BK‐induced cytosolic phospholipase A2 expression via sequential PKC‐δ, p42/p44 MAPK, and NF‐κB activation in rat brain astrocytes

Abstract

Bradykinin (BK), an inflammatory mediator, has been shown to induce cytosolic phospholipase A2 (cPLA2) expression implicating in inflammatory responses in various cell types. However, the detailed mechanisms underlying BK-induced cPLA2 expression in astrocytes remain unclear. RT-PCR and Western blotting analysis showed that BK induced the expression of cPLA2 mRNA and protein, which was inhibited by Hoe140, suggesting the involvement of B2 BK receptors, confirmed by immunofluorescence staining using anti-B2 BK receptor antibody. BK-induced cPLA2 expression and phosphorylation of p42/p44 MAPK was attenuated by PD98059, indicating the involvement of MEK1/2-p42/p44 MAPK in these responses. BK-induced cPLA2 expression might be due to the translocation of NF-kappaB into nucleus which was inhibited by Hoe140, helenalin, and PD98059, implying the involvement of NF-kappaB. Moreover, BK-induced cPLA2 expression was attenuated by rottlerin, suggesting that PKC-delta might be involved in these responses. This hypothesis was supported by the transfection with a dominant negative plasmid of PKC-delta significantly attenuated BK-induced response. In addition, BK-stimulated translocation of PKC-delta from cytosol to membrane fraction was inhibited by rottlerin but not by PD98059, indicating that PKC-delta might be an upstream component of p42/p44 MAPK. Accordingly, BK-induced phosphorylation of p42/p44 MAPK was attenuated by rottlerin but not by helenalin. These results suggest that in RBA-1 cells, BK-induced cPLA2 expression was sequentially mediated through activation of PKC-delta, p42/p44 MAPK, and NF-kappaB. Understanding the regulation of cPLA2 expression induced by BK in astrocytes might provide a new therapeutic strategy of brain injury and inflammatory diseases.