Previous studies have implicated that purine-rich element binding protein B (PURB) is a key regulator of gene transcription and cell physiology. Whether PURB plays a regulatory role in milk synthesis in bovine mammary epithelial cells (BMECs) is not known. We observed that Met and Leu increased PURB expression and nuclear localization. Overexpression of PURB led to increased milk protein and fat synthesis as well as mTOR and SREBP-1c expression whereas PURB knockdown had the opposite effects. The PI3K inhibitor wortmannin totally abolished the stimulation of Met and Leu on PURB expression, and we further confirmed that PURB was required for Met and Leu to stimulate mTOR phosphorylation and SREBP-1c expression. We also demonstrated that PURB binds to the promoters of mTOR and SREBP-1c, and these bindings were increased by Met and Leu stimulation. In summary, our data reveal that PURB is required for amino acids to stimulate mTOR and SREBP-1c gene expression, and PURB is a positive regulator of amino acid-induced PI3K-regulated milk protein and fat synthesis in BMECs.
Keywords: SREBP-1c; amino acid; mTOR; mammary epithelial cell (MEC); purine-rich element binding protein B (PURB).
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