4 A)

4 A). activity of protein phosphatase 2A (PP2A) or PH domain/leucine-rich repeat protein phosphatase1 (PHLPP1) both of which dephosphorylate p-Akt. These findings show that Akt is a direct target of CDDO-Me in the Akt/NF-B/mTOR prosurvival MC-976 signaling axis. Keywords:CDDO-Me, prostate cancer, apoptosis, Akt/NF-B/mTOR signaling, PP2A == Introduction == Synthetic oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its C-28 methyl ester (CDDO-Me) and C-28 imidazole (CDDO-Im) derivatives are potent proapoptotic anticancer agents [14]. Although the anticancer mechanisms of CDDOs are not fully understood, cancer cell differentiation and activation of caspase-dependent and independent apoptosis contribute to the MC-976 antitumor activity of CDDOs [57]. CDDOs inhibit MAP kinases, STATs, NF-B, TGF-/Smad and PPAR signaling [812]. Further, CDDOs exhibit strong chemopreventive activity in mouse models of colon, breast, lung and pancreatic carcinogenesis [1315]. We have previously shown that CDDO-Me inhibits proliferation and induces apoptosis in hormone-sensitive and hormone-refractory prostate cancer cell lines Rabbit Polyclonal to HNRPLL through the activation of procaspases 3, 8, 9, mitochondrial depolarization and the release of cytochrome c from mitochondria [16]. CDDO and CDDO-Me also slowed the development/progression and metastasis of prostate cancer in the TRAMP mouse model of prostate carcinogenesis [17,18]. The induction of apoptosis in prostate cancer cell lines and tumor tissue in TRAMP mice was associated with the inhibition of prosurvival Akt, NF-B and mammalian target of rapamycin (mTOR) signaling proteins [16,19]. However, the mechanism by which CDDO-Me inhibits prosurvival Akt/ NF-B/mTOR signaling has remained undetermined. Akt plays a critical role in the survival and resistant of cancer cells to apoptosis and its prosurvival function is amplified through the activation of NF-B and mTOR, the downstream targets of Akt. The objective of this study was to investigate the mechanism by which CDDO-Me inhibits the activation of Akt in prostate cancer cells. Our data demonstrate that CDDO-Me inhibits the kinase activity of Akt without MC-976 affecting the activity of PDK1, the upstream kinase that phosphorylates and activates Akt. Further, although CDDO-Me reduced the levels of phosphotases such as phosphatase and tensin homolog (PTEN), protein phosphatase 2A (PP2A) and PH domain/leucine-rich repeat protein phosphatase1 (PHLPP1); it had minimal effect on the activity of PP2A. These studies demonstrate for the first time that in Akt/NF-B/mTOR signaling cascade CDDO-Me directly inhibits the activity of Akt without affecting the activity of PDK1 or PP2A phosphatase. == Materials and Methods == == Reagents == CDDO-Me was obtained from the National Cancer Institute, Bethesda, MD through the Rapid Access to Intervention Development Program. Antibodies against p-Akt (ser473), NF-B (p65), p-mTOR (Ser2448), p-caspase-9 (p35), p-Bad (ser136), p-Foxo3a (ser2531) and -actin were purchased from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). Akt immunoassay kit was from EMD Bioscienes (La Jolla, CA) and recombinant PDK1 was purchsed from Calbiochemicals (La Jolla, CA). == Cell culture == LNCaP and PC-3 human prostate cancer cell lines were obtained from American Type Culture Collection (ATCC, Rockville, MD). LNCaP were grown in RPMI-1640 supplemented with 10% FBS, 1% penicillin/streptomycin, and 25 mM HEPES buffer. PC-3 cells were grown in F-12K nutrient mixture (Invitrogen, Camarillo, CA) supplemented with 10% fetal calf serum, 1% penicillin/streptomycin, and 25 mM HEPES buffer. == Measurement of cell viability == 1104cells in 100 l of cell culture medium were seeded into each well of a 96-well plate. After incubation for 24 h, cells were treated with CDDO-Me for 72 h. Cell viability was then determined by the colorimetric MTS assay using CellTiter 96 AQueous One Solution Proliferation Assay System from Promega (Madison, WI). After incubation for 2 h at 37C absorbance was measured at 490 nm using a microplate reader. == Immunoprecipitation == LNCaP and PC-3 cells were washed after treatment with CDDO-Me with cold PBS and lysed in NP 40 cell lysis buffer (Invitrogen, Camarillo, CA) supplemented with phosphatase inhibitor cocktail (sodium fluoride, sodium orthovanadate, sodium pyrophosphate and beta-glycerophosphate), 5 g/mL leupeptin, 1 g/mL aprotinin, 1 g/mL pepstatinin, and 10 g/mL 4-2-aminoethyl-benzenesulfinyl fluoride for 30 min on ice. Supernatants were collected after centrifugation at 14000g for 10 min and protein concentration was determined. Each sample (400 g protein) in 200 l of antibody binding buffer was incubated with anti-p-Akt or anti-p-PDK1 antibody (2 g) for.