Prognostic relevance of Bcl-2 overexpression in surgically treated prostate cancer is not caused by increased copy number or translocation of the gene

BACKGROUND

Overexpression of anti-apoptotic Bcl-2 plays a role in prostate cancer progression, particularly in transformation to androgen-independent disease. Androgen-independent prostate cancers have been shown to harbor Bcl-2 gene copy number gains frequently suggesting that this genetic alteration might play a role in Bcl-2 overexpression. The relation of Bcl-2 overexpression and copy number gains or translocation of the BCL-2 gene in prostate cancer under hormone-naïve conditions is unknown.

METHODS

Prostate cancers of 3,261 hormone-naïve patients undergoing radical prostatectomy were arrayed in a TMA with one tissue core (diameter 0.6 mm) per tumor. Bcl-2 immunohistochemistry, analyzed for Bcl-2 expression level (negative, low, and high), was correlated with clinical, histopathological and molecular (Ki67, p53) tumor features, and biochemical failure. Cancers with high-level Bcl-2 expression were evaluated for genetic aberrations by fluorescence in situ hybridization (FISH).

RESULTS

Bcl-2 expression was significantly up-regulated in tumors with aggressive phenotype as indicated by high Gleason score (P < 0.0001), advanced stage (P < 0.0001), and high proliferation index (P = 0.0114). The different Bcl-2 expression levels translated into significantly different survival curves showing better outcome for patients with lower Bcl-2 levels. The prognostic information obtained from the anti-apoptotic Bcl-2 was independent from the proliferation index (Ki67) of the cancer. FISH analysis detected no copy number gains or translocation of the Bcl-2 gene.

CONCLUSION

Bcl-2 overexpression in prostate cancers under hormone-naïve conditions is not associated with increased copy numbers of the gene. This suggests that these frequently detected genetic alterations in androgen-independent tumors occur late in prostate cancer progression.

E2F3 is the main target gene of the 6p22 amplicon with high specificity for human bladder cancer

Amplification of 6p22 occurs in about 10-20% of bladder cancers and is associated with enhanced tumour cell proliferation. Candidate target genes for the 6p22 amplicon include E2F3 and the adjacent gene NM_017774. To clarify which gene is representing the main target, we compared the prevalence of the amplification and the functional role of both genes. Amplification of E2F3 and NM_017774 was analysed by fluorescence in situ hybridization on a bladder cancer tissue microarray composed of 2317 cancer samples. Both genes showed amplification in 104 of 893 (11.6%) interpretable tumours and were exclusively found co-amplified. Additional gene expression analysis by real-time polymerase chain reaction in 12 tumour-derived cell lines revealed that amplification of 6p22 was always associated with co-overexpression of E2F3 and NM_017774. Furthermore, RNA interference was used to study the influence of reduced gene expression on cell growth. In tumour cells with and without the 6p22 amplicon, knockdown of E2F3 always lead to unequivocal reduction of proliferation, whereas knockdown of NM_017774 was only capable to slow down cell proliferation in non-amplified cells. Our findings point out that E2F3 but not NM_017774 is driving enhanced proliferation of 6p22 amplified tumour cells. We conclude that E2F3 must be responsible for the growth advantage of 6p22 amplified bladder cancer cells.

[Identification of prognostic parameters for renal cell carcinoma by cDNA arrays and cell chips]

We report here an example of how the combined application of cDNA and tumor array can lead to the identification of a novel prognostic marker within a very short time. A cDNA array analysis was performed on 5184 cDNA clones on a filter to screen for genes with differential expression between the renal cancer cell line CRL-1933 and normal kidney tissue to identify genes with relevance in RCC. There were 89 differentially expressed genes in the cancer cell line, one of them coding for vimentin, a cytoplasmic intermediate filament. To determine the in vivo prevalence and prognostic significance of vimentin expression, a renal cancer tissue micro array containing 532 RCC specimen was constructed and vimentin expression was determined by immunohistochemistry. Vimentin expression was frequently seen in clear-cell (51%) and papillary RCC (61%), but rarely in chromophobe RCC (4%) and oncocytomas (12%). These results obtained from minute arrayed tumor samples match with previous findings on vimentin expression in renal tumors. Furthermore, vimentin expression was significantly associated with poor patient prognosis (p < 0.007) independently of grade and stage. These results suggest that tissue microarray analysis provides a rapid and powerful method to determine the prevalence and prognostic significance of novel candidate genes discovered to be involved in cancer development with large-scale cDNA expression arrays. The tissue array can be adapted as a routine tool in research laboratories for analyses of large tumor series at the DNA, RNA or protein level. With such a tool, cancer researchers can study vast numbers of tumor samples in a short time and can generate a wealth of data on the application of tumor markers.

High-throughput tissue microarray analysis to evaluate genes uncovered by cDNA microarray screening in renal cell carcinoma

Many genes and signaling pathways are involved in renal cell carcinoma (RCC) development. However, genetic tumor markers have not gained use in RCC diagnostics and prognosis prediction. Identification and evaluation of new molecular parameters are of utmost importance in cancer research and cancer treatment. Here we present a novel approach to rapidly identify clinically relevant molecular changes in cancer. To identify genes with relevance to RCC, a cDNA array analysis was first performed on 5184 cDNA clones on a filter to screen for genes with differential expression between the renal cancer cell line CRL-1933 and normal kidney tissue. There were 89 differentially expressed genes in the cancer cell line, one of them coding for vimentin, a cytoplasmic intermediate filament. In a second step, a renal cancer tissue microarray containing 532 RCC specimen was used to determine vimentin expression by immunohistochemistry. Vimentin expression was seen frequently in clear cell (51%) and papillary RCC (61%), but rarely in chromophobe RCC (4%) and oncocytomas (12%). Furthermore, vimentin expression was significantly associated with poor patient prognosis (P < 0.007) independent of grade and stage. These results obtained from minute arrayed tumor samples match well with previous findings on vimentin expression in renal tumors. It is concluded that the combination of tumor arrays and cDNA arrays is a powerful approach to rapidly identify and further evaluate genes that play a role in tumor biology.