PKCδ mediates Nrf2-dependent protection of neuronal cells from NO-induced apoptosis

A chemical inhibitor library of 84 compounds was screened to investigate the signaling pathway(s) leading to activation of Nrf2 in response to nitric oxide (NO). We identified the protein kinase C delta (PKCδ) inhibitor rottlerin as the only compound that reduced NO-induced ARE-luciferase reporter activity and diminished NO-induced up-regulation of two Nrf2/ARE-regulated proteins - NAD(P)H:quinone oxidoreductase-1 (NQO1) and hemeoxygenase-1 (HO-1) in SH-Sy5y cells. Rottlerin also sensitized neuroblastoma cells and mouse primary cortical neurons to NO-induced apoptosis. Stable over-expression of PKCδ augmented NO-induced, ARE-dependent gene expression of HO-1 in SH-Sy5y cells, which were more protected from NO killing. Conversely, NO-induced ARE-dependent gene expression was reduced in PKCδ-knockdown SH-EP cells, which displayed greater sensitivity to apoptosis. PKCδ−/− cortical neurons exhibited increased NO-induced apoptosis and less HO-1 mRNA and protein induction compared with wild type neurons. Hence, PKCδ is an important positive modulator of NO-induced Nrf2/ARE-dependent signaling that counteracts NO-mediated apoptosis in neuronal cells.