Expression of tumor-associated membrane antigen, RCAS1, in human colorectal carcinomas and possible role in apoptosis of tumor-infiltrating lymphocytes

Multi-Epitope-Based Vaccines for Colon Cancer Treatment and Prevention

Background

Overexpression of nonmutated proteins involved in oncogenesis is a mechanism by which such proteins become immunogenic. We questioned whether overexpressed colorectal cancer associated proteins found at higher incidence and associated with poor prognosis could be effective vaccine antigens. We explored whether vaccines targeting these proteins could inhibit the development of intestinal tumors in the azoxymethane (AOM)-induced colon model and APC Min mice.

Methods

Humoral immunity was evaluated by ELISA. Web-based algorithms identified putative Class II binding epitopes of the antigens. Peptide and protein specific T-cells were identified from human peripheral blood mononuclear cells using IFN-gamma ELISPOT. Peptides highly homologous between mouse and man were formulated into vaccines and tested for immunogenicity in mice and in vivo tumor challenge. Mice treated with AOM and APC Min transgenic mice were vaccinated and monitored for tumors.

Results

Serum IgG for CDC25B, COX2, RCAS1, and FASCIN1 was significantly elevated in colorectal cancer patient sera compared to volunteers (CDC25B p=0.002, COX-2 p=0.001, FASCIN1 and RCAS1 p<0.0001). Epitopes predicted to bind to human class II MHC were identified for each protein and T-cells specific for both the peptides and corresponding recombinant protein were generated from human lymphocytes validating these proteins as human antigens. Some peptides were highly homologous between mouse and humans and after immunization, mice developed both peptide and protein specific IFN-γ-secreting cell responses to CDC25B, COX2 and RCAS1, but not FASCIN1. FVB/nJ mice immunized with CDC25B or COX2 peptides showed significant inhibition of growth of the syngeneic MC38 tumor compared to control (p<0.0001). RCAS1 peptide vaccination showed no anti-tumor effect. In the prophylactic setting, after immunization with CDC25B or COX2 peptides mice treated with AOM developed significantly fewer tumors as compared to controls (p<0.0002) with 50% of mice remaining tumor free in each antigen group. APC Min mice immunized with CDC25B or COX2 peptides developed fewer small bowel tumors as compared to controls (p=0.01 and p=0.02 respectively).

Conclusions

Immunization with CDC25B and COX2 epitopes consistently suppressed tumor development in each model evaluated. These data lay the foundation for the development of multi-antigen vaccines for the treatment and prevention of colorectal cancer.

Diagnostic and Prognostic Utility of Serum Receptor-Binding Cancer Antigen Expressed on SiSo Cells (RCAS1) Levels in Colon Cancer Patients

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a human tumor-associated antigen that induces cell-cycle arrest and/or apoptosis in cells bearing the RCAS1 receptor. The aim of the present study was to elucidate the diagnostic and prognostic utility of RCAS1 levels in colon cancer patients. Serum RCAS1 levels were determined using a sandwich enzyme-linked immunosorbent assay in 97 colon cancer patients and 20 healthy individuals. The levels were significantly increased in colon cancer patients compared to healthy individuals (p<0.0001). Increased RCAS1 levels were significantly associated with advanced Dukes’ stage (p=0.0079) and high histopathological tumor grade (p=0.0028). Univariate analysis revealed that colon cancer patients with elevated RCAS1 levels had significantly shorter overall survival times (log-rank test, p=0.027). By multivariate analysis, serum RCAS1 was identified as an independent prognostic factor (Cox regression analysis, p=0.033). In conclusion, colon cancer patients with advanced disease stage and grade and poor prognosis showed elevated serum RCAS1 levels. Assessment of serum RCAS1 levels could therefore be considered as a diagnostic and prognostic marker in colon neoplasia.

Reprogramming the tumor microenvironment: tumor-induced immunosuppressive factors paralyze T cells

It has become evident that tumor-induced immuno-suppressive factors in the tumor microenvironment play a major role in suppressing normal functions of effector T cells. These factors serve as hurdles that limit the therapeutic potential of cancer immunotherapies. This review focuses on illustrating the molecular mechanisms of immunosuppression in the tumor microenvironment, including evasion of T-cell recognition, interference with T-cell trafficking, metabolism, and functions, induction of resistance to T-cell killing, and apoptosis of T cells. A better understanding of these mechanisms may help in the development of strategies to enhance the effectiveness of cancer immunotherapies.

Apoptotic function of tumor-associated antigen RCAS1 in oral squamous cell carcinoma

Background

Receptor-binding cancer antigen expressed on SiSo cell (RCAS1) is derived from uterine adenocarcinoma and can induce apoptosis in lymphocytes, allowing tumor cells to escape from immune surveillance. RCAS1 is reportedly expressed in a membranous pattern on tumor cell or soluble one in serum of patients. The aim of this study was to investigate expression patterns of RCAS1 and the effect on apoptosis in oral squamous cell carcinoma (OSCC) cell lines.

Methods

In four kinds of OSCC cell lines (HSC-2, HSC-3, SQUU-A, and SQUU-B), RCAS1 mRNAs and proteins were determined by RT-PCR and immunocytochemistry. Membranous RCAS1 was determined by flow cytometry. Culture supernatants were analyzed for detection of soluble RCAS1 by dot blotting and enzyme-linked immunosorbent assay. Apoptotic ability of RCAS1 on the erythroid leukemia cell line K562 with the putative receptor was evaluated by flow cytometry in co-culture with highly metastatic SQUU-B, with knocked-down RCAS1 cells or in a no-cell contact condition.

Results

RCAS1 mRNA and proteins were expressed in all of OSCC cell lines. Membranous pattern were expressed in all cell lines, while soluble pattern was detected in all supernatants. RCAS1 mRNA, membranous and soluble RCAS1 were significantly seen in SQUU-B more than the other 3 cell lines (P < 0.05). K562 apoptosis was induced in co-culture with each of all cell lines, particularly with SQUU-B. Apoptosis was markedly reduced in co-culture with RCAS1 knockdown cells, but was induced in co-culture without cell contract of SQUU-B.

Conlusions

Our study suggests that RCAS1 has an apoptotic function via membranous/soluble expression pattern in OSCC cells. RCAS1 may thus affect tumor escape from immune surveillance in OSCC by inducing apoptosis.

The role of RCAS1 as a biomarker in diagnosing CRC and monitoring tumor recurrence and metastasis

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) plays an important role in tumor progression by helping tumor cell to escape from host immunological surveillance or modifying the characteristics of connective tissue around. RCAS1 may appropriately reflect the development and prognosis of tumor. In the study, we sought to identify the clinical significance of RCAS1 in colorectal cancer (CRC) diagnosis and tumor recurrence monitoring. Immunohistochemistry (IHC) with tissue array slides was preformed to analyze RCAS1 protein expression in CRC, colorectal polyps, and normal colon tissues. RCAS1 levels in colorectal cancer were significantly higher than those in colorectal polyps and normal colon tissues (P<0.001). Silencing RCAS1 gene in human colonic adenocarcinoma cells decreased cell proliferation and enhanced apoptosis through the p53 signaling pathway. Further analysis by an enzyme-linked immunosorbent assay (ELISA) showed that serum RCAS1 levels in CRC are significantly higher than in healthy controls and polyps (P<0.05), in which the highest serum RCAS1 level is reported in the recurrence group. The serum RCAS1 levels have a significant correlation with clinical stage and pathologic grading. Furthermore, the positive rate of serum RCAS1 in CRC was 82.1 %, which was higher than carcinoembryonic antigen (CEA). Especially in CEA-negative cases, the sensitivity of RCAS1 was 88.2 %. Finally, CRC patients who were followed up showed a serum RCAS1 level which significantly decreased after surgery (P<0.001) and obviously increased in the recurrence group. Taken together, our data demonstrated that RCAS1 is not only a supplementary serological biomarker for CRC diagnosis but also useful for monitoring tumor recurrence. RCAS1 might be a supplementary serological marker for CRC.

Morphological and functional characterization of non-alcoholic fatty liver disease induced by a methionine-choline-deficient diet in C57BL/6 mice

Background. The receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a human tumor-associated antigen that has been considered to play a crucial role in tumor progression by enabling cancer cells to evade immune surveillance. The present study aimed to evaluate the clinical significance of the RCAS1 expression in gastric adenocarcinoma. Material and Methods. RCAS1 protein expression was assessed immunohistochemically on 54 gastric adenocarcinoma tissue samples and was analyzed in relation to clinicopathological parameters, tumor proliferative capacity, and patients' survival. Results. Enhanced RCAS1 expression levels were significantly associated with advanced histopathological stage and presence of organ metastasis (P = 0.0084 and P = 0.0327). Gastric cancer patients with elevated RCAS1 expression levels showed significantly shorter survival times compared to those with low RCAS1 expression (log-rank test, P = 0.0168). In multivariate analysis, histopathological stage and grade of differentiation as well as the RCAS1 expression were identified as independent prognostic factors (Cox regression analysis, P = 0.0204, P = 0.0035, and P = 0.0081). Conclusions. Our data support the evidence that RCAS1 upregulation may contribute to gastric malignant progression, representing a useful biomarker to predict the biological behaviour and prognosis in gastric neoplasia.

Clinical significance of tumor-associated antigen RCAS1 expression in human pancreatic ductal adenocarcinoma

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a human tumor-associated antigen that induces cell cycle arrest and/or apoptosis in RCAS1 receptor-expressing immune cells. The aim of the present study was to evaluate the clinical significance of RCAS1 expression in human pancreatic adenocarcinoma. Immunohistochemical analysis of RCAS1 expression was performed on paraffin-embedded tissue sections obtained from 76 pancreatic adenocarcinoma patients. RCAS1 positivity and overexpression and intensity of the staining were correlated with clinicopathological parameters, proliferative capacity and patient survival. Of the 76 adenocarcinoma patients, 65 (86%) tested positive for RCAS1; of these 65 RCAS1-positive cases, 36 (55%) showed RCAS1 overexpression. RCAS1 positivity was statistically significantly correlated with the histopathological grade of the tumor (P = 0.026), and it showed a trend to be correlated with tumor size (P = 0.071). RCAS1 intensity and overexpression of staining showed a trend to be correlated with the histopathological grade of the tumor (P = 0.061 and P = 0.089, respectively), whereas RCAS1 positivity and the overexpression and intensity of staining were not statistically significantly correlated with the proliferative capacity of the tumor or any other clinicopathological parameter examined nor with patients' survival. Our data provide evidence for the implication of RCAS1 in pancreatic neoplasia. However, the prediction of survival using RCAS1 expression as a marker seems uncertain for this type of cancer.

Biologic significance of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) as a pivotal regulator of tumor growth through angiogenesis in human uterine cancer

BACKGROUND

The expression of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is related significantly to the overall survival of patients with various cancers. RCAS1 reportedly induces apoptotic cell death in peripheral lymphocytes, which may contribute to the escape of tumor cells from immune surveillance. RCAS1 expression also has been related to tumor invasiveness and size in uterine cervical cancer. To clarify whether RCAS1 exacerbates tumor progression, the authors investigated the association between RCAS1 expression and tumor growth potential.

METHODS

The authors constructed small interfering ribonucleic acid (RNA) (siRNA) to target RCAS1. After transfection of siRNA and the RCAS1-encoding gene, growth of tumor cells was assessed in vitro and in vivo. The correlation between RCAS1 expression and angiogenesis was investigated in the transfected cells and in inoculated tumors from nude mice. In addition, the same association was investigated immunohistochemically with tissue samples from patients with uterine cervical cancer.

RESULTS

Knockdown of RCAS1 expression by siRNA significantly suppressed the in vivo growth of SiSo and HOUA tumor cells (P < .005); however, in vitro cell growth was not affected significantly. Enhanced RCAS1 expression significantly promoted in vivo growth, but not in vitro growth, of tumors derived from COS-7 cells (P = .0039). Introduction of the RCAS1-encoding gene increased expression of vascular endothelial growth factor (VEGF). In uterine cervical cancer, RCAS1 expression was associated significantly with VEGF expression (P = .0407) and with microvessel density (P = .0108).

CONCLUSIONS

RCAS1 may be a pivotal regulator of tumor growth through angiogenesis. Continued exploration of the biologic function of RCAS1 may allow the development of novel therapeutic strategies for uterine cancer.

Prognostic significance of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) expression in relation to cadherin expression in patients with colorectal carcinoma

PURPOSE

This study was designed to assess the prognostic value of receptor-binding cancer antigen expressed on SiSo cells expression and its relationship with cadherin expression in patients with colorectal cancer.

METHODS

The expressions of receptor-binding cancer antigen expressed on SiSo cells and E-cadherin were analyzed with special reference to prognosis in 105 patients with colorectal cancer.

RESULTS

Receptor-binding cancer antigen expressed on SiSo cells immunoreactivity was detected in the membrane and cytoplasm of tumor cells and considered to be positive in 48 patients (45.7 percent). The expression of receptor-binding cancer antigen expressed on SiSo cells was significantly correlated with lymph node metastasis (P = 0.0004), venous invasion (P = 0.0062), Dukes stages (P < 0.0001), and serum levels of carcinoembryonic antigen (P = 0.014). Furthermore, receptor-binding cancer antigen expressed on SiSo cells expression was significantly correlated with a poor prognosis (P < 0.001), and multivariate analysis indicated that it was an independent prognostic indicator. The expression of receptor-binding cancer antigen expressed on SiSo cells was more frequently found in tumors with reduced or abnormal expression of E-cadherin. The survival time of patients with reduced/abnormal E-cadherin expression was significantly shorter than that of patients with normal E-cadherin expression among patients with receptor-binding cancer antigen expressed on SiSo cells expression (P = 0.0043) but did not differ for those without receptor-binding cancer antigen expressed on SiSo cells expression (P = 0.17). Furthermore, multivariate analysis revealed that reduced/abnormal expression of E-cadherin was an independent prognostic factor in patients with receptor-binding cancer antigen expressed on SiSo cells expression but not in those without receptor-binding cancer antigen expressed on SiSo cells expression.

CONCLUSIONS

Receptor-binding cancer antigen expressed on SiSo cells expression is significantly correlated with tumor progression and poor prognosis in patients with colorectal cancer. Both reduced E-cadherin and enhanced receptor-binding cancer antigen expressed on SiSo cells expression may be critical for the mechanism of metastasis and recurrence in human colorectal cancer.

The utility of serum receptor-binding cancer antigen expressed on SiSo cells in gastrointestinal tract cancers

BACKGROUND

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a novel tumour marker that has been described in various kinds of cancer. The majority of observations include immunohistochemical studies; however, there are not enough data about the utility of this antigen as a serum tumour marker and its tumour specificity.

AIM

To measure the serum levels of RCAS1 in patients with gastrointestinal (GI) tract cancers and compare them with other GI tract tumour markers.

PATIENTS AND METHODS

Sera collected from patients with GI cancers (14 esophagus, 32 gastric and 36 colon) and from healthy volunteers (30 individuals) were analyzed for RCAS1 and compared with carcinoembryonic antigen (CEA) and cancer antigen 19-9. The relationship between serum RCAS1, tumour stage and tumour grade was also evaluated.

RESULTS

Mean serum RCAS1 level was higher in patients with GI tract cancers compared with the control group (P=0.001). Among GI tract cancers, RCAS1 had lowest and highest sensitivity for esophagus and colon cancer diagnosis, respectively. Serum RCAS1 had a higher sensitivity for malignancy, except in the colon, and lower specificity in all groups compared with CEA. In comparison with cancer antigen 19-9, serum RCAS1 was more sensitive but less specific for all GI cancer groups. Mean serum RCAS1 levels were not statistically significant among histopathological tumour types (P>0.05). Although serum RCAS1 levels were significantly higher in cases with lymph node involvement compared with lymph node-negative cases (P=0.009), there was no difference between cases with and without serosal involvement, vascular invasion and distant metastasis; no correlation was found between tumour size and RCAS1 levels.

CONCLUSIONS

RCAS1 may be used and combined with CEA as a tumour marker in GI tract cancers.

Significance of serum receptor-binding cancer antigen (RCAS1) in pancreatic cancer and benign pancreatobiliary diseases

BACKGROUND/AIMS

RCAS1 is a novel tumor marker, and there are no sufficient data about the utility of this antigen as a serum tumor marker and about its tumor specificity. We aimed at measuring the serum levels of RCAS1 in patients with pancreatic cancer and at determining its diagnostic efficacy.

METHODS

Sera collected from patients with pancreas adenocarcinomas (39 cases) and benign biliary and pancreatic diseases (19 cases) and from healthy volunteers (13 cases) were analyzed for RCAS1 and the results compared with CA19-9. The relation between serum RCAS1 and tumor stage was also evaluated.

RESULTS

The serum RCAS1 levels exceeded the normal limit in 92.3, 26.3, and 23.0% of the patients with pancreatic cancer and benign biliary and pancreatic diseases and healthy volunteers, respectively. RCAS1 had a specificity similar to that of CA19-9 in pancreatic cancer, whereas RCAS1 had a higher sensitivity (p < 0.05). Both tumor markers had similar predictive values of positive and negative tests for pancreatic cancer. The RCAS1 level was less influenced than the CA19-9 level by biliary stenoses. The median serum levels of RCAS1 increased, as the tumor stage increased.

CONCLUSIONS

RCAS1 is a valuable serum marker for the diagnosis of pancreatic cancer. The RCAS1 and CA19-9 levels increase the diagnostic efficiency of each other in pancreatic cancer.

Tumor-associated antigen recognized by the 22-1-1 monoclonal antibody encourages colorectal cancer progression under the scanty CD8+ T cells

PURPOSE

The receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a novel tumor-associated antigen. Although evidence suggests that RCAS1 suppresses immunity by inducing tumor-infiltrating lymphocyte (TIL) apoptosis, RCAS1 function in humans is controversial. RCAS1 overexpression leads to the generation of the Tn glycan antigen (N-acetyl-D-galactosamine, GalNAc) recognized by the 22-1-1 monoclonal antibody. The objective of this study is to examine Tn glycan antigen function in colorectal cancer and to determine its relationship to CD8+ T cells and prognosis.

EXPERIMENTAL DESIGN

Immunohistochemical analyses examined Tn expression in tumor cells and CD8 on TILs in 146 surgically resected colorectal cancer.

RESULTS

Of 146 samples, 68 tumors (47%) were Tn+; 72 tumors (49%) were CD8+. Using Cox multivariate analysis and the Kaplan-Meier method, Tn and CD8 positivity were determined to be mutually independent prognostic factors (P = 0.0266 and 0.0210, respectively). Tn+ patients with CD8+ TILs exhibited better survival than Tn+/CD8- patients (P = 0.0129). For CD8- patients, Tn positivity was associated with decreased survival from that seen in Tn- patients (P = 0.0097), suggesting that Tn exerts a function independent of CD8+ T cells in tumor progression. In all patients and cases with synchronous liver metastases (n = 29), the Tn+/CD8- survival rate was significantly lower than that seen for other groups (P = 0.0001 and 0.0063, respectively). The average number of liver metastases in Tn+/CD8- cases also increased (mean, 8.2 tumors; P = 0.0032). Multivariate analysis identified Tn+/CD8- status and Dukes' staging as independent prognostic factors (P = 0.0016 and < 0.0001, respectively).

CONCLUSIONS

Tn may encourage invasion and innidiation through a mechanism independent of CD8+ T cells. Thus, Tn+/CD8- status is a risk factor for multiple liver metastases development and an independent negative prognostic factor for colorectal cancer.

Expression of RCAS1 in Female Genital Organs

Receptor-binding antigen expressed on a human uterine adenocarcinoma cell line, SiSo (RCAS1), has been reported to be a prognostic factor of various malignant tumors, and it has also been proven to induce apoptosis of lymphoid cells. However, its normal distribution and function have not yet been elucidated. The purpose of this study was to disclose the distribution of RCAS1 expression in normal female genital organs. Immunohistochemical staining using anti-RCAS1 and anti-MIB-1 antibodies was performed on 123 surgical specimens of a histologically normal uterus, ovary, or fallopian tube from 66 patients, and the apoptotic index was determined. In uterine cervical glands, the expression of RCAS1 was seen in 93% of the cases, and it was mainly localized in the superficial cervical glands. Near the areas of squamous metaplasia, RCAS1 was strongly expressed in all samples. In the uterine cervical squamous epithelium, RCAS1 was seen in 84% of cases. In the uterine corpus, RCAS1 was seen in 87% of all cases, and it was mainly expressed in the endometrial glands of basalis layer. There was significant positive correlation between age and RCAS1 expression, but no significant difference was found regarding the endometrial status and RCAS1 expression in endometrium. No significant correlation was found between RCAS1 expression and MIB-1 index/apoptotic index. RCAS1 may affect these metaplastic processes and tumor progression.

Significance of RCAS1 antigen in hepatocellular, cholangiocellular and pancreatic carcinomas

Since receptor-binding cancer antigen expressed on SiSo cells (RCAS1) was first reported as a tumor-associated antigen of gynecologic cancer, its function and practical value as a tumor marker have been investigated in various types of carcinomas. Basic research has indicated that RCAS1 expression in cancer cells contributes to the evasion from immune surveillance and progression of carcinomas. The clinical significance of RCAS1 expression in hepatobiliary and pancreatic carcinomas has also been investigated. In this review, we summarize the clinical application of RCAS1 antigen in hepatic and pancreaticobiliary diseases. We present new data and review current knowledge about the potential of RCAS1 as a tumor marker and the relationship between RCAS1 expression and clinicopathologic parameters. We found that the clinical function of RCAS1 appeared to differ according to the type of carcinoma. In hepatocellular carcinoma, the clinical significance of histological RCAS1 expression was controversial and that of serum RCAS1 levels showed little clinical value. In pancreaticobiliary cancers, high RCAS1 expression in tissue samples was an unfavorable independent prognostic factor. Serum RCAS1 was a superior tumor marker reflecting the disease activity in biliary carcinoma. In pancreatic cancer, serum RCAS1 levels were less useful than in biliary carcinoma but may be available for genetically CA19-9-negative patients and for CA19-9-non-producing cancer. This review also offers suggestions for future studies.

Association between RCAS1 expression and microenvironmental immune cell death in uterine cervical cancer

OBJECTIVE

: The presence of regional lymph node metastasis is one of the prognostic factors for uterine cervical cancer. The development of metastasis requires that cancer cells avoid lymphocyte attack. Impaired lymphocyte function is mediated by apoptotic factors including receptor-binding cancer antigen expressed on SiSo cells (RCAS1), Fas ligand (FasL), and tumor necrosis factor-alpha (TNF-alpha). Our aim was to evaluate the association between expression of these factors and microenvironmental lymphocyte apoptosis in this disease.

METHODS

: Immunohistochemical methods were used to determine the relationship between the expression of RCAS1, FasL, and TNF-alpha, and the number of apoptotic lymphocytes in primary lesions and metastatic lymph nodes in patients with cervical cancer.

RESULTS

: Expression of these apoptosis-inducing molecules was quite different in primary tumors and metastatic lymph nodes: RCAS1 expression in lymph nodes was significantly higher than that in primary lesions (P < 0.0001), whereas FasL and TNF-alpha expressions at these two locations were not significantly different. The number of cells with positive expression of RCAS1, but not of FasL or TNF-alpha, was significantly correlated with the number of apoptotic lymphocytes in uterine cervix and metastatic lymph nodes (P < 0.0001 for both).

CONCLUSION

: RCAS1 expression may be related to tumor cell evasion of immune surveillance via induction of lymphocyte apoptosis in primary lesions and metastatic lymph nodes in uterine cervical cancer.

Reevaluation of the 22-1-1 antibody and its putative antigen, EBAG9/RCAS1, as a tumor marker

Background

Tumor-associated antigens are appreciated as diagnostic markers, but they have also prompted tremendous efforts to develop tumor-specific immunotherapy. A previously cloned tumor-associated antigen, EBAG9, was initially defined by reactivity with the monoclonal antibody 22-1-1. Functionally, the EBAG9-encoded gene-product was believed to induce apoptosis in activated immune cells. However, using a cell-biological approach we identified EBAG9 as a Golgi-resident modulator of O-linked glycan expression, the latter product was then recognized by the 22-1-1 antibody. Secondly, EBAG9 expression was found physiologically in all murine tissues examined. This raised the question if EBAG9 is tumor-specific and mediates apoptosis itself or through O-linked glycans generated, among them the cognate 22-1-1 antigen Tn.

Methods

We have used immunohistochemistry to detect the expression of 22-1-1 and EBAG9 in various tissues. Correlation between expression of both antigens in cell lines was analysed by immunoblot and flow cytometry. Apoptosis was studied by using flow cytometry and Caspase-Glo™ 3/7 assay kit. Cellular distribution of EBAG9 was analysed by electron and confocal microscopy.

Results

Here, we compared expression of the 22-1-1 and EBAG9-defined antigens in normal and neoplastic tissues in situ. In contrast to 22-1-1 staining, EBAG9 is a ubiquitously expressed antigen in all normal and cancerous tissues. Functional studies on the role of 22-1-1 reactive material did not support any evidence for apoptosis induction. Employing electron and confocal microscopy, a refined subcellular localization of EBAG9 at the Golgi was obtained.

Conclusion

We suggest that the estrogen-inducible EBAG9 gene-product and the 22-1-1 defined antigen are structurally and functionally separate antigens.

Expression of RCAS1 in esophageal squamous cell carcinoma is associated with a poor prognosis

BACKGROUND

Receptor-binding cancer antigen expressed on SiSO cells (RCAS1) has been reported to act as a ligand for a receptor present on normal peripheral lymphocytes and to induce apoptotic cell death. We aimed to elucidate the significance of RCAS1 expression in human esophageal squamous cell carcinomas (ESCC).

METHODS

RCAS1 expression was examined immunohistochemically in surgically resected esophageal carcinoma tissues from 114 patients. We also examined the relationships between RCAS1 expressions, the tumor Ki-67 indices (a marker of proliferation), and the number of CD8+ tumor-infiltrating lymphocytes (TILs).

RESULTS

RCAS1 immunoreactivity was detected in the membranes and cytoplasm of the tumor cells. Of the 114 esophageal carcinomas, 39 (34.2%) were strongly positive for RCAS1 immunostaining on the membranes of the cancer cells, 41 (36.0%) were weakly positive, and 34 (29.8%) were negative. A comparison of RCAS1 expression and clinicopathological characteristics in all 114 patients revealed significant associations between RCAS1 expression and lymph node status (P < 0.05), and pathologic stage (P < 0.05). The survival rates of patients with RCAS1-negative tumors were significantly higher than those of patients with both RCAS1-weak positive tumors and RCAS1-strong positive ones (log-rank P < 0.05). Multivariate analysis revealed that RCAS1 positivity was an independent prognostic factor (P < 0.05). The relationship between RCAS1 expression and the numbers of CD8+ T-cells in the primary tumors revealed that RCAS1-negative tumors tended to contain more of these cells than both RCAS1-weak positive tumors and RCAS1-strong positive ones (P = 0.2495).

CONCLUSIONS

RCAS1 may play a significant role in tumor progression via an immune escape mechanism; thus, RCAS1 expression could be used as a predictor of poor prognosis in patients with ESCC.