Asbestos-induced apoptosis is protein kinase Cδ-dependent

Alveolar epithelial and mesothelial cells undergo apoptosis in response to asbestos, a phenomenon that may be important in injury and/or initiation of compensatory proliferation. Here, we report a functional role of protein kinase (PKC)delta in apoptosis by crocidolite asbestos. We first show that asbestos increases the kinase activity of PKCdelta in alveolar type II epithelial cells (C10 line) and causes its translocation to mitochondria, events associated with caspase-9 cleavage and apoptosis as detected by the Apostain technique. Pretreatment of C10 cells with rottlerin (Rot), a PKCdelta-selective inhibitor, before addition of asbestos prevented cleavage of caspase-9 and blocked the appearance of apoptotic cells. Asbestos-induced apoptosis also was inhibited in cells stably expressing a dominant-negative kinase-deficient mutant of PKCdelta (dnPKCdelta), but not dnPKCalpha. Activities of PKCalpha. and PKC increased after exposure to asbestos, but neither isoform migrated to mitochondria. A general inhibitor of PKCs, bisindolylmaleimide I, had no effect on asbestos-induced apoptosis. Hydrogen peroxide (H2O2) induced activation of PKCs delta, alpha, zeta, and theta translocation of PKCdelta to mitochondria, and caspase-9 cleavage. However, H2O2-incluced apoptosis was not inhibited by cell lines stably expressing either dnPKCdelta or dnPKCalpha, suggesting that activation of PKCdelta has a distinct role in the development of asbestos-induced apoptosis.