Physical interaction between p53 and primary response gene Egr-1

The tumor suppressor p53 and primary response gene Egr-1 are nuclear transc ription factors with regulatory roles in signal transduction pathways media ting cellular proliferation and growth arrest as well as the complex geneti c programs controlling differentiation and programmed cell death. We identi fied a physical association between these regulatory proteins in vitro and in vivo. Recombinant p53 and Egr-1 fusion proteins complexed with in vitro translates of Egr-1 or p53, respectively, or with these respective proteins in cell lysates. This protein-protein interaction was detected in vivo by immunoprecipitation and Western blot analysis of serum-activated cellular l ysates with high levels of induced Egr-1 and of human Lung cancer cell line s with constitutive overexpression of Egr-1 and mutant p53. A p53 mutant at codon 154 did not bind Egr-1, while p53 proteins with point mutations at r esidues 156, 246, 247, and 273 associated with this zinc finger transcripti on factor. p53 bound full-length Egr-1 and an Egr-1 mutant with a deletion of the 5' transactivation region but did not associate with Egr-1 protein l acking an internal segment that included the first two zinc finger domains, suggesting that binding may require the presence of intact zinc finger mot ifs. A variant-sized Egr-1 protein expressed by lung fibroblast cell line M RC-9 was also bound by p53. The interaction of these regulatory proteins ma y alter multiple features of their biological activity especially with rega rd to the specificity of transcriptional control.