Screening and identification of a tumor specific methylation phenotype in the colorectal laterally spreading tumor.

OBJECTIVE

We screened and identified the differential expression of the methylation phenotype in the whole genome of colorectal laterally spreading tumor (LSTs).

MATERIALS AND METHODS

3 tissue samples of colorectal polypoid adenomas (PAs), 3 tissue samples of LSTs and 3 tissue samples of colon cancer were analyzed with a high-density gene chip, and about 450,000 methylation sites were detected covering approximately 95% of the CpG islands. The Delta Data screening was taken through a cluster analysis of methylation phenotype differential expression. 50 tissue samples each of PAs patients, LSTs patients, and colorectal cancer patients were selected. Methylation-specific PCR (MSP) was used to detect RASSF1A and WIF-1 methylation levels. He RT-PCR method was used to detect the relative mRNA expression levels for methylation expression identification.

RESULTS

The degree of LST methylation was higher than that of PAs, and 1234 genes were found to have a lower expression when compared to colorectal cancer samples. 764 genes had a higher expression when compared to colorectal cancer, and 559 genes lower expression when compared to PAs. The average methylation level of LSTs was higher than that of PAs, and lower than that of colorectal cancer. The chromosomal location was taken on these 1234 genes, which were higher than that of PAs, and lower than that of colorectal cancer; 518 genes were located on chromosome No. 2 (41.98%), 236 on No. 5 (19.12%), 357 on No. 8 (28.93%), and 123 on No. 10 (9.97%). According to clustering analysis, DNA differentially methylated sites were mainly on genes of cell adhesion molecules regulation, signaling pathways, energy transduction, cell cycle and apoptosis. The positive rate of RASSF1A and WIF-1 methylation in the tissues of LSTs patients were higher than that of PAs, and lower than that of colorectal cancer; differences were statistically significant (p<0.05). The relative expression levels of RASSF1A and WIF-1mRNA in the tissues of LSTs patients were lower than that of PAs, higher than that of colorectal cancer, and the difference was statistically significant (p<0.05).

CONCLUSIONS

The administration of high-density gene chip technology has a good application value to screen the differential expression of LSTs gene methylation phenotype. Results are consistent with the identification results.