Parathyroid hormone-related protein: A developmental regulatory molecule necessary for mammary gland development

Parathyroid hormone-related protein (PTHrP) was originally identified as th e tumor factor responsible for a clinical syndrome known as humoral hyperca lcemia of malignancy. It is now appreciated that PTHrP(3) is a developmenta l regulatory molecule expressed during the formation of a wide variety of o rgans. Recently, our laboratory has demonstrated that PTHrP is necessary fo r mammary gland development. Our studies have suggested that this molecule participates in the regulation of epithelial-mesenchymal interactions durin g embryonic mammary development and perhaps also during adolescent ductal m orphogenesis. In addition, it has been suggested that PTHrP plays a critica l role in the establishment of bone metastases in breast cancer. In this ar ticle, we will discuss the current knowledge of the mechanisms underlying P THrPs actions during normal mammary development and in breast cancer.