EBAG9

Gene Summary

Gene:EBAG9; estrogen receptor binding site associated, antigen, 9
Aliases: EB9, PDAF
Location:8q23.2
Summary:This gene was identified as an estrogen-responsive gene. Regulation of transcription by estrogen is mediated by estrogen receptor, which binds to the estrogen-responsive element found in the 5'-flanking region of this gene. The encoded protein is a tumor-associated antigen that is expressed at high frequency in a variety of cancers. Alternate splicing results in multiple transcript variants. A pseudogene of this gene has been defined on chromosome 10. [provided by RefSeq, Jul 2013]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:receptor-binding cancer antigen expressed on SiSo cells
Source:NCBIAccessed: 15 March, 2017

Ontology:

What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: EBAG9 (cancer-related)

Tsoukalas N, Kostakis ID, Siakavellas S, et al.
The clinical and pathological significance of RCAS1 expression as a prognostic biomarker in non-small cell lung cancer.
In Vivo. 2014 May-Jun; 28(3):375-81 [PubMed] Related Publications
BACKGROUND: Lung cancer remains a major health problem due to its incidence and mortality. Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a protein that can be expressed in cancer cells and is involved in tumor cell escape from immune system surveillance.
AIM: The aim of this study was to evaluate the clinical significance of immunohistochemical staining for RCAS1 in non-small cell lung cancer (NSCLC).
MATERIALS AND METHODS: Tissue microarrays of tumor specimens from 112 consecutive patients with newly diagnosed primary NSCLC were constructed. RCAS1 and Ki-67 immunohistochemistry were studied through computerized image analysis. Associations between RCAS1 and Ki-67 expression and clinico-pathological variables and survival were analyzed.
RESULTS: RCAS1 expression was higher in grade III tumors (p=0.009), regardless of the histological type, and in adenocarcinomas with lymphovascular invasion (p=0.014). A positive correlation between RCAS1 and Ki-67 levels was observed (p=0.002). Moreover, there was an inverse correlation of overall survival with RCAS1 (hazard ratio=0.99, p<0.001) and Ki-67 (hazard ratio=1.05, p=0.003) levels. Particularly, patients with higher expression of RCAS1 or Ki-67 had a significantly shorter survival than those with lower expression.
CONCLUSION: RCAS1 could be a useful immunohistochemical biomarker, indicating not only tumor aggressiveness but also a poorer prognosis for patients with NSCLC.

Han SX, Wang J, Wang LJ, et al.
The role of RCAS1 as a biomarker in diagnosing CRC and monitoring tumor recurrence and metastasis.
Tumour Biol. 2014; 35(6):6149-57 [PubMed] Related Publications
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.

Giaginis C, Efkarpidis T, Alexandrou P, et al.
Increased RCAS1 expression is associated with advanced histopathological stage and poor prognosis in patients with gastric adenocarcinoma.
Dis Markers. 2013; 35(4):213-9 [PubMed] Free Access to Full Article Related Publications
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.

Ijichi N, Shigekawa T, Ikeda K, et al.
Association of positive EBAG9 immunoreactivity with unfavorable prognosis in breast cancer patients treated with tamoxifen.
Clin Breast Cancer. 2013; 13(6):465-70 [PubMed] Related Publications
INTRODUCTION: Breast cancer is primarily a hormone-dependent tumor that is regulated by the status of the estrogen and progesterone receptors. We previously identified EBAG9 as an estrogen-responsive gene in MCF-7 human breast carcinoma cells. Upregulation of EBAG9 expression has been observed in several malignant tumors such as advanced breast cancers, indicating that EBAG9 might contribute to tumor progression.
PATIENTS AND METHODS: In the present study, we generated a monoclonal antibody against EBAG9, and then performed immunohistochemical analysis of EBAG9 expression in specimens obtained from breast cancer patients treated with tamoxifen as an adjuvant therapy.
RESULTS: EBAG9 immunoreactivity was detected in the cytoplasm of breast cancer cells and was significantly elevated in breast cancer samples from patients who relapsed during or after adjuvant tamoxifen treatment. Positive EBAG9 immunoreactivity was significantly correlated with poor patient prognosis.
CONCLUSION: These results suggest that EBAG9 expression in tumor regions is associated with an unfavorable prognosis in breast cancer patients treated with tamoxifen.

Zhang Y, Zhu J, Hong X, et al.
The membrane molecule RCAS1 induces immune cell apoptosis via the RCAS1-RCAS1R pathway.
Int J Mol Med. 2013; 31(6):1319-26 [PubMed] Related Publications
Tumor-associated antigen receptor-binding cancer antigen expressed on SiSo cells (RCAS1) has been identified as an estrogen-responsive gene and reportedly acts as a ligand for a putative receptor present in a variety of human cell lines and peripheral lymphocytes, thus leading them to apoptosis. In this study, we investigated the biological function of RCAS1 in vitro in inducing the apoptosis of immune cells. We detected the expression of the RCAS1 receptor (RCAS1R) in the cell lines, and investigated the mechanisms behind the apoptosis induced by RCAS1. HeLa cells were transfected with recombinant adenovirus Ad-RCAS1. RCAS1 induced the apoptosis of activated T cells, K562 cells and phytohemagglutinin (PHA)-activated Jurkat cells via the RCAS1-RCAS1R pathway. The expression of RCAS1R was induced. The intracellular overexpression of RCAS1 inhibited the growth of Jurkat and K562 cells. The expression of RCAS1 negatively correlated with the expression of glycogen synthase kinase 3β (GSK3β), but positively correlated with the expression of phosphorylated GSK3β (phGSK3β). RCAS1 expression was identified as a brown staining pattern in the breast cancer specimens. These findings may provide insight into the mechanisms through which tumor cells escape from immune surveillance.

Galazka K, Opławski M, Windorbska W, et al.
The immunohistochemical analysis of antigens such as RCAS1 and B7H4 in the cervical cancer nest and within the fibroblasts and macrophages infiltrating the cancer microenvironment.
Am J Reprod Immunol. 2012; 68(1):85-93 [PubMed] Related Publications
INTRODUCTION: The presence of the aggressive phenotype of the tumor seems to be indicated by the local infiltration of cancer cells and by the development of metastases in the lymph nodes. This phenotype is related to the intensity of the suppressive profile of the tumor microenvironment. The aim of our study has been to gather information about the expression of both RCAS1 and B7H4 proteins in the macrophages and fibroblasts present within both the microenvironment of cervical cancer tumors and the cancer cells present on the front of the cancer nest.
METHODS: We analyzed the immunoreactivity levels of such antigens as B7H4 and RCAS1 in the macrophages and fibroblasts of the cancer microenvironment and within the cancer nest in the tissue samples derived from patients on whom both a radical hysterectomy and a lymphadenectomy had been performed following a diagnosis of uterine cervical carcinoma. These patients were then divided into two subgroups according to the extent of the local and distant advancement of the cancer - that is, according to the FIGO stage and the presence or absence of lymph node metastases.
RESULTS: RCAS1 immunoreactivity levels on the front of the cancer nest statistically significantly increase according to the FIGO stage or the extent of the local spread of the disease while B7H4 immunoreactivity levels on the tumor front increase in relation to the extent of the distant spread of the disease or the presence of lymph nodes metastases.
CONCLUSION: The intensity of the suppressive profile of the cervical cancer microenvironment indicated by the presence of both RCAS1 and B7H4 on the front of the tumor and in the macrophages and fibroblasts infiltrating the cancer stroma seems to correlate with the extent of both the local and distant advancement of the disease.

Maeyama Y, Otsu M, Kubo S, et al.
Intracellular estrogen receptor-binding fragment-associated antigen 9 exerts in vivo tumor-promoting effects via its coiled-coil region.
Int J Oncol. 2011; 39(1):41-9 [PubMed] Related Publications
Estrogen receptor-binding fragment-associated antigen 9 (EBAG9) is a tumor-promoting factor of largely unknown function. To assess a causative role of EBAG9 in advanced malignancies, we generated the EG7-OVA and MethA murine tumor cell lines that stably express full-length or truncated EBAG9 protein, using retroviral-mediated gene transduction. Upon subcutaneous inoculation into immunocompetent mice, both cell lines showed marked acceleration of in vivo tumor growth when full-length EBAG9 was overexpressed. Interestingly, deletion of the coiled-coil region, thereby producing truncated EBAG9 protein, abolished the tumor-acceleration effect, establishing the importance of this domain in EBAG9-mediated tumor promotion. However, there was no alteration in in vitro cell proliferation or expression levels of MHC class I and co-stimulatory molecules believed to play a role in immune evasion of tumor cells in these tumor cell lines expressing full-length or truncated EBAG9 protein. Furthermore, both full-length and truncated EBAG9 proteins showed a predominantly cytoplasmic localization in the tumor cells. Collectively, these results suggest that EBAG9 overexpression can be causative in enhancing the malignant properties of tumor cells, and that tumor promotion likely requires EBAG9 intracellular association with as yet unidentified binding partners via the coiled-coil region.

Liby TA, Spyropoulos P, Buff Lindner H, et al.
Akt3 controls vascular endothelial growth factor secretion and angiogenesis in ovarian cancer cells.
Int J Cancer. 2012; 130(3):532-43 [PubMed] Free Access to Full Article Related Publications
The PI3 kinase/Akt pathway is commonly deregulated in human cancers, functioning in such processes as proliferation, glucose metabolism, survival and motility. We have previously described a novel function for one of the Akt isoforms (Akt3) in primary endothelial cells: the control of VEGF-induced mitochondrial biogenesis. We sought to determine if Akt3 played a similar role in carcinoma cells. Because the PI3 kinase/Akt pathway has been strongly implicated as a key regulator in ovarian carcinoma, we tested the role of Akt3 in this tumor type. Silencing of Akt3 by shRNA did not cause an overt reduction in mitochondrial gene expression in a series of PTEN positive ovarian cancer cells. Rather, we find that blockade of Akt3, results in smaller, less vascularized tumors in a xenograft mouse model that is correlated with a reduction in VEGF expression. We find that blockade of Akt3, but not Akt1, results in a reduction in VEGF secretion and retention of VEGF protein in the endoplasmic reticulum (ER). The reduction in secretion under conditions of Akt3 blockade is, at least in part, due to the down regulation of the resident golgi protein and reported tumor cell marker, RCAS1. Conversely, over-expression of Akt3 results in an increase in RCAS1 expression and in VEGF secretion. Silencing of RCAS1 using siRNA inhibits VEGF secretion. These findings suggest an important role for Akt3 in the regulation of RCAS1 and VEGF secretion in ovarian cancer cells.

Ali-Fehmi R, Chatterjee M, Ionan A, et al.
Analysis of the expression of human tumor antigens in ovarian cancer tissues.
Cancer Biomark. 2010; 6(1):33-48 [PubMed] Free Access to Full Article Related Publications
Biomarkers for early detection of cancer have great clinical diagnostic potential. Numerous reports have documented the generation of humoral immune responses that are triggered in response to changes in protein expression patterns in tumor tissues and these biomarkers are referred to as tumor associated antigens (TAAs). Using a high-throughput technology, we previously identified 65 proteins as diagnostically useful TAAs by profiling the humoral immune responses in ovarian cancer (OVCA) patients. Here we determined the expression status of some of those TAAs in tissues from OVCA patients. The protein expression patterns of 4 of those 65 antigens, namely NASP, RCAS1, Nijmegen breakage syndrome1 (NBS1) and eIF5A, along with p53 and Her2 (known molecular prognosticators) and two proteins that interact with NBS1, MRE11 and RAD50, were assessed by immunohistochemistry (IHC). NASP and RCAS1 proteins were more frequently expressed in ovarian cancer tissues than with normal ovarian tissue and serous cystadenomas and MRE11 was less frequently expressed. When evaluated simultaneously, only NASP and MRE11 remained statistically significant with sensitivity of 66% and specificity of 89%. None of these proteins' expression levels were prognostic for survival. Together, our results indicate that occurrence of humoral immune responses against some of these TAAs in OVCA patients is triggered by antigen protein overexpression.

Okayama H, Kumamoto K, Saitou K, et al.
CD44v6, MMP-7 and nuclear Cdx2 are significant biomarkers for prediction of lymph node metastasis in primary gastric cancer.
Oncol Rep. 2009; 22(4):745-55 [PubMed] Related Publications
The aim of this study was to examine the expression of CD44v6, CD54, Cdx2, CXCL5, Cyclin B1, MMP-7, nm23, RCAS1 and Survivin in primary gastric cancer and to investigate whether these molecules were useful in predicting the lymph node status. They were selected as candidates for indicators of lymph node metastasis from various kinds of cancer-associated genes reported previously. In 135 cases of radically resected primary gastric adenocarcinoma, we investigated the association between the expression of these molecules and clinocopathologic factors by immunohistochemistry. The results revealed that the expression of CD44v6 and MMP-7 were significantly associated with lymph node status. By contrast, nuclear Cdx2 expression was found to be inversely correlated with lymph node metastasis. Moreover, multivariate analysis demonstrated that CD44v6, MMP-7 and nuclear Cdx2 were independent predictors for lymph node status. In conclusion, our results suggest that positive expression of both CD44v6 and MMP-7, and negative expression of nuclear Cdx2 may serve as powerful predictors of lymph node metastasis in gastric cancer. Combined evaluation of these markers could be further useful to predict lymph node status clinically.

Giaginis C, Margeli A, Kouraklis G, et al.
Diagnostic and prognostic utility of serum receptor-binding cancer antigen expressed on SiSo cells (RCAS1) levels in colon cancer patients.
Int J Biol Markers. 2009 Apr-Jun; 24(2):70-6 [PubMed] Related Publications
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.

Giaginis C, Giagini A, Theocharis S
Receptor-binding cancer antigen expressed on SiSo cells (RCAS1): a novel biomarker in the diagnosis and prognosis of human neoplasia.
Histol Histopathol. 2009; 24(6):761-76 [PubMed] Related Publications
The receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a novel tumor-associated antigen that induces cell-cycle arrest and/or apoptosis in RCAS1 receptor-bearing human cells. Current evidence has revealed enhanced RCAS1 expression in the tumor malignant stage of several organs, which may play a crucial role in tumor progression by enabling cancer cells to evade immune surveillance. In the last few years, tissue RCAS1 protein expression and circulating levels in biofluids have further been the focus of extensive research as a diagnostic and prognostic marker in several human malignancies. The present article aimed to review the available data so far concerning the clinical significance of RCAS1 in human neoplasia. Reviewing of English literature revealed that tissue RCAS1 expression was associated with important clinicopathological parameters for patients' management and prognosis, being considered as an informative biomarker in several types of human malignancy. In addition, the current evidence supported a crucial role for RCAS1 in tumor immune escape, which renders this receptor a promising target for future (gene) therapeutic approaches. However, the clinical application of circulating RCAS1 concentrations in biofluids as a marker in the management and prognosis of tumor malignancies needs to be further explored, since the data so far are still extremely limited.

Fujimura T, Takahashi S, Urano T, et al.
Estrogen receptor-binding fragment-associated gene 9 expression and its clinical significance in human testicular cancer.
Int J Urol. 2009; 16(3):329-32 [PubMed] Related Publications
OBJECTIVES: We previously demonstrated that estrogen receptor-binding fragment-associated gene 9 (EBAG9) is a tumor promoting factor in renal cell carcinoma (Ogushi T, Cancer Res. 2005; 65: 3700). Here, we evaluated EBAG9 expression and its clinical significance in normal and malignant human testicular tissues.
METHODS: We investigated the expression of EBAG9 in 90 testicular specimens (28 benign testicular tissue and 62 testicular germ cell tumor samples) by immunohistochemistry using rabbit polyclonal anti-EBAG9 antibody.
RESULTS: Positive immunostaining of EBAG9 in the cytoplasm was found in 32 (52%) cancerous lesions, whereas the immunoreactivity of EBAG9 was weak in benign testicular tissues. Serum lactate dehydrogenaze (LDH) level was significantly higher in EBAG9-positive cases (715.0 +/- 727.3) compared with the negative cases (221.4 +/- 126.8) (P = 0.0016). The EBAG9-positive cases among the patients with advanced clinical stage (Stage II and III) more frequently belonged to the intermediate or poor risk group in the International Germ Cell Consensus Prognostic Classification System (IGCCPCS), compared with the EBAG9-negative cases (P = 0.0012).
CONCLUSIONS: These findings suggest that increased expression of EBAG9 may play a significant role in cancer progression and aggressiveness in testicular germ cell tumors.

Kumagai J, Urano T, Ogushi T, et al.
EBAG9 is a tumor-promoting and prognostic factor for bladder cancer.
Int J Cancer. 2009; 124(4):799-805 [PubMed] Related Publications
Upregulation of EBAG9 expression has been observed in several malignant tumors such as advanced breast and prostate cancers, indicating that EBAG9 may contribute to tumor proliferation. In the present study, we assess the role of EBAG9 in bladder cancer. We generated human bladder cancer EJ cells stably expressing FLAG-tagged EBAG9 (EJ-EBAG9) or empty vector (EJ-vector), and investigated whether EBAG9 overexpression modulates cell growth and migration in vitro as well as the in vivo tumor formation of EJ transfectants in xenograft models of BALB/c nude mice. EBAG9 overexpression promoted EJ cell migration, while the effect of EBAG9 to cultured cell growth was rather minimal. Tumorigenic experiments in nude mice showed that the size of EJ-EBAG9-derived tumors was significantly larger than EJ-vector-derived tumors. Loss-of-function study for EBAG9 using small interfering RNA (siRNA) in xenografts with parental EJ cells showed that the intra-tumoral injection of EBAG9 siRNA markedly reduced the EJ tumor formation compared with control siRNA. Furthermore, immunohistochemical study for EBAG9 expression was performed in 60 pathological bladder cancer specimens. Intense and diffuse cytoplasmic immunostaining was observed in 45% of the bladder cancer cases. Positive EBAG9 immunoreactivity was closely correlated with poor prognosis of the patients (p = 0.0001) and it was an independent prognostic predictor for disease-specific survival in multivariate analysis (p = 0.003). Our results indicate that EBAG9 would be a crucial regulator of tumor progression and a potential prognostic marker for bladder cancer.

Tang H, Tang XY, Liu M, Li X
Targeting alpha-fetoprotein represses the proliferation of hepatoma cells via regulation of the cell cycle.
Clin Chim Acta. 2008; 394(1-2):81-8 [PubMed] Related Publications
BACKGROUND: AFP is a biomarker for primary liver cancer, yet little is known about its effect in the pathogenesis of hepatoma. We examined how AFP modulates the proliferation of hepatoma cells.
METHODS: Recombinant adenovirus expressing siRNA against AFP was created. The repression of cell proliferation in vitro and growth of hepatoma in vivo were examined by colony formation assay and tumor xenograft in SCID mice, respectively. Cell cycle was assayed by flow cytometry. Expression profile was determined by microarrays.
RESULTS: siRNA targeting reduced expression of AFP specifically and markedly inhibited the proliferation of hepatoma cells. Local treatment using Adv-AFPsiRNA caused significant repression of the growth of hepatoma derived HepG2 cells in xenograft in SCID mice. Knockdown of AFP resulted in an obvious delay in the G(1)/S transition of cell cycle, but did not affect apoptosis in HepG2 cells. Some genes related to the cell cycle, including SKP2, Cyclin D1, Csk and EBAG9 were identified.
CONCLUSIONS: The endogenous AFP is a critical determinant of the growth of hepatoma cells, which functions by regulating the cell cycle. This study suggests that targeting of AFP with siRNA could be a potential therapeutic approach for hepatoma.

Sonoda K, Miyamoto S, Nakashima M, Wake N
The biological role of the unique molecule RCAS1: a bioactive marker that induces connective tissue remodeling and lymphocyte apoptosis.
Front Biosci. 2008; 13:1106-16 [PubMed] Related Publications
RCAS1 is a receptor-binding cancer antigen which is expressed on human uterine cervical adenocarcinoma cell line (SiSo). Finding a correlation between the expression of this gene and the overall survival of patients with 14 different types of cancer points to the clinical significance of this gene. Moreover, the expression RCAS1 correlates with other clinicopathological parameters including the histological type of cancer, its differentiation, tumor size, clinical stage, the depth of invasion, lymphovascular space involvement, lymph node metastasis, and positive peritoneal cytological results. RCAS1 can induce apoptosis in peripheral lymphocytes in vitro as well as in an increased number of apoptotic tumor-infiltrating lymphocytes. RCAS1 is also believed to contribute to the escape of tumor cells from immune surveillance. RCAS1 is secreted via ectodomain shedding, and its expression is related to changes in the characteristics of the extracellular matrix and to a reduced number of vimentin-positive tumor stromal cells, findings that suggest that RCAS1 may induce connective tissue remodeling. The concentration of RCAS1 in serum or pleural effusions has been found to be significantly higher in patients with several different types of cancer as compared to normal controls. Together, the available data shows that RCAS1 may have value as a biomarker for monitoring therapeutic efficacy. Further exploration of the biological function of RCAS1 should help in the development of new therapeutic strategies against human malignancies.

Sonoda K, Miyamoto S, Yamazaki A, et al.
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.
Cancer. 2007; 110(9):1979-90 [PubMed] Related Publications
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.

Popiela TJ, Rudnicka-Sosin L, Dutsch-Wicherek M, et al.
The metallothionein and RCAS1 expression analysis in breast cancer and adjacent tissue regarding the immune cells presence and their activity.
Neuro Endocrinol Lett. 2006; 27(6):786-94 [PubMed] Related Publications
INTRODUCTION: The generation of proper immune response in the tumor environment seems to be essential in antitumor defense. RCAS1 expression has been shown to participate in the regulation of immune cytotoxic activity, metallothionein participates in the protection of cells against immune mediated apoptosis. Since MT and RCAS1 expression is observed within healthy tumor environment we aimed to focus on the proteins expression in tumor and its healthy adjacent tissue in invasive ductal breast cancer regarding the immune cells presence and activity.
MATERIAL AND METHODS: RCAS1, metallothionein, CD3, CD56, CD4, CD25, CD69, CD68 and CD16 antigens expression was assessed by immunohistochemistry in invasive ductal breast cancer. Tissue samples were obtained from 45 patients and were grouped according to the presence of lymph nodes metastases. Two groups were obtained: with and without lymph nodes metastases.
RESULTS: Significant differences were observed in RCAS1 and metallothionein expression in tumor and significant differences in metallothionein expression in healthy stroma regarding the presence of lymph nodes metastases. The significantly higher RCAS1 expression was noticed in tumor in comparison to stroma in patients with the presence of lymph nodes metastases. No such difference was observed in patients without the metastases. Significantly higher metallothionein expression was identified in tumor than in stroma in both groups of patients, with and without lymph nodes metastases. These changes in RCAS1 and metallothionein expression were significantly related with the changes in the number and activity of immune cells.
CONCLUSION: RCAS1 and metallothionein expression in breast cancer healthy stroma seems to be essential for the coexistence of cytotoxic immune cells and normal epithelial cells. The loss of the ability to compensate the growing cytotoxic immune response in the environment might participate in the development of tumor spread.

Naito A, Narikiyo M, Yamada Y, et al.
A clinical and immunohistochemical study on gastrointestinal mesenchymal tumor (GIMT): RCAS1 as a predictor for recurrence of GIMT.
Oncol Rep. 2005; 14(5):1127-32 [PubMed] Related Publications
Gastrointestinal mesenchymal tumors (GIMTs) are the most common mesenchymal tumors of the gastrointestinal tract. RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a cancer cell-surface antigen and has been identified as a prognostic factor in several cancer types. It is thought that tumor cells escape immune attack by expressing RCAS1, which induces apoptosis in receptor-positive immune cells. The current study was designed to elucidate the histogenesis of these tumors by using various immunohistochemical markers, and identify parameters that will help to establish the criteria of malignancy in the GIMT. We also discuss the clinicopathological significance of RCAS1 expression in the diagnosis and prognosis of GIMTs. A total of 70 cases of GIMTs were reviewed. Immunohistochemistry was performed between 1990 and 2000, with the avidin-biotin-peroxidase complex method on 3 microm-thick sections of formalin-fixed paraffin-embedded specimens of GIMTs. Antibodies to the following antigens were used: KIT (CD117), CD34 alpha-SMA, Desmin, cytokeratin, S-100 protein, p53, and RCAS1. Recurrence-free survival analysis was done with Stat View-J 5.0 statistical packages. Univariate analysis for a recurrence-free prognosis demonstrated that antibody detection of p53 expression (p=0.0333) and expression of RCAS1 (p=0.0008) is correlated with a significantly higher potential of recurrence. On multivariate analysis, tumor size and RCAS1 expression were independently and inversely correlated with recurrence-free survival. The expression of RCAS1 has not previously been reported in GIMT; indeed, our study suggests that the expression of RCAS1 is correlated with recurrence not only in carcinomas, but also in mesenchymal tumors.

Reimer TA, Anagnostopoulos I, Erdmann B, et al.
Reevaluation of the 22-1-1 antibody and its putative antigen, EBAG9/RCAS1, as a tumor marker.
BMC Cancer. 2005; 5:47 [PubMed] Free Access to Full Article Related Publications
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.

Ogushi T, Takahashi S, Takeuchi T, et al.
Estrogen receptor-binding fragment-associated antigen 9 is a tumor-promoting and prognostic factor for renal cell carcinoma.
Cancer Res. 2005; 65(9):3700-6 [PubMed] Related Publications
The estrogen receptor-binding fragment-associated antigen 9 (EBAG9) has been identified as a primary estrogen-responsive gene in human breast cancer MCF7 cells. A high expression of EBAG9 has been observed in invasive breast cancer and advanced prostate cancer, suggesting a tumor-promoting role of the protein in malignancies. Here we show that intratumoral (i.t.) administration of small interfering RNA against EBAG9 exerted overt regression of tumors following s.c. implantation of murine renal cell carcinoma (RCC) Renca cells. Overexpression of EBAG9 did not promote the proliferation of culture Renca cells; however, the inoculated Renca cells harboring EBAG9 (Renca-EBAG9) in BALB/c mice grew faster and developed larger tumors compared with Renca cells expressing vector alone (Renca-vector). After renal subcapsular implantation, Renca-EBAG9 tumors significantly enlarged compared with Renca-vector tumors in BALB/c mice, whereas both Renca-EBAG9 and Renca-vector tumors were developed with similar volumes in BALB/c nude mice. No apparent difference was observed in specific cytotoxic T-cell responses against Renca-EBAG9 and Renca-vector cells; nonetheless, the number of infiltrating CD8+ T lymphocytes was decreased in Renca-EBAG9 subcapsular tumors. Furthermore, immunohistochemical study of EBAG9 in 78 human RCC specimens showed that intense and diffuse cytoplasmic immunostaining was observed in 87% of the cases and positive EBAG9 immunoreactivity was closely correlated with poor prognosis of the patients. Multivariate analysis revealed that high EBAG9 expression was an independent prognostic predictor for disease-specific survival (P = 0.0485). Our results suggest that EBAG9 is a crucial regulator of tumor progression and a potential prognostic marker for RCC.

Okamura Y, Haraguchi T, Morimoto M, et al.
Expression of a tumor-associated antigen, RCAS1, in canine mammary tumors.
J Vet Med Sci. 2004; 66(6):651-8 [PubMed] Related Publications
Receptor-binding cancer antigen expressed on SiSo cells (RCAS1), one of novel cancer cell-surface antigens, is strongly expressed in invasive cancers. RCAS1 inhibits the in vitro growth of lymphocytes such as T cells and natural killer (NK) cells, and induces apoptotic cell death. We investigated the expression of RCAS1 in canine mammary tumor cell lines and tumor cells by immunohistochemistry, and also in situ deoxyribonucleic acid (DNA) fragmentation in tumor-infiltrating lymphocytes (TILs) by the terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling (TUNEL) method. All canine mammary tumor cell lines expressed RCAS1 at both the messenger ribonucleic acid (mRNA) and protein level. Immunohistochemically, RCAS1 was negative in 100% of normal mammary glands, but was expressed in 100% of malignant tumors examined. In most malignant mammary tumors, RCAS1 was localized in the cytoplasm with no polarity of expression. In benign mammary tumors, it was detected on the luminal surface of the tumor cell. RCAS1 expression or localization was significantly correlated with malignancy. In situ DNA fragmentation of CD3-positive TILs was observed in RCAS1-expressing tumors. RCAS1-expressing tumors, indicating a possible induction of apoptotic cell death in TILs through RCAS1 expression. These observations suggest that RCAS1 probably plays an important role in tumor progression and escape from immune surveillance in canine mammary tumors.

Suzuki T, Miki Y, Moriya T, et al.
Estrogen-related receptor alpha in human breast carcinoma as a potent prognostic factor.
Cancer Res. 2004; 64(13):4670-6 [PubMed] Related Publications
Estrogen-related receptor alpha (ERRalpha) was identified as a gene related to estrogen receptor alpha (ERalpha) and belongs to a class of nuclear orphan receptors. ERRalpha binds to estrogen responsive element(s) (ERE) and is considered to be involved in modulation of estrogenic actions. However, biological significance of ERRalpha remains largely unknown. Therefore, we examined the expression of ERRalpha in human breast carcinoma tissues using immunohistochemistry (n = 102) and real-time reverse transcription-PCR (n = 30). ERRalpha immunoreactivity was detected in the nuclei of carcinoma cells in 55% of breast cancers examined, and relative immunoreactivity of ERRalpha was significantly (P = 0.0041) associated with the mRNA level. Significant associations were detected between ERalpha and ERE-containing estrogen-responsive genes, such as pS2 (P < 0.0001) and EBAG9/RCAS1 (P = 0.0214), in breast carcinoma tissues. However, no significant association was detected between ERalpha and pS2 (P = 0.1415) in the ERRalpha-positive cases (n = 56) or between ERalpha and EBAG9/RCAS1 (P = 0.8271) in the ERRalpha-negative group (n = 46). ERRalpha immunoreactivity was significantly associated with an increased risk of recurrence and adverse clinical outcome by both uni- (P = 0.0097 and P = 0.0053, respectively) and multi- (P = 0.0215 and P = 0.0118, respectively) variate analyses. A similar tendency was also detected in the group of breast cancer patients who received tamoxifen therapy after surgery. Results from our study suggest that ERRalpha possibly modulates the expression of ERE-containing estrogen-responsive genes, and ERRalpha immunoreactivity is a potent prognostic factor in human breast carcinoma.

Akahira JI, Aoki M, Suzuki T, et al.
Expression of EBAG9/RCAS1 is associated with advanced disease in human epithelial ovarian cancer.
Br J Cancer. 2004; 90(11):2197-202 [PubMed] Free Access to Full Article Related Publications
Oestrogen receptor-binding fragment associated gene 9, EBAG9, is an oestrogen-responsive gene that was identified in MCF-7 human breast carcinoma cell line. It is identical to RCAS 1, a cancer cell surface antigen possibly involved in immune escape. In the present study, we examined the expression of EBAG9/RCAS1 in human epithelial ovarian cancer using immunohistochemistry, immunoblotting and reverse transcription-polymerase chain reaction (RT-PCR). A total of 90 epithelial ovarian cancer cases were examined immunohistochemically by means of the antibodies for EBAG9 and ERalpha. The correlation between EBAG9 immunoreactivity and clinicopathological parameters was examined. mRNA expression of EBAG9 and ERalpha were evaluated by RT-PCR in 22 cases. The expression for EBAG9 and ERalpha was examined by immunoblotting in 12 ovarian cancer cell lines. EBAG9 immunoreactivity was detected in the surface and cytoplasm of carcinoma cells in 46 out of 90 cases (51.1%). EBAG9 expression was significantly higher in serous histology (P=0.0402) and advanced disease (P=0.0206). No significant relationship was detected between EBAG9 immunoreactivity and overall survival (P=0.689). There was a highly significant correlation between EBAG9 and ER immunoreactivity (P<0.0001). The EBAG9 mRNA was detected in 20 out of 22 cases. In all of the cases that were positive for ERalpha mRNA, they were also positive for EBAG9 mRNA. Immunoreactive band corresponding to EBAG9 was detected in 11 out of 12 of ovarian cancer cell lines, and was consistent with ERalpha expression. In conclusion, the wide distribution of EBAG9 and its relation to advanced disease suggest that this protein may play important roles in epithelial ovarian cancer.

Ikeguchi M, Hirooka Y, Kaibara N
Gene and protein expression of RCAS1 in hepatocellular carcinoma.
Anticancer Res. 2003 Nov-Dec; 23(6D):4967-71 [PubMed] Related Publications
BACKGROUND: RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is expressed on the tumor cell membrane and induces apoptosis in infiltrated lymphocytes. In the present study, the clinical importance of RCAS1 gene and protein expression were analyzed in surgically resected hepatocellular carcinomas (HCCs).
PATIENTS AND METHODS: RCAS1 gene and protein expression levels were evaluated and compared with clinical findings in 60 patients with HCC. Expression levels of RCAS1 messenger RNA (mRNA) from tumors was analyzed quantitatively by real-time reverse transcriptase polymerase chain reaction (RT-PCR). RCAS1 protein expression was analyzed by immunohistochemistry and the percentage of RCAS1-positive cancer cells was counted in each case.
RESULTS: RCAS1 messenger RNA levels significantly positively correlated with protein expression levels. RCAS1 protein expression was detected in 75% of cases and high RCAS1 immunoreactivity was detected in 19 tumors (31.7%). RCAS1 protein expression did not correlate with tumor differentiation, progression, nor disease-free survival. New tumors developed in the residual livers after resection of primary tumors in 39 patients. Treatment with transcatheter arterial embolization (TAE) from hepatic artery was performed in these patients. Survival periods after TAE treatment in these patients were analyzed. The mean survival period of 13 patients who had primary tumors with high RCAS1 protein expression (41.4 months) was significantly longer than that of 26 patients with low expression (23.5 months, p = 0.024). After TAE treatment, a low expression level of RCAS1 protein in primary tumors was recognized as a poor prognostic factor independently of tumor stage, by multivariate analysis, in patients who had developed new tumors in the residual livers.
CONCLUSION: RCAS1 protein expression in primary tumor may be a good marker for the effectiveness of TAE treatment in patients who develop new tumors in the residual livers.

Ikeguchi M, Ohoro S, Maeda Y, et al.
Protein and gene expression of tumor-associated antigen RCAS1 in esophageal squamous cell carcinoma.
Oncol Rep. 2003 Nov-Dec; 10(6):1891-4 [PubMed] Related Publications
RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is expressed on the tumor cell membrane and induces apoptosis on infiltrated immune lymphocytes. RCAS1 has been reported to correlate with the escape of tumor cells from host immune surveillance, and with poor prognosis. However, the clinical importance of RCAS1 protein and gene expression in esophageal squamous cell carcinoma (ESCC) has not been well investigated. In the present study, RCAS1 gene and protein expression levels were evaluated and compared with clinical findings in 67 patients with ESCC. Expression levels of RCAS1 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) messenger RNAs (mRNAs) from tumors and non-cancerous epithelia were analyzed quantitatively by real-time reverse transcriptase polymerase chain reaction (RT-PCR). RCAS1 protein expression was analyzed by immunohistochemistry. The mean RCAS1/GAPDH ratio of tumors (0.7) was not different from that of non-cancerous epithelia (0.7, p=0.715). RCAS1 immunoreactivity was detected in 19 tumors (28.4%). The mean RCAS1/GAPDH ratio of tumors with RCAS1 protein positive (0.6) did not differ from tumors without RCAS1 expression (0.8, p=0.131). RCAS1 gene and protein expressions did not correlate with tumor size, depth of invasion, lymph node metastasis, or patient prognosis. Thus, RCAS1 gene or protein expression may not correlate with tumor progression in ESCC.

Ohshima K, Hamasaki M, Makimoto Y, et al.
Differential chemokine, chemokine receptor, cytokine and cytokine receptor expression in pulmonary adenocarcinoma: diffuse down-regulation is associated with immune evasion and brain metastasis.
Int J Oncol. 2003; 23(4):965-73 [PubMed] Related Publications
Pulmonary adenocarcinoma is frequently associated with brain metastasis at some stage during the disease course. Host immunity, particularly T cell immunity, plays an important role in the clinicopathological features of carcinoma proliferation and metastasis. Cytokines and chemokines are members of a family of small secreted proteins. The relationships between the cytokines and cytokine receptor (R), and between chemokines and chemokine R are important determinants of selectivity in local immunity. RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) and Fas ligand (FasL) are present in neoplastic cells, induce apoptosis of NK/T cells, and play a role in immune evasion. To investigate differences in host immunity between pulmonary adenocarcinoma with and without brain metastasis, we performed gene expression profiling, using chemokine, chemokine R, cytokine and cytokine R DNA chips. In addition, to assess the extent of immune evasion, we examined the expression of RCAS and FasL. We studied five cases of pulmonary adenocarcinoma with brain metastasis (meta) and five cases without brain metastasis (non-meta). The brain meta cases exhibited diffuse down-regulated profiles, in comparison with normal non-carcinomatous lungs, which were used as controls. Non-meta cases also displayed diffuse down-regulation, however the degree was variable. Expression of RCAS and FasL was detected in almost all cases, but was stronger in meta than non-meta cases. Our findings suggested that tumor cells evaded host immunity. In the gene tree analysis, brain meta cases and non-meta cases exhibited distinct clustering. Brain meta cases exhibited significantly lower expression of interleukin 13 receptor alpha2 (IL-13Ralpha2) than non-meta cases. The reduction of IL-13Ralpha2 expression was confirmed by RT-PCR. Immunohistochemically, non-meta adenocarcinoma cells frequently expressed IL-13Ralpha2, however, IL-13Ralpha2 expression was rare or weak in adenocarcinomas with meta. Our results suggested that, in addition to immune evasion, the characteristics of the adenocarcinoma tumors themselves were important for brain metastasis. However, our study demonstrated the enormous potential of gene expression profiling in clarifying the pathogenesis of brain metastasis in pulmonary adenocarcinoma.

Sonoda K, Miyamoto S, Hirakawa T, et al.
Association between RCAS1 expression and clinical outcome in uterine endometrial cancer.
Br J Cancer. 2003; 89(3):546-51 [PubMed] Free Access to Full Article Related Publications
RCAS1, which acts as a ligand for a putative receptor on immune cells such as peripheral lymphocytes and natural killer cells, is strongly expressed in human cancers. RCAS1 can induce these cells to undergo apoptotic cell death, which suggests that RCAS1 expression may prohibit the stromal reaction occurring in a tumour. To clarify the clinical significance of RCAS1 expression in uterine endometrial cancer, we analysed the association between RCAS1 expression and clinicopathologic variables by statistical methods. With the use of immunohistochemical techniques, we performed a retrospective study of RCAS1 expression in resected tumour tissue from 147 patients with uterine endometrial cancer. We evaluated the statistical correlation between RCAS1 expression and clinicopathologic variables. RCAS1 was expressed in 106 of 147 patients with uterine endometrial cancer; 30 of these 147 patients showed RCAS1 overexpression. Overexpression of RCAS1 was significantly correlated with age at surgery, stage, extent of myometrial invasion, and positive peritoneal cytologic results. Multivariate analysis revealed that RCAS1 expression and metastasis were clinically significant prognostic factors for the overall survival. These findings indicated that analysis for RCAS1 expression can provide crucial information about the clinical behaviour of uterine endometrial cancer, which may be valuable for the management of patients with this disease.

Aoki T, Inoue S, Imamura H, et al.
EBAG9/RCAS1 expression in hepatocellular carcinoma: correlation with tumour dedifferentiation and proliferation.
Eur J Cancer. 2003; 39(11):1552-61 [PubMed] Related Publications
The oestrogen-responsive gene, EBAG9, whose product is identical to the cancer cell surface antigen RCAS1, is reported to be associated with tumour progression and invasiveness in various carcinomas. In this study, we examined the expression of EBAG9/RCAS1 in hepatocellular carcinoma (HCC), with special reference to its relationship with the stepwise evolution of HCC. Expression was examined by immunohistochemistry and western blotting analysis in 143 HCCs, as well as in non-cancerous liver tissues. After which, the association between enhanced EBAG9/RCAS1 expression and various clinicopathological parameters including Ki-67 labelling index (LI), a marker of proliferative activity, was evaluated. There was a constant low level of EBAG9/RCAS1 expression in non-cancerous liver tissues, with a regular cytoplasmic distribution. Positive immunoreactivity for EBAG9/RCAS1 was detected on the surface and in the cytoplasm of 84 HCC tumours, with an irregular staining pattern. Enhanced EBAG9/RCAS1 expression was correlated with a lower degree of differentiation and Ki-67 LI. Interestingly, expression was enhanced specifically in the less differentiated lesions within 'nodule-in-nodule' tumours. In conclusion, EBAG9/RCAS1 was associated with HCC tumour dedifferentiation and increased proliferative activity. Its exact functional role remains to be established.

Takahashi S, Urano T, Tsuchiya F, et al.
EBAG9/RCAS1 expression and its prognostic significance in prostatic cancer.
Int J Cancer. 2003; 106(3):310-5 [PubMed] Related Publications
Estrogen receptor-binding fragment-associated gene 9 (EBAG9) has been identified as a primary estrogen-responsive gene from MCF-7 human breast cancer cells (Watanabe T, et al., Mol Cell Biol 1998;18:442-9). EBAG9 is identical with RCAS1 (receptor-binding cancer antigen expressed on SiSo cells), which has been reported as a cancer cell surface antigen implicated in immune escape (Nakashima M, et al., Nat Med 1999;5:938-42). In our present study, we examined EBAG9 expression in human prostatic tissues and investigated its prognostic significance in patients with prostatic cancer. EBAG9 expression in normal prostatic epithelial cells and PC-3, DU145 and LNCaP cancer cells was determined by Western blot analysis. Immunohistochemic analysis was performed in 21 benign and 81 malignant prostatic specimens, and patients' charts were reviewed for clinical, pathologic and survival data. EBAG9 was abundantly expressed in the prostate cancer cells compared to the normal epithelial cells. Strong and diffuse immunostaining in the cytoplasm of EBAG9 was found in 44 of 81 (54%) cancerous tissue samples. EBAG9 expression significantly correlated with advanced pathologic stages and high Gleason score (p = 0.0305 and < 0.0001, respectively). EBAG9 was more frequently expressed at sites of capsular penetration (79%) and lymph node metastasis (100%) compared to intracapsular primary tumors (54%) (p = 0.0264 and 0.0048, respectively). Positive EBAG9 immunoreactivity significantly correlated with poor PSA failure-free survival (p = 0.0059). EBAG9/RCAS1 may play a significant role in cancer progression via an immune escape system. Immunodetection of EBAG9/RCAS1 expression can be a negative prognostic indicator for patients with prostatic cancer.

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