The activity of the murine Bax promoter is regulated by Sp1/3 and E-box binding proteins but not by p53

In human cells the expression of the pro-apoptotic protein Bar appears to b e regulated through p53-dependent transcriptional activation. However, in t he mouse, p53 deficiency does not affect Bar expression. To shed more light on the transcriptional regulation of the bar gene we have analyzed the mur ine bar promoter. We find several E-box and Sp1/Sp3 binding sites as well a s three putative p53 binding sites that are conserved in the human promoter sequence. We can show that both the Spl and the E-box binding sites are ne cessary for proper regulation of bar transcription and show by genomic DMS footprinting that all these sites are occupied in vivo. In contrast, the pu tative p53 binding sites were not occupied by protein in vivo in primary mu rine thymocytes either before or after induction of p53 by DNA damage. More over, p53 was unable to regulate the transcription of bar promoter fragment s up to 6.5 kb in length. Further, steady state levels of bar mRNA did not correlate with Bar protein expression levels in DNA damage-induced cell dea th. Our findings exclude a direct transcriptional transactivation of the ba r gene by p53 in murine cells suggesting a dominance of p53 independent mec hanisms for the regulation of Bar protein expression.