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Genome-Wide Analysis of DNA Methylation in Gastrointestinal Cancer
Published on: September 18, 2020
Promoter hypermethylation downregulates RUNX3 gene expression in colorectal cancer cell lines
Ja-Lok Ku1, Sung-Bum Kang, Young-Kyoung Shin
1Laboratory of Cell Biology, Cancer Research Institute, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea.
Abstract:
It was recently reported that RUNX3 gene expression is significantly downregulated in human gastric cancer cells due to hypermethylation of its promoter region or hemizygous deletion (Cell, 109, 2002). To verify the genetic alterations and methylation status of the RUNX3 gene in colorectal carcinogenesis, we analysed for mutations, loss of heterozygosity (LOH), and RUNX3 gene promoter hypermethylation, in 32 colorectal cancer cell lines. RT-PCR analysis showed undetectable or low RUNX3 expression in 16 cell lines, and no mutations were found in the RUNX3 gene by PCR-SSCP analysis. Of these 16 cell lines, hypermethylation of the RUNX3 promoter was confirmed in 12. The following observations were made: (i) RUNX3 was re-expressed after 5-aza-2'-deoxycytidine treatment, (ii) the RUNX3 promoter was found to be methylated by MS-PCR, and (iii) hypermethylation of the RUNX3 promoter was confirmed by direct sequencing analysis after sodium bisulfite modification in the above 12 cell lines. RUNX3 was neither methylated nor expressed in four cell lines. Of these four, microsatellite instability (MSI) at the RUNX3 locus was found in three, SNU-61 (D1S246), SNU-769A, and SNU-769B (D1S199). This study suggests that transcriptional repression of RUNX3 is caused by promoter hypermethylation of the RUNX3 CpG island in colorectal cancer cell lines, and the results of these experiments may contribute to an understanding of the role of RUNX3 inactivation in the pathogenesis of colorectal cancers.
Insights
RUNX3 gene promoter hypermethylation silences RUNX3 expression in colorectal cancer cell lines. This epigenetic silencing, rather than mutation, is a key mechanism driving colorectal cancer development.
Area of Science:
- Molecular Biology
- Cancer Genetics
- Epigenetics
Background:
- RUNX3 gene expression is downregulated in gastric cancer via promoter hypermethylation or deletion.
- RUNX3 plays a crucial role in tumor suppression.
Purpose of the Study:
- Investigate genetic alterations and methylation status of RUNX3 in colorectal carcinogenesis.
- Determine the role of RUNX3 inactivation in colorectal cancer pathogenesis.
Main Methods:
- Analysis of mutations, loss of heterozygosity (LOH), and RUNX3 promoter hypermethylation in 32 colorectal cancer cell lines.
- Reverse Transcription Polymerase Chain Reaction (RT-PCR) for gene expression.
- Polymerase Chain Reaction-Single Strand Conformation Polymorphism (PCR-SSCP) for mutations.
- Methylation-Specific PCR (MS-PCR) and direct sequencing after sodium bisulfite modification for promoter methylation.
- Treatment with 5-aza-2'-deoxycytidine to assess gene re-expression.
- Microsatellite Instability (MSI) analysis.
Main Results:
- RUNX3 expression was undetectable or low in 16 cell lines, with no mutations detected.
- RUNX3 promoter hypermethylation was confirmed in 12 of these 16 cell lines.
- RUNX3 re-expressed after 5-aza-2'-deoxycytidine treatment in hypermethylated cell lines.
- Four cell lines showed neither methylation nor expression; three exhibited microsatellite instability (MSI) at the RUNX3 locus.
Conclusions:
- Transcriptional repression of RUNX3 in colorectal cancer cell lines is primarily caused by promoter hypermethylation of its CpG island.
- RUNX3 inactivation through promoter hypermethylation is a significant factor in colorectal cancer pathogenesis.
- These findings enhance understanding of RUNX3's role in colorectal cancer development.
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