Abstract
protein (BMP)-2, a member of the transforming growth factor b superfamily, has been shown to act as a tumor suppressor in several cancers by activating signaling cascades that cause cell cycle arrest. In addition, the expression level of BMP-2 is downregulated because of promoter CpG hypermethylation. We hypothesized that impaired regulation of BMP-2 through epigenetic pathways is associated with the pathogenesis of renal cell carcinoma. METHODS: To test this hypothesis, CpG methylation of the BMP-2 gene was analyzed in 3 renal tumor cell lines and 96 renal tumor and matched normal renal tissue. Promoter CpG methylation was analyzed by methylation specific PCR using bisulfite-modified DNA as template. BMP-2 expression was measured by quantitative RT-PCR. RESULTS: BMP-2 mRNA expression was significantly enhanced after 5-aza-2€ treatment in renal tumor cell lines. The prevalence of BMP-2 promoter methylation was significantly higher and BMP-2 mRNA expression was significantly lower in renal tumor samples than in normal kidney samples (p<0.0001, p¼0.014, respectively). Furthermore, a significant correlation was found between BMP-2 promoter methylation and mRNA transcription in the tumors (p<0.001). A significant association of BMP-2 methylation was found with pathologic findings showing pT category and infiltrative growth pattern (p¼0.034). When the expression level of the BMP-2 mRNA transcript was divided into 2 groups based on the mean value, a lower expression was significantly associated with overall survival (OS) after a radical nephrectomy (p¼0.004). Although both promoter CpG methylation and BMP-2 mRNA transcript level were significantly associated with OS in univariate analysis, BMP-2 mRNA expression was shown to be a more significantly independent predictor for OS than methylation status in multivariate analysis. CONCLUSIONS: This is the first clinical study of inactivation of the BMP-2 gene via epigenetic pathways in renal cell carcinoma. Aberrant BMP-2 methylation and the resultant loss of BMP-2 expression might become useful as a molecular marker for prediction of OS after a radical nephrectomy. Source of Funding: none
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