Ken Dick

Essential Role of Phosphoinositide 3-Kinase δ in Neutrophil Directional Movement

Neutrophil chemotaxis is a critical component of the innate immune response. Neutrophils can sense an extremely shallow gradient of chemoattractants and produce relatively robust chemotactic behavior. This directional migration requires cell polarization with actin polymerization occurring predominantly in the leading edge. Synthesis of phosphatidylinositol (3,4,5) trisphosphate (PIP3) by phosphoinositide 3-kinase (PI3K) contributes to asymmetric F-actin synthesis and cell polarization during neutrophil chemotaxis. To determine the contribution of the hemopoietic cell-restricted PI3Kδ in neutrophil chemotaxis, we have developed a potent and selective PI3Kδ inhibitor, IC87114. IC87114 inhibited polarized morphology of neutrophils, fMLP-stimulated PIP3 production and chemotaxis. Tracking analysis of IC87114-treated neutrophils indicated that PI3Kδ activity was required for the directional component of chemotaxis, but not for random movement. Inhibition of PI3Kδ, however, did not block F-actin synthesis or neutrophil adhesion. These results demonstrate that PI3Kδ can play a selective role in the amplification of PIP3 levels that lead to neutrophil polarization and directional migration.

Selective role of PI3Kδ in neutrophil inflammatory responses

Abstract Although members of the class I phosphoinositide 3-kinases (PI3Ks) have been implicated in neutrophil inflammatory responses, the contribution of the individual PI3K isoforms in neutrophil activation has not been tractable with the non-selective inhibitors, LY294002 and wortmannin. We have developed a novel series of PI3K inhibitors that is selective for PI3Kδ, an isoform expressed predominantly in hematopoietic cells. In addition to being selective between members of class I PI3Ks, representatives of these inhibitors such as IC980033 and IC87114 did not inhibit any protein kinases tested. Utilizing these inhibitors we report here a novel role for PI3Kδ in neutrophil activation. Inhibition of PI3Kδ with IC980033 and IC87114 blocked both fMLP- and TNF1α-induced neutrophil superoxide generation and elastase exocytosis. The PI3Kδ inhibitor IC87114 also blocked TNF1α-stimulated elastase exocytosis from neutrophils in a mouse model of inflammation. To our knowledge, this is the first in vivo efficacy demonstration of a PI3Kδ inhibitor in an animal model. Inhibition of PI3Kδ, however, had no effect on in vitro neutrophil bactericidal activity and FcγR-stimulated superoxide generation. Thus, PI3Kδ plays an essential role in certain signaling pathways of neutrophil activation and appears to be an attractive target for the development of an anti-inflammatory therapeutic.