Atypical PKCζ transduces electrophilic fatty acid signaling in pulmonary epithelial cells

Nitric oxide and secondary oxides of nitrogen react with unsaturated fatty acids such as linoleic acid to yield oxidized and nitrated products. Fatty acid nitroalkene derivatives, (e.g. nitrolinoleate [LNO ₂]) are produced by oxidative inflammatory reactions, detected clinically, display potent electrophilic reactivity and induce post-translational protein modifications that mediate adaptive inflammatory signaling responses. LNO ₂ signaling was examined in lung epithelial cells because the alveolar compartment is a rich site for the transduction of redox and inflammatory reactions. LNO ₂ did not directly induce Ca ²⁺ influx in cultured lung epithelial cells, but inhibited bradykinin-induced Ca ²⁺ influx in a cGMP-independent manner. In contrast, LNO ₂ activated MAP kinase (Erk1/2) by a mechanism independent of bradykinin. It was hypothesized that these unique responses were transduced by activation of different protein kinase C isotypes, supported by the observation that LNO ₂-mediated inhibition of Ca ²⁺ influx was blocked by the non-selective PKC inhibitors chelerythine chloride and calphostin C, but not by the calcium dependent "classic" PKC inhibitor Gö6976. Western blot analysis showed that atypical PKCζ was activated by LNO ₂ stimulation, with PKCζ and Erk activation also demonstrated in primary culture of human lung type II cells. Addition of pseudotypical PKCζ substrate peptide reversed LNO ₂-mediated induction of Ca ²⁺ influx and MAP kinase activation. Finally, the electrophilic nature of LNO ₂ resulted in a novel mode of PKCζ activation, covalent adduction of the enzyme. In summary, LNO ₂ mediated signaling in lung type II epithelial cells occurs via a unique pathway involving PKCζ.