Up-regulation of integrin α6β4 expression by mitogens involved in dairy cow mammary development

14-3-3β is essential for milk composition stimulated by Leu/IGF-1 via IGF1R signaling pathway in BMECs

The cell proliferation of bovine mammary epithelial cells (BMECs) and consequent milk synthesis are regulated by multiple factors. The purpose of this study was to examine the effect of 14-3-3β on cellular proliferation and milk fat/β-casein synthesis in BMECs and reveal its underlying mechanisms. In this study, we employed gene function analysis to explore the regulatory effect and molecular mechanisms of 14-3-3β on milk synthesis and proliferation in BMECs. We found that leucine and IGF-1 enhance cell proliferation and milk synthesis in a 14-3-3β-dependent manner and only exhibiting such effect in the presence of 14-3-3β. We further determined that 14-3-3β interacts with the IGF1R self-phosphorylation site and it additionally mediated leucine and IGF-1 to stimulate the synthesis of milk through the IGF1R-AKT-mTORC1 signaling pathway. In summary, our data indicated that 14-3-3β mediates the expression of milk fat and protein stimulated by leucine and IGF-1, leading to lactogenesis through IGF1R signaling pathway in BMECs.

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 β-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 β-casein synthesis, and Cyclin D1 is involved in cell proliferation. In addition, silencing GHR decreased protein levels of β-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 β-casein synthesis and proliferation in BMECs by targeting the GHR and IGF1R signaling pathways.