Genome‐wide analysis of mRNA and microRNA expression in colorectal cancer and adjacent normal mucosa

mRNA expression varies in human cancers. Such altered mRNA expression is negatively regulated by the expression of microRNAs (miRNAs), which play an important role in human tumorigenesis. According to this theory, inverse mRNA/miRNA expression may be a direct driver of cancer development, and certain genetic events may occur prior to the development of any discernible histological abnormalities. We examined the inverse expression between mRNAs and their corresponding miRNAs in colorectal cancer (CRC) and adjacent normal mucosa and performed pathway analysis to identify mRNA/miRNA networks. The cancer samples were divided into first (20 cases) and second (24 cases) cohorts, and 48 samples were obtained from two sections of the normal mucosa adjacent to the tumors from the second cohort. We investigated mRNAs with commonly altered expression in CRC and adjacent normal mucosa using isolated cancer glands and normal crypts from the first cohort, compared with that of distal normal crypts, using an array‐based method. As a result, significant inverse correlations between CEACAM1 and miRNA‐7114‐5p and between AK1 and miRNA‐6780‐5p were found in CRC and adjacent normal mucosa. We validated these correlations in the second cohort using RT‐PCR. To confirm these findings, transfection and immunohistochemical assays were also performed, which verified the inverse correlation between CEACAM1 and miRNA‐7114‐5p. Our findings suggest that the inverse correlations between the CEACAM1/miRNA‐7114‐5p and possibly AK1/miRNA‐6780‐5p pairs play an important role in early CRC development, and may help identify potential molecular targets for early detection of CRC.