Phorbol myristate acetate-induced Egr-1 expression is suppressed by phospholipase D isozymes in human glioma cells.

Early growth response-1 (Egr-1) is involved in the regulation of cell growth. Here, we found that overexpression of phospholipase D (PLD) isozymes decreased tumor promoter phorbol myristate acetate (PMA)-induced Egr-1 expression and transactivation in glioma cells. Suppression of PMA-induced Egr-1 was dependent on the expression level of PLD isozymes. Overexpression of catalytically inactive PLD, treatment with PA, and prevention of PA dephosphorylation by 1-propranolol significantly suppressed PMA-induced Egr-1 expression. PLD-induced suppression of Egr-1 was reversed by inhibition of phosphatidylinositol 3-kinase (PI3K). Taken together, these results suggest that elevated expression and activity of PLD attenuate PMA-induced Egr-1 expression via PI3K pathway.