Naegleria fowleri amoebae express a membrane-associated calcium-independent phospholipase A(2)

Naegleria fowleri, a free-living amoeba, is the causative agent of primary amoebic meningoencephalitis. Previous reports have demonstrated that N. fow leri expresses one or more forms of phospholipase A(2) (PLA(2)) and that a secreted form of this enzyme is involved in pathogenesis. However, the mole cular nature of these phospholipases remains largely unknown. This study wa s initiated to determine whether N. fowleri expresses analogs of the well-c haracterized PLA(2)s that are expressed by mammalian macrophages. Amoeba ce ll homogenates contain a PLA(2) activity that hydrolyzes the substrate that is preferred by the 85 kDa calcium-dependent cytosolic PLA(2), cPLA(2). Ho wever, unlike the cPLA(2) enzyme in macrophages, this activity is largely c alcium-independent, is constitutively associated with membranes and shows o nly a modest preference for phospholipids that contain arachidonate. The am oeba PLA(2) activity is sensitive to inhibitors that block the activities o f cPLA(2)-alpha and the 80 kDa calcium-independent PLA(2), iPLA(2) that are expressed by mammalian cells. One of these compounds, methylarachidonyl fl uorophosphonate, partially inhibits the constitutive release of [H-3]arachi donic acid from pre-labeled amoebae. Together, these data suggest that N. f owleri expresses a constitutively active calcium-independent PLA(2) that ma y play a role in the basal phospholipid metabolism of these cells. (C) 2001 Elsevier Science B.V. All rights reserved.