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Characterization of the phosphoproteins and protein kinase activity in mTOR immunoprecipitates
T Nishiuma1, K Hara, Y Tsujishita
1Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Kobe, Nada-ku, 657-8501, Japan.
Abstract:
The mammalian target of rapamycin, mTOR, has been shown to be an upstream regulator of translational effectors. In the present study, in order to detect potential molecules involved in the mTOR signaling, an in vitro phosphorylation assay using mTOR immunoprecipitates from HEK293 cells was carried out. In addition to the autophosphorylation of mTOR, 32P incorporation into 80-kDa (pp80) and 175-kDa (pp175) bands was observed in mTOR immunoprecipitates. The protein kinase activity toward the recombinant eIF-4E binding protein 1 (4E-BP1) was also detected as previously described. When mTOR immunoprecipitates from HEK293 cells were prepared in the presence of a detergent, Nonidet P-40, the 4E-BP1 kinase activity and 32P incorporation into pp175 dramatically diminished, while the phosphorylation of mTOR and 32P incorporation into pp80 did not change. These results raised a possibility that mTOR may associate with protein cofactors, some of which may be involved in the regulation of kinase activities associated with mTOR.
Insights
This study investigated the mammalian target of rapamycin (mTOR) signaling pathway. Researchers identified potential cofactors associated with mTOR that regulate its kinase activity, suggesting a more complex regulatory network.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- The mammalian target of rapamycin (mTOR) is a key regulator of protein translation.
- Understanding mTOR signaling is crucial for comprehending cellular growth and proliferation.
Purpose of the Study:
- To identify novel molecules involved in mTOR signaling.
- To investigate the regulatory mechanisms of mTOR kinase activity.
Main Methods:
- In vitro phosphorylation assays using mTOR immunoprecipitates from HEK293 cells.
- Analysis of 32P incorporation into specific protein bands (pp80 and pp175).
- Assessment of kinase activity towards eIF-4E binding protein 1 (4E-BP1) in the presence and absence of Nonidet P-40.
Main Results:
- mTOR immunoprecipitates showed autophosphorylation and phosphorylation of pp80 and pp175.
- Kinase activity towards 4E-BP1 and phosphorylation of pp175 were significantly reduced by Nonidet P-40.
- mTOR phosphorylation and pp80 phosphorylation remained unaffected by Nonidet P-40.
Conclusions:
- The results suggest that mTOR associates with protein cofactors.
- These cofactors may play a role in regulating the kinase activities associated with mTOR.
- This highlights a potential layer of regulation within the mTOR signaling pathway.