Auswahl der wissenschaftlichen Literatur zum Thema „Transmembrane mucins“

Mucosal surfaces line our body cavities and provide the interaction surface between commensal and pathogenic microbiota and the host. The barrier function of the mucosal layer is largely maintained by gel-forming mucin proteins that are secreted by goblet cells. In addition, mucosal epithelial cells express cell-bound mucins that have both barrier and signaling functions. The family of transmembrane mucins consists of diverse members that share a few characteristics. The highly glycosylated extracellular mucin domains inhibit invasion by pathogenic bacteria and can form a tight mesh structure that protects cells in harmful conditions. The intracellular tails of transmembrane mucins can be phosphorylated and connect to signaling pathways that regulate inflammation, cell-cell interactions, differentiation, and apoptosis. Transmembrane mucins play important roles in preventing infection at mucosal surfaces, but are also renowned for their contributions to the development, progression, and metastasis of adenocarcinomas. In general, transmembrane mucins seem to have evolved to monitor and repair damaged epithelia, but these functions can be highjacked by cancer cells to yield a survival advantage. This review presents an overview of the current knowledge of the functions of transmembrane mucins in inflammatory processes and carcinogenesis in order to better understand the diverse functions of these multifunctional proteins.

Mucin glycans are an important component of the mucus barrier and a vital defence against physical and chemical damage as well as pathogens. There are 20 mucins in the human body, which can be classified into secreted mucins and transmembrane mucins according to their distributions. The major difference between them is that secreted mucins do not have transmembrane structural domains, and the expression of each mucin is organ and cell-specific. Under physiological conditions, mucin glycans are involved in the composition of the mucus barrier and thus protect the body from infection and injury. However, abnormal expression of mucin glycans can lead to the occurrence of diseases, especially cancer, through various mechanisms. Therefore, targeting mucin glycans for the diagnosis and treatment of cancer has always been a promising research direction. Here, we first summarize the main types of glycosylation (O-GalNAc glycosylation and N-glycosylation) on mucins and the mechanisms by which abnormal mucin glycans occur. Next, how abnormal mucin glycans contribute to cancer development is described. Finally, we summarize MUC1-based antibodies, vaccines, radio-pharmaceuticals, and CAR-T therapies using the best characterized MUC1 as an example. In this section, we specifically elaborate on the recent new cancer therapy CAR-M, which may bring new hope to cancer patients.

Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pulmonary disease with a median survival of 3–5 years after diagnosis. Recent evidence identifies mucins as key effectors in cell growth and tissue remodeling processes compatible with the processes observed in IPF. Mucins are classified in two groups depending on whether they are secreted (secreted mucins) or tethered to cell membranes (transmembrane mucins). Secreted mucins (MUC2, MUC5AC, MUC5B, MUC6-8 and MUC19) are released to the extracellular medium and recent evidence has shown that a promoter polymorphism in the secreted mucin MUC5B is associated with IPF risk. Otherwise, transmembrane mucins (MUC1, MUC3, MUC4, MUC12-17 and MUC20) have a receptor-like structure, sensing the external environment and activating intracellular signal transduction pathways essential for mucosal maintenance and damage repair. In this context, the extracellular domain can be released to the external environment by metalloproteinase action, increased in IPF, thus activating fibrotic processes. For example, several studies have reported increased serum extracellular secreted KL6/MUC1 during IPF acute exacerbation. Moreover, MUC1 and MUC4 overexpression in the main IPF cells has been observed. In this review we summarize the current knowledge of mucins as promising druggable targets for IPF.

Mucins play an essential role in protecting the respiratory tract against microbial infections while also acting as binding sites for bacterial and viral adhesins. The heavily O-glycosylated gel-forming mucins MUC5AC and MUC5B eliminate pathogens by mucociliary clearance. Transmembrane mucins MUC1, MUC4, and MUC16 can restrict microbial invasion at the apical surface of the epithelium. In this study, we determined the impact of host mucins and mucin glycans on epithelial entry of SARS-CoV-2. Human lung epithelial Calu-3 cells express the SARS-CoV-2 entry receptor ACE2 and high levels of glycosylated MUC1, but not MUC4 and MUC16, on their cell surface. The O-glycan-specific mucinase StcE specifically removed the glycosylated part of the MUC1 extracellular domain while leaving the underlying SEA domain and cytoplasmic tail intact. StcE treatment of Calu-3 cells significantly enhanced infection with SARS-CoV-2 pseudovirus and authentic virus, while removal of sialic acid and fucose from the epithelial surface did not impact viral entry. In Calu-3 cells, the transmembrane mucin MUC1 and ACE2 are located to the apical surface in close proximity and StcE treatment results in enhanced binding of purified spike protein. Both MUC1 and MUC16 are expressed on the surface of human organoid-derived air-liquid interface (ALI) differentiated airway cultures and StcE treatment led to mucin removal and increased levels of SARS-CoV-2 replication. In these cultures, MUC1 was highly expressed in non-ciliated cells while MUC16 was enriched in goblet cells. In conclusion, the glycosylated extracellular domains of different transmembrane mucins might have similar protective functions in different respiratory cell types by restricting SARS-CoV-2 binding and entry.

Mucus overproduction and hypersecretion are commonly observed in chronic inflammatory lung disease. Mucins are gel-forming glycoproteins that can be stimulated by a variety of mediators. The present review addresses the mechanisms involved in the upregulation of secreted mucins. Mucin induction by neutrophil elastase, bacteria, cytokines, growth factors, smoke and cystic fibrosis transmembrane conductance regulator malfunction are also discussed.

Generating the barriers that protect our inner surfaces from bacteria and other challenges requires large glycoproteins called mucins. These come in two types, gel-forming and transmembrane, all characterized by large, highly O-glycosylated mucin domains that are diversely decorated by Golgi glycosyltransferases to become extended rodlike structures. The general functions of mucins on internal epithelial surfaces are to wash away microorganisms and, even more importantly, to build protective barriers. The latter function is most evident in the large intestine, where the inner mucus layer separates the numerous commensal bacteria from the epithelial cells. The host's conversion of MUC2 to the outer mucus layer allows bacteria to degrade the mucin glycans and recover the energy content that is then shared with the host. The molecular nature of the mucins is complex, and how they construct the extracellular complex glycocalyx and mucus is poorly understood and a future biochemical challenge.

Mucins are high molecular weight glycoproteins with complex oligosaccharide side chains attached to the apomucin protein backbone by O-glycosidic linkage; they are found in crude mucus gels that protect epithelial surfaces in the major tracts of the body and as transmembrane proteins expressed on the apical cell surface of glandular and ductal epithelia of various organs. Changes in the sequence of glycosylation of mucins in different settings generate a variety of epitopes in the oligosaccharide side chains of mucins, including newly expressed blood-group antigens, distinguishing between normal and diseased states. Tumour-associated epitopes on mucins and their antigenicity make them suitable as immunotargets on malignant epithelial cells and their secretions, creating a surge of interest in mucins as diagnostic and prognostic markers for various diseases, and even influencing the design of mucin-based vaccines. This review discusses the emerging roles of mucins such as MUC1 and MUC4 in cancer and some other diseases, and stresses how underglycosylated and truncated mucins are exploited as markers of disease and to monitor widespread metastasis, making them useful in patient management. Furthermore the type, pattern and amount of mucin secreted in some tissues have been considered in the classification and terminology of neoplasia and in specific organs such as the pancreas. These factors have been instrumental in pathological classification, diagnosis and prognostication of neoplasia.

Human conjunctival epithelium cells (HCEC) line the inner surface of the eyelid and cover the sclera and are continuously subjected to wall shear stresses (WSS). The effects of external forces on the conjunctival epithelium are not fully known. The conjunctival epithelium contains stratified squamous cells that synthesize the membrane-spanning mucins MUC1 and MUC16, which play important roles in protecting the ocular surface. Alterations in both gel-forming and membrane-tethered mucins occur in drying ocular surface diseases. The aim of this study was to explore the mechanobiological characteristics of transmembrane mucin secretion and cellular alterations of primary HCEC exposed to airflow-induced WSS perturbations. We exposed the HCEC to a steady WSS of 0.5 dyne/cm2 for durations of 15 and 30 min. Cytoskeletal alterations and MUC1 secretions were studied using immunohistochemically fluorescent staining with specific antibodies. We investigated for the first time an in vitro model of membrane-tethered mucin secretion by HCEC in response to WSS. The exposure of HCEC to WSS increased the polymerization of F-actin, altered the cytoskeletal shape and reduced the secretion of membrane-tethered MUC1.

Mucins are a family of secreted and transmembrane glycoproteins characterized by a massive domain of dense O-glycosylation on serine and threonine residues. Mucins are intimately involved in immunity and cancer, yet elucidation of the biological roles of their glycodomains has been complicated by their massive size, domain polymorphisms, and variable glycosylation patterns. Here we developed a synthetic route to a library of compositionally defined, high-molecular weight, dual end-functionalized mucin glycodomain constructs via N-carboxyanhydride polymerization. These glycopolypeptides are the first synthetic analogs to our knowledge to feature the native α-GalNAc linkage to serine with molecular weights similar to native mucins, solving a nearly 50-year synthetic challenge. Physical characterization of the mimics revealed insights into the structure and properties of mucins. The synthetic glycodomains were end-functionalized with an optical probe and a tetrazine moiety, which allowed site-specific bioorthogonal conjugation to an engineered membrane protein on live mammalian cells. This strategy in protein engineering will open avenues to explore the biological roles of cell surface mucins.

L’étude de la lubrification orale devient une problématique actuelle pour l’industrie agroalimentaire. Les analyses quantitatives permettent de comprendre et d’anticiper des mécanismes physiologiques, tels que la prédiction des phénomènes d’astringence des produits alimentaires. L’astringence se manifeste par une diminution de la lubrification de la muqueuse orale après la consommation de produits d’origine végétale. Cependant, les recherches actuelles sur la lubrification orale s’appuient sur des matériaux synthétiques qui représentent mal les tissus buccaux. Elles négligent les interactions entre les protéines salivaires sécrétées et les protéines transmembranaires, limitant ainsi la compréhension des mécanismes de lubrification.Cette thèse s’inscrit dans le projet MACARON qui vise à étudier le rôle de la muqueuse orale dans la perception sensorielle. Des modèles in vitro de muqueuse orale qui expriment la protéine transmembranaire MUC1 ont été développés pour simuler les interactions fondamentales entre MUC1 et les protéines salivaires. Ces interactions sont responsables de la lubrification et de l’hydratation des tissus. Par ailleurs, un tribomètre a été conçu pour effectuer des tests tribologiques in vitro sur ces modèles d’épithélium afin de suivre leur état de lubrification.Cette thèse se concentre ainsi sur l’étude des mécanismes moléculaires de la lubrification orale à travers une approche tribologique in vitro, en utilisant des paramètres physiques macro et micrométriques. Ce manuscrit propose en premier lieu une étude sur le rôle crucial de la mucine MUC1 et de sa structure dans la lubrification orale. La présence de MUC1 améliore la lubrification grâce à une meilleure rétention des protéines salivaires à la surface cellulaire. Ensuite, le manuscrit présente une exploration des mécanismes moléculaires de l’astringence. Les essais tribologiques in vitro en présence de composés astringents montrent que ces substances forment des agrégations à la surface épithéliale qui diminuent la lubrification orale. Parallèlement, nos travaux montrent que des mécanismes de protection, notamment la dissociation de MUC1 et l’interaction des protéines riches en proline avec les tanins, atténuent ces effets néfastes sur la lubrification.À travers une étude complémentaire, des corrélations entre la perception sensorielle et nos propriétés physiques mesurées sont établies, démontrant la capacité de notre méthodologie à classer des individus selon leur sensibilité à l’astringence. Enfin, la dernière étude présente le développement d’un nouveau modèle de muqueuse orale visant à reproduire les propriétés mécaniques et physico-chimiques de la muqueuse in vivo.Cette thèse propose une méthodologie innovante pour l’étude de la lubrification orale, en particulier en s’intéressant à des mécanismes responsables de la sensation d’astringence grâce à l’utilisation de modèles de muqueuse toujours plus proches des tissus oraux physiologiques
The study of oral lubrication has become a current concern for the food industry. Quantitative analyses allow for understanding and anticipating physiological mechanisms, such as predicting astringency phenomena in food products. Astringency is characterized by a decrease in oral mucosa lubrication following the consumption of plant-based products. However, current research on oral lubrication relies on synthetic materials that poorly represent oral tissues, neglecting interactions between secreted salivary proteins and transmembrane proteins, thus limiting the understanding of lubrication mechanisms. This thesis is part of the MACARON project, which aims to investigate the role of oral mucosa in sensory perception. In vitro models of oral mucosa expressing the transmembrane protein MUC1 have been developed to simulate fundamental interactions between MUC1 and salivary proteins responsible for tissue lubrication and hydration. Additionally, a tribometer has been designed to perform in vitro tribological tests on these epithelial models to monitor their lubrication state. Thus, this thesis focuses on studying the molecular mechanisms of oral lubrication through an in vitro tribological approach, using macro- and micrometric physical parameters. Firstly, this manuscript provides a study on the crucial role of MUC1 mucin and its structure in oral lubrication. The presence of MUC1 enhances lubrication by improving the retention of salivary proteins on the cell surface. Secondly, the manuscript explores molecular mechanisms of astringency. In vitro tribological tests in the presence of astringent compounds show that these substances form aggregations on the epithelial surface, reducing oral lubrication. Concurrently, our work demonstrates protective mechanisms, including the dissociation of MUC1 and the interaction of proline-rich proteins with tannins, mitigating these adverse effects on lubrication. Through additional study, correlations between sensory perception and our measured physical properties are established, demonstrating the ability of our methodology to classify individuals based on their sensitivity to astringency. Finally, the last study presents the development of a new oral mucosa model aiming to reproduce mechanical and physicochemical properties of in vivo mucosa. This thesis proposes an innovative methodology for studying oral lubrication, particularly focusing on mechanisms responsible for astringency sensation through the use of mucosa models increasingly closer to physiological oral tissues

Background: Excess plugging of small airways is associated with premature death in chronic obstructive pulmonary disease (COPD). Over-expression of beta-epithelial sodium channel (β-ENaC) in airway epithelia in mice resulted in plugging of small airways while cystic fibrosis transmembrane regulator (CFTR) negatively regulated ENaC activity in cell models. Purpose: To test the hypothesis that accumulation of mucus exudates observed with the progression of COPD is related to excess airway epithelial sodium re-absorption as a result of over-expression of β-ENaC and reduced expression of CFTR by small airway epithelia. Methods: Small airway epithelial samples from frozen lungs from patients at different levels of COPD severity were isolated by laser capture microdissection (LCM). β-ENaC, CFTR, and β-actin (control) gene expression was determined by qRT-PCR and compared to expression in entire airways and lung parenchyma surrounding these airways. β-ENaC protein as well as epithelial mucin expression and mucus plugging were localized and quantified after immunohistochemical and periodic acid Schiff staining, respectively. Results: β-ENaC mRNA expression had a strong positive correlation with that of CFTR (p