ELL Protein-associated Factor 2 (EAF2) Inhibits Transforming Growth Factor β Signaling through a Direct Interaction with Smad3

A series of in vitro and in vivo studies has shown that EAF2 can affect multiple signaling pathways involved in cellular processes. However, the molecular mechanisms underlying its effects have remained elusive. Here we report the discovery of a new functional link between EAF2 and TGF-beta signaling. Promoter reporter assays indicated that EAF2 suppresses Smad3 transcriptional activity, resulting in inhibition of TGF-beta signaling. Coimmunoprecipitation assays showed that EAF2 specifically interacts with Smad3 in vitro and in vivo but not with other Smad proteins. In addition, we observed that EAF2 binding does not alter Smad3 phosphorylation but causes Smad3 cytoplasmic retention, competes with Smad4 for binding to Smad3, and prevents p300-Smad3 complex formation. Furthermore, we demonstrated that EAF2 suppresses both TGF-beta -induced G(1) cell cycle arrest and TGF-beta -induced cell migration. This study identifies and characterizes a novel repressor of TGF-beta signaling.