Screening for differentially methylated genes among human colorectal cancer tissues and normal mucosa by microarray chip.

UNLABELLED: High density DNA methylation microarrays were used to study the differences of gene methylation level in six pairs of colorectal cancer (CRC) and adjacent normal mucosa. We analyzed the profile of methylated genes by NimbleGen Microarray and the biologic functions by NIH-NAVID. In addition, preliminary validation studies were done in six pairs of samples by MSP (methylation-specific PCR). A total of 4,644 genes had a difference in methylation levels. Among them 2,296 were hypermethylated (log2ratio > 1), 2,348 genes were hypomethylated (log2ratio < -1), in which 293 hypermethylated and 313 hypomethylated genes were unmapped according to the NIH-NAVID. All these genes were randomly distributed on all the chromosomes. However, chromosome 1 contained the most of the hypermethylated genes (232 genes), followed by chromosome 19 (149 genes), chromosome 11 (144 genes), chromosome 2 (141 genes), chromosomes 3 (127 genes). Through the analysis of the statistics, There were 2 hypermethylated/3 hypomethylated genes involved in six pairs of samples simultaneously, followed by 10/14 in five samples, 34/37 in four samples, 101/113 in three samples, 341/377 in two samples, 1,808/1,804 in one sample. According to gene ontology analysis, some physiological processes play important roles in the cell division and the development of tumor, such as apoptosis, DNA repair, immune, cell cycle, cell cycle checkpoint, cell adhesion and invasion etc. Through Preliminary validation, there were two genes (St3gal6, Opcml) in thirty top-ranking genes shown hypermethylated in six pairs of CRC and adjacent normal mucosa. CONCLUSIONS: High density DNA methylation microarrays is an effective method for screening aberrantly methylated genes in CRC. The methylated genes should be further studied for diagnostic or prognostic markers for CRC.

Snail promotes lymph node metastasis and Twist enhances tumor deposit formation through epithelial-mesenchymal transition in colorectal cancer.

Snail and Twist, transcriptional repressors of E-cadherin as well as inducers of epithelial-mesenchymal transition, play pivotal roles in tumor invasion and metastasis. We investigated the expression of Snail, Twist, and E-cadherin by immunohistochemistry in 193 colorectal cancers, including 79 with positive lymph nodes, 36 with tumor deposits, 39 with both, and 39 with no metastases. Snail was expressed to a greater extent in the group with positive lymph nodes (68.4%), whereas Twist was overexpressed in patients with other metastases (75.0%). Ectopic expression of Snail and Twist correlated with reduced membranous expression of E-cadherin. Importantly, Snail overexpression correlated significantly with lymph node metastasis (P < .0001), whereas Twist up-regulation correlated strongly with other metastases (P < .0001). Multivariate logistic regression analysis showed that Snail was an independent predictor of lymph node metastasis (odds ratio, 4.445; 95% confidence interval, 2.250-8.781; P < .0001), whereas Twist displayed predictive value for metastasis formation (odds ratio, 5.606; 95% confidence interval, 2.829-11.111; P < .0001), suggesting that lymph node and other metastases may follow different signaling pathways. In conclusion, ectopic expression of Snail and Twist contributed to lymph node and disseminated metastasis, respectively, by reducing E-cadherin expression, providing a novel role for Snail and Twist in the progression of colorectal cancer.