The ABC's of Group IV cytosolic phospholipase A2.

The three known human Group IV phospholipase A2 (PLA2) paralogs, Group IVA, IVB and IVC, were overexpressed in Sf9 insect cells using the baculovirus expression system. An endogenous, calcium-independent PLA2 activity was identified in the insect cell lysates, which can be inhibited by bromoenol lactone (BEL). The Group IV PLA2 enzymes were characterized in overexpressing insect cell lysates in the presence of BEL, enabling their differentiation from the endogenous PLA2 activity. Group IVC PLA2 was found to have significant lysophospholipase activity, while Group IVB PLA2 did not. Of the three paralogs, only the Group IVA PLA2 shows enhanced activity in the presence of PIP2, which enables its differential detection in cell homogenates. RT-PCR was used to demonstrate the presence of all three enzymes in human U937 and human WISH cells, while only Group IVA and Group IVB PLA2 were detected in murine P388D1 cells and human astrocytes at the mRNA level.