title: Rapamycin disrupts cyclin/cyclin-dependent kinase/p21/proliferating cell nuclear antigen complexes and cyclin D1 reverses rapamycin action by stabilizing these complexes.
abstract: Rapamycin and its derivatives are promising anticancer agents, but the exact mechanisms by which these drugs induce cell cycle arrest and inhibit tumor growth are unknown. A biochemical analysis of human mammary tumor cell lines indicated that rapamycin-induced antiproliferative effects correlated with down-regulation of cellular p21 levels and the levels of p21 in cyclin-dependent kinase (Cdk) 2 and 4 complexes. Cyclin D1 overexpression reversed rapamycin action and this reversal correlated with increased levels of cellular p21, higher levels of p21 associated with Cdk2, and stabilization of cyclin D1/Cdk2/p21/proliferating cell nuclear antigen (PCNA) complexes. Experiments using a novel cyclin D1-Cdk2 fusion protein or a kinase-dead mutant of the fusion protein indicated that reversal of rapamycin action required not only the formation of complexes with p21 and PCNA but also complex-associated kinase activity. Similar results were observed in vivo. The rapamycin derivative RAD001 (everolimus) inhibited the growth of mouse mammary tumors, which correlated with the disruption of cyclin D1/Cdk2 complexes. The potential implications of these results with respect to the use of rapamycin derivatives in breast cancer therapy are discussed.
authors.affiliation: Department of Pharmacology and Therapeutics and the Shands Cancer Center, University of Florida, 1600 Southwest Archer Road, Gainesville, FL 100267, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Law
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Forrester
authors.forename: Anna
authors.initials: A
authors.lastname: Chytil
authors.forename: Patrick
authors.initials: P
authors.lastname: Corsino
authors.forename: Gail
authors.initials: G
authors.lastname: Green
authors.forename: Bradley
authors.initials: B
authors.lastname: Davis
authors.forename: Thomas
authors.initials: T
authors.lastname: Rowe
authors.forename: Brian
authors.initials: B
authors.lastname: Law
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D019938:Cyclin D1 / Q000096:biosynthesis / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D015674:Mammary Neoplasms, Animal / Q000188:drug therapy; D051379:Mice; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*; D015854:Up-Regulation
chemical_list: D000903:Antibiotics, Antineoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018809:Proliferating Cell Nuclear Antigen; D019938:Cyclin D1; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D020123:Sirolimus