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Introduction
MicroRNAs (miRNAs) are small (18–24 nucleotides) non-coding RNA molecules that act as negative regulators in target gene expression at the post-transcriptional level. Accumulated evidence suggests that these small RNAs occupy a crucial place in the modulation of multiple cellular bioprocesses, for example, cell differentiation, proliferation and apoptosis (1). In addition, abnormal miRNA expression profiles can result in cell dysfunction and subsequently contribute to pathogeneses of various diseases, even cancer (2,3). Research has demonstrated that many miRNAs are specific target oncogenes or cancer suppressor genes and directly participate in the development of cancers (4–6). Notably, miRNAs are reported to play a vital regulatory role in almost every cancer type due to their abundance and cell-type specifcity (7,8).
Colorectal cancer (CRC) is a very common malignant tumor. The incidence of CRC is increasing and it has become the fourth main cause of cancer-associated mortality worldwide (9). In 2012, ~1.36 million people were diagnosed with CRC, and rectal cancer accounted for ~28% and was highly associated with a poor clinical outcome (10,11). In recent years, many differentially expressed miRNAs have been identified in regulating the progression of colon cancer (12,13), however, limited data on miRNAs in rectal cancer are available. Some studies revealed that rectal and colon cancers were two different tumor entities, therefore, they required different treatment strategies due to the differences in the disease-associated genetic and biological factors (14,15). It is also urgent to investigate the miRNA expression profiles in rectal cancer. Currently, Gaedcke et al (16) mapped the expression of 2,090 miRNAs using LNA-enhanced miRCURY microarrays, and revealed 49 differentially expressed miRNAs after conducting comparative analysis of tumor and matched mucosa samples of locally advanced rectal cancer patients. miR-195 was one of the significantly downregulated miRNAs in rectal cancer (16). Studies have demonstrated that miR-195 acts as a tumor suppressor in many types of cancer, for instance, Cai et al (17) indicated that by blocking the expression of ribosomal protein S6 kinase, 70 kDa, polypeptide 1 (RPS6KB1), miR-195 had a marked inhibitory effect on human prostate cancer cell metastasis and angiogenesis. Similarly, in papillary thyroid carcinoma (PTC), miR-195 specifically targeted fibroblast growth factor 2 (FGF2) and cyclin D1 to regulate the proliferative, migratory and invasive capacities of PTC cells (18). miR-195 inhibits the...