Sphingolipids and cholesterol modulate membrane susceptibility to cytosolic phospholipase A(2)

Modulation of cytosolic phospholipase A(2) (cPLA(2)) activity by sphingomye lin (SPH), ceramide (Cer), and cholesterol (Chol) was investigated in CHO-2 B cells activated by the calcium ionophore A23187 and epinephrine. Chol dep letion of CHO-2B cells by treatment with methyl-beta-cyclodextrin (5 mM) re sulted in the inhibition of the release of arachidonic acid whereas the res toration of the level by Chol-loaded cyclodextrin relieved inhibition. Conv ersion of CHO-2B cellular SPH to Cer by Staphylococcus aureus sphingomyelin ase enhanced endogenous cPLA(2) activation as well as uptake by cells of C2 - and C6-ceramide analogs. These results were confirmed in vitro with purif ied human recombinant cPLA(2) acting on a model phospholipid substrate. The enzyme activity was inhibited by SPH but reactivated by Cer as well as by Chol added to glycerophospholipid liposomal substrates containing SPH. The results of this study, which combine in situ and in vitro experimental appr oaches, indicate that membrane microdomains enriched in SPH and Chol play a role in the modulation of the activity of cPLA(2) and in arachidonic acid- derived mediator production.