Nuclear phosphoprotein which forms a tight but non-covalently linked complex with the JUN/AP-1 transcription factor. On TGF-beta activation, forms a multimeric SMAD3/SMAD4/JUN/FOS complex, at the AP1/SMAD-binding site to regulate TGF-beta-mediated signaling. Has a critical function in regulating the development of cells destined to form and maintain the skeleton. It is thought to have an important role in signal transduction, cell proliferation and differentiation.
Heterodimer; with JUN (By similarity). Component of the SMAD3/SMAD4/JUN/FOS complex required for syngernistic TGF-beta-mediated transcription at the AP1 promoter site. Interacts with SMAD3; the interaction is weak even on TGF-beta activation. Interacts with MAFB. Interacts with DSIPI; this interaction inhibits the binding of active AP1 to its target DNA. Interacts with MAFB.