Expression of milk protein genes is induced directly by exogenous STAT5 without prolactin-mediated signal transduction in transgenic mice

STAT5 is a member of the family of STAT (signal transducer for activating t ranscription), which was isolated from nuclear extracts of the lactating gl and of sheep. It was reported that, in vitro, STAT5 could be activated dire ctly by prolactin (PRL) without PRL-mediated signal transduction. The prese nt study was conducted to investigate above the possibility in vivo, using the transgenic mice overexpressing ovine STAT5 (oSTAT5) under the control o f MMTV promoter. Three transgenic mouse lines that expressed the exogenousl y introduced oSTAT5 in their mammary glands were established. The expressio n levels of exogenous oSTAT5 were higher than those of endogenous STAT in t he mammary glands of all of the three transgenic lines. Although the expres sion levels of endogenous milk protein genes, WAP, and beta-casein genes, w ere not correlated with oSTAT5 expression, the expression levels of WAP and p-casein were induced by exogenous oSTAT5 in the transgenic mice. The pres ent study demonstrated, at very least,that STAT5 expression can directly ac tivate the expression of milk protein genes, and particularly the WAP gene without PRL-mediated signal transduction. (C) 1999 Wiley-Liss, Inc.