Interaction and functional cooperation of PEBP2/CBF with Smads. Synergistic induction of the immunoglobulin germline Cα promoter

Smads are signal transducers for members of the transforming growth factor-β (TGF-β) superfamily. Upon ligand stimulation, receptor-regulated Smads (R-Smads) are phosphorylated by serine/threonine kinase receptors, form complexes with common-partner Smad, and translocate into the nucleus, where they regulate the transcription of target genes together with other transcription factors. Polyomavirus enhancer binding protein 2/core binding factor (PEBP2/CBF) is a transcription factor complex composed of α and β subunits. The α subunits of PEBP2/CBF, which contain the highly conserved Runt domain, play essential roles in hematopoiesis and osteogenesis. Here we show that three mammalian α subunits of PEBP2/CBF form complexes with R- Smads that act in TGF-β/activin pathways as well as those acting in bone morphogenetic protein (BMP) pathways. Among them, PEBP2αC/CBFA3/AML2 forms a complex with Smad3 and stimulates transcription of the germline Ig Cα promoter in a cooperative manner, for which binding of both factors to their specific binding sites is essential. PEBP2 may thus be a nuclear target of TGF-β/BMP signaling.