Lysosome-associated membrane proteins: characterization of LAMP-1 of macrophage P388 and mouse embryo 3T3 cultured cells

The spectrum of lysosomal stress and damage responses: from mechanosensing to inflammation

Cells and tissues turn over their aged and damaged components in order to adapt to a changing environment and maintain homeostasis. These functions rely on lysosomes, dynamic and heterogeneous organelles that play essential roles in nutrient redistribution, metabolism, signaling, gene regulation, plasma membrane repair, and immunity. Because of metabolic fluctuations and pathogenic threats, lysosomes must adapt in the short and long term to maintain functionality. In response to such challenges, lysosomes deploy a variety of mechanisms that prevent the breaching of their membrane and escape of their contents, including pathogen-associated molecules and hydrolases. While transient permeabilization of the lysosomal membrane can have acute beneficial effects, supporting inflammation and antigen cross-presentation, sustained or repeated lysosomal perforations have adverse metabolic and transcriptional consequences and can lead to cell death. This review outlines factors contributing to lysosomal stress and damage perception, as well as remedial processes aimed at addressing lysosomal disruptions. We conclude that lysosomal stress plays widespread roles in human physiology and pathology, the understanding and manipulation of which can open the door to novel therapeutic strategies.

PLA2G15 is a Lysosomal BMP Hydrolase and its Targeting Ameliorates Lysosomal Disease

Lysosomes catabolize lipids and other biological molecules, a function essential for cellular and organismal homeostasis. Key to lipid catabolism in the lysosome is bis(monoacylglycero)phosphate (BMP), a major lipid constituent of intralysosomal vesicles and a stimulator of lipid-degrading enzymes. BMP levels are altered in a broad spectrum of human conditions, including neurodegenerative diseases. While a lysosomal BMP synthase was recently discovered, the enzymes that mediate BMP turnover has remained elusive. Here we show that the lysosomal phospholipase PLA2G15 is a physiological BMP hydrolase. We further demonstrate that BMP's resistance to hydrolysis in the lysosome is conferred by the combination of its unique sn2, sn2' esterification position and stereochemistry, as neither feature alone is sufficient to provide this resistance. Purified PLA2G15 catabolizes most BMP species derived from cell and tissue lysosomes under acidic conditions. Furthermore, PLA2G15 catalytic activity against synthesized BMP stereoisomers with primary esters was comparable to its canonical substrates challenging the long-held thought that BMP's unique stereochemistry is sufficient to confer resistance to acid phospholipases. Conversely, BMP with secondary esters and S,S stereoconfiguration is intrinsically stable in vitro and requires acyl migration for hydrolysis in lysosomes. Consistent with our biochemical data, PLA2G15-deficient cells and tissues accumulate multiple BMP species, a phenotype reversible by supplementing wildtype PLA2G15 but not its catalytically dead mutant. In addition, targeting PLA2G15 to increase BMP reverses the cholesterol phenotype in Niemann Pick Disease Type C (NPC1) patient fibroblasts and significantly ameliorates disease pathologies in NPC1-deficient mice leading to extended lifespan. Our findings establish the rules that govern the stability of BMP in the lysosome and identify PLA2G15 as a lysosomal BMP hydrolase and a potential target for therapeutic intervention in neurodegenerative diseases.

Radiotherapy-activated NBTXR3 nanoparticles promote ferroptosis through induction of lysosomal membrane permeabilization

PURPOSE

Radiotherapy-activated NBTXR3 (NBTXR3 + RT) has demonstrated superior efficacy in cancer cell destruction and tumor growth control, compared to radiotherapy (RT), in preclinical and clinical settings. Previous studies highlighted the immunomodulatory properties of NBTXR3 + RT, such as modification of tumor cell immunogenicity/adjuvanticity, producing an effective local tumor control and abscopal effect, related to an enhanced antitumor immune response. Furthermore, NBTXR3 + RT has shown potential in restoring anti-PD1 efficacy in a refractory tumor model. However, the early events leading to these results, such as NBTXR3 endocytosis, intracellular trafficking and primary biological responses induced by NBTXR3 + RT remain poorly understood.

METHODS

We analyzed by transmission electron microscopy endocytosis and intracellular localization of NBTXR3 nanoparticles after endocytosis in various cell lines, in vitro and in vivo. A kinetic of NBTXR3 endocytosis and its impact on lysosomes was conducted using LysoTracker staining, and a RNAseq analysis was performed. We investigated the ability of NBTXR3 + RT to induce lysosomal membrane permeabilization (LMP) and ferroptosis by analyzing lipid peroxidation. Additionally, we evaluated the recapture by cancer cells of NBTXR3 released from dead cells.

RESULTS

NBTXR3 nanoparticles were rapidly internalized by cells mainly through macropinocytosis and in a less extend by clathrin-dependent endocytosis. NBTXR3-containing endosomes were then fused with lysosomes. The day following NBTXR3 addition, we measured a significant increase in LysoTracker lysosome labeling intensity, in vitro as in vivo. Following RT, a significant lysosomal membrane permeabilization (LMP) was measured exclusively in cells treated with NBTXR3 + RT, while RT had no effect. The day post-irradiation, a significant increase in lipid peroxidation, a biomarker of ferroptosis, was measured with NBTXR3 + RT compared to RT. Moreover, we demonstrated that NBTXR3 nanoparticles released from dead cells can be recaptured by cancer cells.

CONCLUSIONS

Our findings provide novel insights into the early and specific biological effects induced by NBTXR3 + RT, especially LMP, not induced by RT in our models. The subsequent significant increase in lipid peroxidation partially explains the enhanced cancer cell killing capacity of NBTXR3 + RT compared to RT, potentially by promoting ferroptosis. This study improves our understanding of the cellular mechanisms underlying NBTXR3 + RT and highlights its potential as an agnostic therapeutic strategy for solid cancers treatment.

Placental response to maternal SARS-CoV-2 infection

The coronavirus disease 2019 (COVID-19) pandemic affected people at all ages. Whereas pregnant women seemed to have a worse course of disease than age-matched non-pregnant women, the risk of feto-placental infection is low. Using a cohort of 66 COVID-19-positive women in late pregnancy, we correlated clinical parameters with disease severity, placental histopathology, and the expression of viral entry and Interferon-induced transmembrane (IFITM) antiviral transcripts. All newborns were negative for SARS-CoV-2. None of the demographic parameters or placental histopathological characteristics were associated with disease severity. The fetal-maternal transfer ratio for IgG against the N or S viral proteins was commonly less than one, as recently reported. We found that the expression level of placental ACE2, but not TMPRSS2 or Furin, was higher in women with severe COVID-19. Placental expression of IFITM1 and IFITM3, which have been implicated in antiviral response, was higher in participants with severe disease. We also showed that IFITM3 protein expression, which localized to early and late endosomes, was enhanced in severe COVID-19. Our data suggest an association between disease severity and placental SARS-CoV-2 processing and antiviral pathways, implying a role for these proteins in placental response to SARS-CoV-2.

LAMP3 deficiency affects surfactant homeostasis in mice

Lysosome-associated membrane glycoprotein 3 (LAMP3) is a type I transmembrane protein of the LAMP protein family with a cell-type-specific expression in alveolar type II cells in mice and hitherto unknown function. In type II pneumocytes, LAMP3 is localized in lamellar bodies, secretory organelles releasing pulmonary surfactant into the extracellular space to lower surface tension at the air/liquid interface. The physiological function of LAMP3, however, remains enigmatic. We generated Lamp3 knockout mice by CRISPR/Cas9. LAMP3 deficient mice are viable with an average life span and display regular lung function under basal conditions. The levels of a major hydrophobic protein component of pulmonary surfactant, SP-C, are strongly increased in the lung of Lamp3 knockout mice, and the lipid composition of the bronchoalveolar lavage shows mild but significant changes, resulting in alterations in surfactant functionality. In ovalbumin-induced experimental allergic asthma, the changes in lipid composition are aggravated, and LAMP3-deficient mice exert an increased airway resistance. Our data suggest a critical role of LAMP3 in the regulation of pulmonary surfactant homeostasis and normal lung function.

LAMP3 is a protein of unknown molecular function with highest expression in alveolar type II cells. In alveolar type II cells, LAMP3 localizes to lamellar bodies, specific lysosome-related organelles that play an important role in secreting pulmonary surfactant, a mixture of hydrophobic proteins and lipids lowering the surface tension between the gas and the liquid phase of the lung in order to prevent alveoli from collapsing. To decipher the physiological function of LAMP3, we generated Lamp3 knockout mice, which are viable and show no apparent phenotype. Under basal conditions, both the protein and lipid composition of pulmonary surfactant are altered, but do not affect the physiological function of the lung. However, under diseased conditions of experimental allergic asthma, changes in the lipid composition are aggravated and are associated with an impaired lung function, suggesting an important role of LAMP3 in the homeostasis of pulmonary surfactant.

Dopamine Transporter Localization in Medial Forebrain Bundle Axons Indicates Its Long-Range Transport Primarily by Membrane Diffusion with a Limited Contribution of Vesicular Traffic on Retromer-Positive Compartments

Dopamine transporter (DAT) controls dopamine neurotransmission by clearing synaptically released dopamine. However, trafficking itineraries of DAT, which determine its cell-surface concentration near synapses, are poorly characterized. It is especially unknown how DAT is transported between spatially distant midbrain somatodendritic and striatal axonal compartments. To examine this "long-range" trafficking, the localization and membrane diffusion of HA-epitope tagged DAT in the medial forebrain bundle (MFB) of a knock-in mouse (both sexes) were analyzed using confocal, super-resolution and EM in intact brain and acute brain slices. HA-DAT was abundant in the plasma membrane of MFB axons, similar to the striatum, although the intracellular fraction of HA-DAT in MFB was more substantial. Intracellular HA-DAT colocalized with VPS35, a subunit of the retromer complex mediating recycling from endosomes, in a subset of axons. Late endosomes, lysosomes, and endoplasmic reticulum were abundant in the soma but minimally present in MFB axons, suggesting that biosynthesis and lysosomal degradation of DAT are confined to soma. Together, the data suggest that membrane diffusion is the main mode of long-range DAT transport through MFB, although the contribution of vesicular traffic can be significant in a population of MFB axons. Based on HA-DAT diffusion rates, plasma membrane DAT in MFB axons turns over with a halftime of ∼20 d, which explains the extremely slow turnover of DAT protein in the brain. Unexpectedly, the mean diameter of DAT-labeled MFB axons was observed to be twice larger than reported for striatum. The implications of this finding for dopamine neuron physiology are discussed.SIGNIFICANCE STATEMENT The dopamine transporter (DAT) is a key regulator of dopamine neurotransmission and a target of abused psychostimulants. In the present study, we examined, for the first time, mechanisms of the long-range traffic of DAT in intact brain and acute brain slices from the knock-in mouse expressing epitope-tagged DAT. Using a combination of confocal, super-resolution and EM, we defined DAT localization and its membrane diffusion parameters in medial forebrain bundle axonal tracts connecting midbrain somatodendritic and striatal axonal compartments of dopaminergic neurons. In contrast to the widely accepted model of long-range axonal transport, our studies suggest that DAT traffics between midbrain and striatum, mainly by lateral diffusion in the plasma membrane with only a limited contribution of vesicular transport in recycling endosomes.

Identification and characterization of differentially expressed genes in hepatopancreas of oriental river prawn Macrobrachium nipponense under nitrite stress

The oriental river prawn Macrobrachium nipponense is a highly adaptable, tolerant, and fecund freshwater prawn that inhabits a wide range of aquatic environments. The hepatopancreas of crustaceans is not only a site for secretion of digestive enzymes, and also plays important roles in several metabolic processes, such as lipid and carbohydrate metabolism. It is the main organ for the detoxification and immunity. In this study, high-throughput sequencing techniques were used to detect the effect of nitrite stress (10 mg/L nitrite-N for 48 h) on gene expression in the hepatopancreas of M. nipponense. A total of 13,769 million reads were harvested, and 94,534 transcripts were de novo assembled using Trinity software and produced 56,054 non-redundant transcripts. A total of 825 differentially expressed genes were obtained comparing 48 h nitrite stress with control group. In the analysis of GO and KEGG database, significant differences were found in 49 pathways. Immune-related pathways under nitrite stress included arginine and proline metabolism, glutamate metabolism, Jak-Stat signaling pathway, endocytosis, wnt signaling pathway, RIG-I-like receptor signaling pathway, TGF-beta signaling pathway, GnRH signaling pathway and phagosome. Apoptosis-related pathway was also significantly altered, such as lysosome and apoptosis. Remarkably, nitrite stress altered the expression patterns of key apoptosis genes (tetraspanins-like protein, LAMP, CD63, caspase 3C and Caspase 1) and immune genes (Serine proteinase-like protein, C-type lectin, daf-36, SOCS-2, alpha-2-macroglobulin), confirmed that nitrite-stress induce immune response and eventually even apoptosis. This study provided a new insight into the role of hepatopancreas in crustaceans, and further investigation will continue.

Anti-fibrosis activity of combination therapy with epigallocatechin gallate, taurine and genistein by regulating glycolysis, gluconeogenesis, and ribosomal and lysosomal signaling pathways in HSC-T6 cells

A previous study by our group indicated that combined treatment with taurine, epigallocatechin gallate (EGCG) and genistein protects against liver fibrosis. The aim of the present study was to elucidate the antifibrotic mechanism of this combination treatment using isobaric tag for relative and absolute quantification (iTRAQ)-based proteomics in an activated rat hepatic stellate cell (HSC) line. In the present study, HSC-T6 cells were incubated with taurine, EGCG and genistein, and cellular proteins were extracted and processed for iTRAQ labeling. Quantification and identification of proteins was performed using two-dimensional liquid chromatography coupled with tandem mass spectrometry. Proteomic analysis indicated that the expression of 166 proteins were significantly altered in response to combination treatment with taurine, EGCG and genistein. A total 76 of these proteins were upregulated and 90 were downregulated. Differentially expressed proteins were grouped according to their association with specific Kyoto Encyclopedia of Genes and Genomes pathways. The results indicated that the differentially expressed proteins hexokinase-2 and lysosome-associated membrane glycoprotein 1 were associated with glycolysis, gluconeogenesis and lysosome signaling pathways. The expression of these proteins was validated using western blot analysis; the expression of hexokinase-2 was significantly decreased and the expression of lysosome-associated membrane glycoprotein 1 was significantly increased in HSC-T6 cells treated with taurine, EGCG and genistein compared with the control, respectively (P<0.05). These results were in accordance with the changes in protein expression identified using the iTRAQ approach. Therefore, the antifibrotic effect of combined therapy with taurine, EGCG and genistein may be associated with the activation of several pathways in HSCs, including glycolysis, gluconeogenesis, and the ribosome and lysosome signaling pathways. The differentially expressed proteins identified in the current study may be useful for treatment of liver fibrosis in the future.

Nanoescapology: progress toward understanding the endosomal escape of polymeric nanoparticles

Using nanoparticles to deliver drugs to cells has the potential to revolutionize the treatment of many diseases, including HIV, cancer, and diabetes. One of the major challenges facing this field is controlling where the drug is trafficked once the nanoparticle is taken up into the cell. In particular, if drugs remain localized in an endosomal or lysosomal compartment, the therapeutic can be rendered completely ineffective. To ensure the design of more effective delivery systems we must first develop a better understanding of how nanoparticles and their cargo are trafficked inside cells. This needs to be combined with an understanding of what characteristics are required for nanoparticles to achieve endosomal escape, along with methods to detect endosomal escape effectively. This review is focused into three sections: first, an introduction to the mechanisms governing internalization and trafficking in cells, second, a discussion of methods to detect endosomal escape, and finally, recent advances in controlling endosomal escape from polymer- and lipid-based nanoparticles, with a focus on engineering materials to promote endosomal escape. WIREs Nanomed Nanobiotechnol 2017, 9:e1452. doi: 10.1002/wnan.1452 For further resources related to this article, please visit the WIREs website.

Brain Region-Specific Trafficking of the Dopamine Transporter

The dopamine (DA) transporter (DAT) controls dopaminergic neurotransmission by removing extracellular DA. Although DA reuptake is proposed to be regulated by DAT traffic to and from the cell surface, the membrane trafficking system involved in the endocytic cycling of DAT in the intact mammalian brain has not been characterized. Hence, we performed immunolabeling and quantitative analysis of the subcellular and regional distribution of DAT using the transgenic knock-in mouse expressing hemagglutinin (HA) epitope-tagged DAT (HA-DAT) and by using a combination of electron microscopy and a novel method for immunofluorescence labeling of HA-DAT in acute sagittal brain slices. Both approaches demonstrated that, in midbrain somatodendritic regions, HA-DAT was present in the plasma membrane, endoplasmic reticulum, and Golgi complex, with a small fraction in early and recycling endosomes and an even smaller fraction in late endosomes and lysosomes. In the striatum and in axonal tracts between the midbrain and striatum, HA-DAT was detected predominantly in the plasma membrane, and quantitative analysis revealed increased DAT density in striatal compared with midbrain plasma membranes. Endosomes were strikingly rare and lysosomes were absent in striatal axons, in which there was little intracellular HA-DAT. Acute administration of amphetamine in vivo (60 min) or to slices ex vivo (10-60 min) did not result in detectable changes in DAT distribution. Altogether, these data provide evidence for regional differences in DAT plasma membrane targeting and retention and suggest a surprisingly low level of endocytic trafficking of DAT in the striatum along with limited DAT endocytic activity in somatodendritic areas.

SIGNIFICANCE STATEMENT

The dopamine transporter (DAT) is the key regulator of the dopamine neurotransmission in the CNS. In the present study, we developed a new approach for studying DAT localization and dynamics in intact neurons in acute sagittal brain slices from the knock-in mouse expressing epitope-tagged DAT. For the first time, the fluorescence imaging analysis of DAT was combined with the immunogold labeling of DAT and quantitative electron microscopy. In contrast to numerous studies of DAT trafficking in heterologous expression systems and dissociated cultured neurons, studies in intact neurons revealed a surprisingly low amount of endocytic trafficking of DAT at steady state and after acute amphetamine treatment and suggested that non-vesicular transport could be the main mechanism establishing DAT distribution within the dopaminergic neuron.

Growth factor signaling to mTORC1 by amino acid-laden macropinosomes

The rapid activation of the mechanistic target of rapamycin complex-1 (mTORC1) by growth factors is increased by extracellular amino acids through yet-undefined mechanisms of amino acid transfer into endolysosomes. Because the endocytic process of macropinocytosis concentrates extracellular solutes into endolysosomes and is increased in cells stimulated by growth factors or tumor-promoting phorbol esters, we analyzed its role in amino acid-dependent activation of mTORC1. Here, we show that growth factor-dependent activation of mTORC1 by amino acids, but not glucose, requires macropinocytosis. In murine bone marrow-derived macrophages and murine embryonic fibroblasts stimulated with their cognate growth factors or with phorbol myristate acetate, activation of mTORC1 required an Akt-independent vesicular pathway of amino acid delivery into endolysosomes, mediated by the actin cytoskeleton. Macropinocytosis delivered small, fluorescent fluid-phase solutes into endolysosomes sufficiently fast to explain growth factor-mediated signaling by amino acids. Therefore, the amino acid-laden macropinosome is an essential and discrete unit of growth factor receptor signaling to mTORC1.

Autophagic flux promotes cisplatin resistance in human ovarian carcinoma cells through ATP-mediated lysosomal function

Lysosomes are involved in promoting resistance of cancer cells to chemotherapeutic agents. However, the mechanisms underlying lysosomal influence of cisplatin resistance in ovarian cancer remain incompletely understood. We report that, compared with cisplatin-sensitive SKOV3 cells, autophagy increases in cisplatin-resistant SKOV3/DDP cells treated with cisplatin. Inhibition of early-stage autophagy enhanced cisplatin-mediated cytotoxicity in SKOV3/DDP cells, but autophagy inhibition at a later stage by disturbing autophagosome-lysosome fusion is more effective. Notably, SKOV3/DDP cells contained more lysosomes than cisplatin-sensitive SKOV3 cells. Abundant lysosomes and lysosomal cathepsin D activity were required for continued autolysosomal degradation and maintenance of autophagic flux in SKOV3/DDP cells. Furthermore, SKOV3/DDP cells contain abundant lysosomal ATP required for lysosomal function, and inhibition of lysosomal ATP accumulation impaired lysosomal function and blocked autophagic flux. Therefore, our findings suggest that lysosomes at least partially contribute to cisplatin resistance in ovarian cancer cells through their role in cisplatin-induced autophagic processes, and provide insight into the mechanism of cisplatin resistance in tumors.

Construction and evaluation of DNA vaccine encoding Hantavirus glycoprotein N-terminal fused with lysosome-associated membrane protein

BACKGROUND

Hantaviral diseases can have a high case fatality rate within the absence of broadly effective antiviral treatments or vaccines. We developed a DNA vaccine targeting the Hantavirus glycoprotein N-terminal (Gn) to major histocompatibility complex class II compartment by fusing the antigen with lysosome-associated membrane protein 1 (LAMP1), which altered antigen presenting pathway and activated the CD4+ T cells.

METHODS

The segments of Gn and LAMP1 were cloned into vector pVAX1, and recombinant plasmid was constructed by inserting Gn sequence into LAMP1, between luminal and the transmembrane/cytoplasmic domains. Subsequently, the protein expression was identified through immunoprecipitation, western blot and Immunofluorescent assay. Adaptive immune responses were assessed by the presence of specific and neutralizing antibodies, interferon (ELISpot results, and cytotoxic T-lymphocyte (CTL) cytotoxicity. Epitope mapping was performed to study the T-cell epitopes. Protective immunity in vivo was evaluated using a novel HTNV-challenging model, and safety evaluation was based on histological and behavioral observations.

RESULTS

Native or LAMP1 targeting HTNV Gn was successfully identified. Humoral immune responses were enhanced, featuring with satisfying titers of specific and neutralizing antibody production. The boosted activities of IFN-γ and CTL cytotoxicity witnessed enhanced cellular immune responses. Effective protection against HTNV in vivo was conferred in all three vaccine groups by the challenge model. Safety was confirmed and one dominant T-cell epitope screened from immunized mice overlapped the specific T-cell hot spot in HFRS patients.

CONCLUSION

LAMP1 targeting strategy successfully enhanced the efficacy of HTNV Gn-based vaccine, which is highly immunogenic and safe, showing promise for immunoprophylaxis against HFRS. Further investigations are warranted in the future.

Lysosome-associated membrane proteins (LAMPs) regulate intracellular positioning of mitochondria in MC3T3-E1 cells

The intracellular positioning of both lysosomes and mitochondria meets the requirements of degradation and energy supply, which are respectively the two major functions for cellular maintenance. The positioning of both lysosomes and mitochondria is apparently affected by the nutrient status of the cells. However, the mechanism coordinating the positioning of the organelles has not been sufficiently elucidated. Lysosome-associated membrane proteins-1 and -2 (LAMP-1 and LAMP-2) are highly glycosylated proteins that are abundant in lysosomal membranes. In the present study, we demonstrated that the siRNA-mediated downregulation of LAMP-1, LAMP-2 or their combination enhanced the perinuclear localization of mitochondria, in the pre-osteoblastic cell line MC3T3-E1. On the other hand, in the osteocytic cell line MLO-Y4, in which both the lysosomes and mitochondria originally accumulate in the perinuclear region and mitochondria also fill dendrites, the effect of siRNA of LAMP-1 or LAMP-2 was barely observed. LAMPs are not directly associated with mitochondria, and there do not seem to be any accessory molecules commonly required to recruit the motor proteins to lysosomes and mitochondria. Our results suggest that LAMPs may regulate the positioning of lysosomes and mitochondria. A possible mechanism involving the indirect and context-dependent action of LAMPs is discussed.

Pompe disease results in a Golgi-based glycosylation deficit in human induced pluripotent stem cell-derived cardiomyocytes

Infantile-onset Pompe disease is an autosomal recessive disorder caused by the complete loss of lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA) activity, which results in lysosomal glycogen accumulation and prominent cardiac and skeletal muscle pathology. The mechanism by which loss of GAA activity causes cardiomyopathy is poorly understood. We reprogrammed fibroblasts from patients with infantile-onset Pompe disease to generate induced pluripotent stem (iPS) cells that were differentiated to cardiomyocytes (iPSC-CM). Pompe iPSC-CMs had undetectable GAA activity and pathognomonic glycogen-filled lysosomes. Nonetheless, Pompe and control iPSC-CMs exhibited comparable contractile properties in engineered cardiac tissue. Impaired autophagy has been implicated in Pompe skeletal muscle; however, control and Pompe iPSC-CMs had comparable clearance rates of LC3-II-detected autophagosomes. Unexpectedly, the lysosome-associated membrane proteins, LAMP1 and LAMP2, from Pompe iPSC-CMs demonstrated higher electrophoretic mobility compared with control iPSC-CMs. Brefeldin A induced disruption of the Golgi in control iPSC-CMs reproduced the higher mobility forms of the LAMPs, suggesting that Pompe iPSC-CMs produce LAMPs lacking appropriate glycosylation. Isoelectric focusing studies revealed that LAMP2 has a more alkaline pI in Pompe compared with control iPSC-CMs due largely to hyposialylation. MALDI-TOF-MS analysis of N-linked glycans demonstrated reduced diversity of multiantennary structures and the major presence of a trimannose complex glycan precursor in Pompe iPSC-CMs. These data suggest that Pompe cardiomyopathy has a glycan processing abnormality and thus shares features with hypertrophic cardiomyopathies observed in the congenital disorders of glycosylation.

Activation of NLRP3 inflammasome by crystalline structures via cell surface contact

Crystalline structures activate the NLRP3 inflammasome, leading to the production of IL-1β, however, the molecular interactions responsible for NLRP3 activation are not fully understood. Cathepsin B release from the ruptured phagolysosome and potassium ion efflux have been suggested to be critical for this activation. Here, we report that Cathepsin B redistribution was not a crucial event in crystal-induced IL-1β production. Silica and monosodium urate crystal-treated macrophages with undisturbed lysosomes demonstrated strong co-localization of ASC and Caspase-1, indicative of NLRP3 inflammasome activation. Importantly, we provided evidence to suggest that macrophage cell membrane binding to immobilized crystals was sufficient to induce IL-1β release, and this activation of the NLRP3 inflammasome was inhibited by blocking potassium efflux. Therefore, this work reveals additional complexity in crystalline structure-mediated NLRP3 inflammasome regulations.

Metallophilic macrophages of the rodent thymus

For a very long time, we studied the metallophilic macrophages of the rodent thymus and in this review our results on morphological, histochemical, enzymehistochemical, immunohistochemical, ultrastructural and functional features of these cells, as well as the molecular regulation of their development, will be presented. Furthermore, the differences between species will also be discussed and the comparisons with similar/related cell types (metallophilic macrophages in the marginal sinus of the spleen, subcapsular sinus of the lymph nodes and germinal centers of secondary lymphoid follicles) will be made. Metallophilic macrophages are strategically positioned in the thymic cortico-medullary zone and are very likely to be involved in: (i) the metabolism, synthesis and production of bioactive lipids, most likely arachidonic acid metabolites, based on their histochemical and enzymehistochemical features, and (ii) the process of negative selection that occurs in the thymus, based on their ultrastructural features and their reactivity after the application of toxic or immunosuppressive/immunomodulatory agents. Taken together, their phenotypic and functional features strongly suggest that metallophilic macrophages play a significant role in the thymic physiology.

Glycosylation-independent lysosomal targeting of acid α-glucosidase enhances muscle glycogen clearance in pompe mice

We have used a peptide-based targeting system to improve lysosomal delivery of acid α-glucosidase (GAA), the enzyme deficient in patients with Pompe disease. Human GAA was fused to the glycosylation-independent lysosomal targeting (GILT) tag, which contains a portion of insulin-like growth factor II, to create an active, chimeric enzyme with high affinity for the cation-independent mannose 6-phosphate receptor. GILT-tagged GAA was taken up by L6 myoblasts about 25-fold more efficiently than was recombinant human GAA (rhGAA). Once delivered to the lysosome, the mature form of GILT-tagged GAA was indistinguishable from rhGAA and persisted with a half-life indistinguishable from rhGAA. GILT-tagged GAA was significantly more effective than rhGAA in clearing glycogen from numerous skeletal muscle tissues in the Pompe mouse model. The GILT-tagged GAA enzyme may provide an improved enzyme replacement therapy for Pompe disease patients.

Crystal structure of the conserved domain of the DC lysosomal associated membrane protein: implications for the lysosomal glycocalyx

Background

The family of lysosome-associated membrane proteins (LAMP) comprises the multifunctional, ubiquitous LAMP-1 and LAMP-2, and the cell type-specific proteins DC-LAMP (LAMP-3), BAD-LAMP (UNC-46, C20orf103) and macrosialin (CD68). LAMPs have been implicated in a multitude of cellular processes, including phagocytosis, autophagy, lipid transport and aging. LAMP-2 isoform A acts as a receptor in chaperone-mediated autophagy. LAMP-2 deficiency causes the fatal Danon disease. The abundant proteins LAMP-1 and LAMP-2 are major constituents of the glycoconjugate coat present on the inside of the lysosomal membrane, the 'lysosomal glycocalyx'. The LAMP family is characterized by a conserved domain of 150 to 200 amino acids with two disulfide bonds.

Results

The crystal structure of the conserved domain of human DC-LAMP was solved. It is the first high-resolution structure of a heavily glycosylated lysosomal membrane protein. The structure represents a novel β-prism fold formed by two β-sheets bent by β-bulges and connected by a disulfide bond. Flexible loops and a hydrophobic pocket represent possible sites of molecular interaction. Computational models of the glycosylated luminal regions of LAMP-1 and LAMP-2 indicate that the proteins adopt a compact conformation in close proximity to the lysosomal membrane. The models correspond to the thickness of the lysosomal glycoprotein coat of only 5 to 12 nm, according to electron microscopy.

Conclusion

The conserved luminal domain of lysosome-associated membrane proteins forms a previously unknown β-prism fold. Insights into the structure of the lysosomal glycoprotein coat were obtained by computational models of the LAMP-1 and LAMP-2 luminal regions.

LRP-1--CD44, a new cell surface complex regulating tumor cell adhesion

The low-density lipoprotein receptor-related protein 1 (LRP-1) is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. In the field of cancer, LRP-1-mediated endocytosis was first associated with antitumor properties. However, recent results suggested that LRP-1 may coordinate the adhesion-deadhesion balance in malignant cells to support tumor progression. Here, we observed that LRP-1 silencing or RAP (receptor-associated protein) treatment led to accumulation of CD44 at the tumor cell surface. Moreover, we evidenced a tight interaction between CD44 and LRP-1, not exclusively localized in lipid rafts. Overexpression of LRP-1-derived minireceptors indicated that the fourth ligand-binding cluster of LRP-1 is required to bind CD44. Labeling of CD44 with EEA1 and LAMP-1 showed that internalized CD44 is routed through early endosomes toward lysosomes in a LRP-1-dependent pathway. LRP-1-mediated internalization of CD44 was highly reduced under hyperosmotic conditions but poorly affected by membrane cholesterol depletion, revealing that it proceeds mostly via clathrin-coated pits. Finally, we demonstrated that CD44 silencing abolishes RAP-induced tumor cell attachment, revealing that cell surface accumulation of CD44 under LRP-1 blockade is mainly responsible for the stimulation of tumor cell adhesion. Altogether, our data shed light on the LRP-1-mediated internalization of CD44 that appeared critical to define the adhesive properties of tumor cells.

Role of CCL19/21 and its possible signaling through CXCR3 in development of metallophilic macrophages in the mouse thymus

We have already shown that metallophilic macrophages, which represent an important component in the thymus physiology, are lacking in lymphotoxin-β receptor-deficient mice. However, further molecular requirements for the development and correct tissue positioning of these cells are unknown. To this end, we studied a panel of mice deficient in different chemokine ligand or receptor genes. In contrast to normal mice, which have these cells localized in the thymic cortico-medullary zone (CMZ) as a distinct row positioned between the cortex and medulla, in plt/plt (paucity of lymph node T cells) mice lacking the functional CCL19/CCL21 chemokines, metallophilic macrophages are not present in the thymic tissue. Interestingly, in contrast to the CCL19/21-deficient thymus, metallophilic macrophages are present in the CCR7-deficient thymus. However, these cells are not appropriately located in the CMZ, but are mostly crowded in central parts of thymic medulla. The double staining revealed that these metallophilic macrophages are CCR7-negative and CXCR3-positive. In the CXCL13-deficient thymus the number, morphology and localization of metallophilic macrophages are normal. Thus, our study shows that CCL19/21 and its possible signaling through CXCR3 are required for the development of thymic metallophilic macrophages, whereas the CXCL13-CXCR5 signaling is not necessary.

Kinetic evidence that newly-synthesized endogenous lysosome-associated membrane protein-1 (LAMP-1) first transits early endosomes before it is delivered to lysosomes

After de novo synthesis of lysosome-associated membrane proteins (LAMPs), they are sorted in the trans-Golgi network (TGN) for delivery to lysosomes. Opposing views prevail on whether LAMPs are targeted to lysosomes directly, or indirectly via prelysosomal stages of the endocytic pathway, in particular early endosomes. Conflicting evidence is based on kinetic measurements with too limited quantitative data for sufficient temporal and organellar resolution. Using cells of the mouse macrophage cell line, P338D(1), this study presents detailed kinetic data that describe the extent of, and time course for, the appearance of newly-synthesized LAMP-1 in organelles of the endocytic pathway, which had been loaded selectively with horse-radish peroxidase (HRP) by appropriate periods of endocytosis. After a 5-min pulse of metabolic labelling, LAMP-1 was trapped in the respective organelles by HRP-catalyzed crosslinking with membrane-permeable diaminobenzidine (DAB). These kinetic observations provide sufficient quantitative evidence that in P338D(1) cells the bulk of newly-synthesized endogenous LAMP-1 first appeared in early endosomes, before it was delivered to late endosomes and lysosomes about 25 min later.

Exploring the human genome with functional maps

Human genomic data of many types are readily available, but the complexity and scale of human molecular biology make it difficult to integrate this body of data, understand it from a systems level, and apply it to the study of specific pathways or genetic disorders. An investigator could best explore a particular protein, pathway, or disease if given a functional map summarizing the data and interactions most relevant to his or her area of interest. Using a regularized Bayesian integration system, we provide maps of functional activity and interaction networks in over 200 areas of human cellular biology, each including information from approximately 30,000 genome-scale experiments pertaining to approximately 25,000 human genes. Key to these analyses is the ability to efficiently summarize this large data collection from a variety of biologically informative perspectives: prediction of protein function and functional modules, cross-talk among biological processes, and association of novel genes and pathways with known genetic disorders. In addition to providing maps of each of these areas, we also identify biological processes active in each data set. Experimental investigation of five specific genes, AP3B1, ATP6AP1, BLOC1S1, LAMP2, and RAB11A, has confirmed novel roles for these proteins in the proper initiation of macroautophagy in amino acid-starved human fibroblasts. Our functional maps can be explored using HEFalMp (Human Experimental/Functional Mapper), a web interface allowing interactive visualization and investigation of this large body of information.

Metallophilic macrophages are fully developed in the thymus of autoimmune regulator (Aire)-deficient mice

Thymic metallophilic macrophages represent a significant component in the thymus physiology. Recently, we showed their presence to be dependent on functional lymphotoxin-beta receptor (LT beta R) signaling pathway. However, it is unknown whether the development of metallophilic macrophages also requires the Autoimmune regulator (Aire) transcription factor, as suggested by some studies for medullary thymic epithelial cells, or perhaps the presence of Aire-expressing thymic epithelial cells themselves. Therefore, we investigated the presence of metallophilic macrophages in Aire-deficient thymus. Our study shows that the metallophilic macrophages are fully developed in the Aire-deficient thymus; their development is not regulated via Aire transcription factor and does not require the presence of Aire-expressing epithelial cells. On the contrary, in alymphoplasia (ALY) mice (deficient in nuclear factor-kappaB-inducing kinase, NIK), which we used as negative control, thymic metallophilic macrophages are completely lacking, similarly as in LT beta R-deficient animals. Together, these results show that the development/maintenance of thymic metallophilic macrophages is executed via LT beta R circumventing the Aire transcription factor. Thus, we shed a new light on the molecular requirements for development of these cells and also show that LT beta R pathway is a common developmental regulator of metallophilic macrophages in different lymphatic organs (i.e., thymus and spleen).

LV-pIN-KDEL: a novel lentiviral vector demonstrates the morphology, dynamics and continuity of the endoplasmic reticulum in live neurones

Background

The neuronal endoplasmic reticulum (ER) is an extensive, complex endomembrane system, containing Ca²⁺ pumps, and Ca²⁺ channels that permit it to act as a dynamic calcium store. Currently, there is controversy over the continuity of the ER in neurones, how this intersects with calcium signalling and the possibility of physical compartmentalisation. Unfortunately, available probes of ER structure such as vital dyes are limited by their membrane specificity. The introduction of ER-targeted GFP plasmids has been a considerable step forward, but these are difficult to express in neurones through conventional transfection approaches. To circumvent such problems we have engineered a novel ER-targeted GFP construct, termed pIN-KDEL, into a 3^rd generation replication-defective, self-inactivating lentiviral vector system capable of mediating gene transduction in diverse dividing and post-mitotic mammalian cells, including neurones.

Results

Following its expression in HEK293 (or COS-7) cells, LV-pIN-KDEL yielded a pattern of fluorescence that co-localised exclusively with the ER marker sec61β but with no other major organelle. We found no evidence for cytotoxicity and only rarely inclusion body formation. To explore the utility of the probe in resolving the ER in live cells, HEK293 or COS-7 cells were transduced with LV-pIN-KDEL and, after 48 h, imaged directly at intervals from 1 min to several hours. LV-pIN-KDEL fluorescence revealed the endoplasmic reticulum as a tubular lattice structure whose morphology can change markedly within seconds. Although GFP can be phototoxic, the integrity of the cells and ER was retained for several weeks and even after light exposure for periods up to 24 h. Using LV-pIN-KDEL we have imaged the ER in diverse fixed neuronal cultures and, using real-time imaging, found evidence for extensive, dynamic remodelling of the neuronal ER in live hippocampal cultures, brain slices, explants and glia. Finally, through a Fluorescence Loss in Photobleaching (FLIP) approach, continuous irradiation at a single region of interest removed all the fluorescence of LV-pIN-KDEL-transduced nerve cells in explant cultures, thus, providing compelling evidence that in neurons the endoplasmic reticulum is not only dynamic but also continuous.

Conclusion

The lentiviral-based ER-targeted reporter, LV-pIN-KDEL, offers considerable advantages over present systems for defining the architecture of the ER, especially in primary cells such as neurones that are notoriously difficult to transfect. Images and continuous photobleaching experiments of LV-pIN-KDEL-transduced neurones demonstrate that the endoplasmic reticulum is a dynamic structure with a single continuous lumen. The introduction of LV-pIN-KDEL is anticipated to greatly facilitate a real-time visualisation of the structural plasticity and continuous nature of the neuronal ER in healthy and diseased brain tissue.

Dynamic control of self-specific CD8+ T cell responses via a combination of signals mediated by dendritic cells

It is acknowledged that T cell interactions with mature dendritic cells (DC) lead to immunity, whereas interactions with immature DC lead to tolerance induction. Using a transgenic murine system, we have examined how DC expressing self-peptides control naive, self-reactive CD8+ T cell responses in vitro and in vivo. We have shown, for the first time, that immature DC can also stimulate productive activation of naive self-specific CD8+ T cells, which results in extensive proliferation, the expression of a highly activated cell surface phenotype, and differentiation into autoimmune CTL. Conversely, mature DC can induce abortive activation of naive CD8+ T cells, which is characterized by low-level proliferation, the expression of a partially activated cell surface phenotype which does not result in autoimmune CTL. Critically, both CD8+ T cell responses are determined by a combination of signals mediated by the DC, and that altering any one of these signals dramatically shifts the balance between autoimmunity and self-tolerance induction. We hypothesize that DC maintain the steady state of self-tolerance among self-specific CD8+ T cells in an active and dynamic manner, licensing productive immune responses against self-tissues only when required.

Granzyme B is expressed in mouse mast cells in vivo and in vitro and causes delayed cell death independent of perforin

Mast cells respond to pathogens and allergens by secreting a vast array of preformed and newly synthesized mediators, including enzymes, vasoactive amines, lipid mediators, cytokines and chemokines, thereby affecting innate and adaptive immune responses and pathogenesis. Here, we present evidence that skin-, but not lung-associated primary mast cells as well as in vitro-differentiated bone marrow-derived mast cells (BMMC) express granzyme (gzm) B, but not gzmA or perforin (perf). GzmB is associated with cytoplasmic granules of BMMC and secreted after Fcepsilon-receptor-mediated activation. BMMC from wild type but not gzmB-deficient mice cause cell death in susceptible adherent target cells, indicating that the perf-independent cytotoxicity of BMMC is executed by gzmB. Furthermore, gzmB induces a disorganization of endothelial cell-cell contacts. The data suggest that activated mast cells contribute, via secreted gzmB, to cell death, increased vascular permeability, leukocyte extravasation and subsequent inflammatory processes in affected tissues.

Dendritic cell-lysosomal-associated membrane protein (LAMP) and LAMP-1-HIV-1 gag chimeras have distinct cellular trafficking pathways and prime T and B cell responses to a diverse repertoire of epitopes

Ag processing is a critical step in defining the repertoire of epitope-specific immune responses. In the present study, HIV-1 p55Gag Ag was synthesized as a DNA plasmid with either lysosomal-associated membrane protein-1 (LAMP/gag) or human dendritic cell-LAMP (DC-LAMP/gag) and used to immunize mice. Analysis of the cellular trafficking of these two chimeras demonstrated that both molecules colocalized with MHC class II molecules but differed in their overall trafficking to endosomal/lysosomal compartments. Following DNA immunization, both chimeras elicited potent Gag-specific T and B cell immune responses in mice but differ markedly in their IL-4 and IgG1/IgG2a responses. The DC-LAMP chimera induced a stronger Th type 1 response. ELISPOT analysis of T cell responses to 122 individual peptides encompassing the entire p55gag sequence (15-aa peptides overlapping by 11 residues) showed that DNA immunization with native gag, LAMP/gag, or DC-LAMP/gag induced responses to identical immunodominant CD4+ and CD8+ peptides. However, LAMP/gag and DC-LAMP/gag plasmids also elicited significant responses to 23 additional cryptic epitopes that were not recognized after immunization with native gag DNA. The three plasmids induced T cell responses to a total of 39 distinct peptide sequences, 13 of which were induced by all three DNA constructs. Individually, DC-LAMP/gag elicited the most diverse response, with a specific T cell response against 35 peptides. In addition, immunization with LAMP/gag and DC-LAMP/gag chimeras also promoted Ab secretion to an increased number of epitopes. These data indicate that LAMP-1 and DC-LAMP Ag chimeras follow different trafficking pathways, induce distinct modulatory immune responses, and are able to present cryptic epitopes.

Metallophilic macrophages are lacking in the thymus of lymphotoxin-beta receptor-deficient mice

Lymphotoxin-beta receptor (LTbetaR) axis plays a crucial role in development and compartmentalization of peripheral lymphatic organs. But, it is also required for the appropriate function and maintenance of structural integrity of the thymus: in LTbetaR-deficient animals the clonal deletion of autoreactive lymphocytes is impaired and differentiation of thymic medullary epithelial cells is disturbed. In this study, using several markers, we showed that thymic metallophilic macrophages were lacking in LTbetaR-deficient mice. In tumor necrosis factor receptor-I (p55)-deficient mice (which we used as positive control) thymic metallophilic cells were located, similarly as in normal mice, in the thymic cortico-medullary zone at the junction of cortex and medulla. These findings show that LTbetaR is necessary for maintenance of metallophilic macrophages in the thymus and provide further evidence that these cells may represent a factor involved in thymic negative selection.

PIN-G--a novel reporter for imaging and defining the effects of trafficking signals in membrane proteins

BACKGROUND

The identification of protein trafficking signals, and their interacting mechanisms, is a fundamental objective of modern biology. Unfortunately, the analysis of trafficking signals is complicated by their topography, hierarchical nature and regulation. Powerful strategies to test candidate motifs include their ability to direct simpler reporter proteins, to which they are fused, to the appropriate cellular compartment. However, present reporters are limited by their endogenous expression, paucity of cloning sites, and difficult detection in live cells.

RESULTS

Consequently, we have engineered a mammalian expression vector encoding a novel trafficking reporter--pIN-G--consisting of a simple, type I integral protein bearing permissive intra/extracellular cloning sites, green fluorescent protein (GFP), cMyc and HA epitope tags. Fluorescence imaging, flow cytometry and biochemical assays of transfected HEK293 cells, confirm the size, topology and surface expression of PIN-G. Moreover, a pIN-G fusion construct, containing a Trans-Golgi Network (TGN) targeting determinant, internalises rapidly from the cell surface and localises to the TGN. Additionally, another PIN-G fusion protein and its mutants reveal trafficking determinants in the cytoplasmic carboxy terminus of Kv1.4 voltage-gated potassium channels.

CONCLUSION

Together, these data indicate that pIN-G is a versatile, powerful, new reporter for analysing signals controlling membrane protein trafficking, surface expression and dynamics.

Activated Macrophages Infected withLegionellaInhibit T Cells by Means of MyD88-Dependent Production of Prostaglandins

To understand how macrophages (Mphi) activated with IFN-gamma modulate the adaptive immune response to intracellular pathogens, the interaction of IFN-gamma-treated bone marrow-derived murine Mphi (BMphi) with Legionella pneumophila was investigated. Although Legionella was able to evade phagosome lysosome fusion initially, and was capable of de novo protein synthesis within IFN-gamma-treated BMphi, intracellular growth of Legionella was restricted. It was determined that activated BMphi infected with Legionella suppressed IFN-gamma production by Ag-specific CD4 and CD8 T cells. A factor sufficient for suppression of T cell responses was present in culture supernatants isolated from activated BMphi following Legionella infection. Signaling pathways requiring MyD88 and TLR2 were important for production of a factor produced by IFN-gamma-treated BMphi that interfered with effector T cell functions. Cyclooxygenase-2-dependent production of PGs by IFN-gamma-treated BMphi infected with Legionella was required for inhibition of effector T cell responses. From these data we conclude that activated Mphi can down-modulate Ag-specific T cell responses after they encounter bacterial pathogens through production of PGs, which may be important in preventing unnecessary immune-mediated damage to host tissues.

Kinesin-2 is a Motor for Late Endosomes and Lysosomes

The bidirectional nature of late endosome/lysosome movement suggests involvement of at least two distinct motors, one minus-end directed and one plus-end directed. Previous work has identified dynein as the minus-end-directed motor for late endosome/lysosome localization and dynamics. Conventional kinesin (kinesin-1) has been implicated in plus-end-directed late endosome/lysosome movement, but other kinesin family members may also be involved. Kinesin-2 is known to drive the movement of pigment granules, a type of lysosomally derived organelle, and was recently found to be associated with purified late endosomes. To determine whether kinesin-2 might also power endosome movement in non-pigmented cells, we overexpressed dominant negative forms of the KIF3A motor subunit and KAP3 accessory subunit and knocked down KAP3 levels using RNAi. We found kinesin-2 to be required for the normal steady-state localization of late endosomes/lysosomes but not early endosomes or recycling endosomes. Despite the abnormal subcellular distribution of late endosomes/lysosomes, the uptake and trafficking of molecules through the conventional endocytic pathway appeared to be unaffected. The slow time-course of inhibition suggests that both kinesin-2 itself and its attachment to membranes do not turn over quickly.

The secreted form of dengue virus nonstructural protein NS1 is endocytosed by hepatocytes and accumulates in late endosomes: implications for viral infectivity

The flavivirus nonstructural protein NS1 is expressed as three discrete species in infected mammalian cells: an intracellular, membrane-associated form essential for viral replication, a cell surface-associated form that may be involved in signal transduction, and a secreted form (sNS1), the biological properties of which remain elusive. To determine the distribution of the dengue virus (DEN) sNS1 protein in vivo, we have analyzed by immunohistological means the tissue tropism of purified DEN sNS1 injected intravenously into adult mice. The sNS1 protein was found predominantly associated with the liver, where hepatocytes appeared to represent a major target cell. We further showed that sNS1 could be efficiently endocytosed by human Huh7 and HepG2 hepatocytes in vitro. After its internalization, the protein was detected intracellularly for at least 48 h without being substantially degraded. Colocalization studies of sNS1 with markers of the endolysosomal compartments revealed that the protein was specifically targeted to lysobisphosphatidic acid-rich structures reminiscent of late endosomes, as confirmed by electron microscopy. Intracellular accumulation of sNS1 in Huh7 cells enhanced the fluid phase uptake of rhodamine-labeled dextran. Furthermore, preincubation of Huh7 cells with sNS1 increased dengue virus production after infection with the homologous strain of DEN-1 virus. Our results demonstrate that the accumulation of DEN sNS1 in the late endosomal compartment of hepatocytes potentializes subsequent dengue virus infection in vitro, raising the possibility that sNS1 may contribute to viral propagation in vivo.

Yeast wall protein 1 of Candida albicans

Yeast wall protein 1 (Ywp1, also called Pga24) of Candida albicans is predicted to be a 533 aa polypeptide with an N-terminal secretion signal, a C-terminal glycosylphosphatidylinositol anchor signal and a central region rich in serine and threonine. In yeast cultures, Ywp1p appeared to be linked covalently to glucans of the wall matrix, but, as cultures approached stationary phase, Ywp1p accumulated in the medium and was extractable from cells with disulfide-reducing agents. An 11 kDa propeptide of Ywp1p was also present in these soluble fractions; it possessed the sole N-glycan of Ywp1p and served as a useful marker for Ywp1p. DNA vaccines encoding all or part of Ywp1p generated analytically useful antisera in mice, but did not increase survival times for disseminated candidiasis. Replacement of the coding sequence of YWP1 with the fluorescent reporter GFP revealed that expression of YWP1 is greatest during yeast exponential-phase growth, but downregulated in stationary phase and upon filamentation. Expression was upregulated when the extracellular phosphate concentration was low. Disruption by homologous recombination of both YWP1 alleles resulted in no obvious change in growth, morphology or virulence, but the Ywp1p-deficient blastoconidia exhibited increased adhesiveness and biofilm formation, suggesting that Ywp1p may promote dispersal of yeast forms of C. albicans.

Forced retraction of spinal root injury enhances activation of p38 MAPK cascade in infiltrating macrophages

Root-rupture injury is a type of preganglionic brachial plexus injury resulting from traction force, where a small section of the spinal root is usually left behind. We have established experimental models of both root-rupture injury with traction force and rhizotomy without traction force in rats and we examined the activation of microglia/ macrophages in both conditions. LGP107 and LGP96, which are rat homologs of lysosome-associated membrane proteins, were most useful as immunohistochemical markers of mononuclear phagocytes. The metabolic activation of macrophages was analyzed by immunohistochemistry with a series of antibodies against tumor necrosis factor-alpha (TNF-alpha), cathepsin B, p38 mitogen-activated protein kinase (MAPK), and mitogen-activated kinase kinase 3 (MKK3). Both root-rupture injury and rhizotomy rapidly induced the aggregation of numerous macrophages from the injured dorsal root to the dorsal funiculus and TNF-alpha was highly expressed by the macrophages in the injured dorsal root at 48 h. Activation of p38 MAPK was preferentially observed in the macrophages at the ruptured dorsal root; however, only slight activation of p38 MAPK was observed at the rhizotomized dorsal root. These findings suggest that traction injury of the spinal root might induce activation of the p38 MAPK cascade and production of TNF-alpha in the infiltrating macrophages, both of which might participate in aggravation of the root injury.

A mouse model of classical late-infantile neuronal ceroid lipofuscinosis based on targeted disruption of the CLN2 gene results in a loss of tripeptidyl-peptidase I activity and progressive neurodegeneration

Mutations in the CLN2 gene, which encodes a lysosomal serine protease, tripeptidyl-peptidase I (TPP I), result in an autosomal recessive neurodegenerative disease of children, classical late-infantile neuronal ceroid lipofuscinosis (cLINCL). cLINCL is inevitably fatal, and there currently exists no cure or effective treatment. In this report, we provide the characterization of the first CLN2-targeted mouse model for cLINCL. CLN2-targeted mice were fertile and apparently healthy at birth despite an absence of detectable TPP I activity. At approximately 7 weeks of age, neurological deficiencies became evident with the onset of a tremor that became progressively more severe and was eventually accompanied by ataxia. Lifespan of the affected mice was greatly reduced (median survival, 138 d), and extensive neuronal pathology was observed including a prominent accumulation of cytoplasmic storage material within the lysosomal-endosomal compartment, a loss of cerebellar Purkinje cells, and widespread axonal degeneration. The CLN2-targeted mouse therefore recapitulates much of the pathology and clinical features of cLINCL and represents an animal model that should provide clues to the normal cellular function of TPP I and the pathogenic processes that underlie neuronal death in its absence. In addition, the CLN2-targeted mouse also represents a valuable model for the evaluation of different therapeutic strategies.

Nicastrin expression in mouse peripheral tissues is not co-ordinated with presenilin and is high in muscle

Nicastrin was the first binding partner of presenilin (PS) shown to be a critical component of the presenilin/gamma-secretase complex essential in development and differentiation, and in generation of Alzheimer's disease Abeta amyloid peptide. To investigate the function of this glycoprotein, we compared nicastrin and presenilin protein expression in various mouse tissues. Western blot analysis of PS1, PS2 and nicastrin indicates their expression levels are not coordinated. In adult mouse, nicastrin is highly expressed in muscle membranes, whereas presenilin levels are very low. By Blue Native electrophoresis, a PS1 complex of 400 kDa was detected in lung, brain, thymus and heart; nicastrin was also detected as a 400-kDa complex in brain but in muscle it was detected with a complex mobility of 240 and 290 kDa, suggesting association with alternate protein complexes. Immunocytochemistry confirms strong intracellular expression of nicastrin in skeletal muscle and blood vessel smooth muscle. These findings suggest a function for nicastrin in muscle other than participation in the gamma-secretase complex.

Proteomics of endoplasmic reticulum-Golgi intermediate compartment (ERGIC) membranes from brefeldin A-treated HepG2 cells identifies ERGIC-32, a new cycling protein that interacts with human Erv46

Cycling proteins play important roles in the organization and function of the early secretory pathway by participating in membrane traffic and selective transport of cargo between the endoplasmic reticulum (ER), the intermediate compartment (ERGIC), and the Golgi. To identify new cycling proteins, we have developed a novel procedure for the purification of ERGIC membranes from HepG2 cells treated with brefeldin A, a drug known to accumulate cycling proteins in the ERGIC. Membranes enriched 110-fold over the homogenate for ERGIC-53 were obtained and analyzed by mass spectrometry. Major proteins corresponded to established and putative cargo receptors and components mediating protein maturation and membrane traffic. Among the uncharacterized proteins, a 32-kDa protein termed ERGIC-32 is a novel cycling membrane protein with sequence homology to Erv41p and Erv46p, two proteins enriched in COPII vesicles of yeast. ERGIC-32 localizes to the ERGIC and partially colocalizes with the human homologs of Erv41p and Erv46p, which mainly localize to the cis-Golgi. ERGIC-32 interacts with human Erv46 (hErv46) as revealed by covalent cross-linking and mistargeting experiments, and silencing of ERGIC-32 by small interfering RNAs increases the turnover of hErv46. We propose that ERGIC-32 functions as a modulator of the hErv41-hErv46 complex by stabilizing hErv46. Our novel approach for the isolation of the ERGIC from BFA-treated cells may ultimately lead to the identification of all proteins rapidly cycling early in the secretory pathway.

Ciz1, Cip1 interacting zinc finger protein 1 binds the consensus DNA sequence ARYSR(0-2)YYAC

The matrin 3 family of nuclear proteins consists of members with potentially diverse activities. Matrin 3 and NP220 share RNA-binding domains, and NP220 has been shown to recognize and bind to the DNA sequence, CCCCC (G/C). We have isolated and characterized another member of the matrin 3 family, designated NP94, from a medulloblastoma. This protein, also named Ciz1, has previously been characterized for its ability to interact with p21(Cip1/Waf1) and contains 3 zinc finger domains and a matrin 3-homologous domain 3. Our immunofluorescence and Northern blot analysis data indicate that Ciz1 is localized in the nucleus and is expressed in a wide range of tissues, especially the pancreas and the brain; within the brain, the highest message levels are found in the cerebellum. A modified selected and amplified binding (SAAB) sequence method was used to identify DNA sequences recognized by Ciz1. From the analysis of the retrieved SAAB sequences and verification using electrophoretic mobility shift assays, we formulated a consensus DNA sequence, ARYSR(0-2)YYAC, recognized by Ciz1. The potential activities of Ciz1, including those involved in brain tumorigenesis, are discussed.

Legionella reveal dendritic cell functions that facilitate selection of antigens for MHC class II presentation

To understand how adaptive immune responses are generated against bacteria that avoid being delivered to lysosomes, interactions between professional antigen-presenting cells (APCs) and the intracellular pathogen Legionella pneumophila were examined. In contrast to murine bone marrow-derived macrophages (BMMs), we show that dendritic cells (DCs) restrict the growth of intracellular Legionella. Similar to what has been reported in BMMs, phagosomes containing Legionella matured into endoplasmic reticulum (ER)-derived organelles after DC internalization. Biogenesis of an ER-derived vacuole did not effectively sequester Legionella antigens from presentation on MHC class II molecules (MHC II). It was determined that proteins synthesized after Legionella had established residence in an ER-derived vacuole were presented by infected APCs. These data indicate that the ability of DCs to restrict intracellular growth of Legionella could be an important property that facilitates priming of protective T cell-mediated immune responses to vacuolar pathogens.

The Th1-specific costimulatory molecule, m150, is a posttranslational isoform of lysosome-associated membrane protein-1

In an earlier report, we had shown a 150-kDa protein termed as M150, isolated from the surface of activated macrophages, to possess costimulatory activity for CD4(+) T cells. Significantly, this protein was found to specifically elicit Th1 responses. In this study, we characterize M150, which belongs to a unique subset of the lysosome-associated membrane protein-1 glycoprotein. Interestingly, the costimulatory activity of M150 depends on its posttranslational modification, which has a distinct glycosylation pattern restricted to macrophages. Furthermore, it has been demonstrated that in addition to stimulating Th1-specific responses, M150 is also capable of driving differentiation of naive CD4(+) T cells into the Th1 subset. This altered posttranslational modification of housekeeping protein appears to represent a novel pathway by which APCs can additionally regulate T cell responses.

Biogenesis ofLeishmania-harbouring parasitophorous vacuoles following phagocytosis of the metacyclic promastigote or amastigote stages of the parasites

Protozoan parasites Leishmania alternate between a flagellated promastigote form and an amastigote form. In their mammalian hosts, Leishmania survive and multiply in macrophages. Both forms can be internalized by these host cells at different stages of the infectious process and eventually establish themselves within parasitophorous vacuoles exhibiting phagolysosomal properties. To determine whether the biogenesis of these organelles differs according to the parasitic stage used to initiate infection, we compared their formation kinetics after phagocytosis of either metacyclic promastigotes or amastigotes of L. amazonensis or of L. major by mouse bone-marrow-derived macrophages pre-exposed or not to IFN-γ. After 10 minutes of contact, an accumulation of F-actin was observed around the promastigotes and amatigotes undergoing phagocytosis or those that had already been internalized. This accumulation was transient and rapidly disappeared at later times. At 30 minutes, most of the promastigotes were located in long, narrow organelles that were exactly the same shape as the parasites. The latter were elongated with their cell bodies near to the macrophage nucleus and their flagella towards the periphery. This suggests that promastigote phagocytosis mainly occurs in a polarized manner, with the cell body entering the macrophages first. Most, if not all, of the phagocytosed promastigotes were located in organelles that rapidly acquired phagolysosomal properties. At 30 minutes, lamp-1, macrosialin, cathepsins B and D were detected in 70-98% of these compartments and about 70% of them were surrounded by rab7p. These late endosome/lysosome `markers' were recruited through fusion with late endocytic compartments. Indeed, when late endosomes/lysosomes were loaded with fluorescein dextran, 81-98% of the promastigote-harbouring compartments contained the endocytic tracer 30 minutes after infection. Electron microscopy of infected macrophages previously loaded with peroxidase confirmed that the phagosomes rapidly fused with late endocytic compartments. When the amastigote stage of L. amazonensiswas used to initiate infection, the kinetics of acquisition of the different late endosome/lysosome `markers' by the phagosomes were similar to those measured after infection with metacyclics. However, more rab7p+-phagosomes were observed at early time points (e.g. 90% were rab7p+ at 30 minutes). The early endosome `markers', EEA1 and the transferrin receptor, were hardly detected in parasite-containing compartments regardless of the parasitic stage used to infect macrophages and the time after infection. In conclusion, both metacyclic- and amastigote-containing phagosomes fuse with late endosomes/lysosomes within 30 minutes. However, with L. amazonensis, the time required for the formation of the huge parasitophorous vacuoles, which are characteristic of this species, was much shorter after infection with amastigotes than after infection with metacyclic promastigotes. This indicates that the initial fusions with late endosomes/lysosomes are followed by a stage-specific sequence of events.

Genetic and phenotypic differences between Legionella pneumophila strains

Legionnaires' disease is a potentially lethal pneumonia that is primarily due to infection by the species Legionella pneumophila, although more than 40 other species are known. Certain L. pneumophila subgroups, particularly serogroup 1, are associated with the majority of the epidemics. The genetic bases for these differences in virulence have not been determined. Three strains, AA100, JR32, and Lp01, have been used in many molecular pathogenesis studies of L. pneumophila. We found genetic differences between these strains by PCR and Southern analyses that may be related to their ability to cause disease. We also examined the distribution of these genetic loci in clinical and environmental isolates of Legionella and found a correlation between the presence of two of these loci, rtxA and lvh, and the ability to cause disease in humans. Examination of the interactions of these strains with host cells suggested that they differ in important phenotypic characteristics including adherence, entry, and intracellular replication. Furthermore, in the mouse model of infection they display differing levels of replication in lungs. These studies emphasize the importance of further investigation into the genetic makeup of these strains, which is likely to lead to the identification of additional factors involved in Legionella pathogenesis.

Lamp-1 is upregulated in human glioblastoma cell lines induced to undergo apoptosis

Lysosome-associated membrane protein (LAMP)-1, one of the major protein components of the lysosomal membrane, is upregulated in the human glioblastoma cell lines, U-373 MG and LN-Z308, which undergo cisplatin-induced apoptosis. These human brain tumor cell lines demonstrated apoptosis in response to cisplatin/nifedipine treatment. Both cell lines demonstrated an apoptotic response by more than one criterion. Apoptosis was demonstrated by DNA fragmentation techniques such as DNA laddering, ApopTag in situ labeling, and an ELISA-based method of detecting liberated oligosomes. These cells also had characteristic morphologic changes and upregulation of bax consistent with apoptosis. LAMP-1 expression at the protein and mRNA level was examined and found to increase with cisplatin/nifedipine treatment. LAMP-1 expression was examined using indirect immunofluorescent staining, Northern blot analysis and Western blot analysis. The finding of an augmentation of LAMP-1 in these cells induced to die is enigmatic. These findings raise the possibility of LAMP-1 involvement in the apoptotic process.

Identification of Icm protein complexes that play distinct roles in the biogenesis of an organelle permissive for Legionella pneumophila intracellular growth

Legionella pneumophila is a bacterial pathogen that can enter the human lung and grow inside alveolar macrophages. To grow within phagocytic host cells, the bacteria must create a specialized organelle that restricts fusion with lysosomes. Biogenesis of this replicative organelle is controlled by 24 dot and icm genes, which encode a type IV-related transport apparatus. To understand how this transporter functions, isogenic L. pneumophila dot and icm mutants were characterized, and three distinct phenotypic categories were identified. Our data show that, in addition to genes that encode the core Dot/Icm transport apparatus, subsets of genes are required for pore formation and modulation of phagosome trafficking. To understand activities required for virulence at a molecular level, we investigated protein-protein interactions. Specific interactions between different Icm proteins were detected by yeast two-hybrid and gel overlay analysis. These data support a model in which the IcmQ-IcmR complex regulates the formation of a translocation channel that delivers proteins into host cells, and the IcmS-IcmW complex is required for export of virulence determinants that modulate phagosome trafficking.

Endocytosis of insulin-like growth factor II by a mini-receptor based on repeat 11 of the mannose 6-phosphate/insulin-like growth factor II receptor

The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-II receptor) plays an important role in controlling the extracellular level of the insulin-like growth factor II (IGF-II) by mediating its binding at the cell surface and delivery to lysosomes. Loss of the receptor is associated with an accumulation of IGF-II, which can cause perinatal lethality if it is systemic, or local proliferation and tumorgenesis if it is spatially restricted. The extracytoplasmic domain of the receptor consists of 15 homologous repeats, of which repeat 11 carries the IGF-II-binding site of the multifunctional receptor. To investigate whether repeat 11 is sufficient to mediate binding and internalization of IGF-II, a construct consisting of repeat 11 fused to the transmembrane and cytoplasmic domain of the M6P/IGF-II receptor was transfected into mouse embryonic fibroblasts. The construct was expressed as a stable membrane protein which binds IGF-II with a 10-fold lower affinity as observed for the M6P/IGF-II receptor and is found at the cell surface and in endosomes. It mediates the internalization of IGF-II and its delivery to lysosomes, suggesting that it can function as a IGF-II mini-receptor controlling the extracellular IGF-II level.

Receptor-mediated endocytosis of soluble and membrane-tethered Sonic hedgehog by Patched-1

Patched (Ptc) is the ligand-binding component of the Hedgehog (Hh) receptor complex. In the Drosophila embryo, Ptc and Hh colocalize in vesicular punctate structures. However, receptor-mediated endocytosis of Hh proteins has not been demonstrated. By using chick neural plate explants, we show that Sonic hedgehog (Shh)-responsive neural precursor cells internalize recombinant and endogenous Shh and provide direct evidence for a gradient of endogenous Shh in the ventral neural tube. Shh internalization is blocked by a monoclonal antibody whose epitope overlaps the Ptc-binding site of Shh. These findings suggest that Shh internalization is mediated by Ptc-1 and may be linked to signaling. Concordantly, transfection of mammalian cell lines with a Ptc-1 cDNA confers the ability to internalize multiple forms of Shh, including transmembrane-anchored Shh, by a dynamin-dependent process.

Identification and subcellular localization of the Legionella pneumophila IcmX protein: a factor essential for establishment of a replicative organelle in eukaryotic host cells

The gram-negative respiratory pathogen Legionella pneumophila infects and grows within mammalian macrophages and protozoan host cells. Upon uptake into macrophages, L. pneumophila establishes a replicative organelle that avoids fusion with endocytic vesicles. There are 24 dot/icm genes on the L. pneumophila chromosome required for biogenesis of this vacuole. Many of the Dot/Icm proteins are predicted to be components of a membrane-bound secretion apparatus similar to type IV conjugal transfer systems. We have been investigating the function of L. pneumophila dot/icm gene products that do not have obvious orthologs in other type IV transfer systems, since these determinants could govern processes unique to phagosome biogenesis. The icmX gene product falls into this category. To understand the role of the IcmX protein in pathogenesis, we have detailed interactions between an L. pneumophila icmX deletion mutant and murine bone marrow-derived macrophages. These data demonstrate that icmX is required for biogenesis of the L. pneumophila replicative organelle. Immunoblot analysis indicates that the icmX gene product is a polypeptide with an estimated molecular mass of 50 kDa. The IcmX protein was localized to the bacterial periplasm, and periplasmic translocation was mediated by an N-terminal sec-dependent leader peptide. A truncated IcmX product was secreted into culture supernatants by wild-type L. pneumophila growing extracellularly in liquid media; however, transport of the IcmX protein into eukaryotic host cells was not detected. Proteins similar in molecular weight to IcmX were identified in other Legionella species by immunoblot analysis using a monoclonal antibody specific for L. pneumophila IcmX protein. From these data, we conclude that the IcmX protein is an essential component of the dot/icm secretion apparatus, and that a conserved mechanism of host cell parasitism exists for members of the Legionellaceae family.

Identification and molecular-genetic characterization of a LAMP/CD68-like protein from Caenorhabditis elegans

Lysosome associated membrane proteins (LAMPs) constitute a family of vertebrate proteins located predominantly in lysosomes, with lesser amounts present in endosomes and at the cell surface. Macrosialin/CD68s are similar to LAMPs in their subcellular distribution and amino acid sequence and presumed structure across the carboxyl terminal two thirds of their length. The functions of LAMPs and CD68s are not known. In the present study, a bioinformatics approach was used to identify a Caenorhabditis elegans protein (LMP-1) with sequence and presumed structural similarity to LAMPs and CD68s. LMP-1 appears to be the only membrane protein in C. elegans that carries a GYXX(phi) vertebrate lysosomal targeting sequence at its C terminus (where (phi) is a large, hydrophobic residue). LMP-1 was found to be present from early embryonic stages through adulthood and to be predominantly localized at the periphery of a population of large, membrane-bound organelles, called granules, that are seen throughout the early embryo but in later stages are restricted to the cells of the intestine. Analysis of an LMP-1 deficient C. elegans mutant revealed that LMP-1 is not required for viability under laboratory conditions, but the absence of LMP-1 leads to an alteration in intestinal granule populations, with apparent loss of one type of granule.