Abstract 1703: Osteoblastic differentiation induced by PSA: Role of Wif-1 and TGF-β

Abstract

Abstract Introduction: The high prevalence of osteoblastic bone metastases in prostate cancer likely involves the production of osteoblast-stimulating factors by prostate cancer cells. The identity of the factors responsible for the homing of circulating prostate cancer cells to the bone remains unknown. Prostate specific antigen (PSA) is a serine protease produced by prostate cancer cells and is an important serological marker for prostate cancer. Our previous studies suggested that PSA may be involved in the induction of osteoblastic differentiation. In this study, we examined the involvement of Wnt inhibitory factor 1 (Wif-1) and Transforming growth factor β (TGF-β) in osteoblastic differentiation induced by PSA in SaOS-2 human osteosarcoma cells. Methods: Microarray analysis of RNAs from Saos-2 cells stably expressing PSA and vector controls was performed and the results were validated by northern blotting. The potential role of Wif-1 and TGF-β in osteoblatic differentiation induced by PSA was examined by alkaline phosphatase assays, luciferase assays and northern analysis. Results: PSA was found to induce bone remodeling in SaOS-2 cells as evidenced by increases in alkaline phosphatase activity, mineral deposition and osteogenic gene expression. Saos-2 cells expressing PSA exhibited markedly upregulated expression of markers of osteoblastic differentiation like collagen type 1, osteocalcin, Runx-2, alkaline phosphatase and bone sialoprotein compared to parental Saos-2 cells and vector controls. Treatment of SaOS cells with exogenous enzymatically active PSA produced similar results, suggesting that osteoblastic differentiation may be regulated by PSA. Among the genes found to be regulated by PSA expression, TGF-β and Wif-1 were examined further. PSA enhanced the expression and activation of TGF-β as shown by higher levels of TGF-β-responsive reporter activity and increase in expression of TGF-β receptors I and II. Overexpression of Wif-1 in SaOS-2 cells enhanced osteogenic gene expression, while inhibition of Wif-1 expression in PSA-expressing cells resulted in reduction of alkaline phosphatase activity, a marker of osteoblastic differentiation. Conclusions: PSA-induced bone remodeling was mediated by enhanced expression of several markers of osteoblastic differentiation and modulation of TGF-β and the Wnt/β-catenin pathways. These results suggest that PSA produced by metastatic prostate cancer cells may participate in bone remodeling in favor of development of osteoblastic metastases. These findings provide a molecular basis for understanding the high prevalence of osteoblastic bone metastases in prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1703.