Receptor component of the CCM signaling pathway which is a crucial regulator of heart and vessel formation and integrity. May act through the stabilization of endothelial cell junctions. Interacts with CCM2 and KRIT1; KRIT1 markedly facilitates interaction with CCM2. Expressed in the endocardium of developing heart. Death at embryonic stages due to heart growth defects. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.