The protein encoded by this gene belongs to the SMAD family which includes proteins similar to Drosophila Mad and C elegans Sma SMAD proteins are signal transducers and transcriptional modulators involved in multiple signaling pathways This protein mediates the transforming growth factor (TGF)-beta signal regulating cell processes like proliferation apoptosis and differentiation It is recruited to TGF-beta receptors via its interaction with the SMAD anchor for receptor activation (SARA) protein Phosphorylation by TGF-beta receptors causes dissociation from SARA and association with SMAD4 which is essential for nuclear translocation In the nucleus it binds to target promoters and forms a transcription repressor complex The protein can also be phosphorylated by activin type 1 receptor kinase mediating activin signaling Alternative splicing results in multiple transcript variants