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Regulation of eIF-4E BP1 phosphorylation by mTOR
K Hara1, K Yonezawa, M T Kozlowski
1Diabetes Unit and Medical Services, Massachusetts General Hospital, and Harvard Medical School, Boston, Massachusetts 02129, USA.
The Journal of Biological Chemistry
|October 23, 1997
Summary
The mechanistic target of rapamycin (mTOR) pathway regulates protein synthesis. This study shows mTOR directly controls both eIF-4E binding protein 1 (4E-BP1) and p70 S6 kinase in parallel, independent pathways.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Insulin and mitogens stimulate protein synthesis via phosphorylation of key regulators.
- Rapamycin inhibits these processes by targeting the mTOR/RAFT-1/FRAP protein complex.
- mTOR's role in regulating p70 S6 kinase phosphorylation is established, but its effect on eIF-4E BP1 is less clear.
Purpose of the Study:
- To investigate the role of mTOR in the regulation of eIF-4E BP1 phosphorylation.
- To determine if mTOR acts upstream of both p70 S6 kinase and eIF-4E BP1.
- To elucidate the relationship between mTOR, p70 S6 kinase, and eIF-4E BP1 regulation.
Main Methods:
- Utilized rapamycin-resistant mTOR mutants to assess in situ phosphorylation.
- Examined the effect of mTOR mutants on both p70 S6 kinase and eIF-4E BP1.
- Investigated the requirement of mTOR's catalytic activity for its regulatory function.
Main Results:
- Rapamycin-resistant mTOR mutants protected eIF-4E BP1 from dephosphorylation, similar to p70 S6 kinase.
- Protection of both targets required an active catalytic domain in the mTOR mutant.
- Mutants of p70 S6 kinase resistant to rapamycin did not protect eIF-4E BP1.
Conclusions:
- mTOR acts as an upstream regulator of both eIF-4E BP1 and p70 S6 kinase.
- These two substrates are regulated by mTOR in parallel, rather than sequentially.
- The findings clarify the signaling network downstream of mTOR in response to growth factors.