Overexpression of transforming growth factor ß1 in malignant prostate cells is partly caused by a runaway of TGF-ß1 auto-induction mediated through a defective recruitment of protein phosphatase 2A by TGF-ß type I receptor.

OBJECTIVES: To elucidate the mechanism of transforming growth factor (TGF)-ß1 overexpression in prostate cancer cells. METHODS: Malignant (PC3, DU145) and benign (RWPE1, BPH1) prostate epithelial cells were used. Phosphatase activity was measured using a commercial kit. Recruitment of the regulatory subunit, Bα, of protein phosphatase 2A (PP2A-Bα) by TGF-ß type I receptor (TßRI) was monitored by coimmunoprecipitation. Blockade of TGF-ß1 signaling in cells was accomplished either by using TGF-ß-neutralizing monoclonal antibody or by transduction of a dominant negative TGF-ß type II receptor retroviral vector. RESULTS: Basal levels of TGF-ß1 in malignant cells were significantly higher than those in benign cells. Blockade of TGF-ß signaling resulted in a significant decrease in TGF-ß1 expression in malignant cells, but not in benign cells. Upon TGF-ß1 treatment (10 ng/mL), TGF-ß1 expression was increased in malignant cells, but not in benign cells. This differential TGF-ß1 auto-induction between benign and malignant cells correlated with differential activation of extracellular signal-regulated kinase (ERK). Following TGF-ß1 treatment, the activity of serine/threonine phosphatase and recruitment of PP2A-Bα by TßRI increased in benign cells, but not in malignant cells. Inhibition of PP2A in benign cells resulted in an increase in ERK activation and in TGF-ß1 auto-induction after TGF-ß1 (10 ng/mL) treatment. CONCLUSIONS: These results suggest that TGF-ß1 overexpression in malignant cells is caused, at least in part, by a runaway of TGF-ß1 auto-induction through ERK activation because of a defective recruitment of PP2A-Bα by TßRI.

17Beta-estradiol at low concentrations acts through distinct pathways in normal versus benign prostatic hyperplasia-derived prostate stromal cells.

The aim of this study was to identify differential responses to low concentrations of 17beta-estradiol (E2) in primary stromal cell cultures derived from either normal organ donors or benign prostatic hyperplasia or hypertrophy (BPH) specimens. Furthermore, we sought to identify the potential mechanism of E2 action in these cell types, through either a genomic or nongenomic mechanism. We initially treated stromal cells derived from five normal prostates or five BPH specimens with low concentrations of E2 (0.001-1.0 nM) and analyzed their growth response. To determine whether genomic or nongenomic pathways were involved, we performed studies using specific estrogen receptor antagonists to confirm transcriptional activity or MAPK inhibitors to confirm the involvement of rapid signaling. Results of these studies revealed a fundamental difference in the mechanism of the response to E2. In normal cells, we found that a nongenomic, rapid E2 signaling pathway is predominantly involved, mediated by G protein-coupled receptor-30 and the subsequent activation of ERK1/2. In BPH-derived prostate stromal cells, a genomic pathway is predominantly involved because the addition of ICI 182780 was sufficient to abrogate any estrogenic effects. In conclusion, prostate stromal cells respond to far lower concentrations of E2 than previously recognized or examined, and this response is mediated through two distinct mechanisms, depending on its origin. This may provide the basis for new insights into the causes of, and possible treatments for, BPH.

A novel anti-proliferative property of clusterin in prostate cancer cells.

Clusterin is a ubiquitous secretory glycoprotein that is known to suppress certain forms of apoptosis. Since apoptosis and proliferation are two opposing cellular events, it remains unclear if clusterin has any effect on cellular proliferation. The objective of the present study was to examine the effects of clusterin on proliferation in a prostate cancer cell line, LNCaP. We found that clusterin inhibited EGF-mediated proliferation in these cells, as measured by (3)H-thymidine incorporation and by cell counting. Clusterin did not bind with EGF nor did it block phosphorylation of the EGF receptor. Treatment of LNCaP cells with EGF resulted in a transient increase in the expression of both c-Fos and c-Jun. Addition of clusterin to these cultures significantly down-regulated the protein level of c-Fos, but not c-Jun. These results demonstrated a novel biological role for clusterin. Clusterin is not only anti-apoptotic but also anti-proliferative. The anti-proliferative event maybe associated with a down-regulation of c-Fos.

Response to a lethal dose of heat shock by a transient up-regulation of clusterin expression followed by down-regulation and apoptosis in prostate and bladder cancer cells.

BACKGROUND: Clusterin is a ubiquitous, secretory glycoprotein with a wide array of functions. Recent studies have implicated that clusterin functioned as heat shock response proteins. The objective of the present study was to determine the fate of clusterin expression in cancer cells, which were subjected to a lethal dose of heat shock, in an attempt to shed light on mechanisms of action of clusterin. METHODS: A prostate cancer line, PC-3, and a bladder cancer line, TSU-Pr1, were selected owing to their aggressive growth behaviors. Apoptosis was assessed by enzymatic activities of terminal deoxynucleotidyl transferase as well as by activities of caspase-3. Cells were exposed to 45 degrees C for a period of 60 min. RESULTS: Both cell lines underwent a transient up-regulation of clusterin expression followed by down-regulation and apoptosis. TSU-Prl cells produced higher levels of clusterin and displayed a greater resistance to apoptosis than did PC-3 cells. The addition of exogenous clusterin to the cultures of PC-3 cells protected apoptosis. Treatment of oligonucleotide antisense to clusterin to the cultures of TSU-Pr1 cells enhanced apoptosis mediated by heat shock. CONCLUSION: Clusterin offers a protection to PC-3 and TSU-Prl cells against heat shock and plays an important role in the cascade of events initiated by heat shock. Prostate 53: 277-285, 2002.