Prolactin activates mammalian target-of-rapamycin through phosphatidylinositol 3-kinase and stimulates phosphorylation of p70S6K and 4E-binding protein-1 in lymphoma cells

Mitogens activate the mammalian target-of-rapamycin (mTOR) pathway through phosphatidylinositol 3-kinase (PI3K). The activated mTOR kinase phosphorylates/ activates ribosomal protein S6 kinase (p70S6K) and phosphorylates/inactivates eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), resulting in the initiation of translation and cell-cycle progression. The prolactin receptor signaling cascade has been implicated in crosstalk with the mTOR pathway, but whether prolactin (PRL) directly activates mTOR is not known. This study showed that PRL stimulated the phosphorylation of mTOR, p70S6K, Akt, and Jak2 kinases in a dose- and time-dependent manner in PRL-dependent rat Nb2 lymphoma cells. PRL-stimulated phosphorylation of mTOR was detected as early as 10 min, closely following the phosphorylation of Akt (upstream of mTOR), but preceding that of the downstream p70S6K. PRL activation of mTOR was inhibited by rapamycin (mTOR inhibitor), LY249002, and wortmannin (P13K inhibitors), but not by AG490 (Jak2 inhibitor), indicating that it was mediated by the P13K/Akt, but not Jak2, pathway. PRL also stimulated phosphorylation of 4E-BP1 in Nb2 cells. PRL-induced phosphorylation of p70S6K and 4E-BP1 was inhibited by rapamycin, but not by okadaic acid (inhibitor of protein phosphatase, PP2A). PRL induced a transient interaction between p70S6K and the catalytic subunit of PP2A (PP2Ac) in 1 and 2 h, whereas a PP2Ac–4E-BP1 complex was constitutively present in quiescent and PRL-treated Nb2 cells. These results suggested that p70S6K and 4E-BP1 were substrates of PP2A and the inhibition of mTOR promoted their dephosphorylation by PP2A. In summary, PRL-stimulated phosphorylation of mTOR is mediated by PI3K. PRL-activated mTOR may phosphorylate p70S6K and 4E-BP1 by restraining PP2A.

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Regulation of Hepatic Insulin-Like Growth Factor-Binding Protein-1 Gene Expression by Insulin: Central Role for Mammalian Target of Rapamycin Independent of Forkhead Box O Proteins

Endocrinology ◽

10.1210/en.2005-0902 ◽

2006 ◽

Vol 147 (5) ◽

pp. 2383-2391 ◽

Cited By ~ 16

Author(s):

Catherine Mounier ◽

Victor Dumas ◽

Barry I. Posner

Keyword(s):

Gene Expression ◽

Rat Liver ◽

Binding Protein ◽

Mammalian Target Of Rapamycin ◽

Pi3 Kinase ◽

Target Of Rapamycin ◽

Mrna Levels ◽

Phosphatidylinositol 3 Kinase ◽

Insulin Inhibition ◽

Phosphatidylinositol 3

The expression of IGF-binding protein-1 (IGFBP-1) is induced in rat liver by dexamethasone and glucagon and is completely inhibited by 100 nm insulin. Various studies have implicated phosphatidylinositol 3-kinase, protein kinase B (Akt), phosphorylation of the transcription factors forkhead in rhabdomyosarcoma 1 (Foxo1)/Foxo3, and the mammalian target of rapamycin (mTOR) in insulin’s effect. In this study we examined insulin regulation of IGFBP-1 in both subconfluent and confluent hepatocytes. In subconfluent hepatocytes, insulin inhibition of IGFBP-1 mRNA levels was blocked by inhibiting PI3 kinase activation, and there was a corresponding inhibition of Foxo1/Foxo3 phosphorylation. In these same cells, inhibition of the insulin effect by rapamycin occurred in the presence of insulin-induced Foxo1/Foxo3 phosphorylation. In confluent hepatocytes, insulin could not activate the phosphatidylinositol 3-kinase (PI3 kinase)-Akt-Foxo1/Foxo3 pathway, but still inhibited IGFBP-1 gene expression in an mTOR-dependent manner. In subconfluent hepatocytes, the serine/threonine phosphatase inhibitor okadaic acid (100 nm) partially inhibited IGFBP-1 gene expression by 40%, but did not produce phosphorylation of either Akt or Foxo proteins. In contrast, 1 nm insulin inhibited the IGFBP-1 mRNA level by 40% and correspondingly activated Akt and Foxo1/Foxo3 phosphorylation to a level comparable to that observed with 100 nm insulin. These results suggest a potential role for a serine/threonine phosphatase(s) in the regulation of IGFBP-1 gene transcription, which is not downstream of mTOR and is independent of Akt. In conclusion, we have found that in rat liver, insulin inhibition of IGFBP-1 mRNA levels can occur in the absence of the phosphorylation of Foxo1/Foxo3, whereas activation of the mTOR pathway is both necessary and sufficient.

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Interferon α Induces Nucleus-independent Apoptosis by Activating Extracellular Signal-regulated Kinase 1/2 and c-Jun NH2-Terminal Kinase Downstream of Phosphatidylinositol 3-Kinase and Mammalian Target of Rapamycin

Molecular Biology of the Cell ◽

10.1091/mbc.e07-04-0358 ◽

2008 ◽

Vol 19 (1) ◽

pp. 41-50 ◽

Cited By ~ 33

Author(s):

Theocharis Panaretakis ◽

Linn Hjortsberg ◽

Katja Pokrovskaja Tamm ◽

Ann-Charlotte Björklund ◽

Bertrand Joseph ◽

...

Keyword(s):

Apoptotic Cell ◽

Mammalian Target Of Rapamycin ◽

Target Of Rapamycin ◽

Interferon Α ◽

Dependent Manner ◽

Phosphatidylinositol 3 Kinase ◽

Extracellular Signal Regulated Kinase ◽

Extracellular Signal ◽

Induced Apoptosis ◽

Phosphatidylinositol 3

Interferon (IFN)α induces apoptosis via Bak and Bax and the mitochondrial pathway. Here, we investigated the role of known IFNα-induced signaling cascades upstream of Bak activation. By pharmacological and genetic inhibition of the kinases protein kinase C (PKC)δ, extracellular signal-regulated kinase (ERK), and c-Jun NH2-terminal kinase (JNK) in U266-1984 and RHEK-1 cells, we could demonstrate that all three enzymes are critical for the apoptosis-associated mitochondrial events and apoptotic cell death induced by IFNα, at a step downstream of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR). Furthermore, the activation of JNK was found to occur in a PKCδ/ERK-dependent manner. Inhibition of these kinases did not affect the canonical IFNα-stimulated Janus tyrosine kinase-signal transducer and activator of transcription signaling or expression of IFN-responsive genes. Therefore, enucleated cells (cytoplasts) were examined for IFNα-induced apoptosis, to test directly whether this process depends on gene transcription. Cytoplasts were found to undergo apoptosis after IFNα treatment, as analyzed by several apoptosis markers by using flow cytometry, live cell imaging, and biochemical analysis of flow-sorted cytoplasts. Furthermore, inhibition of mTOR, ERK, and JNK blocked IFNα-induced apoptosis in cytoplasts. In conclusion, IFNα-induced apoptosis requires activation of ERK1/2, PKCδ, and JNK downstream of PI3K and mTOR, and it can occur in a nucleus-independent manner, thus demonstrating for the first time that IFNα induces apoptosis in the absence of de novo transcription.

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5.8 Deep Phenotyping of Children With ASD, Macrocephaly, and Phosphatidylinositol 3-Kinase/Protein Kinase B/Mammalian Target of Rapamycin (PI3K/AKT/mTOR) Pathway Mutations: Preliminary Findings

Journal of the American Academy of Child & Adolescent Psychiatry ◽

10.1016/j.jaac.2018.09.303 ◽

2018 ◽

Vol 57 (10) ◽

pp. S229

Author(s):

Aaron D. Besterman ◽

Dzung Maria Nguyen ◽

Joshua Sadik ◽

Rujuta Bhatt ◽

Gerhard Hellemann ◽

...

Keyword(s):

Protein Kinase ◽

Protein Kinase B ◽

Mammalian Target Of Rapamycin ◽

Mtor Pathway ◽

Target Of Rapamycin ◽

Phosphatidylinositol 3 Kinase ◽

Children With Asd ◽

Deep Phenotyping ◽

Phosphatidylinositol 3

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Forkhead Box Protein O1 Negatively Regulates Skeletal Myocyte Differentiation through Degradation of Mammalian Target of Rapamycin Pathway Components

Endocrinology ◽

10.1210/en.2007-1470 ◽

2007 ◽

Vol 149 (3) ◽

pp. 1407-1414 ◽

Cited By ~ 38

Author(s):

Ai-Luen Wu ◽

Jeong-Ho Kim ◽

Chongben Zhang ◽

Terry G. Unterman ◽

Jie Chen

Keyword(s):

Myogenic Differentiation ◽

Mammalian Target Of Rapamycin ◽

Akt Signaling ◽

Nutrient Sensing ◽

Mtor Pathway ◽

Target Of Rapamycin ◽

Phosphatidylinositol 3 Kinase ◽

Forkhead Box ◽

Myocyte Differentiation ◽

Phosphatidylinositol 3

The forkhead transcription factor forkhead box protein O1 (FoxO1), a downstream target of phosphatidylinositol 3-kinase/Akt signaling, has been reported to suppress skeletal myocyte differentiation, but the mechanism by which FoxO1 regulates myogenesis is not fully understood. We have previously demonstrated that a nutrient-sensing mammalian target of rapamycin (mTOR) pathway controls the autocrine production of IGF-II and the subsequent phosphatidylinositol 3-kinase/Akt signaling downstream of IGF-II in myogenesis. Here we report a regulatory loop connecting FoxO1 to the mTOR pathway. Inducible activation of a FoxO1 active mutant in the C2C12 mouse myoblasts blocks myogenic differentiation at an early stage and meanwhile leads to proteasome-dependent degradation of a specific subset of components in the mTOR signaling network, including mTOR, raptor, tuberous sclerosis complex 2, and S6 protein kinase 1. This function of FoxO1 requires new protein synthesis, consistent with the idea that a transcriptional target of FoxO1 may be responsible for the degradation of mTOR. We further show that active FoxO1 inhibits IGF-II expression at the transcriptional activation level, through the modulation of mTOR protein levels. Moreover, the addition of exogenous IGF-II fully rescues myocyte differentiation from FoxO inhibition. Taken together, we propose that the mTOR-IGF-II pathway is a major mediator of FoxO’s inhibitory function in skeletal myogenesis.

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A proliferation-inducing ligand mediates follicular lymphoma B-cell proliferation and cyclin D1 expression through phosphatidylinositol 3-kinase–regulated mammalian target of rapamycin activation

Blood ◽

10.1182/blood-2008-09-179762 ◽

2009 ◽

Vol 113 (21) ◽

pp. 5206-5216 ◽

Cited By ~ 34

Author(s):

Mamta Gupta ◽

Stacey R. Dillon ◽

Steven C. Ziesmer ◽

Andrew L. Feldman ◽

Thomas E. Witzig ◽

...

Keyword(s):

Follicular Lymphoma ◽

B Cell ◽

Cyclin D1 ◽

Cell Biology ◽

Mammalian Target Of Rapamycin ◽

Target Of Rapamycin ◽

Dependent Manner ◽

Phosphatidylinositol 3 Kinase ◽

Human Patient ◽

Phosphatidylinositol 3

Abstract A proliferation-inducing ligand (APRIL), as well as its receptors transmembrane activator and calcium-modulating cyclophilin ligand (CAML) interactor (TACI) and B-cell maturation antigen (BCMA), has been shown to be important in B-cell biology, and overexpression of APRIL in mice results in development of lymphoma. Limited data are available on APRIL-specific signaling responses, but knockout models suggest that signaling through TACI is critical to B-cell homeostasis. To better understand the mechanism by which APRIL exerts its effects and how it may contribute to lymphomagenesis, we sought to characterize the outcome of APRIL-TACI interactions. In support of murine studies, we find that APRIL induces proliferation of human patient follicular lymphoma (FL) B cells in a TACI-dependent manner. This study also shows that APRIL is expressed within the tumor microenvironment and that, upon engagement with TACI, APRIL mediates activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Activation of PI3K via APRIL results in phosphorylation of Akt and mammalian target of rapamycin (mTOR) and the mTOR-specific substrates p70S6 kinase and 4E-binding protein 1 in a TACI-dependent manner. APRIL-mediated signaling also results in phosphorylation of Rb and up-regulation of cyclin D1. These studies are the first to characterize APRIL-TACI–specific signaling and suggest a role for this ligand-receptor pair in FL B-cell growth.

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