title: Regulation of cyclin D1 expression by mTORC1 signaling requires eukaryotic initiation factor 4E-binding protein 1.
abstract: There is currently substantial interest in the regulation of cell function by mammalian target of rapamycin (mTOR), especially effects linked to the rapamycin-sensitive mTOR complex 1 (mTORC1). Rapamycin induces G(1) arrest and blocks proliferation of many tumor cells, suggesting that the inhibition of mTORC1 signaling may be useful in cancer therapy. In MCF7 breast adenocarcinoma cells, rapamycin decreases levels of cyclin D1, without affecting cytoplasmic levels of its mRNA. In some cell-types, rapamycin does not affect cyclin D1 levels, whereas the starvation for leucine (which impairs mTORC1 signaling more profoundly than rapamycin) does. This pattern correlates with the behavior of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1, an mTORC1 target that regulates translation initiation). siRNA-mediated knock-down of 4E-BP1 abrogates the effect of rapamycin on cyclin D1 expression and increases the polysomal association of the cyclin D1 mRNA. Our data identify 4E-BP1 as a key regulator of cyclin D1 expression, indicate that this effect is not mediated through the changes in cytoplasmic levels of cyclin D1 mRNA and suggest that, in some cell types, interfering with the amino acid input to mTORC1, rather than using rapamycin, may inhibit proliferation.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Averous
authors.forename: B D
authors.initials: BD
authors.lastname: Fonseca
authors.forename: C G
authors.initials: CG
authors.lastname: Proud
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000096:biosynthesis / Q000235:genetics*; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011506:Proteins; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; D014157:Transcription Factors; D019938:Cyclin D1; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus