DNA damage by nitrogen mustard in a gene containing multiple Sp1-binding sites

The human cytochrome c 1 gene TATA-less promoter contains 10 Sp1-binding elements that regulate the activation of transcription of this gene. Quantitative PCR was used to show that nitrogen mustard induces DNA lesions within this Sp1-binding region following exposure of HeLa cells to clinical levels of the drug. Alkylation of the cytochrome c 1 gene in HeLa cells increased with reaction time up to 4 h following exposure to nitrogen mustard, with 50% of the lesions (approximately 0.8/kb) forming within 1 h. An Sp1 competition assay showed that nitrogen mustard inhibited the binding of Sp1 to the promoter region of the cytochrome c 1 gene in HeLa cells. These results show that nitrogen mustard-induced damage to Sp1-binding sites may contribute to the toxicity of this compound by interfering with the activation of specific genes.