Overexpression of CCAAT displacement protein represses the promiscuously active proximal gp91(phox) promoter

CCAAT displacement protein (CDP) is a transcriptional repressor that restri cts expression of the gp91(phox) gene to mature myeloid cells. CDP interact s with multiple sites within the -450 to +12 bp human gp91(phox) promoter, and downregulation of CDP DNA-binding activity is required for induction of gp91(phox) transcription in mature phagocytes, Truncation of the gp91(phox ) promoter to -102 to +12 bp removes 4 cop-binding sites and reveals a prom iscuous promoter activity that is active in some nonphagocytic cells, A cis -element at -90 bp is required for derepressed transcription and serves as a binding site for multiple transcriptional activators. We now report that this element also serves as a binding site for CDP. The affinity of CDP for this element is relatively weak compared with upstream CDP-binding sites w ithin the promoter, consistent with the promiscuous transcriptional activit y exhibited by the -102 to +12 bp gp91(phox) promoter fragment: Further ana lysis of the proximal promoter reveals an additional weak-affinity CDP-bind ing site centered at approximately -20 bp. Overexpression of cloned CDP rep resses the -102 to +12 bp gp91(phox) promoter, indicating that these proxim al CDP-binding sites are functionally significant. The constellation of tra nscriptional activators and a repressor that interacts with the -90 bp cis- element is identical to that observed for a promoter element at -220 bp, re flecting the highly modular organization of the gp91(phox) promoter. These studies illustrate the complex interplay between transcriptional activators and a repressor that contribute to the myeloid-restricted expression of th e gp91(phox) gene. (C) 1999 by The American Society of Hematology.