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Begimbetova D, Burska AN, Baltabekova A, Kussainova A, Kukanova A, Fazyl F, Ibragimova M, Manekenova K, Makishev A, Bersimbaev RI, Sarbassov DD. The Vitamin C Enantiomers Possess a Comparable Potency in the Induction of Oxidative Stress in Cancer Cells but Differ in Their Toxicity. Int J Mol Sci 2024; 25:2531. [PMID: 38473779 DOI: 10.3390/ijms25052531] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 02/07/2024] [Accepted: 02/10/2024] [Indexed: 03/14/2024] Open
Abstract
The use of vitamin C (VC) in high doses demonstrates a potent tumor suppressive effect by mediating a glucose-dependent oxidative stress in Kirsten rat sarcoma (KRAS) mutant cancer cells. VC with arsenic trioxide (ATO) is a promising drug combination that might lead to the development of effective cancer therapeutics. Considering that a tumor suppressive effect of VC requires its high-dose administration, it is of interest to examine the toxicity of two enantiomers of VC (enantiomer d-optical isomer D-VC and natural l-optical isomer L-VC) in vitro and in vivo. We show that the combinations of L-VC with ATO and D-VC with ATO induced a similar cytotoxic oxidative stress in KrasG12D-expressing mutant cancer cells as indicated by a substantial increase in reactive oxidative species (ROS) production and depolarization of mitochondria. To examine the L-VC and D-VC toxicity effects, we administered high doses of D-VC and L-VC to CD1 mice and carried out an evaluation of their toxic effects. The daily injections of L-VC at a dose of 9.2 g/kg for 18 days were lethal to mice, while 80% of mice remained alive following the similar high-dose administration of D-VC. Following the drug injection courses and histopathological studies, we determined that a natural form of VC (L-VC) is more harmful and toxic to mice when compared to the effects caused by the similar doses of D-VC. Thus, our study indicates that the two enantiomers of VC have a similar potency in the induction of oxidative stress in cancer cells, but D-VC has a distinctive lower toxicity in mice compared to L-VC. While the mechanism of a distinctive toxicity between D-VC and L-VC is yet to be defined, our finding marks D-VC as a more preferable option compared to its natural enantiomer L-VC in clinical settings.
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Affiliation(s)
- Dinara Begimbetova
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
| | - Agata N Burska
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
- School of Medicine, Nazarbayev University, Astana 010000, Kazakhstan
| | | | - Assiya Kussainova
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
- Department of Experimental Medicine, University of Genoa, 16132 Genoa, Italy
- Department of General Biology and Genomics, Institute of Cell Biology and Biotechnology, L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Assiya Kukanova
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
- Department of Oncology, Astana Medical University, Astana 010000, Kazakhstan
| | - Fatima Fazyl
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
| | - Milana Ibragimova
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
| | - Kenzhekyz Manekenova
- Department of Pathological Anatomy, Astana Medical University, Astana 010000, Kazakhstan
| | - Abay Makishev
- Department of Oncology, Astana Medical University, Astana 010000, Kazakhstan
| | - Rakhmetkazhi I Bersimbaev
- Department of General Biology and Genomics, Institute of Cell Biology and Biotechnology, L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Dos D Sarbassov
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
- Department of Biology, School of Sciences and Humanities, Nazarbayev University, Astana 010000, Kazakhstan
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2
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Burska AN, Ilyassova B, Dildabek A, Khamijan M, Begimbetova D, Molnár F, Sarbassov DD. Enhancing an Oxidative "Trojan Horse" Action of Vitamin C with Arsenic Trioxide for Effective Suppression of KRAS-Mutant Cancers: A Promising Path at the Bedside. Cells 2022; 11:3454. [PMID: 36359850 PMCID: PMC9657932 DOI: 10.3390/cells11213454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/19/2022] [Accepted: 10/24/2022] [Indexed: 11/06/2022] Open
Abstract
The turn-on mutations of the KRAS gene, coding a small GTPase coupling growth factor signaling, are contributing to nearly 25% of all human cancers, leading to highly malignant tumors with poor outcomes. Targeting of oncogenic KRAS remains a most challenging task in oncology. Recently, the specific G12C mutant KRAS inhibitors have been developed but with a limited clinical outcome because they acquire drug resistance. Alternatively, exploiting a metabolic breach of KRAS-mutant cancer cells related to a glucose-dependent sensitivity to oxidative stress is becoming a promising indirect cancer targeting approach. Here, we discuss the use of a vitamin C (VC) acting in high dose as an oxidative "Trojan horse" agent for KRAS-mutant cancer cells that can be potentiated with another oxidizing drug arsenic trioxide (ATO) to obtain a potent and selective cytotoxic impact. Moreover, we outline the advantages of VC's non-natural enantiomer, D-VC, because of its distinctive pharmacokinetics and lower toxicity. Thus, the D-VC and ATO combination shows a promising path to treat KRAS-mutant cancers in clinical settings.
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Affiliation(s)
- Agata N. Burska
- Department of Biology, Nazarbayev University, Astana 010000, Kazakhstan
| | | | - Aruzhan Dildabek
- Department of Biology, Nazarbayev University, Astana 010000, Kazakhstan
| | - Medina Khamijan
- Department of Biology, Nazarbayev University, Astana 010000, Kazakhstan
| | - Dinara Begimbetova
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
| | - Ferdinand Molnár
- Department of Biology, Nazarbayev University, Astana 010000, Kazakhstan
| | - Dos D. Sarbassov
- Department of Biology, Nazarbayev University, Astana 010000, Kazakhstan
- National Laboratory Astana, Nazarbayev University, Astana 010000, Kazakhstan
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3
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Wu X, Park M, Sarbassova DA, Ying H, Lee MG, Bhattacharya R, Ellis L, Peterson CB, Hung MC, Lin HK, Bersimbaev RI, Song MS, Sarbassov DD. A chirality-dependent action of vitamin C in suppressing Kirsten rat sarcoma mutant tumor growth by the oxidative combination: Rationale for cancer therapeutics. Int J Cancer 2019; 146:2822-2828. [PMID: 31472018 DOI: 10.1002/ijc.32658] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [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: 12/11/2018] [Revised: 07/25/2019] [Accepted: 08/05/2019] [Indexed: 12/13/2022]
Abstract
Kirsten rat sarcoma (KRAS) mutant cancers, which constitute the vast majority of pancreatic tumors, are characterized by their resistance to established therapies and high mortality rates. Here, we developed a novel and extremely effective combinational therapeutic approach to target KRAS mutant tumors through the generation of a cytotoxic oxidative stress. At high concentrations, vitamin C (VC) is known to provoke oxidative stress and selectively kill KRAS mutant cancer cells, although its effects are limited when it is given as monotherapy. We found that the combination of VC and the oxidizing drug arsenic trioxide (ATO) is an effective therapeutic treatment modality. Remarkably, its efficiency is dependent on chirality of VC as its enantiomer d-optical isomer of VC (d-VC) is significantly more potent than the natural l-optical isomer of VC. Thus, our results demonstrate that the oxidizing combination of ATO and d-VC is a promising approach for the treatment of KRAS mutant human cancers.
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Affiliation(s)
- Xinggang Wu
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX
| | - Mikyung Park
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX
| | - Dilara A Sarbassova
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX
| | - Haoqiang Ying
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX.,The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX
| | - Min Gyu Lee
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX.,The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX
| | - Rajat Bhattacharya
- Department of Surgery, University of Texas M. D. Anderson Cancer Center, Houston, TX
| | - Lee Ellis
- The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX.,Department of Surgery, University of Texas M. D. Anderson Cancer Center, Houston, TX
| | - Christine B Peterson
- Department of Biostatistics, University of Texas M. D. Anderson Cancer Center, Houston, TX
| | - Mien-Chie Hung
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX.,The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX
| | - Hui-Kuan Lin
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC
| | - Rakhmetkazhi I Bersimbaev
- Department of Natural Sciences, The L.N. Gumilyov Eurasian National University, Nur-Sultan, Kazakhstan
| | - Min Sup Song
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX.,The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX.,The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX.,Department of Biology, Nazarbayev University, Nur-Sultan, Kazakhstan
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4
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Abetov DA, Kiyan VS, Zhylkibayev AA, Sarbassova DA, Alybayev SD, Spooner E, Song MS, Bersimbaev RI, Sarbassov DD. Formation of mammalian preribosomes proceeds from intermediate to composed state during ribosome maturation. J Biol Chem 2019; 294:10746-10757. [PMID: 31076509 DOI: 10.1074/jbc.ac119.008378] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [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: 03/12/2019] [Revised: 05/07/2019] [Indexed: 12/28/2022] Open
Abstract
In eukaryotes, ribosome assembly is a rate-limiting step in ribosomal biogenesis that takes place in a distinctive subnuclear organelle, the nucleolus. How ribosomes get assembled at the nucleolar site by forming initial preribosomal complexes remains poorly characterized. In this study, using several human and murine cell lines, we developed a method for isolation of native mammalian preribosomal complexes by lysing cell nuclei through mild sonication. A sucrose gradient fractionation of the nuclear lysate resolved several ribonucleoprotein (RNP) complexes containing rRNAs and ribosomal proteins. Characterization of the RNP complexes with MS-based protein identification and Northern blotting-based rRNA detection approaches identified two types of preribosomes we named here as intermediate preribosomes (IPRibs) and composed preribosome (CPRib). IPRib complexes comprised large preribosomes (105S to 125S in size) containing the rRNA modification factors and premature rRNAs. We further observed that a distinctive CPRib complex consists of an 85S preribosome assembled with mature rRNAs and a ribosomal biogenesis factor, Ly1 antibody-reactive (LYAR), that does not associate with premature rRNAs and rRNA modification factors. rRNA-labeling experiments uncovered that IPRib assembly precedes CPRib complex formation. We also found that formation of the preribosomal complexes is nutrient-dependent because the abundances of IPRib and CPRib decreased substantially when cells were either deprived of amino acids or exposed to an mTOR kinase inhibitor. These findings indicate that preribosomes form via dynamic and nutrient-dependent processing events and progress from an intermediate to a composed state during ribosome maturation.
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Affiliation(s)
- Danysh A Abetov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - Vladimir S Kiyan
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - Assylbek A Zhylkibayev
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - Dilara A Sarbassova
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - Sanzhar D Alybayev
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - Eric Spooner
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142
| | - Min Sup Song
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, Texas 77030
| | - Rakhmetkazhy I Bersimbaev
- Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Nur-Sultan 010000, Kazakhstan, and
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, Texas 77030,; Department of Biology, Nazarbayev University, Nur-Sultan 010000, Kazakhstan.
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5
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Morrison Joly M, Williams MM, Hicks DJ, Jones B, Sanchez V, Young CD, Sarbassov DD, Muller WJ, Brantley-Sieders D, Cook RS. Two distinct mTORC2-dependent pathways converge on Rac1 to drive breast cancer metastasis. Breast Cancer Res 2017; 19:74. [PMID: 28666462 PMCID: PMC5493112 DOI: 10.1186/s13058-017-0868-8] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 06/14/2017] [Indexed: 02/06/2023] Open
Abstract
Background The importance of the mTOR complex 2 (mTORC2) signaling complex in tumor progression is becoming increasingly recognized. HER2-amplified breast cancers use Rictor/mTORC2 signaling to drive tumor formation, tumor cell survival and resistance to human epidermal growth factor receptor 2 (HER2)-targeted therapy. Cell motility, a key step in the metastatic process, can be activated by mTORC2 in luminal and triple negative breast cancer cell lines, but its role in promoting metastases from HER2-amplified breast cancers is not yet clear. Methods Because Rictor is an obligate cofactor of mTORC2, we genetically engineered Rictor ablation or overexpression in mouse and human HER2-amplified breast cancer models for modulation of mTORC2 activity. Signaling through mTORC2-dependent pathways was also manipulated using pharmacological inhibitors of mTOR, Akt, and Rac. Signaling was assessed by western analysis and biochemical pull-down assays specific for Rac-GTP and for active Rac guanine nucleotide exchange factors (GEFs). Metastases were assessed from spontaneous tumors and from intravenously delivered tumor cells. Motility and invasion of cells was assessed using Matrigel-coated transwell assays. Results We found that Rictor ablation potently impaired, while Rictor overexpression increased, metastasis in spontaneous and intravenously seeded models of HER2-overexpressing breast cancers. Additionally, migration and invasion of HER2-amplified human breast cancer cells was diminished in the absence of Rictor, or upon pharmacological mTOR kinase inhibition. Active Rac1 was required for Rictor-dependent invasion and motility, which rescued invasion/motility in Rictor depleted cells. Rictor/mTORC2-dependent dampening of the endogenous Rac1 inhibitor RhoGDI2, a factor that correlated directly with increased overall survival in HER2-amplified breast cancer patients, promoted Rac1 activity and tumor cell invasion/migration. The mTORC2 substrate Akt did not affect RhoGDI2 dampening, but partially increased Rac1 activity through the Rac-GEF Tiam1, thus partially rescuing cell invasion/motility. The mTORC2 effector protein kinase C (PKC)α did rescue Rictor-mediated RhoGDI2 downregulation, partially rescuing Rac-guanosine triphosphate (GTP) and migration/motility. Conclusion These findings suggest that mTORC2 uses two coordinated pathways to activate cell invasion/motility, both of which converge on Rac1. Akt signaling activates Rac1 through the Rac-GEF Tiam1, while PKC signaling dampens expression of the endogenous Rac1 inhibitor, RhoGDI2. Electronic supplementary material The online version of this article (doi:10.1186/s13058-017-0868-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Meghan Morrison Joly
- Department of Cancer Biology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, Rm 749 Preston Research Building, Nashville, TN, 37232, USA
| | - Michelle M Williams
- Department of Cancer Biology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, Rm 749 Preston Research Building, Nashville, TN, 37232, USA
| | - Donna J Hicks
- Department of Cancer Biology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, Rm 749 Preston Research Building, Nashville, TN, 37232, USA
| | - Bayley Jones
- Department of Cancer Biology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, Rm 749 Preston Research Building, Nashville, TN, 37232, USA
| | - Violeta Sanchez
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Christian D Young
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA
| | - William J Muller
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
| | - Dana Brantley-Sieders
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Rebecca S Cook
- Department of Cancer Biology, Vanderbilt University School of Medicine, 2220 Pierce Avenue, Rm 749 Preston Research Building, Nashville, TN, 37232, USA.
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6
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Zeng Z, Liu W, Tsao T, Qiu Y, Zhao Y, Samudio I, Sarbassov DD, Kornblau SM, Baggerly KA, Kantarjian HM, Konopleva M, Andreeff M. High-throughput profiling of signaling networks identifies mechanism-based combination therapy to eliminate microenvironmental resistance in acute myeloid leukemia. Haematologica 2017; 102:1537-1548. [PMID: 28659338 PMCID: PMC5685227 DOI: 10.3324/haematol.2016.162230] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 06/27/2017] [Indexed: 12/20/2022] Open
Abstract
The bone marrow microenvironment is known to provide a survival advantage to residual acute myeloid leukemia cells, possibly contributing to disease recurrence. The mechanisms by which stroma in the microenvironment regulates leukemia survival remain largely unknown. Using reverse-phase protein array technology, we profiled 53 key protein molecules in 11 signaling pathways in 20 primary acute myeloid leukemia samples and two cell lines, aiming to understand stroma-mediated signaling modulation in response to the targeted agents temsirolimus (MTOR), ABT737 (BCL2/BCL-XL), and Nutlin-3a (MDM2), and to identify the effective combination therapy targeting acute myeloid leukemia in the context of the leukemia microenvironment. Stroma reprogrammed signaling networks and modified the sensitivity of acute myeloid leukemia samples to all three targeted inhibitors. Stroma activated AKT at Ser473 in the majority of samples treated with single-agent ABT737 or Nutlin-3a. This survival mechanism was partially abrogated by concomitant treatment with temsirolimus plus ABT737 or Nutlin-3a. Mapping the signaling networks revealed that combinations of two inhibitors increased the number of affected proteins in the targeted pathways and in multiple parallel signaling, translating into facilitated cell death. These results demonstrated that a mechanism-based selection of combined inhibitors can be used to guide clinical drug selection and tailor treatment regimens to eliminate microenvironment-mediated resistance in acute myeloid leukemia.
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Affiliation(s)
- Zhihong Zeng
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Wenbin Liu
- Department of Bioinformatics and Computational Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Twee Tsao
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - YiHua Qiu
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Yang Zhao
- Department of Bioinformatics and Computational Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Ismael Samudio
- Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, BC, Canada
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Steven M Kornblau
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.,Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Keith A Baggerly
- Department of Bioinformatics and Computational Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Hagop M Kantarjian
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Marina Konopleva
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA .,Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Michael Andreeff
- Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX, USA .,Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
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7
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Morrison Joly M, Hicks DJ, Jones B, Sanchez V, Estrada MV, Young C, Williams M, Rexer BN, Sarbassov DD, Muller WJ, Brantley-Sieders D, Cook RS. Rictor/mTORC2 Drives Progression and Therapeutic Resistance of HER2-Amplified Breast Cancers. Cancer Res 2016; 76:4752-64. [PMID: 27197158 DOI: 10.1158/0008-5472.can-15-3393] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 03/16/2016] [Indexed: 02/01/2023]
Abstract
HER2 overexpression drives Akt signaling and cell survival and HER2-enriched breast tumors have a poor outcome when Akt is upregulated. Akt is activated by phosphorylation at T308 via PI3K and S473 via mTORC2. The importance of PI3K-activated Akt signaling is well documented in HER2-amplified breast cancer models, but the significance of mTORC2-activated Akt signaling in this setting remains uncertain. We report here that the mTORC2 obligate cofactor Rictor is enriched in HER2-amplified samples, correlating with increased phosphorylation at S473 on Akt. In invasive breast cancer specimens, Rictor expression was upregulated significantly compared with nonmalignant tissues. In a HER2/Neu mouse model of breast cancer, genetic ablation of Rictor decreased cell survival and phosphorylation at S473 on Akt, delaying tumor latency, penetrance, and burden. In HER2-amplified cells, exposure to an mTORC1/2 dual kinase inhibitor decreased Akt-dependent cell survival, including in cells resistant to lapatinib, where cytotoxicity could be restored. We replicated these findings by silencing Rictor in breast cancer cell lines, but not silencing the mTORC1 cofactor Raptor (RPTOR). Taken together, our findings establish that Rictor/mTORC2 signaling drives Akt-dependent tumor progression in HER2-amplified breast cancers, rationalizing clinical investigation of dual mTORC1/2 kinase inhibitors and developing mTORC2-specific inhibitors for use in this setting. Cancer Res; 76(16); 4752-64. ©2016 AACR.
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Affiliation(s)
| | - Donna J Hicks
- Department of Cancer Biology, Vanderbilt University, Nashville, Tennessee
| | - Bayley Jones
- Department of Cancer Biology, Vanderbilt University, Nashville, Tennessee
| | - Violeta Sanchez
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | | | - Christian Young
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Michelle Williams
- Department of Cancer Biology, Vanderbilt University, Nashville, Tennessee
| | - Brent N Rexer
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas
| | | | - Dana Brantley-Sieders
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee. The Vanderbilt-Ingram Cancer Center at Vanderbilt University, Vanderbilt University, Nashville, Tennessee
| | - Rebecca S Cook
- Department of Cancer Biology, Vanderbilt University, Nashville, Tennessee. The Vanderbilt-Ingram Cancer Center at Vanderbilt University, Vanderbilt University, Nashville, Tennessee.
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8
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Ishizawa J, Kojima K, Chachad D, Ruvolo P, Ruvolo V, Jacamo RO, Borthakur G, Mu H, Zeng Z, Tabe Y, Allen JE, Wang Z, Ma W, Lee HC, Orlowski R, Sarbassov DD, Lorenzi PL, Huang X, Neelapu SS, McDonnell T, Miranda RN, Wang M, Kantarjian H, Konopleva M, Davis RE, Andreeff M. ATF4 induction through an atypical integrated stress response to ONC201 triggers p53-independent apoptosis in hematological malignancies. Sci Signal 2016; 9:ra17. [PMID: 26884599 DOI: 10.1126/scisignal.aac4380] [Citation(s) in RCA: 129] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The clinical challenge posed by p53 abnormalities in hematological malignancies requires therapeutic strategies other than standard genotoxic chemotherapies. ONC201 is a first-in-class small molecule that activates p53-independent apoptosis, has a benign safety profile, and is in early clinical trials. We found that ONC201 caused p53-independent apoptosis and cell cycle arrest in cell lines and in mantle cell lymphoma (MCL) and acute myeloid leukemia (AML) samples from patients; these included samples from patients with genetic abnormalities associated with poor prognosis or cells that had developed resistance to the nongenotoxic agents ibrutinib and bortezomib. Moreover, ONC201 caused apoptosis in stem and progenitor AML cells and abrogated the engraftment of leukemic stem cells in mice while sparing normal bone marrow cells. ONC201 caused changes in gene expression similar to those caused by the unfolded protein response (UPR) and integrated stress responses (ISRs), which increase the translation of the transcription factor ATF4 through an increase in the phosphorylation of the translation initiation factor eIF2α. However, unlike the UPR and ISR, the increase in ATF4 abundance in ONC201-treated hematopoietic cells promoted apoptosis and did not depend on increased phosphorylation of eIF2α. ONC201 also inhibited mammalian target of rapamycin complex 1 (mTORC1) signaling, likely through ATF4-mediated induction of the mTORC1 inhibitor DDIT4. Overexpression of BCL-2 protected against ONC201-induced apoptosis, and the combination of ONC201 and the BCL-2 antagonist ABT-199 synergistically increased apoptosis. Thus, our results suggest that by inducing an atypical ISR and p53-independent apoptosis, ONC201 has clinical potential in hematological malignancies.
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Affiliation(s)
- Jo Ishizawa
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Kensuke Kojima
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. Division of Hematology, Respiratory Medicine and Oncology, Department of Medicine, Saga University, Saga 840-8502, Japan
| | - Dhruv Chachad
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Peter Ruvolo
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Vivian Ruvolo
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Rodrigo O Jacamo
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Gautam Borthakur
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Hong Mu
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Zhihong Zeng
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Yoko Tabe
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. Department of Clinical Laboratory Medicine, Juntendo University School of Medicine, Tokyo 113-8431, Japan
| | | | - Zhiqiang Wang
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Wencai Ma
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Hans C Lee
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Robert Orlowski
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Philip L Lorenzi
- Department of Bioinformatics and Computational Biology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Xuelin Huang
- Department of Biostatistics, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Sattva S Neelapu
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Timothy McDonnell
- Department of Hematopathology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Roberto N Miranda
- Department of Hematopathology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Michael Wang
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Hagop Kantarjian
- Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Marina Konopleva
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - R Eric Davis
- Department of Lymphoma/Myeloma, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
| | - Michael Andreeff
- Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
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9
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Jin G, Lee SW, Zhang X, Cai Z, Gao Y, Chou PC, Rezaeian AH, Han F, Wang CY, Yao JC, Gong Z, Chan CH, Huang CY, Tsai FJ, Tsai CH, Tu SH, Wu CH, Sarbassov DD, Ho YS, Lin HK. Skp2-Mediated RagA Ubiquitination Elicits a Negative Feedback to Prevent Amino-Acid-Dependent mTORC1 Hyperactivation by Recruiting GATOR1. Mol Cell 2015; 58:989-1000. [PMID: 26051179 DOI: 10.1016/j.molcel.2015.05.010] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 04/24/2015] [Accepted: 05/01/2015] [Indexed: 12/27/2022]
Abstract
The regulation of RagA(GTP) is important for amino-acid-induced mTORC1 activation. Although GATOR1 complex has been identified as a negative regulator for mTORC1 by hydrolyzing RagA(GTP), how GATOR1 is recruited to RagA to attenuate mTORC1 signaling remains unclear. Moreover, how mTORC1 signaling is terminated upon amino acid stimulation is also unknown. We show that the recruitment of GATOR1 to RagA is induced by amino acids in an mTORC1-dependent manner. Skp2 E3 ligase drives K63-linked ubiquitination of RagA, which facilitates GATOR1 recruitment and RagA(GTP) hydrolysis, thereby providing a negative feedback loop to attenuate mTORC1 lysosomal recruitment and prevent mTORC1 hyperactivation. We further demonstrate that Skp2 promotes autophagy but inhibits cell size and cilia growth through RagA ubiquitination and mTORC1 inhibition. We thereby propose a negative feedback whereby Skp2-mediated RagA ubiquitination recruits GATOR1 to restrict mTORC1 signaling upon sustained amino acid stimulation, which serves a critical mechanism to maintain proper cellular functions.
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Affiliation(s)
- Guoxiang Jin
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Szu-Wei Lee
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA
| | - Xian Zhang
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA
| | - Zhen Cai
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Yuan Gao
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA
| | - Ping-Chieh Chou
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Abdol Hossein Rezaeian
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Fei Han
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA
| | - Chi-Yun Wang
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Juo-Chin Yao
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Zhaohui Gong
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Chia-Hsin Chan
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Chih-Yang Huang
- Department of Biotechnology, Asia University, Taichung 41354, Taiwan
| | - Fuu-Jen Tsai
- College of Chinese Medicine, China Medical University, Taichung 40402, Taiwan; Department of Medical Genetics, Pediatrics and Medical Research, China Medical University Hospital, Taichung 40402, Taiwan
| | - Chang-Hai Tsai
- Department of Biotechnology, Asia University, Taichung 41354, Taiwan; Center of Molecular Medicine, China Medical University Hospital, Taichung 40402, Taiwan
| | - Shih-Hsin Tu
- Department of Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei 10031, Taiwan
| | - Chih-Hsiung Wu
- Department of Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei 10031, Taiwan; Division of General Surgery, Department of Surgery, Shuang Ho Hospital, Taipei Medical University, Taipei 10031, Taiwan
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA
| | - Yuan-Soon Ho
- Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 10031, Taiwan; School of Medical Laboratory Science and Biotechnology, College of Medical Science and Technology, Taipei Medical University, Taipei 10031, Taiwan; Department of Laboratory Medicine, Taipei Medical University Hospital, Taipei 10031, Taiwan; Comprehensive Cancer Center of Taipei Medical University, Taipei 10031, Taiwan
| | - Hui-Kuan Lin
- Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA; Graduate Institute of Basic Medical Science, China Medical University, Taichung 40402, Taiwan; Department of Biotechnology, Asia University, Taichung 41354, Taiwan.
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10
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Lin A, Piao HL, Zhuang L, Sarbassov DD, Ma L, Gan B. FoxO transcription factors promote AKT Ser473 phosphorylation and renal tumor growth in response to pharmacologic inhibition of the PI3K-AKT pathway. Cancer Res 2014; 74:1682-93. [PMID: 24448243 DOI: 10.1158/0008-5472.can-13-1729] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The PI3K-AKT pathway is hyperactivated in many human cancers, and several drugs to inhibit this pathway, including the PI3K/mTOR dual inhibitor NVP-BEZ235, are currently being tested in various preclinical and clinical trials. It has been shown that pharmacologic inhibition of the PI3K-AKT pathway results in feedback activation of other oncogenic signaling pathways, which likely will limit the clinical utilization of these inhibitors in cancer treatment. However, the underlying mechanisms of such feedback regulation remain incompletely understood. The PI3K-AKT pathway is a validated therapeutic target in renal cell carcinoma (RCC). Here, we show that FoxO transcription factors serve to promote AKT phosphorylation at Ser473 in response to NVP-BEZ235 treatment in renal cancer cells. Inactivation of FoxO attenuated NVP-BEZ235-induced AKT Ser473 phosphorylation and rendered renal cancer cells more susceptible to NVP-BEZ235-mediated cell growth suppression in vitro and tumor shrinkage in vivo. Mechanistically, we showed that FoxOs upregulated the expression of Rictor, an essential component of MTOR complex 2, in response to NVP-BEZ235 treatment and revealed that Rictor is a key downstream target of FoxOs in NVP-BEZ235-mediated feedback regulation. Finally, we show that FoxOs similarly modulate the feedback response on AKT Ser473 phosphorylation and renal tumor growth by other phosphoinositide 3-kinase (PI3K) or AKT inhibitor treatment. Together, our study reveals a novel mechanism of PI3K-AKT inhibition-mediated feedback regulation and may identify FoxO as a novel biomarker to stratify patients with RCC for PI3K or AKT inhibitor treatment, or a novel therapeutic target to synergize with PI3K-AKT inhibition in RCC treatment.
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Affiliation(s)
- Aifu Lin
- Authors' Affiliations: Departments of Experimental Radiation Oncology and Molecular and Cellular Oncology, the University of Texas MD Anderson Cancer Center; and Program of Cancer Biology, the University of Texas Graduate School of Biomedical Sciences, Houston, Texas
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11
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Chen CH, Kiyan V, Zhylkibayev AA, Kazyken D, Bulgakova O, Page KE, Bersimbaev RI, Spooner E, Sarbassov DD. Autoregulation of the mechanistic target of rapamycin (mTOR) complex 2 integrity is controlled by an ATP-dependent mechanism. J Biol Chem 2013; 288:27019-27030. [PMID: 23928304 DOI: 10.1074/jbc.m113.498055] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nutrients are essential for living organisms because they fuel biological processes in cells. Cells monitor nutrient abundance and coordinate a ratio of anabolic and catabolic reactions. Mechanistic target of rapamycin (mTOR) signaling is the essential nutrient-sensing pathway that controls anabolic processes in cells. The central component of this pathway is mTOR, a highly conserved and essential protein kinase that exists in two distinct functional complexes. The nutrient-sensitive mTOR complex 1 (mTORC1) controls cell growth and cell size by phosphorylation of the regulators of protein synthesis S6K1 and 4EBP1, whereas its second complex, mTORC2, regulates cell proliferation by functioning as the regulatory kinase of Akt and other members of the AGC kinase family. The regulation of mTORC2 remains poorly characterized. Our study shows that the cellular ATP balance controls a basal kinase activity of mTORC2 that maintains the integrity of mTORC2 and phosphorylation of Akt on the turn motif Thr-450 site. We found that mTOR stabilizes SIN1 by phosphorylation of its hydrophobic and conserved Ser-260 site to maintain the integrity of mTORC2. The optimal kinase activity of mTORC2 requires a concentration of ATP above 1.2 mM and makes this kinase complex highly sensitive to ATP depletion. We found that not amino acid but glucose deprivation of cells or acute ATP depletion prevented the mTOR-dependent phosphorylation of SIN1 on Ser-260 and Akt on Thr-450. In a low glucose medium, the cells carrying a substitution of SIN1 with its phosphomimetic mutant show an increased rate of cell proliferation related to a higher abundance of mTORC2 and phosphorylation of Akt. Thus, the homeostatic ATP sensor mTOR controls the integrity of mTORC2 and phosphorylation of Akt on the turn motif site.
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Affiliation(s)
- Chien-Hung Chen
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77030
| | - Vladimir Kiyan
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Assylbek A Zhylkibayev
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Dubek Kazyken
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Olga Bulgakova
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Kent E Page
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; Department of Biomedical Engineering, University of Houston, Houston, Texas 77004
| | - Rakhmet I Bersimbaev
- Department of Natural Sciences, L. N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan
| | - Eric Spooner
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142
| | - Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030; University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77030.
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12
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Abstract
Rictor's role in cell migration has been first indicated in the original chemotaxis studies in Dictyostelium and more recent studies reported that rictor is required for migration of cancer cells. How rictor promotes cell migration remains poorly characterized. Based on our proteomics study we have identified a novel functional role of rictor in regulation of cell migration. Here, we discuss our recent finding that rictor by suppressing RhoGDI2 maintains activity of the Rac1/cdc42 GTPases and promotes cell migration. Our finding outlines a critical role of rictor in the regulation of RhoGDI2 activity. This study opens new avenues in the investigation of cancer metastasis by analyzing the rictor dependent post-translational modification of RhoGDI2.
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Affiliation(s)
- Nitin K Agarwal
- Department of Hematopathology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA
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13
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Abstract
Rictor and its binding partner Sin1 are indispensable components of mTORC2 (mammalian Target of Rapamycin Complex 2). The mTORC2 signaling complex functions as the regulatory kinase of the distinct members of AGC kinase family known to regulate cell proliferation and survival. In the early chemotaxis studies in Dictyostelium, the rictor's ortholog has been identified as a regulator of cell migration. How rictor regulates cell migration is poorly characterized. Here we show that rictor regulates cell migration by controlling a potent inhibitor of Rho proteins known as the Rho-GDP dissociation inhibitor 2 (RhoGDI2). Based on our proteomics study we identified that the rictor-dependent deficiency in cell migration is caused by up-regulation of RhoGDI2 leading to a low activity of Rac and Cdc42. We found that a suppression of RhoGDI2 by rictor is not related to the Sin1 or raptor function that excludes a role of mTORC2 or mTORC1 in regulation of RhoGDI2. Our study reveals that rictor by suppressing RhoGDI2 promotes activity of the Rho proteins and cell migration.
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Affiliation(s)
- N K Agarwal
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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14
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Abstract
The mammalian Target Of Rapamycin (mTOR) protein is a central component of the essential and highly conserved signaling pathway that emerged as a critical effector in regulation of cell physiology. Biochemical studies defined mTOR as the protein kinase that exists at least in two distinct complexes. The first complex has been characterized as the nutrient-sensitive mTOR complex 1 that controls cell growth and cell size by regulating protein synthesis and autophagy. The second complex of mTOR has been defined as the component of growth factor signaling that functions as a major regulatory kinase of Akt/PKB. Here, we provide the detailed methods how to purify the functional complexes of mTOR by affinity purification. In the first part, we describe the purification of the distinct mTOR complexes by immunoprecipitation. Purification of the soluble mTOR complexes is explained in the second part of this chapter.
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Affiliation(s)
- Dos D Sarbassov
- Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX, USA.
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15
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Abstract
In higher eukaryotes, growth factors promote anabolic processes and stimulate cell growth, proliferation, and survival by activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway. Deregulation of PI3K/Akt signaling is linked to human diseases, including cancer and metabolic disorders. The PI3K-dependent signaling kinase complex mTORC2 (mammalian target of rapamycin complex 2) has been defined as the regulatory Ser-473 kinase of Akt. The regulation of mTORC2 remains very poorly characterized. We have reconstituted mTORC2 by its assembly in vitro or by co-expression its four essential components (rictor, SIN1, mTOR, mLST8). We show that the functional mTOR kinase domain is required for the mTORC2 activity as the Ser-473 kinase of Akt. We also found that mTOR by phosphorylation of SIN1 prevents its lysosomal degradation. Thus, the kinase domain of mTOR is required for the functional activity of mTORC2, and it controls integrity of mTORC2 by maintaining the protein stability of SIN1.
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Affiliation(s)
- Chien-Hung Chen
- Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA
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16
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Aimbetov R, Chen CH, Bulgakova O, Abetov D, Bissenbaev AK, Bersimbaev RI, Sarbassov DD. Integrity of mTORC2 is dependent on the rictor Gly-934 site. Oncogene 2011; 31:2115-20. [PMID: 21909137 DOI: 10.1038/onc.2011.404] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Growth factor signaling coupled to activation of the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway plays a crucial role in the regulation of cell proliferation and survival. The key regulatory kinase of Akt has been identified as mammalian target of rapamycin complex 2 (mTORC2), which functions as the PI3K-dependent Ser-473 kinase of Akt. This kinase complex is assembled by mTOR and its essential components rictor, Sin1 and mLST8. The recent genetic screening study in Caenorhabditis elegans has linked a specific point mutation of rictor to an elevated storage of fatty acids that resembles the rictor deficiency phenotype. In our study, we show that in mammalian cells the analogous single rictor point mutation (G934E) prevents the binding of rictor to Sin1 and the assembly of mTORC2, but this mutation does not interfere with the binding of the rictor-interacting protein Protor. A substitution of the rictor Gly-934 residue to a charged amino acid prevents formation of the rictor/Sin1 heterodimer. The cells expressing the rictor G934E mutant remain deficient in the mTORC2 signaling, as detected by the reduced phosphorylation of Akt on Ser-473 and a low cell proliferation rate. Thus, although a full length of rictor is required to interact with its binding partner Sin1, a single amino acid of rictor Gly-934 controls its interaction with Sin1 and assembly of mTORC2.
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Affiliation(s)
- R Aimbetov
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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17
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Boulbés DR, Shaiken T, Sarbassov DD. Endoplasmic reticulum is a main localization site of mTORC2. Biochem Biophys Res Commun 2011; 413:46-52. [PMID: 21867682 DOI: 10.1016/j.bbrc.2011.08.034] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Accepted: 08/07/2011] [Indexed: 11/25/2022]
Abstract
The Akt kinase is a critical effector in growth factor signaling. Activation of Akt driven by the growth factor dependent PI3K (phosphatidylinositol-3-OH kinase) is coupled to the plasma membrane translocation and phosphorylation of Akt on two sites by PDK1 (phosphoinositide-dependent protein kinase-1) on Thr-308 and by mTORC2 (mammalian Target of Rapamycin Complex 2) on Ser-473. In our study we examined the sub-cellular localization of mTORC2 and identified that this kinase complex predominantly resides on endoplasmic reticulum (ER). Our immunostaining analysis did not show a substantial co-localization of the mTORC2 component rictor with Golgi, lysosome, clathrin-coated vesicles, early endosomes, or plasma membrane but indicated a strong co-localization of rictor with ribosomal protein S6 and ER marker. Our biochemical study also identified the mTORC2 components rictor, SIN1, and mTOR as the highly abundant proteins in the ER fraction, whereas only small amount of these proteins are detected in the plasma membrane and cytosolic fractions. We found that growth factor signaling does not alter the ER localization of mTORC2 and also does not induce its translocation to the plasma membrane. Based on our study we suggest that the mTORC2-dependent phosphorylation of Akt on Ser-473 takes place on the surface of ER.
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Affiliation(s)
- Delphine R Boulbés
- Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
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18
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Chen CH, Shaikenov T, Peterson TR, Aimbetov R, Bissenbaev AK, Lee SW, Wu J, Lin HK, Sarbassov DD. ER stress inhibits mTORC2 and Akt signaling through GSK-3β-mediated phosphorylation of rictor. Sci Signal 2011; 4:ra10. [PMID: 21343617 DOI: 10.1126/scisignal.2001731] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In response to environmental cues, cells coordinate a balance between anabolic and catabolic pathways. In eukaryotes, growth factors promote anabolic processes and stimulate cell growth, proliferation, and survival through activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. Akt-mediated phosphorylation of glycogen synthase kinase-3β (GSK-3β) inhibits its enzymatic activity, thereby stimulating glycogen synthesis. We show that GSK-3β itself inhibits Akt by controlling the mammalian target of rapamycin complex 2 (mTORC2), a key activating kinase for Akt. We found that during cellular stress, GSK-3β phosphorylated the mTORC2 component rictor at serine-1235, a modification that interfered with the binding of Akt to mTORC2. The inhibitory effect of GSK-3β on mTORC2-Akt signaling and cell proliferation was eliminated by blocking phosphorylation of rictor at serine-1235. Thus, in response to cellular stress, GSK-3β restrains mTORC2-Akt signaling by specifically phosphorylating rictor, thereby balancing the activities of GSK-3β and Akt, two opposing players in glucose metabolism.
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Affiliation(s)
- Chien-Hung Chen
- Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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19
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Boulbes D, Chen CH, Shaikenov T, Agarwal NK, Peterson TR, Addona TA, Keshishian H, Carr SA, Magnuson MA, Sabatini DM, Sarbassov DD. Rictor phosphorylation on the Thr-1135 site does not require mammalian target of rapamycin complex 2. Mol Cancer Res 2010; 8:896-906. [PMID: 20501647 DOI: 10.1158/1541-7786.mcr-09-0409] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In animal cells, growth factors coordinate cell proliferation and survival by regulating the phosphoinositide 3-kinase/Akt signaling pathway. Deregulation of this signaling pathway is common in a variety of human cancers. The PI3K-dependent signaling kinase complex defined as mammalian target of rapamycin complex 2 (mTORC2) functions as a regulatory Ser-473 kinase of Akt. We find that activation of mTORC2 by growth factor signaling is linked to the specific phosphorylation of its component rictor on Thr-1135. The phosphorylation of this site is induced by the growth factor stimulation and expression of the oncogenic forms of ras or PI3K. Rictor phosphorylation is sensitive to the inhibition of PI3K, mTOR, or expression of integrin-linked kinase. The substitution of wild-type rictor with its specific phospho-mutants in rictor null mouse embryonic fibroblasts did not alter the growth factor-dependent phosphorylation of Akt, indicating that the rictor Thr-1135 phosphorylation is not critical in the regulation of the mTORC2 kinase activity. We found that this rictor phosphorylation takes place in the mTORC2-deficient cells, suggesting that this modification might play a role in the regulation of not only mTORC2 but also the mTORC2-independent function of rictor.
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Affiliation(s)
- Delphine Boulbes
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, Texas, USA
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20
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Zeng Z, Sarbassov DD, Samudio IJ, Yee KWL, Munsell MF, Ellen Jackson C, Giles FJ, Sabatini DM, Andreeff M, Konopleva M. Rapamycin derivatives reduce mTORC2 signaling and inhibit AKT activation in AML. Blood 2006; 109:3509-12. [PMID: 17179228 PMCID: PMC1852241 DOI: 10.1182/blood-2006-06-030833] [Citation(s) in RCA: 273] [Impact Index Per Article: 15.2] [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: 12/13/2022] Open
Abstract
The mTOR complex 2 (mTORC2) containing mTOR and rictor is thought to be rapamycin insensitive and was recently shown to regulate the prosurvival kinase AKT by phosphorylation on Ser473. We investigated the molecular effects of mTOR inhibition by the rapamycin derivatives (RDs) temsirolimus (CCI-779) and everolimus (RAD001) in acute myeloid leukemia (AML) cells. Unexpectedly, RDs not only inhibited the mTOR complex 1 (mTORC1) containing mTOR and raptor with decreased p70S6K, 4EPB1 phosphorylation, and GLUT1 mRNA, but also blocked AKT activation via inhibition of mTORC2 formation. This resulted in suppression of phosphorylation of the direct AKT substrate FKHR and decreased transcription of D-cyclins in AML cells. Similar observations were made in samples from patients with hematologic malignancies who received RDs in clinical studies. Our study provides the first evidence that rapamycin derivatives inhibit AKT signaling in primary AML cells both in vitro and in vivo, and supports the therapeutic potential of mTOR inhibition strategies in leukemias.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Carrier Proteins/metabolism
- Cyclin D
- Cyclins/metabolism
- Drug Screening Assays, Antitumor
- Enzyme Activation/drug effects
- Everolimus
- Gene Expression Regulation, Leukemic/drug effects
- Glucose Transporter Type 1/metabolism
- Humans
- Immunosuppressive Agents/pharmacology
- Leukemia, Myeloid, Acute/drug therapy
- Leukemia, Myeloid, Acute/enzymology
- Phosphorylation/drug effects
- Protein Kinase Inhibitors/pharmacology
- Protein Kinases/metabolism
- Proteins/metabolism
- Proto-Oncogene Proteins c-akt/antagonists & inhibitors
- Proto-Oncogene Proteins c-akt/metabolism
- RNA, Messenger/metabolism
- Rapamycin-Insensitive Companion of mTOR Protein
- Regulatory-Associated Protein of mTOR
- Ribosomal Protein S6 Kinases, 70-kDa/metabolism
- Signal Transduction/drug effects
- Sirolimus/analogs & derivatives
- Sirolimus/pharmacology
- TOR Serine-Threonine Kinases
- Transcription, Genetic/drug effects
- U937 Cells
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Affiliation(s)
- Zhihong Zeng
- Section of Molecular Hematology and Therapy, Department of Stem Cell Transplantation, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA
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21
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Sarbassov DD, Ali SM, Sengupta S, Sheen JH, Hsu PP, Bagley AF, Markhard AL, Sabatini DM. Prolonged Rapamycin Treatment Inhibits mTORC2 Assembly and Akt/PKB. Mol Cell 2006; 22:159-68. [PMID: 16603397 DOI: 10.1016/j.molcel.2006.03.029] [Citation(s) in RCA: 2047] [Impact Index Per Article: 113.7] [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] [Received: 02/25/2006] [Revised: 03/24/2006] [Accepted: 03/28/2006] [Indexed: 12/13/2022]
Abstract
The drug rapamycin has important uses in oncology, cardiology, and transplantation medicine, but its clinically relevant molecular effects are not understood. When bound to FKBP12, rapamycin interacts with and inhibits the kinase activity of a multiprotein complex composed of mTOR, mLST8, and raptor (mTORC1). The distinct complex of mTOR, mLST8, and rictor (mTORC2) does not interact with FKBP12-rapamycin and is not thought to be rapamycin sensitive. mTORC2 phosphorylates and activates Akt/PKB, a key regulator of cell survival. Here we show that rapamycin inhibits the assembly of mTORC2 and that, in many cell types, prolonged rapamycin treatment reduces the levels of mTORC2 below those needed to maintain Akt/PKB signaling. The proapoptotic and antitumor effects of rapamycin are suppressed in cells expressing an Akt/PKB mutant that is rapamycin resistant. Our work describes an unforeseen mechanism of action for rapamycin that suggests it can be used to inhibit Akt/PKB in certain cell types.
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Affiliation(s)
- Dos D Sarbassov
- Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Department of Biology, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA
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Abstract
The raptor-mTOR protein complex is a key component of a nutrient-sensitive signaling pathway that regulates cell size by controlling the accumulation of cellular mass. How nutrients regulate signaling through the raptor-mTOR complex is not well known. Here we show that a redox-sensitive mechanism regulates the phosphorylation of the raptor-mTOR effector S6K1, the interaction between raptor and mTOR, and the kinase activity of the raptor-mTOR complex. In cells treated with the oxidizing agents diamide or phenylarsine oxide, S6K1 phosphorylation increased and became insensitive to nutrient deprivation. Conversely, the reducing reagent BAL (British anti-Lewisite, also known as 2,3-dimercapto-1-propanol) inhibits S6K1 phosphorylation and stabilizes the interaction of mTOR and raptor to mimic the state of the complex under nutrient-deprived conditions. Our findings suggest that a redox-based signaling mechanism may participate in regulating the nutrient-sensitive raptor-mTOR complex and pathway.
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Affiliation(s)
- Dos D Sarbassov
- Department of Biology, Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
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Abstract
The mammalian TOR (mTOR) pathway is a key regulator of cell growth and proliferation and increasing evidence suggests that its deregulation is associated with human diseases, including cancer and diabetes. The mTOR pathway integrates signals from nutrients, energy status and growth factors to regulate many processes, including autophagy, ribosome biogenesis and metabolism. Recent work identifying two structurally and functionally distinct mTOR-containing multiprotein complexes and TSC1/2, rheb, and AMPK as upstream regulators of mTOR is beginning to reveal how mTOR can sense diverse signals and produce a myriad of responses.
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Affiliation(s)
- Dos D Sarbassov
- Whitehead Institute, MIT Department of Biology, 9 Cambridge Center, Cambridge, Massachussetts 02142, USA
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Abstract
Deregulation of Akt/protein kinase B (PKB) is implicated in the pathogenesis of cancer and diabetes. Akt/PKB activation requires the phosphorylation of Thr308 in the activation loop by the phosphoinositide-dependent kinase 1 (PDK1) and Ser473 within the carboxyl-terminal hydrophobic motif by an unknown kinase. We show that in Drosophila and human cells the target of rapamycin (TOR) kinase and its associated protein rictor are necessary for Ser473 phosphorylation and that a reduction in rictor or mammalian TOR (mTOR) expression inhibited an Akt/PKB effector. The rictor-mTOR complex directly phosphorylated Akt/PKB on Ser473 in vitro and facilitated Thr308 phosphorylation by PDK1. Rictor-mTOR may serve as a drug target in tumors that have lost the expression of PTEN, a tumor suppressor that opposes Akt/PKB activation.
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Affiliation(s)
- D D Sarbassov
- Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Nine Cambridge Center, Cambridge, MA 02142, USA
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Sarbassov DD, Ali SM, Kim DH, Guertin DA, Latek RR, Erdjument-Bromage H, Tempst P, Sabatini DM. Rictor, a novel binding partner of mTOR, defines a rapamycin-insensitive and raptor-independent pathway that regulates the cytoskeleton. Curr Biol 2004; 14:1296-302. [PMID: 15268862 DOI: 10.1016/j.cub.2004.06.054] [Citation(s) in RCA: 2020] [Impact Index Per Article: 101.0] [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] [Received: 03/18/2004] [Revised: 05/17/2004] [Accepted: 06/07/2004] [Indexed: 12/22/2022]
Abstract
The mammalian TOR (mTOR) pathway integrates nutrient- and growth factor-derived signals to regulate growth, the process whereby cells accumulate mass and increase in size. mTOR is a large protein kinase and the target of rapamycin, an immunosuppressant that also blocks vessel restenosis and has potential anticancer applications. mTOR interacts with the raptor and GbetaL proteins to form a complex that is the target of rapamycin. Here, we demonstrate that mTOR is also part of a distinct complex defined by the novel protein rictor (rapamycin-insensitive companion of mTOR). Rictor shares homology with the previously described pianissimo from D. discoidieum, STE20p from S. pombe, and AVO3p from S. cerevisiae. Interestingly, AVO3p is part of a rapamycin-insensitive TOR complex that does not contain the yeast homolog of raptor and signals to the actin cytoskeleton through PKC1. Consistent with this finding, the rictor-containing mTOR complex contains GbetaL but not raptor and it neither regulates the mTOR effector S6K1 nor is it bound by FKBP12-rapamycin. We find that the rictor-mTOR complex modulates the phosphorylation of Protein Kinase C alpha (PKCalpha) and the actin cytoskeleton, suggesting that this aspect of TOR signaling is conserved between yeast and mammals.
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Affiliation(s)
- D D Sarbassov
- Whitehead Institute for Biomedical Research, Department of Biology, Massachusetts Institute of Technology, Nine Cambridge Center, Cambridge, MA 02142, USA
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Kim DH, Sarbassov DD, Ali SM, Latek RR, Guntur KVP, Erdjument-Bromage H, Tempst P, Sabatini DM. GbetaL, a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR. Mol Cell 2003; 11:895-904. [PMID: 12718876 DOI: 10.1016/s1097-2765(03)00114-x] [Citation(s) in RCA: 710] [Impact Index Per Article: 33.8] [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: 01/09/2023]
Abstract
mTOR and raptor are components of a signaling pathway that regulates mammalian cell growth in response to nutrients and growth factors. Here, we identify a member of this pathway, a protein named GbetaL that binds to the kinase domain of mTOR and stabilizes the interaction of raptor with mTOR. Like mTOR and raptor, GbetaL participates in nutrient- and growth factor-mediated signaling to S6K1, a downstream effector of mTOR, and in the control of cell size. The binding of GbetaL to mTOR strongly stimulates the kinase activity of mTOR toward S6K1 and 4E-BP1, an effect reversed by the stable interaction of raptor with mTOR. Interestingly, nutrients and rapamycin regulate the association between mTOR and raptor only in complexes that also contain GbetaL. Thus, we propose that the opposing effects on mTOR activity of the GbetaL- and raptor-mediated interactions regulate the mTOR pathway.
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Affiliation(s)
- Do-Hyung Kim
- Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Nine Cambridge Center, 02142, USA
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Kim DH, Sarbassov DD, Ali SM, King JE, Latek RR, Erdjument-Bromage H, Tempst P, Sabatini DM. mTOR interacts with raptor to form a nutrient-sensitive complex that signals to the cell growth machinery. Cell 2002; 110:163-75. [PMID: 12150925 DOI: 10.1016/s0092-8674(02)00808-5] [Citation(s) in RCA: 2234] [Impact Index Per Article: 101.5] [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: 12/12/2022]
Abstract
mTOR/RAFT1/FRAP is the target of the immunosuppressive drug rapamycin and the central component of a nutrient- and hormone-sensitive signaling pathway that regulates cell growth. We report that mTOR forms a stoichiometric complex with raptor, an evolutionarily conserved protein with at least two roles in the mTOR pathway. Raptor has a positive role in nutrient-stimulated signaling to the downstream effector S6K1, maintenance of cell size, and mTOR protein expression. The association of raptor with mTOR also negatively regulates the mTOR kinase activity. Conditions that repress the pathway, such as nutrient deprivation and mitochondrial uncoupling, stabilize the mTOR-raptor association and inhibit mTOR kinase activity. We propose that raptor is a missing component of the mTOR pathway that through its association with mTOR regulates cell size in response to nutrient levels.
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Affiliation(s)
- Do-Hyung Kim
- Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA 02142, USA
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Sarbassov DD, Peterson CA. Insulin receptor substrate-1 and phosphatidylinositol 3-kinase regulate extracellular signal-regulated kinase-dependent and -independent signaling pathways during myogenic differentiation. Mol Endocrinol 1998; 12:1870-8. [PMID: 9849961 DOI: 10.1210/mend.12.12.0205] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Activation of the insulin-like growth factor (IGF) autocrine loop is required for myogenic differentiation and results in sustained activation of extracellular signal-regulated kinases-1 and -2 (ERK-1 and -2). We show here that insulin receptor substrate-1 (IRS-1) phosphorylation on tyrosine and serine residues and association with phosphatidylinositol 3-kinase (PI 3-kinase) are also associated with IGF-dependent myogenic differentiation. Down-regulation of IRS-1 is linked to its serine phosphorylation dependent on PI 3-kinase activity and appears required for differentiation to occur, as IRS-1 is not modified and continues to accumulate in a nondifferentiating myoblast cell line. Furthermore, inhibition of PI 3-kinase activity with LY294002 blocks differentiation, as demonstrated by inhibition of myogenin and myosin heavy chain expression and ERK activation. Blocking the Raf/MEK/ERK cascade with PD98059 does not block myogenic differentiation; however, myotubes do not survive. Thus, PI 3-kinase, in association with IRS-1, is involved in an ERK-independent signaling pathway in myoblasts required for IGF-dependent myogenic differentiation and in inducing sustained activation of ERKs necessary for later stages of differentiation.
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Affiliation(s)
- D D Sarbassov
- Donald W. Reynolds Department of Geriatrics, University of Arkansas for Medical Sciences and The Geriatric Research, Education, and Clinical Center, McClellan Veterans Hospital, Little Rock 72205, USA
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Sarbassov DD, Jones LG, Peterson CA. Extracellular signal-regulated kinase-1 and -2 respond differently to mitogenic and differentiative signaling pathways in myoblasts. Mol Endocrinol 1997; 11:2038-47. [PMID: 9415407 DOI: 10.1210/mend.11.13.0036] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In this report we show that extracellular signal-regulated kinase-1 and -2 (ERK-1 and -2) respond differently to signals that elicit proliferation and/or differentiation of myoblasts using the C2C12 cell line and nondifferentiating mutant NFB4 cells derived from them. Induction of differentiation by withdrawal of serum rendered ERKs in C2C12 myoblasts relatively insensitive to restimulation by serum. Instead, myogenic differentiation of C2C12 cells was associated with sustained activation of ERK-2 dependent on the insulin-like growth factor II (IGF-II) autocrine loop. By contrast, mutant NFB4 cells cultured under the same conditions remained proliferative and demonstrated robust activation of ERKs in response to serum. Similarly, a Gi-dependent signaling pathway induced activation of ERKs in NFB4 cells, but not in C2C12 cells, after stimulation by lysophosphatidic acid (LPA). In NFB4 cells partially rescued by prolonged IGF-I treatment, ERK activity remained responsive to Gi-dependent LPA stimulation, whereas rescue of NFB4 cells by constitutive expression of myogenin or MyoD, associated with activation of the IGF-II autocrine loop, rendered the Gi-signaling pathway refractory to LPA stimulation. Relatively high levels of G(alpha i2) were detected in NFB4 cells and IGF-I treated NFB4 cells, which correlated with responsive Gi signaling. Activation of the IGF-II autocrine loop in C2C12 and NFB4 myoblasts or treatment with IGF-II was associated with loss of G(alpha i2) and inhibition of Gi-dependent signaling. Thus, IGF-I and IGF-II activate distinct signaling cascades, with IGF-II eliciting a stronger differentiation effect correlated with down-regulation of G(alpha i2) protein. Short-term stimulation of NFB4 cells with IGF-I, a mitogenic signal for myoblasts, also induced ERK-1 and -2 activation. Transient stimulation of NFB4 cells with IGF-I while blocking activation of Gi-proteins is with pertussis toxin resulted in preferential activation of ERK-2 characteristic of differentiated C2C12 cells, suggesting that proliferation induced by IGF-I is Gi-dependent and separable from the IGF-I-signaling pathway that leads to differentiation.
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Affiliation(s)
- D D Sarbassov
- Department of Medicine, University of Arkansas for Medical Sciences McClellan Veterans Hospital, Little Rock 72205, USA
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Sarbassov DD, Stefanova R, Grigoriev VG, Peterson CA. Role of insulin-like growth factors and myogenin in the altered program of proliferation and differentiation in the NFB4 mutant muscle cell line. Proc Natl Acad Sci U S A 1995; 92:10874-8. [PMID: 7479901 PMCID: PMC40533 DOI: 10.1073/pnas.92.24.10874] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [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: 01/25/2023] Open
Abstract
In the present study we used the mutant muscle cell line NFB4 to study the balance between proliferation and myogenic differentiation. We show that removal of serum, which induced the parental C2C12 cells to withdraw from the cell cycle and differentiate, had little effect on NFB4 cells. Gene products characteristic of the proliferation state, such as c-Jun, continued to accumulate in the mutant cells in low serum, whereas those involved in differentiation, like myogenin, insulin-like growth factor II (IGF-II), and IGF-binding protein 5 (IGFBP-5) were undetectable. Moreover, NFB4 cells displayed a unique pattern of tyrosine phosphorylated proteins, especially in low serum, suggesting that the signal transduction pathway(s) that controls differentiation is not properly regulated in these cells. Treatment of NFB4 cells with exogenous IGF-I or IGF-II at concentrations shown to promote myogenic differentiation in wild-type cells resulted in activation of myogenin but not MyoD gene expression, secretion of IG-FBP-5, changes in tyrosine phosphorylation, and enhanced myogenic differentiation. Similarly, transfection of myogenin expression constructs also enhanced differentiation and resulted in activation of IGF-II expression, showing that myogenin and IGF-II cross-activate each other's expression. However, in both cases, the expression of Jun mRNA remained elevated, suggesting that IGFs and myogenin cannot overcome all aspects of the block to differentiation in NFB4 cells.
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Affiliation(s)
- D D Sarbassov
- Department of Medicine, University of Arkansas for Medical Sciences, McClellan Veterans Hospital, Little Rock 72205, USA
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