In these cells, methylation level of DKK 4 gene promoter was decreased, suggesting that colorectal epithelial cells might up-regulate DKK 4 transcription and expression by down-regulating methylation of DKK 4 gene promoter, and further promote occurrence and development of colorectal cancer by exosomes secreting DKK 4 and inducing APC gene mutation. Here, APC is linked to colorectal cancer.