Activates HECT domain-containing E3 ubiquitin-protein ligases, including ITCH, NEDD4, NEDD4L, SMURF2, WWP1 and WWP2, and consequently modulates the stability of their targets. As a result, may control many cellular processes. Recruits ITCH, NEDD4 and SMURF2 to endosomal membranes. Negatively regulates KCNH2 potassium channel activity by decreasing its cell-surface expression and interfering with channel maturation through recruitment of NEDD4L to the Golgi apparatus and multivesicular body where it mediates KCNH2 degradation (PubMed:26363003). May modulate EGFR signaling. Together with NDFIP1, limits the cytokine signaling and expansion of effector Th2 T-cells by promoting degradation of JAK1, probably by ITCH- and NEDD4L-mediated ubiquitination (By similarity). Forms heterodimers with NDFIP1. Interacts with HECT domain-containing E3 ubiquitin-protein ligases, including NEDD4 (PubMed:12796489). Interacts with NEDD4L (PubMed:26363003). Interacts with PTEN. When phosphorylated at Tyr-167, interacts with SRC and LYN SH2 domain. May thus act as a scaffold that recruits SRC to NDFIP1, enhancing NDFIP1 phosphorylation. Interacts with SLC11A2/DMT1 (PubMed:18776082). May interact with phosphorylated EGFR. Interacts with KCNH2 (PubMed:26363003). Expressed in brain, lung, heart, skeletal muscle, kidney, liver and placenta. By T-cell activation. The PPxY motifs are required for E3 ubiquitin-protein ligase activation and for ubiquitination. Ubiquitinated by NEDD4 and ITCH. Also ubiquitinated by NEDD4L. Ubiquitination by NEDD4 or NEDD4L does not affect turnover (By similarity). Undergoes transient tyrosine-phosphorylation following EGF stimulation, most probably catalyzed by SRC. Phosphorylation on Tyr-151, Tyr-171 and Tyr-177 are dependent on the phosphorylation on Tyr-167. Also phosphorylated by LYN and FYN.