cAMP-response-element-binding-protein binding protein (CBP) and p300 are transcriptional co-activators of early growth response factor-1 (Egr-1)

Egr-1 (early-growth response factor-1) is a sequence-specific transcription factor that plays a regulatory role in the expression of many genes import ant for cell growth, development and the pathogenesis of disease. The trans criptional co-activators CBP (cAMP-response-element-binding-protein-binding protein) and p300 interact with sequence-specific transcription factors as well as components of the basal transcription machinery to facilitate RNA polymerase II recruitment and transcriptional initiation. Here we demonstra te a unique way in which Egr-1 physically and functionally interacts with C BP/p300 to modulate gene transcription. CBP/p300 potentiated Egr-1 mediated expression of 5-lipoxygenase (5-LO) promoter-reporter constructs, and the degree of trans-activation was proportional to the number of Egr-1 consensu s binding sites present in wild-type and naturally occurring mutants of the 5-LO promoter. The N- and C-terminal domains of CBP interact with the tran scriptional activation domain of Egr-1, as demonstrated by a mammalian two- hybrid assay. Direct protein-protein interactions between CBP/p300 and Egr- 1 were demonstrated by glutathione S-transferase fusion-protein binding and co-immunoprecipitation/Western-blot studies. These data suggest that CBP a nd p300 act as transcriptional co-activators for Egr-1-mediated gene expres sion and that variations between individuals in such co-activation could se rve as a genetic basis for variability in gene expression.