Requirement of type III TGF-beta receptor for endocardial cell transformation in the heart

Transforming growth factor-beta (TGF-beta) signaling is mediated by a compl ex of type I (TBRI) and type II (TBRII) receptors. The type III receptor (T BRIII) Lacks a recognizable signaling domain and has no clearly defined rol e in TGF-beta signaling. Cardiac endothelial cells that undergo epithelial- mesenchymal transformation express TBRIII, and here TBRIII-specific antiser a were found to inhibit mesenchyme formation and migration in atrioventricu lar cushion explants. Misexpression of TBRIII in nontransforming ventricula r endothelial cells conferred transformation in response to TGF-beta 2. The se results support a model where TBRIII localizes transformation in the hea rt and plays an essential, nonredundant role in TGF-beta signaling.