Ref-1 is a multifunctional protein that stimulates DNA binding by a number
of transcription factors and serves as the abasic (A/P) endonuclease in bas
e excision repair. Ref-1 was discovered to be a potent activator of p53 DNA
binding in vitro. To address the physiological significance of the effects
of Ref-1 on p53, we have analyzed its role in regulating p53 function in v
ivo, We found that Ref-1 over-expression enhances the ability of p53 to tra
nsactivate a number of p53 target promoters and increases the ability of p5
3 to stimulate endogenous p21 and cyclin G expression. Additionally, it was
observed that Ref-1 associates with p53 in vivo and in vitro. Importantly,
downregulation of Ref-1 (by antisense) causes a marked reduction in p53 in
duction of p21 mRNA and protein, as well as diminished ability of p53 to tr
ansactivate the p21 and Bar promoters. Moreover, Ref-1 levels are correlate
d with the extent of apoptosis induced by p53, Finally, we observed that Re
f-1 cooperates with a DNA-damaging compound, camptothecin, to stimulate the
transcriptional activity of p53. Together these data indicate that Ref-1 i
s a key cellular regulator of p53.