Early growth response-1 regulates lipopolysaccharide-induced suppressor of cytokine signaling-1 transcription

Suppressor of cytokine signaling (SOCS)-1 is a critical regulator of lipopolysaccharide (LPS) tolerance and LPS-induced cytokine production. The mechanisms regulating the transcription of SOCS-1 in response to LPS are not entirely understood. Functional analysis of the SOCS-1 promoter demonstrates that early growth response-1 (Egr-1) is an important transcriptional regulator of SOCS-1. Two Egr-1 binding sites are present within the SOCS-1 promoter as shown by EMSA and supershift analysis. Further, mutation of the Egr-1 binding sites significantly reduces both the basal and LPS-induced transcriptional activity of the promoter. Chromatin immunoprecipitation experiments confirm LPS-induced binding of Egr-1 to the SOCS-1 promoter in vivo. Additionally, Egr-1^-/- macrophages show reduced levels of LPS-induced SOCS-1 expression in comparison with macrophages derived from Egr-1^+/+ littermate controls. These results demonstrate an important role for Egr-1 in regulating both the basal and LPS-induced activity of the SOCS-1 promoter.