Small-molecule inhibitors of linear ubiquitin chain assembly complex (LUBAC), HOIPINs, suppress NF-κB signaling

Nuclear factor-κB (NF-κB) is a crucial transcription factor family involved in the regulation of immune and inflammatory responses and cell survival. The linear ubiquitin chain assembly complex (LUBAC), composed of the HOIL-1L, HOIP, and SHARPIN subunits, specifically generates Met1-linked linear ubiquitin chains through the ubiquitin ligase activity in HOIP, and activates the NF-κB pathway. We recently identified a chemical inhibitor of LUBAC, which we named HOIPIN-1 (HOIP inhibitor-1). To improve the potency of HOIPIN-1, we synthesized 7 derivatives (HOIPIN-2∼8), and analyzed their effects on LUBAC and NF-κB activation. Among them, HOIPIN-8 suppressed the linear ubiquitination activity by recombinant LUBAC at an IC₅₀ value of 11 nM, corresponding to a 255-fold increase over that of HOIPIN-1. Furthermore, as compared with HOIPIN-1, HOIPIN-8 showed 10-fold and 4-fold enhanced inhibitory activities on LUBAC- and TNF-α-induced NF-κB activation respectively, without cytotoxicity. These results indicated that HOIPIN-8 is a powerful tool to explore the physiological functions of LUBAC.

High-Throughput Screening for Linear Ubiquitin Chain Assembly Complex (LUBAC) Selective Inhibitors Using Homogenous Time-Resolved Fluorescence (HTRF)-Based Assay System

The nuclear factor κB (NF-κB) pathway is critical for regulating immune and inflammatory responses, and uncontrolled NF-κB activation is closely associated with various inflammatory diseases and malignant tumors. The Met1-linked linear ubiquitin chain, which is generated by linear ubiquitin chain assembly complex (LUBAC), is important for regulating NF-κB activation. This process occurs through the linear ubiquitination of NF-κB essential modulator, a regulatory subunit of the canonical inhibitor of the NF-κB kinase complex. In this study, we have established a robust and efficient high-throughput screening (HTS) platform to explore LUBAC inhibitors, which may be used as tool compounds to elucidate the pathophysiological role of LUBAC. The HTS platform consisted of both cell-free and cell-based assays: (1) cell-free LUBAC-mediated linear ubiquitination assay using homogenous time-resolved fluorescence technology and (2) cell-based LUBAC assay using the NF-κB luciferase reporter gene assay. By using the HTS platform, we performed a high-throughput chemical library screen and identified several hit compounds with selectivity against a counterassay. Liquid chromatography-mass spectrometry analysis revealed that these compounds contain a chemically reactive lactone structure, which is transformed to give reactive α,β-unsaturated carbonyl compounds. Further investigation revealed that the reactive group of these compounds is essential for the inhibition of LUBAC activity.

Effects of AhR ligands on the production of immunoglobulins in purified mouse B cells

The aryl hydrocarbon receptor (AhR) has been shown to play important roles in the immune system, and contributions of AhR ligands to the differentiation and functions of Th17/Treg cells have recently been established. However, it has not been fully clarified whether AhR plays roles in B cell differentiation and functions. The environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a highly potent AhR agonist, was reported to suppress the production of immunoglobulin M (IgM) in a transformed mouse B cell line. However, TCDD exhibits high toxicity toward cells and has unknown activities except for its action as an AhR agonist. In the present study, we tried to clarify how an endogenously generated AhR agonist affects mouse B cell differentiation and functions in terms of the direct effects on the expression of Ig subclasses in purified mouse B cells stimulated with an anti-CD40 antibody and interleukin-4. The AhR agonist 2-(1'H-indole-3'- carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE), which is derived via tryptophan metabolism, suppressed the expression of not only IgM, but also IgG1 and IgE. ITE was also found to suppress the expression of secreted-type Ig mRNAs and plasma cell-specific genes. These findings indicate that the endogenous AhR agonist suppresses B cell differentiation into Ig-secreting plasma cells.

An improved method for primary culture of rat podocytes

A gentle method to isolate glomeruli simply by cutting renal cortices without forced sieving was devised in our previous study of primary podocyte culture. Yields of glomeruli isolated by this method, however, were too small to perform subculture or biological assays. In the present study, we tried an isolation method with magnetic beads and collagenase to increase the yields. Rat kidneys were perfused with magnetic particles. Renal cortices were digested with collagenase and filtered. Utilizing magnetic particles trapped within glomeruli, glomeruli were collected by attractive power of a magnet and cultured. The number of glomeruli isolated from one adult rat was more than 20,000 and the purity was more than 97%. About half of them were attached to culture dishes and exhibited cellular outgrowths, which were identified as podocytes by their distinct staining for podocyte markers. After 3 days of primary culture, the cellular outgrowths were subcultured. Approximately 60 podocytes were obtained per attached glomerulus. Their significant expression of podocytes markers was demonstrated by immunostaining and quantitative reverse transcriptase-polymerase chain reaction. The isolation method with magnetic beads and collagenase provides a number of glomeruli suitable for primary podocyte culture.

MUC20 suppresses the hepatocyte growth factor-induced Grb2-Ras pathway by binding to a multifunctional docking site of met

A cDNA encoding a novel mucin protein, MUC20, was isolated as a gene that is up-regulated in the renal tissues of patients with immunoglobulin A nephropathy. We demonstrate here that the C terminus of MUC20 associates with the multifunctional docking site of Met without ligand activation, preventing Grb2 recruitment to Met and thus attenuating hepatocyte growth factor (HGF)-induced transient extracellular signal-regulated kinase-1 and -2 activation. Production of MUC20 reduced HGF-induced matrix metalloproteinase expression and proliferation, which require the Grb2-Ras pathway, whereas cell scattering, branching morphogenesis, and survival via the Gab1/phosphatidylinositol 3-kinase (PI3K) pathways was not affected. Thus, MUC20 reduces HGF-induced activation of the Grb2-Ras pathway but not the Gab1/PI3K pathways. We further demonstrate that the cytoplasmic domain of MUC20 has the ability to oligomerize and that the oligomerization augments its affinity for Met. Taken together, these results suggest that MUC20 is a novel regulator of the Met signaling cascade which has a role in suppression of the Grb2-Ras pathway.

Molecular cloning, genomic structure, and expression analysis of MUC20, a novel mucin protein, up-regulated in injured kidney

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis in the world. Here, we identify a cDNA encoding a novel mucin protein, shown previously to be up-regulated in IgAN patients, from a human kidney cDNA library. This protein contains a mucin tandem repeat of 19 amino acids consisting of many threonine, serine, and proline residues and likely to be extensively O-glycosylated; thus, this gene was classified in the mucin family and named MUC20. The human MUC20 gene contains at least four exons and is localized close to MUC4 on chromosome 3q29. We found variations in repeat numbers in the mucin tandem domain, suggesting polymorphism of this region. Northern blot and reverse transcription-PCR analyses revealed that human MUC20 mRNA was expressed most highly in kidney and moderately in placenta, colon, lung, prostate, and liver. Immunohistochemical analysis of human kidney revealed that MUC20 protein was localized in the proximal tubules. Immunoblotting analysis of MUC20 proteins produced in Madin-Darby canine kidney and HEK293 cells indicated the localization of MUC20 protein in a membrane fraction and extensive posttranslational modification. Immunoelectron microscopy of MUC20-producing Madin-Darby canine kidney cells demonstrated that MUC20 protein was localized on the plasma membrane. Expression of MUC20 mRNA in a human kidney cell line was up-regulated by tumor necrosis factor-alpha, phorbol 12-myristate 13-acetate, or lipopolysaccharide. Two species of MUC20 mRNA (hMUC20-L and hMUC20-S), resulting from alternative transcription, were identified in human tissue, whereas only one variant was observed in mouse tissues. Mouse MUC20 mRNA was expressed in the epithelial cells of proximal tubules, and the expression increased dramatically with the progression of lupus nephritis in the kidney of MRL/MpJ-lpr/lpr mice. Moreover, the expression of mouse MUC20 was augmented in renal tissues acutely injured by cisplatin or unilateral ureteral obstruction. These characteristics suggest that the production of MUC20 is correlated with development and progression of IgAN and other renal injuries.

[Serum CA125 measurement is useful in 3 cases with pericardial effusion]

Previously we reported that serum CA125 level is elevated in cases of pericardial effusion. We report three cases in which serum CA125 measurement is useful for assessing clinical status. In case 1, a 19-year-old came to our hospital for cardiac tamponade. Moderate degree of pericardial effusion and high CA125 level were observed. After the pericardectomy the serum CA125 level was normalized and pericardial effusion disappeared. Case 2, a 50-year-old man with mesothelioma and in whom serum CA125 level was elevated with pericardial effusion. After cardiac drainage his condition improved, with decreased CA125 level. However, later the CA125 level rose and recurrent localized pericardial effusion with worsening condition was observed. In case 3, in a 78-year-old woman with pericardial effusion no recurrence was observed after pericardial drainage. Her CA125 value was normal. These results indicated that measurement of CA125 value is a useful marker for assessing the clinical course of this disease.

REPRODUCTIVE POTENTIALS OF RACES 15B AND 56 OF WHEAT STEM RUST

Variations in the prevalence of races 56 and 15B-1 (Can.) of wheat stem rust (Puccinia graminis Pers. f. sp. tritici Erikss. and Henn.) have occurred that cannot be explained by changes in the wheat varieties grown in Western Canada. The reasons for the changes in prevalence were investigated by comparing in growth cabinets the reproductive potentials or aggressiveness of the two races and the factors that might influence them. When a mixture of urediospores of the two races was used to inoculate three susceptible varieties for successive uredial generations, race 56 predominated at 25 and 20 °C, and race 15B-1 (Can.) predominated at 15 °C. Experimentation showed that the urediospores of race 56 were more infective than those of 15B-1 (Can.) and that the incubation period of race 56 was shorter than that of race 15B-1 (Can.). Pustules of race 56 grew faster than those of race 15B-1 (Can.) during early stages of development but those of 15B-1 (Can.) ultimately became larger than those of race 56. Race 56 produced more urediospores per pustule than race 15B-1 (Can.) on the susceptible varieties Little Club, Red Bobs, and Marquis at 15 and 20 °C. Infection density markedly affected competitive abilities. Race 56 tended to predominate in light infections but race 15B-1 (Can.) tended to predominate in heavy infections. Pustule size decreased as infection density increased. The possible significance of these findings under field conditions is discussed. It seems likely that the rise of race 15B-1 (Can.) to predominance in 1950 resulted not only from the selection pressure of the widely grown varieties that were resistant to race 56 and susceptible to 15B-1 (Can.) but from the lower temperatures that prevailed and favored 15B-1 (Can.) over 56. The rise to predominance of race 56 from 1956 to 1961 may have resulted from the greater aggressiveness of that race under the moderate or warm conditions that prevailed.