Methylation of the KEAP1 Gene Promoter Region in Human Colorectal Cancer

Overview

Journal BMC Cancer

Publisher Biomed Central

Specialty Oncology

Date 2012 Feb 14

PMID 22325485

Citations 102

Authors

Naoyuki Hanada

Takenori Takahata

Qiliang Zhou

Xulu Ye

Ruowen Sun

Jugoh Itoh

Atsushi Ishiguro

Hiroshi Kijima

Junsei Mimura

Ken Itoh

Shinsaku Fukuda

Yasuo Saijo

Affiliations

Soon will be listed here.

Abstract

Background: The Keap1-Nrf2 pathway has been reported to be impaired in several cancers. However, the status of Keap1-Nrf2 system in human colorectal cancer (CRC) has not been elucidated.

Methods: We used colorectal cancer (CRC) cell lines and surgical specimens to investigate the methylation status of the KEAP1 promoter region as well as expression of Nrf2 and its downstream antioxidative stress genes, NQO-1 and AKR1C1.

Results: DNA sequencing analysis indicated that all mutations detected were synonymous, with no amino acid substitutions. We showed by bisulfite genomic sequencing and methylation-specific PCR that eight of 10 CRC cell lines had hypermethylated CpG islands in the KEAP1 promoter region. HT29 cells with a hypermethylated KEAP1 promoter resulted in decreased mRNA and protein expression but unmethylated Colo320DM cells showed higher expression levels. In addition, treatment with the DNA methyltransferase inhibitor 5-Aza-dC combined with the histone deacetylase inhibitor trichostatin A (TSA) increased KEAP1 mRNA expression. These result suggested that methylation of the KEAP1 promoter regulates its mRNA level. Time course analysis with the Nrf2-antioxidant response element (ARE) pathway activator t-BHQ treatment showed a rapid response within 24 h. HT29 cells had higher basal expression levels of NQO-1 and AKR1C1 mRNA than Colo320DM cells. Aberrant promoter methylation of KEAP1 was detected in 53% of tumor tissues and 25% of normal mucosae from 40 surgical CRC specimens, indicating that cancerous tissue showed increased methylation of the KEAP1 promoter region, conferring a protective effect against cytotoxic anticancer drugs.

Conclusion: Hypermethylation of the KEAP1 promoter region suppressed its mRNA expression and increased nuclear Nrf2 and downstream ARE gene expression in CRC cells and tissues.

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