MiR-139 suppresses β-casein synthesis and proliferation in bovine mammary epithelial cells by targeting the GHR and IGF1R signaling pathways

Background: MicroRNAs have important roles in many biological processes. However, the role of miR-139 in healthy mammary gland remains unclear. The objective of this study was to investigate the effects of miR-139 on lactation in dairy cows. Results: Here, we found that miR-139 was down-regulated in mid-lactation dairy cow mammary tissues compared with mid-pregnancy tissues. Then, we prioritized two of potential target genes of miR-139 in cow, growth hormone receptor (GHR) and type I insulin-like growth factor receptor (IGF1R) for further functional studies based on their roles in lactation processes. Dual luciferase reporter assays validated direct binding of miR-139 to the 3'-untranslated region (UTR) of GHR and IGF1R. Moreover, over-expression or silencing of miR-139 affected mRNA levels of GHR and IGF1R in cultured bovine mammary epithelial cells (BMECs). Furthermore, over-expression of miR-139 decreased protein levels of beta-casein, proliferation in mammary epithelial cell, and the protein levels of IGF1R and key members of the GHR or IGF1R pathways as well, whereas silencing miR-139 produced the opposite result. Among these signal molecules, signal transducer and activator of transcription-5 (STAT5), protein kinase B (also known as AKT1), mammalian target of rapamycin (mTOR), and p70-S6 Kinase (p70S6K) are involed in beta-casein synthesis, and Cyclin D1 is involved in cell proliferation. In addition, silencing GHR decreased protein levels of beta-casein, IGF1R, and key members of the IGF1R pathway, whereas co-silencing miR-139 and GHR rescued the expression of GHR and reversed GHR silencing effects. Conclusions: Our results demonstrate that GHR and IGF1R are target genes of miR-139 in dairy cow. MiR-139 suppresses beta-casein synthesis and proliferation in BMECs by targeting the GHR and IGF1R signaling pathways.