Nedd4-1 and beta-arrestin-1 are key regulators of Na+/H+ exchanger 1 ubiquitylation, endocytosis, and function

The ubiquitously expressed mammalian Na(+)/H(+) exchanger 1 (NHE1) controls cell volume and pH but is also critically involved in complex biological processes like cell adhesion, cell migration, cell proliferation, and mechanosensation. Pathways controlling NHE1 turnover at the plasma membrane, however, are currently unclear. Here, we demonstrate that NHE1 undergoes ubiquitylation at the plasma membrane by a process that is unprecedented for a mammalian ion transport protein. This process requires the adapter protein β-arrestin-1 that interacts with both the E3 ubiquitin ligase Nedd4-1 and the NHE1 C terminus. Truncation of NHE1 C terminus to amino acid 550 abolishes binding to β-arrestin-1 and NHE1 ubiquitylation. Overexpression of β-arrestin-1 or of wild type but not ligase-dead Nedd4-1 increases NHE1 ubiquitylation. siRNA-mediated knock-down of Nedd4-1 or β-arrestin-1 reduces NHE1 ubiquitylation and endocytosis leading to increased NHE1 surface levels. Fibroblasts derived from β-arrestin-1 and Nedd4-1 knock-out mice show loss of NHE1 ubiquitylation, increased plasmalemmal NHE1 levels and greatly enhanced NHE1 transport compared with wild-type fibroblasts. These findings reveal Nedd4-1 and β-arrestin-1 as key regulators of NHE1 ubiquitylation, endocytosis, and function. Our data suggest a broader role for β-arrestins in the regulation of membrane ion transport proteins than currently known.