Mechanisms of allergy and clinical immunology
Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase regulate induction of Mcl-1 and survival in glucocorticoid-treated human neutrophils

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Background

Glucocorticoids have been shown to inhibit human neutrophil apoptosis, with implications that this might help accentuate neutrophilic inflammation.

Objective

The aim of this study was to investigate the molecular mechanisms involved in glucocorticoid-mediated inhibition of primary human neutrophil apoptosis.

Methods

Primary human neutrophils were isolated from peripheral blood of healthy volunteers and cultured in vitro with dexamethasone.

Results

Here we confirm that dexamethasone, a classical glucocorticoid, significantly inhibited apoptosis of primary human neutrophils. This inhibition was not dependent on transrepression of proapoptotic molecules but was associated with induction of antiapoptotic Mcl-1. Remarkably, glucocorticoid-mediated enhancement of Mcl-1 and survival were significantly suppressed by pharmacologic inhibition of p38 mitogen-activated protein kinase or phosphatidylinositol 3-kinase. Inhibition of the above kinases also blocked glucocorticoid-induced maintenance of mitochondrial transmembrane potential and suppression of caspases.

Conclusion

Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase are protein kinases that regulate the prosurvival effect of glucocorticoids on human neutrophils.

Section snippets

Methods

For details on the methods used in this study, please see the Methods section in the Online Repository at www.jacionline.org.

Glucocorticoids inhibited neutrophil apoptosis

We first confirmed that dexamethasone significantly inhibited spontaneous cell death of neutrophils (P < .001), with an optimal response at 1 μmol/L. By using 2 different methods to quantify apoptosis at 2 different time points, the percentage of nonapoptotic cells was found to increase by approximately 2-fold in cultures with 1 μmol/L dexamethasone to a level similar to that of cultures with 10 ng/mL GM-CSF (see Fig E1 in the Online Repository at www.jacionline.org).

Neutrophils were

Discussion

In this study we provide further insight into the molecular pathways through which glucocorticoids inhibit apoptosis of primary human neutrophils. This inhibition occurs through p38 MAPK and PI3K signaling pathways. These pathways are necessary for the induction of antiapoptotic Mcl-1 protein in neutrophils by glucocorticoids. Mcl-1 enhancement in turn is associated with suppression of downstream pathways of apoptosis (see Fig E8 in the Online Repository at www.jacionline.org). These mechanisms

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    A.S.G. is supported by a CIHR new investigator scholarship and a CIHR research grant. A.S.S. and S.D. are supported by studentships from the CIHR sponsored National Training Program in Allergy and Asthma, the Manitoba Health Research Council, and the HSCF Olenick award for excellence in immunology research.

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

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    Copyright © 2008 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.