Keap1 binds cytokine promoters upon virus infection and moderates their induction by recruiting NFκB p50 and G9a-GLP

Abstract

Innate immunity requires a balance of positive and negative regulators of cytokine transcription. Keap1 deletion in mice alters innate immunity and inflammation. We investigated the influence of Keap1 on cytokine gene induction by Sendai virus infection in mouse embryo fibroblasts (MEFs). Keap1 bound to the Ifnb1, Tnf and Il6 promoters upon virus infection, and moderated viral induction of their transcription. Keap1 was required for viral induction of NF{kappa}B p50 and G9a-GLP lysine methyltransferase binding to these genes. Keap1 formed BiFC complexes with NF{kappa}B p50 that were localized to the nuclei in a subset of cells. Nrf2 counteracted viral induction of Keap1 binding to the promoters, and the effects of Keap1 on NF{kappa}B p50 and on G9a-GLP recruitment. Lysine methyltransferase inhibitors enhanced viral induction of transcription of the genes that were bound by Keap1 only in MEFs with intact Keap1, and not in Keap1-/- MEFs. They also enhanced NF{kappa}B p50 and NF{kappa}B p65 recruitment to these genes only in MEFs with intact Keap1, whereas they inhibited G9a-GLP recruitment. The reciprocal effects of Keap1 and of G9a-GLP lysine methyltransferase activity on chromatin binding by each other constitute a feedback circuit that moderates viral induction of cytokine transcription. SummaryVirus infection induces Keap1 binding to cytokine promoters, which recruits NF{kappa}B p50 and G9a-GLP and moderates their transcription.