We previously proposed a high-throughput strategy to discover serological biomarker candidates of cancer. This strategy focuses on a series of candidate glycoproteins that are specifically expressed in the original tissues (cells) of the target cancer and that carry glycan structures associated with carcinogenesis [Narimatsu, H., et al. FEBS J.2010, 277(1), 95-105]. Here, we examined the effectiveness of our strategy in identifying biomarkers to assess progression of liver fibrosis and for the early detection of hepatocellular carcinoma (HCC). On the basis of the results of lectin array analyses in culture media of hepatoma cell lines, we captured glycopeptides carrying AAL-ligands (fucosylated glycans) or DSA-ligands (branched glycans) from digests of culture media proteins and sera from HCC patients with a background of liver cirrhosis (LC). Glycoproteins were identified by the IGOT-LC-MS method. In all, 21 candidates were selected from 744 AAL-bound glycoproteins for further verification according to (i) their abundance in serum, (ii) their specific expression in liver, and (iii) the availability of antibodies to the glycoproteins. All selected candidates showed enhancement of AAL-reactivity in sera of HCC patients compared with that of healthy volunteers (HV). These results indicate that our glycoproteomic strategy is effective for identifying multiple glyco-biomarker candidates in a high-throughput manner.

Epithelial ovarian cancer (EOC) is often asymptomatic and thus diagnosed at advanced stages with a poor prognosis. False-negative results for the conventional marker CA125 frequently occur in cases of clear cell carcinoma (CCC), a type of EOC; therefore, it is necessary to develop biomarkers with greater sensitivity. We previously reported a strategy to discover glycobiomarker candidates by combined lectin microarray and IGOT-LC/MS analysis. We have now optimized this strategy for discovering EOC biomarkers. Glycopeptides possessing cancerous glycans were enriched from the ascites fluids and culture supernatants of cancer cell lines with a fucose-binding lectin, AAL. IGOT-LC/MS analysis of CCC samples yielded 144 candidate glycoproteins. We selected WFA by lectin microarray as the optimal lectin to distinguish EOC from gastric and colon cancer. The candidates were narrowed by Western analysis of the WFA-bound fraction of ascites fluids. One of the final candidates, WFA-reactive ceruloplasmin, produced higher signals in the ascites fluids of EOC patients, including CCC, in comparison with the benign samples, while CA125 levels were comparable in the sandwich ELISA. Thus, our glycoproteomic strategy featuring efficient enrichment of glycans with disease-related alterations is applicable to various diseases.

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Bacterial sialyltransferases (STs) from marine sources were characterized using glycosphingolipids (GSLs). Bacterial STs were found to be beta-galacotoside STs. There were two types of STs: (1) ST obtained from strains such as ishi-224, 05JTC1 (#1), ishi-467, 05JTD2 (#2), and faj-16, 05JTE1 (#3), which form alpha2-3 sialic acid (Sia) linkages, named alpha2-3ST, (2) ST obtained from strains such as ISH-224, N1C0 (#4), pda-rec, 05JTB2 (#5), and pda-0160, 05JTA2 (#6), which form alpha2-6 Sia linkages, named alpha2-6ST. All STs showed affinity to neolacto- and lacto-series GSLs, particularly in neolactotetraosyl ceramide (nLc(4)Cer). No large differences were observed in the pH and temperature profiles of enzyme activities. Kinetic parameters obtained by Lineweaver-Burk plot analysis showed that #3 and #4 STs had practical synthetic activity and thus it became easily possible to achieve large-scale ganglioside synthesis (100-300 muM) using these recombinant enzymes. Gangliosides synthesized from nLc(4)Cer by alpha2-3 and alpha2-6STs were structurally characterized by several analytical and immunological methods, and they were identified as IV(3)alphaNeuAc-nLc(4)Cer(S2-3PG) and IV(6)alphaNeuAc-nLc(4)Cer (S2-6PG), respectively. Further characterization of these STs using lactotetraosylceramide (Lc(4)Cer), neolactohexaosylceramide (i antigen), and IV(6)kladoLc(8)Cer (I antigen) showed the synthesis of corresponding gangliosides as well. Synthesized gangliosides showed binding activity to the influenza A virus [A/panama/2007/99 (H3N2)] at a similar level to purified S2-3PG and S2-6PG from mammalian sources. The above evidence suggests that these STs have unique features, including substrate specificities restricted to lacto- and neolactoseries GSLs, as well as catalytic potentials for ganglioside synthesis. This demonstrates that efficient in vitro ganglioside synthesis could be a valuable tool for selectively synthesizing Sias modifications, thereby permitting the exploration of unknown functions.

We have established hybridoma cell lines producing monoclonal antibodies (mAbs) directed to N-acetylglucosaminylβ1-3galactose (GlcNAcβ1-3Gal) residue by immunizing BALB/c mice with lactotriaosylceramide (Lc(3)Cer). These obtained hybridoma cells, specific to Lc(3)Cer, were dual immunoglobulin (Ig)-producing cells which secreted both IgM and IgG molecules as antibodies. The established mAbs are able to react with not only Lc(3)Cer but also GlcNAcβ1-3-terminal glycosphingolipids (GSLs) despite branching or lactosamine chain lengths and human transferrin with terminal GlcNAc residues. Comparison of the variable regions of the cloned IgM and IgG by reversed transcription-polymerase chain reaction analysis confirmed that the variable regions determine the specificity, the other amino acids are conserved, and these mAbs are encoded by J558 and Vκ-21family genes. Furthermore, we have analyzed the expression of GSLs with GlcNAcβ1-3 epitope in acute leukemia cell lines and mouse fetal tissues using these mAbs, in which antigens were distributed comparatively. These mAbs are useful for studying the precise distribution of GlcNAcβ1-3Gal-terminating GSL expression in tissues as well as for detecting GSLs carrying terminal GlcNAcβ1-3Gal carbohydrate structure.