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Translocations fusing the strong androgen-responsive gene, TMPRSS2, with ERG or other oncogenic ETS factors may facilitate prostate cancer development. Here, we studied 18 advanced prostate cancers for ETS factor alterations, using reverse transcription-PCR and DNA and RNA array technologies, and identified putative ERG downstream gene targets from the microarray data of 410 prostate samples. Out of the 27 ETS factors, ERG was most frequently overexpressed. Seven cases showed TMPRSS2:ERG gene fusions, whereas the TMPRSS2:ETV4 fusion was seen in one case. In five out of six tumors with high ERG expression, array-CGH analysis revealed interstitial 2.8 Mb deletions between the TMPRSS2 and ERG loci, or smaller, unbalanced rearrangements. In silico analysis of the ERG gene coexpression patterns revealed an association with high expression of the histone deacetylase 1 gene, and low expression of its target genes. Furthermore, we observed increased expression of WNT-associated pathways and down-regulation of tumor necrosis factor and cell death pathways. In summary, our data indicate that the TMPRSS2:ERG translocation is common in advanced prostate cancer and occurs by virtue of unbalanced genomic rearrangements. Activation of ERG by fusion with TMPRSS2 may lead to epigenetic reprogramming, WNT signaling, and down-regulation of cell death pathways, implicating ERG in several hallmarks of cancer with potential therapeutic importance.

The progression of carcinomas is associated with the loss of epithelial morphology and a concomitant acquisition of a more mesenchymal phenotype, which in turn is thought to contribute to the invasive and/or metastatic behavior of the malignant process. Changes in the expression of cadherins, "cadherin switching," plays a critical role during embryogenesis, particularly in morphogenetic processes. Loss of E-cadherin is reported to be associated with a poor prognosis; however, thus far, evidence (R. Umbas, et al., Cancer Res. 54: 3929-3933, 1994) for up-regulation of other cadherins has only been reported in vitro, ie., we have found evidence (M. J. G. Bussemakers et al., Int. J. Cancer, 85: 446-450, 2000) for cadherin switching in prostate cancer cell lines (up-regulation of N-cadherin and cadherin-11, two mesenchymal cadherins, in cell lines that lack a functional E-cadherin-catenin adhesion complex). Here, we report on the immunohistochemical analysis of the expression of N-cadherin and cadherin-11 in human prostate cancer specimens. N-cadherin was not expressed in normal prostate tissue; however, in prostatic cancer, N-cadherin was found to be expressed in the poorly differentiated areas, which showed mainly aberrant or negative E-cadherin staining. Cadherin-11 is expressed in the stroma of all prostatic tumors, in the area where stromal and epithelial cells are found. In addition, cadherin-11 is also expressed in a dotted pattern or at the membrane of the epithelial cells of high-grade cancers. In a number of metastatic lesions, N-cadherin and cadherin-11 are expressed homogeneously. These data raise the possibility that cadherin switching plays an important role in prostate cancer metastasis.

In several cancers, including breast cancer, loss of E-cadherin expression is correlated with a loss of the epithelial phenotype and with a gain of invasiveness. Cells that have lost E-cadherin expression are either poorly invasive with a rounded phenotype, or highly invasive, with a mesenchymal phenotype. Most cells lacking E-cadherin still retain weak calcium-dependent adhesion, indicating the presence of another cadherin family member. We have now examined the expression of the mesenchymal cadherin, cadherin-11, in breast cancer cell lines. Cadherin-11 mRNA and protein, as well as a variant form, are expressed in the most invasive cell lines but not in any of the noninvasive cell lines. Cadherin-11 is localized to a detergent-soluble pool and is associated with both alpha- and beta-catenin. Immunocytochemistry shows that cadherin-11 is localized to the cell membrane at sites of cell-cell contact as well as at lamellipodia-like projections, which do not interact with other cells. These results suggest that cadherin-11 expression may be well correlated with the invasive phenotype in cancer cells and may serve as a molecular marker for the more aggressive, invasive subset of tumors. Cadherin-11 may mediate the interaction between malignant tumor cells and other cell types that normally express cadherin-11, such as stromal cells or osteoblasts or perhaps even with the surrounding extracellular matrix, thus facilitating tumor cell invasion and metastasis.

The KAI1 gene, located on human chromosome 11p11.2, suppresses tumor metastasis when expressed in certain cancer cells. To evaluate whether dysregulation of KAI1 occurs during the progression of human prostatic cancer, protein expression, mutation, and allelic loss of KAI1 were analyzed using a tissue bank of 98 primary cancers and 32 metastases. By immunohistochemical staining, high levels of KAI1 protein are detected in the epithelial but not stromal compartment of normal prostatic and benign prostatic hyperplasia tissue. In epithelial cells, KAI1 protein is expressed on the plasma membrane. KAI1 protein expression is downregulated in more than 70% of the 49 primary prostatic cancers from untreated patients. In 10 such untreated patients, down-regulation of KAI1 protein occurred in all of the lymph node metastases examined. In 15 patients with metastatic disease who had failed androgen ablation therapy, more than 90% of the primary prostatic cancers had downregulation, with 60% having no KAI1 protein expression. Primers derived from the sequences flanking each exon of KAI1 were used to analyze KAI1 mutation and allelic loss by the method of PLR-single-strand conformational polymorphism. Using this method, no point mutation or allelic loss was detected in metastases from 10 patients. No allelic loss was detected in an additional 34 primary and 12 lymph node metastases via microsatellite analysis using the marker D11S1344, which is located in the region of KAI1. These results demonstrate that KAI1 protein expression is consistently down-regulated during the progression of human prostatic cancer and that this down-regulation does not commonly involve either mutation or allelic loss of the KAI1 gene.

Loss of E-cadherin-mediated adhesion is an important step in the progression of many carcinomas. In model systems, it has been shown that cadherin function requires not only proper E-cadherin expression but also its linkage to the cytoskeleton through catenins. Hence, defects in catenins may cause defective E-cadherin function, and catenins as well as E-cadherin might constitute prognostic indicators. Here, we extend our previous study on E-cadherin in bladder cancer (Cancer Res., 53: 3241-3245, 1993). We have evaluated the expression of E-cadherin-associated cytoplasmic molecules (alpha-, beta-, and gamma-catenins and p120cas) to clarify whether or not the pattern of their expression could provide additional prognostic information beyond that from E-cadherin alone. Forty-eight frozen bladder tumor specimens and 9 samples of normal urothelium were studied by immunohistochemistry. A discrepancy between the E-cadherin and catenin expression pattern was seen in 20.8% of cases. Abnormal expression of each molecule is significantly correlated with tumor grade (P < 0.01) and stage (P < 0.01). Reduced expression of all of the molecules correlates with poor survival (P < 0.01 for each variable). Proportional hazard regression analysis showed that beta-catenin, E-cadherin, and alpha-catenin have strong predictive value, whereas plakoglobin and p120cas have a somewhat lower predictive value. Within patients with invasive tumors, those with a normal staining for either E-cadherin, alpha-catenin, or beta-catenin show a trend toward better survival. However, the difference in survival is significant only for E-cadherin (P < 0.05). Thus, beta-catenin, E-cadherin, and alpha-catenin have similar prognostic values. Therefore, from a practical point of view, the expression of any of these proteins can be of prognostic value for patients with bladder cancer.

E-cadherin is an intercellular adhesion protein expressed by most epithelia. Decreased expression of E-cadherin correlates with tumor aggressiveness in most carcinomas. In renal cell carcinoma (RCC), however, this correlation is not well established and the prevalence of negative tumors is higher than in other carcinomas. Our immunofluorescence study of alpha-catenin expression in 20 RCC cell lines revealed a typical honeycomb staining pattern in all of the lines, whereas only six expressed E-cadherin. This suggested that other cadherins are expressed in RCC lines. Indeed, immunoprecipitation with an anti-alpha-catenin antibody resulted in coprecipitation of proteins of Mr 125,000-135,000. Using Western blot, these proteins react with a pan-cadherin antibody. To identify these cadherin related proteins, RT-PCR using degenerated primers and sequence comparisons was carried out. We then assessed the expression of the identified cadherins. N-cadherin mRNA was present in all cell lines; and cadherin 6 mRNA was seen in 16 lines. Cadherin 11 (mRNA) and E-cadherin (protein) were expressed in five and six lines, respectively. A cadherin 4 transcript was observed in only one line, whereas no P-cadherin protein could be detected. Expression of the four main cadherins was also found in normal kidney (two samples tested) and RCC specimens (four samples). Thus, RCC and normal kidney express a complex set of cadherins.

Decreased levels of the cell-cell adhesion molecule E-cadherin are associated with loss of differentiation in a number of human carcinomas. However, the value of E-cadherin as a prognostic marker in these cancers is largely undetermined. A previous study of E-cadherin levels in prostate cancer revealed that almost 50% of tumors examined had reduced or absent levels of this protein (Umbas et al., Cancer Res., 52: 5104-5109, 1992). To determine the potential prognostic significance of this finding, prostate cancer specimens from 89 patients were evaluated immunohistochemically for E-cadherin expression, and the results were related to histopathological grade, tumor stage, presence of metastases, and survival. As previously observed, a significant inverse correlation was found between E-cadherin expression and tumor grade. Importantly, we also found significant correlations between E-cadherin expression and tumor stage and overall survival. Sixty-three percent of the tumors that extended beyond the prostate capsule (T3-4) versus 33% of the tumors confined to the prostate (T1-2) had aberrant expression (chi 2 = 8.1, P < 0.005). Seventy-six percent of the primary tumors from patients that presented with metastases showed aberrant staining compared to 32% from patients without metastases (chi 2 = 14.9; P < 0.001). The life table analysis showed a significantly higher survival rate for patients with normal staining compared to patients with aberrant expression (chi 2 = 20.4, P < 0.001 by log rank test). Moreover, abnormal expression of E-cadherin correlated significantly with progression after radical prostatectomy (P < 0.005). These results suggest that E-cadherin expression can serve as a prognostic indicator for the biological potential of prostate cancer.

In a previous study using the Dunning rat prostate cancer model, we found high mobility group protein I-(Y) [HMG-I(Y)] to be overexpressed in metastatic tumor lines when compared to nonmetastatic lines. Hence, overexpression of this 12-kDa non-histone chromosomal protein may be associated with tumor progression. Firstly, by Northern analysis we showed that HMG-I(Y) expression increases in high grade prostate tumors. These studies, however, required fresh material, and clinical follow-up was limited. To overcome this problem paraffin-embedded material must be made amenable for determination of HMG-I(Y) expression in retrospective studies. RNA in situ hybridization enables the evaluation of mRNA levels in such material. We studied tumors from 71 patients with prostate cancer. The microscopic analysis of each sample included: (a) hybridization on sections with sense HMG-I(Y) and (b) 28S rRNA probes (nonspecific signal); (c) hybridization with antisense 28S rRNA (RNA preservation); (d) hybridization with an antisense HMG-I(Y) probe [quantification of HMG-I(Y) mRNA in the expressing areas]. Data were quantified using an image analysis system. High expression of HMG-I(Y) was observed in regions with high Gleason grade (4 and 5); whereas in lesions of Gleason grade 3, both weak and no expression was observed. In areas of grade 1 and 2, as well as in normal glands, low or no expression was found. We conclude that HMG-I(Y) expression assessed by RNA in situ hybridization is related to tumor differentiation in prostate cancer. These findings indicate that HMG-I(Y) expression may be a marker in prostate cancer diagnosis, and the possible clinical implication of expression of this gene in malignancy is discussed in this report.

E-cadherin, an intercellular adhesion molecule, has been shown to behave like an invasion suppressor gene in vitro. This may explain the inverse relation between expression of E-cadherin and tumor grade that was found in certain cancers. We therefore examined E-cadherin expression in bladder cancer samples from patients with known clinical follow-up. Forty-nine snap-frozen specimens (24 superficial and 25 invasive tumors) and 4 samples of normal urothelium were retrospectively analyzed with anti-E-cadherin monoclonal antibodies. In normal urothelium E-cadherin is expressed homogeneously with a typical membranous staining at cell-cell borders. Decreased expression is found in 5 of 24 superficial tumors and in 19 of 25 invasive cancers. Completely negative tumors are infrequent (4 cases). Most of the time a heterogeneous staining, which may correspond to an unstable E-cadherin expression during tumor development, is seen. Decreased E-cadherin expression correlates with both increased grade and stage (chi 2 = 9.5, P < 0.01, and chi 2 = 14.9, P < 0.005, respectively). More importantly, abnormal E-cadherin expression correlates with shorter survival (log rank test: chi 2 = 16.5, P < 0.001). In keeping with its in vitro invasion suppressor function, decreased E-cadherin expression correlates with the clinical aggressiveness of bladder tumors. This is the first report of E-cadherin as a marker with prognostic value. This parameter must now be tested in a large prospective study to assess its precise clinical relevance.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression is increased in Dunning R-3327 rat prostatic adenocarcinoma cell lines relative to normal rat ventral prostate tissue. GAPDH expression closely correlates with cell motility of Dunning prostate cancer cell lines and accurately distinguishes cell lines with high metastatic potential from those with low metastatic potential. Increased GAPDH expression in the cancer cell lines is not simply related to increased growth rate, since rapidly proliferating normal prostate tissue did not exhibit elevated GAPDH expression.

In the epithelium of secretory acini of the prostate two different cell types can be discriminated on the basis of localization, morphology, and degree of differentiation, the luminal and basal cells. The possibility of a developmental relationship between basal and luminal cells has been a subject of interest in several studies. According to the stem cell model at least three cell types, i.e., stem, amplifying, and transit cells, can be discriminated in the epithelium of prostate secretory acini. We previously reported that in the process of degeneration and regeneration in normal rat prostate a population of cells could be identified as candidates for the amplifying cells. These cells showed a keratin expression profile intermediate between those of basal and luminal cells. We now show, by using keratin antibodies, that also in normal human prostate at least three subpopulations of cells can be identified, one of them putatively representing amplifying cells as defined in the stem cell model. Furthermore, these antibodies were used to obtain a better insight into the different cell types involved in the etiology and progression of prostatic carcinoma. Both primary and hormone-independent prostatic tumors were investigated. Our results indicated that the candidate stem cell population was absent in prostatic carcinoma. Unlike earlier reports on the unique presence of cells with luminal characteristics in prostatic carcinoma, we identified also a population of cells coexpressing basal and luminal cell-type cytokeratins in primary and hormone-independent prostatic carcinoma. Since amplifying cells are defined in the stem cell model as precursors of transit (luminal) cells in the hierarchical pathway of prostatic epithelium differentiation, we postulate that on the basis of the keratin expression profile this subpopulation is most likely the target for neoplastic transformation.

E-cadherin is a Ca(2+)-dependent cell adhesion molecule which plays an important role in normal growth and development via mediation of homotypic, homophilic cell-cell interaction. Recent studies suggest that E-cadherin may be important in neoplastic progression as well, particularly as a suppressor of invasion. We have previously demonstrated that the invasive phenotype of rat prostate cancer cells is associated with the decreased expression of E-cadherin (M. J. G. Bussemakers, R. J. A. Van Moorselaar, L. A. Giroldi, T. Ichikawa, J. T. Isaacs, F. M. J. Debruyne, and J. A. Schalken, Cancer Res., 52:2916-2922, 1992). This is of particular interest, since the locus to which the human E-cadherin gene is mapped is frequently involved in allelic loss in prostate cancer (B. S. Carter, C. M. Ewing, W. S. Ward, B. F. Treiger, T. W. Aalders, J. A. Schalken, J. I. Epstein, and W. B. Isaacs, Proc. Natl. Acad. Sci. USA, 87:8751-8755, 1990; U. S. Bergerheim, K. Kunimi, V. P. Collins, and P. Ekman, Genes, Chromosomes Cancer, 3: 215-220, 1991). Impaired E-cadherin function is likely to be associated with aberrant expression of the protein. We therefore analyzed E-cadherin expression in situ by immunohistochemistry in nonmalignant and malignant specimens of human prostatic tissue. Of 92 tumor samples of either primary or metastatic deposits of prostate cancer, 46 had reduced or absent E-cadherin staining when compared to nomalignant prostate, which uniformly stained strongly positive. There was a statistically significant correlation between the decreased expression of E-cadherin and loss of tumor differentiation. Additionally, certain tumors within a histologically similar group could be distinguished by the presence of mixed populations of E-cadherin-negative and -positive cells. The percentage of tumors with aberrant E-cadherin staining increased when clinically localized tumors were compared to either tumors with extensive local progression or metastatic deposits of prostate cancer, suggesting a correlation between loss of E-cadherin and tumor progression. Taken together, these findings suggest that further exploration of E-cadherin as a candidate invasion suppressor molecule in human prostate cancer is warranted.

Cadherins represent a family of Ca(2+)-dependent cell adhesion molecules involved in homotypic, homophilic cell-cell interactions. Recent studies have shown that the cadherins can play a role in invasive and metastatic behavior. Using the established Dunning R-3327 model system of serially transplantable rat prostate cancers, the expression of E- and P-cadherin in rat prostatic cancer was studied. Analysis within this system demonstrated that whereas E-cadherin was expressed in the normal rat prostate and the well- or moderately differentiated, noninvasive Dunning tumors, no expression, either at the mRNA or at the protein level, could be detected in the invasive sublines. Since not all invasive Dunning tumors studied have metastatic ability, these results suggest that a decreased expression of E-cadherin is correlated with invasive behavior rather than with metastatic ability. Recently, genetic instability occurred in an animal bearing the well differentiated, androgen-responsive, slow growing, nonmetastatic Dunning R-3327-H rat prostate cancer resulting in the progression to an anaplastic, androgen-independent, fast growing, highly metastatic state. This spontaneously arising tumor, termed the AT6 subline, in its original host was heterogeneously composed of both a well differentiated and an anaplastic population of cancer cells in which areas of squamous cell differentiation were occasionally observed. The original animal bearing this heterogeneous AT6 cancer developed multiple metastases, the lung metastases being heterogeneously composed of anaplastic and squamous cell populations. Cytogenetic analysis demonstrated that the lung metastases were derived from a specific subpopulation of cancer cells present in the original AT6 primary tumor. Immunohistochemical studies demonstrated that only the area of lung metastases displaying squamous morphology were positive for E-cadherin. In contrast, the anaplastic areas of the lung metastases and the metastases in other organs were E-cadherin negative. By the first passage of the AT6 tumor only the anaplastic cells were present and no detectable E-cadherin mRNA or protein was found in the primary tumor and metastatic deposits. These results suggest that a decreased expression of E-cadherin is associated with the progression of prostatic cancer.

We have examined the antitumor effects of rat gamma-interferon (IFN-gamma) and human tumor necrosis factor alpha (TNF) against androgen-dependent and -independent Dunning rat prostatic tumors. In vitro studies, using the double layer soft agar assay, showed a very limited antiproliferative activity of the drugs in the dose range tested (1-1000 units IFN-gamma and/or 1-1000 ng TNF/dish). For in vivo studies IFN-gamma and TNF were administered s.c., peritumorally. IFN-gamma was given 3 times/week, 8,000 or 80,000 units/rat, and TNF 5 times/week, 10 or 100 micrograms/rat. IFN-gamma and TNF monotherapy were not significantly effective in inhibiting tumor growth, except for IFN-gamma against the androgen-independent MatLyLu tumor. Combinations of IFN-gamma and TNF had synergistic antiproliferative effects against all four tumor lines tested; however, complete growth inhibitions could not be achieved. Survival studies showed significant increase in survival of tumor-bearing rats.

One of the major problems in the diagnosis of localized prostatic tumors is to predict the aggressiveness of an individual tumor, which is presumably associated with chance to progression. In an attempt to find molecular markers that are specific for aggressive prostatic cancer cells, we compared steady-state mRNA levels of progressionally related prostatic tumors. The Dunning R-3327-H subline, a relatively benign rat prostatic tumor, was compared to the therefrom derived highly aggressive MatLyLu tumor by differential hybridization analysis. The differential screening revealed 26 complementary DNA clones that detected transcripts overexpressed in MatLyLu. Upon further screening on the entire panel of Dunning R-3327 sublines, it appeared that three clones (pBUS1, pBUS19, and pBUS30), detected transcripts specifically expressed in metastatic rat prostatic tumors. The expression pattern of pBUS19 and pBUS30 suggested a relation between these complementary DNAs. Nucleotide sequence analysis, however, could not yet substantiate this. Computer-assisted comparison of the DNA sequences revealed the presence of rat long terminal repeat-like repetitive elements in pBUS19. The differential expression of repetitive elements in progressionally related tumors is interesting, yet similar findings have not been reported in human malignancies. Nucleotide sequence analysis of pBUS1 indicated that this clone is identical or related to high mobility group protein I(Y), a non-histone nuclear protein. From recent studies it appeared that this protein might be implicated in replication and/or transcription processes and is induced in fast proliferating/undifferentiated cells. The overexpression of high mobility group protein I(Y) correlates rather with metastatic ability than with growth rate; hence it may serve as a valuable marker to identify progressionally advanced prostate cancer cells.

The protein designated 7B2 is a recently discovered pituitary polypeptide which is selectively expressed in cells containing secretory granules, such as neurons and endocrine cells. Northern blot analysis of 7B2 gene expression in small cell lung carcinoma (SCLC) cell lines revealed that 7B2 was expressed in all nine cell lines of the classic type tested, but in six of seven SCLC cell lines of the variant type, 7B2 expression could not be detected. In only one of four non-SCLC cell lines tested, 7B2 was expressed. Furthermore, in 16 primary human non-SCLCs, no or only very low expression of 7B2 was found. In the eight primary human SCLCs tested, expression of 7B2 appeared variable: three exhibited a high level of expression; three a low level; while in two cases, expression was very low or not detectable at all. Finally, the three carcinoid tumors tested expressed very high levels of 7B2 mRNA. These data indicate that the 7B2 gene is a useful marker not only to discriminate between classic and variant types of SCLC cell lines, but also in human lung cancer diagnosis.

To identify genes whose expression is down modulated in the process of metastasis, gene expression was analyzed in cell lines derived from Dunning R-3327 rat prostatic tumor sublines. A complementary DNA (cDNA) library from the anaplastic nonmetastasizing subline AT-1 was used for a differential hybridization analysis, using probes derived from mRNAs of the AT-1 and the metastasizing MAT-LyLu subline. In this way 14 cDNA clones were isolated representing 6 differentially expressed genes. The expression levels in a panel of tumor sublines measured with these cDNA clones were tested for correlation with the anaplastic non-metastasizing phenotype. One cDNA clone, designated pSE-1, whose expression was high in all tested sublines with that phenotype, appeared to represent the gene for fibronectin. To further investigate the down modulation of this gene, we studied its expression in AT-2 (anaplastic, nonmetastasizing tumor) and lines derived therefrom that exhibited a high metastatic potential after transfection with the v-Ha-ras oncogene. In the genetically manipulated metastasizing tumor sublines, fibronectin mRNA levels were approximately 4- to 8-fold lowered compared to the nonmetastasizing parental AT-2 line.