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Buj R, Chen CW, Dahl ES, Leon KE, Kuskovsky R, Maglakelidze N, Navaratnarajah M, Zhang G, Doan MT, Jiang H, Zaleski M, Kutzler L, Lacko H, Lu Y, Mills GB, Gowda R, Robertson GP, Warrick JI, Herlyn M, Imamura Y, Kimball SR, DeGraff DJ, Snyder NW, Aird KM. Suppression of p16 Induces mTORC1-Mediated Nucleotide Metabolic Reprogramming. Cell Rep 2020; 28:1971-1980.e8. [PMID: 31433975 PMCID: PMC6716532 DOI: 10.1016/j.celrep.2019.07.084] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 07/01/2019] [Accepted: 07/23/2019] [Indexed: 02/07/2023] Open
Abstract
Reprogrammed metabolism and cell cycle dysregulation are two cancer hallmarks. p16 is a cell cycle inhibitor and tumor suppressor that is upregulated during oncogene-induced senescence (OIS). Loss of p16 allows for uninhibited cell cycle progression, bypass of OIS, and tumorigenesis. Whether p16 loss affects pro-tumorigenic metabolism is unclear. We report that suppression of p16 plays a central role in reprogramming metabolism by increasing nucleotide synthesis. This occurs by activation of mTORC1 signaling, which directly mediates increased translation of the mRNA encoding ribose-5-phosphate isomerase A (RPIA), a pentose phosphate pathway enzyme. p16 loss correlates with activation of the mTORC1-RPIA axis in multiple cancer types. Suppression of RPIA inhibits proliferation only in p16-low cells by inducing senescence both in vitro and in vivo. These data reveal the molecular basis whereby p16 loss modulates pro-tumorigenic metabolism through mTORC1-mediated upregulation of nucleotide synthesis and reveals a metabolic vulnerability of p16-null cancer cells. Senescence bypass through p16 loss predisposes to transformation and tumorigenesis. Buj et al. found that the loss of p16 upregulates nucleotide metabolism through increased mTORC1-mediated translation of RPIA to bypass senescence in an RB-independent manner. Thus, the mTORC1-RPIA axis is a metabolic vulnerability for p16-null cancers.
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Affiliation(s)
- Raquel Buj
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Chi-Wei Chen
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Erika S Dahl
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Kelly E Leon
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Rostislav Kuskovsky
- A.J. Drexel Autism Institute, Drexel University, Philadelphia, PA 19104, USA
| | | | - Maithili Navaratnarajah
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Gao Zhang
- Molecular and Cellular Oncogenesis Program and Melanoma Research Institute, The Wistar Institute, Philadelphia, PA 19104, USA
| | - Mary T Doan
- A.J. Drexel Autism Institute, Drexel University, Philadelphia, PA 19104, USA
| | - Helen Jiang
- A.J. Drexel Autism Institute, Drexel University, Philadelphia, PA 19104, USA
| | - Michael Zaleski
- Department of Pathology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Lydia Kutzler
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Holly Lacko
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Yiling Lu
- Department of Systems Biology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Gordon B Mills
- Department of Cell, Developmental & Cancer Biology, Oregon Health and Sciences University, Portland, OR 97201, USA
| | - Raghavendra Gowda
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Gavin P Robertson
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Joshua I Warrick
- Department of Pathology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Meenhard Herlyn
- Molecular and Cellular Oncogenesis Program and Melanoma Research Institute, The Wistar Institute, Philadelphia, PA 19104, USA
| | - Yuka Imamura
- Department of Pharmacology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Scot R Kimball
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - David J DeGraff
- Department of Pathology, Penn State College of Medicine, Hershey, PA 17033, USA
| | - Nathaniel W Snyder
- A.J. Drexel Autism Institute, Drexel University, Philadelphia, PA 19104, USA
| | - Katherine M Aird
- Department of Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, PA 17033, USA.
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Xu D, Dai W, Kutzler L, Lacko HA, Jefferson LS, Dennis MD, Kimball SR. ATF4-Mediated Upregulation of REDD1 and Sestrin2 Suppresses mTORC1 Activity during Prolonged Leucine Deprivation. J Nutr 2020; 150:1022-1030. [PMID: 31875479 PMCID: PMC7198311 DOI: 10.1093/jn/nxz309] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 11/13/2019] [Accepted: 11/25/2019] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND The protein kinase target of rapamycin (mTOR) in complex 1 (mTORC1) is activated by amino acids and in turn upregulates anabolic processes. Under nutrient-deficient conditions, e.g., amino acid insufficiency, mTORC1 activity is suppressed and autophagy is activated. Intralysosomal amino acids generated by autophagy reactivate mTORC1. However, sustained mTORC1 activation during periods of nutrient insufficiency would likely be detrimental to cellular homeostasis. Thus, mechanisms must exist to prevent amino acids released by autophagy from reactivating the kinase. OBJECTIVE The objective of the present study was to test whether mTORC1 activity is inhibited during prolonged leucine deprivation through ATF4-dependent upregulation of the mTORC1 suppressors regulated in development and DNA damage response 1 (REDD1) and Sestrin2. METHODS Mice (8 wk old; C57Bl/6 × 129SvEV) were food deprived (FD) overnight and one-half were refed the next morning. Mouse embryo fibroblasts (MEFs) deficient in ATF4, REDD1, and/or Sestrin2 were deprived of leucine for 0-16 h. mTORC1 activity and ATF4, REDD1, and Sestrin2 expression were assessed in liver and cell lysates. RESULTS Refeeding FD mice resulted in activation of mTORC1 in association with suppressed expression of both REDD1 and Sestrin2 in the liver. In cells in culture, mTORC1 exhibited a triphasic response to leucine deprivation, with an initial suppression followed by a transient reactivation from 2 to 4 h and a subsequent resuppression after 8 h. Resuppression occurred concomitantly with upregulated expression of ATF4, REDD1, and Sestrin2. However, in cells lacking ATF4, neither REDD1 nor Sestrin2 expression was upregulated by leucine deprivation, and resuppression of mTORC1 was absent. Moreover, in cells lacking either REDD1 or Sestrin2, mTORC1 resuppression was attenuated, and in cells lacking both proteins resuppression was further blunted. CONCLUSIONS The results suggest that leucine deprivation upregulates expression of both REDD1 and Sestrin2 in an ATF4-dependent manner, and that upregulated expression of both proteins is involved in resuppression of mTORC1 during prolonged leucine deprivation.
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Affiliation(s)
- Dandan Xu
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Weiwei Dai
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Lydia Kutzler
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Holly A Lacko
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Michael D Dennis
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA, USA,Address correspondence to SRK (e-mail: )
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Xu D, Shimkus KL, Lacko HA, Kutzler L, Jefferson LS, Kimball SR. Evidence for a role for Sestrin1 in mediating leucine-induced activation of mTORC1 in skeletal muscle. Am J Physiol Endocrinol Metab 2019; 316:E817-E828. [PMID: 30835510 PMCID: PMC6580170 DOI: 10.1152/ajpendo.00522.2018] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Previous studies established that leucine stimulates protein synthesis in skeletal muscle to the same extent as a complete mixture of amino acids, and the effect occurs through activation of the mechanistic target of rapamycin in complex 1 (mTORC1). Recent studies using cells in culture showed that the Sestrins bind leucine and are required for leucine-dependent activation of mTORC1. However, the role they play in mediating leucine-dependent activation of the kinase in vivo has been questioned because the dissociation constant of Sestrin2 for leucine is well below circulating and intramuscular levels of the amino acid. The goal of the present study was to compare expression of the Sestrins in skeletal muscle to other tissues and to assess their relative role in mediating activation of mTORC1 by leucine. The results show that the relative expression of the Sestrin proteins varies widely among tissues and that in skeletal muscle Sestrin1 expression is higher than Sestrin3, whereas Sestrin2 expression is markedly lower. Analysis of the dissociation constants of the Sestrins for leucine as assessed by leucine-induced dissociation of the Sestrin·GAP activity toward Rags 2 (GATOR2) complex revealed that Sestrin1 has the highest affinity for leucine and that Sestrin3 has the lowest affinity. In agreement with the dissociation constants calculated using cells in culture, oral leucine administration promotes disassembly of the Sestrin1·GATOR2 complex but not the Sestrin2 or Sestrin3·GATOR2 complex. Overall, the results presented herein are consistent with a model in which leucine-induced activation of mTORC1 in skeletal muscle in vivo occurs primarily through release of Sestrin1 from GATOR2.
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Affiliation(s)
- Dandan Xu
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
- The Key Laboratory of Aquaculture Nutrition (Ministry of Agriculture), Ocean University of China , Qingdao , P.R. China
| | - Kevin L Shimkus
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
| | - Holly A Lacko
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
| | - Lydia Kutzler
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, Penn State College of Medicine , Hershey, Pennsylvania
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Xu D, Shimkus KL, Lacko HA, Kutzler L, Jefferson LS, Kimball SR. Evidence for a Role for Sestrin1 in Mediating Leucine‐Induced Activation of mTORC1 in Skeletal Muscle. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.lb594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Dandan Xu
- Pennsylvania State University College of MedicineHersheyPA
- Ocean University of ChinaQingdaoPeople's Republic of China
| | | | - Holly A. Lacko
- Pennsylvania State University College of MedicineHersheyPA
| | - Lydia Kutzler
- Pennsylvania State University College of MedicineHersheyPA
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Grainger DL, Kutzler L, Rannels SL, Kimball SR. Validation of a commercially available anti-REDD1 antibody using RNA interference and REDD1-/- mouse embryonic fibroblasts. F1000Res 2016; 5:250. [PMID: 27335637 PMCID: PMC4893971 DOI: 10.12688/f1000research.7691.1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/29/2016] [Indexed: 01/16/2023] Open
Abstract
REDD1 is a transcriptional target gene of p53 and HIF-1, and an inhibitor of mTOR (mechanistic target of rapamycin) complex 1 (mTORC1)-signaling through PP2A-dependent interaction, making it an important convergence point of both tumor suppression and cell growth pathways. In accordance with this positioning, REDD1 levels are transcriptionally upregulated in response to a variety of cellular stress factors such as nutrient deprivation, hypoxia and DNA damage. In the absence of such conditions, and in particular where growth factor signaling is activated, REDD1 expression is typically negligible; therefore, it is necessary to induce REDD1 prior to experimentation or detection in model systems. Here, we evaluated the performance of a commercially available polyclonal antibody recognizing REDD1 by Western blotting in the presence of thapsigargin, a pharmacological inducer of ER stress well known to upregulate REDD1 protein expression. Further, REDD1 antibody specificity was challenged in HEK-293 cells in the presence of RNA interference and with a REDD1
-/- mouse embryonic fibroblast knockout cell line. Results showed reproducibility and specificity of the antibody, which was upheld in the presence of thapsigargin treatment. We conclude that this antibody can be used to reliably detect REDD1 endogenous expression in samples of both human and mouse origin.
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Affiliation(s)
| | - Lydia Kutzler
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA, USA
| | - Sharon L Rannels
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA, USA
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, PA, USA
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Steiner JL, Pruznak AM, Deiter G, Navaratnarajah M, Kutzler L, Kimball SR, Lang CH. Disruption of genes encoding eIF4E binding proteins-1 and -2 does not alter basal or sepsis-induced changes in skeletal muscle protein synthesis in male or female mice. PLoS One 2014; 9:e99582. [PMID: 24945486 PMCID: PMC4063727 DOI: 10.1371/journal.pone.0099582] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Accepted: 05/15/2014] [Indexed: 12/31/2022] Open
Abstract
Sepsis decreases skeletal muscle protein synthesis in part by impairing mTOR activity and the subsequent phosphorylation of 4E-BP1 and S6K1 thereby controlling translation initiation; however, the relative importance of changes in these two downstream substrates is unknown. The role of 4E-BP1 (and -BP2) in regulating muscle protein synthesis was assessed in wild-type (WT) and 4E-BP1/BP2 double knockout (DKO) male mice under basal conditions and in response to sepsis. At 12 months of age, body weight, lean body mass and energy expenditure did not differ between WT and DKO mice. Moreover, in vivo rates of protein synthesis in gastrocnemius, heart and liver did not differ between DKO and WT mice. Sepsis decreased skeletal muscle protein synthesis and S6K1 phosphorylation in WT and DKO male mice to a similar extent. Sepsis only decreased 4E-BP1 phosphorylation in WT mice as no 4E-BP1/BP2 protein was detected in muscle from DKO mice. Sepsis decreased the binding of eIF4G to eIF4E in WT mice; however, eIF4E•eIF4G binding was not altered in DKO mice under either basal or septic conditions. A comparable sepsis-induced increase in eIF4B phosphorylation was seen in both WT and DKO mice. eEF2 phosphorylation was similarly increased in muscle from WT septic mice and both control and septic DKO mice, compared to WT control values. The sepsis-induced increase in muscle MuRF1 and atrogin-1 (markers of proteolysis) as well as TNFα and IL-6 (inflammatory cytokines) mRNA was greater in DKO than WT mice. The sepsis-induced decrease in myocardial and hepatic protein synthesis did not differ between WT and DKO mice. These data suggest overall basal protein balance and synthesis is maintained in muscle of mice lacking both 4E-BP1/BP2 and that sepsis-induced changes in mTOR signaling may be mediated by a down-stream mechanism independent of 4E-BP1 phosphorylation and eIF4E•eIF4G binding.
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Affiliation(s)
- Jennifer L. Steiner
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Anne M. Pruznak
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Gina Deiter
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Maithili Navaratnarajah
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Lydia Kutzler
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Scot R. Kimball
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
| | - Charles H. Lang
- Department of Cellular and Molecular Physiology, and Surgery, Penn State College of Medicine, Hershey, Pennsylvania, United States of America
- * E-mail:
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Kimball SR, Do AND, Kutzler L, Cavener DR, Jefferson LS. Rapid turnover of the mTOR complex 1 (mTORC1) repressor REDD1 and activation of mTORC1 signaling following inhibition of protein synthesis. J Biol Chem 2008; 283:3465-3475. [PMID: 18070882 PMCID: PMC2654224 DOI: 10.1074/jbc.m706643200] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
mTORC1 is a complex of proteins that includes the mammalian target of rapamycin (mTOR) and several regulatory proteins. It is activated by a variety of hormones (e.g. insulin) and nutrients (e.g. amino acids) that act to stimulate cell growth and proliferation and repressed by hormones (e.g. glucocorticoids) that act to reduce cell growth. Curiously, mTORC1 signaling is reported to be rapidly (e.g. within 1-2 h) activated by inhibitors of protein synthesis that act on either mRNA translation elongation or gene transcription. However, the basis for the mTORC1 activation has not been satisfactorily delineated. In the present study, mTORC1 signaling was found to be activated in response to inhibition of either the initiation or elongation phases of mRNA translation. Changes in mTORC1 signaling were inversely proportional to alterations in the expression of the mTORC1 repressor, REDD1, but not the expression of TRB3 or TSC2. Moreover the cycloheximide-induced increase in mTORC1 signaling was significantly attenuated in cells lacking REDD1, showing that REDD1 plays an integral role in the response. Finally, the half-life of REDD1 was estimated to be 5 min or less. Overall, the results are consistent with a model in which inhibition of protein synthesis leads to a loss of REDD1 protein because of its rapid degradation, and in part reduced REDD1 expression subsequently leads to de-repression of mTORC1 activity.
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Affiliation(s)
- Scot R Kimball
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the.
| | - A N Dang Do
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the
| | - Lydia Kutzler
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the
| | - Douglas R Cavener
- Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the
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