Methylation of the ASC gene promoter is associated with aggressive prostate cancer

BACKGROUND. The aim of this study was to investigate the methylation status of apoptosis-associated speck-like protein containing a CARD (ASC; TMS1; PYCARD) in prostate cancer cell lines and human tissues and to determine if those findings correlate with the clinicopathological features of prostate cancer. METHODS. Genomic DNA was isolated from prostate cell lines and microdissected tissues, bisulfite converted and analyzed by methylation specific polymerase chain reaction (MSP). Expression of ASC in prostate cancer cell lines treated with or without methylation inhibitors was determined by quantitative or qualitative RT-PCR. RESULTS. ASC gene expression was silenced or reduced in five prostate cancer cell lines and correlated with methylation status. Treatment of MDAPCa2b prostate cancer cells with the methylation inhibitors 5-aza-2-deoxycitidine and Zebularine reactivated expression of ASC. Of 58 prostate cancer specimens, methylation of the ASC promoter region was present in 65% of primary cancer tissue, 64% (7/11) of cancer-associated high grade-prostatic intraepithelial neoplasia (HG-PIN), and 28% of normal-appearing but adjacent to tumor prostate tissue. While ASC methylation was not related to Gleason score (P = 0.46) or pathological stage (P = 0.75), there was a significantly higher frequency of ASC methylation in the adjacent normal tissue for patients with biochemical recurrence (P = 0.0383). CONCLUSIONS. Methylation of the ASC gene promoter is both a frequent and early event in prostate cancer carcinogenesis. Surprisingly, methylation of the adjacent normal tissue occurs significantly more often in patients who later undergo biochemical recurrence, suggesting a role for inactivation of the ASC gene in the initial stages of aggressive disease.