Identification of a hydrogen peroxide-induced PP1-JNK1-Sp1 signaling pathway for gene regulation

Identification of a hydrogen peroxide-induced PP1-JNK1-Sp1 signaling pathway for gene regulation. Am J Physiol Lung Cell Mol Physiol 291: L983-L992, 2006. First published June 30, 2006; doi: 10.1152/ajplung. 00454.2005. Oxidative stress often results in changes in gene expression through the regulation of transcription factors. In this study, we examine how Sp1 phosphorylation is regulated by H2O2 in a human alveolar epithelial cell line (HAE). Treatment of HAE cells with H2O2 increases phosphorylation of Sp1 and activates JNK. To establish a relationship between JNK and Sp1, we show that JNK activator anisomycin increases Sp1 phosphorylation, and JNK inhibitors as well as dominant-negative JNK1 attenuate H2O2-induced Sp1 phosphorylation. Additionally, JNK1 directly phosphorylates Sp1 in vitro, reducing Sp1 binding to DNA. These results demonstrate the role of JNK in H2O2-induced Sp1 phosphorylation. Because H2O2 inhibits Ser/Thr protein phosphatase-1 (PP1), we examined the role of PP1 in the regulation of JNK. Similar to H2O2, inhibition of PP1 induces phosphorylation of Sp1 and activation of JNK in HAE cells. Inhibition of JNK activity using either inhibitors or dominant-negative mutant JNK1 suppresses PP1 inhibition-induced Sp1 phosphorylation. Furthermore, PP1 directly inactivates JNK1 in vitro. These data suggest that 1) H2O2 increases the phosphorylation level of Sp1, 2) Sp1 is a target of the JNK pathway, 3) PP1 regulates JNK activation, and 4) the "PP1-JNK" pathway plays a role in H2O2-induced Sp1 phosphorylation in lung epithelial cells.