Dual effect of the phorbol ester TPA on arachidonic acid release from HeLa cells

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Abstract
The tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) induces release of arachidonic acid (AA) from HeLa cells with a maximum at 2–3 h. Subsequently the extracellular level of AA decreases. Cycloheximide (CH, 10−5 M) does not influence the release of AA, however, it causes the AA level to remain elevated. In the presence of TPA and CH (i) re-uptake of AA is not altered, (ii) re-incorporation of AA into phosphatidylinositol (and phosphatidylethanolamine) is largely increased, and (iii) the level of lysophosphatidylinositol is elevated. The latter two phenomena can be prevented by fluocinolone acetonide (10−8 M), i.e. by inhibition of phospholipase A2 (PLA2). These data point to a continuously elevated PLA2 activity in the presence of TPA and CH. The phorbol ester appears to induce a proteinaceous principle which diminishes PLA2 activity.

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