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Journal of Lipid Research, Vol. 40, 1701-1709, September 1999
Copyright © 1999 by Lipid Research, Inc.

Original Article

Mechanism(s) of activation of secretory phospholipase A₂s in mouse keratinocytes

Correspondence to: Susan M. Fischer

The differential activation of different members of the phospholipase A₂ (PLA₂) superfamily and their regulation are important as one or more of them regulates the production of eicosanoids and others may contribute to the formation of other lipid mediators. We previously reported the existence of two forms of secretory or sPLA₂ in mouse keratinocytes, namely type I and type II sPLA₂. We show here that mouse keratinocyte sPLA₂s were potently activated by protease treatment and inhibited by protease inhibitors. We also observed that G protein effectors induced substantial release of oleic acid (OA) from prelabeled mouse keratinocytes. A G_i/G₀ protein activator significantly enhanced the hydrolysis of OA and this increase was not responsive to either pertussis toxin or cholera toxin treatment. Although there was a significant negative correlation between intracellular cAMP levels and OA hydrolysis, experimentally increasing cAMP with forskolin treatment had no effect on sPLA₂ activity. Arachidonic acid but not its metabolites was also shown to marginally activate keratinocyte sPLA₂ by 1.5-fold.

These results lead to the conclusion that mouse keratinocyte sPLA₂s can be regulated primarily by proteolytic activation and a G protein pathway.—Li-Stiles, B., and S. M. Fischer. Mechanism(s) of activation of secretory phospholipase A₂s in mouse keratinocytes. J. Lipid Res. 1999. 40: 1701;–1708.

Supplementary key words: arachidonic acid, G protein, keratinocytes, phospholipase A₂, protease, secretory phospholipase A₂

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