The ubiquitin ligase Nedd4 has been proposed to regulate a number of signaling pathways, but its physiological role in mammals has not been characterized. Here we present an analysis of Nedd4-null mice to show that loss of Nedd4 results in reduced insulin-like growth factor 1 (IGF-1) and insulin signaling, delayed embryonic development, reduced growth and body weight, and neonatal lethality. In mouse embryonic fibroblasts, mitogenic activity was reduced, the abundance of the adaptor protein Grb10 was increased, and the IGF-1 receptor, which is normally present on the plasma membrane, was mislocalized. However, surface expression of IGF-1 receptor was restored in homozygous mutant mouse embryonic fibroblasts after knockdown of Grb10, and Nedd4 −/− lethality was rescued by maternal inheritance of a disrupted Grb10 allele. Thus, in vivo, Nedd4 appears to positively control IGF-1 and insulin signaling partly through the regulation of Grb10 function.

. Salt-sensitive hypertension and cardiac hypertrophy in mice deficient in the ubiquitin ligase Nedd4-2. Am J Physiol Renal Physiol 295: F462-F470, 2008. First published June 4, 2008 doi:10.1152 doi:10. /ajprenal.90300.2008 has been proposed to play a critical role in regulating epithelial Na ϩ channel (ENaC) activity. Biochemical and overexpression experiments suggest that Nedd4-2 binds to the PY motifs of ENaC subunits via its WW domains, ubiquitinates them, and decreases their expression on the apical membrane. Phosphorylation of Nedd4-2 (for example by Sgk1) may regulate its binding to ENaC, and thus ENaC ubiquitination. These results suggest that the interaction between Nedd4-2 and ENaC may play a crucial role in Na ϩ homeostasis and blood pressure (BP) regulation. To test these predictions in vivo, we generated Nedd4-2 null mice. The knockout mice had higher BP on a normal diet and a further increase in BP when on a high-salt diet. The hypertension was probably mediated by ENaC overactivity because 1) Nedd4-2 null mice had higher expression levels of all three ENaC subunits in kidney, but not of other Na ϩ transporters; 2) the downregulation of ENaC function in colon was impaired; and 3) NaClsensitive hypertension was substantially reduced in the presence of amiloride, a specific inhibitor of ENaC. Nedd4-2 null mice on a chronic high-salt diet showed cardiac hypertrophy and markedly depressed cardiac function. Overall, our results demonstrate that in vivo Nedd4-2 is a critical regulator of ENaC activity and BP. The absence of this gene is sufficient to produce salt-sensitive hypertension. This model provides an opportunity to further investigate mechanisms and consequences of this common disorder. ion channels; kidney; sodium channels HYPERTENSION AFFECTS MORE than 25% of the adult population in most Westernized countries and is a major cause of coronary artery disease and cerebrovascular disease (9, 10). Despite its prevalence, the etiology of more than 90% of hypertension cases is unknown. Numerous studies revealed that interactions between genetic and environmental factors, especially the generous intake of dietary salt, play a critical role in its pathogenesis and a large body of evidence implicates the inappropriate retention of Na(Cl) by the kidney in the pathophysiology of hypertension (25). One of the most important molecular determinants of Na ϩ excretion is the activity of the epithelial Na ϩ channel (ENaC), a highly regulated, threesubunit ion channel complex that is active in the distal nephron (15,29). The activity of ENaC is regulated by many first and second messengers, the most widely studied of which is aldosterone (13, 22). The importance of ENaC in Na ϩ homeostasis and hypertension is underscored by the discovery that patients with Liddle syndrome, an autosomal dominant form of hypertension, have gain-of-function mutations in ENaC (28).The mutations in the ␤-and ␥-ENaC subunits leading to Liddle syndrome have focused attention on the specific regions of the COOH termini whose modificati...

Nedd4 and Itch are E3 ubiquitin ligases that, in vitro, ubiquitinate similar targets and thus are thought to function similarly. T cells lacking Itch show spontaneous activation and T helper type 2 (TH2) polarization. To test whether the loss of Nedd4 affects T cells in the same way, we generated Nedd4+/+ and Nedd4−/−fetal liver chimeras. Nedd4−/−T cells developed normally but proliferated less, produced less interleukin 2, and provided inadequate help to B cells. Nedd4−/−T cells contain increased amounts of Cbl-b protein, and Nedd4 was required for Cbl-b poly-ubquitination induced by CD28 co-stimulation. These data demonstrate that Nedd4 promotes the conversion of naive T cells into activated T cells. We propose that Nedd4 and Itch ubiquitinate distinct target proteins in vivo.

MCS9.7‐lacZ expression in whole mount staining. Bgal activity was detected in transient (Rahimov et al. [2008] Nat Gen http://www.nature.com/ng/journal/v40/n11/full/ng.242.html), and in stable transgenic murine embryos at E11.5. Optical tomography (OPT) movies showing the Bgal activity of stable transgenic embryo in 2‐D. Counterstaining was done using green pseudocolor and red represent Bgal expression. From Fakhouri et al., Developmental Dynamics 241:340–349, 2012.

Limb-girdle muscular dystrophy type 2D (LGMD2D) is caused by autosomal recessive mutations in the alpha-sarcoglycan gene. An R77C substitution is the most prevalent cause of the disease, leading to disruption of the sarcoglycan-sarcospan complex. To model this common mutation, we generated knock-in mice with an H77C substitution in alpha-sarcoglycan. The floxed neomycin (Neo)-cassette retained at the targeted H77C alpha-sarcoglycan locus caused a loss of alpha-sarcoglycan expression, resulting in muscular dystrophy in homozygotes, whereas Cre-mediated deletion of the floxed Neo-cassette led to recovered H77C alpha-sarcoglycan expression. Contrary to expectations, mice homozygous for the H77C-encoding allele expressed both this mutant alpha-sarcoglycan and the other components of the sarcoglycan-sarcospan complex in striated muscle, and did not develop muscular dystrophy. Accordingly, conditional rescued expression of the H77C protein in striated muscle of the alpha-sarcoglycan-deficient mice prevented the disease. Adding to the case that the behavior of mutant alpha-sarcoglycan is different between humans and mice, mutant human R77C alpha-sarcoglycan restored the expression of the sarcoglycan-sarcospan complex when introduced by adenoviral vector into the skeletal muscle of previously created alpha-sarcoglycan null mice. These findings indicate that the alpha-sarcoglycan with the most frequent missense mutation in LGMD2D is correctly processed, is transported to the sarcolemma, and is fully functional in mouse muscle. Our study presents an unexpected difference in the behavior of a missense-mutated protein in mice versus human patients, and emphasizes the need to understand species-specific protein quality control systems.