TI - AKT-independent phosphorylation of TSC2 and activation of mTOR and ribosomal protein S6 kinase signaling by prostaglandin F2alpha . AB - Prostaglandin F2alpha ( PGF2alpha ) is an important mediator of corpus luteum ( CL ) regression , although the cellular signaling events that mediate this process have not been clearly identified . It is established that PGF2alpha binds to a G-proteincoupled receptor ( GPCR ) to stimulate protein kinase C ( PKC ) and Raf-MEK-Erk signaling in luteal cells . The present experiments were performed to determine whether PGF2alpha stimulates the mammalian target of rapamycin ( mTOR ) /ribosomal protein S6 kinase 1 ( S6K1 ) signaling pathway in steroidogenic luteal cells . We demonstrate that PGF2alpha treatment results in a timeand concentration -dependent stimulation of the phosphorylation and activation of S6K1 . The stimulation of S6K1 in response to PGF2alpha treatment was abolished by the mTOR inhibitor rapamycin . Treatment with PGF2alpha did not increase AKT phosphorylation but increased the phosphorylation of Erk and the tumor suppressor protein tuberous sclerosis complex 2 ( TSC2 ) , an upstream regulator of mTOR . The effects of PGF2alpha were mimicked by the PKC activator PMA and inhibited by U0126 , a MEK1 inhibitor . The activation of mTOR/S6K1 and putative down stream processes involving the translational apparatus ( ie 4EBP1 phosphorylation , release of 4EBP1 binding in m(7) G cap binding assays , and the phosphorylation and synthesis of S6 ) were completely sensitive to treatment with rapamycin , implicating mTOR in the actions of PGF2alpha . Taken together , our data suggest that GPCR activation in response to PGF2alpha stimulates the mTOR pathway which increases the translational machinery in luteal cells . The translation of proteins under the control of mTOR may have implications for luteal development and regression and offer new strategies for therapeutic intervention in PGF2alpha-target tissues .