Phospholipid scramblase 1 (PLSCR1) is a novel substrate of NEDD4-2 (NEDD4L) mediated ubiquitination

NEDD4-2 (human NEDD4L), a ubiquitin ligase, plays an essential role in regulating a number of membrane proteins, including ion channels and transporters. In the kidney, NEDD4-2 deletion results in a progressive loss of tubular cells and salt-sensitive chronic kidney disease. While deregulation of sodium homeostasis due to increased levels and function of the epithelial sodium channel (ENaC) and sodium chloride transporter (NCC), both NEDD4-2 substrates, plays a critical role in kidney damage in this model, other ubiquitination targets may also be important. Here, we employed an affinity purification mass spectrometry approach to identify additional interactors of NEDD4-2 in kidney cells and discovered phospholipid scramblase 1 (PLSCR1) as a new NEDD4-2 substrate. We show that PLSCR1 is a direct interactor and substrate of NEDD4-2. As a result, NEDD4-2 deficiency both in cultured cells and in mouse kidney resulted in increased levels of PLSCR1 protein. We observed increased phosphatidyl serine exposure in NEDD4-2 knockout cells in response to both calcium and apoptotic stimuli and this phenotype was reversed when NEDD4-2 expression was restored. Consistently, apoptotic cells lacking NEDD4-2 showed a higher rate of macrophage clearance. Together, these results indicate that PLSCR1 is a novel substrate of NEDD4-2-mediated ubiquitination and that NEDD4-2 regulates PLSCR1 protein stability and function.