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. May also function as a scaffold protein for MAP2K3-MAP3K3 signaling. Seems to play a major role in the modulation of MAP3K3-dependent p38 activation induced by hyperosmotic shock. Part of a complex with MAP2K3, MAP3K3 and RAC1. Binds RAC1 directly and independently of its nucleotide-bound state. Interacts with PDCD10 (By similarity). Interacts with HEG1 and KRIT1; KRIT1 greatly facilitates the interaction with HEG1. Treatment with sorbitol caused relocalization to ruffle-like structures. Highly expressed in heart, lower expression in kidney, lung and liver (at protein level). Expressed primarily in the developing neural tube at 10.5 dpc. The C-terminal region constitutes an independently folded domain that has structural similarity with the USH1C (harmonin) N-terminus, despite very low sequence similarity. Belongs to the CCM2 family.