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Endotoxin (LPS) stimulates 4E-BP1/PHAS-I phosphorylation in macrophages
M W Potter1, S A Shah, K K Elbirt
1Department of Surgery, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
The Journal of Surgical Research
|April 26, 2001
Summary
Lipopolysaccharide (LPS) stimulates 4E-binding protein 1 (4E-BP1) phosphorylation in macrophages via the FRAP/mTOR pathway, impacting cytokine production. This finding is crucial for understanding translational control in immune responses.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Translational control of cytokine production in macrophages stimulated by lipopolysaccharide (LPS) is not well understood.
- Protein translation initiation involves eukaryotic initiation factor 4E (eIF-4E) binding to mRNA.
- 4E-binding proteins (4E-BP1) inhibit translation initiation and require phosphorylation to release eIF-4E.
Purpose of the Study:
- To investigate whether LPS stimulation alters 4E-BP1 phosphorylation in macrophages.
- To elucidate the signaling pathways involved in LPS-induced 4E-BP1 phosphorylation.
Main Methods:
- Macrophages (rat peritoneal and Raw 264.7) were treated with LPS and signal transduction inhibitors.
- Western blotting was used to detect 4E-BP1 phosphorylation.
- 7-methyl GTP Sepharose pull-down assays were performed to assess eIF-4E and 4E-BP1 association.
Main Results:
- LPS induced 4E-BP1 phosphorylation in macrophages, indicated by a slower migrating band on SDS-PAGE.
- Inhibition of p42/p44 MAPK and p38 MAPK pathways did not affect LPS-induced 4E-BP1 phosphorylation.
- Rapamycin (FRAP/mTOR inhibitor) blocked 4E-BP1 phosphorylation, and 4E-BP1 remained associated with eIF-4E.
Conclusions:
- LPS stimulates 4E-BP1 phosphorylation in macrophages through the FRAP/mTOR signaling pathway.
- This pathway is a key regulator of translational control for cytokine gene expression in macrophages.