title: Combined inhibition of MEK and mammalian target of rapamycin abolishes phosphorylation of cyclin-dependent kinase 4 in glioblastoma cell lines and prevents their proliferation.
abstract: The Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) signaling pathways are aberrantly activated in many tumors, including highly proliferative glioblastomas, but how they are wired with the cell cycle remains imperfectly understood. Inhibitors of MEK/ERK and mTOR pathways are tested as anticancer agents. They are generally considered to induce a G(1) cell cycle arrest through down-regulation of D-type cyclins and up-regulation of p27(kip1). Here, we examined the effect of targeting mTOR by rapamycin and/or MEK by PD184352 in human glioblastoma cell lines. In combination, these drugs cooperatively and potently inhibited the G(1)-S transition and retinoblastoma protein phosphorylation. Their cooperation could not be explained by their partial and differential inhibitory effects on cyclin D1 or D3 but instead by their synergistic inhibition of the activating T172 phosphorylation of cyclin-dependent kinase (CDK) 4. This appeared independent of p27 and unrelated to weak modulations of the CDK-activating kinase activity. The T172 phosphorylation of CDK4 thus appears as a crucial node integrating the activity of both MEK/ERK and mTOR pathways. Combined inhibition of both pathways should be considered as a promising strategy for treatment of tumors harboring a deregulated CDK4 activity.
authors.affiliation: Institute of Interdisciplinary Research, Université Libre de Bruxelles, Campus Erasme, Brussels, Belgium.
authors.forename: Sabine
authors.initials: S
authors.lastname: Paternot
authors.forename: Pierre P
authors.initials: PP
authors.lastname: Roger
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001549:Benzamides / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects; D004338:Drug Combinations; D004353:Drug Evaluation, Preclinical; D005909:Glioblastoma / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors*; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000076223:Regulatory-Associated Protein of mTOR; D016160:Retinoblastoma Protein / Q000378:metabolism; D020123:Sirolimus / Q000008:administration & dosage / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D048868:Adaptor Proteins, Signal Transducing; D001549:Benzamides; D004338:Drug Combinations; D046912:Multiprotein Complexes; D047428:Protein Kinase Inhibitors; D011506:Proteins; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D011494:Protein Kinases; C482128:MAP2K2 protein, human; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020123:Sirolimus