N33 (TUSC3) promoter hypermethylation in serum of prostate cancer patients
Authors: Peter Horak, Jochen Reibenwein, Dietmar Pils, Alexey Teterin, Andreas Kirisits, Katarzyna Elandt, Sandra Tomek, Christoph C. Zielinski, Michael Krainer
Journal: Cancer Research (2006)

Proc Amer Assoc Cancer Res, Volume 47, 2006

3241 

Genetic and epigenetic alterations both contribute to the pathogenesis of prostate cancer. Methylation induced downregulation of gene expression may often provide the basis for the second hit following allele loss according to Knudson’s two hit hypothesis and is associated with several genes involved in prostate cancer tumorigenesis, including GSTP1, AR, RARB, APC, RASSF1. This observation offers a rationale for analysis of aberrant DNA methylation in body fluids of prostate cancer patients. We analyzed serum samples from a cohort of 28 patients with hormone refractory prostate cancer, who received chemotherapy at the Department of Medical Oncology of the Vienna General Hospital between 2001 and 2003. Serum samples were collected before any treatment was initiated as well as every 4 weeks in course of the chemotherapy and stored at -80°C. We quantified the amount of serum DNA using the PicoGreen® reagent and determined a median level of 14.0 (range 6.9-45.8)ng/ml, which is consistent with previous observations. We correlated clinical parameters such as stage, Gleason score, PSA levels and chemotherapy response with the measured DNA amount in serum. We could not define any statistically significant correlation between DNA concentration and clinical parameters. After bisulfite treatment of serum DNA we performed MSP to determine the promoter methylation status of N33 as well as GSTP1, AR , and 14-3-3σ , genes known to be involved in prostate cancer tumorigenesis and methylated. N33 is a putative tumor suppressor gene, spanning ca. 200 kbp on chromosome 8p22 and was originally reported by MacGrogan et al. Promoter hypermethylation and consequent silencing of N33 was described in a majority of cancer cell lines of colonic origin, though not in prostate cancer. However, small homozygous deletions in the region of 8p22 were originally identified in prostate cancer. AR mediates androgen sensitivity and loss of expression may play a key role in development androgen independent prostate cancer. Loss of 14-3-3σ is associated with failure to arrest the cell cycle at the G2/M phase checkpoint after DNA damage, and has been described to occur in prostate cancer. Promoter hypermethylation of GSTP1 was observed in 13/28 (46.4%) cases, of AR in 7/28 (25.0%), of N33 in 3/28 (10.7%) and of 14-3-3σ in 13/28 (46.4%) cases. We related the methylational status of these markers to the available clinical variables. Statistical results of these analyses will be presented. In conclusion, we could determine for the first time a promoter methylation of N33 in prostate cancer patients and explore its usefulness in a panel of already known methylation markers. In view of a relatively low observed percentage of N33 methylation in serum DNA, a larger study is underway to determine the contribution of N33 hypermethylation to tumorigenesis in prostate cancer and to evaluate the presented panel of methylation markers as potential prognostic and diagnostic tool.