Effect of Beta–Sitosterol on Transforming Growth Factor–Beta–1 Expression and Translocation Protein Kinase C Alpha in Human Prostate Stromal Cells in vitro

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Abstract
Background: Today, plant extracts are widely used in the treatment of benign prostatic hyperplasia (BPH). However, the complete mode of action of the active substance, β–sitosterol, is under investigation. The purpose of this study was to investigate the effect of β–sitosterol on the expression of transforming growth factor beta 1 (TGF–β1) and the activity of protein kinase C alpha (PKC–α) in primary prostate stromal cell cultures in vitro.Methods: Tissue samples for primary cell cultures were obtained from patients undergoing transurethral resection of the prostate (TURP). TGF–β1 levels in stromal cell conditioned media following a culture with β–sitosterol were detected in a TGF–β1 specific ELISA assay. Following different incubation periods with β–sitosterol, cells were lysed and fractionated into a Triton–soluble membrane fraction and a cytosol fraction. PKC–α protein was detected using immunoblot analysis.Results: Beta–sitosterol was able to induce the expression and secretion of TGF–β1 significantly between 1.26– and 1.86–fold compared to a cholesterol and the nonsupplemented control in 6 of 8 individual cultures. The total amount of secreted TGF–β1 varied in cells from different patients. Based on its presence in both membrane fraction and cytosol, PKC–α appeared to be constitutively expressed in stromal cells. In the absence of β–sitosterol PKC–α was predominantly found in its membrane–associated active form. Following a culture with β–sitosterol, a translocation of PKC–α from the membrane to the cytosol was observed. This effect was specific for β–sitosterol as compared to cholesterol.Conclusion: This study describes the effect of β–sitosterol on the expression of a multifunctional growth factor (TGF–β1) and the activity of PKC–α membrane in stromal cells of the human prostate in vitro.

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