Mammalian dwarfins are phosphorylated in response to transforming growth factor beta and are implicated in control of cell growth.

The dwarfin protein family has been genetically implicated in transforming growth factor beta (TGF-beta)-like signaling pathways in Drosophila and Caenorhabditis elegans. To investigate the role of these proteins in mammalian signaling pathways, we have isolated and studied two murine dwarfins, dwarfin-A and dwarfin-C. Using antibodies against dwarfin-A and dwarfin-C, we show that these two dwarfins and an immunogenically related protein, presumably also a dwarfin, are phosphorylated in a time- and dose-dependent manner in response to TGF-beta. Bone morphogenetic protein 2, a TGF-beta superfamily ligand, induces phosphorylation of only the related dwarfin protein. Thus, TGF-beta superfamily members may use overlapping yet distinct dwarfins to mediate their intracellular signals. Furthermore, transient overexpression of either dwarfin-A or dwarfin-C causes growth arrest, implicating the dwarfins in growth regulation. This work provides strong biochemical and preliminary functional evidence that dwarfin-A and dwarfin-C represent prototypic members of a family of mammalian proteins that may serve as mediators of signaling pathways for TGF-beta superfamily members.