Natural proteome diversity links aneuploidy tolerance to protein turnover.

Accessing the natural genetic diversity of species unveils hidden genetic traits, clarifies gene functions and allows the generalizability of laboratory findings to be assessed. One notable discovery made in natural isolates of Saccharomyces cerevisiae is that aneuploidy-an imbalance in chromosome copy numbers-is frequent1,2 (around 20%), which seems to contradict the substantial fitness costs and transient nature of aneuploidy when it is engineered in the laboratory3-5. Here we generate a proteomic resource and merge it with genomic1 and transcriptomic6 data for 796 euploid and aneuploid natural isolates. We find that natural and lab-generated aneuploids differ specifically at the proteome. In lab-generated aneuploids, some proteins-especially subunits of protein complexes-show reduced expression, but the overall protein levels correspond to the aneuploid gene dosage. By contrast, in natural isolates, more than 70% of proteins encoded on aneuploid chromosomes are dosage compensated, and average protein levels are shifted towards the euploid state chromosome-wide. At the molecular level, we detect an induction of structural components of the proteasome, increased levels of ubiquitination, and reveal an interdependency of protein turnover rates and attenuation. Our study thus highlights the role of protein turnover in mediating aneuploidy tolerance, and shows the utility of exploiting the natural diversity of species to attain generalizable molecular insights into complex biological processes.

Inorganic sulfur fixation via a new homocysteine synthase allows yeast cells to cooperatively compensate for methionine auxotrophy.

The assimilation, incorporation, and metabolism of sulfur is a fundamental process across all domains of life, yet how cells deal with varying sulfur availability is not well understood. We studied an unresolved conundrum of sulfur fixation in yeast, in which organosulfur auxotrophy caused by deletion of the homocysteine synthase Met17p is overcome when cells are inoculated at high cell density. In combining the use of self-establishing metabolically cooperating (SeMeCo) communities with proteomic, genetic, and biochemical approaches, we discovered an uncharacterized gene product YLL058Wp, herein named Hydrogen Sulfide Utilizing-1 (HSU1). Hsu1p acts as a homocysteine synthase and allows the cells to substitute for Met17p by reassimilating hydrosulfide ions leaked from met17Δ cells into O-acetyl-homoserine and forming homocysteine. Our results show that cells can cooperate to achieve sulfur fixation, indicating that the collective properties of microbial communities facilitate their basic metabolic capacity to overcome sulfur limitation.

De Novo Disruption of the Proteasome Regulatory Subunit PSMD12 Causes a Syndromic Neurodevelopmental Disorder.

Degradation of proteins by the ubiquitin-proteasome system (UPS) is an essential biological process in the development of eukaryotic organisms. Dysregulation of this mechanism leads to numerous human neurodegenerative or neurodevelopmental disorders. Through a multi-center collaboration, we identified six de novo genomic deletions and four de novo point mutations involving PSMD12, encoding the non-ATPase subunit PSMD12 (aka RPN5) of the 19S regulator of 26S proteasome complex, in unrelated individuals with intellectual disability, congenital malformations, ophthalmologic anomalies, feeding difficulties, deafness, and subtle dysmorphic facial features. We observed reduced PSMD12 levels and an accumulation of ubiquitinated proteins without any impairment of proteasome catalytic activity. Our PSMD12 loss-of-function zebrafish CRISPR/Cas9 model exhibited microcephaly, decreased convolution of the renal tubules, and abnormal craniofacial morphology. Our data support the biological importance of PSMD12 as a scaffolding subunit in proteasome function during development and neurogenesis in particular; they enable the definition of a neurodevelopmental disorder due to PSMD12 variants, expanding the phenotypic spectrum of UPS-dependent disorders.

Biallelic Variants in OTUD6B Cause an Intellectual Disability Syndrome Associated with Seizures and Dysmorphic Features.

Ubiquitination is a posttranslational modification that regulates many cellular processes including protein degradation, intracellular trafficking, cell signaling, and protein-protein interactions. Deubiquitinating enzymes (DUBs), which reverse the process of ubiquitination, are important regulators of the ubiquitin system. OTUD6B encodes a member of the ovarian tumor domain (OTU)-containing subfamily of deubiquitinating enzymes. Herein, we report biallelic pathogenic variants in OTUD6B in 12 individuals from 6 independent families with an intellectual disability syndrome associated with seizures and dysmorphic features. In subjects with predicted loss-of-function alleles, additional features include global developmental delay, microcephaly, absent speech, hypotonia, growth retardation with prenatal onset, feeding difficulties, structural brain abnormalities, congenital malformations including congenital heart disease, and musculoskeletal features. Homozygous Otud6b knockout mice were subviable, smaller in size, and had congenital heart defects, consistent with the severity of loss-of-function variants in humans. Analysis of peripheral blood mononuclear cells from an affected subject showed reduced incorporation of 19S subunits into 26S proteasomes, decreased chymotrypsin-like activity, and accumulation of ubiquitin-protein conjugates. Our findings suggest a role for OTUD6B in proteasome function, establish that defective OTUD6B function underlies a multisystemic human disorder, and provide additional evidence for the emerging relationship between the ubiquitin system and human disease.

Ecm29 fulfils quality control functions in proteasome assembly.

The proteasome, the central protease of eukaryotic cells, is composed of one core particle (CP) and one or two adjacent regulatory particles (RP), which contain multiple subunits. Several proteasome-dedicated chaperones govern the assembly of CP and RP, respectively. We sought for proteins that regulate final steps of RP-CP assembly in yeast and found Ecm29, a conserved HEAT-like repeat protein. Here, we show that Ecm29 controls the integrity of RP-CP assemblies. Ecm29 recognizes RP-CP species in which CP maturation is stalled due to the lack of distinct beta subunits. Reconstitution assays revealed that Ecm29 functions as scaffold protein during the remodeling of incompletely matured RP-CP assemblies into regular enzymes. Upon the completion of CP maturation, Ecm29 is degraded and RP-CP is dissociated.

Major Histocompatibility Complex (MHC) Class I Processing of the NY-ESO-1 Antigen Is Regulated by Rpn10 and Rpn13 Proteins and Immunoproteasomes following Non-lysine Ubiquitination.

The supply of MHC class I-restricted peptides is primarily ensured by the degradation of intracellular proteins via the ubiquitin-proteasome system. Depending on the target and the enzymes involved, ubiquitination is a process that may dramatically vary in terms of linkages, length, and attachment sites. Here we identified the unique lysine residue at position 124 of the NY-ESO-1 cancer/testis antigen as the acceptor site for the formation of canonical Lys-48-linkages. Interestingly, a lysine-less form of NY-ESO-1 was as efficient as its wild-type counterpart in supplying the HLA-A*0201-restricted NY-ESO-1157-165 antigenic peptide. In fact, we show that the regulation of NY-ESO-1 processing by the ubiquitin receptors Rpn10 and Rpn13 as a well as by the standard and immunoproteasome is governed by non-canonical ubiquitination on non-lysine sites. In summary, our data underscore the significance of atypical ubiquitination in the modulation of MHC class I antigen processing.

Evidence for anti-apoptotic roles of proteasome activator 28γ via inhibiting caspase activity.

Proteasome activator PA28γ (REGγ, Ki antigen) has recently been demonstrated to display anti-apoptotic properties via enhancing Mdm2-p53 interaction, thereby facilitating ubiquitination and down-regulation of the tumor suppressor p53. In this study we demonstrate a correlation between cellular PA28γ levels and the sensitivity of cells towards apoptosis in different cellular contexts thereby confirming a role of proteasome activator PA28γ as an anti-apoptotic regulator. We investigated the anti-apoptotic role of PA28γ upon UV-C stimulation in B8 mouse fibroblasts stably overexpressing the PA28γ-encoding PSME3 gene and upon butyrate-induced apoptosis in human HT29 adenocarcinoma cells with silenced PSME3 gene. Interestingly, our results demonstrate that PA28γ has a strong influence on different apoptotic hallmarks, especially p53 phosphorylation and caspase activation. In detail, PA28γ and effector caspases mutually restrict each other. PA28γ is a caspase substrate, if PA28γ levels are low. In contrast, PA28γ overexpression reduces caspase activities, including the caspase-dependent processing of PA28γ. Furthermore, overexpression of PA28γ resulted in a nuclear accumulation of transcriptional active p53. In summary, our findings indicate that even in a p53-dominated cellular context, pro-apoptotic signaling might be overcome by PA28γ-mediated caspase inhibition.

Exposure determinants of cadmium in European mothers and their children.

The metal cadmium (Cd) is a widespread environmental pollutant with documented adverse effects on the kidneys and bones from long-term environmental exposure, but with insufficiently elucidated public health consequences such as risk of cardiovascular disease, hormone-related cancer in adults and developmental effects in children. This study is the first pan-European human biomonitoring project that succeeded in performing harmonized measurements of Cd in urine in a comparable way in mother-child couples from 16 European countries. The aim of the study was to evaluate the overall Cd exposure and significant determinants of Cd exposure. A study population of 1632 women (24-52 years of age), and 1689 children (5-12 years of age), from 32 rural and urban areas, was examined within a core period of 6 months in 2011-2012. Women were stratified as smokers and non-smokers. As expected, smoking mothers had higher geometric mean (gm) urinary cadmium (UCd; 0.24 µg/g crea; n=360) than non-smoking mothers (gm 0.18 µg/g crea; n=1272; p<0.0001), and children had lower UCd (gm 0.065 µg/g crea; n=1689) than their mothers at the country level. Non-smoking women exposed to environmental tobacco smoke (ETS) at home had 14% (95% CI 1-28%) higher UCd than those who were not exposed to ETS at home (p=0.04). No influence of ETS at home or other places on UCd levels was detected in children. Smoking women with primary education as the highest educational level of the household had 48% (95% CI 18-86%) higher UCd than those with tertiary education (p=0.0008). The same observation was seen in non-smoking women and in children; however they were not statistically significant. In children, living in a rural area was associated with 7% (95% CI 1-13%) higher UCd (p=0.03) compared to living in an urban area. Children, 9-12 years had 7% (95% CI 1-13%) higher UCd (p=0.04) than children 5-8 years. About 1% of the mothers, and 0.06% of the children, exceeded the tolerable weekly intake (TWI) appointed by EFSA, corresponding to 1.0 µg Cd/g crea in urine. Poland had the highest UCd in comparison between the 16 countries, while Denmark had the lowest. Whether the differences between countries are related to differences in the degree of environmental Cd contamination or to differences in lifestyle, socioeconomic status or dietary patterns is not clear.

Lessons learnt on recruitment and fieldwork from a pilot European human biomonitoring survey.

Within the European Environment and Health Action Plan an initiative to establish a coherent human biomonitoring approach in Europe was started. The project COPHES (COnsortium to Perform Human biomonitoring on a European Scale ) developed recommendations for a harmonized conduct of a human biomonitoring (HBM) survey which came into action as the pilot study DEMOCOPHES (DEMOnstration of a study to COordinate and Perform Human biomonitoring on a European Scale). Seventeen European countries conducted a survey with harmonized instruments for, inter alia, recruitment, fieldwork and sampling, in autumn/winter 2011/2012. Based on the countries' experiences of conducting the pilot study, following lessons learnt were compiled: the harmonized fieldwork instruments (basic questionnaire, urine and hair sampling) turned out to be very valuable for future HBM surveys on the European scale. A school approach was favoured by most of the countries to recruit school-aged children according to the established guidelines and country specific experiences. To avoid a low participation rate, intensive communication with the involved institutions and possible participants proved to be necessary. The communication material should also include information on exclusion criteria and offered incentives. Telephone contact to the participants the day before fieldwork during the survey can prevent the forgetting of appointments and first morning urine samples. To achieve comparable results on the European scale, training of interviewers in all issues of recruitment, fieldwork and sampling through information material and training sessions is crucial. A survey involving many European countries needs time for preparation and conduct. Materials for quality control prepared for all steps of recruitment, fieldwork and sampling proved to be important to warrant reliable results.

T lymphocytes export proteasomes by way of microparticles: a possible mechanism for generation of extracellular proteasomes.

The 20S proteasome is almost exclusively localized within cells. High levels of extracellular proteasomes are also found circulating in the blood plasma of patients suffering from a variety of inflammatory, autoimmune and neoplastic diseases. However, the origin of these proteasomes remained enigmatic. Since the proteome of microparticles, small membrane enclosed vesicles released from cells, was shown to contain proteasomal subunits, we studied whether intact proteasomes are actively released into the extracellular space. Using human primary T lymphocytes stimulated with CaCl2 and the calcium ionophore A23187 to induce membrane blebbing we demonstrate that microparticles contain proteolytically active 20S proteasomes as well as the proteasome activator PA28 and subunits of the 19S proteasome regulator. Furthermore, our experiments reveal that incubation of in vitro generated T lymphocyte-microparticles with sphingomyelinase results in the hydrolysis of the microparticle membranes and subsequent release of proteasomes from the vesicles. Thus, we here show for the first time that functional proteasomes can be exported from activated immune cells by way of microparticles, the dissolution of which may finally lead to the generation of extracellular proteasomes.

The FAT10- and ubiquitin-dependent degradation machineries exhibit common and distinct requirements for MHC class I antigen presentation.

Like ubiquitin (Ub), the ubiquitin-like protein FAT10 can serve as a signal for proteasome-dependent protein degradation. Here, we investigated the contribution of FAT10 substrate modification to MHC class I antigen presentation. We show that N-terminal modification of the human cytomegalovirus-derived pp65 antigen to FAT10 facilitates direct presentation and dendritic cell-mediated cross-presentation of the HLA-A2 restricted pp65(495-503) epitope. Interestingly, our data indicate that the pp65 presentation initiated by either FAT10 or Ub partially relied on the 19S proteasome subunit Rpn10 (S5a). However, FAT10 distinguished itself from Ub in that it promoted a pp65 response which was not influenced by immunoproteasomes or PA28. Further divergence occurred at the level of Ub-binding proteins with NUB1 supporting the pp65 presentation arising from FAT10, while it exerted no effect on that initiated by Ub. Collectively, our data establish FAT10 modification as a distinct and alternative signal for facilitated MHC class I antigen presentation.

Intestinal epithelial c-Maf expression determines enterocyte differentiation and nutrient uptake in mice.

The primary function of the small intestine (SI) is to absorb nutrients to maintain whole-body energy homeostasis. Enterocytes are the major epithelial cell type facilitating nutrient sensing and uptake. However, the molecular regulators governing enterocytes have remained undefined. Here, we identify c-Maf as an enterocyte-specific transcription factor within the SI epithelium. c-Maf expression was determined by opposing Noggin/BMP signals and overlapped with the zonated enrichment of nutrient transporters in the mid-villus region. Functionally, enterocytes required c-Maf to appropriately differentiate along the villus axis. Specifically, gene programs controlling carbohydrate and protein absorption were c-Maf-dependent. Consequently, epithelial cell-specific c-Maf deletion resulted in impaired enterocyte maturation and nutrient uptake, including defects in the adaptation to different nutrient availability. Concomitantly, intraepithelial lymphocytes were less abundant, while commensal epithelial cell-attaching SFB overgrew in a c-Maf-deficient environment, highlighting the close interdependence between the intestinal epithelium, immune system, and microbiota. Collectively, our data identified c-Maf as a key regulator of SI enterocyte differentiation and function, essential for nutrient, immune, and microbial homeostasis.

The metabolic growth limitations of petite cells lacking the mitochondrial genome.

Eukaryotic cells can survive the loss of their mitochondrial genome, but consequently suffer from severe growth defects. 'Petite yeasts', characterized by mitochondrial genome loss, are instrumental for studying mitochondrial function and physiology. However, the molecular cause of their reduced growth rate remains an open question. Here we show that petite cells suffer from an insufficient capacity to synthesize glutamate, glutamine, leucine and arginine, negatively impacting their growth. Using a combination of molecular genetics and omics approaches, we demonstrate the evolution of fast growth overcomes these amino acid deficiencies, by alleviating a perturbation in mitochondrial iron metabolism and by restoring a defect in the mitochondrial tricarboxylic acid cycle, caused by aconitase inhibition. Our results hence explain the slow growth of mitochondrial genome-deficient cells with a partial auxotrophy in four amino acids that results from distorted iron metabolism and an inhibited tricarboxylic acid cycle.

Fluorescent-magnetic hybrid nanoparticles induce a dose-dependent increase in proinflammatory response in lung cells in vitro correlated with intracellular localization.

Iron-platinum nanoparticles embedded in a poly(methacrylic acid) (PMA) polymer shell and fluorescently labeled with the dye ATTO 590 (FePt-PMA-ATTO-2%) are investigated in terms of their intracellular localization in lung cells and potential to induce a proinflammatory response dependent on concentration and incubation time. A gold core coated with the same polymer shell (Au-PMA-ATTO-2%) is also included. Using laser scanning and electron microscopy techniques, it is shown that the FePt-PMA-ATTO-2% particles penetrate all three types of cell investigated but to a higher extent in macrophages and dendritic cells than epithelial cells. In both cell types of the defense system but not in epithelial cells, a particle-dose-dependent increase of the cytokine tumor necrosis factor alpha (TNFalpha) is found. By comparing the different nanoparticles and the mere polymer shell, it is shown that the cores combined with the shells are responsible for the induction of proinflammatory effects and not the shells alone. It is concluded that the uptake behavior and the proinflammatory response upon particle exposure are dependent on the time, cell type, and cell culture.

Blm10 binds to pre-activated proteasome core particles with open gate conformation.

Blm10 is bound to the yeast proteasome core particle, a crucial protease of eukaryotic cells [corrected]. Two gates, at both ends of the CP, control the access of protein substrates to the catalytic cavity of the CP. Normally, substrate access is auto-inhibited by a closed gate conformation unless regulatory complexes are bound to the CP and translocate protein substrates in an ATP-dependent manner. Here, we provide evidence that Blm10 recognizes pre-activated open gate CPs, which are assumed to exist in an equilibrium with inactive closed gate CP. Consequently, single-capped Blm10-CP shows peptide hydrolysis activity. Under conditions of disturbed CP assembly, as well as in open gate mutants, pre-activated CP or constitutively active CP, respectively, prevail. Then, Blm10 sequesters disordered and open gate CP by forming double-capped Blm10(2)-CP in which peptide hydrolysis activity is repressed. We conclude that Blm10 distinguishes between gate conformations and regulates the activation of CP.

Diesel exhaust particles modulate the tight junction protein occludin in lung cells in vitro.

BACKGROUND: Using an in vitro triple cell co-culture model consisting of human epithelial cells (16HBE14o-), monocyte-derived macrophages and dendritic cells, it was recently demonstrated that macrophages and dendritic cells create a transepithelial network between the epithelial cells to capture antigens without disrupting the epithelial tightness. The expression of the different tight junction proteins in macrophages and dendritic cells, and the formation of tight junction-like structures with epithelial cells has been demonstrated. Immunofluorescent methods combined with laser scanning microscopy and quantitative real-time polymerase chain reaction were used to investigate if exposure to diesel exhaust particles (DEP) (0.5, 5, 50, 125 mug/ml), for 24 h, can modulate the expression of the tight junction mRNA/protein of occludin, in all three cell types. RESULTS: Only the highest dose of DEP (125 mug/ml) seemed to reduce the occludin mRNA in the cells of the defence system however not in epithelial cells, although the occludin arrangement in the latter cell type was disrupted. The transepithelial electrical resistance was reduced in epithelial cell mono-cultures but not in the triple cell co-cultures, following exposure to high DEP concentration. Cytotoxicity was not found, in either epithelial mono-cultures nor in triple cell co-cultures, after exposure to the different DEP concentrations. CONCLUSION: We concluded that high concentrations of DEP (125 mug/ml) can modulate the tight junction occludin mRNA in the cells of the defence system and that those cells play an important role maintaining the epithelial integrity following exposure to particulate antigens in lung cells.

Virosomes can enter cells by non-phagocytic mechanisms.

Phagocytosis of fine particles (1 microm) by macrophages is a ligand-receptor-mediated, actin-based process, whereas the entering of smaller particles (< or = 0.2 microm) in macrophages occurs also by other mechanisms. Virosomes with a diameter of 0.12-0.18 microm are widely used as carrier systems for drugs, vectors, and plasmids in cancer therapy or for vaccines. We investigated their interactions with airway cells, in particular penetration into monocyte-derived macrophages. The microscopic analysis of phagocytic cells incubated with virosomes and polystyrene particles showed that virosomes and particles penetrated cells even in the presence of cytochalasin D, a drug inhibiting actin-based phagocytosis. The charge of the virosomes and particles did not influence their penetration. Also, different inhibitors of endocytotic pathways did not prevent the particles and virosomes from penetrating into the cells. Additionally, to study the ability of virosomes to overcome the epithelial airway barrier, a triple cell co-culture model composed of epithelial cells, monocyte-derived macrophages and dendritic cells of the respiratory tract was used. We found virosomes and polystyrene particles in both populations of antigen-presenting cells, monocyte-derived macrophages, and dendritic cells, in the latter even if they were not directly exposed. In conclusion, virosomes are readily taken up by monocyte-derived macrophages, both by conventional phagocytosis and by actin-independent mechanisms. Further, they can penetrate the airway barrier and reach resident dendritic cells. Therefore, virosomes are promising vaccine candidates.

Exhaled nitric oxide distinguishes between subgroups of preschool children with respiratory symptoms.

BACKGROUND: Respiratory symptoms are common in early childhood. The clinical characterization of disease presentation and hence its likely disease progression has so far been proven difficult. OBJECTIVE: To investigate whether exhaled nitric oxide (NO) could be helpful to distinguish between subgroups of nonwheezy and wheezy young children less than 4 years of age. METHODS: Exhaled NO was measured in 391 children (age 3-47 months) with nonwheezy and wheezy respiratory symptoms. Children were divided into 3 groups: children with recurrent cough but no history of wheeze (group 1), with early recurrent wheeze and a loose index for the prediction of asthma at school age (group 2), and with frequent recurrent wheeze and a stringent index for the prediction of asthma at school age (group 3). RESULTS: Children from group 3 showed significantly higher median (interquartile range) fractional exhaled NO (FeNO) levels (11.7 [11.85]) than children from groups 1 (6.5 [5.5]; P < .001) and 2 (6.4 [6.5]; P < .001). No difference in FeNO levels was found between children from groups 1 and 2 (P = .91). CONCLUSION: Wheezy young children less than 4 years of age with a stringent index for the prediction of asthma at school age have elevated levels of FeNO compared with children with recurrent wheeze and a loose index for the prediction of asthma at school age or children with recurrent cough.

20 S proteasomes are imported as precursor complexes into the nucleus of yeast.

The mechanism by which yeast 20 S proteasomes are imported into the nucleus is still unresolved. Here, we provide the first evidence that 20 S proteasomes are imported as precursor complexes into the nucleus. By using the srp1-49 mutant which is deficient in nuclear import of cargos with classical nuclear localization sequences (cNLS), we show that proteasome precursor complexes associate with importin/karyopherin alphabeta, the cNLS receptor, and that they accumulate inside the cytoplasm. Reconstitution assays revealed that only precursor complexes are targeted to the nuclear envelope (NE) by karyopherin alphabeta. In support, the green fluorescent protein (GFP)-labelled maturation factor Ump1, marking precursor complexes, mainly localizes to the nucleus and around the NE. Our data suggest that nuclear 20 S proteasomes are finally matured inside the nucleus.