Low molecular weight group IIA and group V phospholipase A₂ enzymes have different intracellular locations in mouse bone marrow-derived mast cells

The subcellular location of the enzymes of eicosanoid biosynthesis is critical for their co-ordinate action in the generation of leukotrienes and prostaglandins. This activity is thought to occur predominantly at a perinuclear location. Whereas the subcellular locations of cytosolic phospholipase (PL) A₂ and each of the pathway enzymes of eicosanoid generation have been defined, the distribution of the low molecular weight species of PLA₂ has remained elusive because of the lack of antibodies that distinguish among homologous family members. We have prepared affinity- purified rabbit antipeptide IgG antibodies that distinguish mouse group IIA PLA₂ and group V PLA₂. Immunofluorescence staining and immunogold electron microscopy reveal different subcellular locations for the enzymes. Group IIA₂ PLA₂ is present in the secretory granules of mouse bone marrow-derived mast cells, consistent with its putative role in facilitating secretory granule exocytosis and its consequent extracellular action. In contrast, group V PLA₂ is associated with various membranous organelles including the Golgi apparatus, nuclear envelope, and plasma membrane. The perinuclear location of group V PLA₂ is consistent with a putative interaction with translocated cytosolic PLA₂ in supplying arachidonic acid for generation of eicosanoid products, while the location in Golgi cisternae may also reflect its action as a secreted enzyme. The spatial segregation of group IIA PLA₂ and group V PLA₂ implies that these enzymes are not functionally redundant.