Smad1 belongs to the Smad family, which is a protein family of gene products similar to Drosophila genes, such as "Mother Against Peeling" (MAD) and the Caenorhabditis elegans gene SMA. One of the most important proteins regulating TGF - β ligand activity is the SMAD family of proteins. SMAD1 is one of the receptor activated Smads. It is also a signal transducer for BMP signaling and binds to several proteins involved in the ubiquitin proteasome system (UPS). It mediates the signaling of bone morphogenetic protein (BMP), which is involved in a range of biological activities including cell growth, apoptosis, morphogenesis, development, and immune response. In response to BMP ligands, Smad1 can be phosphorylated and activated by BMP receptor kinase. Its phosphorylated form forms a complex with Smad4, which is important for its function in transcriptional regulation.
