Rapamycin disrupts cyclin/cyclin-dependent kinase/p21/proliferating cell nuclear antigen complexes and cyclin D1 reverses rapamycin action by stabilizing these complexes.
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.
Law
Mary
M
Department of Pharmacology and Therapeutics and the Shands Cancer Center, University of Florida, 1600 Southwest Archer Road, Gainesville, FL 100267, USA.
Forrester
Elizabeth
E
Chytil
Anna
A
Corsino
Patrick
P
Green
Gail
G
Davis
Bradley
B
Rowe
Thomas
T
Law
Brian
B
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
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