Rapamycin inhibition of the G1 to S transition is mediated by effects on cyclin D1 mRNA and protein stability.
The immunosuppressant rapamycin has been shown previously to inhibit the G1/S transition in several cell types by prolonging the G1 phase of the cell cycle. This process appears to be controlled, in part, by the rapamycin-sensitive FK506-binding protein-rapamycin-associated protein-p70 S6 kinase (p70(S6k)) pathway and the cyclin-dependent kinases (Cdk). We now show that in serum-stimulated NIH 3T3 cells, rapamycin treatment delays the accumulation of cyclin D1 mRNA during progression through G1. Rapamycin also appears to affect stability of the transcript. The combined transcriptional and post-transcriptional effects of the drug ultimately result in decreased levels of cyclin D1 protein. Moreover, degradation of newly synthesized cyclin D1 protein is accelerated by rapamycin, a process prevented by inclusion of the proteasome inhibitor, N-acetyl-Leu-Leu-norleucinal. The overall effect of rapamycin on cyclin D1 leads, in turn, to impaired formation of active complexes with Cdk4, a process which triggers retargeting of the p27(Kip1) inhibitor to cyclin E/Cdk2. In view of this novel experimental evidence, we discuss a possible mechanism for the rapamycin-induced cell cycle arrest at the G1/S transition.
Hashemolhosseini
S
S
Institute for Experimental Cancer Research, Tumor Biology Center, P. O. Box 1120, 79011 Freiburg, Germany.
Nagamine
Y
Y
Morley
S J
SJ
Desrivières
S
S
Mercep
L
L
Ferrari
S
S
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D018797:Cell Cycle Proteins; D019938:Cyclin D1 / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism / Q000502:physiology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects*; D006360:Heat-Shock Proteins / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010766:Phosphorylation; D011090:Polyenes / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects; D016160:Retinoblastoma Protein / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D020123:Sirolimus; D022021:Tacrolimus Binding Proteins; D014158:Transcription, Genetic / Q000187:drug effects; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D007166:Immunosuppressive Agents; D007976:Leupeptins; D008869:Microtubule-Associated Proteins; D011090:Polyenes; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; C063261:acetylleucyl-leucyl-norleucinal; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019893:Ribosomal Protein S6 Kinases; D018844:Cyclin-Dependent Kinases; D022021:Tacrolimus Binding Proteins; D020123:Sirolimus