TGF-β Effects on Prostate Cancer Cell Migration and Invasion Are Mediated by PGE2 through Activation of PI3K/AKT/mTOR Pathway

TGF-beta plays an important role in the progression of prostate cancer. It exhibits both tumor suppressor and tumor-promoting activities. Correlations between cyclooxygenase (COX)-2 overexpression and enhanced production of prostaglandin (PG)E-2 have been implicated in cancer progression; however, there are no studies indicating that TGF-beta effects in prostate cancer cells involve PGE(2) synthesis. In this study, we investigated TGF-beta regulation of COX-1 and COX-2 expression in prostate cancer cells and whether the effects of TGF-beta on cell proliferation and migration are mediated by PGE(2). COX-1 protein was ubiquitously expressed in prostate cells; however, COX-2 protein levels were detected only in prostate cancer cells. TGF-beta treatment increased COX-2 protein levels and PGE(2) secretion in PC3 cells. Exogenous PGE(2) and PGF(2 alpha) had no effects on cell proliferation in LNCaP, DU145, and PC3 cells whereas PGE(2) and TGF-beta induced migration and invasive behavior in PC3 cells. Only EP2 and EP4 receptors were detected at mRNA levels in prostate cells. The EP4-targeting small interfering RNA inhibited PGE(2) and TGF-beta-induced migration of PC3 cells. TGF-beta and PGE(2) induce activation of PI3K/AKT/mammalian target of rapamycin pathway as indicated by increased AKT, p70S6K, and S6 phosphorylation. Rapamycin completely blocked the effects of TGF-beta and PGE(2) on phosphorylation of p70S6K and S6 but not on AKT phosphorylation. PGE(2) and TGF-beta induced phosphorylation of AKT, which was blocked by antagonists of PGE(2) (EP4) receptors (L161982, AH23848) and PI3K inhibitor (LY294002) in PC3 cells. Pretreatment with L161982 or AH23848 blocked the stimulatory effects of PGE(2) and TGF-beta on cell migration, whereas LY294002 or rapamycin completely eliminated PGE(2), TGF-beta, and epidermal growth factor-induced migration in PC3 cells. We conclude that TGF-beta increases COX-2 levels and PGE(2) secretion in prostate cancer cells which, in turn, mediate TGF-beta effects on cell migration and invasion through the activation of PI3K/AKT/mammalian target of rapamycin pathway. (Endocrinology 154: 1768-1779, 2013)