Prolactin signal transduction mechanisms in the mammary gland: the role of the Jak/Stat pathway.

Prolactin signal transduction in mammary epithelial cells is mediated by a novel, direct signalling system that links the activation of the prolactin receptor at the cell surface to changes in gene transcription in the nucleus. This recently identified pathway is a variant of the Jak/Stat (for Janus kinase/signal transducer and activator of transcription) pathway used by many other growth factors and cytokines. Current data suggest that the key intracellular components of the prolactin signalling pathway are the kinase Jak2 and the transcription factor Stat5. This discovery has exciting implications for the interaction between prolactin and other extracellular signals in both the mammary gland and other tissues. Here we review work that began with attempts to understand the regulation of milk protein gene expression and ultimately demonstrated the central role of the Jak/Stat pathway in prolactin signal transduction in the mammary gland.