Adiposity and age are statistically related to enhanced RASSF1A tumor suppressor gene promoter methylation in normal autopsy kidney tissue.

Age, adiposity, and smoking are risk factors for the development of renal cell carcinoma. Hypermethylation of the RAS association domain family 1A gene (RASSF1A) promoter belongs to the most frequently detected epigenetic alterations in human cancers including renal cell carcinoma. RASSF1A is functionally involved in cell cycle control in normal cells and depletion promotes a number of cellular changes increasing the risk for neoplastic growth. We investigated the hypothesis that age, modulated by the factors adiposity and anthracosis as a surrogate for smoking, is a predictor of RASSF1A promoter methylation in normal kidney tissue. Using a cross-sectional study design, we quantitatively analyzed RASSF1A methylation in 78 normal autopsy kidney tissues by quantitative combined bisulfite and restriction analysis and bisulfite sequencing, and statistically evaluated the degree of relative methylation for a relationship with the predictor age and study factors adiposity and state of anthracosis. Statistical analysis showed that age (regression analysis; P < 0.001), adiposity (univariate analysis; P = 0.016), and state of anthracosis (t test; P = 0.005) are each significantly associated with an increase of RASSF1A promoter methylation in normal kidney tissue. However, only age (P = 0.008) and adiposity (P = 0.008) were identified as independent predictors of RASSF1A promoter methylation using covariance analysis. This study provides statistical evidence that the common cancer risk factors age and adiposity enhance RASSF1A promoter methylation in nonmalignant kidney tissue.