Role of Gα₁₂ and Gα₁₃ as Novel Switches for the Activity of Nrf2, a Key Antioxidative Transcription Factor

Abstract

Gα₁₂ and Gα₁₃ 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 Gα₁₂ and Gα₁₃. A deficiency of Gα₁₂, but not of Gα₁₃, enhanced Nrf2 activity and target gene transactivation in embryo fibroblasts. In mice, Gα₁₂ 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 Gα₁₂ gene knockout. Gα₁₂ deficiency reduced Jun N-terminal protein kinase (JNK)-dependent Nrf2 ubiquitination required for proteasomal degradation, and so did Gα₁₃ deficiency. The absence of Gα₁₂, but not of Gα₁₃, increased protein kinase C δ (PKC δ) activation and the PKC δ-mediated serine phosphorylation of Nrf2. Gα₁₃ gene knockout or knockdown abrogated the Nrf2 phosphorylation induced by Gα₁₂ deficiency, suggesting that relief from Gα₁₂ repression leads to the Gα₁₃-mediated activation of Nrf2. Constitutive activation of Gα₁₃ promoted Nrf2 activity and target gene induction via Rho-mediated PKC δ activation, corroborating positive regulation by Gα₁₃. In summary, Gα₁₂ and Gα₁₃ transmit a JNK-dependent signal for Nrf2 ubiquitination, whereas Gα₁₃ regulates Rho-PKC δ-mediated Nrf2 phosphorylation, which is negatively balanced by Gα₁₂.

SUPPLEMENTAL MATERIAL

This work was supported by Korea Research Foundation grant KRF-2004-015-E00096 (S.G.K.), in part by NIH grant R37GM024236 (M. I. Simon), and by an Ajou University internal research grant (2006; S.C.).

We are grateful to S. Offermanns for helpful discussion regarding this paper.