The clinical significance of tumor-associated antigen RCAS1 expression in the normal, hyperplastic, and malignant uterine endometrium

Tumor-targeted delivery of lnc antisense RNA against RCAS1 by live-attenuated tryptophan-auxotrophic Salmonella inhibited 4T1 breast tumors and metastasis in mice

Emerging chemo- and radiotherapy resistance exacerbated the cancer risk and necessitated novel treatment strategies. Although RNA therapeutics against pro-oncogenic genes are highly effective, tumor-specific delivery remains a barrier to the implementation of this valuable tool. In this study, we report a tryptophan-auxotrophic Salmonella typhimurium strain as an onco-therapeutic delivery system with tumor-targeting ability using 4T1 mice breast-cancer model. The receptor-binding cancer antigen expressed on SiSo cell (RCAS1) is a cancer-specific protein that induces the apoptosis of peripheral lymphocytes and confers tumor immune evasion. We designed a long non-coding antisense-RNA against RCAS1 (asRCAS1) and delivered by Salmonella using a non-antibiotic, auxotrophic-selective, eukaryotic expression plasmid, pJHL204. After in vivo tumor-to-tumor passaging, the JOL2888 (ΔtrpA, ΔtrpE, Δasd + asRCAS1) strain exhibited high sustainability in tumors, but did not last in healthy organs, thereby demonstrating tumor specificity and safety. RCAS1 inhibition in the tumor was confirmed by western blotting and qPCR. In mice, JOL2888 treatment reduced tumor-associated macrophages, improved the T cell population, elicited cell-mediated immunity, and suppressed cancer-promoting genes. Consequently, the JOL2888 treatment significantly decreased the tumor volume by 80%, decreased splenomegaly by 30%, and completely arrested lung metastasis. These findings highlight the intrinsic tumor-targeting ability of tryptophan-auxotrophic Salmonella for delivering onco-therapeutic macromolecules.

Gynecologic Cancer, Cancer Stem Cells, and Possible Targeted Therapies

Gynecologic cancer is one of the main causes of death in women. In this type of cancer, several molecules (oncogenes or tumor suppressor genes) contribute to the tumorigenic process, invasion, metastasis, and resistance to treatment. Based on recent evidence, the detection of molecular changes in these genes could have clinical importance for the early detection and evaluation of tumor grade, as well as the selection of targeted treatment. Researchers have recently focused on cancer stem cells (CSCs) in the treatment of gynecologic cancer because of their ability to induce progression and recurrence of malignancy. This has highlighted the importance of a better understanding of the molecular basis of CSCs. The purpose of this review is to focus on the molecular mechanism of gynecologic cancer and the role of CSCs to discover more specific therapeutic approaches to gynecologic cancer treatment.

Molecular Changes on Maternal-Fetal Interface in Placental Abruption-A Systematic Review

Placental abruption is the separation of the placenta from the lining of the uterus before childbirth. It is an infrequent perinatal complication with serious after-effects and a marked risk of maternal and fetal mortality. Despite the fact that numerous placental abruption risk factors are known, the pathophysiology of this issue is multifactorial and not entirely clear. The aim of this review was to examine the current state of knowledge concerning the molecular changes on the maternal–fetal interface occurring in placental abruption. Only original research articles describing studies published in English until the 15 March 2021 were considered eligible. Reviews, book chapters, case studies, conference papers and opinions were excluded. The systematic literature search of PubMed/MEDLINE and Scopus databases identified 708 articles, 22 of which were analyzed. The available evidence indicates that the disruption of the immunological processes on the maternal–fetal interface plays a crucial role in the pathophysiology of placental abruption. The features of chronic non-infectious inflammation and augmented immunological cytotoxic response were found to be present in placental abruption samples in the reviewed studies. Various molecules participate in this process, with only a few being examined. More advanced research is needed to fully explain this complicated process.

Immune disorder in endometrial cancer: Immunosuppressive microenvironment, mechanisms of immune evasion and immunotherapy

Immunotherapy is an emerging clinical approach that has gained traction over the past decade as a novel treatment option for lung cancer and melanoma. Notably, researchers have made marked improvements in the treatment of endometrial cancer (EC), and potential immune responses have been identified in patients with EC, thereby offering the possibility of exploring immunotherapy for EC. Nevertheless, various needs remain unmet, and immunotherapy applications in EC have yielded limited success, as only a minority of patients exhibited a clinical response. Therefore, further understanding of immune dysfunction associated with EC is still required. The present review describes recent findings regarding the immunosuppressive microenvironment of EC, with emphasis on immune evasion mechanisms and immunotherapy in EC.

High post-treatment serum soluble receptor-binding cancer antigen expressed on SiSo cells (sRCAS1) levels is associated with poor survival of patients with cervical cancer

AIM

Receptor-binding cancer antigen expressed on SiSo cells (sRCAS1) is responsible for induction of selective immunosuppression. In addition, preclinical studies have shown that sRCAS1 levels may reflect cancer aggressiveness. The main aim of our study was to analyze pre- and post-treatment levels of sRCAS1 in the sera of patients treated for cervical cancer and to evaluate whether the levels change during treatment and their impact on patient prognosis.

METHODS

The study included 49 patients suffering from cervical cancer. The early stage cervical cancer patients (14) were treated surgically, while the advanced stage patients (35) underwent radiochemotherapy. Serum sRCAS1 levels were evaluated both before and after intervention with the use of the ELISA method.

RESULTS

We have found that median serum sRCAS1 levels of patients before intervention were not significantly different from the levels assessed after intervention. There were also no differences when pre- and post-treatment levels were compared within the group of early and of advanced stage patients. Serum sRCAS1 levels were not influenced by either the histopathological type of the tumor or the methods of treatment. High post-intervention sRCAS1 levels indicated shortened OS when compared to low sRCAS1 levels. Neither pre-intervention sRCAS1 levels nor the alteration in sRCAS1 levels during treatment were associated with patient prognosis. In multivariate analysis, post-treatment sRCAS1 levels and clinical stage of cervical cancer remained as independent predictors of survival.

CONCLUSION

High post-treatment serum sRCAS1 level in cervical cancer patients seems to be a negative prognostic factor for patient overall survival.

Molecular biology of gynecological cancer

Cancer is a pathological condition in which the balance between cell growth and death is disordered. Various molecules have been reported to be involved in the oncogenic process of invasion, metastasis and resistance to treatment. An exponential growth in the collection of genomic and proteomic data in the past 20 years has provided major advances in understanding the molecular mechanisms of human cancer, which has been applied to diagnostic and treatment strategies. Targeted therapies have been developed and adopted, particularly for advanced, refractory or recurrent cancers, depending on individual molecular profiles. The aim of the present review is to provide a report of the current literature regarding the molecular biology of gynecological cancers.

A disintegrin and metalloproteinase 9 is involved in ectodomain shedding of receptor-binding cancer antigen expressed on SiSo cells

In several human malignancies, the expression of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is associated with aggressive characteristics and poor overall survival. RCAS1 alters the tumor microenvironment by inducing peripheral lymphocyte apoptosis and angiogenesis, while reducing the vimentin-positive cell population. Although proteolytic processing, referred to as "ectodomain shedding," is pivotal for induction of apoptosis by RCAS1, the proteases involved in RCAS1-dependent shedding remain unclear. Here we investigated proteases involved in RCAS1 shedding and the association between tumor protease expression and serum RCAS1 concentration in uterine cancer patients. A disintegrin and metalloproteinase (ADAM) 9 was shown to be involved in the ectodomain shedding of RCAS1. Given the significant correlation between tumor ADAM9 expression and serum RCAS1 concentration in both cervical and endometrial cancer as well as the role for ADAM9 in RCAS1 shedding, further exploration of the regulatory mechanisms by which ADAM9 converts membrane-anchored RCAS1 into its soluble form should aid the development of novel RCAS1-targeting therapeutic strategies to treat human malignancies.

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.

Analysis of RCAS1 immunoreactivity within hydatidiform mole cells and decidual cells according to the applied therapeutic strategy: surgery or surgery followed by chemotherapy

INTRODUCTION

Trophoblast cells cooperate with both maternal immune cells and decidual cells to help develop the suppressive microenvironment of the endometrium. The maternal immune response against hydatidiform mole depends on this suppressive endometrial profile. Since RCAS1 is one of the molecular factors participating in the development of the suppressive profile of the endometrium we decided to examine the immunoreactivity of the RCAS1 within both the trophoblast and decidual cells during the development of hydatidiform mole.

METHODS

We analyzed the immunoreactivity of RCAS1 on both trophoblast and decidual cells derived from patients who underwent curettage because of hydatidiform mole. These patients were then divided into two subgroups according to whether or not they required chemotherapy after the surgical procedure.

RESULT

We observed significantly lower immunoreactivity levels of both RCAS1 within the complete molar lesions of the patients on whom surgery alone was performed when compared to the levels found in those for whom surgery was followed by chemotherapy.

CONCLUSION

RCAS1 staining may provide information regarding the intensity of the immunosuppressive microenvironment of both the molar lesion and the endometrium. This information can prove significant in determining the clinical course of hydatidiform mole.

Accuracy of differential diagnosis for pancreatic cancer is improved in the combination of RCAS1 and CEA measurements and cytology in pancreatic juice

Improvement of diagnostic accuracy for pancreatic cancer in pancreatic disease patients was investigated by examining the combination of three diagnostic methods, i.e., measurements of RCAS1 and CEA levels in pancreatic juice and pancreatic juice cytology. Pancreatic juice was collected from 12 pancreatic cancer (PC) and 26 non-PC patients. RCAS1 and CEA levels were measured by using ELISA. RCAS1 expression on surgically resected tissue was immunohistochemically examined for 2 PC patients. By setting the cutoff level of RCAS1 at 10 U/ml and that of CEA at 18.5 μg/ml, sensitivity of RCAS1 was 42% and that of CEA was 50%. On the other hand, sensitivity and specificity increased from 42% and 85% of RCAS1 alone to 75% and 85% in the examination of RCAS1 + CEA + cytology, and the false-negative rate was also reduced to 25% in this combination. Immunohistochemically, a patient with a high RCAS1 level in pancreatic juice had numerous RCAS1-positive tumor cells in the pancreatic juice. We concluded that RCAS1 and CEA measurements together with cytology in pancreatic juice would be a useful combination method for making a differential diagnosis of PC from non-PC.

The immunohistochemical analysis of RCAS1, HLA-G, and B7H4-positive macrophages in partial and complete hydatidiform mole in both applied therapeutic surgery and surgery followed by chemotherapy

INTRODUCTION

The suppressive microenvironment developing around the implantating ovum in normal pregnant women may correlate with the development in cancer patients of a suppressive microenvironment of neoplasmatic cells derived from trophoblasts, such as occurs in molar lesions. Macrophages are suitable candidates for mediating not only the balance of the maternal defensive immune responses to external antigens, but also a tolerance to tumor cells. The aim of our study has been to gain information about the expression of RCAS1, B7H4, and HLA-G within the macrophages present in the microenvironment of the molar lesion.

METHODS

We analyzed the immunoreactivity of such antigens as B7H4, RCAS1, and HLA-G on the macrophages present in tissue samples derived from patients on whom curettage was performed after a diagnosis of molar pregnancy. These patients were then divided into two subgroups according to whether or not they required chemotherapy after the surgical procedure.

RESULTS

We observed a statistically significant increase in the RCAS1-positive macrophage infiltration within the microenvironment of the molar lesions in patients with partial hydatidiform mole in comparison with those patients who exhibited complete hydatidiform mole. There were no such differences, however, in the infiltration of HLA-G- and B7H4-positive macrophages between the two groups of patients. Additionally, we showed that RCAS1- and HLA-G-positive macrophages are more distinct in those cases of complete molar pregnancy where chemotherapy was necessary after surgical treatment while no such differences with respect to B7H4-positive macrophages were observed.

CONCLUSION

The immune-suppressive endometrial microenvironment represented by suppressive macrophages may have an influence on the clinical course of hydatidiform mole.

Receptor-binding cancer antigen expressed on SiSo cells induces apoptosis via ectodomain shedding

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a secreted antigen that induces apoptosis in putative receptor-expressing cells, including peripheral lymphocytes and natural killer (NK) cells. RCAS1 expression is associated with aggressive characteristics and poor overall survival for 15 different human malignancies. The putative RCAS1 receptor has not been isolated and the mechanism of RCAS1 apoptosis induction remains unclear. This study explores how RCAS1 is involved in apoptosis initiation. The cell lines SiSo and MCF-7, human uterine carcinoma and breast adenocarcinoma, respectively, both express RCAS1, but RCAS1 secretion is undetectable in MCF-7 cells. SiSo and MCF-7 cells were stimulated to induce RCAS1 ectodomain shedding followed by assessment of RCAS1 expression and secretion. Additionally, the RCAS1 putative receptor-expressing human chronic myelogenous leukemia cell line K562 was co-cultured with SiSo, MCF-7, or soluble RCAS1 to follow RCAS1 secretion in apoptosis initiation. RCAS1 secretion was strongly suppressed by inhibitors of metalloproteases, protein kinase C (PKC)-delta, mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase (MEK), epidermal growth factor (EGF), and G-protein-coupled receptor (GPCR). K562 apoptosis could be induced only by co-culturing with SiSo or soluble RCAS1. RCAS1 is thus secreted by ectodomain shedding, which may represent a pivotal step in RCAS1-induced apoptosis initiation.

The association between RCAS1 expression in laryngeal and pharyngeal cancer and its healthy stroma with cancer relapse

BACKGROUND

The purpose of this study has been to establish the level of RCAS1 - a membrane protein expressed in various cancer cells and able to induce apoptosis of CTLs and NK cells in pharyngeal and laryngeal cancer and its clear surgical margin - with respect to clinicopathological features and to patient's follow up and evaluate its possible role in cancer relapse.

METHODS

A total of 122 tissue samples were obtained: 51 samples from laryngeal and pharyngeal squamous cell carcinoma, 51 samples from the clear surgical margins of these tumors, and 20 tissue samples derived from the healthy mucous membranes of the upper respiratory tract mucosa of patients without cancerous tumors. Patients were observed for a total of 4 years following surgical treatment. The level of RCAS1 expression was assessed by immunohistochemistry and Western blot.

RESULTS

RCAS1 was identified in all laryngeal and pharyngeal carcinomas and in almost all the clear surgical margin samples. The level of RCAS1 expression was significantly higher in the cancerous samples than in the clear surgical margins and was determined to be related to the grade of the cancer and the presence of lymph node metastases. In cases of cancer relapse, significantly higher levels of RCAS1 expression were observed in the clear surgical margins.

CONCLUSION

Selective cytotoxic immune cell suppression concomitant with tumor growth and associated with RCAS1 expression seems to be an important event connected with cancer relapse.

Notch signaling in differentiation and function of dendritic cells

Hematopoietic stem cells give rise to multiple lineages of cells. This process is governed by a tightly controlled signaling network regulated by cytokines and a direct cell-cell contact. Notch signaling represents one of the major pathways activated during direct interaction between hematopoietic progenitor cells and bone marrow stroma. A critical role of Notch signaling in differentiation of T- and B-lymphocytes has now been established. Until recently, the role of Notch signaling in the development of myeloid cells and particular dendritic cells remained unclear. In this review, we discuss recent exciting findings that shed light on the critical role of Notch in differentiation and the function of dendritic cells and its impact on immune responses.

Immunohistochemical markers in endometrial hyperplasia: is there a panel with promise? A review

OBJECTIVE

Despite advances in defining the biology of endometrial carcinomas, there has been little progress in determining markers that distinguish preinvasive endometrial proliferations. The goal of this literature review was to identify studies on endometrial hyperplasia (EH) that describe markers with potential to predict response to progestin therapy or potential for progression to invasive disease.

METHODS

Articles published between January 2000 and October 2006 were identified using the key words endometrial hyperplasia and progesterone receptor or estrogen receptor or biologic marker or immunohistochemistry/immunohistochemical. Articles that reported immunohistochemical studies on specimens of human EH +/-endometrioid endometrial carcinoma with a normal comparison group were included. Only those who reported hyperplasia with atypia separately from nonatypical hyperplasia and with a sample size greater than 10 specimens for the sum of complex and atypical samples were included.

RESULTS

A total of 289 abstracts were reviewed and 150 articles potentially met inclusion criteria. Of these, 123 described immunohistochemical studies on human EH specimens. Only 46 met all criteria for analysis of 61 different markers.

CONCLUSIONS

PTEN seems to have the greatest potential for diagnostic utility in EH, perhaps in combination with Bcl-2 and Bax. However, more uniform and rigorous studies are required to confirm these and additional markers' utility diagnostically in a diagnostic panel. As a major clinical priority is to determine which lesions can be treated medically and which require surgical intervention, focusing future studies on markers that distinguish response to hormone therapy or are involved in hormone regulation, will be important future considerations.

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.

RCAS1 decidual immunoreactivity in severe pre-eclampsia: immune cell presence and activity

PROBLEM

Pre-eclampsia seems to be related to the disturbance of immune tolerance regulation during pregnancy. Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) decidual level alterations were concomitant with changes in immune cell number and activity in decidua. As decidual immunomodulating activity participates in the development of immune tolerance during pregnancy, we aimed to evaluate the immunoreactivity level of decidual RCAS1 with respect to the presence and activity of immune cells.

METHOD OF STUDY

RCAS1, CD3, CD56, CD69, and CD25 immunoreactivity was assessed by immunohistochemistry in 30 decidual samples derived from patients with severe pre-eclampsia (sPE) and from a healthy control group.

RESULTS

RCAS1 immunoreactivity was statistically significantly higher in decidual tissue samples derived from patients with sPE tissue than in those derived from healthy patients in whom elective cesarean section at term was performed. A statistically significantly lower number of CD56(+) and CD3(+) cells and lower immunoreactivity level of CD69 were found in patients with sPE compared with those from the control group.

CONCLUSION

The limited immune cells infiltration in decidua during sPE is associated with increase in RCAS1 decidual level.

Analysis of metallothionein, RCAS1 immunoreactivity regarding immune cell concentration in the endometrium and tubal mucosa in ectopic pregnancy during the course of tubal rupture

INTRODUCTION

Tubal rupture seems to be linked to a disturbance in maternal immune response and trophoblast cell invasion. The immunomodulating activity of endometrial cells is necessary for the coexistence of activated immune cells and endometrial cells. RCAS1 and metallothionein (MT) participate in this process.

MATERIAL AND METHODS

Tissue samples derived from fallopian tubes and endometrium were collected during one surgical procedure and divided into three groups: unruptured ectopic pregnancy (EP) without bleeding, unruptured EP with hemorrhage into the peritoneal cavity, and ruptured tubal pregnancy. Immunoreactivity of MT, RCAS1, CD56, CD3, CD69 and CD25 were assessed by immunohistochemical methods.

RESULTS

The number of CD3+ and CD56+ cells as well as CD69 antigen immunoreactivity in ruptured tubal mucosa of EP were statistically significantly higher than those measured for unruptured EP without bleeding, while at the same time the number of CD56+ cells in endometrium was statistically significantly lower. The growth of immune cell numbers in tubal mucosa during tubal rupture was not associated with an adequate MT and RCAS1 level.

CONCLUSION

Tubal perforation seems to be linked to a concentration of immune cells and a growth of their activity without an adequate increase of the level of proteins compensating for immune cell response.

RCAS1 decidual immunoreactivity during placental abruption: immune cell presence and activity

PROBLEM

RCAS1 is a protein responsible for the suppression of cytotoxic immune response during gestation. The present study evaluates the immunoreactivity level of RCAS1 with respect to immune cell status during placental abruption (PA) and retained placental tissue (RPT).

METHOD OF STUDY

RCAS1, CD3, CD56, CD69 and CD25 immunoreactivity was assessed by immunohistochemistry in 66 decidual samples derived from PA and from RPT.

RESULTS

RCAS1 immunoreactivity was statistically significantly higher in decidual tissue samples derived from patients with RPT than in those derived from patients with PA. A statistically significantly lower number of CD56(+) and CD3(+) cells and immunoreactivity level of CD69 were found in patients with RPT, compared to those with PA.

CONCLUSION

Placental abruption seems to be associated with excessive accumulation and activity of CD3(+) and CD56(+) cells in decidua, which processes might, in turn, result from an insufficient RCAS1 decidual level.

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.

Expression of receptor-binding cancer antigen expressed on SiSo cells and estrogen receptor subtypes in the normal, hyperplastic, and carcinomatous endometrium

The objectives were to study the expression of receptor-binding cancer antigen expressed on SiSo cells (RCAS1) and estrogen receptor (ER) subtypes in the normal, hyperplastic, and carcinomatous endometrium and to explore their possible role in carcinogenesis and progression of endometrial carcinoma. Immunohistochemistry and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) were applied to detect protein and messenger RNA expression of RCAS1, ER-alpha, and ER-beta in normal, hyperplastic, and carcinomatous endometrium. Western blotting was also used to detect the RCAS1 protein expression. Immunohistochemistry showed that the high expressions of RCAS1 protein were 0% (0/20), 9.1% (2/22), 40% (8/20), and 68.0% (34/50) in normal, simple, and complex hyperplasia, atypical hyperplasia, and endometrial carcinoma, respectively. There was a significant difference between each group (P < 0.05). The high-level expression of RCAS1 was detected more frequently in endometrial cancer with deep myometrial invasion, vascular invasion, and positive ER-alpha (P < 0.05). Two staining patterns of RCAS1 were observed. All normal, simple, and complex hyperplastic endometrium showed P pattern, while all malignant endometrium were of the D pattern. In atypical endometrium, 25% (5/20) cases showed D pattern. The Western blotting and RT-PCR results correlated with the immunohistochemistry results. The expression and distribution of RCAS1 may be involved in the malignant transformation of endometrium, and RCAS1 coexpression with ER-alpha may be associated with development and metastasis of endometrial carcinoma.

Prognostic significance of RCAS1 expression in relation to the infiltration of dendritic cells and lymphocytes in patients with esophageal carcinoma

RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) expression was determined in 107 esophageal carcinoma patients by immunohistochemical procedures and compared with tumor infiltrating lymphocyte (TIL) and dendritic cell (DC) infiltration to evaluate the effect of RCAS1 on immune responses in esophageal carcinoma. RCAS1 immunoreactivity was detected in 59 of 107 patients (55.1%). RCAS1 expression was significantly correlated with the depth of invasion, lymph node metastasis, and histologic stage. RCAS1 expression tended to be correlated with a lower TIL density in tumors with marked DC infiltration. The survival time for patients with RCAS1-negative tumors was significantly longer than that for patients with RCAS1-positive tumors. Especially, the prognosis was predicted by RCAS1 in cases with marked DC infiltration. Multivariate analysis revealed that RCAS1 expression was an independent prognostic factor. RCAS1 expression may play an important role in evading the immunological defense mechanisms in esophageal carcinoma.

Clinical significance of RCAS1 as a biomarker of uterine cancer

OBJECTIVES

Expression of RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is associated with prognosis of various malignancies including uterine cancer. Proteolytic cleavage of RCAS1 at extracellular domains (ectodomain shedding) yields soluble RCAS1. Although RCAS1 can induce apoptosis in normal peripheral lymphocytes, its biologic function in cancer patients is unclear. Here, we evaluated serum RCAS1 concentrations to clarify its biologic activity in uterine cancer.

METHODS

Via ELISA, we measured serum RCAS1 concentrations in samples from 54 healthy blood donors and 113 patients-63 with cervical cancer and 50 with endometrial cancer. We also counted the peripheral lymphocyte number. We correlated via statistical means the RCAS1 values with patients' clinicopathologic variables. We assessed inhibition of growth of K562 cells, which express the putative RCAS1 receptor, via WST-1 assay of serum samples to clarify RCAS1's biologic activity.

RESULTS

Uterine cancer patients had significantly higher serum RCAS1 concentrations than did healthy blood donors (P<0.05). Patients with adenocarcinoma had significantly higher RCAS1 concentrations than did those with squamous cell carcinoma (P=0.0340). RCAS1 values were also significantly associated with response to treatment (P<0.001). FasL and TNF-alpha serum concentrations were not significantly different for the different groups, however. The WST-1 assay showed that patients' serum induced K562 cell growth inhibition, but this effect partially recovered after immunodepletion of RCAS1. Peripheral lymphocyte number and serum RCAS1 concentration were inversely related (P=0.0310).

CONCLUSION

RCAS1 may be a biomarker of uterine cancer because of its potential to predict results of uterine cancer treatment and inhibit growth of immune cells.

Expression of tumor-associated antigen RCAS1 and its possible involvement in immune evasion in oral squamous cell carcinoma

BACKGROUND

RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is known to induce apoptosis in its receptor-positive cells. The authors investigated RCAS1 expression in oral squamous cell carcinoma (SCC) and its association with the apoptosis of tumor-infiltrating lymphocytes (TILs).

METHODS

In 130 patients with oral SCC, the expression of RCAS1 in tumor cells was immunohistochemically examined and the apoptosis of TILs was examined by Terminal Deoxynucleotidyltransferase-mediated dUTP Nick End Labeling (TUNEL) staining.

RESULTS

RCAS1 was detected both on the cytoplasm and the membrane of tumor cells in 41 of 130 cases (31.5%). Focusing on the expression at the invasive front interacting with host immune cells, RCAS1 was detected in 22 of 130 cases (16.9%). The percentage of TUNEL-positive TILs in cases with RCAS1-positive SCCs was significantly higher than in cases with RCAS1-negative SCCs (P < 0.0001).

CONCLUSIONS

RCAS1 can be expressed on oral SCC cells and may be involved in the tumor escape from the host immune system by inducing the apoptosis of TILs.

The Role of RCAS1 and oxytocinase in immune tolerance during pregnancy

OBJECTIVES

To determine and compare the level of RCAS1 (receptor-binding cancer antigen expressed in SiSo cells) in placentas at term as well as oxytocinase/cystine amino peptidase (CAP) serum level a few days before labor in order to evaluate their possible role in the regulation of maternal immune response during pregnancy and in initiation of labor.

METHODS

We estimated the RCAS1 content in 44 placental tissue samples, using Western blot method. We also assessed CAP serum level by its enzymatic activity, using L-cystine-di-beta-naphthylamide as a synthetic substrate. The statistical analysis was performed using Shapiro-Wilk procedure. Student's t test was applied to compare the differences between parametric data. A value of p < 0.05 was considered significant.

RESULTS

RCAS1 was found in all placental tissue samples examined. The differences in the RCAS1 relative amount depended on the onset of labor, with the highest level in induced labor and the lowest in spontaneous labor. The differences were also observed in the CAP serum level with the highest level in pregnant women whose labor was induced.

CONCLUSIONS

We have observed a link between the expression of the two proteins examined and the onset of the labor. Therefore, we posit that RCAS1 and CAP may play a role in the downregulation of the maternal immune response during pregnancy and may participate in the initiation of the labor.

Invasive potency related to RCAS1 expression in uterine cervical cancer

OBJECTIVES

RCAS1 expression is significantly associated with clinical prognosis in various human cancers, which suggests that RCAS1 may be involved in acquisition of malignant phenotypes. To investigate the relationship between RCAS1 and one such characteristic, tumor invasiveness, we examined RCAS1 expression in cervical neoplasms ranging from the precancerous state to invasive cancer.

METHODS

RCAS1 expression was studied retrospectively via immunohistochemical methods. Samples consisted of biopsy tissue from 90 patients with intraepithelial neoplasia and resected tumor tissue from 154 patients with invasive cancer. Statistical analysis was done to correlate RCAS1 expression and clinicopathologic variables in patients with a depth of cancer cell invasion into stromal tissue of >5 mm.

RESULTS

RCAS1 expression was detected in patients with intraepithelial cancer and invasive cancer but not in patients with dysplasia. The occurrence and degree of RCAS1 expression increased with the depth of invasion. In patients with invasive cancer, RCAS1 overexpression was significantly correlated with invasion of the lymph-vascular space, lymph node metastasis in two or more sites, and tumor volume; RCAS1 expression was not associated with histologic subtype. Overall survival rates for patients with RCAS1 overexpression were significantly shorter than those for patients without RCAS1 overexpression. In connective tissue surrounding tumor cells, the number of cells expressing vimentin significantly decreased in relation to RCAS1 expression level. Moreover, significant associations between expression levels of RCAS1 and those of MMP-1 and laminin-5 were found.

CONCLUSION

RCAS1 may contribute to acquisition of malignant uterine cervical phenotypic characteristics including invasion, metastasis, and tumor growth via connective tissue remodeling.

Novel serum tumor marker, RCAS1, in pancreatic diseases

AIM: As tumor markers for pancreatic carcinoma, carcinoembryonic antigen (CEA) and carbohydrate antigen (CA) 19-9 have been used, but the sensitivity and specificity are not enough for the diagnosis of pancreatic carcinoma.

METHODS: A novel serum tumor marker, RCAS1, was compared with two conventional serum tumor markers, CEA (highly specific for pancreatic cancer) and CA 19-9 (highly sensitive for pancreatic cancer), in 48 patients with pancreatic exocrine tumors.

RESULTS: When the diagnosis of benign or malignant conditions was examined by one tumor marker, the sensitivity of RCAS1 alone (55%) was higher than that of CEA alone (27%) and the specificity of RCAS1 alone (92%) was greater than that of CA19-9 alone (78%). When examined by a combination of two markers, the sensitivity of a combination of RCAS1 and CA19-9 (95%) was superior to those of CA19-9 alone (78%), RCAS1 alone (55%, P = 0.002), CEA alone (27%) (P<0.001), RCAS1 and CEA (59%) and CA19-9 and CEA (82%).

CONCLUSION: These results suggest that the combination of RCAS1 and CA19-9 is highly sensitive for pancreatic carcinoma.

The molecular changes during placental detachment

OBJECTIVES

RCAS1 is a membrane protein that plays a role in the maintenance of maternal immune tolerance during pregnancy. The work presented here demonstrates the results of RCAS1 expression in placenta in cases of placental abruption and patients with retained placental tissue during the third stage of labor.

STUDY DESIGN

The placenta tissue samples were obtained during vaginal and cesarean delivery (derived from 117 pregnancies). Pregnant women were divided into four groups according to the onset of labor and the time of placental detachment in term labors. The samples were analyzed by the Western blot method. Statistical analysis was performed using the Shapiro-Wilk procedure. The Mann-Whitney test and Student's t-test were applied to compare the differences between parametric data.

RESULTS

The average relative amount of RCAS1 observed in those patients with retained placental tissue was statistically significantly higher than in the patients with placental abruption.

CONCLUSION

The differences observed in placental RCAS1 levels confirm the participation of this protein in the inhibition of maternal immune response during gestation. The present results also indicate that RCAS1 participates in the changes in the maternal immune system that take place during parturition and reinforce its potential involvement in the mechanism of placental abruption.

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.

The placental RCAS1 expression during stillbirth

BACKGROUND

Independently of the fetal death cause the beginning and course of stillbirth is closely related with the growing cytotoxic activity at the maternal-fetal interface. RCAS1 participates in the inhibition of maternal immune response during pregnancy. The alterations of RCAS1 protein expression in placental cells seem to determine the beginning of the labor and participate in the placental abruption. The aim of the present study was to investigate RCAS1 expression in placentas obtained following stillbirths or normal term births.

METHODS

RCAS1 expression was evaluated by Western blot method with the use of monoclonal anti-RCAS1 antibody in 67 placental tissue samples. Pregnant women were divided into four groups according to the mode of labor onset--spontaneous or induced, and the type of labor, stillbirth or labor at term. Placental beta-Actin expression was chosen as a control protein. Relative amounts of placental RCAS1 were compared with the use of Student's t-test, whereas beta-Actin control data were compared with the use of Mann-Whitney U test.

RESULTS

The average relative amount of RCAS1 was significantly lower in women with induced stillbirths than in women with induced labor at term. Similarly, significantly lower RCAS1 placental levels were observed in patients with spontaneous stillbirths than in women with spontaneous labor at term. Significant differences in RCAS1 expression were also observed with the respect to the beginning of the stillbirth: spontaneous and induced. Lowest RCAS1 placental levels were observed in women with spontaneous stillbirth.

CONCLUSIONS

These preliminary results indicate that the alterations of RCAS1 expression in the human placenta may be involved in the changes of maternal immune system that take place during stillbirth.

A novel mechanism in suppression of erythropoiesis during inflammation: a crucial role of RCAS1

A novel human tumor-associated antigen, receptor-binding cancer antigen expressed on SiSo cells (RCAS1), induces apoptosis in normal human erythroid progenitor cells, which express putative RCAS1 receptors. In the present study, we investigated a possible role of RCAS1 produced by human peripheral blood monocytes (CD14-positive cells) and monocyte-derived macrophages. RCAS1 was immunohistochemically detected in monocytes as well as macrophages. When macrophages were stimulated with lipopolysaccharide (LPS), the expression of RCAS1 was remarkably enhanced. An increased production of RCAS1 mRNA was observed in LPS-stimulated macrophages by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Soluble RCAS1 molecules were only detected in the culture supernatants obtained from LPS-stimulated macrophages. Moreover, LPS-stimulated macrophages induced cell death of erythroid progenitor cells through RCAS1 production. These results suggest that macrophages may negatively regulate erythropoiesis at least in part through the production of RCAS1 molecules, and this may contribute to the pathogenesis of the anemia seen in patients with inflammatory disorders.

Expression of a tumor-associated antigen, RCAS1, in canine mammary tumors

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.

Expression of EBAG9/RCAS1 is associated with advanced disease in human epithelial ovarian cancer

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 ERα. The correlation between EBAG9 immunoreactivity and clinicopathological parameters was examined. mRNA expression of EBAG9 and ERα were evaluated by RT–PCR in 22 cases. The expression for EBAG9 and ERα 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 ERα 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 ERα 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.

EBAG9/RCAS1 expression and its prognostic significance in prostatic cancer

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.

Association between RCAS1 expression and clinical outcome in uterine endometrial cancer

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.

Molecular cloning of canine RCAS1 cDNA

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a novel cancer cell-surface antigen, strongly expressed in invasive cancers. RCAS1 inhibited the in vitro growth of immunocytes, and induced apoptotic cell death. The cloning of canine RCAS1 cDNA was carried out and identified from the mammary gland tumor of a dog. A canine RCAS1 cDNA of 864 bp in length has an open reading frame of 642 bp nucleotides encoding a protein of 213 deduced amino acids. The predicted amino acid sequence of canine RCAS1 showed 96.2% and 96.7% homologies with those of human and mouse RCAS1 respectively. Canine RCAS1 has an N-terminal transmembrane segment and a coiled-coil structure in the C-terminal protein, which are highly conserved in mouse and human RCAS1.

EBAG9/RCAS1 expression in hepatocellular carcinoma: correlation with tumour dedifferentiation and proliferation

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.

The Golgi protein RCAS1 controls cell surface expression of tumor-associated O-linked glycan antigens

Tumor immunology has received a large impetus from the identification of tumor-associated antigens. Among them, a monoclonal antibody, 22.1.1, was instrumental in defining a novel tumor-associated antigen that was termed "receptor binding cancer antigen expressed on SiSo cells" (RCAS1). RCAS1 was proposed to induce growth arrest and apoptosis on activated immune cells, mediated by a putative death receptor. Structurally, RCAS1 was predicted to exist as a type II transmembrane protein and in a soluble form. Here, we analyzed occurrence, membrane topology, and subcellular localization of the RCAS1-encoded gene product. RCAS1 was shown to be a ubiquitously expressed type III transmembrane protein with a Golgi-predominant localization. Monoclonal antibody 22.1.1 failed to recognize RCAS1, as demonstrated by confocal microscopy. Instead, we showed that the cognate 22.1.1 epitope is identical with the tumor-associated O-linked glycan Tn (N-acetyl-d-galactosamine, GalNAc). Overexpression of RCAS1 in cell lines that are negative for 22.1.1 surface staining led to the generation of Tn and the closely related TF (Thomsen-Friedenreich, Galbeta1-3GalNAc) antigen, thus providing a functional link to the generation of the 22.1.1 epitope. We suggest that RCAS1 modulates surface expression of tumor-associated, normally cryptic O-linked glycan structures and contributes indirectly to the antigenicity of tumor cells.

Overexpression of human tumor-associated antigen, RCAS1, is significantly linked to dedifferentiation of thyroid carcinoma

OBJECTIVE

Counterattack by RCAS1 on carcinoma to cytotoxic T cells and natural killer (NK) cells has been suggested as a contribution to carcinoma progression, because RCAS1 can inhibit their proliferation and induce apoptosis. In this study, we examined RCAS1 expression in various thyroid neoplasms in order to clarify its clinical significance.

METHODS

We studied RCAS1 expression by means of immunohistochemistry using a mouse monoclonal antibody against RCAS1 for normal thyroid epithelium, follicular adenoma, follicular carcinoma, papillary carcinoma and undifferentiated (anaplastic) carcinoma.

RESULTS

Normal epithelium and follicular adenoma did not express or only faintly expressed RCAS1. In thyroid carcinomas. RCAS1 overexpression was more frequently observed in anaplastic (undifferentiated) carcinomas than papillary (p < 0.0001) and follicular carcinomas (p = 0.0018). In follicular carcinoma, the widely invasive type more frequently overexpressed RCAS1 than the minimally invasive type (p = 0.0488). Furthermore, the incidences of RCAS1 overexpression increased with carcinoma dedifferentiation (p < 0.0001).

CONCLUSION

These results suggest that RCAS1 may contribute to the progression of thyroid carcinoma with high biological aggressiveness.

RCAS1 is associated with ductal breast cancer progression

RCAS1/EBAG9 (receptor-binding cancer antigen expressed on SiSo cells/ estrogen receptor-binding fragment-associated gene 9), an estrogen-transcribed protein, has been shown to be expressed in a wide variety of cancers, including uterine, ovarian, and lung cancer cells. Soluble and membranous RCAS1 proteins may play a role in the immune escape of tumor cells by promoting T lymphocyte inhibition of growth and apoptosis. In the present report, the presence of RCAS1 was revealed in human ductal breast cancer biopsies by immunohistochemistry. Its cytoplasmic expression was exhibited in cancer cells obtained from tumor biopsies and in breast cancer cell lines. RCAS1 significantly correlated with tumor grade. In addition, RCAS1 was identified in MCF7 culture supernatants. Those observations suggest that RCAS1 is a new marker for breast cancer progression and a possible mechanism for breast cancer immune escape.

High expression of tumor-associated antigen RCAS1 in pancreatic ductal adenocarcinoma is an unfavorable prognostic marker

RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a recently identified human tumor-associated antigen expressed on various cancer cells. It is thought that tumor cells evade immune surveillance by expression of RCAS1, which induces apoptotic cell death in receptor-positive immune cells. The purpose of our study was to investigate the relation between RCAS1 expression and the clinicopathological variables and clinical outcome in patients with pancreatic adenocarcinoma. Immunohistochemical analysis for RCAS1 was performed on paraffin-embedded specimens of 80 patients (mean age, 62 years) who underwent surgical resection for pancreatic adenocarcinoma. Of the 80 specimens, 77 (96%) were positive for RCAS1. No significant correlation was found between RCAS1 expression and age, gender, depth of invasion, tumor diameter, surgical margin, lymphatic invasion, venous invasion or histopathological grading. Borderline correlations between RCAS1 expression were noted for lymph node metastasis and stage (p = 0.0608 and 0.0934, respectively). RCAS1 expression was very frequently observed and the survival of patients with high RCAS1 expression was significantly shorter than that of those with low expression (p = 0.0012). Multivariate analysis using the Cox regression model indicated that high RCAS1 expression was an independent prognostic factor (risk ratio, 3.090; p = 0.0090). These results suggested that RCAS1 might be a significant tumor marker for pancreatic adenocarcinoma and an unfavorable predictor for prognosis of patients who have undergone surgical resection.