Control of TGF-beta receptor expression in bone.

Bone growth and remodeling are controlled by local and systemic growth factors. The first local bone growth factor purified to homogeneity was transforming growth factor type beta (TGF-beta). On skeletal cells, TGF-beta has multiple effects mediated through at least three distinct cell surface receptors. More recent evidence demonstrated hormone and growth factor dependent alterations in TGF-beta receptor expression on osteoblasts in vitro. Indeed, certain biological responses appear to depend on the proportional expression of the type I TGF-beta receptor. Studies defining the type I TGF-beta receptor gene promoter then revealed that it contained several binding sequences for a nuclear factor that varies in parallel with expression of the osteoblast phenotype. New observations linking these events appear to enhance our understanding of this pivotal growth factor during osteogenesis and systemic bone disease.