Expression of androgen receptor coactivators in normal and cancer prostate tissues and cultured cell lines.

BACKGROUND: In prostate cancer cell lines, androgen receptor (AR) coactivators modulate the transcriptional activity of AR. However, very little is known about their expression in normal prostate tissue and during progression to cancer. METHODS: AR and coactivators ARA54, ARA55, ARA70, and SRC1 RNA were analyzed by RT-PCR in normal and tumoral tissues of the same prostate, in prostate cell lines, and after hormonal treatments of prostate epithelial cells. RESULTS: AR-coactivators were expressed in normal and tumoral tissues and in cultured prostate cells; only ARA55 expression was decreased in tumoral relative to normal tissue of all seven prostates analyzed. It was not expressed in LNCaP and DU145 cancer cells and low in PNT2 immortalized cells in which all coactivator's expression were down regulated by DHT and up regulated by E2. In addition, coactivator's expression was increased in hyperplastic relative to normal prostate fibroblasts. CONCLUSIONS: ARA55 is both an AR coactivator and a focal adhesion protein (Hic-5). Its role in the progression of prostate carcinoma may therefore involve these two different functions. Its decrease in cancer tissue suggests that it plays a different role than that expected, namely, facilitate cell proliferation and therefore mobility and metastasis.

Alterations of expression and regulation of transforming growth factor beta in human cancer prostate cell lines.

TGF beta can promote and/or suppress prostate tumor growth through multiple and opposing actions. Alterations of its expression, secretion, regulation or of the sensitivity of target cells can lead to a favorable environment for tumor development. To gain a better insight in TGF beta function during cancer progression, we have used different cultured human prostate cells: preneoplastic PNT2 cells, the androgen-dependent LNCaP and the androgen-independent PC3 and DU145 prostate cancer cell lines. We have studied by specific ELISA assays in conditioned media (CM), the secretion of TGF beta 1 and TGF beta 2 in basal conditions and after hormonal treatment (DHT or E2) and the expression of TGF beta 1 mRNA by Northern blot. We have also compared the effect of fibroblast CM on TGF beta secretion by the different cell types. Compared to PNT2 cells, cancer cell lines secrete lower levels of active TGF beta which are not increased in the presence of fibroblast CM. LNCaP cells respond to androgen or estrogen treatment by a 10-fold increase of active TGF beta secretion while PC3 and DU145 are unresponsive. In conclusion, prostate cancer cell lines have lost part of their ability to secrete and activate TGF beta, and to regulate this secretion through stromal-epithelial interactions. Androgen-sensitive cancer cells may compensate this loss by hormonal regulation.

Transforming growth factor beta in the human prostate: its role in stromal-epithelial interactions in non-cancerous cell culture.

BACKGROUND: Stromal-epithelial interactions play a critical role in prostate development, but the precise mechanisms are still unknown. Transforming growth factor-beta (TGFbeta) could be a potential mediator of these interactions, but there is as yet no clear demonstration of its role. METHODS: Separate cultures and co-cultures of fibroblasts and epithelial human prostate cells were performed. We measured TGFbeta1 and TGFbeta2 secretion by specific ELISA assay, cell growth by DNA assay, and TGFbeta type II receptor expression by RT-PCR. RESULTS: Co-culture resulted in a 20% inhibition of epithelial cell growth, similar to that obtained after TGFbeta treatment (2 ng/ml for 48 hr), but without affecting fibroblast proliferation. This was accompanied by a five- to six-fold increase in epithelial TGFbeta2 secretion. CONCLUSIONS: These results demonstrate for the first time that TGFbeta2 secretion by prostate epithelial cells is under the direct control of a diffusible factor secreted by fibroblasts. They emphasize the role of TGFbeta in stromal-epithelial interactions.

Hormonal regulation of the androgen receptor expression in human prostatic cells in culture.

The regulation of the androgen receptor (AR) expression was studied using immunocytochemical and Western blot techniques on separate cultures of epithelial cells (PNT2) and fibroblasts of human prostate. In both cell types, immunocytochemistry revealed both nuclear and cytoplasmic staining. Treatment with DHT (5 x 10(-9) M) increased both the intensity of nuclear staining and the number of cells stained. The increase, observed after DHT treatment was markedly decreased by cyproterone acetate (5 x 10(-7) M), confirming a direct action of DHT via the AR. This autoregulation of AR was confirmed by Western blot, and seems to involve transcription and protein synthesis, since it was suppressed by actinomycin D and cycloheximide. In fibroblasts, known to contain an estrogen receptor, estradiol treatment (5 x 10(-7) M) also increases the AR immunostaining. In addition, coculture studies show that epithelial cells require the presence of fibroblasts for optimal expression of the AR. These results demonstrate that prostate epithelial cells and fibroblasts have retained in culture, an hormonal sensitivity correlated with the presence of specific receptors and can serve as a model for the study of hormone action in this tissue in normal or pathological conditions.