Involvement of group IIA secretory phospholipase A2 (GIIA) in NGF-induced neuritogenesis of PC12 cells

Neural cells express a variety of phospholipases A2 (PLA2) but their cellular and subcellular localization, in relation to their functions, is still largely unknown. Meanwhile it is well documented their participation to neurodegenerative pro- cesses, minor attention has been devoted to their participation to cellular functions. Among the enzymes, detected in neural cells and possessing PLA2 activity, those commonly indicated as ‘‘secretory’’ (sPLA2) appear to be involved in peculiar cellular processes depending on their cellular and subcellular localization. Recently, we have reported that in undifferen- tiated PC12 cells group IIA sPLA2 (GIIA) is largely present in mitochondria whereas group V sPLA2 (GV) is mostly localized in the nucleus (Macchioni et al. JBC 279: 37860, 2004). Confocal immunoflorescence analysis, using a monoclonal antibody raised against recombinant rat liver sPLA2, revealed the presence of GIIA in growth cones and tips of neurite when PC12 cells were induced to differentiate in neuronal-like cells by NGF (100 ng/ml). In the same conditions, NGF treatment increased PLA2 activity both in PC12 cells and in the culture medium. Others have attributed the same effects to another sPLA2 isoform (GX) (Masuda et al. JBC 280: 23203, 2005). In order to clarify this aspect, we have overexpressed GIIA-myc in PC12 cells and analysed the localization of the protein by confocal analysis using a monoclonal antibody against the myc-epitope. The results confirmed that NGF moves the enzyme to growth cones and tips of neurites, increases the expression of GIIA-myc and enzyme activity both in the cells and extracellular medium. Thus, we suggest that the transloca- tion of GIIA may be functionally linked to the NGF- dependent neurite outgrowth and GIIA release might be part of a mechanism by which NGF stimulates neuronal differ- entiation.