IGF1/IGF1R and microRNA let-7e down-regulate each other and modulate proliferation and migration of colorectal cancer cells.

MicroRNA let-7 has been reported to be down-regulated in several human cancers and is now characterized as a tumor suppressor. IGF1R is over-expressed in many cancers and IGF1/IGF1R pathway is attractive target for anticancer therapy. However, the crosstalk between let-7 and IGF1/IGF1R are largely unknown. The present study showed IGF1R were significantly over-expressed in colorectal cancer tissues compared with adjacent normal tissues through immunohistochemical analysis. qRT-PCR results showed that let-7a, let-7b and let-7e were down-regulated in colorectal cancer tissues. Bioinformatics analysis revealed that both IGF1 and IGF1R mRNA are potential targets for let-7 miRNA family. Ectopic transfection of let-7e led to a significant reduction in IGF1R at protein level and their downstream Akt inhibition, as well as a reduction in cell proliferation, migration and invasion in colorectal cancer cells, while inhibition of let-7e enhanced the expression of IGF1R. On the other hand, IGF1 stimulation can significantly down-regulate the expression of let-7e in colorectal cancer cells. Taken together, our findings identify a negative feedback regulation between let-7e and IGF1/IGF1R, and suggest that let-7e could be used in IGF1R-targeted therapeutics in anticancer therapy. ABBREVIATIONS: IGF1: insulin-like growth factor 1; IGF1R: IGF1 receptor; miRNA: microRNA; CRC: colorectal cancer; EGFR: epidermal growth factor receptor; HRP: horseradish peroxidase; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide; p-Akt: phospho-Akt; PI3K: phosphoinositide 3-kinase; qRT-PCR: quantitative reverse transcription-PCR; IHC: immunohistochemical; siRNA: small interfering RNA; 3'-UTR: 3'-untranslated region.