Over- and under-expressed microRNAs in human colorectal cancer

MicroRNAs (miRNAs) constitute a class of small (21-23 nucleotides) noncoding RNAs that function as post-transcriptional gene regulators. It is becoming increasingly clear that altered miRNA expression correlates with the pathogenesis of cancers. The purpose of this study was to determine the up-regulated miRNAs in human colorectal cancer. Total RNA was isolated from cancer tissues and corresponding noncancerous tissues from surgically resected colorectal cancers. The expression profiles of miRNAs were determined using a miRNA microarray containing 455 human miRNA probes. The expression status of selected miRNAs in paired clinical samples was then investigated by real-time RT-PCR. Twenty-one miRNAs were identified by miRNA array analysis as overexpressed in colorectal cancer tissues compared to normal epithelial tissues. Among them, the expression of miR-31, miR-183, miR-17-5p, miR-18a, miR-20a and miR-92 were confirmed to be significantly higher in cancer tissues than in normal tissues (P<0.05). In contrast, the expression of miR-143 and miR-145 in cancer tissues were significantly lower than in normal tissues (P<0.05). The miR-18a overexpression group tended to have a poorer clinical prognosis than the low expression group (P=0.07). We identified miRNAs that were overexpressed or under-expressed in colorectal cancers and which may be correlated with colorectal carcinogenesis.