Egr-1 Mediates Transcriptional Repression of COL2A1 Promoter Activity by Interleukin-1 *

Following induction and activation of the early growth response (Egr)-1 transcription factor in human chondrocytes, interleukin-1 (IL-1 ) suppresses the expression of the type II collagen gene (COL2A1), associated with induction of Egr-1 binding activity in nuclear extracts. The COL2A1 proximal promoter contains overlapping binding sites for Egr-1 and Sp1 family members at 119/ 112 bp and 81/ 74 bp. Mutations that block binding of Sp1 and Sp3 to either site markedly reduce constitutive expression of the core promoter. IL-1 -induced Egr-1 binds strongly to the 119/ 112 bp site, and mutations that block Egr-1 binding prevent inhibition by IL-1 . Cotransfection with pCMV-Egr1 potentiates the inhibition of COL2A1 promoter activity by IL-1 , whereas overexpression of dominant-negative Egr-1 mutant, Wilm’s tumor-1 (WT1)/Egr1, Sp1, or Sp3 reverses the inhibition by IL-1 . Cotransfection of pGL2-COL2/ Gal4, in which we substituted the critical residue for Egr-1 binding with a Gal4 binding domain and a pCMVGal4-Egr1 chimera permits an inhibitory response to IL-1 that is reversed by overexpression of Gal4-CBP. Our results indicate that IL-1 -induced activation of Egr-1 binding is required for inhibition of COL2A1 proximal promoter activity and suggest that Egr-1 acts as a repressor of a constitutively expressed collagen gene by preventing interactions between Sp1 and the general transcriptional machinery.