Abstract 1707: Androgen responsiveness of the NKX3.1 gene is regulated by the proto-oncogene ETS1

Abstract

Abstract Expression of the prostatic homeodomain protein NKX3.1 is androgen-regulated in both the normal prostate and in prostate cancer cells. Androgen responsiveness of NKX3.1 is mediated in part by the 3’ untranslated region (3'UTR) of the NKX3.1 gene, within which we have isolated 3 discrete regions of androgen-induced transcriptional regulatory activity including 2 androgen response elements (AREs). The proximal ∼2kb of the 5’ promoter of the NKX3.1 gene is incompletely characterised, however it is not androgen-responsive using conventional luciferase reporter assays. Investigation of the NKX3.1 proximal promoter has identified regulation of promoter activity by the ETS transcription factor, ETS1, which is mediated by an ETS binding site (EBS) located at −1008 relative to the NKX3.1 transcription start site. Overexpression of ETS1 in the LNCaP prostate cancer cell line results in upregulation of NKX3.1 protein levels, supporting a functional role of ETS1 in the regulation of NKX3.1 expression. ETS1 has been reported previously to transactivate the androgen receptor (AR) in a ligand-dependent manner on a subset of androgen-responsive promoters, suggesting cooperativity or co-regulation of AR and ETS1 signalling in prostate cancer cells. Treatment of LNCaP cells with 10−8M 5α-dihydrotestosterone (DHT) results in upregulation of endogenous ETS1 protein levels, while overexpression of exogenous ETS1 causes a concomitant increase in AR expression. A cooperative interaction between ETS1 and the AR on the NKX3.1 promoter is evident in LNCaP cells whereby overexpression of ETS1 is able to induce androgen responsiveness of the initial ∼2kb of the NKX3.1 promoter sequence and in particular the 76bp region surrounding the EBS. Reversal of DHT effects by the antiandrogen bicalutamide indicates an AR-mediated mechanism. ETS1 is overexpressed in a high proportion of prostate cancers with its expression aberrantly localised in the cytoplasm of a subset of prostate tumour cells. Findings of the present study support a complex mechanism of AR-mediated regulation of NKX3.1 expression via multiple regions of the NKX3.1 gene and modified by additional transcription factors in prostate cancer cells. Abnormal expression and/or function of these factors may contribute to the transcriptional deregulation of NKX3.1 expression and the downregulation of NKX3.1 protein levels that is frequently observed in advanced prostate tumours. Similarly, it is also feasible that upregulation of ETS1 contributes to the deregulation of AR signalling in advanced prostate cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1707.