1. ¹Molecular Oncology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried/Munich, Germany
2. ²Institute of Pathology, Thalkirchner Strasse 36, Ludwig-Maximilians University, D-80337 Munich, Germany

Correspondence: H Hermeking, E-mail: herme@biochem.mpg.de

Received 19 April 2004; Revised 28 May 2004; Accepted 17 June 2004; Published online 18 October 2004.

Abstract

In order to identify tumor suppressive genes silenced by CpG methylation in prostate carcinoma (PCa), we determined genome-wide expression changes after pharmacological reversal of CpG methylation-mediated transcriptional repression in three PCa cell lines using microarray analysis. Thereby, epigenetic silencing of the 14-3-3 gene was detected in the cell line LNCaP. 14-3-3 encodes a p53-regulated inhibitor of cell cycle progression. Laser microdissection was used to isolate different cell types present in diseased prostatic tissue. Subsequent methylation-specific PCR analysis showed CpG methylation of 14-3-3 in all 41 primary PCa samples analysed, which was accompanied by a decrease or loss of 14-3-3 protein expression. In contrast, normal prostate epithelial and benign prostate hyperplasia cells showed high levels of 14-3-3 expression. PCa-precursor lesions (prostatic intraepithelial neoplasia) also displayed decreased levels of 14-3-3 expression in luminal cells, which are known to contain shortened telomeres. RNA interference-mediated inactivation of 14-3-3 compromised a DNA damage-induced G₂/M arrest in the PCa cell line PC3. The generality of CpG methylation and downregulation of 14-3-3 expression in PCa suggests that it significantly contributes to the formation of PCa, potentially by allowing the escape from a DNA damage-induced arrest elicited by telomere shortening.