Rapamycin Inhibition of the G1 to S Transition Is Mediated by Effects on Cyclin D1 mRNA and Protein Stability*
- Said Hashemolhosseini‡,
- Yoshikuni Nagamine§,
- Simon J. Morley¶‖,
- Sylvane Desrivières‡**,
- Luka Mercep‡ and
- Stefano Ferrari‡‡
- From the ‡Institute for Experimental Cancer Research, Tumor Biology Center, P. O. Box 1120, 79011 Freiburg, Germany,§Friedrich Miescher Institute, P. O. Box 2543, 4002 Basel, Switzerland, and ¶Department of Biochemistry, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
Abstract
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 (p70S6k) 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 p27Kip1 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.
Footnotes
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↵* This study was supported by the DFG (German Research Council) Grant FE 387/2-1 (to S. F.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‖ Senior Research Fellow of The Wellcome Trust.
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↵** Present address: Biocentre, Dept. of Biochemistry, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
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↵‡ To whom correspondence should be addressed: Dept. of Oncology, Novartis Pharma Ltd., Klybeckstr. 141, 4002 Basel, Switzerland. Tel.: 41-61-696-1715; Fax: 41-61-696-3835; E-mail:stefferrari{at}hotmail.com.
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↵1 The abbreviations used are: FRAP, FK506-binding protein rapamycin-associated protein; LLnL,N-acetyl-Leu-Leu-norleucinal; 5′-TOP, 5′-terminal oligopyrimidine; pRb, retinoblastoma protein; Cdk, cyclin-dependent kinase; PAGE, polyacrylamide gel electrophoresis; GST, glutathione S-transferase.
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↵2 S. J. Morley, unpublished data.
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- Received January 22, 1998.
- Revision received March 13, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
