Cooperation of nuclear transcription factors regulated by steroid and peptide hormones.

Abstract

Cycles of growth, differentiation and apoptosis characterise the fate of mammary epithelial cells throughout the life of the individual. These cellular processes are under the control of steroid and peptide hormones (Topper and Freeman 1980). Growth and limited differentiation occurs during puberty and requires the action of oestrogen, prolactin and members of the transforming growth factor (TGF)-β family. The epithelial cells form ducts and terminal end buds, which grow and extend to the limits of the fat pad. Under the influence of the hormones secreted during pregnancy (oestrogen, prolactin and progesterone) the cells undergo a massive increase in numbers and further differentiate to form the functional lactating gland. Prolactin and its receptor are particularly important for mammary development. Prolactin plays a role in the morphological and biochemical differentiation of the epithelial cells during pregnancy and regulates milk protein synthesis during lactation. It enhances the growth of breast cancer cell lines and has also been found to be expressed in a paracrine fashion in human tumours.