Acidification of the young phagosomes ofParamecium is mediated by proton pumps derived from the acidosomes

Summary Although it is generally accepted that phagosome acidification is induced through the activity of a vacuolar proton pump (V-ATPase) present on the phagosome membrane, exactly how these pumps are delivered to the phagosomes is not well understood. To study this question inParamecium, it was necessary to first show that an authentic V-ATPase was present on their phagosomal membranes. Three antibodies raised against V-ATPases or their subunits were each found to label one or two large digestive vacuoles (DVs) inParamecium multimicronucleatum when immunofluorescence microscopy was used. Using horseradish peroxidase immunocytochemistry to increase sensitivity, about 10 DVs were shown to contain a V-ATPase. In high magnification images and cryoultramicrotomy these proton pumps were found to be located on the acidosomes, suggesting the vacuolar proton pumps on the DVs originate from the acidosomes. The authenticity of the V-ATPase was further confirmed by its sensitivity to cold temperature and to the V-ATPase specific inhibitor, concanamycin B, which at 10 nM doubled the t_1/2 for vacuole acidification. Thus, we conclude that (1) acidosomes and some DVs ofParamecium have a bona-fide concanamycin B-sensitive and cold-sensitive V-ATPase, (2) the V-ATPase is delivered to the young DVs during acidosome fusion, and (3) the V-ATPase is involved in vacuole acidification. Finally, we have now determined thatParamecium has two immunologically related V-ATPases that are involved in two very different functions, (1) the acidification of phagosomes and (2) fluid segregation in the contractile vacuole complexes.Abbreviations BS-FITC bovine serum albumin-fluorescein isothiocyanate - CVC contractile vacuole complex - DV-I to DV-IV digestive vacuole stages 1 to 4 - HRP horseradish peroxidase - V-ATPase vacuolar proton pump     

Sodium butyrate induced alterations in lysosomal enzyme activity

Summary Treatment of cultured HeLa cells with 5 mM sodium butyrate causes an inhibition of growth as well as extensive chemical and morphological differentiation. Lysosomal enzyme activity changes have been associated with both normal and neoplastic growth as well as many aspects of the neoplastic process. The comparative ultrastructural results show that the butyrate-treated cells have a more extensive internal membraneous system than the untreated cells, whereas other organelles seem unaffected by the butyrate treatment. Methods for the histochemical localization of lysosomal acid phosphatase show a twofold increase in particulate reaction product in the butyrate-treated HeLa cells. Isolation of lysosomes followed by a comparative enzyme analysis shows a two to three fold increase in acid phosphatase activity per cell after 24 h of butyrate treatment, as well as three to four fold increase in β-glucuronidase activity. These increases reverse within 24 h of removal of the butyrate from the culture medium. These results as interpreted suggest that butyrate treatment may be preventing sublethal autolysis by arresting the leakage of the lysosomal enzymes from the lysosome into the cytosol and thus allowing the cell to chemically and morphologically differentiate. This work was supported by National Institute of Health Grant HD 14085-03.     

Mycobacterial lysocardiolipin is exported from phagosomes upon cleavage of cardiolipin by a macrophage-derived lysosomal phospholipase A2

Pathogenic mycobacteria are able to survive and proliferate in phagosomes within host macrophages (Mphi). This capability has been attributed in part to their cell wall, which consists of various unique lipids. Some of these are important in the host-pathogen interaction, such as resistance against microbicidal effector mechanisms and modulation of host cell functions, and/or are presented as Ags to T cells. Here we show that two lipids are released from the mycobacterial cell wall within the phagosome of infected Mphi and transported out of this compartment into intracellular vesicles. One of these lipids was identified as lysocardiolipin. Lysocardiolipin was generated through cleavage of mycobacterial cardiolipin by a Ca2+-independent phospholipase A2 present in Mphi lysosomes. This result indicates that lysosomal host cell enzymes can interact with released mycobacterial lipids to generate new products with a different intracellular distribution. This represents a novel pathway for the modification of bacterial lipid Ags.     

Effects of mitogenic stimulation of lymphocytes on lysosomal enzyme activity

Changes in the activities of several lysosomal enzymes were studied during transformation of mouse spleen cells in vitro. The activity of beta-glucuronidase increased during culture in the presence of T or B-cell mitogens, and lymphoblasts contained higher levels of activity than did small, non-transformed lymphocytes. Moreover, lymphoblasts in well-transformed cultures had higher activities than those in poorly-transformed cultures. The activities of other lysosomal enzymes (N-acetyl-beta-glucosaminidase, alpha-mannosidase, beta-glucosidase) also increased during mitogenic stimulation, but each at different rates, although aryl sulphatase was unaffected. Such differences may be of importance when lymphocytes are used for diagnosis of inherited lysosomal deficiency diseases.     

Imaging lysosomal enzyme activity in live cells using self-quenched substrates

Endocytosis, the internalization and transport of extracellular cargo, is an essential cellular process. The ultimate step in endocytosis is the intracellular degradation of extracellular cargo for use by the cell. While live cell imaging and single particle tracking have been well-utilized to study the internalization and transport of cargo, the final degradation step has required separate biochemical assays. We describe the use of self-quenched endocytic cargo to image the intracellular transport and degradation of endocytic cargo directly in live cells. We first outline the fluorescent labeling and quantification of two common endocytic cargos: a protein, bovine serum albumin, and a lipid nanoparticle, low-density lipoprotein. In vitro measurements confirm that self-quenching is a function of the number of fluorophores bound to the protein or particle and that recovery of the fluorescent signal occurs in response to enzymatic degradation. We then use confocal fluorescence microscopy and flow cytometry to demonstrate the use of self-quenched bovine serum albumin with standard fluorescence techniques. Using live cell imaging and single particle tracking, we find that the degradation of bovine serum albumin occurs in an endo-lysosomal vesicle that is positive for LAMP1.     

Matrix metalloproteinase-9 activity detected in body fluids is the result of two different enzyme forms

In vitro activation of matrix metalloproteinase-9 (MMP-9) (Gelatinase B) with MMP-3 shows the presence of two different forms: an 82 kDa, N-terminal truncated form, and a 65 kDa, N- and C-terminal truncated form. So far the presence of the 65 kDa form has not been reported in vivo. Affinity chromatography was performed to separate MMP-9 from MMP-2 and immunoprecipitation to isolate ～65 kDa MMP-9 from 82 kDa MMP-9 in sera of healthy donors. The presence of ～65 kDa active MMP-9 was demonstrated both with gelatin zymography and western blot analysis. The ～65 kDa MMP-9 lacks the haemopexin domain required for the high-affinity binding of the tissue inhibitor TIMP-1, and can be evaluated by activity assay in the presence of TIMP-1. This opens the possibility to investigate the role of this form of MMP-9 that escapes physiological regulation.     

Ca2+ and synaptotagmin VII-dependent delivery of lysosomal membrane to nascent phagosomes

Synaptotagmin (Syt) VII is a ubiquitously expressed member of the Syt family of Ca2+ sensors. It is present on lysosomes in several cell types, where it regulates Ca2+-dependent exocytosis. Because [Ca2+]i and exocytosis have been associated with phagocytosis, we investigated the phagocytic ability of macrophages from Syt VII-/- mice. Syt VII-/- macrophages phagocytose normally at low particle/cell ratios but show a progressive inhibition in particle uptake under high load conditions. Complementation with Syt VII rescues this phenotype, but only when functional Ca2+-binding sites are retained. Reinforcing a role for Syt VII in Ca2+-dependent phagocytosis, particle uptake in Syt VII-/- macrophages is significantly less dependent on [Ca2+]i. Syt VII is concentrated on peripheral domains of lysosomal compartments, from where it is recruited to nascent phagosomes. Syt VII recruitment is rapidly followed by the delivery of Lamp1 to phagosomes, a process that is inhibited in Syt VII-/- macrophages. Thus, Syt VII regulates the Ca2+-dependent mobilization of lysosomes as a supplemental source of membrane during phagocytosis.     

Gamma-secretase is a functional component of phagosomes

Gamma-secretase is a high molecular mass protein complex that catalyzes the intramembrane cleavage of its protein substrates. Two proteins involved in phagocytosis, CD44 and the low density lipoprotein receptor-related protein, are gamma-secretase substrates, suggesting that this complex might regulate some aspects of phagocytosis. Our results indicate that the four components of gamma-secretase, viz. presenilin, nicastrin, APH-1, and PEN-2, are present and enriched on phagosome membranes from both murine macrophages and Drosophila S2 phagocytes. The gamma-secretase components form high molecular mass complexes in lipid microdomains of the phagosome membrane with the topology expected for the functional enzyme. In contrast to the majority of the phagosome proteins studied so far, which appear to associate transiently with this organelle, gamma-secretase resides on newly formed phagosomes and remains associated throughout their maturation into phagolysosomes. Finally, our results indicate that interferon-gamma stimulates gamma-secretase-dependent cleavages on phagosomes and that gamma-secretase activity may be involved in the phagocytic response of macrophages to inflammatory cytokines.     

Changes in lysosomal enzyme activity in the mitotic cycle of L cells

Activities of lysosomal enzymes (acid phosphatase, N-acetyl-beta-D-glucosaminidase, acid lipase and cathepsin D) have been examined in a synchronized culture of mouse L-fibroblasts. Cell synchronization was achieved by the double thymidine block with a subsequent mitotic selection after colcemid treatment. Specific activities of the enzymes studied were found to be higher in S-G2 that in G1. There is a linear increase (approximate doubling) in enzyme activities per cell from G1 to M. Activity of galactosyltransferase, a marker of the Golgi apparatus, declined in mitotic cells in comparison with the interphase cells. Ultrastructural examination of L-cells revealed a reduction of the intracellular membrane system including the Golgi apparatus during mitosis. Changes in the Golgi apparatus activity have been considered as a possible regulatory point of lysosome formation. The data presented are compared with the results of morphological studies of lysosomal system in L-cells.     

Differential and sequential delivery of fluorescent lysosomal probes into phagosomes in mouse peritoneal macrophages

It has previously been inferred that the fusion of a macrophage secondary lysosome with a phagosome delivers the entire lysosomal contents uniformly to the phagosome. We found, however, that different fluorescent lysosomal probes can enter phagosomes at remarkably different rates, even though they are initially sequestered together in the same organelles. Thus, sulforhodamine is almost exclusively delivered to yeast-containing phagosomes within 2 h of phagocytosis. But fluoresceinated, high molecular weight dextran accumulates in the same phagosomes only over a period of approximately 24 h. We postulate that the delivery of lysosomal contents may involve an intermittent and incremental process in which individual components can be selectively and sequentially transferred.     

Lipid-induced NOX2 activation inhibits autophagic flux by impairing lysosomal enzyme activity

Autophagy is a catabolic process involved in maintaining energy and organelle homeostasis. The relationship between obesity and the regulation of autophagy is cell type specific. Despite adverse consequences of obesity on cardiac structure and function, the contribution of altered cardiac autophagy in response to fatty acid overload is incompletely understood. Here, we report the suppression of autophagosome clearance and the activation of NADPH oxidase (Nox)2 in both high fat-fed murine hearts and palmitate-treated H9C2 cardiomyocytes (CMs). Defective autophagosome clearance is secondary to superoxide-dependent impairment of lysosomal acidification and enzyme activity in palmitate-treated CMs. Inhibition of Nox2 prevented superoxide overproduction, restored lysosome acidification and enzyme activity, and reduced autophagosome accumulation in palmitate-treated CMs. Palmitate-induced Nox2 activation was dependent on the activation of classical protein kinase Cs (PKCs), specifically PKCβII. These findings reveal a novel mechanism linking lipotoxicity with a PKCβ-Nox2-mediated impairment in pH-dependent lysosomal enzyme activity that diminishes autophagic turnover in CMs.     

An endogenous MDCK lysosomal membrane glycoprotein is targeted basolaterally before delivery to lysosomes

Using surface immunoprecipitation at 37 degrees C to "catch" the transient apical or basolateral appearance of an endogenous MDCK lysosomal membrane glycoprotein, the AC17 antigen, we demonstrate that the bulk of newly synthesized AC17 antigen is polarly targeted from the Golgi apparatus to the basolateral plasma membrane or early endosomes and is then transported to lysosomes via the endocytic pathway. The AC17 antigen exhibits very similar properties to members of the family of lysosomal-associated membrane glycoproteins (LAMPs). Parallel studies of an avian LAMP, LEP100, transfected into MDCK cells revealed colocalization of the two proteins to lysosomes, identical biosynthetic and degradation rates, and similar low levels of steady-state expression on both the apical (0.8%) and basolateral (2.1%) membranes. After treatment of the cells with chloroquine, newly synthesized AC17 antigen, while still initially targeted basolaterally, appears stably in both the apical and basolateral domains, consistent with the depletion of the AC17 antigen from lysosomes and its recycling in a nonpolar fashion to the cell surface.     

Mobility of late endosomal and lysosomal markers on phagosomes analyzed by fluorescence recovery after photobleaching

During phagosome maturation, the late endosomal marker Rab7 and the lysosomal marker LAMP1 localize to the phagosomes. We investigated the mobility of Rab7 and LAMP1 on the phagosomes in macrophages by fluorescence recovery after photobleaching (FRAP) analysis. Rab7 was mobile between the phagosomal membrane and the cytosol in macrophages that ingested latex beads during phagosome maturation. The addition of interferon-γ (IFN-γ) restricted this mobility, suggesting that Rab7 is forced to bind to the phagosomal membrane by IFN-γ-mediated activation. Immobilization of LAMP1 on the phagosomes was observed irrespective of IFN-γ-activation. We further examined the mobility of Rab7 on the phagosomes containing Mycobacterium bovis BCG by FRAP analysis. The rate of fluorescence recovery for Rab7 on mycobacterial phagosomes was lower than that on the phagosomes containing latex beads, suggesting that mycobacteria impaired the mobility of Rab7 and arrested phagosome maturation.     

Characterization of three rabbit liver lysosomal proteinases with fructose 1,6-bisphosphatase converting enzyme activity

A large number of nucleoside analogs have been found to inactivate S-adenosylhomocysteine (AdoHcy) hydrolase in a time-dependent irreversible manner. There are two classes of these irreversible inhibitors: (A) analogs that inactivate the enzyme in a pseudofirst-order process and are devoid of any side chain at the 5′-OH group; (B) analogs that inactivate the enzyme in a time-dependent but curvilinear process, and generally have a side chain at the 5′ position. Among the more potent irreversible inhibitors are 2-chloroadenosine, 9-β-d-arabinofuranosyladenine (Ara-A), and (±)aristeromycin. Release of adenine base from adenosine or Ara-A in the presence of AdoHcy hydrolase was observed, thus supporting the proposed catalytic mechanism of AdoHcy hydrolase, that entails the transient formation of 3′-ketoadenosine during enzymatic catalysis of either the formation or hydrolysis of AdoHcy. Both Ara-A and adenosine may exert their irreversible inactivation by a suicide mechanism, but nucleosides such as 5′-iodo-5′-deoxyadenosine and 3′-deoxyadenosine are probably strictly irreversible inhibitors per se in view of the catalytic mechanism proposed for AdoHcy hydrolase. Labeling of AdoHcy hydrolase, perhaps covalent in nature, by radioactive Ara-A and adenosine was demonstrated by gel electrophoresis.     

Hydrolysis of phospholipids by a lysosomal enzyme

The phospholipid-hydrolyzing activity of rat liver lysosomes has been studied. These lysosomes contain a phospholipase that cleaves both fatty acid ester linkages of lecithin and of phosphatidyl ethanolamine and releases free fatty acids from both positional isomers of lysolecithin. The enzyme does not require calcium for maximum activity, and is inhibited by diethyl ether and sodium deoxycholate. Mercuric ions and cetyltrimethyl ammonium bromide also inhibit the hydrolysis. Compared with lipase activity, this enzyme is relatively stable to heat. The specific activity of the hydrolysis of lecithin by the lysosomal enzyme is considerably higher than those reported for mitochondrial and microsomal phospholipases. The enzyme resembles other hydrolases of the lysosome in that it has an acid pH optimum (pH 4.5). This enzymic activity is present in both the lysosomal soluble enzyme fraction and in the lysosomal membrane fraction. The enzyme may participate in the intracellular digestion of mitochondria that is carried out by the intact lysosome in vivo. Localized inflammation and changes in vascular permeability following tissue damage could be catalyzed by this phospholipase.     

Estrogen modulation of osteoclast lysosomal enzyme secretion

Osteoclast-mediated bone resorption is accomplished by secretion of lysosomal proteases into an acidic extracellular compartment. We have previously demonstrated that avian osteoclasts and human osteoclast-like giant cell tumor cells respond in vitro to treatment with 17β-estradiol (17β-E₂) by decreased bone resorption activity. To better understand the mechanism by which this is accomplished, we have investigated the effects of 17β-E₂ treatment on lysosomal enzyme production and secretion by isolated avian osteoclasts and multinucleated cells from human giant cell tumors in vitro. Isolated cells were cultured with bone particles in the presence of either vehicle or steroid. The conditioned media and cells were harvested, and the levels of cathepsin B, cathepsin L, β-glucuronidase, lysozyme, and tartrate-resistant acid phosphatase (TRAP) activities were determined. There was a steroid dose-dependent decrease in secreted levels of these enzymes. Cell-associated levels of cathepsin L, β-glucuronidase, and lysozyme decreased, whereas cell-associated levels of cathepsin B and TRAP increased. These changes were measurable at 10^?10 M and maximal at 10^?8 M 17β-E₂. The changes were detectable at 4–18 h of treatment and increased through 24 h of treatment. The response was steroid specific, since the inactive estrogen isomer, 17β-E₂, failed to alter the activity levels. Moreover, the effects of 17β-E₂ were blocked when the cells were treated simultaneously with the estrogen antagonist ICI182–780 in conjunction with 17β-E₂. Human osteoclast-like cells obtained from giant cell tumors of bone responded similarly to estrogen with respect to cathepsin B, cathepsin L, and TRAP activities. However, secretion of β-glucuronidase and lysozyme were not altered by treatment with 10^?8 M 17β-E₂. These data indicate that estrogen effects on osteoclast resorption activity may be mediated by decreasing the secretion of cathepsin B, cathepsin L, and TRAP.