Insulin-Like Growth Factor I Suppresses Bone Morphogenetic Protein Signaling in Prostate Cancer Cells by Activating mTOR Signaling

Case Comprehensive Cancer Center Research Laboratories, The Division of General Medical Sciences-Oncology, Department of Pharmacology, Case Western Reserve University, and Department of Urology, University Hospitals of Cleveland, Cleveland, Ohio 44106, USA.
Cancer Research (Impact Factor: 9.33). 11/2010; 70(22):9106-17. DOI: 10.1158/0008-5472.CAN-10-1119
Source: PubMed


Insulin-like growth factor (IGF) I and bone morphogenetic proteins (BMP) are critical regulators of prostate tumor cell growth. In this report, we offer evidence that a critical support of IGF-I in prostate cancer is mediated by its ability to suppress BMP4-induced apoptosis and Smad-mediated gene expression. Suppression of BMP4 signaling by IGF-I was reversed by chemical inhibitors of phosphoinositide 3-kinase (PI3K), Akt, or mTOR; by enforced expression of wild-type PTEN or dominant-negative PI3K; or by small hairpin RNA-mediated silencing of mTORC1/2 subunits Raptor or Rictor. Similarly, IGF-I suppressed BMP4-induced transcription of the Id1, Id2, and Id3 genes that are crucially involved in prostate tumor progression through PI3K-dependent and mTORC1/2-dependent mechanisms. Immunohistochemical analysis of non-malignant and malignant prostate tissues offered in vivo support for our model that IGF-I-mediated activation of mTOR suppresses phosphorylation of the BMP-activated Smad transcription factors. Our results offer the first evidence that IGF-I signaling through mTORC1/2 is a key homeostatic regulator of BMP4 function in prostate epithelial cells, acting at two levels to repress both the proapoptotic and pro-oncogenic signals of BMP-activated Smads. We suggest that deregulation of this homeostatic control may be pivotal to the development and progression of prostate cancer, providing important implications and new potential targets for the therapeutic intervention of this malignancy.

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    • "For example, Noggin gene expression was upregulated following IGF-1 induced oligodendrocyte differentiation of adult neural precursor cell cultures [22]. Wahdan-Alaswad et al [23] reported that IGF-1 suppressed BMP4-induced apoptosis, BMP signalling activation and expression of inhibitors of differentiation/DNA binding (Id) proteins in prostrate epithelial cells through activation of mammalian target of rapamycin signalling. The Ids are downstream BMP target genes and mediate the inhibitory effects of BMPs on oligodendrocyte differentiaton [24]. "
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    ABSTRACT: Repair in multiple sclerosis involves remyelination, a process in which axons are provided with a new myelin sheath by new oligodendrocytes. Bone morphogenic proteins (BMPs) are a family of growth factors that have been shown to influence the response of oligodendrocyte progenitor cells (OPCs) in vivo during demyelination and remyelination in the adult brain. We have previously shown that BMP4 infusion increases numbers of OPCs during cuprizone-induced demyelination, while infusion of Noggin, an endogenenous antagonist of BMP4 increases numbers of mature oligodendrocytes and remyelinated axons following recovery. Additional studies have shown that insulin-like growth factor-1 (IGF-1) promotes the survival of OPCs during cuprizone-induced demyelination. Based on these data, we investigated whether myelin repair could be further enhanced by sequential infusion of these agents firstly, BMP4 to increase OPC numbers, followed by either Noggin or IGF-1 to increase the differentiation and survival of the newly generated OPCs. We identified that sequential delivery of BMP4 and IGF-1 during cuprizone challenge increased the number of mature oligodendrocytes and decreased astrocyte numbers following recovery compared with vehicle infused mice, but did not alter remyelination. However, sequential delivery of BMP4 and Noggin during cuprizone challenge did not alter numbers of oligodendrocytes or astrocytes in the corpus callosum compared with vehicle infused mice. Furthermore, electron microscopy analysis revealed no change in average myelin thickness in the corpus callosum between vehicle infused and BMP4-Noggin infused mice. Our results suggest that while single delivery of Noggin or IGF-1 increased the production of mature oligodendrocytes in vivo in the context of demyelination, only Noggin infusion promoted remyelination. Thus, sequential delivery of BMP4 and Noggin or IGF-1 does not further enhance myelin repair above what occurs with delivery of Noggin alone.
    PLoS ONE 05/2013; 8(5):e63415. DOI:10.1371/journal.pone.0063415 · 3.23 Impact Factor
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    • "Sources were: Recombinant human TGF-β1 and anti-Survivin (#AF886) (R&D Systems); anti-P-Smad3 (Ser433/435, #9514), anti-P-Smad2 (Ser465/467, #3101), and P-Smad1/5/8 (Ser463/465/Ser426/428, #9511), anti-mTOR (#2972), anti-Raptor (#2114), anti-Rictor (#4978), anti-P-Rb (Ser807/811, #9308), Akt1 (#2967), Akt (Ser473, #927), anti-P-S6 (Ser235/236, #2211) antibodies (Cell Signaling); anti-Survivin (sc-10811) and anti-Smad3 (sc-8332) antibodies (Santa Cruz); anti-β-actin antibody (Sigma); anti-Smad2 (#S66220) antibody (Transduction laboratories); anti-XIAP (#610762, BD Biosciences); anti-P-Smad3 (Ser423/425) was generous gift obtained from Dr. Dr. Ed Leof; U0126 and rapamycin (LC laboratories), perifosine, Ku-0063794 (Selleck Chem); SB431542 (Tocris Bioscience), SB202190, SP600125, LY294002, HTS-466284 and ALK5 inhibitor-II (EMD Millipore), MK2206 (ChemieTek), DMEM/F12 (Invitrogen), characterized fetal bovine serum (FBS) (HyClone). The rat Survivin promoter-luciferase reporter, sh-Survivin, sh-mTOR, sh-Raptor, and sh-Rictor constructs were developed previously [24], [37]. LNCaP, VCaP, DU145, RWPE-1 and HEK-293T cells were obtained from American Type Culture Collection. "
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    ABSTRACT: Survivin is a unique member of the inhibitor of apoptosis (IAP) proteins that is overexpressed in numerous cancers through poorly defined mechanisms. One such mechanism may be through constitutive activation of the insulin-like growth factor-I (IGF-I) signaling pathway, implicated in the development and progression of prostate cancer. Using the pre-neoplastic NRP-152 rat prostate cell line as a model, we showed that IGF-I induces Survivin expression, and that silencing Survivin by lentiviral-mediated small hairpin RNA (shRNA) represses IGF-I-stimulated cell growth, implicating Survivin as a mediator of this growth response. Moreover, our data support that the induction of Survivin by IGF-I occurs through a transcriptional mechanism that is mediated in part by the PI3K/Akt/mTORC1 pathway. Use of various Survivin promoter-luciferase constructs revealed that the CDE and CHR response elements in the proximal region of the Survivin promoter are involved in this IGF-I response. Transforming growth factor (TGF-β) signaling antagonists similarly activated the Surivin promoter and rendered cells refractory to further promoter activation by IGF-I. IGF-I suppressed levels of phospho-Smads 2 and 3 with kinetics similar to that of Survivin induction. Suppression of TGF-β signaling, either by TGF-β receptor kinase inhibitors or by silencing Smads 2 and 3, induced Survivin expression and promoted cell growth similar to that induced by IGF-I. TGF-β receptor antagonists also rescued cells from down-regulation of Survivin expression and growth suppression by pharmacological inhibitors of PI3K, 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-β signaling.
    PLoS ONE 05/2013; 8(5):e61896. DOI:10.1371/journal.pone.0061896 · 3.23 Impact Factor
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    • "Studies with monoclonal antibodies to IGF-1R have implicated this receptor as important in PCa progression in androgen-sensitive as well as -resistant tumor models [22]. Although IGF-1R signaling is mediated in part by the Src pathway, other downstream signaling pathways of IGF-1R are Src independent and unaffected by Src inhibition [14]; these additional pathways have been shown recently to play an important role in PCa cell survival [23]. Activating Src and IGF-1R also activates Akt, a key effector of the PI3K/Akt/mTOR pathway, which is aberrantly activated in the majority of malignancies, promoting cell growth, proliferation, and survival [24], [25].However, whether these inhibitors are equally effective in inhibiting Akt1, 2, and 3 functions is not known, and if combining them produced better results in inhibiting this survival pathway was a goal of this work. "
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    PLoS ONE 12/2012; 7(12):e51189. DOI:10.1371/journal.pone.0051189 · 3.23 Impact Factor
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