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Molecular and Cellular Biology, August 2007, p. 5619-5629, Vol. 27, No. 16
0270-7306/07/$08.00+0     doi:10.1128/MCB.00035-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Human Eukaryotic Release Factor 3a Depletion Causes Cell Cycle Arrest at G1 Phase through Inhibition of the mTOR Pathway{triangledown}

Céline Chauvin, Samia Salhi, and Olivier Jean-Jean*

Unité de Biochimie Cellulaire, UMR 7098 CNRS, Université Pierre et Marie Curie, 9 quai Saint-Bernard, 75005 Paris, France

Received 8 January 2007/ Returned for modification 7 February 2007/ Accepted 30 May 2007

Eukaryotic release factor 3 (eRF3) is a GTPase associated with eRF1 in a complex that mediates translation termination in eukaryotes. Studies have related eRF3 with cell cycle regulation, cytoskeleton organization, and tumorigenesis. In mammals, two genes encode two distinct forms of eRF3, eRF3a and eRF3b, which differ in their N-terminal domains. eRF3a is the major factor acting in translation termination, and its expression level controls termination complex formation. Here, we investigate the role of eRF3a in cell cycle progression using short interfering RNAs and flow cytometry. We show that eRF3a depletion induces a G1 arrest and that eRF3a GTP-binding activity, but not the eRF3a N-terminal domain, is required to restore G1-to-S-phase progression. We also show that eRF3a depletion decreases the global translation rate and reduces the polysome charge of mRNA. Finally, we show that two substrates of the mammalian TOR (mTOR) kinase, 4E-BP1 and protein kinase S6K1, are hypophosphorylated in eRF3a-depleted cells. These results strongly suggest that the G1 arrest and the decrease in translation induced by eRF3a depletion are due to the inhibition of mTOR activity and hence that eRF3a belongs to the regulatory pathway of mTOR activity.

* Corresponding author. Mailing address: Unité de Biochimie Cellulaire, UMR 7098 CNRS-Université Pierre et Marie Curie, 9 quai Saint-Bernard, 75252 Paris Cedex 05, France. Phone: 33 1 44272299. Fax: 33 1 44272215. E-mail: jeanjean{at}snv.jussieu.fr

{triangledown} Published ahead of print on 11 June 2007.

Molecular and Cellular Biology, August 2007, p. 5619-5629, Vol. 27, No. 16
0270-7306/07/$08.00+0     doi:10.1128/MCB.00035-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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