| Development of strategies for more effective treatment of prostate cancer is limited by an incomplete understanding of the mechanisms regulating survival of either normal prostate or prostate cancer cells. Androgen receptor (AR) signaling plays an important role in regulating differentiation and cell survival in the prostate and in prostate cancer. Prostate cancer arises from the AR expressing epithelial cells of the prostate. Adhesion to matrix through integrins is required for survival of most epithelial cells. However, AR-expressing epithelial cells of the prostate are not adherent to matrix. Paradoxically in prostate cancer, the tumor cells both express AR and are adherent to matrix, allowing for interactions between these two signaling pathways. Our hypothesis is that the interaction of cancer cells with the matrix and the integration of signals from integrins and AR regulate their survival, while AR regulates survival of normal cells independently of integrins. We have demonstrated that PC3 and DU145 prostate tumor cell lines require PI3K signaling for cell survival. In addition, adhesion of PC3 cells to laminin 1 promotes survival via integrin-mediated activation of Src leading to increased expression of the pro-survival protein Bcl-xL. In DU145 cells, adhesion to collagen 1 drives survival through activation of EGFR and Erk. During prostate cancer progression, there is increased expression of the laminin 1-binding integrin alpha6beta1. Previous studies have demonstrated that AR can lead to increased expression of alpha6beta1, suggesting that AR may drive cell survival by altering integrin expression. We have demonstrated that expression of AR in PC3 cells can rescue cells from death induced by inhibition of PI3K when adherent to laminin 1. Expression of AR in PC3 cells leads to increased expression of integrin alpha6beta1 and Bcl-xL along with increased activation of NF-kappaB. Blocking each these components individually concurrent with inhibition of PI3K led to death of the AR-expressing cells, suggesting that AR regulates cell survival through enhancement of alpha6beta1/NF-kappaB/Bc1-xL signaling. AR expression in PC3 tumor cells also correlates with increased filopodia formation, Src activity, and cell migration. To assess the role AR in normal cell survival, we generated an in vitro differentiation model. Confluent primary human prostate epithelial cell cultures were treated with KGF and androgen (DHT). After two weeks, a suprabasal cell layer formed in which cells no longer expressed integrins, p63, K5/14, EGFR, FGFR2llllb, or Bcl-2, but instead expressed AR and androgen-induced differentiation markers, including K18/19, TMPRSS2, Nkx3.1, PSMA, KLK2 and secreted PSA. Differentiated prostate cell survival depended on E-cadherin and PI3K, but not KGF, DHT, AR or MAPK. Therefore, while in the prostate tumor cell line PC3, AR and integrin alpha6beta1 cooperate to drive cell survival, neither AR nor integrins were required for survival of differentiated prostate epithelial cells. |
