An atypical protein kinase C, PKC ζ, regulates human eosinophil effector functions

Abstract

Rationale Protein kinase C (PKC) comprises a family of isoenzymes playing key roles in downstream signaling and cell functions. PKCs are grouped according to molecular structure and mode of activation: “conventional” PKCs (α, βI, βII, γ) activated by calcium, phosphatidylserine (PS), and diacylglycerol (DAG); “novel” PKCs (δ, ϵ, μ, θ, η) requiring PS and DAG but not calcium; and “atypical” PKCs (ζ, τ/λ) activated by PS alone. We studied PKC ζ participation in effector functions of human eosinophils stimulated with platelet-activating factor (PAF) or complement component (C) 5a. Methods After pretreating eosinophils with a myristoylated PKC ζ specific inhibitor; a myristoylated PKC η specific inhibitor; bisindolylmaleimide I (Bis I), an inhibitor of conventional and novel PKCs; or rottlerin, a PKC δ inhibitor, we examined PAF- or C5a-evoked functions. Induced PKC translocation was characterized by confocal laser scanning microscopy. Results The PKC ζ inhibitor blocked PAF- or C5a-induced eosinophil superoxide anion generation, degranulation, and adhesion as effectively as Bis I or rottlerin. The PKC η inhibitor had no effect since human eosinophils lack PKC η; this confirmed specificity of PKC ζ inhibitor effects. Neither the PKC ζ inhibitor nor rottlerin affected PAF- or C5a-induced αMβ2 expression, while Bis I enhanced PAF-induced αMβ2 expression. Finally, PAF or C5a induced eosinophil shape changes and translocation of PKC ζ, βII, and δ to the cell membrane. Cell shape and translocation responses were completely inhibited by an actin-polymerization inhibitor, cytochalasin B. Conclusions An atypical PKC, PKC ζ, regulates human eosinophil adhesion and effector functions.