Role of the 6-phosphomannosyl-enzyme receptor in intracellular transport and adsorptive pinocytosis of lysosomal enzymes

Monoolein-based nanoparticles for drug delivery to the central nervous system: A platform for lysosomal storage disorder treatment

Lysosomal Storage Disorders (LSDs) are characterized by an abnormal accumulation of substrates within the lysosome and comprise more than 50 genetic disorders with a frequency of 1:5000 live births. Nanotechnology may be a promising way to circumvent the drawbacks of the current therapies for lysosomal diseases. The blood circulation time and bioavailability of the enzymes or drugs could be improved by inserting them in nanocarriers, which could decrease and/or avoid the need of frequent intravenous infusions along with the minimization or elimination of associated immunogenic responses. Considering the exposed, we aimed to build monoolein-based nanoparticles stabilized by polysorbate 80 as a smart platform able to reach the central nervous system (CNS) to deliver drugs or enzymes inside lysosomes. We developed and characterized the nanoparticles by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-TEM). The nanoparticles showed a diameter of 115 nm, which is compatible with in vivo application. The SAXS patterns of the formulations displayed a single broad correlation peak that was fitted to the Teubner-Strey model confirming that disordered bicontinuous structures were obtained. Cryo-TEM images corroborated this finding and showed nanoparticles with size values that are similar to those determined by DLS. Furthermore, the nanoparticles did not present cytotoxicity when they were incubated with human fibroblasts, and demonstrated hemolytic activity proportional to the negative control, proving to be safe for parenteral administration. Through the use of a fluorescent dye to track the nanoparticles inside the cell, we demonstrated that they reached lysosomes after 1 h of treatment. More interestingly, the fluorescent dye was detected in the CNS of mice just after 3 h of treatment. The nanoparticles show great potential to improve the treatment of LSDs with brain impairment, acting as a smart platform to targeted delivery of drugs or enzymes.

Cell microencapsulation: a potential tool for the treatment of neuronopathic lysosomal storage diseases

Lysosomal storage disorders (LSD) are monogenic diseases caused by the deficiency of different lysosomal enzymes that degrade complex substrates such as glycosaminoglycans, sphingolipids, and others. As a consequence there is multisystemic storage of these substrates. Most treatments for these disorders are based in the fact that most of these enzymes are soluble and can be internalized by adjacent cells via mannose-6-phosphate receptor. In that sense, these disorders are good candidates to be treated by somatic gene therapy based on cell microencapsulation. Here, we review the existing data about this approach focused on the LSD treatments, the advantages and limitations faced by these studies.

Mannose 6-phosphate-independent endocytosis of beta-glucuronidase. II. Purification of a cation-dependent receptor from bovine liver

A new binding protein, which recognizes a specific peptide sequence from pronase digested bovine beta-glucuronidase, has been isolated from bovine liver membranes. Prior work has shown that this peptide (IIIb2) contains a Ser-X-Ser sequence, where X might be a posttranslational modified Trp. This receptor was detergent-extracted from total bovine liver membranes and purified by affinity chromatography on a bovine beta-glucuronidase-Sepharose and a IIIb2 peptide-Sepharose column. Binding of bovine beta-glucuronidase to the isolated receptor requires divalent cations, and their presence was necessary to maintain the receptor-ligand complex. Only the peptide sequence containing the fraction IIIb2 was able to impair the binding of the bovine enzyme to the receptor, no other peptide from bovine beta-glucuronidase had an effect on binding. When analyzed by SDS-PAGE under reducing conditions, two bands were observed, a major band of 78 kDa and a faint band of 72 kDa. Rabbit antibodies against this binding protein revealed the presence of the 78 kDa protein in membranes from bovine liver, human and bovine fibroblasts. These antibodies impaired human fibroblasts endocytosis of the bovine but not of the human beta-glucuronidase, which is taken up by a 300 kDa receptor that recognizes phosphomannosyl moieties in the enzyme.

Mannose 6-phosphate-independent endocytosis of beta-glucuronidase by human fibroblasts. I. Evidence for the existence of a membrane-binding activity

Prior work has shown that endocytosis of bovine beta-glucuronidase by human fibroblasts can be mediated by the existence of a Man6P-independent receptor for the recapture and targeting to lysosomes. In this study, we have isolated a peptide (IIIb2) from pronase digested bovine beta-glucuronidase that behaved as competitive inhibitor of the endocytosis of bovine beta-glucuronidase by human fibroblasts. This peptide contained a Ser-X-Ser sequence, where X is probably a posttranslational modified Trp. Antibodies raised against this peptide impaired the endocytosis of the bovine but not the human beta-glucuronidase, implying that the new recognition marker for the endocytosis of acid hydrolases might reside in a single discrete stretch of amino acid sequence. On the other hand, bovine beta-glucuronidase has been shown to bind specifically to receptors of human fibroblast membranes. The binding was saturable, divalent cation-dependent and was competitively inhibited by the IIIb2 peptide, but not by mannose 6-phosphate. Results presented suggested an interplay between manganese concentrations, temperature and pH on the dissociation of the beta-glucuronidase-receptor complexes. All together, these data reinforce the presence of two endocytic systems for the recapture and targeting of beta-glucuronidase in human fibroblasts.

Human procathepsin B interacts with the annexin II tetramer on the surface of tumor cells

To study potential roles of plasma membrane-associated extracellular cathepsin B in tumor cell invasion and metastasis, we used the yeast two-hybrid system to screen for proteins that interact with human procathepsin B. The annexin II light chain (p11), one of the two subunits of the annexin II tetramer, was one of the proteins identified. We have confirmed that recombinant human procathepsin B interacts with p11 as well as with the annexin II tetramer in vitro. Furthermore, procathepsin B could interact with the annexin II tetramer in vivo as demonstrated by coimmunoprecipitation. Cathepsin B and the annexin II tetramer were shown by immunofluorescent staining to colocalize on the surface of human breast carcinoma and glioma cells. Taken together, our results indicate that the annexin II tetramer can serve as a binding protein for procathepsin B on the surface of tumor cells, an interaction that may facilitate tumor invasion and metastasis.

Murine mucopolysaccharidosis type VII: the impact of therapies on the clinical course and pathology in a murine model of lysosomal storage disease

Murine mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by a recessively inherited deficiency of the lysosomal enzyme beta-glucuronidase. Affected mice have clinical, biochemical and pathological findings similar to those seen in humans with MPS VII (Sly syndrome), including growth retardation, facial dysmorphism, deafness, behavioural deficits and widespread glycosaminoglycan storage in lysosomes in the viscera, skeleton and brain. This mouse model is a useful tool for the evaluation of the effectiveness and experimental therapies for the MPS disorders. Syngeneic bone marrow transplantation performed in newborn MPS VII animals--before clinical evidence of disease is pronounced--prolongs life, improves hearing and bone growth, and prevents lysosomal storage in many sites, but does not correct the central nervous system disease. Enzyme therapy with beta-glucuronidase from the first days of life does reduce lysosomal storage in the brain in murine MPS VII. The enzyme-replaced mice also have reduced visceral lysosomal storage, impressive normalization of their phenotype and an improved life span. The effectiveness of gene therapy for the treatment of lysosomal storage disease has also been tested using the MPS VII model. When transplanted into MPS VII mice, syngeneic haematopoietic stem cells or mouse skin fibroblasts infected with retrovirus expressing beta-glucuronidase decreased storage, but only in the liver and spleen. Injection of an adenovirus vector expressing beta-glucuronidase into the vitreous of the MPS VII mice reduced storage in the retinal pigment epithelium and corneal endothelium. Intravenous administration of the adenovirus vector transduced with the beta-glucuronidase gene reduced liver and spleen storage and, when instilled into the cerebral ventricles, this viral vector caused beta-glucuronidase production in epithelial cells lining the ventricles. Recently, retroviral vector-corrected MPS VII fibroblasts secreting high levels of beta-glucuronidase were engrafted directly into the brains of adult MPS VII mice with resultant reduction in storage in neurons and glia adjacent to the grafts. Future efforts aimed at prolonging expression of the beta-glucuronidase gene by viral vectors and more precisely directing the therapeutic effect to the skeleton and brain will be important in optimizing treatments for murine MPS VII and extending the results of such therapies to humans with MPS.

Immunelectron microscopic localization of cathepsin B in human exocrine glands

The distribution of the lysosomal enzymes cathepsin B, lysozyme, chymotrypsin, and neutrophil elastase was examined in eccrine, apocrine, and sebaceous glands using a postembedding immunogold labeling procedure. Various amounts of cathepsin B were detected in all glands. Lysozyme, however, was detected in apocrine glands only. The other two lysosomal enzymes were not detectable immunologically. In apocrine and eccrine glands, anti-cathepsin B antibody labeled all secretory granules. In sebaceous glands, only the peripheral layer of cells showed immunological activity for cathepsin B. In apocrine glands, granules containing remnants of cristae were more intensively labeled than those lacking cristae which supports the assumption that both granules are derived from mitochondria by acquiring lysosomal enzymes. The enzymes convert mitochondria to granules with cristae and finally to granules without cristae. Thus the difference in morphology is part of a spectrum of the degradation of mitochondria to granules.

Attempted enzyme replacement using human amnion membrane implantations in mucopolysaccharidoses

Amnion membrane implantation has been proposed as an approach to enzyme replacement in mucopolysaccharidoses. Human amnion membranes have been subcutaneously implanted in the abdominal wall in 19 patients with mucopolysaccharidoses (MPS I, II and III). A protocol was developed for the objective evaluation of experimental treatments of these patients. Systematic evaluation of the clinical status before and 6 months after amnion membrane implantation reveals no change in function except improvement in joint mobility. The sum of all joint movements showed improvement from baseline values to 6 months after implantation by ANOVA followed by post-hoc analysis (p less than 0.056). The only specific joint movements to significantly improve after 6 months were shoulder extension (p less than 0.01) and hip internal rotation (p less than 0.05). Serial measurements of the deficient lysosomal enzyme activity in serum and white blood cells did not increase in any patient after amnion membrane implantation. Urinary glycosaminoglycan excretion decreased transiently in 2 of 10 patients after implantation, but a second amnion membrane implantation did not result in any change. Biopsy of the implantation site in 10 patients 6 months after amnion membrane implantation revealed a foreign-body reaction with giant cell formation and fibrosis and no recognizable amnion membrane tissue. We conclude that human amnion membrane implantation is not an effective therapy in mucopolysaccharidoses.

Role of enzyme receptors and inhibitors in regulating proteolytic activities of macrophages

Expression of proteases by neutrophils and other cells with a prominent regulated secretory pathway is determined largely by stimulus-response secretion of proteins prepackaged in high concentration. The regulated secretory pathway is apparently minor in macrophages, and instead proteases are either channeled into lysosomes or secreted constitutively. Posttranslational regulation of macrophage proteases then depends on compartmentalizing enzymes to their sites of primary function. Available data suggest that cells use both specific receptors and inhibitors to accomplish this. Viewed in this context protease inhibitors primarily function to inhibit enzyme not bound to their receptor. Consonant with this model of regulation, connective tissue turnover by macrophages is a contact-dependent process relatively resistant to exogenous macromolecular inhibitors. Although limited information is available regarding determinants that modulate matrix metabolism by human macrophages, this model suggests that determinants of adhesion and colocalization of enzyme and substrate would be as or more important than alterations of inhibitors in the microenvironment of the cell.

Adsorptive endocytosis of lysosomal enzymes by human fibroblasts: presence of two different functional systems that deliver an acid hydrolase to lysosomes

Endocytosis of human spleen beta-glucuronidase by human fibroblasts can be completely impaired by the competitive inhibitor mannose 6-phosphate or by pretreatment with acid phosphatase or endoglycosidases H or F. However, endocytosis of bovine spleen and liver beta-glucuronidase is partially impaired by the same treatments, suggesting that the bovine enzyme contains two endocytosis recognition markers located in separate enzyme domains. The mannose 6-phosphate recognition marker seems to be responsible for approximately 23% of the bovine enzyme endocytosis. The existence of two lysosomal endocytosis systems in human fibroblasts is supported by the following facts: (a) the rate of endocytosis of mannose 6-phosphate-containing human beta-glucuronidase was not affected by the presence of high levels of the bovine enzyme (which has only the other marker). (b) Anti-215K mannose 6-phosphate receptor antibodies selectively impair the endocytosis of the beta-glucuronidase containing mannose 6-phosphate. (c) Weak bases exert a differential effect on human and bovine endocytosis. beta-Glucuronidase internalized by either system is targeted to secondary lysosomes of human beta-glucuronidase-deficient fibroblasts, where it is able to degrade accumulated glycosaminoglycans. These results suggest that human fibroblasts have two different and independent endocytic systems for targeting of acid hydrolases to lysosomes.

Cation-independent mannose 6-phosphate receptor contains covalently bound fatty acid

The cation-independent mannose 6-phosphate receptor (215,000 daltons) was isolated from embryonic bovine tracheal cells and embryonic human skin fibroblasts labelled with [3H]palmitic acid. The tritium label was detected in the protein upon fluorographic analysis of SDS-polyacrylamide gels of the purified receptor. The label was not sensitive to hydroxylamine, methanolic KOH, or beta-mercaptoethanol, but labelled fatty acid was recovered from the protein by acidic methanolysis. Labelled receptor protein could not be isolated from cells grown in the presence of [3H]myristic acid. The results suggest the presence of amide-linked palmitic acid in the structure of the cation-independent mannose 6-phosphate receptor.

Differential cell surface expression of four lysosomal integral membrane proteins (LIMPs) in normal rat kidney cells

Four monoclonal antibodies generated against rat, hepatocyte lysosomal integral membrane protein (LIMPs) (Barriocanal et al., 1986a, b) were used as probes to ascertain the distribution of similar proteins in normal rat kidney (NRK) cells. Comparison of immunoprecipitations of LIMPs 1-4 from hepatocytes and NRK cells revealed a marked similarity in the proteins, in both cell types, as determined by SDS-PAGE. Further, the LIMP epitopes recognized by the antibodies are situated intravesicularly. Ultrastructural immunocytochemistry, using pre-embedding peroxidase, revealed that primary and secondary lysosomes in NRK cells are readily stained with all four antibodies, as well as vesicles in the Golgi region. Immunofluorescence microscopy of non-permeabilized NRK cells with antibodies recognizing LIMPs 1 and 4 illustrated a limited but significant punctate staining pattern of the cell surface. Ultrastructural immunoperoxidase indicated these sites to be cell surface localized coated pits and vesicles. However, it is known that all LIMPs are expressed on the cell surface, albeit at different concentrations, although the total number of each LIMP per cell, respectively, is approximately the same (Barriocanal et al., 1987). Treatment of NRK cells with the acidotropic agent NH4Cl decreased the cell surface expression of LIMPs 1, 3 and 4, but had no effect on LIMP 2. Further, the relative diminution of the cell surface expression varied among the four LIMPs. These results are interpreted to suggest that not all lysosomes contain the same integral membrane proteins in their vesicle container.

Localization of cathepsin L in rat kidney revealed by immunoenzyme and immunogold techniques

Localization of cathepsin L in rat kidney was investigated by immunocytochemical techniques. Kidneys were fixed by perfusion and embedded in Epon or Lowicryl K4M without postosmication. For light microscopy (LM), semi-thin sections of the Epon-embedded material were stained by the immunoenzyme technique after removal of epoxy resin. For electron microscopy (EM), ultra-thin sections of Lowicryl K4M-embedded material were stained by the protein A-gold technique. By LM, reaction deposits for cathepsin L were present in the cytoplasmic granules of proximal tubule cells, but little or no reaction product was noted in distal tubule, collecting tubule, and most of urinary tubules in the medulla. By EM, heavy gold label for cathepsin L was confined exclusively to lysosomes of the proximal tubule cells, but little or no label to those of the other segments. In immunocytochemical control sections, no reaction was observed. These results indicate that a main container of cathepsin L is lysosomes of the proximal tubule and suggest that the enzyme plays a role in the degradation of endocytosed proteins.

Developmental aspects of the lysosomal apparatus. Membrane affinity of N-acetyl-beta-D-glucosaminidase in developing rat liver

The affinity of N-acetyl-beta-D-glucosaminidase by membranes of liver was studied in rats of different ages including fetuses at day 18 of gestation. It was found that membrane bound enzyme activity, extractable with 0.6 KCl, increases from fetal life to adulthood reaching a peak 9 days after birth. In binding assays it was found that the enzyme of fetal, 9 days old, or adult rat has high affinity for membranes of the corresponding age. These bindings were saturable and with a similar KD, but the number of receptor sites was lowest in the fetal stage, and reached a peak 9 days after birth. The fetal enzyme did not bind to adult membranes. These results suggest that the transport system of hepatic lysosomal enzymes undergoes post-natal changes which are synchronic with other parameters of lysosomal apparatus maturation studied by us and other authors as total enzyme activity and intracellular digestion of macromolecules.

46 kd mannose 6-phosphate receptor: cloning, expression, and homology to the 215 kd mannose 6-phosphate receptor

We have isolated cDNA clones encoding the entire sequence of the bovine 46 kd cation-dependent mannose 6-phosphate (CD Man-6-P) receptor. Translation of CD Man-6-P receptor mRNA in Xenopus laevis oocytes results in a protein that binds specifically to phosphomannan-Sepharose, thus demonstrating that our cDNA clones encode a functional receptor. The deduced 279 amino acid sequence reveals a single polypeptide chain that contains a putative signal sequence and a transmembrane domain. Trypsin digestion of microsomal membranes containing the receptor and the location of the five potential N-linked glycosylation sites indicate that the receptor is a transmembrane protein with an extracytoplasmic amino terminus. This extracytoplasmic domain is homologous to the approximately 145 amino acid long repeating domains present in the 215 kd cation-independent Man-6-P receptor.

beta-Galactosidase from rat epididymal fluid is bound by a recognition site attached to membranes of the epididymis different from the phosphomannosyl receptor

In order to know if the beta-galactosidase of the rat epididymal fluid, as other secreted acid hydrolases, carries a marker in its molecule, we studied the binding of this enzyme to cellular membranes of the epididymal tissue. The binding, like that mediated by the phosphomannosyl receptor, was saturable, did not require calcium, had a Kd in the nM range and was inhibited by phosphatase or metaperiodate treatment of the enzyme. However fructose 6-phosphate derivates were more effective competitive inhibitors than mannose 6-phosphate. The binding capacity of the membranes were extractable with Triton X-100 and incorporable into liposomes. Trypsin inhibited the binding capacity of Triton extracts but it did not affect the affinity of intact cellular membranes for beta-galactosidase. The results suggest that a phosphorylated carbohydrate of the enzyme is bound by a recognizing site of the cellular membranes different from the phosphomannosyl receptor.

Immunocytochemical localization of cathepsins B and H in rat liver

Light and electron microscopic localization of cathepsins B and H in rat liver was investigated by immunoenzyme and protein A-gold techniques. For light microscopy (LM), semi-thin sections of the Epon-embedded material were stained by the immunoenzyme technique after removal of epoxy resin. For electron microscopy (EM), ultra-thin sections of the Lowicryl K4M-embedded material were stained by the protein A-gold technique. By LM, reaction deposits for cathepsins B and H were present in the cytoplasmic granules of parenchymal cells and endothelial cells, and Kupffer cells. The sinus-lining cells and the parenchymal cells showed the similar staining intensity. By EM, gold particles were present exclusively in lysosomes of all the cell types cited above. The same results were obtained from quantitative analysis. In addition, Golgi complexes themselves were mostly negative but some small vesicles on the trans side of them were labeled for these proteinases. The results indicate that cathepsins B and H are present in the lysosomes of rat liver and that these enzymes seem to be transported by small vesicles from endoplasmic reticulum to lysosomes via tubuloreticular network of the trans Golgi region.

Intracellular traffic of the mannose 6-phosphate receptor and its ligands

The role of the mannose 6-phosphate recognition marker and the phosphomannosyl receptor in the intracellular transport of acid hydrolases is well established. Several details of the process, however, are presently unclear and warrant further investigation (Table 1). The development of in vitro systems for the reconstitution of receptor-mediated endocytosis and intracellular transport, together with the application of the techniques of molecular biology to this field, should lead to major advances in our understanding of the targeting of enzymes to lysosomes.

On the heterogeneous glycosylation of the membranes of the trans Golgi network in rabbit luteal cells

In rabbit luteal cells the transmost element (G2) of the Golgi apparatus bears cytochemical resemblances to the limiting membrane of lysosomes and it was suggested that lysosomal membranes may originate from the above element. But in the normal Golgi apparatus it cannot be made out whether the considered molecules are indeed membrane bound. Perfusing the rabbit ovary with buffer containing monensin or ammonium chloride allowed to vesiculate the trans Golgi network (G2-G1) selectively. Controls showed a well-preserved ultrastructure. Parts of the limiting membrane of the vacuoles derived from the transmost reticulum (G2) were spiny coated and carried an osmiophilic inner layer. They also showed a heavy precipitate for acid phosphatase (AcPase) and were strongly stained with phosphotungstic acid (PTA) at low pH. By neutralizing the acidic groups, involved in the PTA-staining, it was possible to show that the same membranes were more heavily glycosylated. The MvB's and the limiting membrane of lysosomes showed the same staining characteristics. The other membrane domains revealed a gradient in PTA staining and in AcPase activity. It is concluded that the trans Golgi network (G2-G1) is an acidic compartment. The presence of differentially glycosylated membranes reveals a sorting mechanism for membranous components. The highly glycosylated membrane stretches seem to be involved in endocytosis and in the formation of lysosomal membranes.

Lysosomal membrane dynamics: structure and interorganellar movement of a major lysosomal membrane glycoprotein

The biochemistry and intracellular transit of an integral membrane glycoprotein of chicken fibroblast lysosomes were studied with monoclonal antibody techniques. The glycoprotein had an apparent molecular weight of 95,000-105,000. Structural analysis involving metabolic labeling with [35S]methionine and cleavage with glycosidases revealed the presence of numerous oligosaccharide chains N-linked to a core polypeptide of apparent molecular weight 48,000. A primary localization of the glycoprotein to lysosomes was demonstrated by the coincidence of antibody binding sites with regions of acridine orange uptake, electron immunocytochemical labeling on the inner surface of lysosome-like vacuolar membranes, and preferential association of the glycoprotein with lysosome-enriched subcellular fractions from Percoll gradients. In addition, small quantities of the glycoprotein were detected on endocytic vesicle and plasma membranes. To study the intracellular pathway of the glycoprotein, we used a monoclonal antibody whose binding to the glycoprotein at the cell surface had no effect on the number or subcellular distribution of antigen molecules. Incubation of chicken fibroblasts with monoclonal antibody at 37 degrees C led to the rapid uptake and subsequent delivery of antibody to lysosomes, where antibody was degraded. This process continued undiminished for many hours on cells continuously exposed to the antibody and was not blocked by the addition of cycloheximide. The rate at which antigen sites were replenished in the plasma membrane of cells prelabeled with antibody (t1/2 = 2 min) was essentially equivalent to the rate of internalization of antibody bound to cell surfaces. These results suggest that there is a continuous and rapid exchange of this glycoprotein between plasma membrane and the membranes of endosomes and/or lysosomes.

Immunocytochemical localization of cathepsin H in rat kidney. Light and electron microscopic study

Light and electron microscopic localization of cathepsin H in rat kidney was studied using post-embedding immunocytochemical techniques. For light microscopy, Epon sections of the kidney were stained by immunoenzyme method after removal of Epon and for electron microscopy, ultrathin sections of the Lowicryl K4M-embedded material were labeled by protein A-gold (pAg) technique. By light microscopy, fine granular staining was found in throughout the nephron, but the staining intensity considerably varied. The strongest staining was noted in the S1 segment of the proximal tubules followed by the S2 and S3 segments and the medullary collecting tubules. The glomeruli, the distal tubules, and the cortical collecting tubules were weakly stained. By electron microscopy, a gold label was found exclusively in lysosomes, which showed various sizes and labeling intensity. The results were quite consistent with the light microscopic results. The labeling intensity tended to increase as the matrix of lysosomes was condensed. Quantitative analysis of the labeling density of lysosomes demonstrated that the highest labeling density is found in the S1 segment of the proximal tubules and the labeling density of other renal segments is significantly low levels. The results indicate that a main site for cathepsin H in rat kidney is the S1 segment of the proximal tubules.

Microtubules and the organization of the Golgi complex

Electron microscopic and cytochemical studies indicate that microtubules play an important role in the organization of the Golgi complex in mammalian cells. During interphase microtubules form a radiating pattern in the cytoplasm, originating from the pericentriolar region (microtubule-organizing centre). The stacks of Golgi cisternae and the associated secretory vesicles and lysosomes are arranged in a circumscribed juxtanuclear area, usually centered around the centrioles, and show a defined orientation in relation to the rough endoplasmic reticulum. Exposure of cells to drugs such as colchicine, vinblastine and nocodazole leads to disassembly of microtubules and disorganization of the Golgi complex, most typically a dispersion of its stacks of cisternae throughout the cytoplasm. These alterations are accompanied by disturbances in the intracellular transport, processing and release of secretory products as well as inhibition of endocytosis. The observations suggest that microtubules are partly responsible for the maintenance and functioning of the Golgi complex, possibly by arranging its stacks of cisternae three-dimensionally within the cell and in relation to other organelles and ensuring a normal flow of material into and away from them. During mitosis, microtubules disassemble (prophase) and a mitotic spindle is built up (metaphase) to take care of the subsequent separation of the chromosomes (anaphase). The breaking up of the microtubular cytoskeleton is followed by vesiculation of the rough endoplasmic reticulum and partial atrophy, as well as dispersion of the stacks of Golgi cisternae. After completion of the nuclear division (telophase), the radiating microtubule pattern is re-established and the rough endoplasmic reticulum and the Golgi complex resume their normal interphase structure. This sequence of events is believed to fulfil the double function to provide tubulin units and space for construction of the mitotic spindle and to guarantee an approximately equal distribution of the rough endoplasmic reticulum and the Golgi complex on the two daughter cells.

Localization of cathepsin D in rat liver. Immunocytochemical study using post-embedding immunoenzyme and protein A-gold techniques

Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.

Chromogenic immunodetection of human serum albumin and alpha-L-fucosidase clones in a human hepatoma cDNA expression library

A human hepatoma cDNA library was constructed in lambda gt11, a bacteriophage vector that was designed to express cDNA-encoded antigenic determinants in Escherichia coli. The cDNA expression library contained approximately 8 X 10(6) recombinant phages with an average insert size of 780 bp. The feasibility of using a chromogenic immunodetection procedure to isolate cDNA clones was proved by isolating a human serum albumin (HSA) cDNA clone. An approximately 1.0-kb cDNA clone was then isolated by screening the library with rabbit anti-human alpha-L-fucosidase antibodies. The identity of the alpha-L-fucosidase cDNA clone was confirmed by DNA sequence analysis and a comparison of the predicted amino acid sequence to the amino acid sequences of human alpha-L-fucosidase tryptic peptides.

Immunocytochemistry of lysosomal hydrolases and their precursor forms in normal and mutant human cells

The acid hydrolases alpha-glucosidase, beta-galactosidase, N-acetyl-beta-D-hexosaminidase, beta-glucocerebrosidase and cathepsin D were studied immunocytochemically in normal and mutant human cells using monoclonal and affinity-purified polyclonal antibodies. For light microscopy, Rhodamine or Fluorescein-labelled conjugates were used, and for electron microscopy protein A-gold conjugates were employed. With the double labelling procedure, it was found that in normal fibroblasts every lysosome contained all the enzymes studied. The method described also enabled us to demonstrate the presence or absence of mutant enzyme protein in fibroblasts derived from patients with a genetic lysosomal enzyme deficiency. Immunoreactive acid hydrolases or their precursor forms were found in the rough endoplasmic reticulum, the cisternae of the Golgi complex, Golgi associated vesicles and lysosomes. This is in agreement with the present concept that the Golgi complex plays an essential role in the processing and targeting of lysosomal enzymes.

Cathepsin D-mediated processing of procollagen: lysosomal enzyme involvement in secretory processing of procollagen

The proteolytic removal of the extension COOH-terminal propeptide from procollagen has been examined in vitro. A crude enzyme activity was identified in a whole-chicken-embryo extract that acted at acid pH and appeared to be similar to one identified previously [Davidson, J. M., McEneany , L. S. G. & Bornstein , P. (1979) Eur. J. Biochem. 100, 551-558]. This activity was inhibitable by pepstatin but not by leupeptin, suggesting that it might be cathepsin D. Cathepsin D was purified 907-fold from chicken livers by affinity chromatography on pepstatin-aminohexyl-Sepharose 4B and was found to remove the COOH propeptides from procollagen. At pH 6.0, the site of cleavage appeared to shift from the COOH telopeptide to the COOH telopeptide/propeptide junction, based upon the difference in electrophoretic migration of the cleavage products, although determining the actual cleavage site will require end-group analysis. A model for the involvement of cathepsin D in the in vivo processing of procollagen is presented.

Chloroquine: its effect on leucocyte auto- and heterophagocytosis

The effect of chloroquine on phagocytosis and leucocyte ultrastructure has been examined. Incubation of neutrophils in 50 micrograms/ml chloroquine for 15 minutes produced a significant inhibition of latex particle uptake. After 90 minutes both 50 and 5 micrograms/ml inhibited phagocytosis while 7 of 9 cases were also inhibited at 0.5 micrograms/ml. However, after 4 hours 50 micrograms/ml chloroquine caused neutrophil granule vacuolation and a massive increase in autophagosomes in other cell types. Incubation in 5 to 0.05 micrograms/ml, which includes therapeutic plasma levels, had no effect on neutrophil ultrastructure but produced a dose-related increase in the number of lymphocytes containing autophagosomes, reflecting altered lysosomal function. As the antimalarial effect of chloroquine is manifested by giant autophagosome formation in Plasmodium, a common antirheumatic and antimalarial mechanism of action is postulated.

The confined function model of the Golgi complex: center for ordered processing of biosynthetic products of the rough endoplasmic reticulum

The organized and characteristic elements of the Golgi complex (GC) are the stacked smooth-surfaced cisternae, which are found in the centrosphere of all eukaryotic cells. These cisternae, in conjunction with other associated smooth-surfaced membranes, are responsible for executing net unidirectional intracellular transport (ICT) from the rough endoplasmic reticulum (RER) toward more distally located structures. This chapter focuses on the broad range of accessory activities that occur during transport, the family of “posttranslational modifications.” These events are, in all likelihood, not essential for the “primary” function of the GC yet they are crucial in allowing the cell to tailor its biosynthetic products for its own needs and the needs of the organism as a whole. In addition to modifying products of the rough endoplasmic reticulum, the GC may be involved in processing events because of its participation in other routes of vesicular traffic—for example, centripetal traffic from the cell surface. Various nonequivalent criteria have been used to ascribe processing events to the GC-autoradiography, preparative or analytic subcellular fractionation, interruption by ICT inhibitors, and delay in the impact of cycloheximide.

Intracellular membrane traffic: pathways, carriers, and sorting devices

Multiple pathways of intracellular membrane traffic have been detected in various cell types. The major established routes are (a) the exocytosis pathway, utilized in secretory cells for the discharge of secretory products, and which is also believed to be used for delivery of intrinsic membrane glycoproteins in all cell types; (b) the plasmalemma to Golgi route, also highly developed in secretory cells, which is believed to be utilized for the recovery and recycling of the membranes of containers used in packaging of secretory products (i.e., secretory granules or vesicles); (c) the lysosomal pathway, which is available in all cells but is the major route utilized in phagocytic cells; (d) the transcellular route, which represents the major type of traffic encountered in nonfenestrated, capillary endothelial cells and also appears to be the preferred route for the transport of immunoglobulins (intact) across cells; and (e) the biosynthetic pathways used for transport of secretory products, lysosomal enzymes, and membrane proteins from the ER to the Golgi complex and for transport of lysosomal enzymes from the Golgi complex to lysosomes in all cell types. It has become clear that cells repeatedly reutilize or recycle the vesicular membranes involved in carrying out these various transport operations. Clathrin-coated vesicles have been found to be involved in transport along all the routes detected so far, suggesting that there are multiple populations of coated vesicles with different transport functions in every cell. It has become clear that considerable sorting of membrane constituents and ligands takes place at the plasmalemma (receptor-mediated uptake), in the Golgi complex, and in endosomes. The Golgi complex is the intracellular site where much of the biosynthetic and recycling membrane traffic converges and where products are sorted and directed to their correct destinations. In summary, we have become aware of the existence of multiple pathways of membrane traffic and of the extensive reutilization or recycling of membranes that occurs in cells. The basic pathways are similar in all cells except that some are emphasized or deemphasized according to the predominant function and organization of a given cell type. What now remains to be done is to determine how these transporting membranes and the membranes of the receiving compartments are constructed, how their specific interactions are controlled, and how individual cell types utilize these pathways to carry out their specific functions.(ABSTRACT TRUNCATED AT 400 WORDS)