Egr-1 deficient mice are otherwise normal, but respond to catecholamine-induced stress in an exaggerated manner with evidence of heart failure. Egr-1 is a transcriptional activator and repressor that controls transcription via DNA binding and/or protein:protein binding to other transcriptional factors. To determine the mechanism of the increased response we compared the expression pattern of isoproterenol treated deficient and wild-type mice using microarrays. Among the genes identified as discordantly expressed was the sodium calcium exchanger –1 (NCX1). NCX1 RNA and protein expression was increased in the deficient mice indicating that Egr-1 normally negatively controls NCX1 expression in vivo. To molecularly determine the mechanism of Egr-1 control of NCX1 we performed chromatin immunopreciptiation (ChIP)of formalin-fixed H9c2 cells using anti-Egr-1 antibody. We amplified NCX1 promoter DNA from the ChIP samples. The upstream cardiac NCX1 promoter does not contain consensus Egr-1 binding sites, but does contain SPI, AP1 and NFAT sites. Reciprocal Western and IP experiments demonstrated Egr-1 complex formation with the proteins SP1, c-Jun and NFAT3. These data suggest that Egr-1 negatively controls NCX1 expression through protein:protein binding with one or more of these proteins at the NCX1 promoter.

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