<it>RASSF1A </it>promoter methylation and expression analysis in normal and neoplastic kidney indicates a role in early tumorigenesis

Abstract

Abstract Background Epigenetic silencing of the RAS association domain family 1A (RASSF1A) tumor suppressor gene promoter has been demonstrated in renal cell carcinoma (RCC) as a result of promoter hypermethylation. Contradictory results have been reported for RASSF1A methylation in normal kidney, thus it is not clear whether a significant difference between RASSF1A methylation in normal and tumor cells of the kidney exists. Moreover, RASSF1A expression has not been characterized in tumors or normal tissue as yet. Results Using combined bisulfite restriction analysis (COBRA) we compared RASSF1A methylation in 90 paired tissue samples obtained from primary kidney tumors and corresponding normal tissue. Bisulfite sequence analysis was carried out using both pooled amplicons from the tumor and normal tissue groups and subclones obtained from a single tissue pair. Expression of RASSF1A was analyzed by the use of tissue arrays and immunohistochemistry. We found significantly increased methylation in tumor samples (mean methylation, 20%) compared to corresponding normal tissues (mean methylation, 11%; P Conclusion Our methylation and expression data support the hypothesis that RASSF1A is involved in early tumorigenesis of renal cell carcinoma.