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.