We previously reported that zymosan-stimulated, protein kinase C (PKC)-dependent arachidonic
acid liberation occurs with association of Ca2+-independent phospholipase A2 (iPLA2)
with the membranes of macrophage-like P388D1 cells. In the present study, the possible
involvement of PKC isoforms (alpha, beta, delta, and epsilon) on the increase in iPLA2
was examined. Stimulation of P388D1 cells with zymosan induced increases in iPLA2
activity and protein in the membranes and liberation of arachidonic acid. In the stimulated
cells, PKCalpha, PKCdelta, and PKCepsilon, but not PKCbeta, were increased in the
membranes. The zymosan-induced increase in iPLA2 activity was suppressed by pretreatment
with 4beta-phorbol 12-myristate 13-acetate for 10 hr, by which PKCalpha and PKCdelta,
but not PKCbeta and PKCepsilon, were depleted, and by Gö6976, a PKCalpha inhibitor,
but not rottlerin, a PKCdelta inhibitor. The zymosan-induced release of arachidonic
acid was also reduced by the PKC depletion and Gö6976. However, stimulation with 4beta-phorbol
12-myristate 13-acetate alone did not increase iPLA2 activity in the membranes. Furthermore,
the depletion of intracellular Ca2+ also impaired the zymosan-induced increase in
iPLA2 activity in the membranes. However, no increase in iPLA2 activity was observed
upon stimulation with Ca2+-mobilizing agents (ionomycin or thapsigargin). Cytochalasin
D, an inhibitor of actin polymerization, suppressed the zymosan-induced increases
in iPLA2 activity and protein in the membranes and the release of arachidonic acid.
These results suggest that zymosan stimulates an increase in iPLA2 in the membranes
of P388D1 cells probably through activation of PKCalpha in concert with cytochalasin
D-sensitive events.