Abstract
We showed previously that E-type prostanoid (EP) 4 receptor activation protects against allergic responses by inhibiting eosinophil migration via phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC). Phosphoinositide-dependent kinase 1 (PDK1) has also been implicated in the regulation of neutrophil migration.
This study was carried out to elucidate whether PDK1 mediates the inhibitory effects of EP4 receptors on human eosinophil effector function.
Therefore, PDK1 signaling was investigated in shape change, chemotaxis, CD11b, respiratory burst and Ca(2+) flux assays. PDK1 expression and activity were assessed by immunofluorescence (A), Western blot (B) and flow cytometry (C).
PDK1 inhibitors prevented the effects of EP4 agonists on shape change, integrin expression, chemotaxis, Ca(2+) flux and respiratory burst. Depending on the cellular function, PDK1 acts in a PI3K-dependent or –independent manner. EP4 stimulation caused PDK1 phosphorylation and induced nuclear shuttling of PDK1. The EP4-induced effect was effectively reversed by the Akt inhibitor triciribine. In support of this finding, the EP4 agonist induced a PI3K/PDK1-dependent increase in Akt phosphorylation.
Our data illustrate a critical role for PDK1 in transducing inhibitory signals on eosinophil effector function. Thus, our results suggest that PDK1 might serve as a novel therapeutic target in diseases involving eosinophilic inflammation, such as asthma.
- © 2014 ERS
