乳腺癌中KAI1蛋白表达与临床病理特征的相关性

目的:研究KAI1蛋白在人乳腺癌中的表达及其与临床病理特征的相关性。方法:应用免疫组织化学S-P法检测107例乳腺癌及30例癌旁乳腺组织中的KAI1蛋白表达情况。结果:乳腺癌组中KAI1蛋白高表达率显著低于正常乳腺组织(P<0.05)。正常组织及非侵袭性乳腺癌中,KAI1蛋白呈高表达;反之,在浸润性乳腺癌中KAI1表达减少。伴有腋窝淋巴结转移的61例乳腺癌中,KAI1蛋白高表达率为21.3%(13/61),无腋窝淋巴结转移组46例中,KAI1蛋白高表达率为39.0%(18/46),两者差异有显著性(P<0.05)。同时发现KAI1蛋白表达与肿瘤大小、年龄无相关性。结论:在乳腺癌进展过程中,KAI1蛋白表达降低在乳腺癌浸润和转移过程中起着重要的作用,检测KAI1蛋白表达可能成为监测人乳腺癌进展及临床上判断其预后的重要参考指标。     

KAI1 metastasis suppressor protein is down-regulated during the progression of human endometrial cancer.

PURPOSE: KAI1 is a metastasis suppressor gene located on human chromosome 11p11.2. It is a member of the structurally distinct family of cell surface glycoprotein, transmembrane 4 protein superfamily. KAI1 was initially isolated as a gene that suppressed metastasis of rat prostate tumor cells. Decreased KAI1 expression has been observed recently in various human cancers, including pancreatic, lung, hepatic, colorectal, breast, ovarian, esophageal, and cervical cancers. Frequent down-regulation of the KAI1 protein was also observed in endometrial cancer cell lines. The aim of this study was to determine whether this gene is altered in human endometrial carcinoma. In addition, its prognostic significance in this tumor was also evaluated. EXPERIMENTAL DESIGN: Tumor specimens from 18 cases with various degrees of endometrial hyperplasia, 97 primary endometrial carcinomas with various stages, and 28 metastatic lesions of this cancer were examined in this study. Using the method of immunohistochemistry, we characterized the KAI1 protein expression in the 143 endometrial tumors. Expression of KAI1 at RNA level was also examined in 35 of the 143 samples using a real-time quantitative PCR method. The data from immunohistochemical analysis were correlated with various clinicopathological factors. RESULTS: High levels of KAI1 protein expression were detected in almost all of the specimens with endometrial hyperplasia (17 of 18). In contrast, loss of KAI1 expression occurred in an increasing frequency (27.8-71.4%) from early stages of primary endometrial carcinomas to metastatic tumors (P < 0.001). In addition, more poorly differentiated tumors demonstrated significantly lower KAI1 expression as compared with the well-differentiated tumors (P < 0.001). It was also found that patients with KAI1-negative tumors had a lower survival rate than those with KAI1-decreased or positive tumors (P = 0.0042 and 0.0286, respectively). However, in multivariate analysis, the prognostic significance of KAI1 expression was inferior to tumor stage. CONCLUSION: These data suggest that KAI1 expression is down-regulated in advanced endometrial cancer. Clinically it may be a useful indicator of the tumor progression and may provide prognostic information on the outcome of this disease.     

Analysis of normal epithelial cell specific-1 (NES1)/kallikrein 10 mRNA expression by in situ hybridization, a novel marker for breast cancer.

PURPOSE: Normal epithelial cell specific-1 (NES1)/kallikrein 10 gene is expressed in normal mammary and prostate epithelial cells, but the expression of NES1 mRNA and protein is markedly reduced in established breast and prostate cancer cell lines although the NES1 gene is intact. Here, we wished to assess whether NES1 expression is down-regulated in primary breast cancers. EXPERIMENTAL DESIGN: We developed and used an in situ hybridization technique with an antisense NES1 probe to detect NES1 mRNA in sections of normal breast specimens, typical and atypical ductal hyperplasia, ductal carcinoma in situ, and infiltrating ductal carcinoma. RESULTS: All of the 30 normal breast specimens showed high NES1 expression. Notably, 18 (75%) of 24 typical and atypical breast hyperplasia specimens showed high NES1 expression, with weak-to-moderate expression in 6 (25%). Significantly, 13 (46%) of 28 ductal carcinoma in situ specimens lacked NES1 expression, and the remaining 15 (54%) showed weak-to-moderate expression. Finally, 29 of 30 (97%) infiltrating ductal carcinoma grades I-III samples lacked NES1 mRNA, with weak expression in the remaining one sample. CONCLUSIONS: Our results demonstrate that NES1 mRNA is expressed in normal breast tissue and benign lesions, with loss of NES1 expression during tumor progression. We suggest that NES1 expression may serve as a molecular tool in the study of breast cancer progression. Studies with larger series of specimens should help assess whether NES1 expression can be a diagnostic and/or prognostic marker in breast and other cancers.     

Overexpression of KAI1 suppresses in vitro invasiveness and in vivo metastasis in breast cancer cells.

KAI1 is a metastasis suppressor gene for human prostate cancer and is also involved in the progression of a variety of other human cancers. Previously, we have demonstrated that KAI1 expression was down-regulated in metastatic breast cancer cell lines as well as in highly aggressive breast cancer specimens. To determine whether KAI1 expression is responsible for the metastasis suppression in breast cancer, we transfected the human KAI1 cDNA into two highly malignant breast cancer cell lines, LCC6 and MDA-MB-231, which both have low levels of endogenous KAI1 expression. Parental, vector-only transfectants and KAI1 transfectant clones were injected into the mammary fat pads and tail veins, respectively, of athymic nude mice and assessed for both spontaneous and experimental lung metastasis. High KAI1 expression significantly suppressed the metastatic potential of KAI1-transfected LCC6 cells. Metastasis suppression correlated with the reduced rate of tumor growth and a decreased clonogenicity in soft agar. Furthermore, KAI1 expression significantly suppressed the in vitro cell invasion in KAI1-transfected MDA-MB-231 cells. Our results suggested that KAI1 may function as a negative regulator of breast cancer metastasis.     

Loss of KAI1 expression in the progression of colorectal cancer

The transmembrane 4 superfamily member KAI1 (CD82) has been shown to inhibit pulmonary metastases in experimental metastasis models of prostate cancer and melanoma. KAI1 expression is decreased in the progression of common solid epithelial tumors of adulthood, including lung, prostate, breast, esophageal, gastric, pancreatic, and bladder cancers. The purpose of our study was to investigate KAI1 expression in the progression of human colorectal cancer. We first analyzed 20 colorectal cancer cell lines by immunoblot techniques. KAI1 was expressed heterogeneously, with the tumor cell lines having a more complex degree of glycosylation compared with that of the normal colonic tissue. KAI1 was highly expressed in the primary SW480 colon cancer cell line but was down-regulated 15-fold in the matched metastatic SW620 cell line. We also investigated KAI1 protein expression by immunohistochemistry in tissues from 84 patients with colorectal cancer. Each tissue section was assigned a KAI1 mean score (KMS) from 0 to 300 based on the product of the percentage of cells that stained for KAI1 and the intensity of the stain (1, 2, or 3). In 84 patients with colorectal cancer, KAI1 was expressed at high levels in normal colonic mucosa (KMS 226) but was expressed at lower levels in the primary tumors (KMS 65; P < 0.0001). In a subset of 12 patients with stage IV metastatic disease, we observed a progressive down-regulation of KAI1, from the normal adjacent colonic mucosa (KMS 193) to the primary tumor (KMS 72; P = 0.0001) to the liver metastasis (KMS 25; tumor compared with metastasis, P = 0.0135). We found no correlation between loss of KAI1 expression and stage of disease. In 10 patients, we also noted loss of KAI1 expression in the transition from normal colonic mucosa (KMS 237) to adenoma (KMS 174) to carcinoma (KMS 62; P < 0.0167 for all three comparisons). We conclude that the down-regulation of KAI1 occurs early in the progression of colorectal cancer.     

Elevated TRF2 in advanced breast cancers with short telomeres

Telomere repeat binding factor 2 (TRF2) binds directly to telomeres and preserves the structural integrity of chromosome ends. In vitro models suggest that expression of TRF2 protein increases during mammary cancer progression. However, a recent study has reported that TRF2 mRNA levels tend to be lower in clinical specimens of malignant breast tissue. Here, we conduct the first large-scale investigation to assess the levels and cellular localization of the TRF2 protein in normal, pre-malignant and malignant breast tissues. Breast tissue arrays, containing normal, ductal carcinoma in situ (DCIS) and invasive carcinoma specimens, were used to assess the expression and localization of TRF2 protein. Telomere lengths were semi-quantitatively measured using a pantelomeric peptide nucleic acid probe. A mixed effects modeling approach was used to assess the relationship between TRF2 expression and telomeric signal scores across disease states or clinical staging. We demonstrate that TRF2 is exclusively nuclear with a trend toward lower expression with increased malignancy. More case-to-case variability of TRF2 immunostaining intensity was noted amongst the invasive carcinomas than the other disease groups. Invasive carcinomas also displayed variable telomere lengths while telomeres in normal mammary epithelium were generally longer. Statistical analyses revealed that increased TRF2 immunostaining intensity in invasive carcinomas is associated with shorter telomeres and shorter telomeres correlate with a higher TNM stage. All immortalized and cancer cell lines within the array displayed strong, nuclear TRF2 expression. Our data indicate that elevated expression of TRF2 is not a frequent occurrence during the transformation of breast cancer cells in vivo, but higher levels of this telomere-binding protein may be important for protecting advanced cancer cells with critically short telomeres. Our findings also reinforce the concept that serially propagated cancer cells, although tumor-derived, may not model all types of authentic tumors especially those demonstrating genetic heterogeneity.     

Expression of KAI1/CD82 in distant metastases from estrogen receptor-negative breast cancer

The tetraspanin protein superfamily member KAI1 suppresses tumor growth and metastasis in animal models and is downregulated in various human malignancies. In breast cancer, KAI1 is preferentially lost in estrogen receptor (ER)-positive tumors. Interestingly, most ER-negative primary breast cancers retain KAI1 expression. This study aimed to evaluate whether or not KAI1 is downregulated during progression to metastasis of these carcinomas. Expression of KAI1, ER, progesterone receptor, c-ErbB2, and Ki67 was analyzed in tissue microarrays comprising a large collection of distant organ metastases from human breast cancers ( n  = 92) by immunohistochemistry. Results were compared with a previously characterized set of primary breast tumors ( n  = 209). Immunoreactivity for KAI1 was observed in one-third of the metastases and was associated with lack of ER expression ( P  = 0.005). The high frequency of KAI1-positive cases in ER-negative primary tumors was maintained in ER-negative metastases. Expression of KAI1 was also observed in MDA-MB-468 and SK-BR-3, two ER-negative breast cancer cell lines of metastatic origin. Moreover, a reanalysis of independent microarray gene expression data indicated maintenance of KAI1 mRNA expression in metastases from ER-negative breast cancers. Furthermore, in a series of matched pairs of mammary carcinomas and metachronous distant metastases, all metastases from KAI1-positive/ER-negative primary tumors were KAI1-positive as well. Collectively, these findings demonstrate that the expression of KAI1 is maintained during progression to metastasis in a large proportion of ER-negative mammary carcinomas. This has significant implications for the use of KAI1 as a clinical marker and the understanding of the metastatic process in human breast cancer. ( Cancer Sci 2009; 100: 1767–1771)     

Clinical implications of mRNA expression of KAI1 in ovarian cancer with or without metastasis

Background. KAI1 is a potential metastasis suppressor gene for prostate cancer. Decreased expression of KAI1 mRNA has been shown to be associated with the formation of metastasis and the progression of prostate, lung, breast, pancreatic, and bladder cancer. It has also been reported, however, that KAI1 expression is unchanged in metastatic and nonmetastatic esophageal and gastric cancer. We performed the present study to investigate the function of KAI1 in the progression and/or metastasis of ovarian cancer. Methods. We investigated the mRNA expression levels of the KAI1 gene, using quantitative polymerase chain reaction (PCR), in 29 ovarian tumors (1 adenoma, 2 low- malignant potential tumors, 9 adenocarcinomas without metastasis, and 17 adenocarcinomas with metastasis), seven ovarian cancer cell lines, and two normal ovaries. Using a thermal cycler, we found that the KAI1 gene was amplified in parallel with an internal control gene, β-Actin. The relative expression ratio (KAI1/β-Actin) as measured by densitometry was used to evaluate gene expression. Immunohistochemical localization of the KAI1 protein in ovarian cancer tissues was confirmed by the avidin-biotin peroxidase complex (ABC) method. Results. The mRNA expression levels of KAI1 were consistent in normal ovary, ovarian tumor samples, and ovarian cancer cell lines. No statistically significant difference in the KAI1 mRNA expression level was found in ovarian cancer samples with or without metastasis. Immunohistochemistry revealed that the KAI1 protein was expressed in the cell membranes of ovarian cancer cells. Conclusions. Our results suggest that reductions in KAI1 mRNA expression are not involved in either the progression or metastasis of ovarian carcinomas. Received: April 22, 1999 / Accepted: July 26, 1999     

Epigenetic suppression of secreted frizzled related protein 1 (SFRP1) expression in human breast cancer

Expression of Secreted frizzled related protein 1 (SFRP1), a recently identified tumor suppressor gene encoding a WNT signaling antagonist, has been found to be frequently down-regulated in breast cancer and is associated with disease progression and poor prognosis. Here, we investigated the role of epigenetic silencing of SFRP1 in breast cancer cell lines and primary breast tumors. Through analyses by methylation-specific PCR and bisulfite sequencing, promoter methylation of SFRP1 was detected in 88% (7/8) of breast cancer cell lines, 17% (1/6) of grade 1 of ductal carcinoma in situ (DCIS), 69% (9/13) of grade 2 and 3 of DCIS, 68% (19/28) of invasive ductal carcinomas (IDC) and 33% (6/18) of lobular carcinomas but not in any (0/14) of normal mammoplasty specimens and mammary epithelial organoids examined. Real-time RT-PCR studies indicated that loss or downregulation of SFRP1 expression in tumors is frequently associated with promoter hypermethylation. In addition, breast cancer cell lines with SFRP1 promoter hypermethylation reexpressed SFRP1 mRNA after treatment with 5-azaC, implying that DNA methylation is the predominant epigenetic mechanism for SFRP1 gene silencing. These findings suggest that frequent downregulation of SFRP1 expression in breast cancer can be attributed, in large part, to aberrant promoter hypermethylation in conjunction with or without histone deacetylation. Based on the frequency of tumor-specific hypermethylation in this gene, SFRP1 could provide a valuable marker for breast cancer.     

Expression Levels of Tetraspanin KAI1/CD82 in Breast Cancers in North Indian Females

Background: Carcinogenesis is a multifaceted intricate cellular mechanism of transformation of the normal functions of a cell into neoplastic alterations. Metastasis may result in failure of conventional treatment and death Hence, research on metastatic suppressors in cancer is a high priority. The metastatic suppressor gene CD82, also known as KAI1, is a member of the transmembrane 4 superfamily which was first identified in carcinoma of prostate. Little work has been done on this gene in breast cancer. Herein, we aimed to determine the gene and protein level expression of CD82/KAI1 in breast cancer and its role as a prognosticator. Materials and Methods: In this study, 83 histologically proven cases of breast cancer and a similar number of controls were included. Patient age ranged from 1870 years. Quantitative Real Time Polymerase Chain Reaction (qRT PCR) and immunohistochemistry (IHC) were used to investigate KAI1 expression at gene and protein levels, respectively. Statistical analysis was done to correlate expression of KAI1 and clinicopathological parameters. Results: It was revealed that: (i) KAI1 was remarkably diminished in metastatic vs non metastatic breast cancer both at the gene and the protein levels (P<.05); (ii) KAI1 expression levels were strongly correlated with TNM staging, histological grade and advanced stage (p<0.001) and no association was found with any other studied parameter; (iii) Lastly, a significant correlation was observed between expression of KAI1 and overall median survival of BC patients (P 0.04). Conclusions: Our results suggest that lack of expression of the KAI1 might indicate a more aggressive form of breast cancer. Loss of KAI1 may be considered a significant prognostic marker in predicting metastatic manifestation. When evaluated along with the clinical and pathological factors, KAI1 expression may be beneficial to tailor aggressive therapeutic strategies for such patients.     

An alternatively spliced KAI1 mRNA is expressed at low levels in human bladder cancers and bladder cancer cell lines and is not associated with invasive behaviour

Levels of the KAI1 metastasis suppressor are reduced in advanced stages of many human cancers, leading to the loss of KAI1 function. A recent study has suggested that the loss of KAI1 function may also occur via alternative splicing of KAI1 mRNA which deletes an exon encoding a critical 28 amino acids from the protein. Using PCR, 20 bladder tumours at differing stage and grade, a non-tumourigenic urothelial cell line (SV-HUC-1) and 17 bladder cancer cell lines were examined for expression of this alternatively spliced (AS) KAI1 mRNA. Full-length KAI1 mRNA was present in all tumour samples and low levels of AS KAI1 mRNA in 15/20 samples. There was no association between the presence or absence of AS mRNA and clinicopathological characteristics of these tumours. Low levels of AS KAI1 mRNA were present in SV-HUC-1 and 14/17 bladder cancer cell lines. There was no association between the presence or absence of AS KAI1 mRNA and tumourigenicity, or in vivo invasive abilities of these cell lines. In all cell lines expressing AS KAI1 mRNA, levels were 3- to 5-fold lower than levels of wild-type mRNA, irrespective of wild-type mRNA levels. Low levels of an alternatively spliced form of KAI1 mRNA are present in most bladder cancer tumours and tumour cell lines, but are not associated with invasive behaviour.     

High levels of DJ-1 protein in nipple fluid of patients with breast cancer

As we have previously demonstrated that some breast cancer cell lines secrete DJ-1 protein, we examined here whether breast cancer cells secrete DJ-1 protein in vivo. To this end, the levels of DJ-1 protein present in 136 specimens of nipple fluid was examined by enzyme-linked immunosorbent assay (ELISA). The average concentration of DJ-1 protein detected in diluted samples from 47 patients with invasive ductal carcinoma (IDC) was 22.4 ng/mL, while it was 18.6 ng/mL in 26 patients with ductal carcinoma in situ (DCIS). In contrast, the average DJ-1 concentration in samples from 63 women with benign lesions was 2.7 ng/mL, demonstrating that higher DJ-1 protein levels were detected in nipple fluid in the presence of cancer cells than in the presence of benign lesions (P < 0.0001). When a cut-off level of 3.0 ng/mL was applied, the higher level of DJ-1 was shown to be of significant clinical value for predicting the presence of breast cancer (85.9% specificity, 75% sensitivity; P < 0.0001). Multivariate logistic analysis that included established factors such as nipple discharge cytology, ductoscopic cytology, and carcinoembryonic antigen level further showed that the level of DJ-1 protein alone is of significant value for predicting the presence of breast cancer. Immunohistochemistry and in situ hybridization also showed that the low expression of DJ-1 protein, despite high mRNA expression, was significantly correlated with high DJ-1 protein levels in the nipple fluid. These data indicate that breast cancer cells secrete DJ-1 protein in vivo, and that its level is a potential indicator of breast cancer in patients with nipple discharge.     

MDR1和Anxa2在乳腺癌组织中的表达与侵袭转移的关系研究

探讨乳腺癌组织中多药耐药基因（MDR1）和膜联蛋白（Anxa2）表达的相关性及其与乳腺癌转移的关系。方法:应用荧光定量PCR的方法检测20例配对的乳腺导管内癌、100例乳腺浸润性导管癌、70例癌旁正常组织中MDR1和Anxa2 mRNA的相对表达情况。结果:MDR1 mRNA在乳腺导管内癌中的表达水平明显高于癌旁正常组织（P=0.005）,乳腺浸润性导管癌组织中mRNA的表达明显高于癌旁正常组织（P=0.017）和导管内癌（P=0.019 6）。Anxa2 mRNA在乳腺导管内癌中表达与癌旁正常组织相比无显著性差异（P=0.188 9）,但是在乳腺浸润性导管癌组织中的表达明显高于导管内癌（P=0.000 8）和癌旁正常组织（P<0.000 1）;MDR1和Anxa2 mRNA的表达升高均与患者出现淋巴结转移有关（P<0.01）;2种基因在乳腺浸润性导管癌中的表达呈正相关（P<0.000 1）。结论:在肿瘤进展过程中,MDR1和Anxa2 mRNA表达上调与乳腺癌的淋巴结转移有关,二者之间表达具有正相关提示肿瘤细胞的多药耐药的获得和肿瘤侵袭转移之间有着密切联系。      

Identification of CRASH, a gene deregulated in gynecological tumors

We have identified CRASH, a human asparaginase-like protein which is composed of 308 amino acids and exhibits 32% homology to human aspartylglucosaminadase at the amino acid level. Database analysis revealed that the gene corresponding to CRASH is composed of 7 exons and 6 introns. Steady-state level of CRASH mRNA was found to be increased in 5 cell lines derived from metastatic lesions compared with 2 cell lines derived from primary mammary carcinoma and HMEC (human mammary epithelial cells). We found that the mRNA level of CRASH correlates with the metastatic propensity of several isogenic human colon cancer and pancreatic carcinoma cell lines. CRASH corresponds to a recently identified sperm autoantigen and furthermore we have demonstrated inducibility of CRASH mRNA by androgen and progesterone. Investigation of several types of human cancers and their corresponding normal tissues revealed high levels of CRASH mRNA in uterine, mammary and ovarian tumors compared with the corresponding normal tissues. CRASH mRNA expression was analysed in breast cancer samples with disclosed clinico-pathological features and corresponding normal tissues. The levels of CRASH mRNA were significantly up-regulated in tumors compared with normal breast tissues and correlate with lack of estrogen receptor expression of the tumors.     

Reduced KAI1 expression in pancreatic cancer is associated with lymph node and distant metastases

KAI1 belongs to a structurally distinct family of membrane glycoproteins, which function via cell-cell and cell-extracellular matrix interactions, thereby potentially influencing the ability of cancer cells to invade tissues and to metastasize into lymph nodes and distant organs. In the present study, we examined KAI1 expression in lymph node and liver metastases in comparison with primary pancreatic cancer to evaluate its influence on metastasis. KAI1 mRNA analysis was performed by Northern blot analysis and in situ hybridization. In addition, the respective protein was studied by immunostaining. Fourteen primary pancreatic cancer samples in which no lymph node metastases were present and 25 primary pancreatic cancer samples in which lymph node metastases were present at the time of tumor resection were included. In 20 of these cases, primary pancreatic cancer tissues and corresponding lymph node metastases from the same patient were studied. Furthermore, 11 liver metastases were available for KAI1 analysis. Increased steady-state levels of KAI1 mRNA were found in 33/39 (85%) primary pancreatic cancers in comparison with normal controls. Statistical analysis of KAI1 mRNA levels and clinical parameters of the patients revealed that KAI1 mRNA levels were significantly higher in non-metastasized tumors compared with tumors in which lymph node or distant metastases were present. In lymph node metastases KAI1 mRNA expression was lower than in the corresponding primary tumors: In 14 of 20 lymph node metastases no KAI1 mRNA expression and in 6 of 20 lymph node metastases only weak KAI1 mRNA levels were present in some cancer cells. Cancer cells of distant metastases were devoid of or exhibited low KAI1 mRNA levels compared with those of primary pancreatic cancers. A similar pattern was observed by immunostaining. These data support the hypothesis that KAI1 gene expression might influence the metastatic ability of pancreatic cancer cells in vivo. Reduction of KAI1 appears to promote cancer cell spread in lymph nodes and distant organs. Int. J. Cancer (Pred. Oncol.) 79:349–355, 1998. © 1998 Wiley-Liss, Inc.     

Cyclooxygenase-2 expression during immortalization and breast cancer progression

Identification of molecular aberrations in premalignant human mammary epithelial cells (hMEC), the precursors for breast cancers, is a central goal in breast cancer biology. Recent studies implicated expression of cyclooxygenase 2 (COX-2) as a marker to identify precursor cells for breast cancer. In this study, we analyzed COX-2 expression in preselection and postselection hMEC cells and observed similar COX-2 levels in both cells. Interestingly, immortalization of postselection cells using various methods leads to a dramatic decrease in COX-2 expression. Similar to immortal cells, the majority of breast cancer cell lines expressed low levels of COX-2 protein. Finally, analyses of COX-2 expression in a series of specimens from reduction mammoplasty, adenosis, ductal carcinoma in situ, and infiltrating ductal carcinoma showed down-regulation of COX-2 expression during tumor progression. Importantly, down-regulation of COX-2 using small interfering RNA in cells showed no effect on cell proliferation, anchorage-independent growth, migration, or invasion. These results show that (a) COX-2 overexpression does not seem to predict a breast cancer precursor cell and does not provide advantage for the cell to be transformed; (b) inhibition of COX-2 does not affect hMEC growth and oncogenic behavior in the conditions analyzed; and (c) COX-2 expression is decreased in breast cancer cell lines and cancer specimens as compared with normal mammary epithelial cells.     

KAI1/CD82 is a novel target of estrogen receptor-mediated gene repression and downregulated in primary human breast cancer

The cell-surface glycoprotein KAI1 suppresses tumor growth and metastasis in various animal models. Downregulation of KAI1 has been implicated in the progression of cancer. However, the mechanisms of KAI1 inactivation are poorly understood. This is the first study that investigates expression and regulation of KAI1 in human breast cancer. KAI1 expression was analyzed on custom-made tissue microarrays comprising 209 well-characterized breast cancers and normal mammary gland tissue. Strong KAI1 immunoreactivity was observed throughout the normal mammary gland epithelium. In breast cancer tissue, KAI1 immunoreactivity was lost in 161/209 (77%) cases. Strikingly, KAI1 was preferentially lost in estrogen receptor (ER)-positive breast cancers (p < 0.001). This was validated by real-time RT-PCR analyses showing a 7.5-fold downregulation of KAI1 mRNA in ER-positive relative to ER-negative tumors (p = 0.028). Notably, this was also corroborated by Affymetrix microarray expression data of an independent cohort of 49 breast cancers. Class comparison analysis identified KAI1 as downregulated in ER-positive tumors. Subsequently, human breast cancer cell lines were employed to test a potential role of ER-activity in the downregulation of KAI1, as suggested by our expression analyses. Exposure of ER-positive breast cancer cells to fulvestrant, a clinically approved ER-antagonist that reverses ER-mediated gene repression, induced a significant upregulation of KAI1 and inhibited cell proliferation as well as migration. In summary, we demonstrate for the first time that KAI1 is a target of ER-mediated gene-repression, and thus, it is downregulated in ER-positive breast cancer. Importantly, KAI1 might be reinducible by endocrine therapy with ER-antagonists in patients suffering from ER-positive breast cancer.