Mika K. Kaneko

Involvement of the Snake Toxin Receptor CLEC-2, in Podoplanin-mediated Platelet Activation, by Cancer Cells

Podoplanin (aggrus), a transmembrane sialoglycoprotein, is involved in tumor cell-induced platelet aggregation, tumor metastasis, and lymphatic vessel formation. However, the mechanism by which podoplanin induces these cellular processes including its receptor has not been elucidated to date. Podoplanin induced platelet aggregation with a long lag phase, which is dependent upon Src and phospholipase Cγ2 activation. However, it does not bind to glycoprotein VI. This mode of platelet activation was reminiscent of the snake toxin rhodocytin, the receptor of which has been identified by us as a novel platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2) (Suzuki-Inoue, K., Fuller, G. L., Garcia, A., Eble, J. A., Pohlmann, S., Inoue, O., Gartner, T. K., Hughan, S. C., Pearce, A. C., Laing, G. D., Theakston, R. D., Schweighoffer, E., Zitzmann, N., Morita, T., Tybulewicz, V. L., Ozaki, Y., and Watson, S. P. (2006) Blood 107, 542–549). Therefore, we sought to evaluate whether CLEC-2 serves as a physiological counterpart for podoplanin. Association between CLEC-2 and podoplanin was confirmed by flow cytometry. Furthermore, their association was dependent on sialic acid on O-glycans of podoplanin. Recombinant CLEC-2 inhibited platelet aggregation induced by podoplanin-expressing tumor cells or lymphatic endothelial cells, suggesting that CLEC-2 is responsible for platelet aggregation induced by endogenously expressed podoplanin on the cell surfaces. These findings suggest that CLEC-2 is a physiological target protein of podoplanin and imply that it is involved in podoplanin-induced platelet aggregation, tumor metastasis, and other cellular responses related to podoplanin.

Enhanced Expression of Aggrus (T1alpha/Podoplanin), a Platelet-Aggregation-Inducing Factor in Lung Squamous Cell Carcinoma

Aggrus (T1α/podoplanin, known as a specific marker for type I alveolar cells or lymphatic endothelial cells) is a transmembrane sialoglycoprotein that aggregates platelets. Previously, we showed that upregulated expression of Aggrus occurs in colorectal tumors or testicular tumors and could be associated with platelet-aggregating activity and metastatic ability. In testicular tumors, Aggrus is specifically expressed in seminoma. The present study investigates Aggrus expression in human primary lung cancer tissues of different types. Microarray analysis demonstrated that aggrus was significantly expressed in squamous cell carcinoma (10/15; 66.7%). Immunohistochemical analysis also showed that the incidence of positive staining in sections of squamous cell carcinoma (7/8; 87.5%) was higher than that in adenocarcinoma (2/13; 15.4%). Furthermore, Aggrus expression was detected in a squamous cell carcinoma cell line, NCI-H226, by real-time PCR. These findings indicated that overexpression of Aggrus occurred in squamous cell carcinoma of the lung. Therefore, Aggrus could be a useful diagnostic marker for squamous cell carcinoma of the lung.

Aggrus: a diagnostic marker that distinguishes seminoma from embryonal carcinoma in testicular germ cell tumors.

Aggrus (also known as T1α/podoplanin) is a membrane sialoglycoprotein whose function in tumors is unknown. We recently determined that Aggrus possessed the ability of inducing platelet aggregation and that its expression was frequently upregulated in colorectal tumors. Thus, Aggrus expression might be associated with tumor-induced platelet aggregation and tumor metastasis. Here we show, by means of cancer profiling array and real-time PCR, that aggrus mRNA expression is frequently upregulated in testicular germ cell tumors when compared with the surrounding normal tissue. Immunohistochemical staining revealed that Aggrus protein expression was detected in 10 of 11 seminomas (90.9%), but its expression was not observed in embryonal carcinomas (0/4; 0%). Specific markers for seminomas have not been reported, and Aggrus is a potential diagnostic marker for seminomas and may be associated with malignancies of the testis.

Podoplanin expression in primary central nervous system germ cell tumors: a useful histological marker for the diagnosis of germinoma

Podoplanin, a mucin-like transmembrane sialoglycoprotein, promotes platelet aggregation and may be involved in cancer cell migration, invasion, metastasis, and malignant progression. Podoplanin/aggrus is highly expressed in testicular seminoma, suggesting that it may be a sensitive marker for testicular seminomas. Here we investigated the expression of podoplanin in central nervous system (CNS) germ cell tumors (GCTs) by immunohistochemical staining of tumor samples from 62 patients. In 40 of 41 (98%) germinomas (including germinomatous components in mixed GCTs), podoplanin was diffusely expressed on the surface of germinoma cells; lymphocytes, interstitial cells, and syncytiotrophoblastic giant cells were negative for podoplanin. Except for immature teratomas (12/17; 71%), podoplanin expression was absent in non-germinomatous GCTs, including seven teratomas, seven embryonal carcinomas, seven yolk sac tumors, and seven choriocarcinomas. In immature teratomas, focal podoplanin staining was observed in fewer than 10% of immature squamous and columnar epithelial cells. Thus, podoplanin expression may be a sensitive immunohistochemical marker for germinoma in CNS GCTs. As such, it may be useful for diagnosis, for monitoring the efficacy of treatment, and as a potential target for antibody-based therapy.

Engineering of mucin-type human glycoproteins in yeast cells

Mucin-type O-glycans are the most typical O-glycans found in mammalian cells and assume many different biological roles. Here, we report a genetic engineered yeast strain capable of producing mucin-type sugar chains. Genes encoding Bacillus subtilis UDP-Gal/GalNAc 4-epimerase, human UDP-Gal/GalNAc transporter, human ppGalNAc-T1, and Drosophila melanogaster core1 β1–3 GalT were introduced into Saccharomyces cerevisiae. The engineered yeast was able to produce a MUC1a peptide containing O-glycan and also a mucin-like glycoprotein, human podoplanin (hPod; also known as aggrus), which is a platelet-aggregating factor that requires a sialyl-core1 structure for activity. After in vitro sialylation, hPod from yeast could induce platelet aggregation. Interestingly, substitution of ppGalNAc-T1 for ppGalNAc-T3 caused a loss of platelet aggregation-inducing activity, despite the fact that the sialyl-core1 was detectable in both hPod proteins on a lectin microarray. Most of O-mannosylation, a common modification in yeast, to MUC1a was suppressed by the addition of a rhodanine-3-acetic acid derivative in the culture medium. The yeast system we describe here is able to produce glycoproteins modified at different glycosylation sites and has the potential for use in basic research and pharmaceutical applications.

Characterization of Anti-podoplanin Monoclonal Antibodies: Critical Epitopes for Neutralizing the Interaction Between Podoplanin and CLEC-2

Podoplanin (Aggrus) is a mucin-type sialoglycoprotein that is known as a useful marker for lymphatic endothelium and tumor-initiating cells (TICs). Interaction between podoplanin and C-type lectin-like receptor-2 (CLEC-2) is reported to be critical for podoplanin-induced platelet aggregation and cancer metastasis. Recently, several anti-human podoplanin antibodies have been created; however, these anti-podoplanin antibodies have not been well characterized. Five anti-podoplanin antibodies (NZ-1, D2-40, AB3, 18H5, and a rabbit polyclonal antibody) were investigated using ELISA, Western blot, and flow cytometry with synthesized podoplanin peptides and deletion mutants of recombinant podoplanin. The epitope of NZ-1 is platelet aggregation-stimulating (PLAG) domain-2/3; the epitope of D2-40, AB3, and 18H5 is PLAG1/2. The epitopes of D2-40 and AB3 are quite similar, although 18H5 is different from D2-40 and AB3. Using flow cytometric analysis, NZ-1 partially inhibited the interaction between podoplanin and CLEC-2, although other antibodies did not. In conclusion, the two most frequently used anti-podoplanin antibodies, D2-40 and AB3, have similar properties, although several studies have reported differences. NZ-1 neutralizes the interaction between podoplanin and CLEC-2, which may lead to the development of therapeutic antibodies against podoplanin-dependent cancer metastasis.

A Cancer-specific Monoclonal Antibody Recognizes the Aberrantly Glycosylated Podoplanin

Podoplanin (PDPN/Aggrus/T1α), a platelet aggregation-inducing mucin-like sialoglycoprotein, is highly expressed in many cancers and normal tissues. A neutralizing monoclonal antibody (mAb; NZ-1) can block the association between podoplanin and C-type lectin-like receptor-2 (CLEC-2) and inhibit podoplanin-induced cancer metastasis, but NZ-1 reacts with podoplanin-expressing normal cells such as lymphatic endothelial cells. In this study, we established a cancer-specific mAb (CasMab) against human podoplanin. Aberrantly glycosylated podoplanin including keratan sulfate or aberrant sialylation, which was expressed in LN229 glioblastoma cells, was used as an immunogen. The newly established LpMab-2 mAb recognized both an aberrant O-glycosylation and a Thr55-Leu64 peptide from human podoplanin. Because LpMab-2 reacted with podoplanin-expressing cancer cells but not with normal cells, as shown by flow cytometry and immunohistochemistry, it is an anti-podoplanin CasMab that is expected to be useful for molecular targeting therapy against podoplanin-expressing cancers.

Association of α2-HS glycoprotein (AHSG, fetuin-A) polymorphism with AHSG and phosphate serum levels

Alpha2-HS glycoprotein (AHSG), also known as fetuin-A, is a plasma protein displaying high-affinity interaction with calcium phosphate, by which ectopic vascular calcification is prevented. This investigation has attempted to evaluate the relationship between AHSG polymorphism and serum levels of AHSG and calcium-related parameters. AHSG levels in unrelated individuals were measured by quantitative rocket immunoelectrophoresis and were 581±38, 542±31, and 494±23mg/l for three major genotypes of AHSG1 homozygotes (n=99), heterozygotes (n=55), and AHSG2 homozygotes (n=22), respectively (differences were significant: P<0.001). The circulating AHSG level was therefore influenced by the genetic polymorphism with the additive reduction in the AHSG2 allele. Statistical analysis of simple and multiple regression models revealed no associations between AHSG levels and serum values of total calcium, albumin-corrected total calcium, and ionized calcium. However, the AHSG levels demonstrated a significant negative correlation with free phosphate levels (P<0.001), indicating that AHSG is a novel determinant of serum phosphate. The AHSG polymorphism is attributable to the hereditary variation of AHSG and phosphate serum levels, which may affect skeletal development and chronic disorders such as vascular calcification.

Establishment of a novel monoclonal antibody SMab-1 specific for IDH1-R132S mutation

Isocitrate dehydrogenase 1 (IDH1) mutations, which are early and frequent genetic alterations in gliomas, are specific to a single codon in the conserved and functionally important Arginine 132 (R132) in IDH1. We earlier established a monoclonal antibody (mAb), IMab-1, which is specific for R132H-containing IDH1 (IDH1-R132H), the most frequent IDH1 mutation in gliomas. To establish IDH1-R132S-specific mAb, we immunized mice with R132S-containing IDH1 (IDH1-R132S) peptide. After cell fusion using Sendai virus envelope, IDH1-R132S-specific mAbs were screened in ELISA. One mAb, SMab-1, reacted with the IDH1-R132S peptide, but not with other IDH1 mutants. Western-blot analysis showed that SMab-1 reacted only with the IDH1-R132S protein, not with IDH1-WT protein or IDH1 mutants, indicating that SMab-1 is IDH1-R132S-specific. Furthermore, SMab-1 specifically stained the IDH1-R132S-expressing glioblastoma cells in immunocytochemistry and immunohistochemistry, but did not react with IDH1-WT or IDH1-R132H-containing glioblastoma cells. We newly established an anti-IDH1-R132S-specific mAb SMab-1 for use in diagnosis of mutation-bearing gliomas.

Recombinant anti-podoplanin (NZ-1) immunotoxin for the treatment of malignant brain tumors

Our study demonstrates the glioma tumor antigen podoplanin to be present at very high levels (>90%) in both glioblastoma (D2159MG, D08‐0308MG and D08‐0493MG) and medulloblastoma (D283MED, D425MED and DAOY) xenografts and cell line. We constructed a novel recombinant single‐chain antibody variable region fragment (scFv), NZ‐1, specific for podoplanin from the NZ‐1 hybridoma. NZ‐1‐scFv was then fused to Pseudomonas exotoxin A, carrying a C‐terminal KDEL peptide (NZ‐1‐PE38KDEL). The immunotoxin (IT) was further stabilized by a disulfide (ds) bond between the heavy‐chain and light‐chain variable regions as the construct NZ‐1‐(scdsFv)‐PE38KDEL. NZ‐1‐(scdsFv)‐PE38KDEL exhibited significant reactivity to glioblastoma and medulloblastoma cells. The affinity of NZ‐1‐(scdsFv), NZ‐1‐(scdsFv)‐PE38KDEL and NZ‐1 antibody for podoplanin peptide was 2.1 × 10−8 M, 8.0 × 10−8 M and 3.9 × 10−10 M, respectively. In a protein stability assay, NZ‐1‐(scdsFv)‐PE38KDEL retained 33–98% of its activity, whereas that of NZ‐1‐PE38KDEL declined to 13% of its initial levels after incubation at 37°C for 3 days. In vitro cytotoxicity of the NZ‐1‐(scdsFv)‐PE38KDEL was measured in cells isolated from glioblastoma xenografts, D2159MG, D08‐0308MG and D08‐0493MG, and in the medulloblastoma D283MED, D425MED and DOAY xenografts and cell line. The NZ‐1‐(scdsFv)‐PE38KDEL IT was highly cytotoxic, with an 50% inhibitory concentration in the range of 1.6–29 ng/ml. Significantly, NZ‐1‐(scdsFv)‐PE38KDEL demonstrated tumor growth delay, averaging 24 days (p < 0.001) and 21 days (p < 0.001) in D2159MG and D283MED in vivo tumor models, respectively. Crucially, in the D425MED intracranial tumor model, NZ‐1‐(scdsFv)‐PE38KDEL caused a 41% increase in survival (p ≤ 0.001). In preclinical studies, NZ‐1‐(scdsFv)‐PE38KDEL exhibited significant potential as a targeting agent for malignant brain tumors.