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A study was conducted on the biophysical characterization of six peptides (m1-m6) representing the predicted amino-terminal membrane-spanning domain of cystic fibrosis transmembrane conductance regulator. The results indicate that the peptides exhibit an increase in Beta-sheet in trifluoroethanol, an inducer of alpha-helices. The findings also show that the possible functional role of m6 is manifested through a shift in secondary structure.

Natural mutagenesis study of the human 5alpha-reductase 2 isozyme reveals that specific amino acid residues are crucial for substrate and cofactor binding. The mutations are expressed in DNA transfected mammalian cells, and 13 out of the 22 mutations result in enzyme inactivation. The remaining mutations alter the substrate or cofactor binding. All mutations reduce the protein half-life and optimal pH.

Abstract Background Aggresomes are pericentrosomal accumulations of misfolded proteins, chaperones and proteasomes. Their positioning near the centrosome, like that of other organelles, requires active, microtubule-dependent transport. Linker proteins that can associate with the motor protein dynein, organelles, and microtubules are thought to contribute to the active maintenance of the juxtanuclear localization of many membrane bound organelles and aggresomes. Hook proteins have been proposed to serve as adaptors for the association of cargos with dynein for transport on microtubules. Hook2 was shown to localize to the centrosome, bind centriolin, and contribute to centrosomal function. Results Here we show that overexpression of hook2 promotes the accumulation of the cystic fibrosis transmembrane regulator in aggresomes without altering its biochemical properties or its steady state level. A dominant negatively acting form of hook2 that lacks the centriolin binding C-terminal inhibits aggresome formation. Conclusion We propose that hook2 contributes to the establishment and maintenance of the pericentrosomal localization of aggresomes by promoting the microtubule-based delivery of protein aggregates to pericentriolar aggresomes.

In a multinational placebo‐controlled phase III clinical trial in 2,185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease, treatment with the Nrf2 activator bardoxolone methyl increased estimated glomerular filtration rate, a measure of kidney function, but also resulted in increases in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma glutamyl transferase. These increases in liver enzyme level(s) were maximal after 4 weeks of treatment and reversible, trending back toward baseline through week 48. Total bilirubin concentrations did not increase, and no cases met Hy's Law criteria, although two subjects had ALT concentrations that exceeded 10 × the upper limit of the population reference range leading to discontinuation of treatment. Animal and cell culture experiments suggested that the increases in ALT and AST induced by bardoxolone methyl may be related to its pharmacological activity. Bardoxolone methyl significantly induced the mRNA expression of ALT and AST isoforms in cultured cells. Expression of ALT and AST isoforms in liver and kidney also positively correlated with Nrf2 status in mice. Overall, these data suggest that the increases in ALT and AST observed clinically were, at least in part, related to the pharmacological induction of aminotransferases via Nrf2 activation, rather than to any intrinsic form of hepatotoxicity. [ABSTRACT FROM AUTHOR]

Bardoxolone methyl and related triterpenoids are well tolerated and efficacious in numerous animal models potentially relevant to patients with Type 2 diabetes and chronic kidney disease. These agents enhance glucose control and regulate lipid accumulation in rodent models of diabetes and obesity, and improve renal function, reduce inflammation, and prevent structural injury in models of renal disease. However, a recent study in Zucker diabetic fatty (ZDF) rats noted poor tolerability with the bardoxolone methyl analog RTA 405 within 1 mo after treatment initiation, although this study was confounded in part by the use of an impure RTA 405 batch. To investigate these discordant observations, the present studies were conducted to further characterize triterpenoids in rodent models of diabetes and obesity. A follow-up study was conducted in ZDF rats with two related triterpenoids (RTA 405 and dh404) for 1.5 mo. Consistent with previous rodent experience, and in contrast to the more recent ZDF report, ZDF rats administered RTA 405 or dh404 exhibited no adverse clinical signs, had laboratory values similar to controls, and exhibited no evidence of adverse liver or kidney histopathology. Additionally, RTA 405 was well tolerated in streptozotocin-induced Type 1 diabetic rats and high-fat-diet-induced obese mice. The present results are consistent with the overall published body of data obtained with triterpenoids and provide further evidence that these molecules are well tolerated without adverse effects on hepatobiliary or renal function in rodent models of diabetes and obesity. [ABSTRACT FROM AUTHOR]

Ischemic acute kidney injury (AKI) triggers expression of adaptive (protective) and maladaptive genes. Agents that increase expression of protective genes should provide a therapeutic benefit. We now report that bardoxolone methyl (BARD) ameliorates ischemic murine AKI as assessed by both renal function and pathology. BARD may exert its beneficial effect by increasing expression of genes previously shown to protect against ischemic AKI, NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ), and heme oxygenase 1 (HO-1). Although we found that BARD alone or ischemia-reperfusion alone increased expression of these genes, the greatest increase occurred after the combination of both ischemia-reperfusion and BARD. BARD had a different mode of action than other agents that regulate PPARγ and Nrf2. Thus we report that BARD regulates PPARγ, not by acting as a ligand but by increasing the amount of PPARγ mRNA and protein. This should increase ligand-independent effects of PPARγ. Similarly, BARD increased Nrf2 mRNA; this increased Nrf2 protein by mechanisms in addition to the prolongation of Nrf2 protein half-life previously reported. Finally, we localized expression of these protective genes after ischemia and BARD treatment. Using double-immunofluorescence staining for CD31 and Nrf2 or PPARγ, we found increased Nrf2 and PPARγ on glomerular endothelia in the cortex; Nrf2 was also present on cortical peritubular capillaries. In contrast, HO-1 was localized to different cells, i.e., tubules and interstitial leukocytes. Although Nrf2-dependent increases in HO-1 have been described, our data suggest that BARD's effects on tubular and leukocyte HO-1 during ischemic AKI may be Nrf2 independent. We also found that BARD ameliorated cisplatin nephrotoxicity. [ABSTRACT FROM AUTHOR]

The multipass membrane protein APH-1, found in the γ-secretase complex together with presenilin, nicastrin, and PEN-2, is essential for Notch signaling in Caenorhabditis elegans embryos and is required for intramembrane proteolysis of Notch and β-amyloid precursor protein in mammalian and Drosophila cells. In C. elegans, a mutation of the conserved transmembrane Gly123 in APH-1 (mutant or28) leads to a notch/glp-1 loss-of-function phenotype. In this study, we show that the corresponding mutation in mammalian APH-1aL (G122D) disrupts the physical interaction of APH-1aL with hypoglycosylated immature nicastrin and the presenilin holoprotein as well as with mature nicastrin, presenilin, and PEN-2. The G122D mutation also reduced γ-secretase activity in intramembrane proteolysis of membrane-tethered Notch. Moreover, we found that the conserved transmembrane Gly122, Gly126, and Gly130 in the fourth transmembrane region of mammalian APH-1aL are part of the membrane helix-helix interaction GXXXG motif and are essential for the stable association of APH1aL with presenilin, nicastrin, and PEN-2. These findings suggest that APH-1 plays a GXX G-dependent scaffolding role in both the initial assembly and subsequent maturation and maintenance of the active γ-secretase complex. [ABSTRACT FROM AUTHOR]

In a multinational placebo-controlled phase III clinical trial in 2,185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease, treatment with the Nrf2 activator bardoxolone methyl increased estimated glomerular filtration rate, a measure of kidney function, but also resulted in increases in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma glutamyl transferase. These increases in liver enzyme level(s) were maximal after 4 weeks of treatment and reversible, trending back toward baseline through week 48. Total bilirubin concentrations did not increase, and no cases met Hy's Law criteria, although two subjects had ALT concentrations that exceeded 10 × the upper limit of the population reference range leading to discontinuation of treatment. Animal and cell culture experiments suggested that the increases in ALT and AST induced by bardoxolone methyl may be related to its pharmacological activity. Bardoxolone methyl significantly induced the mRNA expression of ALT and AST isoforms in cultured cells. Expression of ALT and AST isoforms in liver and kidney also positively correlated with Nrf2 status in mice. Overall, these data suggest that the increases in ALT and AST observed clinically were, at least in part, related to the pharmacological induction of aminotransferases via Nrf2 activation, rather than to any intrinsic form of hepatotoxicity., (© 2020 The Authors. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of the American Society for Clinical Pharmacology and Therapeutics.)

Ischemic acute kidney injury (AKI) triggers expression of adaptive (protective) and maladaptive genes. Agents that increase expression of protective genes should provide a therapeutic benefit. We now report that bardoxolone methyl (BARD) ameliorates ischemic murine AKI as assessed by both renal function and pathology. BARD may exert its beneficial effect by increasing expression of genes previously shown to protect against ischemic AKI, NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ), and heme oxygenase 1 (HO-1). Although we found that BARD alone or ischemia-reperfusion alone increased expression of these genes, the greatest increase occurred after the combination of both ischemia-reperfusion and BARD. BARD had a different mode of action than other agents that regulate PPARγ and Nrf2. Thus we report that BARD regulates PPARγ, not by acting as a ligand but by increasing the amount of PPARγ mRNA and protein. This should increase ligand-independent effects of PPARγ. Similarly, BARD increased Nrf2 mRNA; this increased Nrf2 protein by mechanisms in addition to the prolongation of Nrf2 protein half-life previously reported. Finally, we localized expression of these protective genes after ischemia and BARD treatment. Using double-immunofluorescence staining for CD31 and Nrf2 or PPARγ, we found increased Nrf2 and PPARγ on glomerular endothelia in the cortex; Nrf2 was also present on cortical peritubular capillaries. In contrast, HO-1 was localized to different cells, i.e., tubules and interstitial leukocytes. Although Nrf2-dependent increases in HO-1 have been described, our data suggest that BARD's effects on tubular and leukocyte HO-1 during ischemic AKI may be Nrf2 independent. We also found that BARD ameliorated cisplatin nephrotoxicity.

Bulk protein degradation in the cell is catalyzed by the ubiquitin-proteasome system (UPS). At the heart of the UPS is the proteasome, a large multisubunit tightly-regulated protease. The UPS performs key functions in protein quality control by monitoring and eliminating potentially toxic misfolded or damaged proteins. When the capacity of this protease system is exceeded, misfolded protein substrates aggregate and are assembled through an active and regulated process to form an aggresome. Aggresomes are dynamic structures, formed as a general response to an overload of improperly folded proteins. Assembly of aggresomes occurs at the centrosome, a perinuclear structure that also serves as a site for the recruitment and concentration of components of the UPS, including the proteasome, its regulators, and other proteins typically involved in protein quality control. Thus, in addition to other cellular activities, the centrosome may play a central role in protein quality control, sitting at the crossroads of protein folding, degradation, and aggregation.