Originally published In Press as doi:10.1074/jbc.M404945200 on August 3, 2004
J. Biol. Chem., Vol. 279, Issue 44, 46023-46034, October 29, 2004
Molecular Cross-talk between MEK1/2 and mTOR Signaling during Recovery of 293 Cells from Hypertonic Stress*
Susanne Naegele and
Simon J. Morley, A Senior Research Fellow of The Wellcome Trust
From the
Biochemistry Laboratory, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
To investigate the role for initiation factor phosphorylation in de novo translation, we have studied the recovery of human kidney cells from hypertonic stress. Previously, we have demonstrated that hypertonic shock causes a rapid inhibition of protein synthesis, the disaggregation of polysomes, the dephosphorylation of eukaryotic translation initiation factor (eIF)4E, 4E-BP1, and ribosomal protein S6, and increased association of 4E-BP1 with eIF4E. The return of cells to isotonic medium promotes a transient activation of Erk1/2 and the phosphorylation of initiation factors, promoting an increase in protein synthesis that is independent of a requirement for eIF4E phosphorylation. As de novo translation is associated with the phosphorylation of 4E-BP1, we have investigated the role of the signaling pathways required for this event by the use of cell-permeable inhibitors. Surprisingly, although rapamycin, RAD001, wortmannin, and LY294002 inhibited the phosphorylation of 4E-BP1 and its release from eIF4E, they did not prevent the recovery of translation rates. These data suggest that only a small proportion of the available eIF4F complex is required for maximal translation rates under these conditions. Similarly, prevention of Erk1/2 activity alone with low concentrations of PD184352 did not impinge upon de novo translation until later times of recovery from salt shock. However, U0126, which prevented the phosphorylation of Erk1/2, ribosomal protein S6, TSC2, and 4E-BP1, attenuated de novo protein synthesis in recovering cells. These results indicate that the phosphorylation of 4E-BP1 is mediated by both phosphatidylinositol 3-kinase-dependent rapamycin-sensitive and Erk1/2-dependent signaling pathways and that activation of either pathway in isolation is sufficient to promote de novo translation.
Received for publication, May 4, 2004
, and in revised form, August 3, 2004.
* This research was supported by Grants 040800 and 050703 from The Wellcome Trust. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
To whom correspondence should be addressed. Tel.: 01273-678544; Fax: 01273-678433; E-mail: s.j.morley{at}sussex.ac.uk.
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