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 (By similarity). May 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 (By similarity). Part of a complex with MAP2K3, MAP3K3 and RAC1. Binds RAC1 directly and independently of its nucleotide-bound state (By similarity). Interacts with HEG1 and KRIT1; KRIT1 greatly facilitates the interaction with HEG1 (By similarity). Interacts with PDCD10. The C-terminal region constitutes an independently folded domain that has structural similarity with the USH1C (harmonin) N-terminus, despite very low sequence similarity. The disease is caused by variants affecting the gene represented in this entry. Belongs to the CCM2 family.