Members of the transforming growth factor-beta (TGF-Beta) superfamily play critical roles in controlling cell growth and differentiation. Effects of TGF-Beta family ligands are mediated by Smad proteins. The Smad nuclear interacting protein (SNIP1) contains a forkhead-associated (FHA) domain and acts as a nuclear inhibitor of CBP/p300. SNIP1 potently inhibits the activity of NF-kappa B, which binds the C/H1 domain of CBP/p300, by competing for the binding site. SNIP1 is also thought to induce expression of Cyclin D1 to promote cellular proliferation. SNIP1 is ubiquitously expressed with high expression in heart and skeletal muscle.