Ubiquitination is a critical protein modification system in the cell. Misregulation in protein ubiquitination can lead to many pathophysiological conditions. The process of ubiquitination involves a series of enzymes, including the ubiquitin-protein ligases (E3s), which are primary determinants of specificity for ubiquitination. Nedd4-2, a HECT type of ubiquitin ligase, is responsible for ubiquitinating a number of ion channels and transporters to aid in their internalization, and thus inhibiting their function. Nedd4-2 is known to regulate the epithelial Na+ channel (ENaC), a major substrate responsible for Na+ balance, blood volume and blood pressure maintenance. It’s been shown that in Liddle’s syndrome mutations in ENaC subunits abolish its ubiquitination via Nedd4-2, leading to an increase of ENaC on the cell surface, elevated ENaC activity, and hypertension. Prior work in our laboratory with Nedd4-2 KO mouse model showed increased ENaC activity and excessive lung fluid clearance in newborn animals, resulting in perinatal lethality. The Nedd4-2 KO animals that survive birth die by 3 weeks of age due, primarily to, severe lung inflammation. Recently it was suggested that cystic fibrosis transmembrane conductance regulator (CFTR), an epithelial chloride ion channel, interacts with Nedd4-2. Nedd4-2-deficient animals show severe lung inflammation and some characteristics of Cystic Fibrosis, we propose that Nedd4-2 might also regulate CFTR, in addition to ENaC. Indeed, preliminary data suggest that both CFTR and ENaC expression is elevated in the lungs of Nedd4-2 knockout mice. This model will be further used to investigate links between ENaC and CFTR and how this may associate with complex channelopathies. Our recent data indicate that loss of Nedd4-2 results in polycystic kidney. Part of my research is to characterise this phenotype and determine the role of Nedd4-2 in this pathological condition.

1.Brill, S. R. et al. (1996). "Immunolocalization of ion transport proteins in human autosomal dominant polycystic kidney epithelial cells."  PNAS 93(19): 10206.2.Boase, NA et al (2011)  Respiratory distress and perinatal lethality in Nedd4-2 deficient mice. Nature Commun. 2:287.3.Caohuy, H et al  (2009) Rescue of DF508-CFTR by the SGK1/NEDD4-2 signalling pathway. J BiolChem 284(37):25241-252534.       Masporo, E et al     (2013)  Structure of a ubiquitin-loaded HECT ligase reveals the molecular basis for catalytic priming.Nat Struct Mol Biol.696–70.