Breast Tumorigenesis: Interaction of Two Signaling Pathways--TGF--Beta VersusEstrogen Receptor

摘要

The Smad protein family has been genetically implicated in transforming growthfactor 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 Smads, Smad1 and Smad5. Using antibodies against Smad1 and Smad5, we show that these two Smads and an immunogenically related protein, presumably also a Smad, 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 Smad protein. Thus, TGF-BETA superfamily members may use overlapping yet distinct Smads to mediate their intracellular signals. Furthermore, transient overexpression of either Smad1 or Smad5 causes growth arrest, implicating the Smads in growth regulation. This work provides strong biochemical and preliminary functional evidence that Smad1 and Smad5 represent prototypic members of a family of mammalian proteins that may serve as mediators of signaling pathways for TGF-BETA superfamily members.