While autocrine stimulation of cells by Activin A and/or its family member transforming
growth factor β (TGF-β) is a phenomenon observed in a variety of cell types, little is known of
putative intracellular signaling loops of these cytokines. Intracellular actions of several
peptide hormones, growth factors, as well as of extracellular signaling enzymes and DNA-
binding proteins, either within target cells or within their cells of synthesis have been shown.
Although these intracrine moieties are structurally diverse, they share certain characteristics …