Relationship between expression of the KAI1 metastasis suppressor and other markers of advanced bladder cancer

Endocytosis: a pivotal pathway for regulating metastasis

A potentially important aspect in the regulation of tumour metastasis is endocytosis. This process consists of internalisation of cell-surface receptors via pinocytosis, phagocytosis or receptor-mediated endocytosis, the latter of which includes clathrin-, caveolae- and non-clathrin or caveolae-mediated mechanisms. Endocytosis then progresses through several intracellular compartments for sorting and routing of cargo, ending in lysosomal degradation, recycling back to the cell surface or secretion. Multiple endocytic proteins are dysregulated in cancer and regulate tumour metastasis, particularly migration and invasion. Importantly, four metastasis suppressor genes function in part by regulating endocytosis, namely, the NME, KAI, MTSS1 and KISS1 pathways. Data on metastasis suppressors identify a new point of dysregulation operative in tumour metastasis, alterations in signalling through endocytosis. This review will focus on the multicomponent process of endocytosis affecting different steps of metastasis and how metastatic-suppressor genes use endocytosis to suppress metastasis.

Gene expression analysis of human prostate cell lines with and without tumor metastasis suppressor CD82

BACKGROUND

Tetraspanin CD82 is a tumor metastasis suppressor that is known to down regulate in various metastatic cancers. However, the exact mechanism by which CD82 prevents cancer metastasis is unclear. This study aims to identify genes that are regulated by CD82 in human prostate cell lines.

METHODS

We used whole human genome microarray to obtain gene expression profiles in a normal prostate epithelial cell line that expressed CD82 (PrEC-31) and a metastatic prostate cell line that does not express CD82 (PC3). Then, siRNA silencing was used to knock down CD82 expression in PrEC-31 while CD82 was re-expressed in PC3 to acquire differentially-expressed genes in the respective cell line.

RESULTS

Differentially-expressed genes with a P < 0.05 were identified in 3 data sets: PrEC-31 (+CD82) vs PrEC-31(-CD82), PC3-57 (+CD82) vs. PC3-5 V (-CD82), and PC3-29 (+CD82) vs. PC3-5 V (-CD82). Top 25 gene lists did not show overlap within the data sets, except (CALB1) the calcium binding protein calbindin 1 which was significantly up-regulated (2.8 log fold change) in PrEC-31 and PC3-29 cells that expressed CD82. Other most significantly up-regulated genes included serine peptidase inhibitor kazal type 1 (SPINK1) and polypeptide N-acetyl galactosaminyl transferase 14 (GALNT14) and most down-regulated genes included C-X-C motif chemokine ligand 14 (CXCL14), urotensin 2 (UTS2D), and fibroblast growth factor 13 (FGF13). Pathways related with cell proliferation and angiogenesis, migration and invasion, cell death, cell cycle, signal transduction, and metabolism were highly enriched in cells that lack CD82 expression. Expression of two mutually inclusive genes in top 100 gene lists of all data sets, runt-related transcription factor (RUNX3) and trefoil factor 3 (TFF3), could be validated with qRT-PCR.

CONCLUSION

Identification of genes and pathways regulated by CD82 in this study may provide additional insights into the role that CD82 plays in prostate tumor progression and metastasis, as well as identify potential targets for therapeutic intervention.

Up-regulation of DRAM2 promotes tolerance of bladder transitional cell carcinoma to gemcitabine

INTRODUCTION

Bladder transitional cell carcinoma (BTCC) is one of the most prevalent human malignant diseases. Gemcitabine is commonly applied in the treatment of BTCC while acquired gemcitabine resistance has caused a severe impediment to recovery. This study aimed to investigate the function of DRAM2 in regulating gemcitabine resistance of BTCC.

MATERIAL AND METHODS

GSE77883 was introduced to screen out the differentially expressed autophagy-related genes in T24 cells and gemcitabine-resistant T24-GEM cells. After establishing T24-GEM cells ourselves, aberrant expression of DRAM2 was detected by qRT-PCR and Western blot. After stably manipulating the expression of DRAM2 in T24 and T24-GEM cells, the changes of cell biological functions under gemcitabine treatment were compared, including cell viability, apoptosis and autophagy, using colony formation, flow cytometry and electron microscopy respectively.

RESULTS

DRAM2 was up-regulated in gemcitabine-resistant T24-GEM cells. Silencing of DRAM2 in T24-GEM cells inhibited the cell autophagy induced by treatment with gemcitabine and contributed to attenuated gemcitabine resistance. Also, overexpression of DRAM2 in T24 cells enhanced the autophagy, strengthened the chemoresistance and decreased the cell apoptosis rate under the treatment with gemcitabine.

CONCLUSIONS

Our data suggested that downregulation of DRAM2 rescued the sensitivity of T24-GEM cells to gemcitabine, providing an appropriate therapeutic target for BTCC treatment.

Suppression of C6 gliomas via application of rat hyperplasia gene

BACKGROUND

Among all neurological tumors, tumor incidence of the neuroepithelial tissue is the highest, where 50% are gliomas. Treatment for gliomas has traditionally included surgery and adjuvant therapy. With advancements in medicine, gene therapy has entered the clinical setting, in which control of tumor growth, tumor volume and decrease of supply of blood to the tumor have been observed. Rat hyperplasia suppressor gene (rHSG) has been proven to inhibit the injury-mediated proliferation of vascular smooth muscle cells.

METHODS

A recombinant adenovirus, Adv-rHSG-GFP, was constructed and characterized by in vitro and in vivo studies. The function of rHSG on cell proliferation was determined in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) exclusion assay and plate clone formation, while a C6/Sprague Dawley rat glioma model was established to observe the effect of rHSG in vivo.

RESULTS

Overexpression of rHSG displayed a strong effect on suppressing C6 cells proliferation in vitro and growth of glioma in vivo, which suggests the use of rHSG as a possible treatment strategy for glioma. p21Cip1, p27Kip1 and proliferating cell nuclear antigen were found to be involved in the tumor suppression mechanism of rHSG.

CONCLUSIONS

rHSG can markedly inhibit of the growth of rat glioma cells. The suppression mechanism of rHSG may be related to cell cycle regulation, which shows that rHSG is a potential therapeutic target of glioma tumor. This preclinical study supports a further in-depth study on the effect of rHSG on cell proliferation, migration and change in the extracellular matrix component of glioma cells.

Quantitative proteomics of fractionated membrane and lumen exosome proteins from isogenic metastatic and nonmetastatic bladder cancer cells reveal differential expression of EMT factors

Cancer cells secrete soluble factors and various extracellular vesicles, including exosomes, into their tissue microenvironment. The secretion of exosomes is speculated to facilitate local invasion and metastatic spread. Here, we used an in vivo metastasis model of human bladder carcinoma cell line T24 without metastatic capacity and its two isogenic derivate cell lines SLT4 and FL3, which form metastases in the lungs and liver of mice, respectively. Cultivation in CLAD1000 bioreactors rather than conventional culture flasks resulted in a 13- to 16-fold increased exosome yield and facilitated quantitative proteomics of fractionated exosomes. Exosomes from T24, SLT4, and FL3 cells were partitioned into membrane and luminal fractions and changes in protein abundance related to the gain of metastatic capacity were identified by quantitative iTRAQ proteomics. We identified several proteins linked to epithelial-mesenchymal transition, including increased abundance of vimentin and hepatoma-derived growth factor in the membrane, and casein kinase II α and annexin A2 in the lumen of exosomes, respectively, from metastatic cells. The change in exosome protein abundance correlated little, although significant for FL3 versus T24, with changes in cellular mRNA expression. Our proteomic approach may help identification of proteins in the membrane and lumen of exosomes potentially involved in the metastatic process.

Metastasis suppressor KAI1/CD82 attenuates the matrix adhesion of human prostate cancer cells by suppressing fibronectin expression and β1 integrin activation

KAI1/CD82, a tetraspanin membrane protein functions as a metastasis suppressor in many types of human cancers and has been shown to regulate cell adhesion properties. In the present study, we investigated the underlying mechanism of KAI1/CD82-mediated changes in cell adhesion to the extracellular matrix using human prostate cancer cells. We found that high KAI1/CD82 expression attenuated short-term cell adhesion to uncoated- or fibronectin-coated plates. Moreover, high KAI1/CD82 expression generated an extracellular environment unfavorable for cell adhesion as compared to low KAI1/CD82 expression, suggesting KAI1/CD82-dependent regulation of extracellular matrix (ECM) molecule(s) expression and/or secretion. Among ECM components examined, fibronectin exhibited decreased expression and secretion in high KAI1/CD82-expressing cells. Furthermore, high KAI1/CD82 expression interfered with the activation of β (1) integrin at the cell surface while total β (1) integrin levels remained unchanged, concomitant with reduced formation of focal adhesion complex and decreased bundling of actin filaments. Finally, high KAI1/CD82 expression significantly retarded cell motility in a scratch wound assay. Taken together, our results strongly suggest that KAI1/CD82 attenuates the activation of β (1) integrin, and thereby down-regulates outside-in signaling of β (1) integrin, leading to the reduction of focal adhesion formation and fibronectin expression/secretion, which subsequently interferes with cell adhesion properties and motility.

Down-regulation of TM4SF is associated with the metastatic potential of gastric carcinoma TM4SF members in gastric carcinoma

Background

The aim of this study was to clarify the clinical significance of TM4SF members CD9, CD63 and CD82 in human gastric carcinoma.

Methods

By employing RT-PCR and immunohistochemistry, we studied the expression of CD9, CD63 and CD82 in 49 paired tissue specimens of normal gastric mucosa and carcinoma. All tissues were obtained from patients who underwent curative surgery.

Results

All normal gastric epithelium and gastric ulcer tissues strongly expressed transcripts and proteins of CD9, CD63 and CD82 as compared with corresponding controls. We found a significant correlation between CD63 mRNA level and different pM statuses (P = 0.036). Carcinomas in M0 stage revealed a stronger expression of CD63 than carcinomas in M1 stage. Expression of CD9 protein was found significantly stronger in pN0, pM0 than in advanced pN stages (P = 0.03), pM1 (P = 0.013), respectively. We found the relationship between CD63 expression, gender (p = 0.09) and nodal status (p = 0.028), respectively. Additionally, advanced and metastasized tumor tissues revealed significantly down-regulated CD82 protein expression (p = 0.033 and p = 0, respectively), which correlated with the tumor pTNM stage (p = 0.001).

Conclusion

The reduction of CD9, CD63 and CD82 expression are indicators for the metastatic potential of gastric carcinoma cells. Unlike their expression in other tumor types, the constitutive expression of CD63 may indicate that this factor does play a direct role in human gastric carcinogenesis.

Metastasis suppressors in human benign prostate, intraepithelial neoplasia, and invasive cancer: their prospects as therapeutic agents

Despite advances in diagnosis and treatment of prostate cancer, development of metastases remains a major clinical challenge. Research efforts are dedicated to overcome this problem by understanding the molecular basis of the transition from benign cells to prostatic intraepithelial neoplasia (PIN), localized carcinoma, and metastatic cancer. Identification of proteins that inhibit dissemination of cancer cells will provide new perspectives to define novel therapeutics. Development of antimetastatic drugs that trigger or mimic the effect of metastasis suppressors represents new therapeutic approaches to improve patient survival. This review focuses on different biochemical and cellular functions of metastasis suppressors known to play a role in prostate carcinogenesis and progression. Ten putative metastasis suppressors implicated in prostate cancer are discussed. CD44s is decreased in both PIN and cancer; Drg-1, E-cadherin, KAI-1, RKIP, and SSeCKS show similar expression between benign epithelia and PIN, but are downregulated in invasive cancer; whereas, maspin, MKK4, Nm23 and PTEN are upregulated in PIN and downregulated in cancer. Moreover, the potential role of microRNA in prostate cancer progression, the understanding of the cellular distribution and localization of metastasis suppressors, their mechanism of action, their effect on prostate invasion and metastasis, and their potential use as therapeutics are addressed.

KAI1/CD82 decreases Rac1 expression and cell proliferation through PI3K/Akt/mTOR pathway in H1299 lung carcinoma cells

Although the KAI1/CD82 protein has been reported to inhibit cell metastasis in many studies, its mechanism of action has not yet been fully elucidated. In the present study, we investigated the possible effects of KAI1/CD82 on the metastatic phenotype in H1299 lung carcinoma cells. These studies were based on the pivotal role that the acquisition of motile phenotype plays on the initial steps of metastasis. KAI1/CD82-mediated morphological changes were observed using phase contrast microscopy. We report here, that a KAI1/CD82-induced phenotypic change was involved in the decrease of Rac1 expression and GTPase activity. However, we found that KAI1/CD82 did not regulate Rac1 mRNA levels. This suggests the existence of another regulatory mechanism of Rac1 protein maturation or activation. To identify the signaling pathway of Rac1 regulation, we investigated the PI3K/Akt/mTOR pathway, since the PI3K/Akt pathway regulates Rac1 activation and mTOR is known to play a regulatory role in protein translation. H1299/CD82-transfectants showed lower mTOR expression and cell growth than the control group. The data obtained from this study suggested that KAI1/CD82 decreased the metastatic phenotype of H1299 lung carcinoma cells by down-regulating Rac1 expression through the PI3K/Akt/mTOR pathway.

Assessing interactions between mdm-2, p53, and bcl-2 as prognostic variables in muscle-invasive bladder cancer treated with neo-adjuvant chemotherapy followed by locoregional surgical treatment

BACKGROUND

Tumor proliferation and apoptosis may be influenced by the mdm-2 gene product, which can block the antiproliferative effects of p53. bcl-2, one of a family of related genes that regulates the apoptotic pathway, exhibits a negative influence. Both individual and cooperative effects of these gene products may affect the biological behavior of primary bladder cancers and long-term outcome to standard therapy.

METHODS

This study retrospectively evaluated the association with survival of mdm-2, p53, and bcl-2 expression in 59 patients with muscle-invasive, node-negative transitional cell carcinoma (TCC) treated with neo-adjuvant chemotherapy followed by locoregional surgery. Each marker was defined as an altered phenotype if >or=20% malignant cells in the primary tumor exhibited staining; normal or minimal expression was defined as <20% cells exhibiting staining.

RESULTS

Altered mdm-2, p53, and bcl-2 expression was observed in 37%, 54%, and 46% of patients, respectively. In single marker analysis, altered p53 expression correlated with long-term survival (P = 0.05) but mdm-2 (P = 0.42) or bcl-2 (P = 0.17) did not. In the multiple-marker analysis, a prognostic index simultaneously assessing mdm-2, p53, and bcl-2 correlated with survival (P = 0.01). The 5-year survival for patients in which all markers were normally expressed was 54% compared with 25% in those with all three markers aberrantly expressed. Patients with aberrant expression of either one or two markers had an intermediate 5-year survival (49%). There was no association of molecular markers either alone or in combination with pathologic downstaging after neo-adjuvant chemotherapy.

CONCLUSION

The cooperative effects of phenotypes determined by mdm-2, p53, and bcl-2 expression may predict survival in patients with muscle-invasive TCC of the bladder.

Uroplakin Ib gene transcription in urothelial tumor cells is regulated by CpG methylation

Uroplakin Ib is a structural protein on the surface of urothelial cells. Levels of uroplakin Ib mRNA are dramatically reduced or absent in many transitional cell carcinomas, but the molecular mechanisms responsible remain undetermined. Previously, we showed that loss of uroplakin Ib expression correlated with CpG methylation of Sp1/NFkappaB-binding motifs within the proximal promoter. In this study, we show that reporter activity was completely blocked by the methylation of three CpG pairs in this promoter region. Gel shift analysis using purified proteins or nuclear extracts showed that Sp1 and NFkappaB bound to motifs encompassing two of the three CpG pairs. Interestingly, the methylation of these two CpG sites did not prevent the binding of proteins to the promoter in gel shift analyses. Additionally, mutation of these two CpGs did not affect reporter activity, but mutation of 6-bp fragment spanning each CpG partially inhibited reporter activity, suggesting that these sites were functional. A requirement for both Sp1 and NFkappaB in regulating reporter activity was confirmed in transfection experiments using plasmids expressing individual proteins. Our data suggest that the methylation of specific CpG sites can silence the uroplakin Ib promoter, at least in part, by blocking the binding of Sp1 and NFkappaB, although other factors may be involved.

KAI1/CD82, a tumor metastasis suppressor

Tetraspanin KAI1/CD82 is a wide-spectrum tumor metastasis suppressor. KAI1/CD82 suppresses tumor metastasis by primarily inhibiting cancer cell motility and invasiveness. In tetraspanin-enriched microdomain, KAI1/CD82 associates with the proteins important for cell migration such as cell adhesion molecule, growth factor receptor, and signaling molecule. Likely, KAI1/CD82 down-regulates the functions of these motility-related proteins to inhibit cell migration. The loss of KAI1/CD82 expression in invasive and metastatic cancers is due to a complex, epigenetic mechanism that probably involves transcription factors such as NFkappaB, p53, and beta-catenin.

KAI1 promoter activity is dependent on p53, junB and AP2: evidence for a possible mechanism underlying loss of KAI1 expression in cancer cells

A molecular mechanism to explain reduced KAI1 expression in invasive and metastatic tumour cells remains elusive. In this report, we extend an earlier study in bladder cells to confirm that a 76 bp region of the KAI1 promoter (residues -922 to -847), with binding motifs for p53, AP1 and AP2, is required for high level activity of a KAI1 reporter in prostate cancer cell lines. Gel shift and supershift experiments supported binding of p53, junB and heterodimers of AP2alpha/AP2gamma or AP2beta/AP2gamma to this sequence. Introduction of mutations into specific motifs demonstrated an essential requirement for p53 and junB to reporter activity, and that functional synergy between these two factors enhanced activity. A further elevation of reporter activity required AP2. Roles of individual p53, junB and AP2 proteins, as well as functional synergy between p53 and junB, were confirmed in transfection experiments. Western blotting analysis showed that an absence of wild-type p53, and/or a loss of junB and AP2 protein expression, correlated with downregulation of KAI1 mRNA levels in a series of prostate cancer cell lines. A loss of p53 function and/or expression of junB, combined with reduced expression of specific AP2 proteins may underly downregulated KAI1 expression in tumour cells.

Expression and regulation of MIM (Missing In Metastasis), a novel putative metastasis suppressor gene, and MIM-B, in bladder cancer cell lines

It has been proposed that a 356 amino acid protein encoded by the MIM (Missing In Metastasis) gene on Chromosome 8q24.1, is a bladder cancer metastasis suppressor. Recently, Machesky and colleagues [Biochem. J. 371 (2003) 463] identified MIM-B, a 759 amino acid protein, of which the C-terminal 356 amino acids are almost identical to MIM. Importantly, PCR primers and Northern Blotting probes used in the studies of MIM in bladder cancer did not distinguish between sequences specific for MIM or MIM-B, thus the importance of either protein to bladder cancer remains unclear. We have used primer sequences specific for either MIM or MIM-B to explore the possible functional significance of MIM and MIM-B to bladder cancer cell behaviour. We have compared MIM and MIM-B mRNA levels in a non-tumourigenic, non-invasive, transformed uro-epithelial cell line versus 15 bladder cancer cell lines of differing in vitro invasive abilities, as well as in five cell lines clonally isolated from the BL17/2 bladder tumour cell line, whose in vitro and in vivo invasive abilities have been determined. MIM and MIM-B mRNA levels varied widely between cell lines. Down-regulation of MIM and MIM-B occurred in 6/15 (40%) lines but lines showing down-regulation differed between MIM and MIM-B. Reduced levels of MIM and MIM-B in BL17/2 were further reduced in 2/5 (40%) sublines (MIM and MIM-B). Importantly, there was no association between MIM or MIM-B expression and invasive behaviour in vivo or in vitro. Treatment of representative cell lines with 5-aza-2-deoxycytidine failed to induce MIM or MIM-B expression. Furthermore, there was no association between MIM or MIM-B mRNA levels and p53 functional status. Our data indicate that down-regulation of MIM and/or MIM-B expression can occur in bladder cancer cell lines but is not associated with increased invasive behaviour. Our data also suggest that in those cell lines with reduced levels of MIM and MIM-B mRNA, down-regulation is unlikely to be due to promoter hypermethylation or loss of p53 function.

Decreased expression of KAI1 metastasis suppressor gene is a recurrence predictor in primary pTa and pT1 urothelial bladder carcinoma

OBJECTIVE

To examine the expression of the KAI1 metastasis suppressor gene and to evaluate its relationship with tumor recurrence in primary pTa and pT1 urothelial bladder carcinoma.

METHODS

Samples were obtained from 87 patients after transurethral resection (TUR). Tumor stage and grade were reviewed in 33 patients with pTa and in 54 patients with pT1, with a mean follow-up time of 47.4 +/- 30.1 months. The KAI1 protein immunohistochemical assay was performed. Prognosis was analyzed using the Kaplan-Meier method and Cox's proportional hazards model. Correlation between KAI1 expression and recurrence according to each clinicopathological factor was comparatively evaluated using the chi-squared test.

RESULTS

Decreased expression of KAI1 protein failed to reach statistical significance for stage (P = 0.25) or morphology of tumor stem (P = 0.19), but it was significantly related to tumor size (P = 0.016). The recurrence-free 5-year survival rates of the group with decreased KAI1 expression was 69.7%, which was significantly higher than the 22.2% for the KAI1-positive group (P < 0.0001). In univariate and multivariate analyses, decreased expression of KAI1 protein, stage pT1, tumor size >3 cm and sessile tumors were independent prognosis factors of recurrence. Despite the lower recurrence rate expected by considering only the clinicopathological factors, decreased KAI1 expression was able to identify the group with a high risk of recurrence.

CONCLUSIONS

Downregulated KAI1 expression in bladder tumors tends to relate to stage and morphology of the tumor stem and was significantly correlated to tumor size. Decreased expression of KAI1 was associated with the degree of invasiveness and progression of the cancer and was an independent prognostic factor of recurrence in primary pTa and pT1 urothelial bladder carcinoma.

Downregulation of KAI1 mRNA in localised prostate cancer and its bony metastases does not correlate with p53 overexpression

Recent data have proposed that transcription of the KAI1 metastasis suppressor gene is directly mediated by p53 and that loss of KAI1 expression in advanced prostate cancer is simply due to loss of p53 function after mutation. To investigate this possibility, we have examined KAI1 mRNA (by in situ hybridisation) and p53 protein expression (by immunohistochemistry) as an indicator of wildtype or mutant p53, in a series of 77 paraffin-embedded prostate tissue samples, including post-mortem normal prostates (2), benign prostatic hyperplasia (10), localised cancer (grades 4-6, 25; grades 7-9, 21) and prostate-derived bony metastases (19). Overall, we confirmed that expression of KAI1 mRNA decreased from normal tissue, through localised cancer to bony metastases (P=0.055, tending to significance), while levels of p53 staining significantly increased with cancer progression (P=0.046). These were consistent with the possibility that loss of p53 function might be responsible for loss of KAI1 mRNA. However, by close examination of KAI1 and p53 in adjacent tissue sections, we found no correlation between decreased levels of KAI1 mRNA and overexpression of p53 protein (P=0.497). In addition, high levels of KAI1 mRNA could be identified in samples irrespective of p53 staining. Our data suggest that mutation of p53 is independent of the loss of KAI1 mRNA, and do not support a role for p53 in regulating the expression of KAI1.

KAI1 expression in thyroid neoplasms: its linkage with clinicopathologic features in papillary carcinoma

KAI1 is a metastasis suppressor gene located on human chromosome 11p11.2. Previous studies have shown that the down-regulation of KAI1 mRNA and decreased expression of its gene product are significantly linked to carcinoma progression, including metastatic ability. In this study, we investigated KAI1 protein expression in thyroid neoplasms. KAI1 overexpression was observed in 64.0% of papillary carcinoma cases, and the incidence was significantly higher than in cases of follicular carcinoma (20.0%) (p = 0.0001). In papillary carcinomas, decreased KAI1 expression was frequently observed in cases invading beyond the thyroid capsule (p = 0.001), as well as in lymph node metastases (p = 0.0047) and poorly differentiated lesions (p = 0.0299). Furthermore, in anaplastic carcinoma, the incidence of KAI1 overexpression was lower than in papillary carcinoma (p < 0.0001), and only 4.2% of the cases overexpressed this gene. These results suggest that KAI1 down-regulation is significantly related to the progression of papillary carcinoma, including lymph node metastasis, and its anaplastic transformation.

KAI1/CD82 protein expression in primary prostate cancer and in BPH associated with cancer

Current prognostic methods in primary prostate cancer cannot accurately identify patients with clinically significant disease at highest risk of developing metastases. This study examined KAI1/CD82 metastasis suppressor expression by quantitative immunohistochemical analysis of benign prostatic hyperplasia (BPH) and prostate cancer specimens. Altogether, prostate cancers exhibited significant KAI1 overexpression compared to BPH not associated with cancer (P = 0.022). Increased KAI1 expression in well and moderately differentiated cancers, above levels seen in BPH, with decreased expression in poorly differentiated cancers was observed. Interestingly, KAI1 expression in BPH associated with cancers was significantly higher than in BPH not associated with cancer (P = 0.009). Thus, KAI1 overexpression may restrain onset and early stage prostate cancer development, whilst its loss may predispose the patient to more aggressive cancer behaviour. Altered KAI1 expression in prostate cancers and BPH associated with cancer may have important diagnostic roles.

Identification of regulatory regions within the KAI1 promoter: a role for binding of AP1, AP2 and p53

The mechanism underlying loss of KAI1 gene expression in invasive and metastatic tumour cells is unknown. A possible scenario could involve altered expression or function of protein factors normally involved in regulating KAI1 transcription. To explore this possibility, we have initiated a study to characterise regulatory elements of the KAI1 promoter, using as a model, two bladder cancer cell lines (BL13 and HT1376) expressing high levels of endogenous KAI1 messenger RNA (mRNA). Transfection experiments using reporter plasmids with progressive KAI1 promoter deletions, identified a 76 bp region upstream of the transcription initiation site which contained putative binding motifs for AP2, p53 and AP1, as essential for reporter activity. DNA-binding studies using nuclear extracts from both cell lines, showed that AP1 and AP2 formed specific complexes with oligonucleotides containing KAI1 promoter motifs. Mutation of either motif abrogated reporter activity and abolished specific complex formation. In BL13 cells (endogenous wildtype p53), but not in HT1376 cells (endogenous mutant p53), mutation of the p53-binding motif also abrogated reporter activity and abolished specific complex formation in gel shift assays. These data suggested that a combination of AP2, p53 and AP1 binding to specific motifs within the KAI1 promoter might be required for high level promoter activity and that loss of expression or function of these factors might contribute to loss of KAI1 expression in invasive tumours and tumour cell lines. To explore this possibility, we examined levels of these proteins in nuclear extracts of BL13 and HT1376, as well as three bladder cancer cell lines which expressed little or no KAI1 mRNA. Our data suggested that a loss of KAI1 mRNA was not simply due to absence of AP2, AP1 or p53 expression.

Frequent low level expression in Ewing sarcoma family tumors and widespread absence of the metastasis suppressor KAI1/CD82 in neuroblastoma

The transmembrane 4 superfamily member KAI1/CD82, a metastasis suppressor, is correlated inversely with the progression and invasion of several tumors. It is capable of inhibiting metastasis without affecting tumorigenicity per se. KAI1/CD82 expression is down-regulated in the progression of common solid epithelial tumors of adulthood. Mutation of p53 is suggested to be involved in the modulation of KAI1. As little is known about its expression and possible prognostic impact in pediatric tumors, we investigated KAI1/CD82 expression in cell lines and primary tumor samples from pediatric tumors of neuroectodermal origin, neuroblastoma and Ewing's sarcoma family tumor. Twenty-four of 29 Ewing's sarcoma family tumor cell lines, independent of p53 status, showed KAI1 mRNA positivity by reverse transcription-PCR analysis in contrast to zero of eight neuroblastoma cell lines. Among 13 primary Ewing's sarcoma family tumor samples from patients with different disease extension, KAI1 mRNA expression was low as detected by reverse transcription-PCR. Twenty of 30 primary neuroblastoma specimens were KAI1-negative by immunofluorescence analysis whereas the remaining 10 gave weak to moderate staining patterns. There was no apparent correlation of KAI1 expression with any clinical or genetic features of the patients whose tumor samples were studied. Consequently, KAI1 may not be of prognostic relevance in this group of tumors although there may be some role for KAI1 modulation in the biology of these neuroectodermal tumors.

Relationship between expression of KAI1 metastasis suppressor gene, mRNA levels and p53 in human bladder and prostate cancer cell lines

The molecular basis for the loss of KAI1 expression in invasive and metastatic tumors and tumor cell lines is not understood. Recently, identification of a sequence with homology to the consensus p53-binding motif in the promoter of the KAI1 metastasis suppressor gene, has led to a proposal that transcriptional regulation by p53 controls expression of KAI1, and that a dramatic down-regulation of KAI1 mRNA levels in invasive tumors and many tumor cell lines, is directly due to loss of p53 function. We have tested this hypothesis by assessing KAI1 mRNA levels in a series of 22 cell lines derived from bladder and prostate cancers, in which we confirmed the p53 gene sequence and characterized the functional status of the endogenous p53 protein. We anticipated that cell lines expressing p53 capable of transactivation should express high levels of KAI1 mRNA compared with cell lines expressing defective p53, or which were p53-null. KAI1 mRNA levels were determined by northern analysis using a full-length KAI1 cDNA probe, and varied widely between cell lines examined. However, there was no association between these levels and p53 status. Furthermore, transfection of representative cell lines with wild-type p53, or exposure to DNA damaging agents, had no effect on KAI1 mRNA levels. Our data suggest that p53 is not a major factor regulating levels of KAI1 mRNA in bladder and prostate cancer cell lines.

Methylation of a CpG island within the promoter region of the KAI1 metastasis suppressor gene is not responsible for down-regulation of KAI1 expression in invasive cancers or cancer cell lines

The molecular basis for downregulation of the KAI1 metastasis suppressor gene in invasive and metastatic human cancers is unknown. We have used bisulphite methylation analysis of DNA from paraffin-embedded invasive bladder tumour samples and from bladder cancer cell lines to determine if hypermethylation of a CpG island within the KAI1 promoter is responsible for this effect. Representative invasive tumour cell lines were also exposed to 5-aza-2-deoxycytidine. We found no evidence for hypermethylation of the CpG island and suggest that mechanisms other than promoter hypermethylation are responsible for reduced KAI1 expression in invasive bladder tumours and tumour cell lines.

Inverse correlation between KAI1 mRNA levels and invasive behaviour in bladder cancer cell lines

We have previously shown that levels of KAI1 mRNA are dramatically reduced in invasive human bladder cancers. To further investigate the role of KAI1 in bladder cancer, we have examined the relationship between KAI1 mRNA levels and cell behaviour in 18 bladder cancer cell lines and a virus-transformed uro-epithelial cell line. We found that low KAI1 mRNA levels correlated with increased in vitro invasive ability, reduced Ca(2+)-dependent and -independent cell-cell adhesion and reduced adhesion to fibronectin. These data support the idea that loss of KAI1 expression is an important factor in tumour cell invasive behaviour.