Deubiquitinating enzymes (DUBs) are crucially involved in controlling signal transductions, and reverse ubiquitination by removing the ubiquitin from protein substrates. The Hippo signaling has an important role in tissue growth, cell proliferation, differentiation, and apoptosis. Since disruption of the Hippo signaling is associated with a number of diseases, it is imperative to investigate the molecular mechanism of the Hippo signaling.
DUB screening was performed using the kidney of the mouse unilateral ureteric obstruction (UUO) model to identify the cellular mechanism of the DUB-regulated Hippo signaling. In addition, kidney cells were used to confirm cell proliferation and protein levels in the Hippo signaling pathway. Densitometric analysis was conducted to compare the expression level of proteins using Image J.
We found that YOD1, also known as OTU1, is downregulated in the mouse UUO model. We also demonstrated that YOD1 binds to and deubiquitinates neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4). Furthermore, we observed that YOD1 suppresses NEDD4-induced cell proliferation.
YOD1 regulates the Hippo signaling pathway through NEDD4, and the K63-linked polyubiquitin chain of NEDD4 plays an important role. Also, our results indicate that YOD1 plays an important role in kidney diseases.
© Copyright by the Author(s). Published by Cell Physiol Biochem Press.

Although neural progenitor proliferation along the ventricular zone is regulated by β-catenin through Wnt signaling, the cytoskeletal mechanisms that regulate expression and localization of these proteins are not well understood. Our prior studies have shown that loss of the actin-binding Filamin A (FlnA) and actin-nucleating protein Formin 2 (Fmn2) impairs endocytosis of low-density-lipoprotein-receptor-related protein 6 (Lrp6), thereby disrupting β-catenin activation, resulting in decreased brain size. Here, we report that activated RhoA-GTPase disengages Fmn2 N- to C-terminal binding to promote Fmn2 activation and redistribution into lysosomal vesicles. Fmn2 colocalizes with β-catenin in lysosomes and promotes its degradation. Further, Fmn2 binds the E3 ligase Smurf2, enhances Smurf2-dependent ubiquitination, and degradation of Dishevelled-2 (Dvl2), thereby initiates β-catenin degradation. Finally, Fmn2 overexpression disrupts neuroepithelial integrity, neuronal migration, and proliferation-phenotypes in E13 mouse embryos, as seen with loss of Fmn2+FlnA function. Conversely, co-expression of Dvl2 with Fmn2 rescues the proliferation defect due to Fmn2 overexpression in mouse embryos. These findings suggest that there is a homeostatic feedback mechanism in the cytoskeletal-dependent regulation of neural proliferation within the cerebral cortex. Upstream, Fmn2 promotes proliferation by stabilizing the Lrp6 receptor, leading to β-catenin activation. Downstream, RhoA-activated Fmn2 promotes lysosomal degradation of Dvl2, leading to β-catenin degradation.
© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

The liver is the only organ in mammals that fully regenerates even after major injury. To identify orchestrators of this regenerative response, we performed quantitative large-scale proteomics analysis of cytoplasmic and nuclear fractions from normal versus regenerating mouse liver. Proteins of the ubiquitin-proteasome pathway were rapidly upregulated after two-third hepatectomy, with the ubiquitin ligase Nedd4-1 being a top hit. In vivo knockdown of Nedd4-1 in hepatocytes through nanoparticle-mediated delivery of small interfering RNA caused severe liver damage and inhibition of cell proliferation after hepatectomy, resulting in liver failure. Mechanistically, we demonstrate that Nedd4-1 is required for efficient internalization of major growth factor receptors involved in liver regeneration and their downstream mitogenic signaling. These results highlight the power of large-scale proteomics to identify key players in liver regeneration and the importance of posttranslational regulation of growth factor signaling in this process. Finally, they identify an essential function of Nedd4-1 in tissue repair.
Copyright © 2017 Elsevier Inc. All rights reserved.

The biological function of the PTEN tumor suppressor is mainly attributed to its lipid phosphatase activity. This study demonstrates that mammalian PTEN is a protein tyrosine phosphatase that selectively dephosphorylates insulin receptor substrate-1 (IRS1), a mediator of insulin and IGF signals. IGF signaling was defective in cells lacking NEDD4, a PTEN ubiquitin ligase, whereas AKT activation triggered by EGF or serum was unimpaired. Defective IGF signaling caused by NEDD4 deletion, including phosphorylation of IRS1 and AKT, was rescued by PTEN ablation. We demonstrate the nature of PTEN as an IRS1 phosphatase by direct biochemical analysis and cellular reconstitution, showing that NEDD4 supports insulin-mediated glucose metabolism and is required for the proliferation of IGF1 receptor-dependent but not EGF receptor-dependent tumor cells. Thus, PTEN is a protein phosphatase for IRS1, and its antagonism by NEDD4 promotes signaling by IGF and insulin.

Skeletal muscle atrophy is a consequence of muscle inactivity resulting from denervation, unloading and immobility. It accompanies many chronic disease states and also occurs as a pathophysiologic consequence of normal aging. In all these conditions, ubiquitin-dependent proteolysis is a key regulator of the loss of muscle mass, and ubiquitin ligases confer specificity to this process by interacting with, and linking ubiquitin moieties to target substrates through protein:protein interaction domains. Our previous work suggested that the ubiquitin-protein ligase Nedd4-1 is a potential mediator of skeletal muscle atrophy associated with inactivity (denervation, unloading and immobility). Here we generated a novel tool, the Nedd4-1 skeletal muscle-specific knockout mouse (myo(Cre);Nedd4-1(flox/flox)) and subjected it to a well validated model of denervation induced skeletal muscle atrophy. The absence of Nedd4-1 resulted in increased weights and cross-sectional area of type II fast twitch fibres of denervated gastrocnemius muscle compared with wild type littermates controls, at seven and fourteen days following tibial nerve transection. These effects are not mediated by the Nedd4-1 substrates MTMR4, FGFR1 and Notch-1. These results demonstrate that Nedd4-1 plays an important role in mediating denervation-induced skeletal muscle atrophy in vivo.