Stress activation of mammary epithelial cell xanthine oxidoreductase is mediated by p38 MAPK and CCAAT/enhancer-binding protein-beta.

Xanthine oxidoreductase (XOR) catalyzes the formation of uric acid from xanthine and hypoxanthine and is recognized as a source of reactive oxygen and nitrogen species. Unexpectedly, XOR was found to play an essential role in milk secretion in the differentiating mammary gland, where it is an integral component of the milk fat globule. XOR gene expression in both mammary glands and differentiating mammary epithelial cells in culture is regulated by the lactogenic hormones prolactin and cortisol.