Mir-145 Is Involved In The Proliferation Of Bovine Mammary Epithelial Cells And Regulates Bovine Insulin Receptor Substrate 1

MicroRNAs (miRNAs) are short noncoding RNAs that can regulate target gene expression at the posttranscriptional level. It has been reported that bta-miR-145 shows differential expression between the different lactation stages of bovine mammary glands, but the function of bta-miR-145 in normal mammary glands remains unknown. The overexpression of bta-miR-145 significantly decreased the proliferation of mammary epithelial cells (p < .05), and this effect was reversed upon bta-miR-145 inhibition. Using several miRNA prediction programmes, insulin receptor substrate 1 (IRS1) was predicted to be a potential target of miR-145. Using the DAVID database, many predicted targets of bta-miR-145 were found to be involved in the MAPK signalling pathway associated with cell proliferation, including IRS1. Bovine IRS1 3'RACE sequencing and reference comparison revealed that possible binding sites for bta-miR-145 still exist in IRS1. The IRS1 mRNA level was not affected by the transfection of primary bovine mammary epithelial cells with 150 pmol of a bta-miR-145 mimic or 300 pmol of a bta-miR-145 inhibitor for 24 h (pBMEC, p > .05), whereas the IRS1 protein level was changed significantly after bta-miR-145 mimic or inhibitor transfection for 72 h (p < .05). Taken together, these results suggest that bta-miR-145 is involved in the proliferation of bovine mammary epithelial cells by targeting IRS1, which is related to the MAPK signalling pathway.