Effects of ammonia on processing and secretion of precursor and mature lysosomal enzyme from macrophages of normal and pale ear mice: evidence for two distinct pathways

The endolysosomal system in conventional and unconventional protein secretion

Most secreted proteins are transported through the "conventional" endoplasmic reticulum-Golgi apparatus exocytic route for their delivery to the cell surface and release into the extracellular space. Nonetheless, formative discoveries have underscored the existence of alternative or "unconventional" secretory routes, which play a crucial role in exporting a diverse array of cytosolic proteins outside the cell in response to intrinsic demands, external cues, and environmental changes. In this context, lysosomes emerge as dynamic organelles positioned at the crossroads of multiple intracellular trafficking pathways, endowed with the capacity to fuse with the plasma membrane and recognized for their key role in both conventional and unconventional protein secretion. The recent recognition of lysosomal transport and exocytosis in the unconventional secretion of cargo proteins provides new and promising insights into our understanding of numerous physiological processes.

Unconventional secretion of FABP4 by endosomes and secretory lysosomes

Adipocytes secrete fatty acid binding protein 4, which influences glucose production in hepatocytes and insulin secretion in pancreatic β-cells, but the mechanisms of its secretion are unclear. Villeneuve et al. show that FABP4 is secreted unconventionally through enclosure within endosomes and secretory lysosomes.

An appreciation of the functional properties of the cytoplasmic fatty acid binding protein 4 (FABP4) has advanced with the recent demonstration that an extracellular form secreted by adipocytes regulates a wide range of physiological functions. Little, however, is known about the mechanisms that mediate the unconventional secretion of FABP4. Here, we demonstrate that FABP4 secretion is mediated by a membrane-bounded compartment, independent of the conventional endoplasmic reticulum–Golgi secretory pathway. We show that FABP4 secretion is also independent of GRASP proteins, autophagy, and multivesicular bodies but involves enclosure within endosomes and secretory lysosomes. We highlight the physiological significance of this pathway with the demonstration that an increase in plasma levels of FABP4 is inhibited by chloroquine treatment of mice. These findings chart the pathway of FABP4 secretion and provide a potential therapeutic means to control metabolic disorders associated with its dysregulated secretion.

Lysosomal storage causes cellular dysfunction in mucolipidosis II skin fibroblasts

Mucolipidosis II (ML-II) is a fatal inherited metabolic disease caused by deficiency of GlcNAc-phosphotransferase, which plays a role in generating the mannose 6-phosphate recognition marker on lysosomal enzymes. In ML-II, many lysosomal acid hydrolases are mistargeted out of cells, and lysosomes become filled with undigested substrates, which explains inclusion cell disease as an alternative name for this disease. In this study, we revealed various cellular phenotypes in ML-II skin fibroblasts. We quantitated phospholipid and cholesterol within cells and showed ~2-fold accumulation in ML-II as compared with normal cells. Lysosomal pH of ML-II cells was higher than that of normal cells (5.29 ± 0.08 versus 4.79 ± 0.10, p < 0.001). The proliferated lysosomes in ML-II cells were accumulated ~3-fold in amount as compared with normal cells. Intracellular logistics including endocytosis and mannose 6-phosphate receptor recycling were impaired in ML-II cells. To confirm whether these ML-II cellular phenotypes derive from deficient lysosomal acid hydrolases within lysosomes, we performed supplementation of lysosomal enzymes using a partially purified total enzyme mixture, which was derived from the conditioned culture medium of normal skin fibroblasts after NH(4)Cl treatment. This supplementation corrected all of the previously described ML-II phenotypes. In addition, the autophagic and mitochondrial impairment that we have previously reported improved, and inclusion bodies disappeared on electron micrography following total lysosomal enzyme supplementation. Our results indicate that various cellular phenotypes in ML-II are caused by the deficiency of many lysosomal enzymes and massive accumulation of undigested substrates.

Reduced proteasomal activity contributes to the accumulation of carbonylated proteins in chronic experimental autoimmune encephalomyelitis

We have recently shown that several carbonylated proteins, including glial fibrillary acidic protein, β-actin and β-tubulin, accumulate within cerebellar astrocytes during the chronic phase of myelin-oligodendrocyte glycoprotein (MOG)(35-55) peptide-induced experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice. As protein carbonyls cannot be repaired and there is less oxidative stress in chronic than in acute EAE, we hypothesized that the accumulation of carbonylated proteins in these animals may be due to a defect in the degradation of the modified proteins. Alternatively, oxidized proteins in chronic EAE mice may be more resistant to proteolysis. Using lipopolysaccharide-stimulated astrocytes and several protease inhibitors we identified the 20S proteasome as the proteolytic system responsible for the elimination of most oxidized proteins. We also discovered that the chymotrysin-like and caspase-like activities of the 20S proteasome are impaired in chronic EAE, while the amount of proteasome was unchanged. Proteasome failure in these animals was confirmed by the build-up of ubiquitinated proteins, mostly within astrocytes. In a cell-free system, carbonylated proteins from EAE mice with acute and chronic disease seem to be equally sensitive to proteasomal degradation. Altogether, the results support the notion that diminished activity of the 20S proteasome is a major contributor to the accumulation of carbonylated proteins in astrocytes of chronic EAE mice.

Interaction of Hermansky-Pudlak Syndrome genes in the regulation of lysosome-related organelles

Hermansky-Pudlak Syndrome (HPS) is a genetically heterogeneous disease caused by abnormalities in the synthesis and/or trafficking of lysosome-related organelles (LROs) including melanosomes, lamellar bodies of lung type II cells and platelet dense granules. At least 15 genes cause HPS in mice, with a significant number specifying novel subunits of protein complexes termed BLOCs (Biogenesis of Lysosome-related Organelles Complexes). To ascertain whether BLOC complexes functionally interact in vivo, mutant mice doubly or triply deficient in protein subunits of the various BLOC complexes and/or the AP-3 adaptor complex were constructed and tested for viability and for abnormalities of melanosomes, lung lamellar bodies and lysosomes. All mutants, including those deficient in all three BLOC complexes, were viable though the breeding efficiencies of multiple mutants involving AP-3 were severely compromised. Interactions of BLOC protein complexes with each other and with AP-3 to affect most LROs were apparent. However, these interactions were tissue and organelle dependent. These studies document novel biological interactions of BLOC and AP-3 complexes in the biosynthesis of LROs and assess the role(s) of HPS protein complexes in general health and physiology in mammals. Double and triple mutant HPS mice provide unique and practical experimental advantages in the study of LROs.

BLOC-3, a protein complex containing the Hermansky-Pudlak syndrome gene products HPS1 and HPS4

The Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by defective lysosome-related organelles. HPS results from mutations in either one of six human genes named HPS1 to HPS6, most of which encode proteins of unknown function. Here we report that the human HPS1 and HPS4 proteins are part of a complex named BLOC-3 (for biogenesis of lysosome-related organelles complex 3). Co-immunoprecipitation experiments demonstrated that epitope-tagged and endogenous HPS1 and HPS4 proteins assemble with each other in vivo. The HPS1.HPS4 complex is predominantly cytosolic, with a small amount being peripherally associated with membranes. Size exclusion chromatography and sedimentation velocity analyses of the cytosolic fraction indicate that HPS1 and HPS4 form a moderately asymmetric protein complex with a molecular mass of approximately 175 kDa. HPS4-deficient fibroblasts from light ear mice display normal distribution and trafficking of the lysosomal membrane protein, Lamp-2, in contrast to fibroblasts from AP-3-deficient pearl mice (HPS2), which exhibit increased trafficking of this lysosomal protein via the plasma membrane. Similarly, light ear fibroblasts display an apparently normal accumulation of Zn2+ in intracellular vesicles, unlike pearl fibroblasts, which exhibit a decreased intracellular Zn2+ storage. Taken together, these observations demonstrate that the HPS1 and HPS4 proteins are components of a cytosolic complex that is involved in the biogenesis of lysosomal-related organelles by a mechanism distinct from that operated by AP-3 complex.

The secretory route of the leaderless protein interleukin 1beta involves exocytosis of endolysosome-related vesicles

Interleukin 1beta (IL-1beta), a secretory protein lacking a signal peptide, does not follow the classical endoplasmic reticulum-to-Golgi pathway of secretion. Here we provide the evidence for a "leaderless" secretory route that uses regulated exocytosis of preterminal endocytic vesicles to transport cytosolic IL-1beta out of the cell. Indeed, although most of the IL-1beta precursor (proIL-1beta) localizes in the cytosol of activated human monocytes, a fraction is contained within vesicles that cofractionate with late endosomes and early lysosomes on Percoll density gradients and display ultrastructural features and markers typical of these organelles. The observation of organelles positive for both IL-1beta and the endolysosomal hydrolase cathepsin D or for both IL-1beta and the lysosomal marker Lamp-1 further suggests that they belong to the preterminal endocytic compartment. In addition, similarly to lysosomal hydrolases, secretion of IL-1beta is induced by acidotropic drugs. Treatment of monocytes with the sulfonylurea glibenclamide inhibits both IL-1beta secretion and vesicular accumulation, suggesting that this drug prevents the translocation of proIL-1beta from the cytosol into the vesicles. A high concentration of extracellular ATP and hypotonic medium increase secretion of IL-1beta but deplete the vesicular proIL-1beta content, indicating that exocytosis of proIL-1beta-containing vesicles is regulated by ATP and osmotic conditions.

Mouse models of Hermansky Pudlak syndrome: a review

Hermansky Pudlak Syndrome (HPS) is a recessively inherited disease affecting the contents and/or the secretion of several related subcellular organelles including melanosomes, lysosomes, and platelet dense granules. It presents with disorders of pigmentation, prolonged bleeding, and ceroid deposition, often accompanied by severe fibrotic lung disease and colitis. In the mouse, the disorder is clearly multigenic, caused by at least 14 distinct mutations. Studies on the mouse mutants have defined the granule abnormalities of HPS and have shown that the disease is associated with a surprising variety of phenotypes affecting many tissues. This is an exciting time in HPS research because of the recent molecular identification of the gene causing a major form of human HPS and the expected identifications of several mouse HPS genes. Identifications of mouse HPS genes are expected to increase our understanding of intracellular vesicle trafficking, lead to discovery of new human HPS genes, and suggest diagnostic and therapeutic approaches toward the more severe clinical consequences of the disease.

The mouse pale ear (ep) mutation is the homologue of human Hermansky-Pudlak syndrome

The recessive mutation at the pale ear (ep) locus on mouse chromosome 19 was found to be the homologue of human Hermansky-Pudlak syndrome (HPS). A positional cloning strategy using yeast artificial chromosomes spanning the HPS locus was used to identify the HPS gene and its murine counterpart. These genes and their predicted proteins are highly conserved at the nucleotide and amino acid levels. Sequence analysis of the mutant ep gene revealed the insertion of an intracisternal A particle element in a protein-coding 3' exon. Here we demonstrate that mice with the ep mutation exhibit abnormalities similar to human HPS patients in melanosomes and platelet-dense granules. These results establish an animal model of HPS and will facilitate biochemical and molecular analyses of the functions of this protein in the membranes of specialized intracellular organelles.

Mouse pale ear (ep) is homologous to human Hermansky-Pudlak syndrome and contains a rare 'AT-AC' intron

Hermansky-Pudlak syndrome (HPS) is a rare, often fatal, autosomal recessive disorder in which albinism, bleeding and lysosomal storage are associated with defects of diverse cytoplasmic organelles, including melanosomes, platelet dense granules and lysosomes. Similar multi-organellar defects occur in the Chediak-Higashi syndrome (CHS), as well as in a large number of different mouse mutants. The HPS gene is located in 10q23, and two genetically distinct mouse loci, pale ear (ep) and ruby-eye (ru), both with mutant phenotypes similar to human HPS, map close together in the homologous region of murine chromosome 19, suggesting that one of these loci might be homologous to human HPS. We recently identified the human HPS gene, which encodes a novel ubiquitously-expressed transmembrane protein of unknown function. Here, we describe characterization of the mouse Hps cDNA and genomic locus, and identification of pathologic Hps gene mutations in ep but not in ru mice, establishing mouse pale ear as an animal model for human HPS. The phenotype of homozygous ep mutant mice encompasses those of both HPS and CHS, suggesting that these disorders may be closely related. In addition, the mouse and human HPS genes both contain a rare 'AT-AC' intron, and comparison of the sequences of this intron in the mouse and human genes identified conserved sequences that suggest a possible role for pre-mRNA secondary structure in excision of this rare class of introns.

Drug-induced lysosomal storage of sulphated glycosaminoglycans

1. Certain compounds (e.g., the immunomodulator tilorone and congeners) are able to induce lysosomal storage of sulphated glycosaminoglycans (GAG), thus, producing cytological and biochemical alterations reminiscent of the inherited mucopolysaccharidoses. The drug-induced GAG storage has been studied in cultured fibroblasts of several species and in rats, and it is likely to occur also in humans. 2. The cytological hallmarks of GAG storage are enlarged lysosomes congested with material that is intensely stained by cationic dyes. With respect to fixation techniques, one has to keep in mind that the GAGs are highly water-soluble and are leached during conventional fixation and tissue processing. Biochemically, the elevation of GAG contents in tissues and cultured fibroblasts is due to storage of dermatan sulphate, predominantly. 3. The molecular structure of the potent inducers of GAG storage is characterized by a planar tricyclic aromatic ring system that is symmetrically substituted with two side chains of 4-5 sigma bond length, each carrying a protonizable nitrogen atom. The lysosomal storage of GAG is accompanied by lysosomal accumulation of the inducing drug, with the molar ratio of drug to GAG-disaccharide unit amounting to > 1:1. The reversibility of GAG storage is rather slow. 4. The pathogenic mechanisms underlying the drug side effects are discussed and the following hypothesis is put forward: The compounds in question are lysosomotropic weak bases. They get trapped in the acidic lysosomes and accumulate highly there. Physicochemical data suggest that the drugs form complexes with the sulphated GAGs, particularly with dermatan sulphate: The positively charged nitrogen atoms of the drug side chains interact with the negative charges of sulphate and carboxy groups of the GAGs, thereby crosslinking at least two GAG helices. Moreover, the interlinking drug molecules form parallel stacks resulting from interaction of the aromatic pi-electrons of the planar ring systems. This further stabilizes the complexes. The GAGs within the complexes are thought to be resistant to the degrading lysosomal enzymes. 5. Drug-induced GAG storage has not been directly demonstrated in man. Yet, clinical reports on keratopathy and basophilic cytoplasmic inclusions in blood lymphocytes of tilorone-treated patients suggest that this drug side effect may also occur in man.

Dictyostelium discoideum cells lacking the 34,000-dalton actin-binding protein can grow, locomote, and develop, but exhibit defects in regulation of cell structure and movement: a case of partial redundancy

Cells lacking the Dictyostelium 34,000-D actin-bundling protein, a calcium-regulated actin cross-linking protein, were created to probe the function of this polypeptide in living cells. Gene replacement vectors were constructed by inserting either the UMP synthase or hygromycin resistance cassette into cloned 4-kb genomic DNA containing sequences encoding the 34-kD protein. After transformation and growth under appropriate selection, cells lacking the protein were analyzed by PCR analyses on genomic DNA, Northern blotting, and Western blotting. Cells lacking the 34-kD protein were obtained in strains derived from AX2 and AX3. Growth, pinocytosis, morphogenesis, and expression of developmentally regulated genes is normal in cells lacking the 34-kD protein. In chemotaxis studies, 34-kD- cells were able to locomote and orient normally, but showed an increased persistence of motility. The 34-kD- cells also lost bits of cytoplasm during locomotion. The 34-kD- cells exhibited either an excessive number of long and branched filopodia, or a decrease in filopodial length and an increase in the total number of filopodia per cell depending on the strain. Reexpression of the 34-kD protein in the AX2-derived strain led to a "rescue" of the defect in the persistence of motility and of the excess numbers of long and branched filopodia, demonstrating that these defects result from the absence of the 34-kD protein. We explain the results through a model of partial functional redundancy. Numerous other actin cross-linking proteins in Dictyostelium may be able to substitute for some functions of the 34-kD protein in the 34-kD cells. The observed phenotype is presumed to result from functions that cannot be adequately supplanted by a substitution of another actin cross-linking protein. We conclude that the 34-kD actin-bundling protein is not essential for growth, but plays an important role in dynamic control of cell shape and cytoplasmic structure.

Multiple host defense defects in failure of C57BL/6 ep/ep (pale ear) mice to resolve visceral Leishmania donovani infection

Euthymic C57BL/L ep/ep (pale ear [PE]) mice halt the visceral replication of intracellular Leishmania donovani but fail to properly resolve infection. A previous study identified an isolated defect in tissue granuloma formation in these mice; CD4+ and CD8+ cell number, gamma interferon (IFN-gamma) production, and macrophage antimicrobial activity in vitro were all intact. New in vivo results reported here suggest a considerably more complex immune defect, with evidence indicating (i) enhanced control over L. donovani after transfer of normal C57BL/6 spleen cells, (ii) a partially suppressive Th2 cell-associated response mediated by interleukin-4 (IL-4) but not reversed by CD4+ cell depletion, (iii) absent responses to endogenous Th1 cell lymphokines (IFN-gamma and IL-2) but preserved responsiveness to endogenous tumor necrosis factor alpha, (iv) absent responses to exogenous treatment with recognized antileishmanial cytokines (IFN-gamma, IL-2, IL-12, and granulocyte-macrophage colony-stimulating factor [GM-CSF]) not corrected by transfer of C57BL/6 spleen cells, and (v) a deficient response to antimony chemotherapy. Defective hepatic granuloma formation was not corrected by transfer of C57BL/6 spleen cells or by anti-IL-4 administration. While treatment with IL-2 and GM-CSF modified the tissue reaction and induced selected effector cells to encase tissue macrophages, no antileishmanial activity resulted. Together, these observations suggest that the failure of PE mice to resolve visceral L. donovani infection likely represents expression of multiple suboptimal immune responses and/or partial defects, probably involving a combination of T-cell dysfunction, a Th2 cell response, and target cell (macrophage) hyporesponsiveness.

The pathway of secretion of proteinases in Trichomonas vaginalis

Trichomonads secrete large amounts of hydrolytic enzymes into liquid growth medium. Proteinase release by Trichomonas vaginalis has been quantified after resuspension of the parasite in a simple buffered maltose medium. After 6 h incubation, 70-90% of each of two cysteine proteinase activities, one towards benzyloxycarbonyl-arginyl-arginine 4-nitroanilide (Z-RR-Nan) and the other active towards N-benzoyl-prolyl-phenylalanyl-arginine 4-nitroanilide (Bz-PFR-Nan), was extracellular. This release was insensitive to changes in pH within the range from 5.5 to 8.6 but was partially inhibited by chloride ions. The secretion of activity towards Bz-PFR-Nan was temperature-sensitive but was still detectable down to 14 degrees C. Neither this nor other cysteine proteinase activities were detectable on the surface of parasites. Release was stimulated by various amines and monensin, suggesting that secretion was from or via acidic compartments. The intracellular activity towards Bz-PFR-Nan could be totally and irreversibly inhibited by treating the parasites with benzyloxycarbonyl-phenylalanyl-alanine diazomethylketone (Z-FA-DMK), without otherwise harming the cells. Regeneration and routing of the proteinases responsible for this activity was followed after removal of the inhibitor. There was a significant rise in the intracellular level of activity before it became detectable in the medium. The release of this activity was accelerated by amines and monensin, but the build-up of enzyme activity within cells was not prevented. Organelles containing cysteine proteinases banded as a single peak in Percoll density gradients. The density of these increased when cells were treated with dextran. The activity towards Bz-PFR-Nan which reappeared after Z-FA-DMK treatment has a similar distribution. The proteinase-containing fraction could be distinguished from an early (5 min) endosome fraction, suggesting that it was composed of late endosomes/lysosomes. Thus these results imply that the secretion pathway for proteinases necessarily involves lysosomes/late endosomes.

Tilorone-induced lysosomal storage of sulphated glycosaminoglycans can be separated from tilorone-induced enhancement of lysosomal enzyme secretion

This investigation deals with a drug side-effect. The immunomodulatory drug tilorone (2,7-bis[2-(diethylamino)ethoxy]fluoren-9-one) and congeners induce lysosomal storage of sulphated glycosaminoglycans (GAGs) in animals and in cultured cells. At high tilorone concentrations, GAG storage in cultured fibroblasts was previously reported to be accompanied, and presumably caused by, disturbance of intracellular targeting of lysosomal enzyme precursors, which leads to enhanced secretion and thus loss of lysosomal enzymes. The purpose of the present study was to examine whether the GAG storage induced in cultured bovine fibroblasts by low tilorone concentrations is also accompanied by enhanced lysosomal enzyme release. Enhanced secretion of beta-hexosaminidase (EC 3.2.1.52) was taken as indicating the intracellular mistargeting of lysosomal enzyme precursors. Dose-response curves were established for (a) the intracellular accumulation of 35S-GAGs and (b) the release of beta-hexosaminidase after exposure (72 hr) to tilorone (1-35 microM). For positive controls, the classical lysosomotropic agents NH4Cl (1-30 mM) and chloroquine (1-60 microM) were used. With NH4Cl, 35S-GAG storage was accompanied by enhanced enzyme release throughout the concentration range (EC50 at 3.3 mM for either effect). With chloroquine, low concentrations (< or = 5 microM) caused a small increase in 35S-GAG accumulation without abnormal enzyme secretion; at higher concentrations both drug effects were produced (EC50 around 15 microM for either effect). With tilorone, low concentrations (< or = 5 microM) caused marked 35S-GAG accumulation without enhancement of enzyme release. The EC50 for tilorone-induced 35S-GAG storage was 3 microM, as opposed to 15 microM for enzyme release. The results indicate that GAG storage induced by low concentrations of tilorone is due to mechanisms other than mistargeting and loss of lysosomal enzymes. On the basis of previous results it may be hypothesized that tilorone and other symmetrically substituted dicationic compounds form complexes with the polyanionic GAG chains and thereby impair their enzymic degradation.

Pilocarpine-induced lysosomal enzyme secretion, from bovine trabecular meshwork cells

It has long been held that pilocarpine-induced ciliary muscle contraction causes a mechanical change in the configuration of the trabecular meshwork, thereby increasing its fluid conductance. Though the results of many studies are consistent with this theory, other findings suggest a direct action of pilocarpine on the meshwork. We used cultured bovine trabecular meshwork (BTM) cells to study the cell biological effects of pilocarpine, chemically a weak base, and demonstrated increased vacuolization of the BTM cells after incubation with pilocarpine, reflecting a trapping of the protonated base inside the lysosomes. We also showed that pilocarpine enhanced the release of lysosomal hydrolases into the medium. We hypothesize that this is clinically relevant and that the pilocarpine-induced release of hydrolases modifies the extracellular matrix of the trabecular meshwork, thereby increasing its fluid conductance.

Molecular map of chromosome 19 including three genes affecting bleeding time: ep, ru, and bm

The mouse ruby eye (ru) and pale ear (ep) pigment dilution genes cause platelet storage pool deficiency (SPD) and prolonged bleeding times. The brachymorphic (bm) gene, in addition to causing skeletal abnormalities, is also associated with prolonged bleeding times. All three hemorrhagic genes are found within 10 cM on Chromosome (Chr) 19. In this study, 15 microsatellite markers and five cDNAs, spanning 21 cM of Chr 19, were mapped in relation to the bm, ep, and ru genes in 457 progeny of an interspecific backcross utilizing the highly inbred strain PWK derived from the Mus musculus musculus species. Several markers were found to be closely linked to the three genes and should be useful as entry points in their eventual molecular identification.

Lysosomal storage diseases: mechanisms of enzyme replacement therapy

Lysosomal diseases result from deficiency of one of the many enzymes involved in the normal, step-wise breakdown of macromolecules. Studies in vitro have shown that cells from enzyme-deficient patients can be corrected by an exogenous supply of the missing enzyme. This occurs by receptor-mediated endocytosis of normal enzyme added to tissue culture medium and also by direct transfer from normal leukocytes during cell-to-cell contact. Immunohistochemical analysis has revealed that these processes have similar pathways of intracellular transport of the acquired enzymes, which ultimately reach mature lysosomes in the recipient cells. Moreover, recent studies suggest that both mechanisms are important in the therapy of lysosomal storage diseases by bone marrow transplantation. Advances in gene technology are likely to improve the successful treatment of these disorders, by facilitating the large scale production of clinically effective proteins and also by enabling the stable and safe introduction of normal lysosomal genes into cells of affected patients.

Sandy: a new mouse model for platelet storage pool deficiency

Sandy (sdy) is a mouse mutant with diluted pigmentation which recently arose in the DBA/2J strain. Genetic tests indicate it is caused by an autosomal recessive mutation on mouse Chromosome 13 near the cr and Xt genetic loci. This mutation is different genetically and hematologically from previously described mouse pigment mutations with storage pool deficiency (SPD). The sandy mutant has diluted pigmentation in both eyes and fur, is fully viable and has prolonged bleeding times. Platelet serotonin levels are extremely low although ATP dependent acidification activity of platelet organelles appears normal. Also, platelet dense granules are extremely reduced in number when analysed by electron microscopy of unfixed platelets. Platelets have abnormal uptake and flashing of the fluorescent dye mepacrine. Secretion of lysosomal enzymes from kidney and from thrombin-stimulated platelets is depressed 2- and 3-fold, and ceroid pigment is present in kidney. Sandy platelets have a reduced rate of aggregation induced by collagen. The sandy mutant has an unusually severe dense granule defect and thus may be an appropriate model for cases of human Hermansky-Pudlak syndrome with similarly extreme types of SPD. It represents the tenth example of a mouse mutant with simultaneous defects in melanosomes, lysosomes and/or platelet dense granules.

Role of lysosomal and cytosolic pH in the regulation of macrophage lysosomal enzyme secretion

Rapid and parallel secretion of lysosomal beta-N-acetylglucosaminidase and preloaded fluorescein-labelled dextran was initiated in macrophages by agents affecting intracellular pH (methylamine, chlorpromazine, and the ionophores monensin and nigericin). In order to evaluate the relative role of changes in lysosomal and cytosolic pH, these parameters were monitored by using pH-sensitive fluorescent probes [fluorescein-labelled dextran or 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein]. All agents except chlorpromazine caused large increases in lysosomal pH under conditions where they induced secretion. By varying extracellular pH and ion composition, the changes in lysosomal and cytosolic pH could be dissociated. Secretion was then found to be significantly modulated by changes in cytosolic pH, being enhanced by alkalinization and severely inhibited by cytosolic acidification. However, changes in cytosolic pH in the absence of stimulus were unable to initiate secretion. Dissociation of the effects on lysosomal and cytosolic pH was also achieved by combining stimuli with either nigericin or acetate. Further support for a role of intracellular pH in the control of lysosomal enzyme secretion was provided by experiments where bicarbonate was included in the medium. The present study demonstrates that an increase in lysosomal pH is sufficient to initiate lysosomal enzyme secretion in macrophages and provides evidence for a significant regulatory role of cytosolic pH.

Effect of glycosylation inhibitors and acidotropic amines on the synthesis, processing, and intracellular-extracellular distribution of alpha-L-fucosidase in B-lymphoblastoid cells

N-Methyldeoxynojirimycin, 1-deoxymannojirimycin, and monensin interferred with normal processing of asparagine-linked oligosaccharide chains of alpha-L-fucosidase in lymphoid cells by blocking conversion of high-mannose oligosaccharides of newly made precursor enzyme to complex oligosaccharides of mature intracellular and extracellular forms of enzyme. These compounds did not substantially alter the distribution of newly made alpha-L-fucosidase between intracellular and extracellular compartments. Thus, sorting of newly made alpha-L-fucosidase molecules that are retained intracellularly from molecules that are eventually secreted does not require terminal glycosylation or the trimming of glucose or alpha-D-(1----2)-linked mannose residues from carbohydrate chains. Chloroquine and ammonium chloride had no substantial effect on the structural processing or on the intracellular-extracellular distribution of alpha-L-fucosidase in lymphoid cells. In other cell types, these weak bases caused a massive secretion and an intracellular deficiency of acid hydrolases. The different responses to weak bases in lymphoid cells and the other cell types can be explained either by an inability of these agents to neutralize the pH of intracellular organelles in lymphoid cells or by a routing mechanism in lymphoid cells that is independent of pH.

Cell contact induces the synthesis of a lysosomal enzyme precursor in lymphocytes and its direct transfer to fibroblasts

The activity of a lysosomal enzyme, alpha-D-mannosidase (EC 3.2.1.24), increased markedly in normal lymphocytes when they were cultured together with fibroblasts from a patient with an inherited deficiency of this enzyme. Cell-to-cell contact was obligatory for this increase in activity, which also required new protein synthesis. The enzyme induced in the co-cultured lymphocytes was a high molecular weight form of alpha-D-mannosidase that was not detected in lymphocytes cultured alone, which had only the low molecular weight mature enzyme. It was this precursor form alone that was directly transferred to the mannosidosis fibroblasts, where it was present initially in organelles of low density. When the culture period was extended the lymphocyte precursor enzyme was transported to the heavy lysosomes in the recipient cells, and correctly processed to the functionally effective mature enzyme.

Cycling of the integral membrane glycoprotein, LEP100, between plasma membrane and lysosomes: kinetic and morphological analysis

LEP100 (an integral membrane glycoprotein, Mr = 100,000) occurs in three subcellular compartments: lysosome (approximately 90% of the molecules), endosome (5%-8%), and plasma membrane (2%-3%). Rate constants for movement to and from each compartment have been estimated. The movement of LEP100 from endosomes to lysosomes was blocked by chloroquine, causing redistribution to a new steady state in which about 30% of LEP100 molecules were localized in clathrin-coated patches on the cell surface, while intracellular LEP100 occurred in nearby endocytic vesicles. The cell-surface and endosomal pools of LEP100 remained in rapid equilibrium (t1/2 about 5 min). These results support the existence of a hitherto unappreciated pathway of membrane flow from lysosomes. The lysosome should not be considered simply a terminal target of membrane trafficking.

Fibronectin-degrading proteases from the membranes of transformed cells

The local degradation of fibronectin substrata by Rous sarcoma virus-transformed chick embryonic fibroblasts requires cell-contact-related metalloendoprotease and serine-protease activities. Using fibronectin-containing SDS gels, two large proteases with apparent molecular weights of 120K and 150K were found only in the membrane fraction of transformed cells and were absent in normal cells. Both 120K and 150K proteases were active at neutral pH, but showed preferential inhibitor sensitivities of serine and metal proteases, respectively. The 150K protease appeared to account for most of the proteolytic activity since metalloendoprotease inhibitors completely blocked proteolytic activity of the 150K in fibronectin gels, more than 80% of the fibronectin-degrading activity of solubilized membranes, and largely suppressed the appearance of fibronectin degradation spots in cultures of transformed cells.

Effects of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma cells. A flow-cytometry and cytochemical study

The effect of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma (Neuro-2a) cells were studied using fluorescein-labeled dextran, concanavalin A conjugated with fluorescein isothiocyanate, and cationized ferritin as tracers. Ammonia treatment increased the rate of endocytosis of cationized ferritin as well as the number of cell elements involved in the process. Moreover, the number of cytoplasmic components containing acid phosphatase activity was also found to increase following ammonia treatment. In contrast, flow-cytometric analyses showed that, under experimental conditions, exposure to ammonia did not alter the intralysosomal pH and had little effect on the fluid-phase and receptor-mediated endocytosis of fluorescein-labeled dextran and concanavalin-A fluorocrome, respectively.

Coordinately increased lysozymuria and lysosomal enzymuria induced by maleic acid

During the acute renal tubular dysfunction of Fanconi syndrome and type 2 renal tubular acidosis (FS/RTA2) induced by maleic acid in the unanesthetized dog, we observed: 30 minutes after the onset of FS/RTA2, the urinary excretion of lysosomal enzymes, N-acetyl-beta-glucosaminidase (NAG), beta-glucuronidase (beta-gluc) and beta-galactosidase (beta-galac), increased simultaneously with the anticipated increase in renal clearance of lysozyme; the severities of all these hyperenzymurias increased rapidly, progressively, and in parallel, all reaching a peak some 60 to 80 minutes after their onset; thereafter, while the FS/RTA2 continued undiminished in severity, the severity of the hyperenzymurias decreased rapidly, greatly, progressively, and in parallel; and sodium phosphate loading strikingly attenuated the FS/RTA2 and the hyperenzymurias. Thus, the maleic acid-induced FS/RTA2 is attended by an acute reversible-complex derangement in the renal tubular processing of proteins that: affects not only lysozyme which is normally filtered, but also NAG and other lysosomal enzymes, which are not; and is to some extent functionally separable from that of FS/RTA2. The findings suggest that the derangements in renal processing of lysozyme and lysosomal enzymes are linked, and that a phosphate-dependent metabolic abnormality in the proximal tubule can participate in the pathogenesis of both these derangements and the FS/RTA2.

Subcellular distribution of acid alpha-glucosidase in fibroblasts and of antigenically cross-reactive material in Pompe's disease fibroblasts

From fibroblasts of two cases of Pompe's disease (acid alpha-glucosidase deficiency), one of the childhood type (RH-SF-1) and one of the adult type (RH-SF-2), and normal fibroblasts, antigenically cross-reactive material and acid alpha-glucosidase were immunoprecipitated and analysed by immunoelectrotransfer blotting. The acid alpha-glucosidase and antigenically cross-reactive material (which reacts with antibody raised against normal acid alpha-glucosidase) revealed a precursor form of molecular weight 97,000 and two major components of 79,000 and 76,000. When monensin was added to the fibroblast culture, the two major components of normal acid alpha-glucosidase were decreased, whereas the large molecular weight precursor was increased. On the other hand, the 97,000 molecular weight component of cross-reactive material in the Pompe's fibroblasts (RH-SF-1 and RH-SF-2) was only slightly increased on monensin treatment. The fibroblasts were pulse-chase labelled with [2-H3] mannose and 32Pi. The cross-reactive material and acid alpha-glucosidase were precipitated with anti acid alpha-glucosidase antibody, and after sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), fluorography was performed. The radiolabel of 3H in the cross-reactive material of RH-SF-1 and -2 was weak, and 32P in the cross-reactive material of both fibroblasts was very weak when compared with those of the acid alpha-glucosidase. The radiolabel of 32P in the cross-reactive material of RH-SF-1 was extremely weak. Immunofluorescence histochemistry revealed a granular localization of acid alpha-glucosidase in the normal fibroblast cytoplasm, and a diffuse distribution of cross-reactive material in the cytoplasm of RH-SF-1 and -2. Immuno-electron microscopic examinations showed a normal acid alpha-glucosidase localization on the inner side of the lysosomal membrane and also diffusely in the lysosome; when treated with monensin, it was present on the trans part of the Golgi apparatus. Antigenically cross-reactive material, however, was found in the cytoplasm and endoplasmic reticulum. Some lysosomal localization was observed sporadically. Even after monensin treatment, it was not demonstrated on the Golgi apparatus.

Cytochemical localization of beta-galactosidase in resident and inflammatory peritoneal macrophages from C57BL mice

A cytochemical method for the detection of beta-galactosidase (beta-Gase) in mouse peritoneal macrophages was used to study the ultrastructural localization of this enzyme in these cells. It was found that the reaction product for beta-Gase was localized in the perinuclear cisternae, the endoplasmic reticulum, the Golgi complex, lysosomes, vesicles and on the cell surface of peritoneal macrophages from untreated C57BL mice. When examined by X-ray microanalysis the crystalline reaction product was found to contain bromine, an element present in the indolyl substrate which was used to identify beta-Gase. Injection of Proprionibacterium acnes (P. acnes) intraperitoneally or BCG intravenously caused a visible loss in beta-Gase from all the organelles and from the cell surface of the macrophages.