Evaluation of Keap1 gene expression and methylation levels in biopsy specimens of patients with and without gastric cancer

Abstract

Abstract Background: Kelch–like ECH–associated protein 1 (Keap1) is a cytoplasmic anchor of nuclear factor erythroid 2–related factor 2 (Nrf2), which mediates the regulation of genes involved in apoptosis and cell survival. Epigenetic events such as aberrant DNA methylation is emerging as a possible mechanism for dysregulation of the Keap1 in cancer. However, the impacts of Keap1 methylation and expression on gastric cancer (GC) development and progression have not yet been investigated. Methods: We analyzed the Keap1 promoter methylation and its mRNA or protein expression in endoscopic biopsies from 60 GC patients compared with those in non–GC individuals by methylated DNA immunoprecipitation (MeDIP) assay, quantitative real–time PCR and immunohistochemistry, respectively. Results: The methylation level of Keap1 in GC was remarkably higher than that in non–GC biopsies (p<0.001). In contrast, the mRNA and protein expression of Keap1 were clearly down–regulated in GC in comparison with the non–GC tissues (p<0.001). In addition, there were significant differences in both Keap1 methylation or expression levels between the low and high histological grade. Statistical analysis revealed that Keap1 expression inversely correlates to its promoter methylation in GC (r =–0.55, p<0.001). Conclusion: Our results reflect an epigenetic regulation of Keap1 expression, and highlight the importance of Keap1 downregulation and its promoter hypermethylation in GC pathogenesis. Key words: Clinicopathological criteria; DNA methylation; Gastric cancer; Keap1; MeDIP; Nrf2