Objective: To identify the association of his tone H3 lysine 9 (H3-K9) methylation with DNA methylation and the expression of the mismatch repair gene hMLH1 in human gastric cancer cells.
Methods: Gastric cancer cells of the lines BGC-823 and MGC-803 were cultured and treated with 5-Aza-2'-deoxycytidine (5-Aza-dC), a demethylation agent, for 72 hour. Chromatin immunoprecipitation (ChIP) assay was used to assess the status of histone H3 lysine 9 methylation in the promoter regions of hMLH1 gene. Methylation-specific PCR (MSP) was used to evaluate the effect of 5-Aza-dC on DNA methylation status. RT-PCR was used to examine the hMLH1 gene expression.
Results: In the MGC-803 cells, silenced hMLH1 gene was characterized by DNA methylation and histone H3-K9 hypermethylation; 5-Aza-dC demethylated the DNA and reduced the histone H3-K9 methylation at silenced loci and resulted in reactivation of hMLH1 gene therein. Contrary to the MGC-803 cells, BGC-823 cells expressed hMLH1 gene with DNA demethylation and histone H3-K9 hypomethylation; and 5-Aza-dC had no effects on the gene expression, DNA methylation, and histone H3-K9 methylation therein.
Conclusion: Hypermethylation of DNA in the promoter region is related to transcriptional silencing of hMLH1 gene. Histone H3-K9 methylation in different regions of the promoter studied correlates with DNA methylation status of hMLH1 gene in gastric cancer cells. Alteration of DNA methylation affects histone H3-K9 methylation. 5-Aza-dC can control hMLH1 expression, DNA methylation, and histone H3-K9 methylation in the promoter.