds, enzyme inhibitors and recent signal transduction inhibitors have been discovered from microorganisms and plants. Therefore, it should be possible to find antimetastatic compounds from these sources, if a simple assay system is available. We isolated several enzyme inhibitors from nature to inhibit experimental metastasis. Leupeptin is an old protease inhibitor and inhibited blood-borne lung metastasis of hepatoma cells in rats. A leupeptin analogue inhibiting urokinase inhibited in vitro invasion of human fibrosarcoma cells. Alpha-glucosidase inhibitors such as epi-CPL and baicalein inhibited in vitro invasion and in vivo metastasis of mouse melanoma cells. A mannosidase inhibitor, mannostatin A, also inhibited in vitro invasion of mouse melanoma cells. Oncogene function inhibitors induce normal phenotypes in the oncogene-expressing cells. As expected, they inhibited tumor cell invasion in vitro.

Determination of serum total lipid and free N-acetylneuraminic acid in genitourinary malignancies by fluorimetric high performance liquid chromatography. Relevance of free N-acetylneuraminic acid as tumour marker

The reliability of total sialic acid (TSA), lipid sialic acid (LSA) and free sialic acid (FSA) as markers in genitourinary malignancies was evaluated in 20 normal subjects, 21 patients with prostatic cancer, 22 patients with urinary bladder cancer and 14 patients with renal cell carcinoma. We introduce the new concept of 'corrected' lipid sialic acid (CLSA), which expresses the actual concentration of sialic acid bound to glycolipds by subtracting the concentration of FSA determined by a novel ultrafiltration method. TSA did not show significant differences with respect to normal controls, except for renal cell carcinoma, whose mean value (879 +/- 145 micrograms/ml) showed a P value < 0.001. Instead, CLSA showed only significant differences (P = 0.001), with respect to normal controls in stage I and in all grades of renal cell carcinoma. While all data indicated significant increases (P = 0.001) in the FSA values, (means +/- S.D.) of 0.621 +/- 0.272 micrograms/ml were found in patients with prostatic cancer, 0.796 +/- 0.443 micrograms/ml in patients with urinary bladder cancer and 0.667 +/- 0.146 micrograms/ml in patients with renal cell carcinoma. Separate TSA and CLSA measurements appeared to be of limited value in the detection of genitourinary malignancies. However, results show that FSA was the most sensitive of the three markers tested for detecting malignancies.

Urinary excretion of sialic acid in patients with bladder tumors

The pre- and post-treatment urinary total sialic acid/creatinine (TSA/Cr) ratios of patients with bladder tumor (n = 60) were determined. We found a significant increase in the mean urinary TSA/Cr ratio in patients with bladder tumors than in healthy people (99.80 +/- 15.60 micrograms/g Cr, 52.57 +/- 15.60 micrograms/g Cr, P < 0.001). We determined that the mean post-treatment TSA/Cr ratio of 44 patients was significantly lower than their pretreatment ratio and this value also decreased to the level in healthy people. (TSA/Cr; healthy people, 52.57 +/- 15.60 micrograms/g Cr, P < 0.001). The patients with decreased TSA/Cr ratio in the post-treatment period showed complete or partial regression of their disease. In 8 patients, urinary TSA/Cr ratio in the post-treatment period increased to 105 +/- 14.5 micrograms/g Cr value. In clinical and pathologic evaluation, it was shown that disease progressed in all of these 8 patients. The mean post-treatment TAS/Cr ratio of 8 patients did not differ from the pretreatment ratio (87.44 +/- 20.20 micrograms/Cr) and it was shown that their clinical status did not change. These findings show that urinary excretion of TSA correlates with the clinical status of bladder tumor and it could be used to follow the course of the disease, and follow-up treatment.

Characterization of human ovarian epithelial tumors (ex vivo) by proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy (1H MRS) offers an alternative investigational modality that will assist current pathologic techniques in the diagnosis of human ovarian epithelial tumors. Histologically normal human ovarian tissue (n = 12) was compared with ovarian benign fibromas (n = 3) and surface epithelial-stromal tumors (benign, n = 18; proliferating, n = 9; frankly malignant, n = 30) ex vivo by 1H MRS. The distinction between carcinomatous and benign or normal tissue (P<0.0001; Student's t-test) was made on one-dimensional (1-D) 1H MR spectra utilizing differences in resonance intensities of cellular lipid, creatine/phosphocreatine and lysine. The sensitivity and specificity of the test were 87% and 91%, respectively. Two-dimensional (2-D) MRS of carcinomatous biopsies showed multiple crosspeaks attributable to cell-surface fucosylation that correlated with tumor grade and loss of cellular differentiation. The multiple fucose crosspeaks were absent in spectra from normal ovary and benign tumors. The distinction between carcinomatous and normal or benign tissue based on MR-visible fucosylation gave a sensitivity and specificity of 88% and 97%, respectively. Proliferating tumors exhibited a range of cell-surface fucosylation patterns indicative of malignant potential.

Structure-function analysis of human alpha 1-->3fucosyltransferases. A GDP-fucose-protected, N-ethylmaleimide-sensitive site in FucT-III and FucT-V corresponds to Ser178 in FucT-IV

Human alpha 1-->3fucosyltransferases constitute a family of closely related membrane-bound enzymes distinguished by differences in acceptor specificities and inherent protein biochemical properties. One such biochemical property is sensitivity to enzyme inactivation by sulfhydral-group modifying reagents such as N-ethylmaleimide. The basis for this property has been studied using a fusion protein of FucT-III and FucT-V composed of Protein A coupled to the catalytic domain of the enzyme. The results indicate that modification of FucT-V by 5,5'-dithiobis(2-nitrobenzoic acid) resulted in efficient enzyme inactivation that could be reversed by excess thiol reagent suggesting that the free sulfhydral group on the enzyme was required for activity. Recombinant forms of both FucT-III and FucT-V were irreversibly inactivated by N-ethylmaleimide and could be effectively protected from inactivation by GDP-fucose and GDP but not by UDP-galactose, fucose, or N-acetyllactosamine. Analysis of the distribution of Cys residues in aligned sequences of cloned human alpha 1-->3fucosyltransferases indicated one site, Cys143 of FucT-III and Cys156 of FucT-V, corresponded to the highly conservative replacement of Ser178 in FucT-IV, an enzyme insensitive to N-ethylmaleimide. A site-directed mutagenesis experiment was performed to replace Ser178 of FucT-IV with a Cys residue. The mutant FucT-IV enzyme was active; however, the Km for GDP-fucose was increased about 3-fold compared to the native enzyme to 28 +/- 3 microM. This enzyme was N-ethylmaleimide sensitive and could be partially protected by GDP-fucose but not N-acetyllactosamine. These results support the importance of Ser178 of FucT-IV in donor substrate binding and strongly suggest analogous Cys residues are the GDP-fucose protectable, N-ethylmaleimide-sensitive sites present in FucT-III and -V.

Expression of galactoside-specific endogenous lectins and their ligands in human oral squamous cell carcinoma

Human endogenous lectins have a wide spectrum of biological functions. The present study analyses the expression of beta-galactoside specific and N-acetyl-D-galactosamine specific endogenous lectins in oral squamous cell carcinomas using biotinylated neoglycoproteins. The expression pattern of beta-galactosyl-containing glycoconjugates or ligands of beta-galactoside specific lectins in these tissues was also studied using an endogenous biotinylated lectin, the human 14-kDa lectin. For comparison a galactoside specific plant lectin from mistletoe, Viscum album was also employed. The results demonstrate that oral squamous cell carcinomas mainly express accessible binding sites for lactosylated neoglycoprotein (90%) while few carcinomas expressed mild amount of N-acetyl-D-galactosamine specific binding sites (40%). There was no difference in the binding patterns of these probes between well and less differentiated carcinomas. Expression of these neoglycoprotein binding sites were mostly concentrated in immature basaloid cells, indicating a possible association with cell proliferation. The binding pattern of D-galactosyl specific lectins (human 14-kDa and mistletoe lectins) showed conspicuous differences. This feature emphasizes the caution that needs to be exercised in interpreting the biological significance of results attained using plant lectins on human tissue.

Gangliosides associated with primary brain tumors and their expression in cell lines established from these tumors

Human primary brain tumors differ in their ganglioside composition when compared to adjacent tissues. One ganglioside found in all malignant glioma specimens, but not detected in normal adult brain, is 3'-isoLM1, a ganglioside of the lacto series. This ganglioside was also identified in medulloblastomas with astrocytic differentiation and in brain tissues containing benign proliferating astrocytes. The appearance of 3'-isoLM1 was seen over large regions of brain from glioma but was found mainly in areas either adjacent to the macroscopic tumor or areas corresponding to the tumor in the opposite hemisphere. A high concentration of 3'-isoLM1 was also seen in the corpus callosum, the anatomical structure along which glioma cells may migrate to the opposite brain hemisphere. Ganglioside expressed by cell lines established from primary malignant brain tumors varied widely among cell lines and within a given cell line propagated under different conditions. In in vitro-cultured glioma and medulloblastoma cell lines, gangliosides of the ganglio series dominated and the expression of the lacto series gangliosides, including 3'-isoLM1 was low if at all detectable. However, in vivo growth of solid subcutaneous tumors in nude mice or rats led to a significantly increased expression of the often dominant gangliosides of the lacto series and revealed a decreased expression of ganglio series gangliosides. In conclusion, these findings indicate that environmental factors could strongly influence the expression of gangliosides that may lead to a switch from the ganglio to the lacto series. These results also suggest that ganglioside 3'-isoLM1 is associated with proliferating astrocytes, of both neoplastic and non-neoplastic origin and that this ganglioside may be involved in cell-cell recognition and attachment during development and tumor cell migration.

Interpretation and clinical significance of alkaline phosphatase isoenzyme patterns

Alkaline phosphatase (ALP, EC 3.1.3.1) is a membrane-bound metalloenzyme that consists of a group of true isoenzymes, all glycoproteins, encoded for by at least four different gene loci: tissue-nonspecific, intestinal, placental, and germ-cell ALP. Through posttranslational modifications of the tissue-nonspecific gene, for example, through differences in carbohydrate composition, bone and liver ALP are formed. Nowadays, most commercially available methods for separating or measuring ALP isoenzymes are easy to perform and sensitive and allow for reproducible and quantitative results. As more isoenzymes and isoforms have been characterized, confusion has arisen due to the many different names they were given. For the sake of simplicity and because of structural analogies, we propose an alternative nomenclature for the ALP isoenzymes and isoforms based on their structural characteristics: soluble, dimeric (Sol), anchor-bearing (Anch), and membrane-bound (Mem) liver, bone, intestinal, and placental ALP. Together with lipoprotein-bound liver ALP and immunoglobulin-bound ALP, these names largely fit the many forms of ALP one can encounter in human serum and tissues. The clinically relevant isoenzymes are sol-liver, Mem-liver, lipoprotein-bound liver, and Sol-intestinal ALP in liver diseases, and Sol-bone and Anch-bone ALP in bone diseases. Many different isoenzyme patterns can be found in malignancies and renal diseases. This test provides the clinician with valuable information for diagnostic purposes as well as for follow-up of patients and monitoring of treatment. However, ALP isoenzyme determination will only provide clinically useful information if the patterns are correctly interpreted. In this respect, care should be taken to use the proper reference ranges, taking into account the age and sex of the patient. A normal total ALP activity does not rule out the presence of an abnormal isoenzyme pattern, particularly in children. Separating ALP into its isoenzymes adds considerable value to the mere assay of total ALP activity.

Sialyltransferase activity in FR3T3 cells transformed with ras oncogene: decreased CMP-Neu5Ac:Gal beta 1-3GalNAc alpha-2,3-sialyltransferase

We have investigated the activity of CMP-Neu5Ac:Gal beta 1-3GalNAc alpha-2,3-sialyltransferase (EC 2.4.99.4) in FR3T3 cells transformed by the Ha-ras oncogene in which we have previously demonstrated the higher expression of the beta-galactosidase alpha-2,6-sialyltransferase (EC 2.4.99.1) [21]. We demonstrate that the presence of the activated ras gene decreases the activity of this specific alpha-2,3-sialyltransferase fourfold. According to the kinetic parameters and to mixing experiments, we can assume that this decreased enzymatic activity reflects a decrease in the number of active O-glycan alpha-2,3-sialyltransferase polypeptides in ras-transformed cells. However, no change in the binding of Peanut agglutinin was observed on the cell surface of ras-transformed FR3T3 suggesting that no change in the sialylation of O-glycan core 1 appeared in these cells, although the activity of the alpha-2,3-sialyltransferase was decreased.

Stable expression of a cDNA encoding a human beta 1 --> 3galactosyltransferase responsible for lacto-series type 1 core chain synthesis in non-expressing cells: variation in the nature of cell surface antigens expressed

Transient expression of a human colonic adenocarcinoma Colo 205 cell derived cDNA in cell lines which ordinarily express only neolacto-series glycolipids has resulted in the expression of a beta 1 --> 3galactosyltransferase gene responsible for synthesis of glycolipids based upon the lacto-series type 1 core chain. Calcium phosphate transfected cells were panned on anti-IgM coated plates after initial treatment with a combination of monoclonal antibodies specific for type 1 chain terminal structures (TE-3) and a very broadly specific antibody reactive with multiple type 1 chain derivatives (TE-2). Adherent cells after panning were capable of efficiently transferring Gal in beta 1 --> 3-linkage to the acceptor glycolipid Lc3. Using these reagents, clones of stably transfected human colonic adenocarcinoma HCT-15 cells were produced and isolated. Parental HCT-15 cells do not express type 1 chain based antigens. The nature of the type 1 chain based antigens produced in each of these clones was analyzed by solid phase antibody binding assays. Three types of behavior were observed. Formation of type 1 terminal structures that were either exclusively sialylated or fucosylated, or a mixture of sialylated and fucosylated determinants occurred. In contrast, no difference in type 2 antigen expression between any clone and the parental cells was observed. These data suggest that coordination of subsequent reactions capable of modifying type 1 chain structures is not the same in all clones. The relationship of these results to aspects of cellular regulation of carbohydrate biosynthesis is discussed.

Formation of homogeneous carbohydrate-lectin cross-linked precipitates from mixtures of D-galactose/N-acetyl-D-galactosamine-specific lectins and multiantennary galactosyl carbohydrates

Quantitative precipitation studies have shown that the Man/Glc-specific lectin concanavalin A (ConA) forms homogeneous (homopolymeric) cross-linked precipitates with individual asparagine-linked oligomannose and bisected hybrid-type glycopeptides in the presence of binary mixtures of the carbohydrates [Bhattacharyya, L., Khan, M. I. & Brewer, C. F. (1988) Biochemistry 27, 8762-8767]. The results indicate that the ConA-glycopeptide precipitates are highly organized cross-linked lattices that are unique for each carbohydrate. Using similar techniques, the present study shows that the Gal-specific lectins from Erythrina indica and Ricinus communis (agglutinin I) form homogeneous cross-linked complexes with individual carbohydrates in binary mixtures of triantennary and tetraantennary complex-type oligosaccharides with terminal Gal residues. Conversely, binary mixtures of Gal/GalNAc-specific lectins from E. indica, Erythrina cristagalli, Erythrina flabelliformis, R. communis, soybean (Glycine max), and Wistaria floribunda (tetramer) in the presence of a naturally occurring or synthetic branched-chain oligosaccharide with terminal GalNAc or Gal residues provide evidence for the formation of separate cross-linked lattices between each lectin and the carbohydrate. The present results therefore demonstrate the formation of homogeneous lectin-carbohydrate cross-linked lattices in (a) a mixture of branched-chain complex-type oligosaccharides in the presence of a specific Gal/GalNAc-binding lectin, and (b) a mixture of lectins with similar physicochemical and carbohydrate binding properties in the presence of an oligosaccharide. These findings show that lectin-carbohydrate cross-linking interactions provide a high degree of specificity which may be relevant to their biological functions as receptors.

Presence of an essential lysine residue in a GDP-fucose protected site of the alpha 1----3fucosyltransferase from human small cell lung carcinoma NCl-H69 cells

The NCI-H69 cell alpha 1----3fucosyltransferase has been purified from a 0.2% Triton X-100R solubilized enzyme fraction by GDP-hexanolamine-Sepharose affinity chromatography and Superose 12 gel filtration. Photoaffinity labeling experiments with 125I-GDP-hexanolaminyl-4-azidosalicylic acid present in concentrations equivalent to 0.5 and 1 times Ki of the inhibitor for the enzyme indicated that labeling of the 45-kDa protein band could be inhibited by addition of 400 microM GDP-fucose but was not effected by similar concentrations of either GDP-mannose or GDP-glucose. The purified enzyme was applied to studies intended to define catalytically essential amino acid residues of the protein. Incubation of the enzyme in the presence of increasing concentrations of pyridoxal 5'-phosphate was found to result in irreversible inactivation of the enzyme after NaBH4 reduction. The donor substrate, GDP-fucose, was found to protect the enzyme from inactivation. Little or no protection was found for either GDP-mannose or the acceptor substrate nLc4. Pyridoxal 5'-phosphate was shown to behave as a competitive inhibitor with respect to GDP-fucose with a Ki of 105 microM. Labeling with 3H-pyridoxal 5'-phosphate resulted in the incorporation of approximately 8 mol pyridoxal 5'-phosphate per mole subunit. Parallel experiments containing GDP-fucose indicated protection of one site per subunit correlated with GDP-fucose binding. Acid hydrolysis and chromatographic analysis of the 3H-pyridoxylated protein indicated greater than 95% of the 3H label was recovered as pyridoxyl-lysine irrespective of whether GDP-fucose was present or not during labeling. These studies indicate the presence of a catalytically essential lysine residue associated with GDP-fucose binding to this enzyme. This information will be of value in further studies of this and other alpha 1----3fucosyltransferases and may suggest a practical basis for modulation of enzyme activity in the cell.

Monoclonal antibodies recognizing normal and retrovirus-transformed chicken hematopoietic cells

The avian hematopoietic system has long been an invaluable model to study the mechanisms of cell growth and differentiation. We have developed six MAbs against either chicken embryonic hematopoietic precursor cells or retrovirus-transformed cells. MAbs Mo1, Mo2, and Mo3 recognized transformation-associated markers expressed in AMV-transformed nonproducer cell line-BM2. Not only were these markers expressed 7 to 10 folds higher on BM2 than on normal monocytic cells, but their expression was drastically reduced when BM2 cells were induced to differentiate into macrophages by PMA. The control of marker expression is associated with v-myb-transforming cascade, since another monocytic lineage-specific oncogene, v-myc, did not enhance the expression of these markers. MAb Em1 detected a marker that is normally present in 20% of the cells from the 30/50% interface of a discontinuous percoll gradient of normal 4-day-embryo yolk sac. Its expression is also found in AEV-transformed cells and MSB1 cells. The epitope for Em1 was exposed after neuraminidase treatment on erythroleukemia cell line 6C2, which suggested that sialylation and/or glycosylation is pivotal in regulating the expression of specific markers in differentiation pathways during embryogenesis and tumorigenesis. MAb Em2 recognized proliferating hematopoietic cells after the fourth day of embryogenesis. MAb Em3, on the other hand, is presumed to be specific for an oncofetal antigen expressed in various transformed cells but only in 10% of the cells from 30/50% interface of a discontinuous percoll gradient of normal 4-day-embryo yolk sac. These MAbs will be useful for dissecting the expression of differentiation markers within normal versus abnormal differentiation pathways in molecular terms.

Lipid-associated sialic acid levels in human breast cyst fluids

Benign mammary gross cystic disease is the most common breast lesion. Women with apocrine changes of epithelium lining the cysts are at higher risk for developing breast cancer than the normal female population. Sialic acid has drawn considerable interest because of carbohydrate aberrations in malignant cells. The current investigation determined the concentrations of lipid-associated sialic acid (LASA) in 62 breast cyst fluids and sera. Data analyses show a significant increase in the mean values of LASA in metabolically active apocrine cysts when compared to the cysts with Na+/K+ > 3 (flattened cysts) (p < 0.001). The greater LASA levels in cyst fluids with lower intracystic Na+/K+ ratios could represent an altered expression of biosynthetic activity of the surrounding apocrine cell surface sialoglycolipid metabolism, providing a possible explanation of why women with apocrine cysts may be at greater cancer risk and being useful in further studies on functional stage changes in the cysts and their relationship to breast cancer.