A minimal Bcl-x promoter is activated by Brn-3a and repressed by p53

The Brn-3a transcription factor stimulates the expression of the anti-apopt otic Bcl-2 and Bcl-x proteins and protects neuronal cells from apoptosis. H ere we show that a minimal Bcl-x promoter is activated by Brn-3a and that t his stimulation is prevented by the pro-apoptotic p53 protein. Both these e ffects are mediated via Bcl-x promoter sequences, which are indistinguishab le from those required for minimal basal promoter activity. A newly describ ed upstream Bcl-x promoter is also activated by Brn-3a with this activation being prevented by p53. Hence, Brn-3a-mediated activation of two distinct Bcl-x promoters and of the Bcl-2 promoter is blocked by p53 whereas this is not observed for Brn-3a activated promoters derived from genes not involve d in inhibiting apoptosis. p53 therefore appears to specifically target the activation by Brn-3a of promoters derived from genes with an anti-apoptoti c effect and this may be involved in the pro-apoptotic activity of p53.