Sp1-like sequences mediate human caspase-3 promoter activation by p73 and cisplatin

Abstract

Caspase-3 is a cysteine protease that plays a central role in the execution of apoptosis induced by a wide variety of stimuli. However, little is known about the mechanisms involved in the regulation of caspase-3 gene transcription. This study was carried out to characterize the human caspase-3 promoter and to understand the mechanisms involved in the induction of caspase-3 gene expression in response to the anticancer drug cisplatin and p<SUP>73</SUP>. Caspase-3 gene expression was induced by treatment of cells with cisplatin, which also induced p<SUP>73</SUP> protein in HeLa and K562 cells. The human caspase-3 promoter was cloned and characterized. p<SUP>73</SUP>β strongly activated the caspase-3 promoter, whereas p<SUP>73</SUP>α showed less activation. Cisplatin treatment increased caspase-3 promoter activity. Basal and cisplatin-induced promoter activity was inhibited by the p<SUP>73</SUP> inhibitor p<SUP>73</SUP>DD. Deletion analysis defined a minimal promoter of 120 base pairs, which showed good basal and p<SUP>73</SUP>β -induced activity. The examination of the minimal promoter sequence showed several putative Sp1 sites, but no p<SUP>53</SUP>/p<SUP>73</SUP> site. The caspase-3 promoter was activated by Sp1 in Sp1-deficient Drosophila SL-2 cells. Sp1-induced promoter activity was further enhanced by p<SUP>73</SUP>β in SL-2 cells. Mutation of Sp1 sites in the minimal promoter resulted in a loss of basal and p<SUP>73</SUP>-induced promoter activity. These results show that caspase-3 gene transcription is induced by cisplatin, which is mediated partly by p<SUP>73</SUP>. We have identified p<SUP>73</SUP> and Sp1 as activators of the caspase-3 promoter. Sp1-like sequences in the minimal promoter not only sustain basal promoter activity, but also mediate p<SUP>73</SUP>-induced activation of the promoter