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The role of mTOR signaling in the regulation of protein synthesis and muscle mass during immobilization in mice.

You JS, Anderson GB, Dooley MS, Hornberger TA - Dis Model Mech (2015)

Bottom Line: Unexpectedly, the effects of isometric contractions were also independent of eIF4F complex formation.Similar to isometric contractions, overexpression of Rheb in immobilized muscles enhanced mTOR signaling, cap-dependent translation and global protein synthesis, and prevented the reduction in fiber size.Furthermore, these results indicate that the activation of mTOR signaling is a viable target for therapies that are aimed at preventing muscle atrophy during periods of mechanical unloading.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA.

No MeSH data available.


Related in: MedlinePlus

eIF4F formation is enhanced by immobilization in a rapamycin-sensitive manner, but not further enhanced by isometric contractions. Mice were treated as in Fig. 3 and pre-cleared homogenates from EDL muscles were subjected to immunoprecipitation (IP) of eIF4E followed by western blot analysis for 4E-BP1, eIF4G and eIF4E to obtain the ratio of (A) 4E-BP1:eIF4E and (B) eIF4G:eIF4E. (C) Whole homogenates (WH) were subjected to western blot analysis for the total (T) and phosphorylated (P) forms of various proteins. All values were expressed relative to the values obtained in the IC−/IM−/RAP− group and presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05. IC, isometric contractions; IM, immobilization; RAP, rapamycin.
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DMM019414F5: eIF4F formation is enhanced by immobilization in a rapamycin-sensitive manner, but not further enhanced by isometric contractions. Mice were treated as in Fig. 3 and pre-cleared homogenates from EDL muscles were subjected to immunoprecipitation (IP) of eIF4E followed by western blot analysis for 4E-BP1, eIF4G and eIF4E to obtain the ratio of (A) 4E-BP1:eIF4E and (B) eIF4G:eIF4E. (C) Whole homogenates (WH) were subjected to western blot analysis for the total (T) and phosphorylated (P) forms of various proteins. All values were expressed relative to the values obtained in the IC−/IM−/RAP− group and presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05. IC, isometric contractions; IM, immobilization; RAP, rapamycin.

Mentions: To gain insight into the molecular mechanisms through which the activation of mTOR signaling promotes cap-dependent translation/protein synthesis during immobilization, we first examined the effects of immobilization on the association of eIF4E with 4E-BP1 and eIF4G. As described in the Introduction, mTOR-dependent increases in 4E-BP1 phosphorylation can lead to the dissociation of 4E-BP1 from eIF4E while simultaneously enhancing the association of eIF4E with eIF4G (i.e. the formation of eIF4F complex, which is crucial for the cap-dependent initiation of translation). Consistent with these mechanisms, we found that immobilization induced a decrease in the ratio of 4E-BP1:eIF4E and an increase in the ratio of eIF4G:eIF4E, and that these events were sensitive to the inhibitory effects of rapamycin (compare 1st, 3rd and 5th bars from the left in Fig. 5A,B). Interestingly, the immobilization-induced increase in eIF4F formation did not seem to be entirely inhibited by rapamycin, and this effect might be explained by our observation of a rapamycin-insensitive increase in the S209 phosphorylation of eIF4E, which can stabilize the eIF4F complex (Fig. 5C) (Bu et al., 1993). In either case, our results suggest that an mTOR-dependent increase in the formation of the eIF4F complex contributes to the increase in cap-dependent translation and, thereby, an alleviation of the decrease in protein synthesis that occurs during immobilization.Fig. 5.


The role of mTOR signaling in the regulation of protein synthesis and muscle mass during immobilization in mice.

You JS, Anderson GB, Dooley MS, Hornberger TA - Dis Model Mech (2015)

eIF4F formation is enhanced by immobilization in a rapamycin-sensitive manner, but not further enhanced by isometric contractions. Mice were treated as in Fig. 3 and pre-cleared homogenates from EDL muscles were subjected to immunoprecipitation (IP) of eIF4E followed by western blot analysis for 4E-BP1, eIF4G and eIF4E to obtain the ratio of (A) 4E-BP1:eIF4E and (B) eIF4G:eIF4E. (C) Whole homogenates (WH) were subjected to western blot analysis for the total (T) and phosphorylated (P) forms of various proteins. All values were expressed relative to the values obtained in the IC−/IM−/RAP− group and presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05. IC, isometric contractions; IM, immobilization; RAP, rapamycin.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4582099&req=5

DMM019414F5: eIF4F formation is enhanced by immobilization in a rapamycin-sensitive manner, but not further enhanced by isometric contractions. Mice were treated as in Fig. 3 and pre-cleared homogenates from EDL muscles were subjected to immunoprecipitation (IP) of eIF4E followed by western blot analysis for 4E-BP1, eIF4G and eIF4E to obtain the ratio of (A) 4E-BP1:eIF4E and (B) eIF4G:eIF4E. (C) Whole homogenates (WH) were subjected to western blot analysis for the total (T) and phosphorylated (P) forms of various proteins. All values were expressed relative to the values obtained in the IC−/IM−/RAP− group and presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05. IC, isometric contractions; IM, immobilization; RAP, rapamycin.
Mentions: To gain insight into the molecular mechanisms through which the activation of mTOR signaling promotes cap-dependent translation/protein synthesis during immobilization, we first examined the effects of immobilization on the association of eIF4E with 4E-BP1 and eIF4G. As described in the Introduction, mTOR-dependent increases in 4E-BP1 phosphorylation can lead to the dissociation of 4E-BP1 from eIF4E while simultaneously enhancing the association of eIF4E with eIF4G (i.e. the formation of eIF4F complex, which is crucial for the cap-dependent initiation of translation). Consistent with these mechanisms, we found that immobilization induced a decrease in the ratio of 4E-BP1:eIF4E and an increase in the ratio of eIF4G:eIF4E, and that these events were sensitive to the inhibitory effects of rapamycin (compare 1st, 3rd and 5th bars from the left in Fig. 5A,B). Interestingly, the immobilization-induced increase in eIF4F formation did not seem to be entirely inhibited by rapamycin, and this effect might be explained by our observation of a rapamycin-insensitive increase in the S209 phosphorylation of eIF4E, which can stabilize the eIF4F complex (Fig. 5C) (Bu et al., 1993). In either case, our results suggest that an mTOR-dependent increase in the formation of the eIF4F complex contributes to the increase in cap-dependent translation and, thereby, an alleviation of the decrease in protein synthesis that occurs during immobilization.Fig. 5.

Bottom Line: Unexpectedly, the effects of isometric contractions were also independent of eIF4F complex formation.Similar to isometric contractions, overexpression of Rheb in immobilized muscles enhanced mTOR signaling, cap-dependent translation and global protein synthesis, and prevented the reduction in fiber size.Furthermore, these results indicate that the activation of mTOR signaling is a viable target for therapies that are aimed at preventing muscle atrophy during periods of mechanical unloading.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA.

No MeSH data available.


Related in: MedlinePlus