Abstract 5060: Dietary sodium, potassium and fluid intake and clear cell renal cell cancer: heterogeneous effects by DNA methylation of genes involved in renal salt homeostasis
Authors: Deckers Ivette A. G. , Brandt Piet A. van den , Engeland Manon van , Soetekouw Patricia M. M. B. , Baldewijns Marcella M. L. L. , Keszei András P. , Schouten Leo J. 
Published: May 2015

Abstract
Introduction: Sodium, potassium and fluid play a key role in renal salt homeostasis. We showed that sodium intake is associated with higher renal cell cancer (RCC) risk. Promoter CpG island methylation, leading to silencing of tumor suppressor genes, may also affect RCC carcinogenesis. We investigated whether associations between sodium, potassium and fluid intake and RCC risk differed for RCC subtypes defined by promoter methylation of genes involved in renal salt homeostasis.
Methods: The Netherlands Cohort Study (NLCS) with case-cohort design included 120,852 subjects aged 55-69 years. Diet was measured with a food frequency questionnaire. After 20.3 years of follow-up, paraffin-embedded tumor blocks from 454 incident RCC cases were collected, of which 80% had clear cell (cc) histology. Methylation-specific PCR was used to analyze promoter CpG island methylation in tumor DNA. Genes involved in renal salt homeostasis were of interest if exhibiting 1) promoter CpG island methylation in ccRCC cell lines and not in normal kidney tissue in a genome-wide methylation screen (MBD-affinity massive parallel sequencing) and 2) ccRCC-specific down-regulation in public expression data. We identified ARHGDIG, ATP1A1, SCNN1B and SLC8A3 as candidate genes, which were then combined into a methylation sum score and categorized representing no (0 genes methylated), low (1 gene methylated) and high (≥2 genes methylated) methylation. Cox regression analyses were stratified accordingly and included 4,439 subcohort members and 348 ccRCC cases.
Results: ARHGDIG, ATP1A1, SCNN1B and SLC8A3 were methylated in 22.7%, 16.4%, 42.2% and 5.5% of ccRCC tumors. High sodium intake increased overall ccRCC risk [HR(95%CI): 1.42(1.06-1.89)] regardless of methylation status (P-heterogeneity = 0.69). High potassium intake was differently associated with ccRCC risk (P-heterogeneity = 0.02); ccRCC risk was lower for tumors without methylation [HR(95%CI): 0.59(0.36-0.98)], but higher for tumors with high methylation [HR(95%CI): 1.50(0.89-2.52)]. For fluid intake, HRs similarly differed across the methylation subtypes, but heterogeneity was not significant (P-heterogeneity = 0.45). Individual gene analyses showed that SCNN1B was most indicative of the heterogeneous effects.
Discussion: Our findings indicate for the first time a joint influence of diet and epigenetics to determine ccRCC risk. By investigating specific dietary intakes and DNA methylation in selected genes we provide a biological rational for the role of renal salt homeostasis in the development of ccRCC. In particular, we show that, besides sodium intake, also potassium and fluid intake may be implicated in ccRCC etiology, when the epigenetic environment is considered. Further exploration of the temporal relationship and exact pathological pathway is however warranted.
Citation Format: Ivette A. G. Deckers, Piet A. van den Brandt, Manon van Engeland, Patricia M. M. B. Soetekouw, Marcella M. L. L. Baldewijns, András P. Keszei, Leo J. Schouten. Dietary sodium, potassium and fluid intake and clear cell renal cell cancer: heterogeneous effects by DNA methylation of genes involved in renal salt homeostasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5060. doi:10.1158/1538-7445.AM2014-5060