Overexpression of transcription factor AP-2 stimulates the PA promoter of the human uracil-DNA glycosylase (UNG) gene through a mechanism involving derepression

The P-A promoter in the human uracil-DNA glycosylase gene (UNG) directs expression of the nuclear form (UNG2) of UNG proteins. Using a combination of promoter deletion and mutation analyses, and transient transfection of HeLa cells, we show that repressor and derepressor activities are contained within the region of DNA marked by P-A. Footprinting analysis and electrophoretic mobility shift assays of P-A and putative AP-2 binding regions with HeLa cell nuclear extract and recombinant AP-2 alpha protein indicate that AP-2 transcription factors are central in the regulated expression of UNG2 mRNA. Chromatin immuno-precipitation with AP-2 antibody demonstrated that endogenous AP-2 binds to the P-A promoter in vivo. Overexpression of AP-2 alpha, -beta or -gamma all stimulated expression from a P-A-luciferase reporter gene construct approximately 3- to 4-fold. Interestingly, an N-terminally truncated AP-2 alpha, lacking the activation domain but retaining the DNA binding and dimerization domains, stimulated P-A to a level approaching that of full-length AP-2, suggesting that AP-2 overexpression stimulates P-A activity by a mechanism involving derepression rather than activation, possibly by neutralizing an inhibitory effect of endogenous AP-2 or AP-2-like factors. (C) 2009 Elsevier B.V. All rights reserved.