Gastric Cancer
Copyright ©2007 Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Dec 14, 2007; 13(46): 6166-6171
Published online Dec 14, 2007. doi: 10.3748/wjg.v13.i46.6166
Re-expression of methylation-induced tumor suppressor gene silencing is associated with the state of histone modification in gastric cancer cell lines
Chun-Feng Meng, Xin-Jiang Zhu, Guo Peng, Dong-Qiu Dai
Chun-Feng Meng, Xin-Jiang Zhu, Guo Peng, Dong-Qiu Dai, Department of Surgical Oncology, The First Affiliated Hospital, China Medical University, Shenyang 110001, Liaoning Province, China
Author contributions: All authors contributed equally to the work.
Supported by National Natural Science Foundation of China, No. 30271477, No. 30572162
Correspondence to: Dr. Dong-Qiu Dai, Department of Surgical Oncology, The First Affiliated Hospital, China Medical University, No.155, Nanjing North Street, Heping District, Shenyang 110001, Liaoning Province, China. daidq63@163.com
Telephone: +86-24-83283560 Fax: +86-24-22703576
Received: July 18, 2007
Revised: September 15, 2007
Accepted: October 21, 2007
Published online: December 14, 2007
Abstract

AIM: To identify the relationship between DNA hyper-methylation and histone modification at a hyperme-thylated, silenced tumor suppressor gene promoter in human gastric cancer cell lines and to elucidate whether alteration of DNA methylation could affect histone modification.

METHODS: We used chromatin immunoprecipitation (ChIP) assay to assess the status of histone acetylation and methylation in promoter regions of the p16 and mutL homolog 1 (MLH1) genes in 2 gastric cancer cell lines, SGC-7901 and MGC-803. We used methylation-specific PCR (MSP) to evaluate the effect of 5-Aza-2’-deoxycytidine (5-Aza-dC), trichostatin A (TSA) or their combination treatment on DNA methylation status. We used RT-PCR to determine whether alterations of histone modification status after 5-Aza-dC and TSA treatment are reflected in gene expression.

RESULTS: For the p16 and MLH1 genes in two cell lines, silenced loci associated with DNA hypermethylation were characterized by histone H3-K9 hypoacetylation and hypermethylation and histone H3-K4 hypomethylation. Treatment with TSA resulted in moderately increased histone H3-K9 acetylation at the silenced loci with no effect on histone H3-K9 methylation and minimal effects on gene expression. In contrast, treatment with 5-Aza-dC rapidly reduced histone H3-K9 methylation at the silenced loci and resulted in reactivation of the two genes. Combined treatment with 5-Aza-dC and TSA was synergistic in reactivating gene expression at the loci showing DNA hypermethylation. Similarly, histone H3-K4 methylation was not affected after TSA treatment, and increased moderately at the silenced loci after 5-Aza-dC treatment.

CONCLUSION: Hypermethylation of DNA in promoter CpG islands is related to transcriptional silencing of tumor suppressor genes. Histone H3-K9 methylation in different regions of the promoters studied correlates with DNA methylation status of each gene in gastric cancer cells. However, histone H3-K9 acetylation and H3-K4 methylation inversely correlate with DNA methylation status of each gene in gastric cancer cells. Alteration of DNA methylation affects histone modification.

Keywords: Gastric cancer; DNA hypermethylation; Histone methylation; Histone acetylation; p16; mutL homolog 1; 5-Aza-2’-deoxycytidine; Trichostatin A