Macroautophagy, a major self-degradation pathway in eukaryotic cells, utilizes autophagosomes to transport self-material to lysosomes for degradation. While microtubular transport is crucial for the proper function of autophagy, the exact roles of factors responsible for positioning autophagosomes remain incompletely understood. In this study, we performed a loss-of-function genetic screen targeting genes potentially involved in microtubular motility. A genetic background that blocks autophagosome-lysosome fusions was used to accurately analyze autophagosome positioning. We discovered that pre-fusion autophagosomes move towards the non-centrosomal microtubule organizing center (ncMTOC) in Drosophila fat cells, which requires a dynein-dynactin complex. This process is regulated by the small GTPases Rab7 and Rab39 together with their adaptors: Epg5 and ema, respectively. The dynein-dependent movement of vesicles toward the nucleus/ncMTOC is essential for efficient autophagosomal fusions with lysosomes and subsequent degradation. Remarkably, altering the balance of kinesin and dynein motors changes the direction of autophagosome movement, indicating a competitive relationship where normally dynein-mediated transport prevails. Since pre-fusion lysosomes were positioned similarly to autophagosomes, it indicates that pre-fusion autophagosomes and lysosomes converge at the ncMTOC, which increases the efficiency of vesicle fusions.
Proper functioning of the precisely controlled endolysosomal system is essential for maintaining the homeostasis of the entire cell. Tethering factors play pivotal roles in mediating the fusion of different transport vesicles, such as endosomes or autophagosomes with each other or with lysosomes. In this work, we uncover several new interactions between the endolysosomal tethering factors Rabenosyn-5 (Rbsn) and the HOPS and CORVET complexes. We find that Rbsn binds to the HOPS/CORVET complexes mainly via their shared subunit Vps18 and we mapped this interaction to the 773-854 region of Vps18. Based on genetic rescue experiments, the binding between Rbsn and Vps18 is required for endosomal transport and is dispensable for autophagy. Moreover, Vps18 seems to be important for β1 integrin recycling by binding to Rbsn and its known partner Vps45.
Kutatasunk soran uj hajlamosito geneket irtunk le, melyet kozrejatszhatnak a gluten-enteropathia (coeliakia) kialakulasaban, ezek befolyasoljak a T lymphocytak ereset es kollaboraciojat a B sejtekkel, a toll-like receptorokat es a gyulladas soran termelődő cytokineket. Megallapitottuk, hogy a coeliakia kialakulasa es klinikai megjelenese asszociaciot mutat a haptoglobin polimorfizmussal is, melyről a mi kozlesunket kovetően fuggetlen kutatok igazoltak, hogy egyik altipusa azonos vekonybel permeabilitasaban kulcsszerepet jatszo zonulin molekulaval. A kutatas soran azonositottuk a coeliakia-specifikus autoantitestek fő kotőhelyet az autoantigen, a 2-es tipusu transzglutaminaz enzim felszinen. Megallapitottuk, hogy a coeliakia antitestek betegseg-specifikusan ugyanazt a komplex, haromdimenzios epitopot ismerik fel. Sejtkulturaban a coeliakia antitestek gatoljak az erek kepződeset es fokozzak azok permeabilitasat, elsősorban a RhoA tulzott aktivalasan keresztul. Megszerveztuk es elvegeztuk az első reprezentativ coeliakia szűrővizsgalatot Magyarorszagon. Megallapitottuk, hogy a coeliakia hazai előfordulasa 1.3% korul van a magyar gyermekek es fiatal felnőttek koreben. A szűrővizsgalatokra egyszerű, helyszini antitest kimutatason alapulo szűrő eljarast validaltunk. Kimutattuk, hogy a klinikailag fel nem ismert coeliakia kedvezőtlenul befolyasolja a hepatitis vedőoltasra adott immunvalaszt es az antitestek szerepet jatszanak idegrendszeri szovődmeny (ataxia) kialakulasaban. | This research identified new susceptibility genes for coeliac disease, a common autoimmune enteropathy triggered by gluten peptides ingested with dietary cereals. The novel genes are mostly related to T-lymphocyte development, collaboration of T and B cells, toll-like receptors and cytokines. We also described association with haptoglobin polymorphism, a master regulator of intestinal permeability also known as zonulin. Predisposing alleles of these genes create a more inflammatory environment in the gut and in multiple copies confer additional risk to HLA-DQ alleles. We identified the main binding epitope of coeliac disease anti-transglutaminase 2 autoantibodies. This epitope has a complex, three-dimensional structure and is disease-specific. Patient antibodies targeting this epitope enhance the enzymatic activity of transglutaminase 2 and cause disturbances in the angiogenesis and vascular permeability in cell culture models via the inappropriate activation of RhoA. We performed the first representative population screening for coeliac disease in Hungary and established that the prevalence is around 1.3% in both children and young adults. The methodology of the screening has been advanced by the application of rapid, onsite antibody detection. Unrecognised coeliac disease was found to predispose to a defective immune response to hepatitis B vaccination (reversible after treatment) and we showed the contribution of coeliac disease antibodies in the late neural complications.
Autophagy ensures the lysosome-mediated breakdown and recycling of self-material, as it not only degrades obsolete or damaged intracellular constituents but also provides building blocks for biosynthetic and energy producing reactions. Studies in animal models including Drosophila revealed that autophagy defects lead to the rapid decline of neuromuscular function, neurodegeneration, sensitivity to stress (such as starvation or oxidative damage), and stem cell loss. Of note, recently identified human Atg gene mutations cause similar symptoms including ataxia and mental retardation. Physiologically, autophagic degradation (flux) is known to decrease during aging, and this defect likely contributes to the development of such age-associated diseases. Many manipulations that extend lifespan (including dietary restriction, reduced TOR kinase signaling, exercise or treatment with various anti-aging substances) require autophagy for their beneficial effect on longevity, pointing to the key role of this housekeeping process. Importantly, genetic (eg. Atg8a overexpression in either neurons or muscle) or pharmacological (eg. feeding rapamycin or spermidine to animals) promotion of autophagy has been successfully used to extend lifespan in Drosophila, suggesting that this intracellular degradation pathway can rejuvenate cells and organisms. In this review, we highlight key discoveries and recent progress in understanding the relationship of autophagy and aging in Drosophila.
Two related multisubunit tethering complexes promote endolysosomal trafficking in all eukaryotes: Rab5-binding CORVET that was suggested to transform into Rab7-binding HOPS. We have previously identified miniCORVET, containing Drosophila Vps8 and three shared core proteins, which are required for endosome maturation upstream of HOPS in highly endocytic cells (Lőrincz et al., 2016a). Here, we show that Vps8 overexpression inhibits HOPS-dependent trafficking routes including late endosome maturation, autophagosome-lysosome fusion, crinophagy and lysosome-related organelle formation. Mechanistically, Vps8 overexpression abolishes the late endosomal localization of HOPS-specific Vps41/Lt and prevents HOPS assembly. Proper ratio of Vps8 to Vps41 is thus critical because Vps8 negatively regulates HOPS by outcompeting Vps41. Endosomal recruitment of miniCORVET- or HOPS-specific subunits requires proper complex assembly, and Vps8/miniCORVET is dispensable for autophagy, crinophagy and lysosomal biogenesis. These data together indicate the recruitment of these complexes to target membranes independent of each other in Drosophila, rather than their transformation during vesicle maturation.
Celiac disease is a multi-systemic autoimmune disease of the small bowel induced by gluten in genetically predisposed subjects. Highly specific and gluten-dependent production of auto-antibodies targeting self-proteins of the transglutaminase family occurs in the intestinal mucosa. These anti-transglutaminase antibodies are found deposited in intestinal and extra-intestinal tissue where they might exert biological effects, together with the intestinal mucosal gliadin-specific T lymphocytes. We conducted a brief review on antitransglutaminase antibodies effects, discussing their roles in the pathogenesis of several clinical manifestations of celiac disease. Keywords: Genetic gluten intolerance, intestinal anti-transglutaminase antibodies, auto-immunity
ABSTRACT Objective: Deamidated gliadin peptides are efficient antigens in diagnostic tests for celiac disease, and results correlate better with transglutaminase 2–based assays than those with native gliadin. We investigated whether deamidated gliadin antigens are structurally similar to transglutaminase 2 or could mimic transglutaminase epitopes. Patients and Methods: Serum samples from 74 celiac and 65 control patients, and 13 different transglutaminase 2–specific monoclonal mouse antibodies were investigated for their binding to commercially available deamidated gliadin peptides using enzyme‐linked immunosorbent assay, competition studies, and molecular modelling. Results: The enzyme‐linked immunosorbent assay with deamidated gliadin peptides had 100% sensitivity and 98.5% specificity in patients. Deamidated gliadin epitopes also were recognized by 3 transglutaminase‐specific monoclonal antibodies, and antibodies affinity‐purified with deamidated gliadin peptides from celiac patient sera reacted with transglutaminase but did not show endomysial binding. The binding of the monoclonal antibodies to deamidated gliadin was inhibited dose dependently by full‐length recombinant human transglutaminase, its fragments containing the binding sites of these monoclonal antibodies, or by celiac patient antibodies. Deamidated gliadin peptides decreased the binding of transglutaminase‐specific monoclonal antibodies to transglutaminase. Three different cross‐reacting transglutaminase epitopes were found, of which 2 are located in the C‐terminal domain and 1 is conformational. The binding of celiac serum samples to deamidated gliadin peptides could not be abolished by transglutaminase or by any of the transglutaminase‐specific monoclonals, indicating that celiac sera also contain additional antibodies to gliadin epitopes different from transglutaminase. Conclusions: Certain deamidated gliadin–derived peptides and transglutaminase 2 epitopes have similar 3‐dimensional appearance. This homology may contribute to the induction of transglutaminase autoantibodies by molecular mimicry.
The closely related endolysosomal tethering complexes HOPS and CORVET play pivotal roles in the homo- and heterotypic fusion of early and late endosomes, respectively, and HOPS also mediates the fusion of lysosomes with incoming vesicles including late endosomes and autophagosomes. These heterohexameric complexes share their four core subunits that assemble with additional two, complex-specific subunits. These features and the similar structure of the complexes could allow the formation of hybrid complexes, and the complex specific subunits may compete for binding to the core. Indeed, our biochemical analyses revealed the overlap of binding sites for HOPS-specific VPS41 and CORVET-specific VPS8 on the shared core subunit VPS18. We found that the overexpression of CORVET-specific VPS8 or Tgfbrap1 decreased the amount of core proteins VPS11 and VPS18 that are assembled with HOPS-specific subunits VPS41 or VPS39, indicating reduced amount of assembled HOPS. In line with this, we observed the elevation of both lipidated, autophagosome-associated LC3 protein and the autophagic cargo p62 in these cells, suggesting impaired autophagosome-lysosome fusion. In contrast, overexpression of HOPS-specific VPS39 or VPS41 did not affect the level of assembled CORVET or autophagy. VPS8 or Tgfbrap1 overexpression also induced Cathepsin D accumulation, suggesting that HOPS-dependent biosynthetic delivery of lysosomal hydrolases is perturbed, too. These indicate that CORVET-specific subunit levels fine-tune HOPS assembly and activity in vivo.
Abstract In this review, we present recent scientific advances about integrin trafficking in the endo-lysosomal system. In the last few years, plenty of new information has emerged about the endo-lysosomal system, integrins, and the mechanism, how exactly the intracellular trafficking of integrins is regulated. We review the internalization and recycling pathways of integrins, and we provide information about the possible ways of lysosomal degradation through the endosomal and autophagic system. The regulation of integrin internalization and recycling proved to be a complex process worth studying. Trafficking of integrins, together with the regulation of their gene expression, defines cellular adhesion and cellular migration through bidirectional signalization and ligand binding. Thus, any malfunction in this system can potentially (but not necessarily) lead to tumorigenesis or metastasis. Hence, extensive examinations of integrins in the endo-lysosomal system raise the possibility to identify potential new medical targets . Furthermore, this knowledge can also serve as a basis for further determination of integrin signaling- and adhesion-related processes.
