A pathway involving protein kinase Cδ up-regulates cytosolic phospholipase A ₂α in airway epithelium

Cytosolic phospholipase A ₂α (cPLA ₂α) catalyzes the hydrolysis of glycerophospholipids at the sn-2 position to liberate fatty acids. Although cPLA ₂α has been implicated in various cellular processes, the detailed mechanism of its expression remains to be elucidated. Here we report that phorbol 12-myristate 13-acetate (PMA) up-regulates cPLA ₂α in A549 airway epithelium cells, and that this effect is sensitive to rottlerin, a potent inhibitor of protein kinase Cδ (PKCδ). Consistent with this observation, a dominant negative mutant of PKCδ reduced cPLA ₂α induction in response to PMA. Up-regulation of cPLA ₂α by PMA was also inhibited by PDTC, an inhibitor of nuclear factor-kappa B (NF-κB), and degradation of IκB and subsequent activation of NF-κB occurred in response to PMA treatment. These findings indicate that PMA induces expression of cPLA ₂α at the transcriptional level via an NF-κB-dependent mechanism. In addition, activation of the NF-κB promoter by PMA was diminished by pretreatment with DPI, a flavoenzyme inhibitor as well as by rottlerin, suggesting a role for reactive oxygen species (ROS) as well as PKCδ. Consistent with this, PMA stimulated the production of ROS and this was blocked by inhibiting PKCδ. Our results suggest that PKCδ and ROS lie upstream of NF-κB, and we conclude that a PKCδ-ROS-NF- κB cascade plays a pivotal role in cPLA ₂α induction by PMA.