Dysadherin overexpression in pancreatic ductal adenocarcinoma reflects tumor aggressiveness: relationship to e-cadherin expression

Prognostic significance of dysadherin expression in epithelioid sarcoma and its diagnostic utility in distinguishing epithelioid sarcoma from malignant rhabdoid tumor

Dysadherin is a cancer-associated cell membrane glycoprotein, which downregulates E-cadherin and promotes metastasis. We studied the clinicopathological features in 72 cases of epithelioid sarcoma and in six cases of malignant rhabdoid tumor, and also assessed the immunohistochemical expression of dysadherin, E-cadherin and MIB-1 in epithelioid sarcoma and malignant rhabdoid tumor cases. In addition, we compared dysadherin mRNA expression between epithelioid sarcoma and malignant rhabdoid tumor cell lines, using RT-PCR and real-time quantitative RT-PCR analysis. Immunohistochemical dysadherin expression was more frequently observed in proximal-type epithelioid sarcoma (71%) in comparison with distal-type epithelioid sarcoma (36%) (P = 0.037). Furthermore, seven proximal-type epithelioid sarcoma cases mimicking malignant rhabdoid tumor (histologically classified as the large cell type, accompanied by frequent rhabdoid cells and located in deep soft tissue) were all positive for dysadherin (100%), whereas dysadherin expression was not detected at all in any of the true six malignant rhabdoid tumors (0%). Cell lines established from proximal-type epithelioid sarcoma revealed significantly higher levels of dysadherin mRNA expression, compared with the levels seen in malignant rhabdoid tumor cell lines by real-time quantitative RT-PCR (P = 0.0433). Epithelioid sarcoma patients with dysadherin expression survived for a significantly shorter time than those without dysadherin expression (P = 0.001). In multivariate analysis, dysadherin immunopositivity (P = 0.0004) was one of the two independent adverse prognostic factors. We conclude that dysadherin expression in epithelioid sarcoma is a significant poor prognostic factor and that it is a powerful diagnostic marker for distinguishing epithelioid sarcoma, including the proximal-type epithelioid sarcoma, from malignant rhabdoid tumor. In epithelioid sarcoma, especially in proximal-type epithelioid sarcoma, increased cell disadhesion and motility by dysadherin plays an important role to acquire aggressive biological behavior. However, in malignant rhabdoid tumor, cell growth cycle that is regulated by hSNF5/INI1 gene seems to be critical to lethal biological behavior rather than dysadherin.

Aberrant expression of β- and γ-catenin is an independent prognostic marker in oral squamous cell carcinoma

Alteration in expression of E-cadherin and catenins is associated with loss of differentiation, acquisition of an invasive phenotype and poor clinical outcome in many types of cancer. To identify molecular prognostic markers, membrane expression levels of E-cadherin, and alpha-, beta- and gamma-catenin in biopsy samples (n=135) of oral squamous cell carcinoma (OSCC) were evaluated immunohistochemically in relation to preoperative tumour-related features, clinical course and prognostic value, and were found to be significantly correlated with an endophytic growth pattern and pathologically proved lymph-node metastasis. Alteration of expression of E-cadherin, and alpha-, beta- and gamma-catenin was also significantly correlated with poor disease-specific 5-year survival (P=0.0096, 0.0434, 0.0005 and 0.0005, respectively). Multivariate Cox proportional hazard regression analysis showed that alteration of beta- and gamma-catenin expression was a significantly independent prognostic parameter for survival (P=0.0112 and 0.0088, respectively), as was the case with endophytic growth pattern and advanced N-category. These results indicate that patients with OSCC and absent or reduced membrane expression of beta- and gamma-catenin should be considered a high-risk group for regional lymph-node metastasis and poor prognosis.

Expression patterns of dysadherin and E-cadherin in lymph node metastases of colorectal carcinoma

Reduction/loss of E-cadherin is associated with the development and progression of many epithelial tumors, while in a limited number of neoplasms, E-cadherin is re-expressed in metastases. Dysadherin, recently characterized by members of our research team, has an anti-cell-cell adhesion function and downregulates E-cadherin in a posttranscriptional manner. Colorectal cancer (CRC) is one of the most common tumors in the developed world, and lymph node metastases are harbingers of aggressive behavior. The aim of the present study was to examine the dysadherin and E-cadherin expression patterns in lymph node metastases vs primary CRC. Dysadherin and E-cadherin expression was examined immunohistochemically in 78 patients with CRC, Dukes' stage C in the primary tumor and in one lymph node metastasis. Dysadherin was expressed in 42% while E-cadherin immunoreactivity was reduced in 45% of primary tumors. In lymph nodes, 33 and 81% of metastatic tumors were positive for dysadherin and E-cadherin, respectively. Dysadherin expression was not correlated with E-cadherin expression in the primary tumor with a reverse correlation evident in the lymph node metastases. Our results suggest that different mechanisms govern E-cadherin expression in the primary tumor and the corresponding lymph node metastases.

FXYD proteins: new regulators of Na-K-ATPase

FXYD proteins belong to a family of small-membrane proteins. Recent experimental evidence suggests that at least five of the seven members of this family, FXYD1 (phospholemman), FXYD2 (gamma-subunit of Na-K-ATPase), FXYD3 (Mat-8), FXYD4 (CHIF), and FXYD7, are auxiliary subunits of Na-K-ATPase and regulate Na-K-ATPase activity in a tissue- and isoform-specific way. These results highlight the complexity of the regulation of Na+ and K+ handling by Na-K-ATPase, which is necessary to ensure appropriate tissue functions such as renal Na+ reabsorption, muscle contractility, and neuronal excitability. Moreover, a mutation in FXYD2 has been linked to cases of human hypomagnesemia, indicating that perturbations in the regulation of Na-K-ATPase by FXYD proteins may be critically involved in pathophysiological states. A better understanding of this novel regulatory mechanism of Na-K-ATPase should help in learning more about its role in pathophysiological states. This review summarizes the present knowledge of the role of FXYD proteins in the modulation of Na-K-ATPase as well as of other proteins, their regulation, and their structure-function relationship.

Dysadherin Expression in Head and Neck Squamous Cell Carcinoma

Dysadherin is a recently characterized cancer-associated cell membrane glycoprotein that has a crucial role to cell-cell adhesiveness. The aim of this study was to examine dysadherin expression in head and neck squamous cell carcinoma (HNSCC). A total of 108 tissue specimens of patients with HNSCC were examined using immunostaining for dysadherin, E-cadherin, and the specific lymphatic endothelium marker D2-40. We quantified dysadherin and E-cadherin expression, assessed intratumoral (ILD) and peritumoral lymphatic density (PLD), and examined the possible associations of all the above parameters with clinicopathologic features and outcome. Finally, we used double staining with dysadherin and D2-40 to examine the expression pattern of dysadherin simultaneously with the lymphovasculature environment of HNSCC. High dysadherin expression was correlated with higher clinical stage (chi2, P = 0.01), with the presence of lymph node metastasis at the time of diagnosis (chi2, P = 0.02), and with increased ILD (chi2, P = 0.001). We observed an impressive reverse association between increased dysadherin expression and decreased E-cadherin expression (chi2, P < 0.001). Surprisingly, dysadherin-positive cancer cells usually gathered around areas of high intratumoral lymphatic vessel concentration, surrounding and invading small intratumoral lymphatics. Higher clinical stage and increased dysadherin expression were found to be the only significant independent prognostic factors for overall survival (hazard ratio, 3.94; 95% confidence interval, 1.09-14.27 for clinical stage; hazard ratio, 3.92; 95% confidence interval, 1.46-10.51 for dysadherin). The loss of intercellular adhesiveness and increased dysadherin expression seems to be related to lymphangiogenesis in HNSCC, but this should be confirmed by additional studies. Dysadherin expression might be a promising prognostic marker for separation of patients at higher risk.

Involvement of dysadherin and E-cadherin in the development of testicular tumours

Testicular neoplasms are comprised of a variety of histologically different forms, and their pathogenesis has not been elucidated. Dysadherin is a recently described cell membrane glycoprotein, which has an anticell–cell adhesion function and downregulates E-cadherin. In this study, we examined immunohistochemically the expression of E-cadherin and dysadherin in 120 testicular neoplasms (37 seminomas-26 classic, five spermatocytic and six anaplastic-, 45 embryonal carcinomas, 10 mixed germ cell tumours, two yolk sac tumours, 10 mature and eight immature teratomas and eight non-Hodgkin B-cell lymphomas), clinical stage I. The intensity, the expression pattern and the percentage of neoplastic cell staining was recorded and correlated with the histologic type and vascular/lymphatic invasion. Dysadherin was not expressed in non-neoplastic germ cells, neither in CIS/ITGCNU, but it was highly expressed in all types of germ cell tumours, that demonstrated either embryonic phenotype or somatic differentiation, in most terminally differentiated neoplasms, and in all lymphomas. Dysadherin expression did not correlate with vascular invasion. Increased dysadherin expression was correlated with aberrant E-cadherin expression in most tumours. In 17% of embryonal carcinomas colocalisation of dysadherin and membranous E-cadherin staining was noted. This is the first report on dysadherin expression and its association with E-cadherin in testicular tumours. Since dysadherin is not normally expressed in non-neoplastic testis, it is conceivable that it plays a role in the neoplastic transformation of germ cells. In testicular tumours, as in other neoplasms, dysadherin downregulates E-cadherin expression, at least in part.

Possible detection of pancreatic cancer by plasma protein profiling

The survival rate of pancreatic cancer patients is the lowest among those with common solid tumors, and early detection is one of the most feasible means of improving outcomes. We compared plasma proteomes between pancreatic cancer patients and sex- and age-matched healthy controls using surface-enhanced laser desorption/ionization coupled with hybrid quadrupole time-of-flight mass spectrometry. Proteomic spectra were generated from a total of 245 plasma samples obtained from two institutes. A discriminating proteomic pattern was extracted from a training cohort (71 pancreatic cancer patients and 71 healthy controls) using a support vector machine learning algorithm and was applied to two validation cohorts. We recognized a set of four mass peaks at 8,766, 17,272, 28,080, and 14,779 m/z, whose mean intensities differed significantly (Mann-Whitney U test, P < 0.01), as most accurately discriminating cancer patients from healthy controls in the training cohort [sensitivity of 97.2% (69 of 71), specificity of 94.4% (67 of 71), and area under the curve value of 0.978]. This set discriminated cancer patients in the first validation cohort with a sensitivity of 90.9% (30 of 33) and a specificity of 91.1% (41 of 45), and its discriminating capacity was further validated in an independent cohort at a second institution. When combined with CA19-9, 100% (29 of 29 patients) of pancreatic cancers, including early-stage (stages I and II) tumors, were detected. Although a multi-institutional large-scale study will be necessary to confirm clinical significance, the biomarker set identified in this study may be applicable to using plasma samples to diagnose pancreatic cancer.

Interaction with the Na,K-ATPase and Tissue Distribution of FXYD5 (Related to Ion Channel)

FXYD5 (related to ion channel, dysadherin) is a member of the FXYD family of single span type I membrane proteins. Five members of this group have been shown to interact with the Na,K-ATPase and to modulate its properties. However, FXYD5 is structurally different from other family members and has been suggested to play a role in regulating E-cadherin and promoting metastasis (Ino, Y., Gotoh, M., Sakamoto, M., Tsukagoshi, K., and Hirohashi, S. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 365-370). The goal of this study was to determine whether FXYD5 can modulate the Na,K-ATPase activity, establish its cellular and tissue distribution, and characterize its biochemical properties. Anti-FXYD5 antibodies detected a 24-kDa polypeptide that was preferentially expressed in kidney, intestine, spleen, and lung. In kidney, FXYD5 resides in the basolateral membrane of the connecting tubule, the collecting tubule, and the intercalated cells of the collecting duct. However, there is also labeling of the apical membrane in long thin limb of Henle's loop. FXYD5 was effectively immunoprecipitated by antibodies to the alpha subunit of Na,K-ATPase and the anti-FXYD5 antibody immunoprecipitates alpha. Co-expressing FXYD5 with the alpha1 and beta1 subunits of the Na,K-ATPase in Xenopus oocytes elicited a more than 2-fold increase in pump activity, measured either as ouabain-blockable outward current or as ouabain-sensitive (86)Rb(+) uptake. Thus, as found with other FXYD proteins, FXYD5 interacts with the Na,K-ATPase and modulates its properties.

Prognostic significance of dysadherin expression in patients with non–small cell lung cancer

OBJECTIVE

The aim of this study was to evaluate the expression of dysadherin and E-cadherin and to investigate their clinical significance as prognostic factors in non-small cell lung cancer.

METHODS

Non-small cell lung cancer specimens were obtained from 131 patients undergoing clinically indicated operations at the Department of General and Cardiothoracic Surgery, Kanazawa University Hospital, between 1995 and 1997. All patients had undergone curative resection of the primary tumor, including systematic lymph node dissection. The avidin-biotin-peroxidase complex method was used for immunostaining of dysadherin and E-cadherin.

RESULTS

Among the 131 lung cancer specimens, 46 (35.1%) tumors were positively stained with dysadherin. Preserved membranous E-cadherin staining was present in 45.8% (60/131) of cases. In this analysis dysadherin expression was not correlated with E-cadherin expression (P = .1333), but a significant association was observed between dysadherin expression and survival time. The overall survival of patients with dysadherin-positive tumors was significantly worse than that of those with dysadherin-negative tumors (P = .0059). Patients with reduced E-cadherin immunopositivity survived significantly shorter than those with preserved E-cadherin immunopositivity (P = .0406). The overall survival of patients with positive dysadherin and reduced E-cadherin expression was significantly worse than that of patients with negative dysadherin and preserved E-cadherin expression (P = .0002). Multivariate analysis revealed the independent prognostic value of dysadherin positivity, reduced E-cadherin expression, and lymph node metastasis on overall survival.

CONCLUSIONS

Dysadherin expression is an independent prognostic factor of survival in patients with non-small cell lung cancer, and combined immunohistochemical analysis of dysadherin and E-cadherin expression might provide further prognostic information.

Clinicopathologic significance of dysadherin expression in cutaneous malignant melanoma: immunohistochemical analysis of 115 patients

BACKGROUND

The E-cadherin-mediated cell adhesion system is frequently inactivated by multiple mechanisms and is involved in tumor progression in many types of cancer. Recently, the authors reported a novel cell membrane glycoprotein, dysadherin, which has an anti-cell-cell adhesion function and down-regulates E-cadherin.

METHODS

Expression of both dysadherin and E-cadherin was investigated immunohistochemically in 115 patients with cutaneous malignant melanoma to determine the correlation between the 2 molecules and their associations with both patient survival and the clinicopathologic features of the tumors.

RESULTS

Dysadherin and E-cadherin were expressed at the cell membranes of melanoma cells. Fifty-two percent of the tumors showed dysadherin immunopositivity, and 91% of the tumors showed reduced E-cadherin immunopositivity. There was no significant inverse correlation between dysadherin expression and E-cadherin expression. Increased dysadherin expression was significantly correlated with nodular subtype (P = 0.042), Clark level (P < 0.001), tumor thickness (P < 0.001), ulceration (P = 0.008), lymph node metastasis (P < 0.001), high TNM classification (P < 0.001), and poor patient survival (P < 0.001). Multivariate analysis of patient survival revealed that increased dysadherin expression was a significant predictor of poor survival (P < 0.001).

CONCLUSIONS

Thus, increased expression of dysadherin was a significant indicator of poor prognosis in patients with cutaneous malignant melanoma.

Prognostic significance of dysadherin expression in tongue cancer: immunohistochemical analysis of 91 cases

The E-cadherin-mediated cell adhesion system is frequently inactivated by multiple mechanisms and is involved in tumor progression in many types of cancer. Recently we have reported a novel cell membrane glycoprotein, dysadherin, which has an anti-cell-cell adhesion function and downregulates E-cadherin. Expressions of dysadherin and E-cadherin were investigated immunohistochemically in 91 patients with squamous cell carcinoma of the tongue to determine the correlation between the 2 molecules and their associations with the clinicopathologic features of the tumors and with patient survival. Dysadherin was expressed at the cell membranes of many cancer cells. Twenty-five percent of the tumors showed dysadherin immunopositivity in more than 50% of the cancer cells. Sixty-nine percent of the tumors showed reduced E-cadherin immunopositivity. There was an inverse correlation between dysadherin expression and E-cadherin expression (P = 0.0001). Increased dysadherin expression was significantly correlated with an infiltrative type of growth pattern (P = 0.001), high tumor-node-metastasis (TNM) stage (P = 0.024), and poor patient survival (P = 0.003). After adjusting for growth pattern, TNM stage, and other clinicopathologic features, increased dysadherin expression and reduced E-cadherin expression were both significant predictors of poor survival (P = 0.0006). Increased dysadherin expression is a significant indicator of poor prognosis in patients with squamous cell carcinoma of the tongue.

Prognostic significance of dysadherin expression in cervical squamous cell carcinoma

The protein and mRNA expression of dysadherin was studied in a series of squamous cell cervical carcinomas, and their clinicopathological associations and prognostic value were explored. Immunohistochemistry was used to assess protein expression of dysadherin in 206 patients with squamous cell cervical carcinoma, FIGO stage Ia-IVb. Frozen tissues from 20 cases in which the tumors showed variable dysadherin protein expression were used for laser capture microdissection (LCM) and processed for RTPCR detection of dysadherin mRNA. Immunohistochemically, all the dysadherin-positive staining was membranous. Positive cell membranous dysadherinpositive staining was often observed at the edge of tumor nests, although strong immunoreactivity throughout whole tumor nests was also seen in some tumors. Basal cells of the normal cervical epithelia were positive for dysadherin while its expression in the squamous cell cervical carcinomas was variable. Among the 206 tumors, 23 (11.2%) were negative, 53 (25.7%) were scored 1+, 54 (26.2%) were scored 2+ and 76 (36.9%) were scored 3+. In the 20 tumors analyzed, mRNA expression of dysadherin basically corresponded to its protein expression. No significant correlation between expression of dysadherin and age, FIGO stage or lymph node status was observed. Higher level of dysadherin expression, however, was significantly associated with shorter overall survival (p=0.04). We conclude that there is dysadherin protein expression in basal and parabasal cells of normal cervical epithelia, and higher level of dysadherin protein expression in squamous cell cervical carcinoma is predictive of a shorter overall survival, indicating that dysadherin may be a valuable prognostic marker in cervical carcinoma.

Clinical significance of dysadherin expression in gastric cancer patients

PURPOSE

Dysadherin, a cancer-associated cell membrane glycoprotein, has been reported to down-regulate E-cadherin expression and promote metastasis. To evaluate the role of dysadherin in gastric cancer, we examined dysadherin and E-cadherin expression in gastric cancer patients.

EXPERIMENTAL DESIGN

Dysadherin and E-cadherin expression were evaluated in 276 gastric cancer patients by immunohistochemistry, and the results were compared with the clinicopathological findings of the subjects.

RESULTS

Dysadherin was not expressed in normal gastric epithelium. Both dysadherin and E-cadherin were localized to the cell membrane. Dysadherin expression was sometimes largely localized to infiltrating tumor cells or cells dissociating. Ninety gastric cancer patients (32.6%) were positive for dysadherin, and 151 patients (54.7%) showed preservation of E-cadherin expression. Expression of dysadherin was associated with moderately differentiated carcinoma and hematogenous metastasis, whereas reduced expression of E-cadherin showed an association with poorly differentiated carcinoma and peritoneal dissemination. As a result, dysadherin positivity and reduced E-cadherin expression were associated with a poor prognosis. In addition, patients with both dysadherin positivity and reduced E-cadherin had the worst prognosis. Multivariate analysis revealed that reduced E-cadherin expression was an independent prognostic factor, but dysadherin expression was not.

CONCLUSION

Combined analysis of dysadherin and E-cadherin expression may help to predict the prognosis and the mode of metastasis in gastric cancer patients. Patients with dysadherin positivity have a higher risk of hematogenous metastasis, whereas patients with reduced E-cadherin expression have an increased risk of peritoneal dissemination.

Dysadherin expression facilitates cell motility and metastatic potential of human pancreatic cancer cells

Dysadherin is a membrane glycoprotein expressed strongly in several human cancers. Overexpression of dysadherin in tumor cells is closely associated with malignant phenotype (e.g., metastasis) and poor prognosis. In our analysis, six pancreatic cancer cell lines showed a positive correlation between dysadherin expression and cell motility. Introduction of small interfering RNA (siRNA) against dysadherin into the Panc-1 cell line caused reduction of dysadherin expression and suppression of cell motility. In contrast, stable transfection of a dysadherin expression vector into the Capan-1 cell line increased cell motility. In vivo, the metastatic potential of orthotopically transplanted Capan-1 tumor cells in severe combined immunodeficient mice was increased by dysadherin overexpression. Cell morphology and actin organization were also influenced by modulation of dysadherin expression. Cells transfected with dysadherin siRNA tended to have a relatively larger, more spread shape and increased transverse actin stress fibers compared with parent cells and cells transfected with control siRNA. Our study suggests that dysadherin is able to modulate actin structures, stimulate cell motility, and contribute directly to the metastatic potential of human pancreatic cancer cells.

Prognostic significance of dysadherin expression in esophageal squamous cell carcinoma

OBJECTIVE

Dysadherin is a cancer-associated cell membrane glycoprotein that has been reported to downregulate E-cadherin expression and promote metastasis. To evaluate the role of dysadherin in metastasis of esophageal squamous cell carcinoma (ESCC), we examined dysadherin and E-cadherin expression in patients with this cancer.

METHODS

Dysadherin and E-cadherin expression was evaluated in 117 ESCC patients (pT1, 31; pT2, 30; pT3, 39; pT4, 17) by immunohistochemistry. The findings were compared with the clinicopathological data of the patients.

RESULTS

Both dysadherin and E-cadherin were localized to the cell membrane. Thirty patients (29.1%) had tumors positive for dysadherin and 41 patients (35.0%) had tumors positive for E-cadherin. Tumors showing dysadherin positivity and negative E-cadherin expression had a significantly worse prognosis than other tumors. When the patients with dysadherin- positive tumors were combined with E-cadherin-negative patients, this group had a worse prognosis (p < 0.0001). Cox multivariate analysis revealed that dysadherin expression was an independent prognostic factor for ESCC (p = 0.003), but E-cadherin expression was not.

CONCLUSION

Combined analysis of dysadherin and E-cadherin expression may help to predict the prognosis of patients with ESCC. Our results suggested that expression of dysadherin by this cancer may partly explain the poor prognosis of patients with preservation of E-cadherin expression.

Cadherins in cancer

The presence of a functional E-cadherin/catenin cell-cell adhesion complex is a prerequisite for normal development and maintenance of epithelial structures in the mammalian body. This implies that the acquisition of molecular abnormalities that disturb the expression or function of this complex is related to the development and progression of most, if not all, epithelial cell-derived tumors, i.e. carcinomas. E-cadherin downregulation is indeed correlated with malignancy parameters such as tumor progression, loss of differentiation, invasion and metastasis, and hence poor prognosis. Moreover, E-cadherin has been shown to be a potent invasion suppressor as well as a tumor suppressor. Disturbed expression profiles of the E-cadherin/catenin complex have been demonstrated in histological sections of many human tumor types. In different kinds of carcinomas, biallelic downregulation of the E-cadherin gene, resulting in tumor-restricted decrease or even complete loss of E-cadherin expression, appears to be caused by a variety of inactivation mechanisms. Gene deletion due to loss of heterozygosity of the CDH1 locus on 16q22.1 frequently occurs in many carcinoma types. However, somatic inactivating mutations resulting in aberrant E-cadherin expression by loss of both wild-type alleles is rare and restricted to only a few cancer types. A majority of carcinomas thus seems to show deregulated E-cadherin expression by other mechanisms. The present evidence proposes transcriptional repression as a powerful and recurrent molecular mechanism for silencing E-cadherin expression. The predominant mechanisms emerging in most carcinomas are hypermethylation of the E-cadherin promoter and expression of transrepressor molecules such as SIP1, Snail, and Slug that bind sequence elements in the proximal E-cadherin promoter. Interestingly, complex differential expression of other cadherins seems to be associated with loss of E-cadherin and to reinforce effects of this loss on tumor progression. Multiple agents can upregulate and stabilize the E-cadherin/catenin complex. Especially for those tumors with transcriptional and thus reversible downregulation of E-cadherin expression, these drug agents offer important therapeutic opportunities.

Aberrant O-glycosylation inhibits stable expression of dysadherin, a carcinoma-associated antigen, and facilitates cell-cell adhesion

Recently, we identified dysadherin, a novel carcinoma-associated glycoprotein, and showed that overexpression of dysadherin in human hepatocarcinoma PLC/PRF/5 cells could suppress E-cadherin-mediated cell-cell adhesion and promote tumor metastasis. The present study shows evidence that dysadherin is actually O-glycosylated. This was based on a direct carbohydrate composition analysis of a chimera protein of an extracellular domain of dysadherin fused to an Fc fragment of immunoglobulin. To assess the importance of O-glycosylation in dysadherin function, dysadherin-transfected hepatocarcinoma cells were cultured in a medium containing benzyl-alpha-GalNAc, a modulator of O-glycosylation. This treatment facilitated homotypic cell adhesion among dysadherin transfectants accompanied with morphological changes, indicating that the anti-adhesive effect of dysadherin was weakened. Modification of O-glycan synthesis also resulted in down-regulation of dysadherin expression and up-regulation of E-cadherin expression in dysadherin transfectants but did not affect E-cadherin expression in mock transfectants. Structural analysis of O-glycans released from the dysadherin chimera proteins indicated that a series of O-glycans with core 1 and 2 structures are attached to dysadherin, and their sialylation is remarkably inhibited by benzyl-alpha-GalNAc treatment. However, sialidase treatment of the cells did not affect calcium-dependent cell aggregation, which excluded the possibility that sialic acid itself is directly involved in cell-cell adhesion. We suggest that aberrant O-glycosylation in carcinoma cells inhibits stable expression of dysadherin and leads to the up-regulation of E-cadherin expression by an unknown mechanism, resulting in increased cell-cell adhesion. The carbohydrate-directed approach to the regulation of dysadherin expression might be a new strategy for cancer therapy.

Cell adhesion system and human cancer morphogenesis

Cell-cell adhesion determines the polarity of cells and participates in the maintenance of the cell societies called tissues. Cell-cell adhesiveness is generally reduced in human cancers. Reduced intercellular adhesiveness allows cancer cells to disobey the social order, resulting in destruction of histological structure, which is the morphological hallmark of malignant tumors. Reduced intercellular adhesiveness is also indispensable for cancer invasion and metastasis. A tumor-suppressor gene product, E-cadherin, and its undercoat proteins, catenins, which connect cadherins to actin filaments, are located at lateral borders, concentrating on adherens junctions, of epithelial cells and establish firm cell-cell adhesion. The E-cadherin cell adhesion system in cancer cells is inactivated by various mechanisms that reflect the morphological and biological characteristics of the tumor. Silencing of the E-cadherin gene by DNA hypermethylation around the promoter region occurs frequently, even in precancerous conditions. In diffuse infiltrating cancers, mutations are found in the genes for E-cadherin and alpha- and beta-catenins. At the invading front of cancers, the E-cadherin cell adhesion system is inactivated by tyrosine phosphorylation of beta-catenin; an oncogene product, c-erbB-2 protein, is found to associate directly with beta-catenin. The E-cadherin cell adhesion system cross-talks with the Wingless/Wnt signaling pathway through beta-catenin, and expression of genes, which participate in cancer morphogenesis, may be regulated in conjunction with the Wingless/Wnt signaling pathway. Dysadherin, a newly identified cancer-associated cell membrane glycoprotein, down-regulates E-cadherin and promotes cancer metastasis. In conclusion, inactivation of the E-cadherin cell adhesion system by both genetic and epigenetic mechanisms plays a significant role during multistage human carcinogenesis.