When cultured in GM3, NRP-152 cells undergo increased cell death/growth arrest by rapamycin (Fig. Transforming growth factor (TGF-) signaling antagonists similarly activated the Surivin promoter and rendered cells refractory to further promoter activation by IGF-I. IGF-I suppressed Arctigenin levels of phospho-Smads 2 and 3 with kinetics comparable to that of Survivin induction. Suppression of TGF- signaling, either by TGF- receptor kinase inhibitors or by silencing Smads 2 and 3, induced Survivin expression and promoted cell growth comparable to that induced by IGF-I. TGF- receptor antagonists also rescued cells from down-regulation of Survivin expression and growth suppression by pharmacological inhibitors of PI3K, ARHGEF7 Akt, MEK and mTOR. Sh-RNA gene silencing studies suggest that mTORC1 induces while mTORC2 represses the expression of Survivin by IGF-I. Taken together, these results suggest that IGF-I signaling through a PI3K/Akt/mTORC1 mechanism elevates expression of Survivin and promotes growth of prostate epithelial cells by suppressing Smad-dependent autocrine TGF- signaling. Introduction Survivin (also called BIRC5) is the smallest member of the (TRII) and TRI, which upon TGF- ligand binding form Arctigenin a receptor tetrameric complex. TRI (also known as Alk5), which is usually activated through phosphorylation by TRII kinase, recruits and phosphorylates the two C-terminal serines of Smads 2 and 3. Such phosphorylation exposes their nuclear import sequence, promoting their nuclear localization where they engage in transcriptional control of numerous targets [25], [27], [28]. TGF- is usually well recognized to function as a tumor suppressor of the prostate [29], [30], [31], [32], [33], [34], related to its ability to arrest cell growth and/or induce apoptosis of normal or preneoplastic prostate epithelial cells [35]. Our laboratory previously reported that an intact TGF- signaling pathway transcriptionally downregulates Survivin expression through a mechanism that is dependent on Smads 2 and 3, and two cell cycle repressor elements (within the Survivin proximal promoter), namely a (forward) and (reverse). Quantitative (Q) PCR was performed using the Bio-Rad CFX Connect Real-Time Detection System and Invitogen SYBR Green Real-Time PCR Grasp Mix using the above primers and conditions. Transient transfection and luciferase assay Cells were transfected using polyethylenimine method as before [43]. In brief, NRP-152 Arctigenin cells were plated in 12-well dishes at a density of 1105 cells/1 ml/well in GM3 medium or 5104 cells/well in GM2.1 and transiently transfected for 3 h with 400 ng of rat Survivin-promoter-luc constructs (Full length (FL) or truncations (Trunc #1C4)), 20 ng of CMV-Renilla, and 600 ng of vacant vector per well. After 3 h of transfection, cells were washed once with 1PBS and incubated overnight in GM3 or in GM2.1, as indicated. Cells were then treated with or without LR3-IGF-I (2 nM) in the presence or absence of various brokers, and after 24 h of treatment cells were extracted with passive lysis buffer for measuring dual luciferase activity (Promega Corporation) with a ML3000 Microtiter Plate Luminometer. Adenovirus Adenovirus shuttle vectors (pDC515) that direct the expression of WT-Akt1 (AdMax-Myc-Akt1WT), Active-Akt1 (AdMax-Myc-Akt1Myr), KD-Akt1 (AdMax-Myc-Akt1K179M), DN-P85 (AdMax-Myc-p85SH2N), and CA-P110 (AdMax-Myc-p110CAAX) were constructed using the AdMax system (Microbix Biosystems) and high-titer adenoviruses were prepared and titered as described previously [19], [41]. In brief, cells were plated overnight in 6-well dishes at a density Arctigenin of 2105 cells/2 ml GM3/well with or without doxycycline. For adenoviral contamination, cells were infected for 2 h by AdMax-cont, AdMax-Akt (WT, Active, KD), AdMax-DN-P85 (DN: Dominant unfavorable form of PI3K), or AdMax-CA-P110 Arctigenin (CA: constitutively active form of PI3K), and washed once with PBS followed by addition of 2 ml of GM3. Cells were then incubated overnight for recovery and treated with TGF- (10 ng/ml) or IGF-I (2 nM) for the indicated occasions. Unless mentioned, all the chemical inhibitor treatments were added 2 h prior to addition of IGF-I. Silencing mTOR, Rictor and Raptor in NRP-152 cells.
