Proteotoxic stresses stimulate dissociation of UBL4A from the tail-anchored protein recognition complex.

Inclusion body formation is associated with cytotoxicity in a number of neurodegenerative diseases. However, the molecular basis of the toxicity caused by the accumulation of aggregation-prone proteins remains controversial. In this study, we found that disease-associated inclusions induced by elongated polyglutamine chains disrupt the complex formation of BAG6 with UBL4A, a mammalian homologue of yeast Get5. UBL4A also dissociated from BAG6 in response to proteotoxic stresses such as proteasomal inhibition and mitochondrial depolarization. These findings imply that the cytotoxicity of pathological protein aggregates might be attributed in part to disruption of the BAG6-UBL4A complex that is required for the biogenesis of tail-anchored proteins.

Water-Soluble Ionic Metal-Organic Polyhedra as a Versatile Platform for Enzyme Bio-immobilization.

Metal-organic polyhedra (MOPs) can act as elementary structural units for the design of modular porous materials; however, their association with biological systems remains greatly restricted by their typically low stabilities and solubilities in water. Herein, we describe the preparation of novel MOPs bearing either anionic or cationic groups and exhibiting a high affinity for proteins. Simple mixing of the protein bovine serum albumin (BSA) and ionic MOP aqueous solutions resulted in the spontaneous formation of MOP-protein assemblies, in a colloidal state or as solid precipitates depending on the initial mixing ratio. The versatility of the method was further illustrated using two enzymes, catalase and cytochrome c, with different sizes and isoelectric points (pI's) below and above 7. This mode of assembly led to the high retention of catalytic activity and enabled recyclability. Furthermore, the co-immobilization of cytochrome c with highly charged MOPs resulted in a substantial 44-fold increase of its catalytic activity.

Long-term results of total hip arthroplasty using Charnley Elite-Plus stem and the effect of stem geometry on radiographic distal femoral cortical hypertrophy.

BACKGROUND: The Elite-Plus stem has two shape variations: roundback and flanged. The correlation between the radiographic results and stem geometry has not been previously investigated. The objective of this study was to evaluate the long-term primary total hip arthroplasty results using Elite-Plus stems, and the effect of stem geometry on radiographic distal femoral cortical hypertrophy. METHODS: We retrospectively evaluated, radiographically, 156 patients (173 hips) who underwent total hip arthroplasty between April 1998 and November 2005, and were followed up for >5 years, postoperatively. Radiographic factors affecting distal femoral cortical hypertrophy were analysed using multivariable logistic regression analysis. RESULTS: The mean follow-up period was 11.6 (5-17.8) years. During follow-up, femoral components were revised in 7 hips; one was revised due to aseptic loosening. Another femoral component was loosened and waiting for revision. The 10- and 15-year survival rates for aseptic stem loosening were 100% and 98.1% (95% CI: 92.5-99.5), respectively. Distal femoral cortical hypertrophy occurred in 23 hips (14.8%), and more often with roundback type (34.1%) than with flanged type (7.2%). Distal femoral cortical hypertrophy was observed in 34.8% of hips with valgus alignment, 11.3% with neutral alignment, and 12.5% with varus alignment. Multivariable logistic regression analysis showed that roundback stem shape and valgus stem alignment significantly affected the occurrence of distal femoral cortical hypertrophy. CONCLUSIONS: The Elite-Plus stem has excellent long-term clinical and radiographic results in Japanese patients. The occurrence of distal femoral cortical hypertrophy significantly depends on the shape and alignment of Elite-Plus stems.

Structure of a BAG6 (Bcl-2-associated athanogene 6)-Ubl4a (ubiquitin-like protein 4a) complex reveals a novel binding interface that functions in tail-anchored protein biogenesis.

BAG6 is an essential protein that functions in two distinct biological pathways, ubiquitin-mediated protein degradation of defective polypeptides and tail-anchored (TA) transmembrane protein biogenesis in mammals, although its structural and functional properties remain unknown. We solved a crystal structure of the C-terminal heterodimerization domains of BAG6 and Ubl4a and characterized their interaction biochemically. Unexpectedly, the specificity and structure of the C terminus of BAG6, which was previously classified as a BAG domain, were completely distinct from those of the canonical BAG domain. Furthermore, the tight association of BAG6 and Ubl4a resulted in modulation of Ubl4a protein stability in cells. Therefore, we propose to designate the Ubl4a-binding region of BAG6 as the novel BAG-similar (BAGS) domain. The structure of Ubl4a, which interacts with BAG6, is similar to the yeast homologue Get5, which forms a homodimer. These observations indicate that the BAGS domain of BAG6 promotes the TA protein biogenesis pathway in mammals by the interaction with Ubl4a.

Enhancing Performances of Enzyme/Metal-Organic Polyhedra Composites by Mixed-Protein Co-Immobilization.

Protein immobilization using water-soluble ionic metal-organic polyhedra (MOPs) acting as porous spacers has recently been demonstrated as a potent strategy for the preparation of biocatalysts. In this article, we describe a mixed-protein approach to achieve biocomposites with adjustable enzyme contents and excellent immobilization efficiencies, in a systematic and well-controlled manner. Self-assembly of either cationic or anionic MOPs with bovine serum albumin or egg white lysozyme combined with enzymes (alkaline phosphatase, laccase or cytochrome c) led to solid-state catalysts with a high retention of enzyme activity. Furthermore, for all these systems, the dilution of enzymes within the solid-state composite led to noticeably improved catalytic performances, with both higher specific activity and affinity for substrate.

Efficient water-based purification of metal-organic polyhedra by centrifugal ultrafiltration.

An efficient water-based purification strategy for metal-organic polyhedra (MOPs) using commercially available centrifugal ultrafiltration membranes was developed. Having a diameter above 3 nm, MOPs were almost fully retained by the filters, while free ligands and other impurities were washed away. MOP retention also enabled efficient counter-ion exchange. This method paves the way for the application of MOPs with biological systems.

Potential of PALBI-T score as a prognostic model for hepatocellular carcinoma in alcoholic liver disease.

BACKGROUND AND AIM: With the control of viral hepatitis, alcoholic hepatocellular carcinoma (HCC) is becoming increasingly important in Japan. In alcoholic cirrhosis, the impact of portal hypertension is significant. Thus, it may be difficult to predict prognosis accurately with the reported prognostic scores. Here we propose the platelet-albumin-bilirubin tumor nodes metastasis (TNM) score (PALBI-T score) as a prognostic model for HCC in alcoholic liver disease, and investigate its usefulness. The PALBI-T score is an integrated score based on the TNM stage and PALBI grade including platelets, reflecting portal hypertension. METHODS: This study included 163 patients with alcoholic HCC treated at our Center from 1997 to 2018. We compared the prognostic prediction abilities of the Japan Integrated Staging (JIS) score, ALBI-T score, and PALBI-T score. The PALBI-T score was calculated similarly to the JIS and ALBI-T scores. Areas under the receiver operating characteristic curve (AUC) were calculated for predicting overall survival (OS). RESULTS: In predicting the 1-year survival, the JIS score had a larger AUC (AUC = 0.925) than the ALBI-T score (AUC = 0.895) and PALBI-T score (AUC = 0.891). On the other hand, there was no significant difference in predicting OS among the integrated scores. The PALBI-T score (AUC = 0.740) had the largest AUC, and the JIS score (AUC = 0.729) and ALBI-T score (AUC = 0.717) were not significantly different from the PALBI grade (AUC = 0.634). The PALBI grade reflected the degree of portal hypertension. CONCLUSION: In patients with alcoholic HCC, the Japan Integrated Staging score is useful for predicting short-term prognosis. The PALBI-T score, which reflects portal hypertension, appears to be a more valid prognostic score for predicting long-term prognosis.

Scythe regulates apoptosis through modulating ubiquitin-mediated proteolysis of the Xenopus elongation factor XEF1AO.

Scythe was originally identified as a novel Reaper-binding anti-apoptotic protein, although the mechanisms of its functions remain largely obscure. Our previous analysis revealed that Scythe can bind to a proteasomal subunit via N-terminal domains and that the domains are required for appropriate development of Xenopus embryos. In the present study, we show evidence that the N-terminus of Scythe interacts with XEF1AO, a maternal form of Xenopus laevis EF1A that was suggested to be a potential inducer of apoptosis in vertebrates, and that the binding enhances the poly-ubiquitin modification and subsequent degradation of XEF1AO. Scythe is required for degradation of XEF1AO, since immunodepletion of Scythe from embryonic extracts stabilized XEF1AO significantly. Furthermore, we show that apoptosis induced by accumulation of XEF1AO can be suppressed by co-expression of the full-length form of Scythe. These observations indicate that the proteolytic regulation of XEF1AO, mediated through Scythe, is essential to prevent inappropriate accumulation of XEF1AO and resulting apoptotic events during the course of Xenopus development.

A conserved island of BAG6/Scythe is related to ubiquitin domains and participates in short hydrophobicity recognition.

BAG6 (also called Scythe) interacts with the exposed hydrophobic regions of newly synthesized proteins and escorts them to the degradation machinery through mechanisms that remain to be elucidated. In this study, we provide evidence that BAG6 physically interacts with the model defective protein substrate CL1 in a manner that depends directly on its short hydrophobicity. We found that the N terminus of BAG6 contains an evolutionarily conserved island tentatively designated the BAG6 ubiquitin-linked domain. Partial deletion of this domain in the BAG6 N-terminal fragment abolished in cell recognition of polyubiquitinated polypeptides as well as the hydrophobicity-mediated recognition of the CL1 degron in cell and in vitro. These observations suggest a mechanism whereby the BAG6 ubiquitin-linked domain provides a platform for discriminating substrates with shorter hydrophobicity stretches as a signal for defective proteins.

Unique proteasome subunit Xrpn10c is a specific receptor for the antiapoptotic ubiquitin-like protein Scythe.

The Rpn10 subunit of the 26S proteasome can bind to polyubiquitinoylated and/or ubiquitin-like proteins via ubiquitin-interacting motifs (UIMs). Vertebrate Rpn10 consists of five distinct spliced isoforms, but the specific functions of these variants remain largely unknown. We report here that one of the alternative products of Xenopus Rpn10, named Xrpn10c, functions as a specific receptor for Scythe/BAG-6, which has been reported to regulate Reaper-induced apoptosis. Deletional analyses revealed that Scythe has at least two distinct domains responsible for its binding to Xrpn10c. Conversely, an Xrpn10c has a UIM-independent Scythe-binding site. The forced expression of a Scythe mutant protein lacking Xrpn10c-binding domains in Xenopus embryos induces inappropriate embryonic death, whereas the wild-type Scythe did not show any abnormality. The results indicate that Xrpn10c-binding sites of Scythe act as an essential segment linking the ubiquitin/proteasome machinery to the control of proper embryonic development.

BAG6/BAT3: emerging roles in quality control for nascent polypeptides.

BAG6 (also known as BAT3/Scythe) is a ubiquitin-like protein that is thought to participate in a variety of seemingly unrelated physiological and pathological processes, such as apoptosis, antigen presentation and the T-cell response. Recent studies have shown that BAG6 is essential for the quality control of aggregation-prone polypeptide biogenesis. It forms part of a complex that determines the fate of newly synthesized client proteins for membrane insertion, ubiquitin-mediated degradation and/or aggregate formation. A biologically relevant transmembrane protein family has recently been shown to be a major client of BAG6, suggesting that many of the known diverse BAG6 functions can be interpreted by BAG6-mediated control of membrane protein biogenesis. In this review, we summarize the current understanding of the physiological roles of BAG6 with a particular focus on quality control for nascent chain polypeptides.

BAG-6 is essential for selective elimination of defective proteasomal substrates.

BAG-6/Scythe/BAT3 is a ubiquitin-like protein that was originally reported to be the product of a novel gene located within the human major histocompatibility complex, although the mechanisms of its function remain largely obscure. Here, we demonstrate the involvement of BAG-6 in the degradation of a CL1 model defective protein substrate in mammalian cells. We show that BAG-6 is essential for not only model substrate degradation but also the ubiquitin-mediated metabolism of newly synthesized defective polypeptides. Furthermore, our in vivo and in vitro analysis shows that BAG-6 interacts physically with puromycin-labeled nascent chain polypeptides and regulates their proteasome-mediated degradation. Finally, we show that knockdown of BAG-6 results in the suppressed presentation of MHC class I on the cell surface, a procedure known to be affected by the efficiency of metabolism of defective ribosomal products. Therefore, we propose that BAG-6 is necessary for ubiquitin-mediated degradation of newly synthesized defective polypeptides.

Association of Rpn10 with high molecular weight complex is enhanced during retinoic acid-induced differentiation of neuroblastoma cells.

The ubiquitin-binding Rpn10 protein serves as an ubiquitin receptor that delivers client proteins to the 26S proteasome, the protein degradation complex. It has been suggested that the ubiquitin-dependent protein degradation is critical for neuronal differentiation and for preventing neurodegenerative diseases. Our previous study indicated the importance of Rpn10 in control of cellular differentiation (Shimada et al., Mol Biol Cell 17:5356-5371, 2006), though the functional relevance of Rpn10 in neuronal cell differentiation remains a mystery to be uncovered. In the present study, we have examined the level of Rpn10 in a proteasome-containing high molecular weight (HMW) protein fraction prepared from the mouse neuroblastoma cell line Neuro2a. We here report that the protein level of Rpn10 in HMW fraction from un-differentiated Neuro2a cells was significantly lower than that of other cultured cell lines. We have found that retinoic acid-induced neural differentiation of Neuro2a cells significantly stimulates the incorporation of Rpn10 into HMW fractions, although the amounts of 26S proteasome subunits were not changed. Our findings provide the first evidence that the modulation of Rpn10 is linked to the control of retinoic acid-induced differentiation of neuroblastoma cells.