We studied the regulation of arachidonic acid (AA) release by guanosine 5'-O-(3-thiotriphosphate (GTPγS) and Ca2+ in electropermeabilized HL60 granulocytes. Stimulation of AA release by GTPγS and Ca2+ was mediated by phospholipase A2 (PLA2) and required the presence of MgATP (EC50: 100- 250 μM). The nucleotide effects were Ca2+-dependent (maximal effects detected at 1 μM free cation). UTP and ATPγS, which stimulate AA release in intact HL60 granulocytes with potencies and efficacies similar to those of ATP, were ineffective in supporting the effects of GTPγS in electropermeabilized cells. Pretreatment with pertussis toxin affected stimulation of AA release by ATP in intact cell, without altering the nucleotide effects in permeabilized cells. We observed the protein kinase C- dependent phosphorylation of PLA2 in permeabilized HL60 granulocytes, together with a correlation between the effects of phorbol esters and staurosporine on this reaction and on AA release. ATP-independent activation of PLA2 by GTPγS and/or Ca2+ was measured in subcellular fractions prepared from HL60 granulocytes. These data appear consistent with a model in which PLA2 activity in resting HL60 granulocytes is subjected to an inhibitory constraint that prevents its activation by Ca2+ and G-proteins. Removal of this constraint, either by the protein kinase C-dependent phosphorylation of the enzyme in vivo or physical disruption of the regulatory assembly (e.g. by N2 cavitation), allows its activation by Ca2+ and G-proteins.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of Biological Chemistry|
|State||Published - 1992|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology