[Hormone and cytokine receptors in bone cells]

Growth, differentiation and functions of osteoblastic and osteoclastic cells are maintained by coordinate actions of bone-seeking hormones and cytokines. The actions of these regulatory factors develop via the interaction with their specific receptors. Many of the receptors for these factors such as parathyroid hormone, calcitonin, vitamin D, transforming growth factor-beta, insulin-like growth factors, and other cytokines have been cloned, and the intracellular signal transduction systems are being clarified. In addition, growing body of evidence indicates that the interactions between integrins and extracellular matrix proteins also play an important role in the regulation of growth and differentiation of both osteoblastic and osteoclastic cells. Current understanding about the receptors for these hormones, cytokines and matrix proteins are summarized, and the roles of these receptors in the regulation of bone metabolism are discussed.