Overexpression of Transforming Growth Factor β1 in Malignant Prostate Cells is Partly Caused by a Runaway of TGF-β1 Auto-induction Mediated Through a Defective Recruitment of Protein Phosphatase 2A by TGF-β Type I Receptor

OBJECTIVES To elucidate the mechanism of transforming growth factor (TGF)-beta 1 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, B alpha, of protein phosphatase 2A (PP2A-B alpha) by TGF-beta type I receptor (T beta RI) was monitored by coimmunoprecipitation. Blockade of TGF-beta 1 signaling in cells was accomplished either by using TGF-beta-neutralizing monoclonal antibody or by transduction of a dominant negative TGF-beta type II receptor retroviral vector. RESULTS Basal levels of TGF-beta 1 in malignant cells were significantly higher than those in benign cells. Blockade of TGF-beta signaling resulted in a significant decrease in TGF-beta 1 expression in malignant cells, but not in benign cells. Upon TGF-beta 1 treatment (10 ng/mL), TGF-beta 1 expression was increased in malignant cells, but not in benign cells. This differential TGF-beta 1 auto-induction between benign and malignant cells correlated with differential activation of extracellular signal-regulated kinase (ERK). Following TGF-beta 1 treatment, the activity of serine/threonine phosphatase and recruitment of PP2A-B alpha by T beta RI 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-beta 1 auto-induction after TGF-beta 1 (10 ng/mL) treatment. CONCLUSIONS These results suggest that TGF-beta 1 overexpression in malignant cells is caused, at least in part, by a runaway of TGF-beta 1 auto-induction through ERK activation because of a defective recruitment of PP2A-B alpha by T beta RI. UROLOGY 76: 1519.e8-1519.e13, 2010. (C) 2010 Elsevier Inc.