Purpose: Alterations of fibroblast growth factors (FGFs) and their receptors contribute to prostate cancer progression by enhancing cellular proliferation, survival, and motility. The Sprouty gene family negatively regulates FGF signaling and may limit the ability of FGFs to enhance tumor progression. Sprouty1 is down regulated in human prostate cancers and Sprouty1 expression can markedly inhibit prostate cancer proliferation in vitro. Sprouty4 has been shown to negatively regulate both proliferation and cell migration in other systems. We therefore examined whether Sprouty4 expression was altered in prostate cancer.
Experimental design: Expression of Sprouty4 was examined by in situ hybridization and quantitative RT-PCR. Methylation of the Sprouty4 gene promoter was assessed using bisulfite modification and sequencing. The effect of Sprouty4 expression on cell migration was determined using an in vitro wounding assay.
Results: By in situ hybridization Sprouty4 is expressed in normal prostatic epithelial cells and is decreased in a subset of prostate cancers. Quantitative RT-PCR confirms that Sprouty4 expression is decreased in approximately one half of prostate cancers. Analysis of the 5'-regulatory region revealed a CpG island approximately 1 kb upstream of the transcription initiation site, the proximal portion of which was preferentially methylated in prostate cancer tissues. More than one half of all prostate cancer DNAs were methylated in this region and methylation was significantly correlated with decreased Sprouty4 expression as determined by quantitative RT-PCR. When overexpressed in prostate cancer cell lines, Sprouty4 did not inhibit cell proliferation but did inhibit cell migration.
Conclusions: Sprouty4 expression is down regulated in human prostate cancer by DNA methylation and this decreased expression may contribute to increased cell migration.
Prostate 66:613-624, 2006. (c) 2005 Wiley-Liss, Inc.