Downregulation of miR‑143 modulates KRAS expression in colorectal carcinoma cells.

MicroRNAs (miRs) are a class of non‑coding small RNAs that have been demonstrated to be involved in the pathogenesis of human cancer. There is even evidence that microRNAs can act as oncogenes or tumor suppressors. Although microRNA expression profiles have been characterized in colorectal carcinoma, their precise physiological functions are largely unknown. It has become clear that the activated KRAS Proto‑Oncogene, GTPase (KRAS) oncogene plays an important role in colorectal carcinogenesis. In the present study, it was found that the level of mature miR‑143 was lower in colorectal carcinoma tissues compared with that observed in normal adjacent tissues. A lack of miR‑143 was detected in human colorectal carcinoma cell lines, SW480, LoVo and HT‑29, compared to the high expression observed in normal colon epithelial cell line NCM460. pcDNA3.1‑pri‑miR‑143 and its mutant were successfully constructed and transfected into colorectal carcinoma cells. Increased accumulation of mature miR‑143 was observed in the pcDNA3.1‑pri‑miR‑143‑transfected cells. In SW480 cells, transfection of pcDNA3.1‑pri‑miR‑143 resulted in a 35 and 47% reduction in cell growth after incubation for 4 and 5 days, respectively, compared with transfection of the pcDNA3.1‑pri‑miR‑143 mutant; while in LoVo cells, transfection of pcDNA3.1‑pri‑miR‑143 resulted in a 33 and 46% reduction in cell growth respectively. In contrast, transfection of pcDNA3.1‑pri‑miR‑143 had no significantly effects on HT‑29 cell growth. We also found that transfection of pcDNA3.1‑pri‑miR‑143 had no effect on levels of KRAS mRNA, but resulted in a 58% decrease in the KRAS protein level in the transfected SW480 cells, while an approximate 54 and 43% KRAS protein reduction in LoVo and HT‑29 cells, respectively, compared with the pcDNA3.1‑pri‑miR‑143 mutant. Two fragments containing the putative complementary site were cloned into the pGL3 vector, constructing the luciferase reporter pGL3‑KRAS‑CS1 and pGL3‑KRAS‑CS2. Cotransfection of pcDNA3.1‑pri‑miR‑143 with pGL3‑KRAS‑CS1 and pGL3‑KRAS‑CS2 respectively resulted in 4.6‑ and 3.3‑fold inhibition of luciferase activity in the SW480 cells, while a 4.0‑ and 3.2‑fold inhibition of luciferase activity in the LoVo cells, 3.7‑ and 3.1‑fold inhibition in the HT‑29 cells. Differences in pGL3‑KRAS‑CS1 and pGL3‑KRAS‑CS2 activity were not significant. Our results revealed that increased accumulation of miR‑143 is likely to modulate levels of KRAS protein expression at the post‑transcriptional level by interacting specifically with the complementary site, and consequently inhibiting proliferation of the transfected cells.