Data from 15-Deoxy-Δ<sup>12,14</sup>-Prostaglandin J<sub>2</sub> Inhibits Transcriptional Activity of Estrogen Receptor-α via Covalent Modification of DNA-Binding Domain

Abstract

<div>Abstract<p>The cyclopentenone 15-deoxy-Δ<sup>12,14</sup>-prostaglandin J<sub>2</sub> (15d-PGJ<sub>2</sub>) inhibits proliferation of cancer cells, including breast cancers, by peroxisome proliferator-activated receptor-γ (PPARγ)–dependent and PPARγ-independent mechanisms. However, little is known about its effect on the transcriptional activity of estrogen receptor-α (ERα) that plays vital roles in the growth of breast cancers. Here, we show that 15d-PGJ<sub>2</sub> inhibits both 17β-estradiol (E<sub>2</sub>)–dependent and E<sub>2</sub>-independent ERα transcriptional activity by PPARγ-independent mechanism. In addition, 15d-PGJ<sub>2</sub> directly modifies ERα protein via its reactive cyclopentenone moiety, evidenced by incorporation of biotinylated 15d-PGJ<sub>2</sub> into ERα, both <i>in vitro</i> and <i>in vivo</i>. Nanoflow reverse-phase liquid chromatography tandem mass spectrometry analysis identifies two cysteines (Cys<sup>227</sup> and Cys<sup>240</sup>) within the COOH-terminal zinc finger of ERα DNA-binding domain (DBD) as targets for covalent modification by 15d-PGJ<sub>2</sub>. Gel mobility shift and chromatin immunoprecipitation assays show that 15d-PGJ<sub>2</sub> inhibits DNA binding of ERα and subsequent repression of ERα target gene expression, such as <i>pS2</i> and <i>c-Myc</i>. Therefore, our results suggest that 15d-PGJ<sub>2</sub> can block ERα function by covalent modification of cysteine residues within the vulnerable COOH-terminal zinc finger of ERα DBD, resulting in fundamental inhibition of both hormone-dependent and hormone-independent ERα transcriptional activity. [Cancer Res 2007;67(6):2595–602]</p></div>