DEAD-box helicase 6 (DDX6) is a new negative regulator for milk synthesis and proliferation of bovine mammary epithelial cells.

Milk synthesis of bovine mammary gland is a complex biological process that is regulated by hormones and nutrients, but the mechanism of these regulations still needs further research. DEAD-box helicase 6 (DDX6) is an important member of the RNA helicase family, involved in the regulation of mRNA storage and translation in different systems, but its physiological role and mechanism are largely unclear. In this study, we describe DDX6 as a potentially novel negative regulator for milk synthesis and proliferation of bovine mammary epithelial cells (BMECs). Treatment of BMECs with amino acids (methionine or leucine) or hormones (estrogen or prolactin) decreased the expression of DDX6. DDX6 expression was lower in mammary tissues of lactation period than in mammary tissues of puberty and dry period. Notably, overexpressing DDX6 in BMECs significantly decreased milk synthesis, cell proliferation, and protein levels of p-mTOR, SREBP-1c, and cyclin D1, while inhibiting DDX6 had the opposite effect. Taken together, these results reveal that DDX6 is a new negative regulator to control milk synthesis and proliferation of BMECs.