Cracking the Monoubiquitin Code of Genetic Diseases.

Ubiquitination is a versatile and dynamic post-translational modification in which single ubiquitin molecules or polyubiquitin chains are attached to target proteins, giving rise to mono- or poly-ubiquitination, respectively. The majority of research in the ubiquitin field focused on degradative polyubiquitination, whereas more recent studies uncovered the role of single ubiquitin modification in important physiological processes. Monoubiquitination can modulate the stability, subcellular localization, binding properties, and activity of the target proteins. Understanding the function of monoubiquitination in normal physiology and pathology has important therapeutic implications, as alterations in the monoubiquitin pathway are found in a broad range of genetic diseases. This review highlights a link between monoubiquitin signaling and the pathogenesis of genetic disorders.

Facile Semisynthesis of Ubiquitylated Peptides with the Ligation Auxiliary 2-Aminooxyethanethiol.

The posttranslational modification of cellular proteins by ubiquitin (Ub), called ubiquitylation, is indispensable for the normal growth and development of eukaryotic organisms. In order to conduct studies that elucidate the precise mechanistic roles for Ub, access to site-specifically and homogenously ubiquitylated proteins and peptides is critical. However, the low abundance, heterogeneity, and dynamic nature of protein ubiquitylation are significant limitations toward such studies. Here we provide a facile expressed protein ligation method that does not require specialized apparatus and permits the rapid semisynthesis of ubiquitylated peptides by using the atom-efficient ligation auxiliary 2-aminooxyethanethiol.

Impaired autophagy promotes bile acid-induced hepatic injury and accumulation of ubiquitinated proteins.

Chronic exposure to hydrophobic bile acids such as chenodeoxycholic acid (CDCA) and cholic acid (CA) in the liver during cholestasis causes hepatotoxicity and inflammatory response. However, the detailed mechanisms regarding the role of autophagy in cholestatic hepatotoxicity remain largely unknown. Here we determined autophagic clearance in livers of bile duct-ligated mice, in which bile acids accumulate, and in human hepatoma HepG2 cells treated with CDCA and CA. The accumulation of bile acids caused defective autophagic clearance, shown by the accumulation of insoluble p62 and ubiquitinated proteins and cell death accompanied by caspase-3 processing. Hepatocytes exposed to bile acids also showed the accumulation of autophagosomes via suppressed autophagy flux. Treatment of CDCA markedly suppressed Beclin-1 expression, which exhibits a higher cytotoxicity than CA. Moreover, pharmacological or genetic inhibition of autophagy enhanced bile acid-induced cell death. Finally, in vivo, bile duct ligation led to aberrant accumulation of p62 and ubiquitinated proteins in the liver. Our data demonstrate that inhibited autophagy is an essential component of liver injury during cholestasis.

Plasma proteasomal chymotrypsin-like activity correlates with prostate cancer progression.

Previously, we demonstrated that inhibition of proteasomal chymotrypsin-like (CT-like) activity in human prostate cancer (PCa) PC-3 cultures and PC-3 xenografts results in accumulation of ubiquitinated proteins, followed by induction of cell death. Studies have shown that plasma CT-like proteasomal activity may be a powerful biomarker for risk stratification in hematologic malignancies. We hypothesized that circulating proteasomes could also be used to stratify risk for patients with PCa. A total of 109 patients with suspected PCa underwent prostatic biopsies were enrolled. Subjects were divided into non-cancer, low-risk PCa, and high-risk PCa groups. Three different proteasomal activity markers (CT-like, caspase-like, and trypsin-like) were measured and compared among the three groups. The proteasomal target proteins, Ub-prs, Hsp70, Bax, and P27 in plasma and prostate tissues were also evaluated. Multivariate analysis was used to assess whether CT-like activity was a predictor of PCa progression. Only proteasomal CT-like activity in the high-risk group was statistically higher than in the non-cancer group (P < 0.05). The expression of Ub-prs, Hsp70, Bax, and P27 protein was decreased in both plasma and PCa tissue of high-risk patients. CT-like activity was found to be an independent predictor of high-risk PCa. Subjects with CT-like activity ≥55 had a 2.15-fold higher risk of having high-risk PCa as compared to those with a CT-like activity of <55 (P = 0.021). We found CT-like activity to be an independent predictor of high-risk PCa, and as such, it may be a good candidate as a biomarker for high-risk PCa detection and stratification.

Blockade of the formation of insoluble ubiquitinated protein aggregates by EGCG3"Me in the alloxan-induced diabetic kidney.

BACKGROUND: Renal accumulation of reactive carbonyl compounds (RCCs) has been linked to the progression of diabetic nephropathy. We previously demonstrated that carbonyl stress induces the formation of amino-carbonyl cross-links and sharply increases the content of ß-sheet-rich structures, which is the seed of insoluble aggregates formation, and tea catechin (-)-epigallocatechin 3-gallate (EGCG) can reverse this process in vitro and in vivo. In this study, methylated derivative (-)-epigallocatechin-3-O-(3-O-methyl)-gallate (EGCG3"Me) was hypothesized to neutralize carbonyl stress mediating the formation of insoluble ubiquitinated protein (IUP) aggregates, and reduce the early development of diabetic nephropathy. METHODS AND RESULTS: Diabetes was induced in mice by intraperitoneally injecting alloxan monohydrate (200 mg/kg/d) twice and administering EGCG3"Me by gavage for 15 d. Reagent case and western blot results showed that, in diabetic kidneys, the carbonyl proteins in the serum increased; and in insoluble protein fraction, 4-hydroxynonenal-modified proteins, IUP aggregates and p62 accumulated; FT-IR study demonstrated that the lipid content, anti-parallel ß-sheet structure and aggregates increased. EGCG3"Me treatment could effectively reverse this process, even better than the negative control treatment. CONCLUSIONS: EGCG3"Me exhibiting anti-ß-sheet-rich IUP aggregate properties, maybe represents a new strategy to impede the progression of diabetic nephropathy and other diabetic complications.