Acts as an inhibitor of the small GTPase RHOA and plays several roles in the regulation of myoblast and hair cell differentiation, lymphocyte T proliferation and neutrophil polarization. Plays a role in fetal mononuclear myoblast differentiation by promoting filopodia and myotube formation. Maintains naive T lymphocytes in a quiescent state and prevents chemokine-induced T lymphocyte responses, such as cell adhesion, polarization and migration. Involved also in the regulation of neutrophil polarization, chemotaxis and adhesion. Required for normal development of inner and outer hair cell stereocilia within the cochlea of the inner ear. Plays a role for maintaining the structural organization of the basal domain of stereocilia. Involved in mechanosensory hair cell function. Required for normal hearing. Homooligomer; homooligomerization is regulated by RHOC and leads to the formation of concatemers through the association of N- and C-termini. Interacts with NCAM. Belongs to the RIPOR family.