Lactogenic hormones regulate mammary protein synthesis in bovine mammary epithelial cells via the mTOR and JAK-STAT signal pathways

The expression of CSN3, hormone receptor, the expression of genes regulating the mTOR, JAK-STAT signal pathways, and the relative content of kappa-casein as well as total casein were determined in the present study to explore the mechanism of the effect of lactogenic hormones on milk-protein synthesis in bovine mammary epithelial cells. The results showed that apoptosis of the cells was increased by inhibitor LY294002, while the expressions of genes encoding PKB, Rheb, PRAS40 and S6K1 in the mTOR signal pathway, JAK2, STAT5A in the JAK-STAT signal pathway, and genes encoding INSR, PRLR, NR3C1 and CSN3 were all downregulated, and the relative contents of kappa-casein and total casein were decreased in the mammary epithelial cells compared with those in the control group. Comparatively, the inhibitory effects of AG-490 were more profound than those of LY294002, and the double block using both inhibitors had a greater effect than the single block. The CSN3 gene expression was downregulated and the content of milk casein was decreased by the inhibitors. In addition, the expression of the hormone receptor genes was downregulated. Our results suggest that lactogenic hormones, via their receptors in the membrane, regulated the JAK-STAT and m-TOR signal pathways, and affected cell proliferation and apoptosis, leading to changes in milk-protein synthesis.