NEDL1, a Novel Ubiquitin-protein Isopeptide Ligase for Dishevelled-1, Targets Mutant Superoxide Dismutase-1

Abstract

Approximately 20% of familial amyotrophic lateral sclerosis (FALS) arises from germ-line mutations in the superoxide dismutase-1 (SOD1) gene. However, the molecular mechanisms underlying the process have been elusive. Here, we show that a neuronal homologous to E6AP carboxyl terminus (HECT)-type ubiquitin-protein isopeptide ligase (NEDL1) physically binds translocon-associated protein-␦ and also binds and ubiquitinates mutant (but not wild-type) SOD1 proportionately to the disease severity caused by that particular mutant. Immunohistochemically, NEDL1 is present in the central region of the Lewy body-like hyaline inclusions in the spinal cord ventral horn motor neurons of both FALS patients and mutant SOD1 transgenic mice. Two-hybrid screening for the physiological targets of NEDL1 has identified Dishevelled-1, one of the key transducers in the Wnt signaling pathway. Mutant SOD1 also interacted with Dishevelled-1 in the presence of NEDL1 and caused its dysfunction. Thus, our results suggest that an adverse interaction among misfolded SOD1, NEDL1, translocon-associated protein-␦, and Dishevelled-1 forms a ubiquitinated protein complex that is included in potentially cytotoxic protein aggregates and that mutually affects their functions, leading to motor neuron death in FALS.Amyotrophic lateral sclerosis (ALS) 1 is a progressive, fatal, neurodegenerative disease that is characterized by selective loss of motor neurons in the spinal cord, brain stem, and motor cortex. The sporadic and familial forms of the disease have similar clinical and pathological features. About 10% of ALS cases are familial, and mutation of superoxide dismutase-1 (SOD1) is found in 20% of familial ALS (FALS) patients (1, 2). Mice that express mutant SOD1 transgenes develop an age-dependent ALS phenotype independent of levels of dismutase activity, suggesting that FALS pathology is because of a toxic gain of function in SOD1 and that the abnormal protein structure of mutant SOD1 is critical in the pathogenesis of motor neuron death (3-6). Recently, proteasome expression and activity have been reported to decrease with age in the spinal cord (7,8). Furthermore, mutant SOD1 turns over more rapidly than wild-type SOD1, and an inhibitor of proteasome action inhibits this turnover and thus selectively increases the steadystate level of mutant SOD1 (8). These results suggest the involvement of the ubiquitin-proteasome function in the cause of FALS. However, the biochemical nature of this gain-of-function mutation in SOD1 and the mechanism by which SOD1 mutations cause the degeneration of motor neurons have remained elusive.We show here the identification of a novel HECT-type ubiquitin-protein isopeptide ligase (E3), NEDL1, which is expressed in neuronal tissues, including the spinal cord, and selectively binds to and ubiquitinates mutant (but not wildtype) SOD1. NEDL1 is physically associated with transloconassociated protein-␦ (TRAP-␦), one of the endoplasmic reticulum (ER) translocon components that has previously been reported to bind mutant SOD...

RNF43 interacts with NEDL1 and regulates p53-mediated transcription

“…Furthermore, it has been reported that NEDL1 interacts with p53 and enhances transcriptional activity of p53 and p53-mediated apoptotic cell death. These findings suggest that NEDL1 regulates cell proliferation and differentiation, stress responses, and DNA-damage responses [15,16].…”

“…A novel HECT-type E3 ubiquitin ligase, NEDL1, has been reported to be expressed in neuronal tissues including the spinal cord and to selectively bind to and ubiquitinate mutant (but not wild-type) SOD1 and Dvl1 [15]. Furthermore, it has been reported that NEDL1 interacts with p53 and enhances transcriptional activity of p53 and p53-mediated apoptotic cell death.…”

WW domain containing E3 ubiquitin protein ligase 1 targets the full-length ErbB4 for ubiquitin-mediated degradation in breast cancer

“…Similar results were observed for HECW1. HECW1 (NEDL1) has been shown to be an E3 ligase for Dvl-1 (Miyazaki et al, 2004) and to cooperate with p53 to induce apoptosis independent of its E3 ligase activity (Li et al, 2008a). Thus, WWP1, Itch and HECW1 additively suppress the ErbB4 expression in some breast cancers.…”

Translocon‐associated protein subunit Trap‐γ/Ssr3 is required for vascular network formation in the mouse placenta

“…This is activated when cells are exposed to hostile conditions such as oxidative stress, viral infection and glucose deprivation (Kunst et al, 1997;Miyazaki et al, 2004;Nagasawa et al, 2007). Inhibition of TRAP complex function by depletion of the Trap-g subunit might influence not only efficient protein translocation but also the UPR pathway.…”

“…Subsequently, the TRAP complex induced by the unfolded protein response (UPR) pathway might discriminate ER-associated degradation substrates from correctly folded substrates, which results in accelerating degradation (Nagasawa et al, 2007). One of the four TRAP subunits, Trap d also binds misfolded dismutase-1 superoxide, but not the wild-type form, with the ubiquitin-protein isopeptide ligase and this forms an ubiquitinated protein complex (Kunst et al, 1997;Miyazaki et al, 2004). Therefore, the TRAP complex might be involved in the UPR pathway to maintain cellular homeostasis when cells are exposed to unfavorable conditions, such as oxidative stress, viral infections, and glucose deprivation.…”