Purification and characterization of human lysosomal membrane glycoproteins

UDP-GlcNAc-1-Phosphotransferase Is a Clinically Important Regulator of Human and Mouse Hair Pigmentation

UDP-GlcNAc-1-phosphotransferase, a product of two separate genes (GNPTAB, GNPTG), is essential for the sorting and transportation of lysosomal enzymes to lysosomes. GNPTAB gene defects cause extracellular missorting of lysosomal enzymes resulting in lysosomal storage diseases, namely mucolipidosis type II and mucolipidosis type III alpha/beta, which is associated with hair discoloration. Yet, the physiological functions of GNPTAB in the control of hair follicle (HF) pigmentation remain unknown. To elucidate these, we have silenced GNPTAB in organ-cultured human HFs as a human ex vivo model for mucolipidosis type II. GNPTAB silencing profoundly inhibited intrafollicular melanin production, the correct sorting of melanosomes, tyrosinase activity, and HMB45 expression in the HF pigmentary unit and altered HF melanocyte morphology in situ. In isolated primary human HF melanocytes, GNPTAB knockdown significantly reduced melanogenesis, tyrosinase activity, and correct tyrosinase protein sorting as well as POMC expression and caused the expected lysosomal enzyme missorting in vitro. Moreover, transgenic mice overexpressing an inserted missense mutation corresponding to that seen in human mucolipidosis type II and mucolipidosis type III alpha/beta showed significantly reduced HF pigmentation, thus corroborating the in vivo relevance of our ex vivo and in vitro findings in the human system. This identifies GNPTAB as a clinically important enzymatic control of human HF pigmentation, likely by directly controlling tyrosinase sorting and POMC transcription in HF melanocytes.

Interaction of Trypanosoma cruzi Gp82 With Host Cell LAMP2 Induces Protein Kinase C Activation and Promotes Invasion

The surface molecule gp82 of metacyclic trypomastigote (MT) forms of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, mediates the host cell invasion, a process critical for the establishment of infection. Gp82 is known to bind to the target cell in a receptor-dependent manner, triggering Ca²⁺ signal, actin cytoskeleton rearrangement and lysosome spreading. The host cell receptor for gp82 was recently identified as LAMP2, the major lysosome membrane-associated protein. To further clarify the mechanisms of MT invasion, we aimed in this study at identifying the LAMP2 domain that interacts with gp82 and investigated whether target cell PKC and ERK1/2, previously suggested to be implicated in MT invasion, are activated by gp82. Interaction of MT, or the recombinant gp82 (r-gp82), with human epithelial HeLa cells induced the activation of Ca²⁺-dependent PKC and ERK1/2. The LAMP2 sequence predicted to bind gp82 was mapped and the synthetic peptide based on that sequence inhibited MT invasion, impaired the binding of r-gp82 to HeLa cells, and blocked the PKC and ERK1/2 activation induced by r-gp82. Treatment of HeLa cells with specific inhibitor of focal adhesion kinase resulted in inhibition of r-gp82-induced PKC and ERK1/2 activation, as well as in alteration of the actin cytoskeleton architecture. PKC activation by r-gp82 was also impaired by treatment of HeLa cells with inhibitor of phospholipase C, which mediates the production of diacylglycerol, which activates PKC, and inositol 1,4,5-triphosphate that releases Ca²⁺ from intracellular stores. Taken together, our results indicate that recognition of MT gp82 by LAMP2 induces in the host cell the activation of phosholipase C, with generation of products that contribute for PKC activation and the downstream ERK1/2. This chain of events leads to the actin cytoskeleton disruption and lysosome spreading, promoting MT internalization.

Structural and functional diversity of neutrophil glycosylation in innate immunity and related disorders

The granulated neutrophils are abundant innate immune cells that utilize bioactive glycoproteins packed in cytosolic granules to fight pathogenic infections, but the neutrophil glycobiology remains poorly understood. Facilitated by technological advances in glycoimmunology, systems glycobiology and glycoanalytics, a considerable body of literature reporting on novel aspects of neutrophil glycosylation has accumulated. Herein, we summarize the building knowledge of the structural and functional diversity displayed by N- and O-linked glycoproteins spatiotemporally expressed and sequentially brought-into-action across the diverse neutrophil life stages during bone marrow maturation, movements to, from and within the blood circulation and microbicidal processes at the inflammatory sites in peripheral tissues. It transpires that neutrophils abundantly decorate their granule glycoproteins including neutrophil elastase, myeloperoxidase and cathepsin G with peculiar glyco-signatures not commonly reported in other areas of human glycobiology such as hyper-truncated chitobiose core- and paucimannosidic-type N-glycans and monoantennary complex-type N-glycans. Sialyl Lewis^x, Lewis^x, poly-N-acetyllactosamine extensions and core 1-/2-type O-glycans are also common neutrophil glyco-signatures. Granule-specific glycosylation is another fascinating yet not fully understood feature of neutrophils. Recent literature suggests that unconventional biosynthetic pathways and functions underpin these prominent neutrophil-associated glyco-phenotypes. The impact of glycosylation on key neutrophil effector functions including extravasation, degranulation, phagocytosis and formation of neutrophil extracellular traps during normal physiological conditions and in innate immune-related diseases is discussed. We also highlight new technologies that are expected to further advance neutrophil glycobiology and briefly discuss the untapped diagnostic and therapeutic potential of neutrophil glycosylation that could open avenues to combat the increasingly prevalent innate immune disorders.

HHV-7 U21 exploits Golgi quality control carriers to reroute class I MHC molecules to lysosomes

The human herpesvirus-7 (HHV-7) U21 glycoprotein binds to class I major histocompatibility complex (MHC) molecules in the endoplasmic reticulum (ER) and reroutes them to lysosomes. How this single viral glycoprotein efficiently redirects the U21/class I MHC complex to the lysosomal compartment is poorly understood. To investigate the trafficking of HHV-7 U21, we followed synchronous release of U21 from the ER as it traffics through the secretory system. Sorting of integral membrane proteins from the trans-Golgi network (TGN) has been shown to occur through tubular carriers that emanate from the TGN or through vesicular carriers that recruit GGA (Golgi-localized, γ-ear–containing, ARF-binding protein), clathrin adaptors, and clathrin. Here, we present evidence for the existence of a third type of Golgi-derived carrier that is vesicular, yet clathrin independent. This U21-containing carrier also carries a Golgi membrane protein engineered to form inducible oligomers. We propose that U21 employs the novel mechanism of forming oligomeric complexes with class I MHC molecules that result in sorting of the oligomeric U21/class I MHC complexes to Golgi-­derived quality control carriers destined for lysosomes.

Molecular evolution of autophagy rate-limiting factor LAMP2 in placental mammals

Autophagy is the cellular process of removal of misfolded or damaged macromolecules and organelles. Experimental studies have demonstrated autophagy as a major mechanism of lifespan extension in long-lived mammals such as bats and mole rat rodents. Moreover, the role of this biological process has been well documented in protection against age-associated diseases and viral infection. However, studies on the molecular adaptive changes of autophagy factors during evolution are scarce. Here, we conducted a bioinformatics study of the molecular evolution of the Lysosomal Associated Membrane Protein 2 (LAMP2), as a rate-limiting factor in the lysosomal degradation stage of autophagy (the communal step of two of autophagy types: macroautophagy and chaperone-mediated). Analyzing LAMP2 across placental mammals, our phylogenetic-based maximum likelihood analyses indicate that the majority of the coding sites undergo purifying selection. However, around 27% of sites display a relaxation of purifying constraints (average ω = 0.42128), among which, 14 particular sites undergo positive selection (ω > 1). These sites are mostly located in the first luminal domain of LAMP2 (N-domain), with a hotspot region in the 135-144 codons interval. Therefore, the N-domain may account for the functional diversity and regulation of LAMP2. In addition, the identified positive selection sites could act as key regulatory sites in the LAMP2 function. On the other hand, testing the rate of evolution in LAMP2 along different clades of placental mammals revealed a relatively relaxed evolution in LAMP2 along megabats' clade. It is not clear yet whether an expedited evolution of LAMP2 in megabats has contributed to their reported up-regulation of autophagy. Finally, our data indicate positive selection sites along the ancestral branch of the clades of rodents, mouse-related rodents, and mole-rats; and suggest the potentially important regulatory role of these sites in LAMP2. Identifying the residues under positive selection, our findings pave the way for future experimental investigations to define how these selective substitutions have functionally affected autophagy.

Host cell protein LAMP-2 is the receptor for Trypanosoma cruzi surface molecule gp82 that mediates invasion

Host cell invasion by Trypanosoma cruzi metacyclic trypomastigote (MT) is mediated by MT-specific surface molecule gp82, which binds to a still unidentified receptor, inducing lysosome spreading and exocytosis required for the parasitophorous vacuole formation. We examined the involvement of the major lysosome membrane-associated LAMP proteins in MT invasion. First, human epithelial HeLa cells were incubated with MT in the presence of antibody to LAMP-1 or LAMP-2. Antibody to LAMP-2, but not to LAMP-1, significantly reduced MT invasion. Next, HeLa cells depleted in LAMP-1 or LAMP-2 were generated. Cells deficient in LAMP-2, but not in LAMP-1, were significantly more resistant to MT invasion than wild-type controls. The possibility that LAMP-2 might be the receptor for gp82 was examined by co-immunoprecipitation assays. Protein A/G magnetic beads cross-linked with antibody directed to LAMP-1 or LAMP-2 were incubated with HeLa cell and MT detergent extracts. Gp82 bound to LAMP-2 but not to LAMP-1. Binding of the recombinant gp82 protein to wild-type and LAMP-1-deficient cells, which was dose dependent and saturable, had a similar profile and was much higher as compared with LAMP-2-depleted cells. These data indicate that MT invasion is accomplished through recognition of gp82 by its receptor LAMP-2.

LAMP1 Overexpression Predicts for Poor Prognosis in Diffuse Large B-cell Lymphoma

INTRODUCTION

Lysosomal-associated membrane protein 1 (LAMP1) is a lysosomal and plasma membrane protein that contributes to tumor metastatic potential and differentiation.

PATIENTS AND METHODS

We performed immunohistochemical staining to investigate LAMP1 protein expression levels in 122 diffuse large B-cell lymphoma (DLBCL) tumor samples and 45 reactive hyperplasia tissues. Correlations between LAMP1 expression, various clinicopathologic features, and patient prognosis were evaluated by univariate and multivariate analyses.

RESULTS

LAMP1 expression was greater in the DLBCL tissues than in the reactive hyperplasia tissues. High LAMP1 expression was significantly associated with a high international prognostic index (score, 3-5; P = .023) and elevated lactate dehydrogenase level (P = .028). Moreover, high LAMP1 expression (P = .026), elevated serum lactate dehydrogenase level (P = .011), and high international prognostic index (P < .001) were independently associated with worse overall survival and progression-free survival.

CONCLUSION

These data provide the first evidence that LAMP1 expression is associated with a poor prognosis in patients with DLBCL.

Sorting protein VPS33B regulates exosomal autocrine signaling to mediate hematopoiesis and leukemogenesis

Certain secretory proteins are known to be critical for maintaining the stemness of stem cells through autocrine signaling. However, the processes underlying the biogenesis, maturation, and secretion of these proteins remain largely unknown. Here we demonstrate that many secretory proteins produced by hematopoietic stem cells (HSCs) undergo exosomal maturation and release that is controlled by vacuolar protein sorting protein 33b (VPS33B). Deletion of VPS33B in either mouse or human HSCs resulted in impaired exosome maturation and secretion as well as loss of stemness. Additionally, VPS33B deficiency led to a dramatic delay in leukemogenesis. Exosomes purified from either conditioned medium or human plasma could partially rescue the defects of HSCs and leukemia-initiating cells (LICs). VPS33B co-existed in exosomes with GDI2, VPS16B, FLOT1, and other known exosome markers. Mechanistically, VPS33B interacted with the GDI2/RAB11A/RAB27A pathway to regulate the trafficking of secretory proteins as exosomes. These findings reveal an essential role for VPS33B in exosome pathways in HSCs and LICs. Moreover, they shed light on the understanding of vesicle trafficking in other stem cells and on the development of improved strategies for cancer treatment.

Direct regulation of LAMP1 by tumor-suppressive microRNA-320a in prostate cancer

Advanced prostate cancer (PCa) metastasizes to bone and lymph nodes, and currently available treatments cannot prevent the progression and metastasis of the disease. Therefore, an improved understanding of the molecular mechanisms of the progression and metastasis of advanced PCa using current genomic approaches is needed. Our miRNA expression signature in castration-resistant prostate cancer (CRPC) revealed that microRNA-320a (miR‑320a) was significantly reduced in cancer tissues, suggesting that miR‑320a may be a promising anticancer miRNA. The aim of this study was to investigate the functional roles of miR‑320a in naïve PCa and CRPC cells and to identify miR‑320a-regulated genes involved in PCa metastasis. The expression levels of miR‑320a were significantly reduced in naïve PCa, CRPC specimens, and PCa cell lines. Restoration of mature miR‑320a in PCa cell lines showed that miR‑320a significantly inhibited cancer cell migration and invasion. Moreover, we found that lysosomal-associated membrane protein 1 (LAMP1) was a direct target of miR‑320a in PCa cells. Silencing of LAMP1 using siRNA significantly inhibited cell proliferation, migration, and invasion in PCa cells. Overexpression of LAMP1 was observed in PCa and CRPC clinical specimens. Moreover, downstream pathways were identified using si-LAMP1-transfected cells. The discovery of tumor-suppressive miR‑320a-mediated pathways may provide important insights into the potential mechanisms of PCa metastasis.

Role of tumor cell surface lysosome-associated membrane protein-1 (LAMP1) and its associated carbohydrates in lung metastasis

PURPOSE

Expression of lysosome-associated membrane protein-1 (LAMP1) on the surface correlates with metastatic potential of B16 melanoma cells. Downregulation of their expression in high metastatic (B16F10) cells reduced their surface expression and metastatic potential. Present investigations explore if overexpression of LAMP1 on the surface of low metastatic (B16F1) cells augment their metastatic ability, and if so, how?

METHODS

B16F1 cells were transduced with lentiviral vector carrying mutant-LAMP1 (Y386A) (mutLAMP1). Surface expression of LAMP1 and carbohydrates was analyzed by flow cytometry, immunofluorescence and/or immunoprecipitation and Western blotting. Cell spreading and motility were assessed on components of extracellular matrix (ECM) (fibronectin) and basement membrane (BM) (matrigel), and galectin-3-coated coverslips/plates. Metastatic potential was assessed using experimental metastasis assay.

RESULTS

Pre-incubation with anti-LAMP1 antibodies significantly reduced lung metastasis of B16F10 cells. Overexpression of mutLAMP1 significantly increased its surface expression on B16F1 cells, resulting in increased cellular spreading and motility on fibronectin and matrigel. LAMP1 is the major carrier of poly-N-acetyllactosamine (polyLacNAc) on B16F10 cells. However, significantly higher expression of mutLAMP1 had no effect on galectin-3 binding on cell surface or on spreading or motility of cells on galectin-3-coated coverslips/plates. These cells also failed to show any gain in metastatic ability. This could be because LAMP1 from these cells carried significantly lower levels of polyLacNAc in comparison with B16F10 cells.

CONCLUSIONS

PolyLacNAc on B16F10 cells and galectin-3 on lungs are the major participants in melanoma metastasis. Although surface LAMP1 promotes interactions with organ ECM and BM, carbohydrates on LAMP1 play a decisive role in dictating lung metastasis.

Impairment of the Cellular Distribution and Stability of the Erythropoietin Receptor Through the Direct Targeting of Aristolochic Acid

Aristolochic acid (AA) nephropathy is complicated with early onset and severe anemia. The molecular pathological mechanism of AA-induced anemia remains unclear. The aim of this study was to evaluate the putative pathological roles of the erythropoietin receptor (EPOR) in AA-induced anemia in both AA nephropathy zebrafish and cultured human renal tubular cells (HK2). Immunofluorescence staining experiments revealed that AA colocalizes with the EPOR in zebrafish embryos as well as in the cytoplasm of HK2 cells. After exogenous EPO stimulation, the EPOR was detected in the plasma membrane of HK cells. However, cotreatment with AA and EPO inhibited EPOR signaling and its membrane localization upon EPO stimulation. The results of studies with a protein synthesis inhibitor and a lysosome inhibitor revealed that AA accelerates the lysosomal degradation of EPOR. The molecular docking results suggest that AA may interact with the N-terminus of EPOR. Together with the results of light absorption and in vitro competition assays, we concluded that AA treatment impairs EPOR membrane localization, accelerates its lysosomal degradation, and consequently downregulates EPOR signaling by direct targeting. The results of this study may further detail the pathological mechanism of severe anemia complicated with AA nephropathy.

ATP13A2/PARK9 regulates secretion of exosomes and α-synuclein

Kufor-Rakeb syndrome (KRS) is caused by loss-of-function mutations in ATP13A2 (PARK9) and characterized by juvenile-onset parkinsonism, pyramidal signs, and cognitive decline. Previous studies suggested that PARK9 deficiency causes lysosomal dysfunction and α-synuclein (α-syn) accumulation, whereas PARK9 overexpression suppresses toxicity of α-syn. However, the precise mechanism of PARK9 effect on lysosomes and α-syn has been unknown. Here, we found that overexpressed PARK9 localized to multivesicular bodies (MVBs) in the human H4 cell line. The results from patient fibroblasts showed that loss of PARK9 function leads to decreased number of the intraluminal vesicles in MVBs and diminished release of exosomes into culture media. By contrast, overexpression of PARK9 results in increased release of exosomes in H4 cells and mouse primary cortical neurons. Moreover, loss of PARK9 function resulted in decreased secretion of α-syn into extracellular space, whereas overexpressed PARK9 promotes secretion of α-syn, at least in part via exosomes. Finally, we found that PARK9 regulates exosome biogenesis through functional interaction with the endosomal sorting complex required for transport machinery. Together, these data suggest the involvement of PARK9 in the biogenesis of exosomes and α-syn secretion and raise a possibility that disruption of these pathways in patients with KRS contributes to the disease pathogenesis.

Regulation of melanoma metastasis to lungs by cell surface Lysosome Associated Membrane Protein-1 (LAMP1) via galectin-3

Lysosome Associated Membrane Protein-1 (LAMP1), which lines the lysosomes, is often found to be expressed on surface of metastatic cells. We previously demonstrated that its surface expression on B16 melanoma variants correlates with metastatic potential. To establish the role of cell surface LAMP1 in metastasis and to understand the possible mechanism by which it facilitates lung colonization, LAMP1 was downregulated in high metastatic B16F10 cells using shRNAs cloned in a doxycycline inducible vector. This also resulted in significantly decreased LAMP1 on the cell surface. Being a major carrier of poly-N-acetyllactosamine (polyLacNAc) substituted β1,6 branched N-oligosaccharides, the high affinity ligands for galectin-3, LAMP1 down regulation also resulted in appreciably decreased binding of galectin-3 to the cell surface. LAMP1 has been shown to bind to Extracellular Matrix (ECM), Basement Membrane (BM) components and also to galectin-3 (via carbohydrates) which is known to get incorporated into the ECM and BM. Although, LAMP1 downregulation had a marginal effect on cellular spreading and motility on fibronectin and matrigel, it significantly altered the same on galectin-3, and ultimately leading to notably reduced lung metastasis. The results thus for the first time provide direct evidence that cell surface LAMP1 facilitates lung metastasis by providing ligands for galectin-3 which has been shown to be expressed in highest amounts on lungs and constitutively on its vascular endothelium.

Adaptor protein complexes AP-1 and AP-3 are required by the HHV-7 Immunoevasin U21 for rerouting of class I MHC molecules to the lysosomal compartment

The human herpesvirus-7 (HHV-7) U21 gene product binds to class I major histocompatibility complex (MHC) molecules and reroutes them to a lysosomal compartment. Trafficking of integral membrane proteins to lysosomes is mediated through cytoplasmic sorting signals that recruit heterotetrameric clathrin adaptor protein (AP) complexes, which in turn mediate protein sorting in post-Golgi vesicular transport. Since U21 can mediate rerouting of class I molecules to lysosomes even when lacking its cytoplasmic tail, we hypothesize the existence of a cellular protein that contains the lysosomal sorting information required to escort class I molecules to the lysosomal compartment. If such a protein exists, we expect that it might recruit clathrin adaptor protein complexes as a means of lysosomal sorting. Here we describe experiments demonstrating that the μ adaptins from AP-1 and AP-3 are involved in U21-mediated trafficking of class I molecules to lysosomes. These experiments support the idea that a cellular protein(s) is necessary for U21-mediated lysosomal sorting of class I molecules. We also examine the impact of transient versus chronic knockdown of these adaptor protein complexes, and show that the few remaining μ subunits in the cells are eventually able to reroute class I molecules to lysosomes.

Combined biochemical and cytological analysis of membrane trafficking using lectins

We have tested the application of high-mannose-binding lectins as analytical reagents to identify N-glycans in the early secretory pathway of HeLa cells during subcellular fractionation and cytochemistry. Post-endoplasmic reticulum (ER) pre-Golgi intermediates were separated from the ER on Nycodenz-sucrose gradients, and the glycan composition of each gradient fraction was profiled using lectin blotting. The fractions containing the post-ER pre-Golgi intermediates are found to contain a subset of N-linked α-mannose glycans that bind the lectins Galanthus nivalis agglutinin (GNA), Pisum sativum agglutinin (PSA), and Lens culinaris agglutinin (LCA) but not lectins binding Golgi-modified glycans. Cytochemical analysis demonstrates that high-mannose-containing glycoproteins are predominantly localized to the ER and the early secretory pathway. Indirect immunofluorescence microscopy revealed that GNA colocalizes with the ER marker protein disulfide isomerase (PDI) and the COPI coat protein β-COP. In situ competition with concanavalin A (ConA), another high-mannose specific lectin, and subsequent GNA lectin histochemistry refined the localization of N-glyans containing nonreducing mannosyl groups, accentuating the GNA vesicular staining. Using GNA and treatments that perturb ER-Golgi transport, we demonstrate that lectins can be used to detect changes in membrane trafficking pathways histochemically. Overall, we find that conjugated plant lectins are effective tools for combinatory biochemical and cytological analysis of membrane trafficking of glycoproteins.

A homozygous nonsense mutation in the gene for Tmem79, a component for the lamellar granule secretory system, produces spontaneous eczema in an experimental model of atopic dermatitis

BACKGROUND

Flaky tail (ma/ma Flg(ft/ft)) mice have a frameshift mutation in the filaggrin (Flg(ft)) gene and are widely used as a model of human atopic dermatitis associated with FLG mutations. These mice possess another recessive hair mutation, matted (ma), and develop spontaneous dermatitis under specific pathogen-free conditions, whereas genetically engineered Flg(-/-) mice do not.

OBJECTIVE

We identified and characterized the gene responsible for the matted hair and dermatitis phenotype in flaky tail mice.

METHODS

We narrowed down the responsible region by backcrossing ma/ma mice with wild-type mice and identified the mutation using next-generation DNA sequencing. We attempted to rescue the matted phenotype by introducing the wild-type matted transgene. We characterized the responsible gene product by using whole-mount immunostaining of epidermal sheets.

RESULTS

We demonstrated that ma, but not Flg(ft), was responsible for the dermatitis phenotype and corresponded to a Tmem79 gene nonsense mutation (c.840C>G, p.Y280*), which encoded a 5-transmembrane protein. Exogenous Tmem79 expression rescued the matted hair and dermatitis phenotype of Tmem79(ma/ma) mice. Tmem79 was mainly expressed in the trans-Golgi network in stratum granulosum cells in the epidermis in both mice and humans. The Tmem79(ma/ma) mutation impaired the lamellar granule secretory system, which resulted in altered stratum corneum formation and a subsequent spontaneous dermatitis phenotype.

CONCLUSIONS

The Tmem79(ma/ma) mutation is responsible for the spontaneous dermatitis phenotype in matted mice, probably as a result of impaired lamellar granule secretory system and altered stratum corneum barrier function.

Surface CD107a/LAMP-1 protects natural killer cells from degranulation-associated damage

Cytotoxic lymphocytes are important for immune responses against viral infections and cancer. They are able to kill target cells through the release of cytotoxic granules (CGs) without being harmed in the process. Because the lysosomal-associated membrane proteins (LAMPs) appear on the cell surface after CG exocytosis, we hypothesized that some of these proteins might be involved in transiently protecting cytotoxic lymphocytes from self-destruction. Intracellular expression of CD107a/LAMP-1, and to a lesser extent that of CD107b/LAMP-2, correlated with lymphocyte CG content. Engineered surface expression of CD107a/LAMP-1, but not of CD107b/LAMP-2, reduced the granule-mediated killing of transfected target cells. This was dependent on glycosylation of the CD107a/LAMP-1 hinge. Moreover, surface expression of CD107a/LAMP-1 reduced binding of perforin to cells. Importantly, knockdown of CD107a/LAMP-1 in primary human natural killer (NK) cells and deficiency of CD107a/LAMP-1 in mice resulted in increased NK cell apoptosis upon target cell-induced degranulation. Thus, our data support a novel role of CD107a/LAMP-1 in the protection of NK cells from degranulation-associated suicide, which may represent a general mechanism to transiently limit self-destruction by cytotoxic lymphocytes upon target cell killing.

Novel contrasting and labeling procedures for correlative microscopy of thawed cryosections

One of the major challenges for correlative microscopy is the preparation of the sample; the protocols for transmission electron microscopy (TEM) and fluorescence microscopy (FM) often prove to be incompatible. Here, we introduce 2+Staining: an improved contrasting procedure for Tokuyasu sections that yields both excellent positive membrane contrast in the TEM and bright fluorescence of the probe labeled on the section. 2+Staining involves the contrasting of the immunolabeled sections with 1% osmium tetroxide, 2% uranyl acetate and lead citrate in sequential steps, followed by embedding in 1.8% methyl cellulose. In addition, we demonstrate an amplification of the fluorescent signal by introducing additional antibody incubation steps to the immunolabeling procedure. The methods were validated using the integrated laser and electron microscope (iLEM), a novel tool for correlative microscopy combining FM and TEM in a single setup. The approaches were tested on HL-60 cells labeled for lysosomal-associated membrane protein 2 (LAMP-2) and on sections of muscle from a facioscapulohumeral dystrophy mouse model. Yielding excellent results and greatly expediting the workflow, the methods are of great value for those working in the field of correlative microscopy and indispensible for future users of integrated correlative microscopy.

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.

Secreted autotransporter toxin (Sat) triggers autophagy in epithelial cells that relies on cell detachment

The secreted autotransporter toxin, Sat, which belongs to the subfamily of serine protease autotransporters of Enterobacteriaceae, acts as a virulence factor in extraintestinal and intestinal pathogenic strains of Escherichia coli. We observed that HeLa cells exposed to the cell-free culture supernatant of recombinant strain AAEC185p(Sat-IH11128) producing the Sat toxin (CFCS(Sat) ), displayed dramatic disorganization of the F-actin cytoskeleton before loosening cell-to-cell junctions and detachment. Examination of the effect of Sat on GFP-microtubule-associated protein light chain 3 (LC3) HeLa cells revealed that CFCS(Sat) -induced autophagy follows CFCS(Sat) -induced F-actin cytoskeleton rearrangement. The induced autophagy shows an acceleration of the autophagy flux soon after Sat treatment, followed later by a blockade of the flux leading to the accumulation of large GFP-LC3-positive vacuoles in the cell cytoplasm. CFCS(Sat) did not induce cell detachment in autophagy-deficient mouse embryonic fibroblasts in contrast with wild-type mouse embryonic fibroblasts. The CFCS(Sat) -induced large GFP-LC3 dots do not display the characteristics of autophagolysosomes including expression of cathepsin D and Lamp-1 and 2 proteins, and Lysotracker Red- and DQ-BSA-positive labelling. We provide evidences that CFCS(Sat) -induced autophagy is not a cell response intended to get rid of the intracellular toxin. By a pharmacological blockers approach, we found that the blockade of Erk1/2 and p38 MAPKs, but not JNK, inhibited the CFCS(Sat) -induced autophagy and cell detachment whereas phosphatidylinositol-3 kinase blockers inhibiting canonical autophagy were inactive. When attached CFCS(Sat) -treated cells start to detach they showed caspase-independent cell death and rearrangements of the focal adhesion-associated vinculin and paxillin. Collectively, our results support that Sat triggers autophagy in epithelial cells that relies on its cell-detachment effect.

Role for LAMP-2 in endosomal cholesterol transport

The mechanisms of endosomal and lysosomal cholesterol traffic are still poorly understood. We showed previously that unesterified cholesterol accumulates in the late endosomes and lysosomes of fibroblasts deficient in both lysosome associated membrane protein-2 (LAMP-2) and LAMP-1, two abundant membrane proteins of late endosomes and lysosomes. In this study we show that in cells deficient in both LAMP-1 and LAMP-2 (LAMP(-/-)), low-density lipoprotein (LDL) receptor levels and LDL uptake are increased as compared to wild-type cells. However, there is a defect in esterification of both endogenous and LDL cholesterol. These results suggest that LAMP(-/-) cells have a defect in cholesterol transport to the site of esterification in the endoplasmic reticulum, likely due to defective export of cholesterol out of late endosomes or lysosomes. We also show that cholesterol accumulates in LAMP-2 deficient liver and that overexpression of LAMP-2 retards the lysosomal cholesterol accumulation induced by U18666A. These results point to a critical role for LAMP-2 in endosomal/lysosomal cholesterol export. Moreover, the late endosomal/lysosomal cholesterol accumulation in LAMP(-/-) cells was diminished by overexpression of any of the three isoforms of LAMP-2, but not by LAMP-1. The LAMP-2 luminal domain, the membrane-proximal half in particular, was necessary and sufficient for the rescue effect. Taken together, our results suggest that LAMP-2, its luminal domain in particular, plays a critical role in endosomal cholesterol transport and that this is distinct from the chaperone-mediated autophagy function of LAMP-2.

Human decay-accelerating factor and CEACAM receptor-mediated internalization and intracellular lifestyle of Afa/Dr diffusely adhering Escherichia coli in epithelial cells

We used transfected epithelial CHO-B2 cells as a model to identify the mechanism mediating internalization of Afa/Dr diffusely adhering Escherichia coli. We provide evidence that neither the alpha5 or beta1 integrin subunits nor alpha5beta1 integrin functioned as a receptor mediating the adhesion and/or internalization of Dr or Afa-III fimbria-positive bacteria. We also demonstrated that (i) whether or not the AfaD or DraD invasin subunits were present, there was no difference in the cell association and entry of bacteria and that (ii) DraE or AfaE-III adhesin subunits are necessary and sufficient to promote the receptor-mediated bacterial internalization into epithelial cells expressing human decay-accelerating factor (DAF), CEACAM1, CEA, or CEACAM6. Internalization of Dr fimbria-positive E. coli within CHO-DAF, CHO-CEACAM1, CHO-CEA, or CHO-CEACAM6 cells occurs through a microfilament-independent, microtubule-dependent, and lipid raft-dependent mechanism. Wild-type Dr fimbria-positive bacteria survived better within cells expressing DAF than bacteria internalized within CHO-CEACAM1, CHO-CEA, or CHO-CEACAM6 cells. In DAF-positive cells, internalized Dr fimbria-positive bacteria were located in vacuoles that contained more than one bacterium, displaying some of the features of late endosomes, including the presence of Lamp-1 and Lamp-2, and some of the features of CD63 proteins, but not of cathepsin D, and were acidic. No interaction between Dr fimbria-positive-bacterium-containing vacuoles and the autophagic pathway was observed.

Infectious adenovirus type 2 transport through early but not late endosomes

Receptor-mediated endocytosis is a major gate for pathogens into cells. In this study, we analyzed the trafficking of human adenovirus type 2 and 5 (Ad2/5) and the escape-defective temperature-sensitive Ad2-ts1 mutant in epithelial cancer cells. Ad2/5 and Ad2-ts1 uptake into endosomes containing transferrin, major histocompatibility antigen 1 and the Rab5 effector early endosome antigen 1 (EEA1) involved dynamin, amphiphysin, clathrin and Eps15. Cointernalization experiments showed that most of the Ad2/5 and Ad2-ts1 visited the same EEA1-positive endosomes. In contrast to Ad2/5, Ad2-ts1 required functional Rab5 for endocytosis and lysosomal transport and was sensitive to the phosphatidyl-inositol-3 (PI3)-kinase inhibitor wortmannin or the ubiquitin-binding protein Hrs for sorting from early to late endosomes. Endosomal escape of Ad2 was not affected by incubation at 19 degrees C, which blocked membrane sorting in early endosomes and inhibited Ad2-ts1 transport to lysosomes. Unlike Semliki Forest Virus (SFV), sorting of Ad2-ts1 to late endosomes was independent of Rab7 and Ad2/5 infection independent of EEA1. The data indicate that Ad2/5 and Ad2-ts1 use an invariant machinery for clathrin-mediated uptake to early endosomes. We suggest that the infectious Ad2 particles are either directly released from early endosomes to the cytosol or sorted by a temperature-insensitive and PI3-kinase-independent mechanism to an escape compartment different from late endosomes or lysosomes.

An immunohistochemical approach to differentiate hepatic lipidosis from hepatic phospholipidosis in rats

Hepatocellular vacuolation can be a diagnostic challenge since cytoplasmic accumulations of various substances (lipid, water, phospholipids, glycogen, and plasma) can have a similar morphology. Cytoplasmic accumulation of phospholipids following administration of cationic amphiphilic drugs (CAD) can be particularly difficult to differentiate from nonphosphorylated lipid accumulations at the light microscopic level. Histochemical methods (Sudan Black, Oil Red-O, Nile Blue, etc.) can be used to identify both nonphosphorylated and/or phosphorylated lipid accumulations, but these techniques require non-paraffin-embedded tissue and are only moderately sensitive. Thus, electron microscopy is often utilized to achieve a definitive diagnosis based upon the characteristic morphologic features of phospholipid accumulations; however, this is a low throughput and labor intense procedure. In this report, we describe the use of immunohistochemical staining for LAMP-2 (a lysosome-associated protein) and adipophilin (a protein that forms the membrane around non-lysosomal lipid droplets) to differentiate phospholipidosis and lipidosis, respectively in the livers of rats. This staining procedure can be performed on formalin-fixed paraffin embedded tissues, is more sensitive than histochemistry, and easier to perform than ultrastructural evaluation.

Roles of LAMP-1 and LAMP-2 in lysosome biogenesis and autophagy

The lysosomal membrane proteins LAMP-1 and LAMP-2 are estimated to contribute to about 50% of all proteins of the lysosome membrane. Surprisingly, mice deficient in either LAMP-1 or LAMP-2 are viable and fertile. However, mice deficient in both LAMP-1 and LAMP-2 have an embryonic lethal phenotype. These results show that these two major lysosomal membrane proteins share common functions in vivo. However, LAMP-2 seems to have more specific functions since LAMP-2 single deficiency has more severe consequences than LAMP-1 single deficiency. Mutations in LAMP-2 gene cause a lysosomal glycogen storage disease, Danon disease, in humans. LAMP-2 deficient mice replicate the symptoms found in Danon patients including accumulation of autophagic vacuoles in heart and skeletal muscle. In embryonic fibroblasts, mutual disruption of both LAMPs is associated with an increased accumulation of autophagic vacuoles and unesterified cholesterol, while protein degradation rates are not affected. These results clearly show that the LAMP proteins fulfil functions far beyond the initially suggested roles in maintaining the structural integrity of the lysosomal compartment.

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.

Unifying nomenclature for the isoforms of the lysosomal membrane protein LAMP-2

The present nomenclature of the splice variants of the lysosome-associated membrane protein type 2 (LAMP-2) is confusing. The LAMP-2a isoform is uniformly named in human, chicken, and mouse, but the LAMP-2b and LAMP-2c isoforms are switched in human as compared with mouse and chicken. We propose to change the nomenclature of the chicken and mouse b and c isoforms to agree with that currently used for the human isoforms. To avoid confusion in the literature, we further propose to adopt the use of capital letters for the updated nomenclature of all the isoforms in all three species: LAMP-2A, LAMP-2B, and LAMP-2C.

Infectious bronchitis virus 3a protein localizes to a novel domain of the smooth endoplasmic reticulum

All coronaviruses possess small open reading frames (ORFs) between structural genes that have been hypothesized to play important roles in pathogenesis. Infectious bronchitis virus (IBV) ORF 3a is one such gene. It is highly conserved among group 3 coronaviruses, suggesting that it has an important function in infection. IBV 3a protein is expressed in infected cells but is not detected in virions. Sequence analysis predicted that IBV 3a was a membrane protein; however, only a fraction behaved like an integral membrane protein. Microscopy and immunoprecipitation studies demonstrated that IBV 3a localized to the cytoplasm in a diffuse pattern as well as in sharp puncta in both infected and transfected cells. These puncta did not overlap cellular organelles or other punctate structures. Confocal microscopy demonstrated that IBV 3a puncta lined up along smooth endoplasmic reticulum (ER) tubules and, in a significant number of instances, were partially surrounded by these tubules. Our results suggest that IBV 3a is partially targeted to a novel domain of the smooth ER.

Mechanism of uptake and incorporation of the non-human sialic acid N-glycolylneuraminic acid into human cells

N-Glycolylneuraminic acid (Neu5Gc) is a widely expressed sialic acid in mammalian cells. Although humans are genetically deficient in producing Neu5Gc, small amounts are present in human cells in vivo. A dietary origin was suggested by human volunteer studies and by observing that free Neu5Gc is metabolically incorporated into cultured human carcinoma cells by unknown mechanisms. We now show that free Neu5Gc uptake also occurs in other human and mammalian cells. Inhibitors of certain non-clathrin-mediated endocytic pathways reduce Neu5Gc accumulation. Studies with human mutant cells show that the lysosomal sialic acid transporter is required for metabolic incorporation of free Neu5Gc. Incorporation of glycosidically bound Neu5Gc from exogenous glycoconjugates (relevant to human gut epithelial exposure to dietary Neu5Gc) requires the transporter as well as the lysosomal sialidase, which presumably acts to release free Neu5Gc. Thus, exogenous Neu5Gc reaches lysosomes via pinocytic/endocytic pathways and is exported in free form into the cytosol, becoming available for activation and transfer to glycoconjugates. In contrast, N-glycolylmannosamine (ManNGc) apparently traverses the plasma membrane by passive diffusion and becomes available for conversion to Neu5Gc in the cytosol. This mechanism can also explain the metabolic incorporation of chemically synthesized unnatural sialic acids, as reported by others. Finally, to our knowledge, this is the first example of delivery to the cytosol of an extracellular small molecule that cannot cross the plasma membrane, utilizing fluid pinocytosis and a specific lysosomal transporter. The approach could, thus, potentially be generalized to any small molecule that has a specific lysosomal transporter but not a plasma membrane transporter.

Heterogeneity in primary and metastatic prostate cancer as defined by cell surface CD profile

Cluster designation (CD) antigens are cell surface markers that can be used to identify constituent cell populations of an organ. We have previously determined the CD phenotype of normal prostate parenchymal cells and are now extending this analysis to prostate cancer. Since expression of CD antigens is associated with cellular differentiation, cancer cells may differ from their normal counterpart in their CD profile. Compared with luminal secretory cells, prostate adenocarcinoma cells are frequently negative for CD10 and CD13, express increased levels of the cell activation molecule CD24, and decreased levels of the apoptosis-associated multifunctional enzyme CD38. Expression of CD57, CD63, CD75s, CD107a, CD107b, CD164, and CD166 by cancer cells is similar to that of secretory cells. Prostate basal epithelial cells do not express the CD antigens characteristic of prostate secretory cells; and the basal cell CD markers, CD29, CD44, CD49b, CD49f, CD104, and nerve growth factor receptor (NGFR) are not expressed by cancer cells. The preferential expression of secretory cell-associated CD markers by prostate cancer cells suggests a closer lineage relationship between cancer cells and secretory cells than basal cells. Although the above cancer CD phenotype was the most frequently seen, some prostate cancers contained populations of CD10- and/or CD13-positive cells, and CD57-negative cells. Furthermore, the cancer phenotype of tumor metastasis is different. Despite its low frequency in primary tumors, CD10 is expressed by virtually all of the nodal metastases of prostate cancer. In addition, stromal fibromuscular cells associated with primary prostate cancer differ from stromal cells in benign prostate tissue by an increased level of expression of the cell activation molecule, CD90. In summary, our data show that the CD marker expression profile of prostate cancer cells most closely resembles that of secretory prostate epithelial cells and that some prostate cancers consist of heterogeneous cell populations as distinguished by CD-marker expression profiles.

The potentials of MS-based subproteomic approaches in medical science: the case of lysosomes and breast cancer

Because of the great number of women who are diagnosed with breast cancer each year, and though this disease presents the lowest mortality rate among cancers, breast cancer remains a major public health problem. As for any cancer, the tumorigenic and metastatic processes are still hardly understood, and the biochemical markers that allow either a precise monitoring of the disease or the classification of the numerous forms of breast cancer remain too scarce. Therefore, great hopes are put on the development of high-throughput genomic and proteomic technologies. Such comprehensive techniques should help in understanding the processes and in defining steps of the disease by depicting specific genes or protein profiles. Because techniques dedicated to the current proteomic challenges are continuously improving, the probability of the discovery of new potential protein biomarkers is rapidly increasing. In addition, the identification of such markers should be eased by lowering the sample complexity; e.g., by sample fractionation, either according to specific physico-chemical properties of the proteins, or by focusing on definite subcellular compartments. In particular, proteins of the lysosomal compartment have been shown to be prone to alterations in their localization, expression, or post-translational modifications (PTMs) during the cancer process. Some of them, such as the aspartic protease cathepsin D (CatD), have even been proven as participating actively in the disease progression. The present review aims at giving an overview of the implication of the lysosome in breast cancer, and at showing how subproteomics and the constantly refining MS-based proteomic techniques may help in making breast cancer research progress, and thus, hopefully, in improving disease treatment.

Human dendritic cell lysosome-associated membrane protein expressed in lung type II pneumocytes

Human dendritic cell LAMP (hDC-LAMP) is a unique member of the lysosome-associated membrane protein (LAMP) family with a tissue distribution initially described as restricted to major histocompatibility class II (MHC II) compartments of activated DC before the translocation of MHC II to the cell surface [Immunity 9 (1998) 325]. In this report, we show that hDC-LAMP is also expressed by lung type II pneumocytes, another cell type with constitutive expression of MHC II. A recombinant hDC-LAMP protein and a monospecific anti-hDC-LAMP polyclonal antibody were prepared. The antibody reacted specifically with hDC-LAMP sequences of hDC-LAMP protein expressed in transfected cells and with a 54 kDa protein of normal human lung tissue with properties corresponding to those of transgene expressed hDC-LAMP. Immunohistochemical analysis of hDC-LAMP in human lung showed its presence in alveolar type II epithelial cells (type II pneumocytes) as well as in cells in the interfollicular area of bronchus-associated lymph nodes, where interdigitating DCs are concentrated, and with lesser staining of alveolar macrophages. The native protein contained approximately 16% carbohydrates, most of which are sialyl N-linked oligosaccharides, with an acidic isoelectric point (pI 4.8). The restricted localization of this protein to lung type II pneumocytes and DCs is in contrast to hLAMP-1, which was present in many cell types of the lung and lymph node. Type II pneumocytes are known to express MHC II and the abundant expression of hDC-LAMP in these cells as well as in DCs suggests its possible relationship to specific MHC II related function(s) of DC and type II pneumocytes.

Sorting of Von Willebrand factor to lysosome-related granules of haematopoietic cells

The aim of this work was to investigate sorting mechanisms of von Willebrand factor (VWF) when expressed in haematopoietic cells. The processing and sorting of both the wild-type VWF and a multimerization defective propeptide-mutant (VWF(m)) were investigated after expression in the 32D cell line. Normal proteolytic processing was observed for both proteins, however the processing of VWF(m) was much slower and a large portion was unprocessed. Results from subcellular fractionation and immunoelectron microscopy confirmed that a part of VWF, but not VWF(m), was targeted to lysosome-related granules. Partial constitutive secretion was also observed for all forms of VWF and VWF(m). Inhibition of acidification by chloroquine blocked VWF processing but allowed unprocessed pro-VWF targeting to dense organelles. In conclusion, our observations are consistent with VWF multimerization being of importance in cellular retention and targeting to lysosome-related organelles in haematopoietic cells, suggesting a role of protein aggregation for sorting in these cells.

The delta region of outer-capsid protein micro 1 undergoes conformational change and release from reovirus particles during cell entry

Cell entry by reoviruses requires a large, transcriptionally active subvirion particle to gain access to the cytoplasm. The features of this particle have been the subject of debate, but three primary candidates-the infectious subvirion particle (ISVP), ISVP*, and core particle forms-that differ in whether putative membrane penetration protein micro 1 and adhesin sigma1 remain particle bound have been identified. Experiments with antibody reagents in this study yielded new information about the steps in particle disassembly during cell entry. Monoclonal antibodies specific for the delta region of micro 1 provided evidence for a conformational change in micro 1 and for release of the delta proteolytic fragment from entering particles. Antiserum raised against cores provided evidence for entry-related changes in particle structure and identified entering particles that largely lack the delta fragment inside cells. Antibodies specific for sigma1 showed that it is also largely shed from entering particles. Limited coimmunostaining with markers for late endosomes and lysosomes indicated the particles lacking delta and sigma1 did not localize to those subcellular compartments, and other observations suggested that both the particles and free delta were released into the cytoplasm. Essentially equivalent findings were obtained with native ISVPs and highly infectious recoated particles containing wild-type proteins. Poorly infectious recoated particles containing a hyperstable mutant form of micro 1, however, showed no evidence for the in vitro and intracellular changes in particle structure normally detected by antibodies, and these particles instead accumulated in late endosomes or lysosomes. Recoated particles with hyperstable micro 1 were also ineffective at mediating erythrocyte lysis in vitro and promoting alpha-sarcin coentry and intoxication of cells in cultures. Based on these and other findings, we propose that ISVP* is a transient intermediate in cell entry which mediates membrane penetration and is then further uncoated in the cytoplasm to yield particles, resembling cores, that largely lack the delta fragment of micro 1.

A role for GRIP domain proteins and/or their ligands in structure and function of the trans Golgi network

tGolgin-1 (golgin-245, trans golgi p230) and golgin-97 are members of a family of peripheral membrane proteins of unknown function that localize to the trans Golgi network (TGN) through a conserved C-terminal GRIP domain. We have probed for GRIP protein function by assessing the consequences of overexpressing isolated GRIP domains. By semi-quantitative immunofluorescence microscopy we found that high level expression of epitope-tagged, GRIP domain-containing fragments of tGolgin-1 or golgin-97 specifically altered the characteristic pericentriolar distribution of TGN integral membrane and coat components. Concomitantly, vesicular transport from the TGN to the plasma membrane and furin-dependent cleavage of substrate proteins in the TGN were inhibited. Mutagenesis of a conserved tyrosine in the tGolgin-1 GRIP domain abolished these effects. GRIP domain overexpression had little effect on the distribution of most Golgi stack resident proteins and no effect on markers of other organelles. Electron microscopy analyses of GRIP domain-overexpressing cells revealed distended perinuclear vacuoles and a proliferation of multivesicular late endosomes to which the TGN resident protein TGN46 was largely mislocalized. These studies, the first to address the function of GRIP domain-containing proteins in higher eukaryotes, suggest that some or all of these proteins and/or their ligands function in maintaining the integrity of the TGN by regulating resident protein localization.

Evidence that HIV budding in primary macrophages occurs through the exosome release pathway

Lipid rafts are specialized regions of cell membranes enriched in cholesterol and sphingolipids that are involved in immune activation and signaling. Studies in T-cells indicate that these membrane domains serve as sites for release of human immunodeficiency virus (HIV). By budding through lipid rafts in T-cells, HIV selectively incorporates raft markers and excludes non-raft proteins. This process has been well studied in T-cells, but it is unknown whether lipid rafts serve as budding sites for HIV in macrophages. Recently, we proposed a new model of retroviral biogenesis called the Trojan exosome hypothesis (Gould, S. J., Booth, A., and Hildreth, J. E. K. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 10592-10597). This model proposes that retroviruses coopt the existing cellular machinery for exosomal release. Here, we performed the first test designed to differentiate between the lipid raft hypothesis of retroviral biogenesis and the Trojan exosome hypothesis. Using macrophages, we examined the relative abundance of several host proteins on the cell surface, in lipid rafts, and on both HIV particles and exosomes derived from these cells. Our results show significant differences in the abundance of host proteins on the cell surface and in HIV. Moreover, our data demonstrate discordance in the abundance of some proteins in lipid rafts and in HIV. Finally, our data reveal a strong concordance between the host cell protein profile of exosomes and that of HIV. These results strongly support the Trojan exosome hypothesis and its prediction that retroviral budding represents exploitation of a pre-existing cellular pathway of intercellular vesicle trafficking.

HIV-1 p55Gag encoded in the lysosome-associated membrane protein-1 as a DNA plasmid vaccine chimera is highly expressed, traffics to the major histocompatibility class II compartment, and elicits enhanced immune responses

Several genetic vaccines encoding antigen chimeras containing the lysosome-associated membrane protein (LAMP) translocon, transmembrane, and cytoplasmic domain sequences have elicited strong mouse antigen-specific immune responses. The increased immune response is attributed to trafficking of the antigen chimera to the major histocompatibility class II (MHC II) compartment where LAMP is colocalized with MHC II. In this report, we describe a new form of an HIV-1 p55gag DNA vaccine, with the gag sequence incorporated into the complete LAMP cDNA sequence. Gag encoded with the translocon, transmembrane and cytoplasmic lysosomal membrane targeting sequences of LAMP, without the luminal domain, was poorly expressed, did not traffic to lysosomes or MHC II compartments of transfected cells, and elicited a limited immune response from DNA immunized mice. In contrast, addition of the LAMP luminal domain sequence to the construct resulted in a high level of expression of the LAMP/Gag protein chimera in transfected cells that was further increased by including the inverted terminal repeat sequences of the adeno-associated virus to the plasmid vector. This LAMP/Gag chimera with the complete LAMP protein colocalized with endogenous MHC II of transfected cells and elicited strong cellular and humoral immune responses of immunized mice as compared with the response to DNA-encoding native Gag, with a 10-fold increase in CD4+ responses, a 4- to 5-fold increase in CD8+ T-cell responses, and antibody titers of >100,000. These results reveal novel roles of the LAMP luminal domain as a determinant of Gag protein expression, lysosomal trafficking, and possibly of the immune response to Gag.

A novel method of imaging lysosomes in living human mammary epithelial cells

Cancer cells invade by secreting degradative enzymes which, under normal conditions, are sequestered in lysosomal vesicles. The ability to noninvasively label lysosomes and track lysosomal trafficking would be extremely useful to understand the mechanisms by which degradative enzymes are secreted in the presence of pathophysiological environments, such as hypoxia and acidic extracellular pH, which are frequently encountered in solid tumors. In this study, a novel method of introducing a fluorescent label into lysosomes of human mammary epithelial cells (HMECs) was evaluated. Highly glycosylated lysosomal membrane proteins were labeled with a newly synthesized compound, 5-dimethylamino-naphthalene-1-sulfonic acid 5-amino-3,4,6-trihydroxy-tetrahydro-pyran-2-ylmethyl ester (6-O-dansyl-GlcNH2). The ability to optically image lysosomes using this new probe was validated by determining the colocalization of the fluorescence from the dansyl group with immunofluorescent staining of two well-established lysosomal marker proteins, LAMP-1 and LAMP-2. The location of the dansyl group in lysosomes was also verified by using an anti-dansyl antibody in Western blots of lysosomes isolated using isopycnic density gradient centrifugation. This novel method of labeling lysosomes biosynthetically was used to image lysosomes in living HMECs perfused in a microscopy-compatible cell perfusion system.

Apolipoprotein B is synthesized in selected human non-hepatic cell lines but not processed into mature lipoprotein

We studied apolipoprotein B100 (apoB) metabolism in a series of non-hepatic cell lines (HT29 colon adenocarcinoma, HeLa cervical epithelioid carcinoma, and 1321N1J astrocytoma human cell lines) and in the human hepatoma cell line HepG2. ApoB mRNA was detected by reverse transcription polymerase chain reaction in each non-hepatic cell line. ApoB was detected in HepG2 cells by immunoprecipitation, Western blotting, and immunocytochemistry using a polyclonal anti-human low-density lipoprotein (LDL) antibody, an anti-human apoB peptide antibody, and several monoclonal anti-apoB antibodies. ApoB was identified in the three non-hepatic cell lines by each method using the anti-apoB peptide and monoclonal antibodies, but not with the anti-LDL antibody. Immunocytochemistry indicated that epitopes of apoB were evident throughout the endoplasmic reticulum, and gel mobility of newly labeled apoB and immunoblot with anti-ubiquitin showed that apoB was highly ubiquinated in non-hepatic cells. The observations that apoB is synthesized in non-hepatic cell lines but never recognized by the anti-LDL antibody suggests that apoB is not processed into a nascent lipoprotein in these cells. Immunocytochemical localization of apoB epitopes at many locations throughout non-hepatic cells raises the exciting possibility that apoB can be used for other purposes in these cells.

Influences of the lysosomal associated membrane proteins (Lamp-1, Lamp-2) and Mac-2 binding protein (Mac-2-BP) on the prognosis of pancreatic carcinoma

BACKGROUND

Lamps and Mac-2-BP are ligands of galectin-3, and they were suggested to influence tumor proliferation and metastasis formation. The authors studied the expression of Lamp-1, Lamp-2, and Mac-2-BP in pancreatic carcinoma and evaluated their influence on patient prognosis.

METHODS

Northern blot analysis, in situ hybridization, and immunohistochemistry were performed in 12 normal and 28 pancreatic carcinoma tissue samples and in pancreatic carcinoma cell lines. The molecular findings in the tumor samples were correlated with the prognosis and histopathologic tumor characteristics. In addition, in Lamp-1 transfected CAPAN-1 pancreatic carcinoma cells, cell proliferation was analyzed.

RESULTS

Lamp-1, Lamp-2, and Mac-2-BP were overexpressed in 61% (1.6-fold increase, not significant), 71% (3.0-fold increase, P < 0.01), and 93% (5.6-fold increase, P < 0.01) of the pancreatic carcinoma samples. Lamp-1 and Lamp-2 immunoreactivity was present at the luminal side of the ductal carcinoma cells whereas Mac-2-BP immunoreactivity was diffusely spread over the whole cytoplasm and the nucleolus of ductal carcinoma cells. Correlation of the molecular data with clinical patient parameters revealed that patients whose tumors exhibited high Lamp-1 mRNA expression lived significantly longer (median, 17 months) after tumor resection than patients whose tumors exhibited low to moderate Lamp-1 mRNA levels (median, 8 months; P < 0.02). No relation between Lamp-2 and Mac-2-BP mRNA expression and any of the histopathologic parameters was found. Lamp-1 transfected CAPAN-1 cells showed decreased cell growth compared with the nontransfected cells.

CONCLUSIONS

Lamp-1 might influence local tumor progression rather than the formation of tumor metastasis in pancreatic carcinoma, whereas Mac-2-BP and Lamp-2 seem to have little influence on these parameters in pancreatic carcinoma.

Expression of lysosome-associated membrane proteins in human colorectal neoplasms and inflammatory diseases

The lysosome-associated membrane proteins (LAMPs)-1 and -2 are major constituents of the lysosomal membrane. These molecules are known to be among the most glycosylated proteins of several types of cells and cancer cells, and their expression in cancer cells is marked by a distinct difference in the structures of the oligosaccharides as compared to nonmalignant cells. We analyzed by immunohistochemistry the intensity and distribution of LAMP-1 and LAMP-2 in 9 human colorectal cancer cases and in 16 control cases, including inflammatory diseases (diverticulitis, ulcerative colitis, and Crohn's disease). LAMP proteins were expressed more intensely in the epithelium of colorectal neoplasms than in normal mucosa (P < 0.05), and no significant differences were found between adenoma and cancer cells (P > 0.05) in the same tissue section. Further, in sites of inactive inflammatory diseases and nonneoplastic areas in cancer specimens, no significant increases in epithelial LAMP proteins were observed, even in the proliferative zone of the lower crypt epithelium. Northern blot analysis showed increased expression of LAMP-1 and LAMP-2A in two of three colorectal cancers examined and increased LAMP-2B in all three cancers. Our findings suggest that LAMPs are related to neoplastic progression, but there is no direct association between the expression of LAMP molecules and cell proliferation.

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.

Sphingomyelin trafficking in Chlamydia pneumoniae-infected cells

Chlamydia pneumoniae is a bacterial obligate intracellular parasite with a developmental cycle common to all members of the genus Chlamydia. Like other chlamydiae, the developmental cycle of C. pneumoniae occurs entirely within a membrane-bound intracellular vacuole, termed an inclusion, that is non-fusogenic with endosomal or lysosomal compartments. To characterize the vesicular interactions of the C. pneumoniae inclusion, we used a fluorescent analogue of ceramide, (N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]-6-aminocaproyl-Derythro-sphingosine (C6-NBD-Cer), that has previously been used to characterize the endogenous synthesis and transport of sphingolipids from the Golgi apparatus to Chlamydia trachomatis and Chlamydia psittaci inclusions. Sphingolipids are trafficked to C. pneumoniae inclusions in a time-, temperature- and energy-dependent manner with properties very similar to the delivery of sphingomyelin to C. trachomatis inclusions. These results indicate that interactions of the inclusion with a subset of sphingomyelin-containing exocytic vesicles is a property common to all species of chlamydiae.

Two acidic amino acid residues, Asp(470) and Glu(471), contained in the carboxyl cytoplasmic tail of a major lysosomal membrane protein, LGP85/LIMP II, are important for its accumulation in secondary lysosomes

Lysosomal membrane glycoprotein termed LGP85 or LIMP II has a COOH-terminal cytoplasmic tail whose amino acid sequence is R(459)GQGSMDEGTADERAPLIRT(478). Two acidic amino acid residues, D(470) and E(471), in the cytoplasmic tail of LGP85 are crucial for its binding to adaptor-like complex AP-3. In the present study we investigated their role(s) in intracellular distributions of LGP85 using two alanine substitution mutants at D(470) and E(471) (defined as D470A and E471A, respectively). Immunofluorescence analysis showed that D470A and E471A are localized to endocytic organelles as well as wild-type LGP85. However, the subcellular fractionation study revealed that D470A and E471A are different from wild-type LGP85 in the distribution among early endosomes, late endosomes, and lysosomes. A major portion of wild-type LGP85 existed in the densest lysosomal fraction. In contrast, a significant amount of D470A existed in the early endosomal fraction with a light buoyant density, while less D470A resided in the lysosomal fraction. E471A broadened from the early endosomal fraction to the lysosomal fraction without the high lysosomal peak. These findings indicate that the two acidic residues, D(470) and E(471), play an important role in regulation of LGP85 movement within the endocytic pathway, which finally makes the highest concentration of LGP85 in the dense secondary lysosomes.

Functional HLA-DM on the surface of B cells and immature dendritic cells

HLA-DM (DM) plays a critical role in antigen presentation through major histocompatibility complex (MHC) class II molecules. DM functions as a molecular chaperone by keeping class II molecules competent for antigenic peptide loading and serves as an editor by favoring presentation of high-stability peptides. Until now, DM has been thought to exert these activities only in late endosomal/lysosomal compartments of antigen-presenting cells. Here we show that a subset of DM resides at the cell surface of B cells and immature dendritic cells. Surface DM engages in complexes with putatively empty class II molecules and controls presentation of those antigens that rely on loading on the cell surface or in early endosomal recycling compartments. For example, epitopes derived from myelin basic protein that are implicated in the autoimmune disease multiple sclerosis are down-modulated by DM, but are presented in the absence of DM. Thus, this novel concept of functional DM on the surface may be relevant to both protective immune responses and autoimmunity.

Identification of cation-independent mannose 6-phosphate receptor/insulin-like growth factor type-2 receptor as a novel target of autoantibodies

Two human monoclonal autoantibodies, B-33 and B-24, were generated from the B cells of a patient with scleroderma. Both monoclonal antibodies (mAbs) were composed of mu and lambda chains, and recognized cytoplasmic vesicular structures by indirect immunofluorescence on Hep-2 cell line slides, although mAb B-24 showed an additional diffuse cytoplasmic staining pattern. By Western blot, mAb B-24 exhibited a polyreactive-like binding pattern, whereas mAb B-33 failed to recognize any electroblotted Hep-2 antigen. The polyreactive versus monospecific behaviour of mAbs B-24 and B-33 was further confirmed by enzyme-linked immunosorbent assay (ELISA) with a variety of foreign and autoantigens. The N-terminal sequence of a protein band isolated by affinity chromatography with mAb B-33 was identical to that of cation-independent mannose 6-phosphate receptor (CI-MPR), also known as the insulin-like growth factor type-2 receptor (IGF-2R). Immunofluorescence experiments on Hep-2 cell line slides demonstrated a striking co-localization between the staining pattern exhibited by these mAbs and the pattern obtained using a goat anti-CI-MPR serum, indicating the recognition by B-24 and B-33 of a structure located predominantly in late endosomes. Sequence analysis of the V-region gene segments of B-33 and B-24 showed both to be identical, except for the existence of a point mutation in B-33 located in the H-complementarity-determining region 3 (H-CDR3) (position 100D), which produces a non-conservative replacement of Gly by Ser. This single replacement appears to be responsible for the dramatic change in reactivity of human mAb B-33. The data shown here provide new evidence of the critical role played by the H-CDR3 region in distinguishing a polyspecific from a monospecific antibody. A population study demonstrated the existence of immunoglobulin G (IgG) reactivity against CI-MPR/IGF-2R in serum specimens from five individuals with different pathological conditions, thus indicating that this molecule is a potential target for the human autoimmune response.

Identification of CD66a and CD66b as the Major Galectin-3 Receptor Candidates in Human Neutrophils

The mammalian lectin galectin-3 is a potent stimulus of human neutrophils, provided that the receptor(s) for the lectin has been mobilized to the cell surface before activation. We have recently shown that the receptors for galectin-3 are stored in intracellular mobilizable granules. Here we show supportive evidence for this in that DMSO-differentiated (neutrophil-like) HL-60 cells, which lack gelatinase and specific granules, are nonresponsive when exposed to galectin-3. Neutrophil granules were subsequently used for isolation of galectin-3 receptors by affinity chromatography. Proteins eluted from a galectin-3-Sepharose column by lactose were analyzed on SDS-polyacrylamide gels and showed two major bands of 100 and 160 kDa and a minor band of 120 kDa. By immunoblotting, these proteins were shown to correspond to CD66a (160 kDa), CD66b (100 kDa), and lysosome-associated membrane glycoprotein-1 and -2 (Lamp-1 and -2; 120 kDa). The unresponsive HL-60 cells lacked the CD66 Ags but contained the Lamps, implying that neutrophil CD66a and/or CD66b may be the functional galectin-3 receptors. This conclusion was supported by the subcellular localization of the CD66 proteins to the gelatinase and specific granules in resting neutrophils.

Cathepsin S controls the trafficking and maturation of MHC class II molecules in dendritic cells

Before a class II molecule can be loaded with antigenic material and reach the surface to engage CD4+ T cells, its chaperone, the class II-associated invariant chain (Ii), is degraded in a stepwise fashion by proteases in endocytic compartments. We have dissected the role of cathepsin S (CatS) in the trafficking and maturation of class II molecules by combining the use of dendritic cells (DC) from CatS(-/-) mice with a new active site-directed probe for direct visualization of active CatS. Our data demonstrate that CatS is active along the entire endocytic route, and that cleavage of the lysosomal sorting signal of Ii by CatS can occur there in mature DC. Genetic disruption of CatS dramatically reduces the flow of class II molecules to the cell surface. In CatS(-/-) DC, the bulk of major histocompatibility complex (MHC) class II molecules is retained in late endocytic compartments, although paradoxically, surface expression of class II is largely unaffected. The greatly diminished but continuous flow of class II molecules to the cell surface, in conjunction with their long half-life, can account for the latter observation. We conclude that in DC, CatS is a major determinant in the regulation of intracellular trafficking of MHC class II molecules.