Inhibits Prostate Cancer Cell Motility through Activation of ALK2-Smad1 SignalingPublic Deposited
Prostate cancer (PCa) is the most commonly diagnosed cancer (1:6), and the second most common cause of cancer-related deaths in American men (>27,000/year). Metastasis is largely responsible for these deaths. During metastasis, tumor cells travel from the prostate to a distant organ where they establish a secondary tumor. Cell motility is essential to this process; therefore, therapeutic intervention of this process could inhibit metastasis. Developing anti-motility therapies necessitates an understanding of how PCa cells regulate cell motility. Endoglin, a transforming growth factor beta (TGFβ) auxiliary receptor, is a regulator of cell motility and its expression is lost during PCa progression. As we were the first to show endoglin regulated motility in epithelial cells, this project sought to decipher its mechanism, as well as, determine the therapeutic relevance of the associated regulatory pathway. Smads are TGFβ signaling molecules activated by activin receptor-like kinases (ALKs). Endoglin was shown to activate the Smad subtype, Smad1 (via phosphorylation and promoter activation). Using siRNA to knockdown Smad1 and the ALK subtype, ALK2, we demonstrated both were necessary for endoglin-mediated inhibition of cell motility. Soy-based diets correlate with lower incidence of metastatic PCa. We previously demonstrated that genistein, a soy isoflavone, inhibits TGFβ-induced motility <em>in vitro</em> and metastasis <em>in vivo</em>. Since genistein appears to inhibit PCa metastasis and endoglin expression is lost early in PCa progression, we investigated the relevancy of endoglin expression to genistein's efficacy. We found that genistein reversed the endoglin deficiency phenotype in PCa cells. Using siRNA to knockdown endoglin, endoglin was shown to be unnecessary for genistein-mediated inhibition of PCa cell motility. Using Smad1 promoter assays, and vector-mediated over expression or siRNA-mediated knockdown of either Smad1 or ALK2, we went on to demonstrate that genistein activated the Smad1-ALK2 pathway. By using an ALK2 kinase deficient construct, we demonstrated that genistein-mediated activation of this pathway was dependent upon ALK2 kinase function. In summary, our findings have elucidated a mechanism underlying the increased metastatic potential of PCa cells which are endoglin deficient. Additionally, our results support the notion that individuals with endoglin-deficient PCa will benefit from genistein treatment.