Phospholipase A2 in hemocytes of the tobacco hornworm,Manduca sexta

Abstract

On the hypothesis that prostaglandins and other eicosanoids mediate nodulation responses to bacterial infections in insects, we describe an intracellular phospholipase A2 (PLA2) in homogenates prepared from hemocytes collected from the tobacco hornworm, Manduca sexta. PLA2 hydrolyzes fatty acids from the sn‐2 position of phospholipids. Some PLA2s are thought to be the first and rate‐limiting step in biosynthesis of prostaglandins and other eicosanoids. The hemocyte PLA2 activity was sensitive to hemocyte homogenate protein concentration (up to 250 μg protein/reaction), pH (optimal activity at pH 8.0), and the presence of a Ca2+ chelator. Like PLA2s from mammalian sources, the hemocyte PLA2 was inhibited by the phospholipid analog oleyoxyethyl phosphorylcholine. Whereas most intracellular PLA2s require Ca2+ for catalytic activity, some PLA2s, including the hemocyte enzyme, are Ca2+‐independent. The hemocyte PLA2 exhibited a preference for arachidonyl‐associated substrate over palmitoyl‐associated substrate. These findings show that M. sexta hemocytes express a PLA2 that shows a marked preference for hydrolyzing arachidonic acid from phospholipids. The biological significance of this enzyme relates to cellular immune responses to bacterial infections. The hemocyte PLA2 may be the first biochemical step in synthesis of the eicosanoids that mediate cellular immunity in insects. © 1996 Wiley‐Liss, Inc.

Eicosanoids mediate prophenoloxidase release from oenocytoids in the beet armyworm Spodoptera exigua

“…Moreover, the hemocyte PLA 2 showed a marked preference for arachidonic acid-linked phospholipid substrate (Schleusener and Stanley-Samuelson, 1996). This hemocyte PLA 2 is further divided into cytosolic and membranebound types according to their sensitivity to PLA 2 inhibitors, in which membrane-bound PLA 2 exhibits a specific sensitivity to BPB and is associated with cellular immune reactions .…”

“…Induction of PLA 2 activity has been confirmed in hemocytes of M. sexta in response to bacterial challenge (Tunaz et al, 2003;Stanley and Miller, 2006). While PLA 2 associated with immune reaction has not been identified at the molecular level in insects, catalytic characteristics of non-digestive PLA 2 presumably involved in eicosanoid pathway have been analyzed in preparations from fat body and hemocytes in M. sexta (Uscian and Stanley-Samuelson, 1993;Schleusener and Stanley-Samuelson, 1996). These intracellular PLA 2 s hydrolyze fatty acids from the sn-2 position of phospholipids and show calcium independence in catalytic activity.…”

Eicosanoid actions in insect cellular immune functions

“…We later learned the situation is more complex. Early in our work, we characterized a hemocytic PLA 2 that showed a marked preference for substrate containing AA in the sn ‐2 position (Schleusener & Stanley, 1996), most likely a cytosolic PLA 2 (cPLA 2 ). In our more recent work with tobacco hornworm hemocytes (Park et al., 2004a, 2005), we found hemocytes express at least two forms of PLA 2 , a cPLA 2 and a secretory PLA 2 (sPLA 2 ).…”

Roles of Peroxinectin in PGE2-Mediated Cellular Immunity in Spodoptera exigua

“…Yet, for several reasons the received orthodoxy informs that PLA 2 , COX, and LOX are the three main pillars of insect eicosanoid biosynthesis, as known from the mammalian model. First, insect PLA 2 activity that favors arachidonyl-containing PL substrate has been described in M. sexta hemocytes [33]. More recently, Kim and his colleagues identified four PLA 2 –encoding genes that act in eicosanoid-mediated immune responses in T. castaneum [29].…”