Association of PITX2 mRNA down-regulation in prostate cancer with promoter hypermethylation and poor prognosis

Abstract

Background: Hypermethylation of the PITX2 (paired-like homeodomain transcription factor 2) gene promoter is strongly associated with recurrence after radical prostatectomy. We hypothesized that PITX2 hypermethylation leads to PITX2 silencing and that decreased PITX2 expression is likewise associated with poor prognosis in prostate cancers. Moreover, it is unknown so far how PITX2 hypermethylation relates to other molecular changes in prostate cancer, such as ERG oncogenic activation in about half of all cases.

Objective: To investigate how PITX2 expression and methylation are related, whether biochemical recurrence after radical prostatectomy can be predicted by PITX2 mRNA levels, and how changes in PITX2 relate to ERG overexpression.

Material and methods: We measured PITX2 and ERG expression in 45 cancerous and 13 benign tissues from patients undergoing radical prostatectomy (age range: 59-74 years). Methylation of the PITX2 gene was analyzed in an extended series of 93 cancers. Follow-up was performed for all patients for a 98-month median period. Additionally, expression and methylation changes of PITX2 were investigated in prostate carcinoma cell lines. Gene expression and methylation were determined by quantitative RT-PCR and methylation-specific PCR, respectively. Biochemical recurrence defined as a total PSA of >0.2 ng/ml on 2 consecutive tests was considered as the surrogate endpoint for survival analysis.

Results: PITX2 expression was significantly and strongly decreased in prostate cancer compared to benign tissues. Cases with decreased PITX2 experienced significantly earlier biochemical recurrences. PITX2 down-regulation was associated with PITX2 promoter hypermethylation in tumor samples and cell lines. PITX2 hypermethylation was more pronounced in cases with ERG overexpression.

Conclusions: PITX2 down-regulation is associated with promoter hypermethylation and is a good predictor of clinical outcomes after radical prostatectomy. PITX2 methylation might be influenced by oncogenic ERG.