title: Curcumin disrupts the Mammalian target of rapamycin-raptor complex.
abstract: Curcumin (diferuloylmethane), a polyphenol natural product of the plant Curcuma longa, is undergoing early clinical trials as a novel anticancer agent. However, the anticancer mechanism of curcumin remains to be elucidated. Recently, we have shown that curcumin inhibits phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1), two downstream effector molecules of the mammalian target of rapamycin complex 1 (mTORC1) in numerous cancer cell lines. This study was designed to elucidate the underlying mechanism. We observed that curcumin inhibited mTORC1 signaling not by inhibition of the upstream kinases, such as insulin-like growth factor 1 receptor (IGF-IR) and phosphoinositide-dependent kinase 1 (PDK1). Further, we found that curcumin inhibited mTORC1 signaling independently of protein phosphatase 2A (PP2A) or AMP-activated protein kinase AMPK-tuberous sclerosis complex (TSC). This is evidenced by the findings that curcumin was able to inhibit phosphorylation of S6K1 and 4E-BP1 in the cells pretreated with PP2A inhibitor (okadaic acid) or AMPK inhibitor (compound C), or in the cells expressing dominant-negative (dn) PP2A, shRNA to PP2A-A subunit, or dn-AMPKalpha. Curcumin did not alter the TSC1/2 interaction. Knockout of TSC2 did not affect curcumin inhibition of mTOR signaling. Finally, we identified that curcumin was able to dissociate raptor from mTOR, leading to inhibition of mTORC1 activity. Therefore, our data indicate that curcumin may represent a new class of mTOR inhibitor.
authors.affiliation: Department of Biochemistry and Molecular Biology, Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130-3932, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Beevers
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
authors.forename: Yan
authors.initials: Y
authors.lastname: Luo
authors.forename: Nicholas J G
authors.initials: NJ
authors.lastname: Webster
authors.forename: Shile
authors.initials: S
authors.lastname: Huang
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D003474:Curcumin / Q000494:pharmacology*; D019073:HT29 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D000076223:Regulatory-Associated Protein of mTOR; D012208:Rhabdomyosarcoma / Q000188:drug therapy / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D046912:Multiprotein Complexes; C000631429:PDK1 protein, human; D010750:Phosphoproteins; D011506:Proteins; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; C486009:TESC protein, human; D014157:Transcription Factors; D017526:Receptor, IGF Type 1; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D003474:Curcumin