Activin Receptors and Cellular Signaling by the Receptor Serine Kinase Family

AN EMERGING theme in cell signaling research is the multifunctional nature of many growth factors and cytokines. Proteins purified based on distinct activities are often found to have identical structures; furthermore, different members of large growth factor families have similar, although subtly distinct, effects on diverse sets of cells. Such related factors often have related receptors, activation of which turns on common cellular signaling pathways. Understanding both the specificity and the overlap of growth factor signaling will involve elucidation of the unique and shared features of those receptors and their intracellular targets. The activins are growth and differentiation factors that are produced by, and exert effects on, a broad range of cells and tissues (reviewed in Refs. 1–5). With the cloning of several activin receptors, as well as the development of biological models for assessing activin and activin receptor function, substantial progress has been made in understanding the mechanism of action of these potent molecules.