CXCR4 and colorectal carcinoma: In CRC cell lines our results suggest that 5mC present within CpG island region #1 of the promoter may contribute to CXCR4 gene silencing in HCT116 and RKO cells as negligible levels of CXCR4 mRNA and no protein were detected in HCT116 cells and no CXCR4 protein was detected in RKO cells.