The mycotoxin fumonisin B1 transcriptionally activates the p21 promoter through a cis-acting element containing two Sp1 binding sites

Abstract

Fumonisin B1 (FB1) is a food-borne mycotoxin produced by Fusarium moniliforme. Structurally FB1 resembles sphingoid bases, and ingestion of FB1 causes several animal diseases. FB1 will cause hepatic carcinoma in rats and is implicated as a cofactor in esophageal or hepatic carcinoma. Previous studies concluded that FB1 repressed cyclin-dependent kinase 2 (CDK2) activity but induced CDK inhibitors p21(Waf1/Cip1), p27(Kip1), and p57(Kip2) in monkey kidney cells (CV-1). In contrast, CV-1 cells transformed by simian virus 40 are resistant to the antiproliferative or apoptotic effects of FB1. Consequently, FB1 treatment of CV-1 cells leads to cell cycle arrest and apoptosis. In this study, we demonstrate that FB1 transcriptionally activates the p21 promoter. Functional analysis of the p21 promoter by reporter gene assays mapped the FB1-responsive region to -124 to -47. DNase I footprinting analysis revealed two protected motifs that span the FB1-responsive region, -124 to -101 (footprint II) and -89 to -67 (footprint III). Further studies demonstrated that DNA sequences from -124 to -101 were sufficient for FB1 stimulation DNA sequences from -124 to -101 contain two Sp1 binding sites, and gel shift assays provided evidence that nuclear factors specifically bind to this region. Disruption of the two Sp1 binding sites abrogated the binding of nuclear proteins and prevented activation by FB1. Taken together, these results suggest that Sp1 or Sp1- related proteins mediate FB1-induced activation of the p21 promoter.