Down-regulates signaling from heterotrimeric G-proteins by increasing the GTPase activity of the alpha subunits, thereby driving them into their inactive GDP-bound form. Down-regulates G-protein-mediated release of inositol phosphates and activation of MAP kinases. Binds EFNB1 and EFNB2 (By similarity). Binds the GNB1-GNG2 heterodimer. Long isoforms are cytoplasmic and associated with the plasma membrane (PubMed:9858594). Short isoforms are nuclear (PubMed:10749886). Phosphorylated by cyclic GMP-dependent protein kinase. ISGylated. Nuclear.