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Phosphatidylinositol 3-kinase activity negatively regulates stability of cyclooxygenase 2 mRNA
Martha M Monick1, Pamela K Robeff, Noah S Butler
1University of Iowa Roy J. and Lucille A. Carver College of Medicine and Veterans Administration Medical Center, Iowa City, Iowa 52242, USA. matha.monick@uiowa.edu
Abstract:
Human alveolar macrophages have both lipopolysaccharide (LPS)-induced and constitutive phosphatidylinositol 3-kinase (PI3K) activity. We observed that blocking PI3K activity increased release of prostaglandin E2 after LPS exposure, and increasing PI3K activity (interleukin-13) decreased release of prostaglandin E2 after LPS exposure. This was not because of an effect of PI3K on phospholipase 2 activity. PI3K inhibition resulted in an increase in cyclooxygenase 2 (COX2) protein, mRNA, and mRNA stability. PI3K negatively regulated activation of the p38 pathway (p38, MKK3/6, and MAPKAP2), and an active p38 was necessary for COX2 production. The data suggest that PI3K inhibition of p38 modulates COX2 expression via destabilization of LPS-induced COX2 mRNA.
Insights
Blocking phosphatidylinositol 3-kinase (PI3K) activity in human macrophages increases prostaglandin E2 release by upregulating cyclooxygenase 2 (COX2) via the p38 pathway. This reveals a novel mechanism for inflammatory mediator production.
Area of Science:
- Immunology
- Cellular Biology
- Molecular Biology
Background:
- Human alveolar macrophages exhibit both lipopolysaccharide (LPS)-induced and constitutive phosphatidylinositol 3-kinase (PI3K) activity.
- Prostaglandin E2 (PGE2) is a key inflammatory mediator released by macrophages.
Purpose of the Study:
- To investigate the role of PI3K activity in regulating PGE2 release in human alveolar macrophages.
- To elucidate the molecular mechanisms by which PI3K influences cyclooxygenase 2 (COX2) expression and PGE2 production.
Main Methods:
- Pharmacological inhibition and activation of PI3K in human alveolar macrophages.
- Stimulation with lipopolysaccharide (LPS).
- Measurement of prostaglandin E2 release.
- Analysis of cyclooxygenase 2 (COX2) protein and mRNA levels.
- Investigation of the p38 mitogen-activated protein kinase (MAPK) pathway activation.
Main Results:
- Blocking PI3K activity increased PGE2 release following LPS exposure, while PI3K activation decreased it.
- PI3K inhibition led to increased COX2 protein, mRNA, and mRNA stability, independent of phospholipase A2 activity.
- PI3K negatively regulated the p38 pathway, which was essential for COX2 production.
Conclusions:
- PI3K negatively regulates COX2 expression and PGE2 release in LPS-stimulated human alveolar macrophages.
- PI3K inhibition enhances COX2 expression by increasing mRNA stability and activating the p38 pathway.
- These findings identify a novel PI3K-p38-COX2 signaling axis controlling inflammatory responses in macrophages.