Abstract

Expression of the human DNA topoisomerase IIα (topo IIα) gene is positively regulated by the binding of the nuclear factor Y (NF-Y) transcription factor to four of five inverted CCAAT boxes (ICBs) located in its promoter. We have demonstrated previously that expression of the p53 tumor suppressor inhibits human topo IIα promoter activity in murine (10)1 cells. In this report, we demonstrate that the inhibition of topo IIα gene expression by wild-type p53 correlates with the decreased binding of the transcription factor NF-Y to the first four ICBs of the topo IIα promoter. The expression of mutant p53 does not affect the binding of NF-Y. In NIH3T3 cells, we show that topo II-targeted drugs inhibit the binding of NF-Y to ICB sites in the topo IIα promoter. This effect is seen not only with drugs that result in DNA strand breaks but also with drugs that inhibit the catalytic activity of topo II, and even with the mitotic spindle inhibitor, vinblastine. Further experiments with p53-null (10)1 cells treated with these same drugs also demonstrate decreased NF-Y binding to the topo IIα ICBs. The data presented points to the existence of both p53-dependent and -independent mechanisms for regulating NF-Y binding to ICBs in the topo IIα promoter and thus the modulation of topo IIα gene expression.