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 p⁷³. Caspase-3 gene expression was induced by treatment of cells with cisplatin, which also induced p⁷³ protein in HeLa and K562 cells. The human caspase-3 promoter was cloned and characterized. p⁷³β strongly activated the caspase-3 promoter, whereas p⁷³α showed less activation. Cisplatin treatment increased caspase-3 promoter activity. Basal and cisplatin-induced promoter activity was inhibited by the p⁷³ inhibitor p⁷³DD. Deletion analysis defined a minimal promoter of 120 base pairs, which showed good basal and p⁷³β -induced activity. The examination of the minimal promoter sequence showed several putative Sp1 sites, but no p⁵³/p⁷³ site. The caspase-3 promoter was activated by Sp1 in Sp1-deficient Drosophila SL-2 cells. Sp1-induced promoter activity was further enhanced by p⁷³β in SL-2 cells. Mutation of Sp1 sites in the minimal promoter resulted in a loss of basal and p⁷³-induced promoter activity. These results show that caspase-3 gene transcription is induced by cisplatin, which is mediated partly by p⁷³. We have identified p⁷³ 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 p⁷³-induced activation of the promoter.