Monoclonal antibody (5F3) defining renal cell carcinoma-associated antigen disialosyl globopentaosylceramide (V3NeuAcIV6NeuAcGb5), and distribution pattern of the antigen in tumor and normal tissues

Characterization and application of active human α2,6-sialyltransferases ST6GalNAc V and ST6GalNAc VI recombined in Escherichia coli

Eukaryotic sialyltransferases play key roles in many physiological and pathological events. The expression of active human recombinant sialyltransferases in bacteria is still challenging. In the current study, the genes encoding human N-acetylgalactosaminide α2,6-sialyltransferase V (hST6GalNAc V) and N-acetylgalactosaminide α2,6-sialyltransferase VI (hST6GalNAc VI) lacking the N-terminal transmembrane domains were cloned into the expression vectors, pET-32a and pET-22b, respectively. Soluble and active forms of recombinant hST6GalNAc V and hST6GalNAc VI when coexpressed with the chaperone plasmid pGro7 were successfully achieved in Escherichia coli. Further, lactose (Lac), Lacto-N-triose II (LNT II), lacto-N-tetraose (LNT), and sialyllacto-N-tetraose a (LSTa) were used as acceptor substrates to investigate their activities and substrate specificities. Unexpectedly, both can transfer sialic acid onto all those substrates. Compared with hST6GalNAc V expressed in the mammalian cells, the recombinant two α2,6-sialyltransferases in bacteria displayed flexible substrate specificities and lower enzymatic efficiency. In addition, an important human milk oligosaccharide disialyllacto-N-tetraose (DSLNT) can be synthesized by both human α2,6-sialyltransferases expressed in E. coli using LSTa as an acceptor substrate. To the best of our knowledge, these two active human α2,6-sialyltransferases enzymes were expressed in bacteria for the first time. They showed a high potential to be applied in biotechnology and investigating the molecular mechanisms of biological and pathological interactions related to sialylated glycoconjugates.

Pathophysiological roles and applications of glycosphingolipids in the diagnosis and treatment of cancer diseases

Glycosphingolipids (GSLs) are major amphiphilic glycolipids present on the surface of living cell membranes. They have important biological functions, including maintaining plasma membrane stability, regulating signal transduction, and mediating cell recognition and adhesion. Specific GSLs and related enzymes are abnormally expressed in many cancer diseases and affect the malignant characteristics of tumors. The regulatory roles of GSLs in signaling pathways suggest that they are involved in tumor pathogenesis. GSLs have therefore been widely studied as diagnostic markers of cancer diseases and important targets of immunotherapy. This review describes the tumor-related biological functions of GSLs and systematically introduces recent progress in using diverse GSLs and related enzymes to diagnose and treat tumor diseases. Development of drugs and biomarkers for personalized cancer therapy based on GSL structure is also discussed. These advances, combined with recent progress in the preparation of GSLs derivatives through synthetic biology technologies, suggest a strong future for the use of customized GSL libraries in treating human diseases.

Expression of Ganglioside Disialosyl Globopentaosyl Ceramide in Prostate Biopsy Specimens as a Predictive Marker for Recurrence after Radical Prostatectomy

Carbohydrate antigens are associated with carcinogenesis, cancer invasion, and metastasis and their expression reflect biological activities of various cancers. We previously reported that expression of disialosyl globopentaosyl ceramide (DSGb5), one of carbohydrate antigens, in radical prostatectomy specimens independently predicted biochemical recurrence (i.e., elevating serum prostate specific antigen without recurrent lesions in the image) after radical prostatectomy. However, it is important to evaluate the prognosis at the diagnosis. In this study we investigated DSGb5 expression in prostate biopsy specimens to develop a novel biomarker for providing appropriate management. Between 2005 and 2011, patients who underwent both prostate biopsy and radical prostatectomy in our institution were included. The median follow-up period was 88 months. DSGb5 expression was assessed by immunohistochemical staining and defined 116 patients as high DSGb5 expression (42 patients) or low DSGb5 expression (74 patients). High DSGb5 expression was significantly associated with lymphovascular invasion in radical prostatectomy specimens on both univariate and multivariable analyses (p = 0.028, 0.027). On multivariable analysis, Gleason Score in prostatectomy specimen, positive resection margin, and DSGb5 expression in the biopsy specimen were independently associated with biochemical recurrence-free survival following radical prostatectomy (p = 0.004, 0.008, 0.024). When targeting only patients with negative resection margin, DSGb5 expression was significantly associated with biochemical recurrence-free survival on both univariate and multivariable analyses (p = 0.006, 0.007). DSGb5 expression in prostate biopsy specimens is predictive of lymphovascular invasion and biochemical recurrence-free survival following radical prostatectomy. DSGb5 is a potential biomarker for preoperatively predicting oncological outcomes of prostate cancer.

[Analysis of Target Molecules towards Anti-cancer Therapeutic Antibodies]

Target molecules of existing anti-cancer therapeutic monoclonal antibodies (mAbs) are divided into 1) receptor-type tyrosine kinases, such as human epidermal growth factor receptor (HER) family, 2) differentiation antigens, such as CD20 (Rituxan target), 3) angiogenesis-related molecules, and 4) immune checkpoint molecules (PD-1, etc.). We have recently reported a novel therapy targeting lymphangiogenesis, but not angiogenesis, using an anti-LYVE-1 (lymphatic vessel endothelial hyaluronan receptor 1) mAb. At present, many transporters are not considered to be target molecules for the cancer therapy; however, our study strongly suggested that the inhibition of cancer metabolism by mAbs against amino acid transporters will play a significant role in future cancer therapies. Most anti-cancer therapeutic mAbs bind cell-surface molecules on viable cancer cells: therefore, it is necessary to produce mAbs recognizing epitopes on the extracellular domains of native and non-denatured proteins. We concluded that viable cancer cells or cells transfected with cDNA encoding target proteins are suitable immunogens for the production of anti-cancer therapeutic mAbs. We introduce our efforts to develop seeds for therapeutic mAbs using whole cancer cells and transfectants as the immunogen. As many target candidates in the future are multi-pass membrane proteins, such as 12-pass amino acid transporter proteins belonging to the solute carrier (SLC) family, and their possible immunogenic extracellular regions are small, the production of specific mAbs is highly difficult. In this review, we summarize the successful preparation and characterization of mAbs recognizing the extracellular domain of oncoproteins, including transporters.

Clinicopathological significance of ganglioside DSGb5 expression in renal cell carcinoma

Disialosyl globopentaosylceramide (DSGb5) is a ganglioside originally isolated from tissue extracts of renal cell carcinoma (RCC) with metastasis. Previous in vitro experiments have suggested that DSGb5 promotes metastasis by enhancing the migration of RCC cells and downregulating NK cell cytotoxicity against RCC cells. In this study, we investigated the clinicopathological significance of DSGb5 expression in RCC and outcomes of RCC patients. A total of 156 RCC patients who underwent surgical treatments at our hospital from January 2007 through December 2012 were analyzed in this study. The expression of DSGb5 in RCC specimens was examined by immunohistochemical staining with monoclonal antibody 5F3. The immunostaining intensity of RCC tissues was assessed in comparison with that in benign renal tubules as an internal positive control. The relationship between DSGb5 expression and clinicopathological characteristics was investigated and recurrence free survival following surgery was evaluated. Microvascular invasion was observed in 68% (n = 19/28) and in 45% (n = 58/128) of the DSGb5 high expression group and low expression group, respectively (p = 0.031). Of 156 patients with a median follow up of 51 months, 18 patients (12%) developed metastasis following surgery. Patients in the DSGb5 high expression group showed significantly lower recurrence-free survival as compared with those in the DSGb5 low expression group (log-rank P = 0.047). In the present study, DSGb5 expression was associated with microvascular invasion in RCC tissues, and patients with DSGb5 high expression showed significantly lower recurrence-free survival rates. These findings suggest that DSGb5 expressed in RCC is correlated with metastasis and is a potential predictor for identifying patients who experience metastasis after surgery.

Ganglioside, disialosyl globopentaosylceramide (DSGb5), enhances the migration of renal cell carcinoma cells

About one third of renal cell carcinoma (RCC) patients exhibit metastasis upon initial presentation. However, the molecular basis for RCC metastasis is not fully understood. A ganglioside, disialosyl globopentaosylceramide (DSGb5), was originally isolated from RCC tissue extracts, and its expression is correlated with RCC metastatic potential. DSGb5 is synthesized by GalNAc α2,6-sialyltransferase VI (ST6GalNAcVI) and is expressed on the surface of RCC cells. Importantly, DSGb5 binds to sialic acid-binding Ig-like lectin-7 (Siglec-7) expressed on natural killer (NK) cells, thereby inhibiting NK-cell cytotoxicity. However, the role of DSGb5 in RCC progression remains obscure. To address this issue, we used ACHN cells derived from malignant pleural effusion of a patient with metastatic RCC. Using the limiting dilution method, we isolated three independent clones with different DSGb5 expression levels. Comparison of these clones indicated that the cloned cells with high DSGb5 expression levels exhibited greater migration potential, compared to the clone with low DSGb5 expression levels. In contrast, DSGb5 expression levels exerted no significant effect on cell proliferation. We then established the ACHN-derived cell lines that stably expressed siRNA against ST6GalNAcVI mRNA or control siRNA. Importantly, the ST6GalNAcVI-knockdown cells expressed low levels of DSGb5. We thus demonstrated the significantly decreased migration potential of the ST6GalNAcVI-knockdown cells with low DSGb5 expression levels, compared to the control siRNA-transfected cells expressing high DSGb5 levels, but no significant difference in the cell proliferation. Thus, DSGb5 expression may ensure the migration of RCC cells. We propose that DSGb5 expressed on RCC cells may determine their metastatic capability.

Ganglioside disialosyl globopentaosylceramide is an independent predictor of PSA recurrence-free survival following radical prostatectomy

BACKGROUND

Disialosyl globopentaosylceramide (DSGb5) is a ganglioside originally isolated from renal cell carcinoma (RCC) tissue that has been associated with RCC metastasis. However, in prostate cancer, the expression of DSGb5 has not yet been fully assessed. In this study, we investigated DSGb5 expression in prostate tissues and the relationship between DSGb5 expression and clinicopathological characteristics of prostate cancer patients.

METHODS

A total of 130 patients who underwent radical prostatectomy (RP) at our hospital between January 2005 and December 2007 were analyzed in this study. The expression of DSGb5 in prostatectomy specimens was examined by immunohistochemical analysis with monoclonal antibody 5F3 (anti-DSGb5). Associations between 5F3 expression and clinicopathological findings were investigated and the factors that affected PSA failure-free survival were assessed by Kaplan-Meier analysis and a Cox regression model.

RESULTS

When immunoreactivities of 5F3 were measured, negative to strong staining was observed in prostate cancer tissue, whereas strong staining was observed in benign prostate glands. These expression patterns suggest that DSGb5 may act as a differentiation antigen in cancerization. The PSA failure-free survival was significantly higher in the 5F3 intact expression group than in the 5F3 reduced expression group (log-rank P=0.0220). On multivariate analysis, 5F3 intact expression showed significantly worse PSA failure-free survival following RP.

CONCLUSIONS

5F3 expression reflects the clinical and pathological features of prostate cancer and is correlated with the outcomes following RP. Further studies are necessary to clarify the functional roles of DSGb5 and establish a novel biomarker for prostate cancer.

Ganglioside DSGb5, preferred ligand for Siglec-7, inhibits NK cell cytotoxicity against renal cell carcinoma cells

In renal cell carcinoma (RCC), the presence of higher gangliosides correlates with systematic metastasis. Disialosyl globopentaosylceramide (DSGb5) was identified previously as one of the major gangliosides from RCC tissues. Siglec-7 (sialic acid-binding Ig-like lectin-7), expressed on natural killer (NK) cells as an inhibitory receptor, has a striking preference for internally branched α2,6-linked disialic gangliosides such as DSGb5. To clarify the functional role of DSGb5 in RCC metastases, we have investigated whether DSGb5 expressed on RCC cells can modulate NK cell cytotoxicity in a Siglec-7-dependent manner. The binding activity of RCC cells to Siglec-7-Fc fusion protein was specifically inhibited by anti-DSGb5 monoclonal antibody and transfection of siRNA for ST6GalNAcVI (synthetase of DSGb5). These observations showed that Siglec-7-Fc fusion protein specifically bound to DSGb5 expressed on RCC cells. In contrast, the sialic acid-binding site of Siglec-7 on NK cells was masked by cis interactions with endogenous sialoconjugates at the cell surface, but it could be unmasked by sialidase treatment of the NK cells. Following sialidase treatment of NK cells, NK cell cytotoxicity against RCC cells with high DSGb5 expression was significantly decreased relative to cells with low DSGb5 expression. These findings indicate that such NK cell cytotoxicity against RCC cells could be inhibited by the interaction between Siglec-7 on effecter cells and DSGb5 on target cells. The results of the present study suggest that DSGb5 expressed on RCC cells can downregulate NK cell cytotoxicity in a DSGb5-Siglec-7-dependent manner and that RCC cells with DSGb5 create favorable circumstance for their own survival and metastases.

The repertoire of glycan determinants in the human glycome

The number of glycan determinants that comprise the human glycome is not known. This uncertainty arises from limited knowledge of the total number of distinct glycans and glycan structures in the human glycome, as well as limited information about the glycan determinants recognized by glycan-binding proteins (GBPs), which include lectins, receptors, toxins, microbial adhesins, antibodies, and enzymes. Available evidence indicates that GBP binding sites may accommodate glycan determinants made up of 2 to 6 linear monosaccharides, together with their potential side chains containing other sugars and modifications, such as sulfation, phosphorylation, and acetylation. Glycosaminoglycans, including heparin and heparan sulfate, comprise repeating disaccharide motifs, where a linear sequence of 5 to 6 monosaccharides may be required for recognition. Based on our current knowledge of the composition of the glycome and the size of GBP binding sites, glycoproteins and glycolipids may contain approximately 3000 glycan determinants with an additional approximately 4000 theoretical pentasaccharide sequences in glycosaminoglycans. These numbers provide an achievable target for new chemical and/or enzymatic syntheses, and raise new challenges for defining the total glycome and the determinants recognized by GBPs.

TNF-alpha and TLR agonists increase susceptibility to HIV-1 transmission by human Langerhans cells ex vivo

Genital coinfections increase an individual's risk of becoming infected with HIV-1 by sexual contact. Several mechanisms have been proposed to explain this, such as the presence of ulceration and bleeding caused by the coinfecting pathogen. Here we demonstrate that Langerhans cells (LCs) are involved in the increased susceptibility to HIV-1 in the presence of genital coinfections. Although LCs are a target for HIV-1 infection in genital tissues, we found that immature LCs did not efficiently mediate HIV-1 transmission in an ex vivo human skin explant model. However, the inflammatory stimuli TNF-alpha and Pam3CysSerLys4 (Pam3CSK4), the ligand for the TLR1/TLR2 heterodimer, strongly increased HIV-1 transmission by LCs through distinct mechanisms. TNF-alpha enhanced transmission by increasing HIV-1 replication in LCs, whereas Pam3CSK4 acted by increasing LC capture of HIV-1 and subsequent trans-infection of T cells. Genital infections such as Candida albicans and Neisseria gonorrhea not only triggered TLRs but also induced TNF-alpha production in vaginal and skin explants. Thus, during coinfection, LCs could be directly activated by pathogenic structures and indirectly activated by inflammatory factors, thereby increasing the risk of acquiring HIV-1. Our data demonstrate a decisive role for LCs in HIV-1 transmission during genital coinfections and suggest antiinflammatory therapies as potential strategies to prevent HIV-1 transmission.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Identification and expression of a sialyltransferase responsible for the synthesis of disialylgalactosylgloboside in normal and malignant kidney cells: downregulation of ST6GalNAc VI in renal cancers

Although disialyl glycosphingolipids such as GD3 and GD2 have been considered to be associated with malignant tumours, whether branched-type disialyl glycosphingolipids show such an association is not well understood. We investigated the sialyltransferases responsible for the biosynthesis of DSGG (disialylgalactosylgloboside) from MSGG (monosialylgalactosylgloboside). Among six GalNAc:alpha2,6-sialyltransferases cloned to date, we focused on ST6GalNAc III, V and VI, which utilize sialylglycolipids as substrates. In vitro enzyme analyses revealed that ST6GalNAc III and VI generated DSGG from MSGG with V(max)/K(m) values of 1.91 and 4.16 respectively. Transfection of the cDNA expression vectors for these enzymes resulted in DSGG expression in a renal cancer cell line. Although both ST6GalNAc III and VI genes were expressed in normal kidney cells, the expression profiles of ST6GalNAc VI among 20 renal cancer cell lines correlated clearly with those of DSGG, suggesting that the sialyltransferase involved in the synthesis of DSGG in the kidney is ST6GalNAc-VI. ST6GalNAc-VI and DSGG were found in proximal tubule epithelial cells in normal kidney tissues, while they were downregulated in renal cancer cell lines and cancer tissues. All these findings indicated that DSGG was suppressed during the malignant transformation of the proximal tubules as a maturation arrest of glycosylation.

Clustering of monosialyl-Gb5 initiates downstream signalling events leading to invasion of MCF-7 breast cancer cells

Invasion is a complex process controlled by secretion and activation of proteases, alteration of integrin levels and GSL (glycosphingolipid) patterns. Differential organization of GSLs with specific membrane proteins and signal transducers in GEMs (GSL-enriched microdomains), initiates signalling events to modify cellular phenotype. Although the GSL monosialyl-Gb5 has been linked with invasion, its functional role in invasion is poorly described and understood. To investigate this problem, we induced the invasion of human breast cancer cells and subsequently explored the underlying mechanism. In the present study, the invasion of human MCF-7 breast cancer cells is highly dependent on clustering of monosialyl-Gb5, and the subsequent activation of monosialyl-Gb5-associated focal adhesion kinase and cSrc in GEM leading to the downstream activation of extracellular-signal-regulated kinase (ERK). As a result, we observed increased expression levels and activity of matrix metalloproteinases-2 and -9, which correlated with decreased expression of integrins alpha1 and beta1. Together these results suggest that the organization of crucial molecules in GEMs of MCF-7 cells is critical for their invasive properties.

RM2 antigen (beta1,4-GalNAc-disialyl-Lc4) as a new marker for prostate cancer

Although prostate-specific antigen (PSA) has been widely used for early detection of prostate cancer, PSA has problems with specificity and prediction of pathological stage. Therefore, a new marker for prostate cancer is urgently required. We examined expression of a novel carbohydrate antigen, beta1,4-GalNAc-disialyl-Lc(4), defined by the monoclonal antibody RM2, in prostate cancer using 75 cases of radical prostatectomy specimens. RM2 immunoreactivity was negative to weak in all benign glands, and weak to moderate in high-grade prostatic intraepithelial neoplasia. In prostatic adenocarcinoma, RM2 immunoreactivity was negative to weak (lower expression) in 20 cases, and moderate to strong (higher expression) in 55 cases. A clear difference of RM2 expression level was observed between Gleason patterns 3 and >/=4. Higher expression of RM2 antigen was significantly associated with primary Gleason pattern >/=4, high Gleason score (>/=8), larger tumor volume and advanced tumor stage. Furthermore, 5-year PSA failure-free survival was significantly lower in the higher expression group. However, no significant relationship was observed between RM2 expression level and preoperative serum PSA. Western blot analysis in prostate cancer cell lines PC3 and LNCap revealed that major 49-kDa and minor 39-kDa glycoproteins were common to both cells, but there was an increase of 59- and 125-kDa glycoproteins unique to LNCap and an increase of 88- and 98-kDa glycoproteins unique to PC3. RM2 antigen is a new histological marker for prostate cancer that may reflect the Gleason grading system. Identification of the glycoproteins carrying the RM2 antigen will provide new insights into the properties of prostate cancer.

Glycosphingolipid-dependent cross-talk between glycosynapses interfacing tumor cells with their host cells: essential basis to define tumor malignancy

Status of tumor progression (either remaining in situ, or becoming invasive/metastatic) may be defined largely by subtle interactions ('cross-talk') in a microenvironment formed by interfacing tumor cell and host cell membrane domains (termed 'glycosynapses') involved in glycosylation-dependent cell adhesion and signaling. Functional roles of tumor-associated gangliosides, organized in glycosynapses of three types of tumor cell lines, are discussed. Gangliosides function as adhesion receptors or as 'sensors' that can be stimulated by antibodies, with consequent activation of signal transducers leading to enhanced motility and invasiveness.

Monosialyl-Gb5 organized with cSrc and FAK in GEM of human breast carcinoma MCF-7 cells defines their invasive properties

Two human mammary carcinoma cell variants, MCF-7/AZ and MCF-7/6, show the same composition in their glycosphingolipid-enriched microdomain (GEM) with regard to globo-series structures Gb3, Gb4, Gb5, monosialyl-Gb5, GM2, and cSrc and FAK. Both variants are non-invasive into collagen gel layer, and showed similar motility in wound migration assay. Whereas invasiveness and motility of MCF-7/AZ cells were enhanced greatly by treatment with mAb RM1 directed to monosialyl-Gb5, the same RM1 treatment had no effect on MCF-7/6. cSrc and FAK of MCF-7/AZ, but not MCF-7/6, were activated by RM1 treatment. Thus, malignancy of MCF-7 is highly dependent on monosialyl-Gb5, and its activation of cSrc and FAK in GEM.