The Inhibitory Effects of Gossypol on Human Prostate Cancer Cells-PC3 are Associated with Transforming Growth Factor Beta₁ (TGFβ₁) Signal Transduction Pathway

Abstract

Background: Racemic gossypol [(±)-GP], a naturally occurring polyphenolic yellow pigment present in cottonseed products, inhibits in vitro proliferation of Dunning prostate cancer cells (MAT-LyLu), human prostate cancer cells derived from a bone marrow metastasis (PC3), MCF-7 and primary cultured human prostate cells. (±)-GP also has the ability to inhibit the metastasis of lung and lymph nodes of the androgen-independent rodent prostate cancer cell line, MAT-LyLu, after implantation into Copenhagen rats. Materials and Methods: The effects of (±)-GP on the proliferation of human prostate cancer PC3 cells were determined by thymidine incorporation assay and doublingtime (DT) determination. The mechanisms of action of (±)-GP on the proliferation of PC3 cells were determined by RT-PCR analysis, ELISA assay and Western blot analysis. Results: The results show that (±)-GP caused reductions in DNA synthesis and prolonged the DTs in PC3 cells. RT-PCR and ELISA results show that (±)-GP elevate the mRNA expression and protein secretion of transforming growth factor beta₁ (TGFβ₁) in PC3 cells. Consistent with these findings, (±)-GP has been shown to decrease the cyclin D₁ mRNA expression and protein expression in PC3 cells. Furthermore, the growth inhibition of PC3 cells by conditioned media collected from the (±)-GP-treated-PC3 cells was completely reversed by addition of 25μg/ml of mouse monoclonal anti-TGFβ₁-,β₂,-β₃ antibody, suggesting the involvement of TGFβ₁ in (±)-GPinduced growth inhibition of PC3 cells. Conclusion: These results indicate that the inhibitory effects of (±)-GP on the proliferation of human prostate cancer PC3 cells are associated with induction of TGFβ₁, which in turn influences the expression of the cell cycle-regulatory protein, cyclin D₁, in prostate cancer cells.