CHARACTERIZATION OF NUCLEAR SECRETORY PHOSPHOLIPASE A2 (sPLA2)

The presence of phospholipase A (PLA ) activities in mammalian 22 brain has been reported in several studies (Farooqui et al., J. Neu- rochem. 69:889, 1997). The identity and subcellular distribution of various enzymes, belonging to different groups (G), are still largely unknown. Various groups of PLA2s mRNAs are ubiquitously expressed in brain, with relatively similar levels detected in all regions (Molloy et al., Neurosc. Lett. 258:139, 1998). Using confocal immunofluores- cence and immuno electron microscopy, we showed that GIIA sPLA2 and GV sPLA2 are both present in neural cell lines (U251 astrocytoma and PC12 pheocromocytoma) but with different localization. GIIA is largely localized in perinuclear mitochondria while GV appears to be concentrated in the nucleus (Macchioni et al., JBC, 279:37860, 2004). Aim of this study is to establish whether or not nuclei prepared from rat brain cortex contained sPLA2 activity and eventually provide the identification of the enzyme (s). To this aim, glial and neuronal nuclei were purified from rat brain cortex (Thompson J. Neurochem. 21:19, 1973) and PLA2 activity was assayed. Under our experimental condi- tions, both fractions possessed PLA2 activity and their biochemical properties indicated the presence of a secretory enzyme. The enzyme was identified as GV by Western Blot analysis and by inhibition studies with Indoxam (Shionogi) (Suzuki, N. et al. J. Biol. Chem. 275:5785, 2000), thus confirming previous findings with cultured neural cells. Interestingly, GIIA was not present in the nuclear fractions. We con- clude that PLA2 activity present in the nuclei of neural cells is largely, if not exclusively, due to the presence of GV but its function in this cell compartment it is not known.