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Allergic inflammation has crucial roles in allergic diseases such as asthma. It is therefore important to understand why and how the immune system responds to allergens. Here we found that full-length interleukin 33 (IL-33), an alarmin cytokine with critical roles in type 2 immunity and asthma, functioned as a protease sensor that detected proteolytic activities associated with various environmental allergens across four kingdoms, including fungi, house dust mites, bacteria and pollens. When exposed to allergen proteases, IL-33 was rapidly cleaved in its central 'sensor' domain, which led to activation of the production of type 2 cytokines in group 2 innate lymphoid cells. Preventing cleavage of IL-33 reduced allergic airway inflammation. Our findings reveal a molecular mechanism for the rapid induction of allergic type 2 inflammation following allergen exposure, with important implications for allergic diseases.

Mycolic acids are major and specific long-chain fatty acids of the cell envelope of several important human pathogens such as Mycobacterium tuberculosis, M. leprae, and Corynebacterium diphtheriae. Their biosynthesis is essential for mycobacterial growth and represents an attractive target for developing new antituberculous drugs. We have previously shown that the pks13 gene encodes condensase, the enzyme that performs the final condensation step of mycolic acid biosynthesis and is flanked by two genes, fadD32 and accD4. To determine the functions of the gene products we generated two mutants of C. glutamicum with an insertion/deletion within either fadD32 or accD4. The two mutant strains were deficient in mycolic acid production and exhibited the colony morphology that typifies the mycolate-less mutants of corynebacteria. Application of multiple analytical approaches to the analysis of the mutants demonstrated the accumulation of a tetradecylmalonic acid in the ⌬fadD32::km mutant and its absence from the ⌬accD4::km strain. The parental corynebacterial phenotype was restored upon the transfer of the wild-type fadD32 and accD4 genes in the mutants. These data demonstrated that both FadD32 and AccD4-containing acyl-CoA carboxylase are required for the production of mycolic acids. They also prove that the proteins catalyze, respectively, the activation of one fatty acid substrate and the carboxylation of the other substrate, solving the long-debated question of the mechanism involved in the condensation reaction. We used comparative genomics and applied a combination of molecular biology and proteomic technologies to the analysis of proteins that co-immunoprecipitated with AccD4. This resulted in the identification of AccA3 and AccD5 as subunits of the acyl-CoA carboxylase. Finally, we used conditionally replicative plasmids to show that both the fadD32 and accD4 genes are essential for the survival of M. smegmatis. Thus, in addition to Pks13, FadD32 and AccD4 are promising targets for the development of new antimicrobial drugs against pathogenic species of mycobacteria and related microorganisms.

The last steps of the biosynthesis of mycolic acids, essential and specific lipids of Mycobacterium tuberculosis and related bacteria, are catalyzed by proteins encoded by the fadD32-pks13-accD4 cluster. Here, we produced and purified an active form of the Pks13 polyketide synthase, with a phosphopantetheinyl (P-pant) arm at both positions Ser-55 and Ser-1266 of its two acyl carrier protein (ACP) domains. Combination of liquid chromatography-tandem mass spectrometry of protein tryptic digests and radiolabeling experiments showed that, in vitro, the enzyme specifically loads long-chain 2-carboxyacyl-CoA substrates onto the P-pant arm of its C-terminal ACP domain via the acyltransferase domain. The acyl-AMPs produced by the FadD32 enzyme are specifically transferred onto the ketosynthase domain after binding to the P-pant moiety of the N-terminal ACP domain of Pks13 (N-ACP Pks13 ). Unexpectedly, however, the latter step requires the presence of active FadD32. Thus, the couple FadD32-(N-ACP Pks13 ) composes the initiation module of the mycolic condensation system. Pks13 ultimately condenses the two loaded fatty acyl chains to produce ␣-alkyl ␤-ketoacids, the precursors of mycolic acids. The developed in vitro assay will constitute a strategic tool for antimycobacterial drug screening.

A posttranslational protein O-mannosylation process resembling that found in fungi and animals has been reported in the major human pathogen Mycobacterium tuberculosis (Mtb) and related actinobacteria. However, the role and incidence of this process, which is essential in eukaryotes, have never been explored in Mtb. We thus analyzed the impact of interrupting O-mannosylation in the nonpathogenic saprophyte Mycobacterium smegmatis and in the human pathogen Mtb by inactivating the respective putative protein mannosyl transferase genes Msmeg_5447 and Rv1002c. Loss of protein O-mannosylation in both mutant strains was unambiguously demonstrated by efficient mass spectrometry-based glycoproteomics analysis. Unexpectedly, although the M. smegmatis phenotype was unaffected by the lack of manno-proteins, the Mtb mutant had severely impacted growth in vitro and in cellulo associated with a strong attenuation of its pathogenicity in immunocompromised mice. These data are unique in providing evidence of the biological significance of protein O-mannosylation in mycobacteria and demonstrate the crucial contribution of this protein posttranslational modification to Mtb virulence in the host.protein glycosylation | O-glycosylation | proteomics

In eukaryotic cells, intracellular protein breakdown is mainly performed by the ubiquitin–proteasome system. Proteasomes are supramolecular protein complexes formed by the association of multiple sub-complexes and interacting proteins. Therefore, they exhibit a very high heterogeneity whose function is still not well understood. Here, using a newly developed method based on the combination of affinity purification and protein correlation profiling associated with high-resolution mass spectrometry, we comprehensively characterized proteasome heterogeneity and identified previously unknown preferential associations within proteasome sub-complexes. In particular, we showed for the first time that the two main proteasome subtypes, standard proteasome and immunoproteasome, interact with a different subset of important regulators. This trend was observed in very diverse human cell types and was confirmed by changing the relative proportions of both 20S proteasome forms using interferon-γ. The new method developed here constitutes an innovative and powerful strategy that could be broadly applied for unraveling the dynamic and heterogeneous nature of other biologically relevant supramolecular protein complexes.

BackgroundTo date, all studies conducted on breast cancer diagnosis have focused on the expression of the full-length 66-kDa estrogen receptor alpha (ERα66). However, much less attention has been paid to a shorter 46-kDa isoform (ERα46), devoid of the N-terminal region containing the transactivation function AF-1. Here, we investigated the expression levels of ERα46 in breast tumors in relation to tumor grade and size, and examined the mechanism of its generation and its specificities of coregulatory binding and its functional activities.MethodsUsing approaches combining immunohistochemistry, Western blotting, and proteomics, antibodies allowing ERα46 detection were identified and the expression levels of ERα46 were quantified in 116 ERα-positive human breast tumors. ERα46 expression upon cellular stress was studied, and coregulator bindings, transcriptional, and proliferative response were determined to both ERα isoforms.ResultsERα46 was expressed in over 70% of breast tumors at variable levels which sometimes were more abundant than ERα66, especially in differentiated, lower-grade, and smaller-sized tumors. We also found that ERα46 can be generated via internal ribosome entry site-mediated translation in the context of endoplasmic reticulum stress. The binding affinities of both unliganded and fully-activated receptors towards co-regulator peptides revealed that the respective potencies of ERα46 and ERα66 differ significantly, contributing to the differential transcriptional activity of target genes to 17β estradiol (E2). Finally, increasing amounts of ERα46 decrease the proliferation rate of MCF7 tumor cells in response to E2.ConclusionsWe found that, besides the full-length ERα66, the overlooked ERα46 isoform is also expressed in a majority of breast tumors. This finding highlights the importance of the choice of antibodies used for the diagnosis of breast cancer, which are able or not to detect the ERα46 isoform. In addition, since the function of both ERα isoforms differs, this work underlines the need to develop new technologies in order to discriminate ERα66 and ERα46 expression in breast cancer diagnosis which could have potential clinical relevance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0780-7) contains supplementary material, which is available to authorized users.

The neurotropic virus Borna disease virus (BDV) persists in the central nervous systems of a wide variety of vertebrates and causes behavioral disorders. BDV represents an intriguing example of a virus whose persistence in neurons leads to altered brain function in the absence of overt cytolysis and inflammation. The bases of BDV-induced behavioral impairment remain largely unknown. To better characterize the neuronal response to BDV infection, we compared the proteomes of primary cultures of cortical neurons with and without BDV infection. We used two-dimensional liquid chromatography fractionation, followed by protein identification by nanoliquid chromatography-tandem mass spectrometry. This analysis revealed distinct changes in proteins implicated in neurotransmission, neurogenesis, cytoskeleton dynamics, and the regulation of gene expression and chromatin remodeling. We also demonstrated the selective interference of BDV with processes related to the adaptative response of neurons, i.e., defects in proteins regulating synaptic function, global rigidification of the cytoskeleton network, and altered expression of transcriptional and translational repressors. Thus, this work provides a global view of the neuronal changes induced by BDV infection together with new clues to understand the mechanisms underlying the selective interference with neuronal plasticity and remodeling that characterizes BDV persistence.The analysis of the response of a host cell to a pathogenic microorganism represents a daunting task, as it often results in complex and numerous changes in gene expression (37). Generally, these changes strongly depend on the nature of the pathogen interaction with its host. In the case of the central nervous system (CNS), the deleterious consequences of viral infection are often due to the cytopathic nature of viral replication (25, 38), or, alternatively, they can result from the immune response to the virus (31). However, some viruses can also persist in the CNS and cause diseases without an overt cytopathic effect or inflammation (1). These viral models provide a unique opportunity to unravel the molecular mechanisms underlying virus-induced neuronal dysfunction. A better understanding of the pathological consequences of viral persistence in the CNS may help to shed light on the pathogenesis of many neurological diseases of unclear etiology where viruses are thought to play a role (34, 47).Infection with Borna disease virus (BDV) represents an ideal paradigm for the investigation of the neuronal consequences due to the persistence of a noncytolytic virus. BDV is an enveloped virus with a nonsegmented, negative-strand RNA genome (13, 44). BDV infects a wide variety of mammals (35), possibly including humans (6, 29). Infected hosts develop a large spectrum of neurological disorders, ranging from immune-mediated diseases to behavioral alterations without inflammation (35, 41), reminiscent of symptoms observed in certain human neuropsychiatric diseases (28). These neurobehavioral manifestations reflect th...