The human zinc finger protein EGR-4 acts as autoregulatory transcriptional repressor

The human EGR-4 (AT133) gene represents one member of a family of four related zinc finger proteins, that are simultaneously and coordinately induced in resting cells upon growth stimulation. In order to characterise the function of the EGR-4 zinc finger protein, we have expressed the protein in the eukaryotic baculovirus system. The recombinant EGR-4 protein has a molecular mass of 78 kDa, as demonstrated by SDS-PAGE and Western blotting. DNA binding studies revealed that the EGR-4 protein binds to the EGR consensus motif GCGTGGGCG, but not to the G-rich regulatory ZIP-element of the human IL-2 gene, that is a binding site for EGR-1. EGR-4 functions as transcriptional repressor. Overexpression of EGR-4 mediates repression of a minimal c-fos promoter through a threefold EGR consensus site. Furthermore the EGR-4 protein displays autoregulatory activities. This protein downregulates expression of its own gene promoter in a dose dependent manner. A G-rich region in the EGR-4 promoter, located at position -106 to -82, could be identified as binding site for the recombinant EGR-4 protein. A comparison of the two related zinc finger proteins EGR-4 and EGR-1 revealed for each protein distinct and specific DNA binding- and transcriptional regulatory activities.