title: MEK drives cyclin D1 hyperelevation during geroconversion.
abstract: When the cell cycle becomes arrested, MTOR (mechanistic Target of Rapamycin) converts reversible arrest into senescence (geroconversion). Hyperexpression of cyclin D1 is a universal marker of senescence along with hypertrophy, beta-Gal staining and loss of replicative/regenerative potential (RP), namely, the ability to restart proliferation when the cell cycle is released. Inhibition of MTOR decelerates geroconversion, although only partially decreases cyclin D1. Here we show that in p21- and p16-induced senescence, inhibitors of mitogen-activated/extracellular signal-regulated kinase (MEK) (U0126, PD184352 and siRNA) completely prevented cyclin D1 accumulation, making it undetectable. We also used MEL10 cells in which MEK inhibitors do not inhibit MTOR. In such cells, U0126 by itself induced senescence that was remarkably cyclin D1 negative. In contrast, inhibition of cyclin-dependent kinase (CDK) 4/6 by PD0332991 caused cyclin D1-positive senescence in MEL10 cells. Both types of senescence were suppressed by rapamycin, converting it into reversible arrest. We confirmed that the inhibitor of CDK4/6 caused cyclin D1 positive senescence in normal RPE cells, whereas U0126 prevented cyclin D1 expression. Elimination of cyclin D1 by siRNA did not prevent other markers of senescence that are consistent with the lack of its effect on MTOR. Our data confirmed that a mere inhibition of the cell cycle was sufficient to cause senescence, providing MTOR was active, and inhibition of MEK partially inhibited MTOR in a cell-type-dependent manner. Second, hallmarks of senescence may be dissociated, and hyperelevated cyclin D1, a marker of hyperactivation of senescent cells, did not necessarily determine other markers of senescence. Third, inhibition of MEK was sufficient to eliminate cyclin D1, regardless of MTOR.
authors.affiliation: Department of Cell Stress Biology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA.
authors.forename: O V
authors.initials: OV
authors.lastname: Leontieva
authors.forename: Z N
authors.initials: ZN
authors.lastname: Demidenko
authors.forename: M V
authors.initials: MV
authors.lastname: Blagosklonny
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001549:Benzamides / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D059447:Cell Cycle Checkpoints / Q000187:drug effects* / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000187:drug effects* / Q000235:genetics; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors; D051361:Cyclin-Dependent Kinase 6 / Q000037:antagonists & inhibitors; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D000903:Antibiotics, Antineoplastic; D001549:Benzamides; D002070:Butadienes; C530104:CCND1 protein, human; C000614131:CDKN2A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D009570:Nitriles; D010879:Piperazines; D011725:Pyridines; D034741:RNA, Small Interfering; C113580:U 0126; D019938:Cyclin D1; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C500026:palbociclib; D020123:Sirolimus