Differential behavior of sPLA 2-V and sPLA 2-X in human neutrophils

Abstract

Neutrophils and differentiated PLB-985 cells contain various types of PLA 2s including the 85 kDa cytosolic PLA 2 (cPLA 2), Ca 2+-independent PLA 2 (iPLA 2) and secreted PLA 2s (sPLA 2s). The present study focuses on the behavior of sPLA 2s in neutrophils and PLB cells and their relationship to cPLA 2α. The results of the present research show that the two types of sPLA 2 present in neutrophils, sPLA 2-V and sPLA 2-X, which are located in the azurophil granules, are differentially affected by physiological stimuli. While sPLA 2-V is secreted to the extacellular milieu, sPLA 2-X is detected on the plasma membranes after stimulation. Stimulation of neutrophils with formyl-Met–Leu–Phe (fMLP), opsonized zymosan (OZ) or A23187 resulted in a different kinetics of sPLA 2 secretion as detected by its activity in the neutrophil supernatants. Neutrophil priming by inflammatory cytokines or LPS enhanced sPLA 2 activity detected in the supernatant after stimulation by fMLP. This increased activity was due to increased secretion of sPLA 2-V to the supernatant and not to release of sPLA 2-X. sPLA 2 in granulocyte-like PLB cells exhibit identical characteristics to neutrophil sPLA 2, with similar activity and optimal pH of 7.5. Granulocyte-like cPLA 2α-deficient PLB cells serve as a good model to study whether sPLA 2 activity is regulated by cPLA 2α. Secretion and activity of sPLA 2 were found to be similar in granulocyte-like PLB cells expressing or lacking cPLA 2α, indicating that they are not under cPLA 2α regulation.