LIPOPOLYSACCHARIDE INDUCES EXPRESSION OF EGR-1 IN MACROPHAGES THROUGHUPSTREAM CARG BOX (SERUM RESPONSE) ELEMENTS

The protein product of the early response gene, Egr-1, is required for macrophage differentiation. Egr-1 mRNA is induced by lipopolysacchari de within minutes in murine peritoneal macrophages through an effect o n the rate of transcription of Egr-1. Therefore, we undertook a series of studies to characterize Egr-1 protein induced by LPS and to define enhancer elements in the Egr-1 promoter which mediate the effect of L PS in murine macrophages. Salmonella minnesota Re 595 LPS (10 ng/ml or higher) induced Egr-1 protein of 80 kDa within 45 min in thioglycolla te-elicited peritoneal macrophages. The promoter region of Egr-1 conta ins six serum response elements (SRE) which each contain a core CArG b ox. CAT activity in LPS-treated macrophages transfected with Egr-1-CAT constructs containing the two most upstream 5' SREs was increased 4.7 -fold whereas CAT activity in macrophages transfected with constructs lacking these two most upstream SREs was not affected by LPS. LPS indu ced CAT activity in macrophages transfected with constructs containing tetramers of each of the two most 5' SREs upstream of a heterologous promoter linked to CAT, Mutation of the CArG box abolished the effect of LPS. These findings suggest that the CArG box elements within the t wo most upstream SREs may mediate the effect of LPS on transcription o f Egr-1.