Role of G alpha(12) and g alpha(13) as novel switches for the activity of Nrf2, a key antioxidative transcription factor

Abstract

G alpha(12) and G alpha(13) function as molecular regulators responding to extracellular stimuli. NF-E2-related factor 2 (Nrf2) is involved in a protective adaptive response to oxidative stress. This study investigated the regulation of Nrf2 by G alpha(12) and G alpha(13). A deficiency of G alpha(12), but not of G alpha(13), enhanced Nrf2 activity and target gene transactivation in embryo fibroblasts. In mice, G alpha(12) knockout activated Nrf2 and thereby facilitated heme catabolism to bilirubin and its glucuronosyl conjugations. An oligonucleotide microarray demonstrated the transactivation of Nrf2 target genes by G alpha(12) gene knockout. G alpha(12) deficiency reduced Jun N-terminal protein kinase (JNK)-dependent Nrf2 ubiquitination required for proteasomal degradation, and so did G alpha(13) deficiency. The absence of G alpha(12), but not of G alpha(13), increased protein kinase C delta (PKC delta) activation and the PKC delta-mediated serine phosphorylation of Nrf2. G alpha(13) gene knockout or knockdown abrogated the Nrf2 phosphorylation induced by G alpha(12) deficiency, suggesting that relief from G alpha(12) repression leads to the G alpha(13)-mediated activation of Nrf2. Constitutive activation of G alpha(13) promoted Nrf2 activity and target gene induction via Rho-mediated PKC delta activation, corroborating positive regulation by G alpha(13). In summary, G alpha(12) and G alpha(13) transmit a JNK-dependent signal for Nrf2 ubiquitination, whereas G alpha(13) regulates Rho-PKC delta-mediated Nrf2 phosphorylation, which is negatively balanced by G alpha(12).