Wild-type p53 enhances annexin IV gene expression in ovarian clear cell adenocarcinoma.

The protein annexin IV (ANX4) is elevated specifically and characteristically in ovarian clear cell adenocarcinoma (CCA), a highly malignant histological subtype of epithelial ovarian cancer. On the basis of the hypothesis that the expression of ANX4 in CCA is regulated by a unique transcription mechanism, we explored the cis-elements involved in CCA-specific ANX4 expression using a luciferase reporter. We compared the transcriptional activities of the region from -1534 to +1010 relative to the ANX4 transcription start site in CCA and non-CCA-type cell lines, and found that two repeated binding motifs for the tumor suppressor protein, p53, in the first intron of ANX4 were involved in CCA-specific transcriptional activity. Furthermore, chromatin immunoprecipitation showed that endogenous p53 bound to this site in CCA cell lines. Moreover, the use of short interference RNA to silence the p53 gene decreased the transcriptional activity and mRNA expression of ANX4 in CCA cell lines. Thus, the ANX4 gene is, at least in part, regulated by p53 in CCA cells. Mutations in the p53 gene were absent and levels of p53 target genes were higher in several CCA-derived cell lines. Although the expression of ANX4 is typically low in these non-CCA cell lines, ANX4 levels were elevated more than three-fold by the overexpression of wild-type but not mutant p53. Therefore, we conclude that the ANX4 gene is a direct transcriptional target of p53, and its expression is enhanced by wild-type p53 in CCA cells.