Gene expression and epigenetic discovery screen reveal methylation of SFRP2 in prostate cancer

Abstract

Aberrant activation of Wnts is common in human cancers, including prostate. Hypermethylation associated transcriptional silencing of Wnt antagonist genes SFRPs (Secreted Frizzled-Related Proteins) is a frequent oncogenic event. The significance of this is not known in prostate cancer. The objectives of our study were to (i) profile Wnt signaling related gene expression and (ii) investigate methylation of Wnt antagonist genes in prostate cancer. Using TaqMan Low Density Arrays, we identified 15 Wnt signaling related genes with significantly altered expression in prostate cancer; the majority of which were upregulated in tumors. Notably, histologically benign tissue from men with prostate cancer appeared more similar to tumor (r 5 0.76) than to benign prostatic hyperplasia (BPH; r 5 0.57, p < 0.001). Overall, the expression profile was highly similar between tumors of high (! 7) and low ( 6) Gleason scores. Pharmacological demethylation of PC-3 cells with 5-Aza-CdR reactivated 39 genes (! 2-fold); 40% of which inhibit Wnt signaling. Methylation frequencies in prostate cancer were 10% (2/20) (SFRP1), 64.86% (48/74) (SFRP2), 0% (0/20) (SFRP4) and 60% (12/20) (SFRP5). SFRP2 methylation was detected at significantly lower frequencies in high-grade prostatic intraepithelial neoplasia (HGPIN; 30%, (6/20), p 5 0.0096), tumor adjacent benign areas (8.82%, (7/69), p < 0.0001) and BPH (11.43% (4/35), p < 0.0001). The quantitative level of SFRP2 methylation (normalized index of methylation) was also significantly higher in tumors (116) than in the other samples (HGPIN 5 7.45, HB 5 0.47, and BPH 5 0.12). We show that SFRP2 hypermethylation is a common event in prostate cancer. SFRP2 methylation in combination with other epigenetic markers may be a useful biomarker of prostate cancer.Prostate cancer is the most commonly diagnosed noncutaneous malignancy and third leading cause of cancer related deaths in men in the Western world.1 The heterogeneous nature of the disease results in a broad spectrum of clinical behavior from slow-growing indolent tumors to aggressive, metastatic disease. The Gleason grading system is a pathologic determinant of disease biology and prognosis, based on the glandular pattern of the tumor, serving as an independent prognostic factor. The predominant (primary) and next most prevalent (secondary) architectural patterns are graded from 1-5 (well differentiated-poorly differentiated) and summed, yielding an overall Gleason score, which is indicative of potential behavior, with Gleason score !7 predictive of a poor prognosis. 2,3Wnt (wingless-type)/b-catenin signaling is a major regulator of cell proliferation, migration and differentiation, controlling tissue homeostasis and tumor progression. 4 The binding of a canonical Wnt ligand to its cell-surface receptor complex, consisting of Frizzled (FZD) and one of two low-density-lipoprotein-receptor-related proteins (LRP-5 and LRP-6), initiates a signaling cascade that activates disheveled (DVL), which releases b-catenin (CTTNB1) from an inhibitory complex ...

Secreted Frizzled-Related Protein 2 (sFRP2) promotes osteosarcoma invasion and metastatic potential

“…Specifically, studies in several malignances have demonstrated downregulation of sFRP2 via epigenetic promoter hypermethylation, suggesting a possible role as a tumor suppressor [26, 27]. However, recently reports provide evidence that sFRP2 can enhance tumor aggressiveness or progression in several cancers, including melanoma, renal cancer, angiosarcoma, and breast cancer.…”

Secreted frizzled related proteins: Implications in cancers

“…Also, hyperactive Wnt signalling has been linked with androgen-independent growth through crosstalk with the androgen receptor [34], development of bone metastasis [35], and self-renewal of prostate cancer stem cells [36]. The heterogeneity of prostate cancer is also due to a broad spectrum of genetic and epigenetic abnormalities.…”

“…To understand the crucial role of Wnt signalling pathway in prostate cancer, Perry et al [36] examined the role of Wnt antagonists (SFRPs) in prostate cancer cell lines, namely, LNCaP, PC-3, DU145, and 22Rv1, on a set of 20 tumour specimens obtained from men undergoing radical prostatectomy. It was reported that SFRP2 was methylated in 70% of tumour specimens and SFRP5…”

The defect of SFRP2 modulates an influx of extracellular calcium in B lymphocytes

“…As previously reported, the expression of SFRP2 was down-regulated by methylation in cancer [14, 15]. Because calcium signaling was reduced by defect of Sfrp2 , down-regulation of SFRP2 is assumed to impair the calcium signal transduction in each tissue or cell.…”