Effects of phorbol ester on phospholipase D and mitogen-activated protein kinase activities in T-lymphocyte cell lines.

The effects of phorbol 12-myristate 13-acetate (PMA) on the activities of phospholipase D (PLD3), mitogen-activated protein kinase (ERK), and c-Jun N-terminal kinase (JNK) were studied in Jurkat, a human T cell line, and EL4, a murine T-cell line. PMA treatment rapidly activated PLD in Jurkat, as detected either in intact or broken cells. In contrast, PMA did not stimulate PLD activity in EL4 cells. PLD activity was not detected in membranes prepared from EL4 cells. Jurkat, but not EL4, expresses a 120-kDa protein recognized by an anti-PLD antibody. In both Jurkat and EL4 cells, PMA caused activation of ERKs. Incubation of EL4 cells with bacterial PLD increased phosphatidic acid levels, but did not activate ERK. In both EL4 and Jurkat cells, co-stimulation with PMA and ionomycin stimulated JNK activity. These results show that activation of PLD is not required for activation of ERKs or JNKs by PMA in T-cell lines. Thus, while PLD activity is expressed in some T-cell lines, the role of this enzyme and its products in T-cell activation remain to be elucidated.