Cathepsin D of rat spleen. Affinity purification and properties of two types of cathepsin D

Endosomes and lysosomes are involved in early steps of Tl(III)-mediated apoptosis in rat pheochromocytoma (PC12) cells

The mechanisms that mediate thallium (Tl) toxicity are still not completely understood. The exposure of rat pheochromocytoma (PC12) cells to Tl(I) or Tl(III) activates both mitochondrial (Tl(I) and Tl(III)) and extrinsic (Tl(III)) pathways of apoptosis. In this work we evaluated the hypothesis that the effects of Tl(III) may be mediated by the damage to lysosomes, where it might be incorporated following the route of iron uptake. PC12 cells exposed for 3 h to 100 μM Tl(III) presented marked endosomal acidification, effect that was absent when cells were incubated in a serum-free medium and that was fully recovered when the latter was supplemented with transferrin. After 6 h of incubation the colocalization of cathepsins D and B with the lysosomal marker Lamp-1 was decreased together with an increase in the total activity of the enzymes. A permanent damage to lysosomes after 18 h of exposure was evidenced from the impairment of acridine orange uptake. Cathepsin D caused the cleavage of pro-apoptotic protein BID that is involved in the activation of the intrinsic pathway of apoptosis. Supporting that, BID cleavage and the activation of caspase 3 by Tl(III) were fully prevented when cells were preincubated with cathepsin D inhibitor (pepstatin A) and only partially prevented when cathepsin B inhibitor (E64d) was used. None of these inhibitors affected BID cleavage or caspase 3 activation in Tl(I)-treated cells. Together, experimental results support the role of Tl(III) uptake by the acidic cell compartments and their involvement in the early steps of Tl(III)-mediated PC12 cells apoptosis.

Cathepsin D from the hepatopancreas of the cuttlefish (Sepia officinalis): purification and characterization

Cathepsin D from the hepatopancreas of cuttlefish ( Sepia officinalis ) was purified to homogeneity by precipitation with ammonium sulfate (30-60%, w/v), Sephadex G-100 gel filtration, Mono-S cation-exchange chromatography, Sephadex G-75 gel filtration, and Mono-S FPLC with a 54-fold increase in specific activity and 17% recovery. The molecular weight of the purified cathepsin D was estimated to be 37.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On the basis of the native-PAGE and hemoglobin zymography, the purified protease appeared as a single band. The optimum pH and temperature for the cathepsin D activity were pH 3.0 and 50 °C, respectively, using hemoglobin as a substrate. The purified enzyme was completely inhibited by pepstatin A; however, no inhibition was observed with phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid. Moreover, the activity was strongly inhibited by SDS and molybdate and enhanced by ATP. The purified cathepsin D was activated by Mg(2+), Ni(2+), Zn(2+), Cu(2+), Cd(2+), Sr(2+), and Co(2+) ions, whereas it was not affected by Na(+), K(+), and Ca(2+) ions. The N-terminal amino acid sequence of the first 13 amino acids of the purified cathepsin D was APTPEPLSNYMDA. S. officinalis cathepsin D, which showed high homology with cathepsin D from marine vertebrates and invertebrates, had a Pro residue at position 6 and a Ser residue at position 8, where Thr and Lys are common in all marine vertebrates cathepsins D. S. officinalis cathepsin D showed high efficiency for the hydrolysis of myofibrillar proteins extracted from cuttlefish muscle.

Proteomics identification of azaspiracid toxin biomarkers in blue mussels, Mytilus edulis

Azaspiracids are a class of recently discovered algae-derived shellfish toxins. Their distribution globally is on the increase with mussels being most widely implicated in azaspiracid-related food poisoning events. Evidence that these toxins were bound to proteins in contaminated mussels has been shown recently. In the present study characterization of these proteins in blue mussels, Mytilus edulis, was achieved using a range of advanced proteomics tools. Four proteins present only in the hepatopancreas of toxin-contaminated mussels sharing identity or homology with cathepsin D, superoxide dismutase, glutathione S-transferase Pi, and a bacterial flagellar protein have been characterized. Several of the proteins are known to be involved in self-defense mechanisms against xenobiotics or up-regulated in the presence of carcinogenic agents. These findings would suggest that azaspiracids should now be considered and evaluated as potential tumorigenic compounds. The presence of a bacterial protein only in contaminated mussels was an unexpected finding and requires further investigation. The proteins identified in this study should assist with development of urgently required processes for the rapid depuration of azaspiracid-contaminated shellfish. Moreover they may serve as early warning indicators of shellfish exposed to this family of toxins.

A new approach for distinguishing cathepsin E and D activity in antigen-processing organelles

Cathepsin E (CatE) and D (CatD) are the major aspartic proteinases in the endolysosomal pathway. They have similar specificity and therefore it is difficult to distinguish between them, as known substrates are not exclusively specific for one or the other. In this paper we present a substrate-based assay, which is highly relevant for immunological investigations because it detects both CatE and CatD in antigen-processing organelles. Therefore it could be used to study the involvement of these proteinases in protein degradation and the processing of invariant chain. An assay combining a new monospecific CatE antibody and the substrate, MOCAc-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys(Dnp)-D-Arg-NH2[where MOCAc is (7-methoxycoumarin-4-yl)acetyl and Dnp is dinitrophenyl], is presented. This substrate is digested by both proteinases and therefore can be used to detect total aspartic proteinase activity in biological samples. After depletion of CatE by immunoprecipitation, the remaining activity is due to CatD, and the decrease in activity can be assigned to CatE. The activity of CatE and CatD in cytosolic, endosomal and lysosomal fractions of B cells, dendritic cells and human keratinocytes was determined. The data clearly indicate that CatE activity is mainly located in endosomal compartments, and that of CatD in lysosomal compartments. Hence this assay can also be used to characterize subcellular fractions using CatE as an endosomal marker, whereas CatD is a well-known lysosomal marker. The highest total aspartic proteinase activity was detected in dendritic cells, and the lowest in B cells. The assay presented exhibits a lower detection limit than common antibody-based methods without lacking the specificity.

The Role of the Cathepsin E Propeptide in Correct Folding, Maturation and Sorting to the Endosome

Cathepsin E (CE) is an endosomal aspartic proteinase of the A1 family that is highly homologous to the lysosomal aspartic proteinase cathepsin D (CD). Newly synthesized CE undergoes several proteolytic processing events to yield mature CE, from which the N-terminal propeptide usually comprising 39 amino acids is removed. To define the role of the propeptide of CE in its biosynthesis and processing, we constructed two fusion proteins using chimeric DNAs encoding the CE propeptide fused to the mature CD tagged with HA at the COOH terminus (termed ED-HA) and encoding the CD propeptide fused to the mature CE (termed DE). Pulse-chase analysis revealed that wild-type CE expressed in human embryonic kidney cells is autoproteolytically processed into mature CE within a 12-h chase, whereas the chimeric DE failed to be converted into mature CE even after a 24-h chase. The DE chimera was nevertheless capable of acid-dependent autoactivation in vitro to yield a catalytically active form, although its specificity constants (kcat/Km) were considerably high but less (35%) than those of the wild-type CE. By contrast, the chimeric ED-HA expressed in HeLa cells underwent neither processing into a catalytically active enzyme nor acid-dependent autoactivation in vitro. The ED-HA protein was less stable than wt-CD-HA, as determined on pulse-chase analysis and on trypsin digestion. These data indicate that the propeptide of CE is essential for the correct folding, maturation, and targeting of this protein to its final destination.

A new selective substrate for cathepsin E based on the cleavage site sequence of α2-macroglobulin

Cathepsin E is an intracellular aspartic proteinase of the pepsin family predominantly expressed in cells of the immune system and believed to contribute to homeostasis by participating in host defense mechanisms. Studies on its enzymatic properties, however, have been limited by a lack of sensitive and selective substrates. For a better understanding of the importance of this enzymein vivo, we designed and synthesized a highly sensitive peptide substrate for cathepsin E based on the sequence of the specific cleavage site of α2-macroglobulin. The substrate constructed, MOCAc-Gly-Ser-Pro-Ala-Phe-Leu-Ala-Lys(Dnp)-D-Arg-NH2[where MOCAc is (7-methoxycoumarin-4-yl)acetyl and Dnp is dinitrophenyl], derived from the cleavage site sequence of human α2-macroglobulin, was the most sensitive and selective for cathepsin E, withkcat/Kmvalues of 8–11 μM-1S-1, whereas it was resistant to hydrolysis by the analogous aspartic proteinases cathepsin D and pepsin, as well as the lysosomal cysteine proteinases cathepsins B, L, and H. The assay allows the detection of a few fmol of cathepsin E, even in the presence of plasma and cell lysate, and gives accurate results over a wide enzyme concentration range. This substrate might represent a useful tool for monitoring and accurately quantifying cathepsin E, even in crude enzyme preparations.

Novel aspartyl proteinase associated to fat body histolysis during Ceratitis capitata early metamorphosis

During larva to adult transition, the larval fat body of the Medfly (Ceratitis capitata) progressively disintegrates to be replaced by the adult one, after imago ecdysis. Here we show that a temporal correlation exists among the microscopy images of fat body progressive disintegration, the activation of fat body lysosomes (as judged by acid phosphatase activity), and the activity of a novel fat body aspartyl proteinase. The enzyme was purified and partially characterized. This proteinase exhibited a wide range of acid isoforms with isoelectric points from 5.6 to 7.3, an optimum pH of 3.0 for hemoglobin digestion, and was completely inhibited by pepstatin A. The apparent molecular weight was estimated (42 +/- 1 kDa) and the protein was characterized as N-glycosylated, judging from affinity to Concanavalin A. From the biochemical characteristics, the enzyme that we called "Early Metamorphosis Aspartyl Proteinase" (EMAP) appears to be similar to mammalian Cathepsin D. However, the N-terminal sequence of EMAP showed no similarity with any known animal Cathepsins and exhibited an important instability to neutral and alkaline pH. This feature seems to be a peculiar characteristic of insect aspartyl proteinases. The temporal activity profile of EMAP during metamorphosis correlated well with the microscopy images of fat body cell autolytic death. Our data support the notion that EMAP is a metamorphosis-specific lysosomal proteinase, mostly expressed during larval fat body histolysis.

Analysis of post-lysosomal compartments

Lysosomes are acidic intracellular compartments and are regarded as degradative and the end point, of the endocytic pathway. Here we provide evidence for the generation of acid hydrolase poor and non-acidic post-lysosomal compartments in NRK cells that have accumulated non-digestible macromolecules, Texas red-dextran (TR-Dex), within lysosomes. When TR-Dex was fed to the cells for 6h, most of the internalized TR-Dex colocalized with a lysosomal enzyme, cathepsin D. With an increase in the chase period, however, the internalized TR-Dex gradually accumulated in cathepsin D-negative vesicles. These vesicles were positive for a lysosomal membrane protein, LGP85, and their formation was inhibited by treatment of the cells with U18666A, which impairs membrane transport out of late endosomal/lysosomal compartments, thereby suggesting that the vesicles are derived from lysosomes. Interestingly, these compartments are non-acidic as judged for the DAMP staining. The results, therefore, suggest that the excess accumulation of non-digestible macromolecules within lysosomes induces the formation of acid hydrolase poor and non-acidic post-lysosomal compartments. The fact that treatment of the cells with lysosomotropic amines or a microtubule-depolymerization agent resulted in extensive colocalization of TR-Dex with cathepsin D further indicates that the formation of the post-lysosomal compartments depends on the lysosomal acidification and microtubule organization. Furthermore, these results suggest bi-directional membrane transport between lysosomes and the post-lysosomal compartments, which implies that the latter are not resting compartments.

Disruption of structural and functional integrity of alpha 2-macroglobulin by cathepsin E

alpha 2-Macroglobulin (alpha 2M) is an abundant glycoprotein with the intrinsic capacity for capturing diverse proteins for rapid delivery into cells. After internalization by the receptor- mediated endocytosis, alpha 2M-protein complexes were rapidly degraded in the endolysosome system. Although this is an important pathway for clearance of both alpha 2M and biological targets, little is known about the nature of alpha 2M degradation in the endolysosome system. To investigate the possible involvement of intracellular aspartic proteinases in the disruption of structural and functional integrity of alpha 2M in the endolysosome system, we examined the capacity of alpha 2M for interacting with cathepsin E and cathepsin D under acidic conditions and the nature of its degradation. alpha 2M was efficiently associated with cathepsin E under acidic conditions to form noncovalent complexes and rapidly degraded through the generation of three major proteins with apparent molecular masses of 90, 85 and 30 kDa. Parallel with this reaction, alpha 2M resulted in the rapid loss of its antiproteolytic activity. Analysis of the N-terminal amino-acid sequences of these proteins revealed that alpha 2M was selectively cleaved at the Phe811-Leu812 bond in about 100mer downstream of the bait region. In contrast, little change was observed for alpha 2M treated by cathepsin D under the same conditions. Together, the synthetic SPAFLA peptide corresponding to the Ser808-Ala813 sequence of human alpha 2M, which contains the cathepsin E-cleavage site, was selectively cleaved by cathepsin E, but not cathepsin D. These results suggest the possible involvement of cathepsin E in disruption of the structural and functional integrity of alpha 2M in the endolysosome system.

Role of LAMP-2 in lysosome biogenesis and autophagy

In LAMP-2-deficient mice autophagic vacuoles accumulate in many tissues, including liver, pancreas, muscle, and heart. Here we extend the phenotype analysis using cultured hepatocytes. In LAMP-2-deficient hepatocytes the half-life of both early and late autophagic vacuoles was prolonged as evaluated by quantitative electron microscopy. However, an endocytic tracer reached the autophagic vacuoles, indicating delivery of endo/lysosomal constituents to autophagic vacuoles. Enzyme activity measurements showed that the trafficking of some lysosomal enzymes to lysosomes was impaired. Immunoprecipitation of metabolically labeled cathepsin D indicated reduced intracellular retention and processing in the knockout cells. The steady-state level of 300-kDa mannose 6-phosphate receptor was slightly lower in LAMP-2-deficient hepatocytes, whereas that of 46-kDa mannose 6-phosphate receptor was decreased to 30% of controls due to a shorter half-life. Less receptor was found in the Golgi region and in vesicles and tubules surrounding multivesicular endosomes, suggesting impaired recycling from endosomes to the Golgi. More receptor was found in autophagic vacuoles, which may explain its shorter half-life. Our data indicate that in hepatocytes LAMP-2 deficiency either directly or indirectly leads to impaired recycling of 46-kDa mannose 6-phosphate receptors and partial mistargeting of a subset of lysosomal enzymes. Autophagic vacuoles may accumulate due to impaired capacity for lysosomal degradation.

Involvement of cathepsin E in exogenous antigen processing in primary cultured murine microglia

We have attempted to elucidate an involvement of cathepsin E (CE) in major histocompatibility complex class II-mediated antigen presentation by microglia. In primary cultured murine microglia, CE was localized mainly in early endosomes and its expression level was markedly increased upon stimulation with interferon-gamma. Pepstatin A, a specific inhibitor of aspartic proteases, significantly inhibited interleukin-2 production from an OVA-(266-281)-specific T helper cell hybridomas upon stimulation with native OVA presented by interferon-gamma-treated microglia. However, pepstatin A failed to inhibit the presentation of OVA-(266-281) peptide. The possible involvement of CE in the processing of native OVA into antigenic peptide was further substantiated by that digested fragments of native OVA by CE could be recognized by OVA-specific Th cells. Cathepsin D also degraded native OVA into antigenic peptide, whereas microglia prepared from cathepsin D-deficient mice retained an ability for antigen presentation. On the other hand, the requirement for cysteine proteases such as cathepsins S and B in the processing of invariant chain (Ii) was confirmed by immunoblot analyses in the presence of their specific inhibitors. In conclusion, CE is required for the generation of an antigenic epitope from OVA but not for the processing of Ii in microglia.

One-step subcellular fractionation of rat liver tissue using a Nycodenz density gradient prepared by freezing-thawing and two-dimensional sodium dodecyl sulfate electrophoresis profiles of the main fraction of organelles

In the present study, we describe a new procedure using freezing-thawing to density gradient solution of Nycodenz for one-step separation of organelles from the rat liver and subsequent proteome analysis of subcellular fractions. To prepare two-dimensional electrophoresis (2-D PAGE) profiles of tissue organelles, we performed one-step subcellular fractionation of rat liver homogenate using a density gradient of Nycodenz solution, which resulted in the separation of the cytosolic fraction from the postnuclear supernatant. The density gradient of Nycodenz was prepared from a 20% solution in a centrifuge tube by freezing-thawing overnight at -20 degrees C and at room temperature for a few hours without the initial centrifugation procedure. The shape of the gradient density curve was dependent on Nycodenz concentration and tube size. After fractionation, the protein profiles were examined using one-dimensional sodium dodecyl sulfate (SDS)-PAGE. The organelles were confirmed using Western blotting. Our results indicate that our procedure provides a simple method for the separation of organelle fractions from the rat liver tissue.

A simple procedure for the isolation of rat kidney lysosomes

BACKGROUND

A procedure for the isolation of highly purified lysosomes from normal rat kidney is described.

METHODS

The method depends on the swelling of mitochondria when the postnuclear supernatant fraction is incubated with 2 mM Ca2+. The lysosomes can then be separated from the swollen mitochondria by Percoll density gradient centrifugation.

RESULTS

The lysosomal fraction obtained by our method was enriched more than 30-fold in terms of marker enzymes with a yield of about 11%. Electron microscopic examination and the measurement of the activities of marker enzymes for various subcellular organelles indicated that our lysosomal preparation was essentially free from contamination by other organelles.

CONCLUSION

We believe that this procedure for isolating kidney lysosome will be useful in the study of the mechanisms of specific modification, processing and catabolism of proteins.

Purification and characterization of cathepsin D from normal human breast tissue

The lysosomal aspartyl protease cathepsin D is present in most mammalian cells and is active in the catabolism of intracellular and endocytosed proteins. It appears to be overexpressed and abnormally secreted in breast cancer cells, and may contribute to the process of tumor metastasis. In the present study, cathepsin D was purified 4500-fold from normal human breast tissue using pepstatin-agarose, DEAE Sephadex, and Sephadex G-75 chromatography. The resulting enzyme on SDS-PAGE contained five protein bands (47, 31, 29, 13, and 12kDa) which were all immunoreactive on western blot analysis using anti-cathepsin D polyclonal antibodies. The isoform profile of purified cathepsin D consisted of three major peaks at approximate pI 7.3, 6.8, and 6.3, and a broad area of lower activity between pI of 5.0 and 2.0. The purified enzyme had a broad pH optimum centered around pH 3.3. Lectin blotting indicated that cathepsin D is a glycoprotein which is recognized by Galanthus nivalis agglutinin and concanavalin A, suggesting the presence of mannose residues. However, Sambucus nigra agglutinin, Tetragonolobus purpureas agglutinin, Triticum vulgaris agglutinin, and Erythrina cristagalli agglutinin failed to recognize cathepsin D, suggesting a lack of lectin-available sialic acid, fucose, N-acetylglucosamine, and galactose residues, respectively.

Endocytic trafficking of megalin/RAP complexes: dissociation of the complexes in late endosomes

Megalin (gp330) is a member of the low-density lipoprotein receptor gene family. Like other members of the family, it is an endocytic receptor that binds a number of specific ligands. Megalin also binds the receptor-associated protein (RAP) that serves as an exocytic traffic chaperone and inhibits ligand binding to the receptor. To investigate the fate of megalin/RAP complexes, we bound RAP glutathione-S-transferase fusion protein (RAP-GST) to megalin at the surface of L2 yolk sac carcinoma cells and followed the trafficking of the complexes by immunofluorescence and immunogold labeling and by their distribution on Percoll gradients. We show that megalin/RAP-GST complexes, which are internalized via clathrin-coated pits, are delivered to early endosomes where they accumulate during an 18 degrees C temperature block and colocalize with transferrin and transferrin receptor. Upon release from the temperature block, the complexes travel to late endosomes where they colocalize with rab7 and can be coprecipitated with anti-RAP-GST antibodies. Dissociation of the complex occurs in late endosomes and is most likely triggered by the low pH (approximately 5.5) of this compartment. RAP is then rapidly delivered to lysosomes and degraded whereas megalin is recycled to the cell surface. When the ligand, lipoprotein lipase, was bound to megalin, the receptor was found to recycle through early endosomes. We conclude that in contrast to receptor/ligand complexes, megalin/RAP complexes traffic through late endosomes, which is a novelty for members of the low-density lipoprotein receptor gene family.

Immunohistochemical localization of cathepsins D and E in human gastric cancer: a possible correlation with local invasive and metastatic activities of carcinoma cells

The immunohistochemical localization of cathepsins D and E in 44 cases of human gastric carcinoma, using antibodies specific for each enzyme, were investigated. Cathepsin D- and E- positive carcinoma cells were present in all samples. However, the staining intensity varied from cell to cell in the same carcinoma tissue as well as among samples. The most intense immunostaining of both cathepsins was often found in the cells, which were present at the advancing margin of the carcinoma tissues. The incidence of this peculiar localization of intensely stained carcinoma cells significantly correlated with the progression of the carcinoma tissue (D, P < .05; E, P < .01) and with occurrence of the lymph node metastasis (D and E, P < .05). There was no statistical significance between this localization and the histological type (differentiation) of the carcinoma tissues. Cathepsin-positive inflammatory cells infiltrated in and around the carcinoma tissue, and intensely stained inflammatory cells were often located in the stroma at the border of the carcinoma tissue. However, no statistical correlation was noted between the localization of cathepsin-positive inflammatory cells at the border and the stage of progression or the incidence of metastasis. These results indicated that cathepsins D and E in the carcinoma cells located at the advancing margin play an important role in the invasion and subsequent metastasis of human gastric carcinoma. Meanwhile, cathepsin-positive inflammatory cells seem to be less responsible for the biological behavior of carcinoma cells than those in the carcinoma cells themselves.

Purification and characterization of a digestive cathepsin D proteinase isolated from Tribolium castaneum larvae (Herbst)

A digestive proteinase was isolated from larval extracts of Tribolium castaneum. The enzyme was partially purified using gel-filtration and ion-exchange chromatography. It is an acidic proteinase with a maximal activity at pH 3. Considering its inhibition by Pepstatin A, plus its selectivity to hydrolyze hemoglobin but not bovine serum albumin, it was classified as Cathepsin D proteinase. Its relative molecular weight is 22 kDa and it shows a high sensitivity to temperature. Unlike other cathepsin D found in animals, this enzyme is free of carbohydrate, and its activity is not affected by the presence of different anions which are known to affect the activity of plant aspartic proteinases.

Biochemical assessment of acute myocardial ischaemia

AIMS

To evaluate the efficacy of biochemical parameters in different fluids in the diagnosis of myocardial infarction of different causes, analysed after death.

METHODS

The myoglobin concentration and total creatine kinase (CK) and creatine kinase MB isoenzyme (CK-MB) activities were measured in serum, pericardial fluid, and vitreous humour from seven diagnostic groups of cadavers classified according to the severity of myocardial ischaemia and cause of death. Lactate dehydrogenase (LDH) and myosin were measured only in serum and pericardial fluid, and cathepsin D only in pericardial fluid. Routine haematoxylin and eosin and acridine orange staining were used for microscopy studies of heart tissue.

RESULTS

In pericardial fluid there were substantial differences between the different groups with respect to CK, CK-MB, and LDH activities and myosin concentrations. The highest values were found in cases with morphological evidence of myocardial ischaemia.

CONCLUSIONS

Biochemical parameters, which reach the pericardial fluid via passive diffusion and ultrafiltration due to a pressure gradient, were thus detectable in this fluid earlier than in serum in cases with myocardial ischaemia. These biochemical parameters may be of use for ruling out myocardial ischaemia in those controversial cases in which reliable morphological findings are lacking.

Purification and characterization of recombinant human cathepsin E

The human cathepsin E was purified from the culture supernatant of Pichia pastoris strain transformed with a human cathepsin E expression plasmid. Purification was performed by a three-step procedure, TSKgel Phenyl-5PW, Toyopearl HW55S and TSKgel DEAE-5PW column chromatographies. The purified recombinant cathepsin E had the molecular mass of around 82-kDa with the amino-terminal sequence started with Ile37 of the predicted amino acid sequence, suggesting the human cathepsin E was accumulated in the culture suparnatant as the mature dimer enzyme. The result of endoglycosidase-H digestion followed by Western blot analysis of the purified recombinant cathepsin E suggested that the human cathepsin E expressed in Pichia pastoris received N-linked high-mannose type glycosylation.

Both cathepsin B and cathepsin D are necessary for processing of ovalbumin as well as for degradation of class II MHC invariant chain

The effect of highly selective inhibitors of cathepsins on the processing of ovalbumin (OVA) and the presentation of an OVA-derived antigenic peptide (OVA323-339) by antigen presenting cells (APC) was investigated. Both CA-074 (a specific inhibitor of cathepsin B) and pepstatin A (a specific inhibitor of cathepsin D) showed an inhibitory effect on the IL-2 production from an OVA-specific, I-Ad-restricted helper T (Th) cell clone upon stimulation with OVA presented by the I-Ad-positive APC. In contrast, the presentation of the antigenic epitope, OVA323-339, to the same Th clone was not inhibited by either CA-074 or pepstatin A alone, nor even by the mixture of both inhibitors. When APC were treated with cathepsin inhibitor for 24 h, and then antigen and Th were added to the culture, the presentation of not only OVA but also an OVA-derived antigenic peptide was inhibited by either cathepsin inhibitor alone. In addition, the expression of invariant chain on APC was significantly augmented by the pretreatment of APC with either cathepsin inhibitor. Two main conclusions are drawn from these results. First, not only aspartyl protease, such as cathepsin D, but also thiol protease, such as cathepsin B, is involved in antigen processing by APC. Second, both cathepsin B and cathepsin D are necessary for degradation of the invariant chain (Ii) from the MHC class II alpha beta heterodimer in endosomes in order to express functional MHC class II molecules for binding antigenic peptides.

High molecular weight aspartic endopeptidase generates a coronaro-constrictory peptide from the beta-chain of hemoglobin

Studying the influence of brain cathepsin D (EC 3.4.23.5) and high molecular weight (HMW) aspartic endopeptidase (EC 3.4.23.-) on the processing of hypothalamic calmodulin-binding coronaro-constrictory peptide factors from the beta-chain of globin it was found that only HMW aspartic endopeptidase generates the fragment 31-40 of the beta-chain of bovine hemoglobin (Hb) by cleavage of the Leu30-Leu31 and Phe40-Phe41 bonds. Digestion of the beta-chain of globin was performed at 37 degrees C at an enzyme/substrate ratio of 1:80 at pH 3.5 using different times of incubation (from 4 h to 10 h). The resulting peptides were separated by reversed-phase high-performance liquid chromatography (HPLC) and then identified by amino acid analysis and Edman degradation. The differences in specificity and activity of these two brain aspartic proteinases could be explained by their different structural features. Our finding provides evidence for a different biological function of these two enzymes. Data obtained give us reason to suppose that HMW aspartic proteinase probably can participate in the processing of the coronaro-constrictory peptide in vivo by limited proteolysis of Hb or Hb-like protein.

Cathepsin D as a vitality marker in human skin wounds

This paper shows the results obtained by studying the lysosomal enzyme Cathepsin D as a potential marker for the vitality of wounds in human specimens. We have analyzed 53 samples using enzymological and histological techniques. Our results show the ability of Cathepsin D to establish the vital origin of wounds inflicted 5 minutes or less before death, where the specific activity of cathepsin D reached 0.055 units at the wound edge and 0.01 units in their respective controls (P < 0.001). As previously demonstrated in an experimental series, Cathepsin D seems to be a very useful marker of high forensic interest in especially difficult cases. Further studies are in progress to check the influence of different factors such as drugs intake and clinical conditions on Cathepsin D activity.

Purification and immunohistochemical localization of aspartic proteinases in rat epidermis

Investigation of skin cathepsin E (EC 3.4.23.-) has been totally ignored compared to skin cathepsin D (ED 3.4.23.5). In this study both cathepsins E and D were simultaneously purified to homogeneity up to 370 and 640 times, respectively, from 2-day-old rat epidermis. The total aspartic proteinase activity of rat epidermis detected after Q-Sepharose column chromatography was attributed to 27% cathepsin E, 63% cathepsin D, and 10% other enzymes. The purified enzymes showed that cathepsin E (90 kDa) is a dimer of 45 kDa subunits whereas cathepsin D is a monomer of 42 kDa. Other biochemical properties of epidermal cathepsins E and D were similar to those reported from other tissue sources. Immunologically cathepsins E and D were distinct from each other and localization of the two enzymes differed in both rat and human skin by immunohistochemistry. Cathepsin E was distributed diffusely in the cytoplasm of almost all epidermal cells, though its concentration increased above suprabasal cells, whereas cathepsin D appeared in particulate form only in cells of the granular layer. The findings indicate that two aspartic proteinases that have similar enzymatic properties exist in the epidermis. They are, however, differentially distributed in the organ, presumably for different functions during the process of keratinization.

Hepatic accumulation of lysosomes and defective transcytotic vesicular pathways in cirrhotic rat liver

To investigate the potential role of lysosomes in cirrhosis, we analyzed the activity of lysosomal enzymes in rats exposed long-term to phenobarbital and carbon tetrachloride. The activity of lysosomal enzymes was markedly increased in the homogenate of cirrhotic livers (e.g., arylsulfatase 9 +/- S.D.2 vs. 16 +/- 6 nmoles.min-1.mg-1 in control rats and cirrhotic rats, respectively; p less than 0.001). The corresponding plasma levels were also increased (7 +/- 1 vs. 12 +/- 3 nmoles.min-1.mg-1; p less than 0.01), whereas biliary excretion was diminished (16 +/- 7 vs. 7 +/- 2 pmol.min-1.gm liver-1; p less than 0.05) in cirrhotic rats. Stereological quantification of lysosomes visualized cytochemically revealed an increase of pericanalicular lysosomes averaging 1.5 +/- 0.4 around a canaliculus in controls and 3.7 +/- 1.0 in cirrhotic rats (p less than 0.01). Because this suggested a defect in the transcellular vesicular pathway, we investigated the biliary excretion of horseradish peroxidase and epidermal growth factor in perfused livers. Bile flow and total horseradish peroxidase excretion were similar in control rats and cirrhotic rats. However, the early peak of biliary horseradish peroxidase excretion--usually taken as evidence of paracellular transport--was increased in cirrhotic rats (13 +/- 7 vs. 57 +/- 22%; p less than 0.01), whereas the second peak--reflecting the transcellular vesicular pathway(s)--was markedly reduced (87 +/- 7 vs. 43 +/- 22%; p less than 0.001). A similar reduction in the biliary excretion of intact epidermal growth factor and of its degradation products was found. These results demonstrate an increased number of lysosomes in hepatocytes of cirrhotic livers; this appears to be the result of accumulation rather than proliferation, in view of the reduced transcellular vesicular movement of different markers into bile.

A non-autophagic pathway for diversion of ER secretory proteins to lysosomes

Intracisternal granules (ICG) develop in the rough ER of hyperstimulated thyrotrophs or thyroid hormone-secreting cells of the anterior pituitary gland. To determine the fate of these granules, we carried out morphological and immunocytochemical studies on pituitaries of thyroxine-treated, thyroidectomized rats. Under these conditions the ER of thyrotrophs is dramatically dilated and contains abundant ICG; the latter contain beta subunits of thyrotrophic hormone (TSH-beta). Based on purely morphologic criteria, intermediates were identified that appeared to represent stages in the transformation of a part rough/part smooth ER cisterna into a lysosome. Using immunocytochemical and cytochemical markers, two major types of intermediates were distinguished: type 1 lacked ribosomes but were labeled with antibodies against both ER markers (PDI, KDEL, ER membrane proteins) and a lysosomal membrane marker, lgp120. They also were reactive for the lysosomal enzyme, acid phosphatase, by enzyme cytochemistry. Type 2 intermediates were weakly reactive for ER markers and contained both lgp120 and lysosomal enzymes (cathepsin D, acid phosphatase). Taken together these results suggest that in hyperstimulated thyrotrophs part rough/part smooth ER elements containing ICG lose their ribosomes, their membrane is modified, and they sequentially acquire a lysosome-type membrane and lysosomal enzymes. The findings are compatible with the conclusion that a pathway exists by which under certain conditions, secretory proteins present in the ER as well as ER membrane and content proteins can be degraded by direct conversion of ER cisternae into lysosomes.

Human liver cathepsin D. Purification, crystallization and preliminary X-ray diffraction analysis of a lysosomal enzyme

The two-chain form of active cathepsin D, a glycosylated, lysosomal aspartic proteinase, has been isolated from human liver. Isoelectric focusing revealed two major species of enzyme that differed by approximately 0.2 pI unit. Crystals suitable for X-ray diffraction analysis were prepared from acidic solutions using precipitation with ammonium sulfate. The hexagonal crystals diffracted X-rays to beyond 3.1 A resolution and belonged to space group P6(1) (or P6(5)) with cell constants a = b = 125.9 A, c = 104.1 A, gamma = 120.0 degrees. The crystals likely contain two molecules in the asymmetric unit, giving a solvent content of 56% (v/w). Biochemical analysis of crystals indicated that both isoforms were present in approximately equimolar proportions. Full structure determination of the enzyme is underway.

Isolation and sequencing of a cDNA clone encoding rat liver lysosomal cathepsin D and the structure of three forms of mature enzymes

We isolated and sequenced a cDNA clone corresponding to the entire coding sequence of rat liver lysosomal cathepsin D. The deduced amino acid sequence revealed that cathepsin D consists of 407 amino acid residues (Mr 44,608) and the 20 NH2-terminal residues seem to constitute a cleavable signal peptide after which 44 amino acid residues follow as a propeptide. Two putative N-linked glycosylation sites and aspartic acid in the active site are as well conserved as those of human lysosomal cathepsin D. In the NH2-terminal sequence analysis of two isolated heavy chains of the mature enzyme, the termini were assigned as tryptophan (118th residue) and glycine (165th or 166th residue), respectively, hence demonstrates that the two heavy chains derive from a split of the single chain of cathepsin D at position between 117th and 118th or between 164th and 165th or 165th and 166th amino acids. We conclude that cathepsin D in rat liver lysosomes is a mixture of three forms composed of a single and two two-chain forms. However, the amounts of the two two-chain forms are low compared with that of the single chain form. Densidometric determination after SDS-PAGE revealed that the two two-chain forms account for less than 5% of the single chain form. There is a 82% similarity in amino acid level between rat and human liver lysosomal cathepsin D.

Bafilomycin A1 inhibits the targeting of lysosomal acid hydrolases in cultured hepatocytes

Effects of bafilomycin A1, an inhibitor of vacuolar H(+)-ATPase, on the synthesis and processing of cathepsin D and cathepsin H were investigated in primary cultured rat hepatocytes. Pulse-chase experiments showed that after being synthesized as procathepsin D and procathepsin H the precursors were converted into mature forms in the control cells as the chase time elapsed. However, in the presence of 5 x 10(-7) M of bafilomycin A1, both precursors were largely secreted into the medium and no mature forms were found within the cells. Thus bafilomycin A1 mimics lysosomotropic amines with regard to perturbation of the targeting of lysosomal acid hydrolases. In contrast, bafilomycin A1 was found not to inhibit processings of proalbumin and procomplement component 3, which are thought to occur at the acidic trans-Golgi, implying that the proteolytic event of the proproteins is not sensitive to an increase of intra-Golgi pH. The results suggest that bafilomycin A1 is useful as a pH-perturbant to study the role of acidity in living cells.

Characterization of a cathepsin-H-like enzyme from a human melanoma cell line

A cathepsin-H-like enzyme has been isolated from cultured human melanoma cells (G 361 cell line). The enzyme is similar to cathepsin H(s) of normal tissues in molecular weight, enzymatic characteristics (substrates, inhibitors, pH optima, Km values), and immunoreactivity. The inactive form of the enzyme with a molecular mass of 40 kDa has been found in the culture medium. The inactive enzyme is activated by acid pH, pepsin, and cathepsin-D-like enzyme treatments and converted into a form with a molecular mass of 28 kDa. The activated extracellular cathepsin-H-like enzyme and the active intracellular enzyme exhibit the same characteristics. The melanoma-derived cathepsin-H-like enzyme degrade fibrinogen and fibronectin, but not laminin or type-IV collagen. We conclude that the extracellular cathepsin-H-like enzyme may have important functions, together with other proteinases, in the destruction of extracellular matrix components, thus enabling proliferation, migration, and metastasis to occur.

Cathepsins D and E in normal, metaplastic, dysplastic, and carcinomatous gastric tissue: an immunohistochemical study

Immunohistochemical distributions of cathepsins D and E were determined in normal mucosa, metaplastic, dysplastic, and cancerous lesions of the human stomach. Cathepsins D and E were localised in the foveolar epithelium and parietal cells of the normal gastric mucosa, but their intracytoplasmic distributions were different - cathepsin E distribution was even and diffuse in the cytoplasm while cathepsin D was found in coarse intracytoplasmic granules. Chronic inflammation and ulcer did not influence the distribution of these enzymes. No positive staining was obtained in the incomplete type of intestinal metaplasia, dysplasia, and well differentiated adenocarcinoma. Tumour cells of signet ring cell carcinoma and poorly differentiated adenocarcinoma cells, however, gave strong and diffuse stainings for cathepsins D and E in the cytoplasm. The results suggest that the distribution of cathepsins D and E is related to each specialised function of the foveolar epithelium and the parietal cells, and that their disappearance is associated with development of well differentiated adenocarcinoma from intestinal metaplasia.

Brefeldin A inhibits the targeting of cathepsin D and cathepsin H to lysosomes in rat hepatocytes

Effect of brefeldin A on the transport of lysosomal acid hydrolases (cathepsins D and H) was investigated in primary cultured rat hepatocytes. Both cathepsins were synthesized as proenzymes and progressively converted to mature enzymes in the control cells. However, BFA strongly inhibited the appearance of the mature enzymes in the cells in a dose dependent manner, suggesting that transport of newly synthesized lysosomal enzymes from the endoplasmic reticulum to lysosomes is blocked by the drug. The inhibitory effect by brefeldin A was reversible. Upon recovery from brefeldin A-intoxication, procathepsin D was effectively targeted into lysosomes, whereas a substantial amount of procathepsin H was found to be missorted, resulting in its secretion into the culture medium.

Isolation of cathepsin D using three-phase partitioning in t-butanol/water/ammonium sulfate

A 6-h procedure for the isolation of bovine cathepsin D is described. The procedure involves essentially only two steps; three-phase partitioning in t-butanol/water/ammonium sulfate followed by affinity chromatography on pepstatin-agarose. The major advantage of this new method over previous methods is the greatly reduced time required to obtain comparably pure cathepsin D.

Evidence that aspartic proteinase is involved in the proteolytic processing event of procathepsin L in lysosomes

Our recent studies have shown that cathepsin L is first synthesized as an enzymatically inactive proform in endoplasmic reticulum and is successively converted into an active form during intracellular transport and we postulated that aspartic proteinases would be responsible for the intracellular propeptide-processing step of procathepsin L accompanied by the activation of enzyme (Y. Nishimura, T. Kawabata, and K. Kato (1988) Arch. Biochem. Biophys. 261, 64-71). To better understand this proposed mechanism, we investigated the effect of pepstatin, a potent inhibitor of aspartic proteinases, on the intracellular processing kinetics of cathepsin L analyzed by pulse-chase experiments in vivo with [35S]methionine in the primary cultures of rat hepatocytes. In the pepstatin-treated cells, the proteolytic conversion of cellular procathepsin L of 39 kDa to the mature enzyme was significantly inhibited and considerable amounts of proenzyme were found in the cell after 5-h chase periods. Further, the subcellular fractionation experiments demonstrated that the intracellular processing of procathepsin L in the high density lysosomal fraction was significantly inhibited and that considerable amounts of the procathepsin L form were still observed in the light density microsomal fraction after 2 h of chase. These results suggest that pepstatin treatment caused a significant inhibitory effect on the intracellular processing and also on the intracellular movement of procathepsin L from the endoplasmic reticulum to the lysosomes. These findings provide the first evidence showing that aspartic proteinase may play an important role in the intracellular proteolytic processing and activation of lysosomal cathepsin L in vivo. Therefore, we suggest that cathepsin D, a major lysosomal aspartic proteinase, is more likely to be involved in this proposed model in the lysosomes.

Quantitation and immunohistochemical localization of cathepsins E and D in rat tissues and blood cells

The distribution of cathepsins E and D in various rat tissues and blood cells was determined by immunoprecipitation and by immunohistochemistry with discriminative antibodies specific for each enzyme. While cathepsin D was detected in all of the tissues and blood cells tested (except for erythrocytes), cathepsin E had a relatively limited distribution. The cathepsin E content was highest in the stomach and was succeeded in the following order by the urinary bladder, thymus, spleen, cervical lymph node and bone marrow. Significant amounts of cathepsin E were also found in the colon, rectum, jejunum, skin, lung, kidney and submandibular gland. The other tissues tested had little or no detectable cathepsin E content. Of the blood cells tested, lymphocytes and peritoneal neutrophils contained high levels of cathepsin E. Erythrocytes had cathepsin E only as aspartic proteinases. When the subcellular localization of cathepsin E in the neutrophils was investigated by fractionation of the postnuclear supernatants, the enzyme behaved as a soluble cytosolic enzyme. In contrast, cathepsin D was mainly associated with the granular fraction. The immunohistochemical localization of cathepsins E and D was clearly different in the stomach, large intestines, kidney and urinary bladder, but was similar in the lymph node and spleen. The tissue-fixed macrophages, which were notable in the skeletal and cardiac muscle tissues, submucosal layers of the gastrointestinal tracts, salivary gland, lung and trachea, also exhibited similar intense immunoreactivities demonstrative of both cathepsins E and D.

Human spleen cathepsin D: its characterization and localization in human spleen

1. The cathepsin D was purified 1830-fold under mild conditions by a rapid procedure, based on two-step affinity chromatography. 2. Its molecular weight, amino acid composition and substrate specificity were shown to display minor differences from materials of other origins. 3. Inhibition with thiol compounds was found to be a specific phenomenon of the cathepsin D from the human spleen. 4. Production of antiserum specific for purified cathepsin D was demonstrated by immunodiffusion test, an immunoadsorbent column and immunoblotting of the crude enzyme in SDS gel. 5. In an immunocytochemical study, the antigenic sites for this enzyme were found to be localized in the reticuloendothelial system of the human spleen. 6. The role of this enzyme in human spleen cell was discussed.

Identification of latent procathepsins B and L in microsomal lumen: characterization of enzymatic activation and proteolytic processing in vitro

Procathepsins B and L in the hepatic endoplasmic lumen were identified as having a molecular weight of 39,000 by immunoblot analysis. The proenzymes were then purified to remove the mature enzymes by concanavalin A-Sepharose chromatography. The concanavalin A-adsorbed fractions containing the proenzymes showed no appreciable activities of cathepsins B and L. When those fractions were incubated at pH 3.0, the enzymatic activities markedly increased: the activities of cathepsins B and L after 36 h incubation were 60 and 210 times those of the controls, respectively. Immunoblot analysis showed that after 36 h incubation the proenzymes disappeared and the mature enzymes increased. Thus the proenzymes were processed to the mature enzymes under acidic conditions of pH 3.0. The marked increases of enzymatic activities and the conversion of the proenzymes to the mature forms were completely blocked with pepstatin, which is a potent inhibitor of aspartic proteases. The results strongly suggested that a processing protease for procathepsins B and L might be cathepsin D, a major lysosomal aspartic protease. Indeed, lysosomal cathepsin D could convert microsomal procathepsin B to the mature enzyme in vitro. Therefore, procathepsins B and L seem first to be synthesized as enzymatically inactive forms in endoplasmic reticulum and successively may be converted into active forms by cathepsin D in lysosomal compartments.

Identification of T-kinin-Leu(T-kinin-containing peptide) released from T-kininogen by cathepsin D of granulomatous tissues in rats

Acid proteinases of granulomatous tissues in rats with carrageenin-induced inflammation released kinin from T-kininogen. By column chromatography on pepstatin-Sepharose 4B, two types of acid proteinase seems to be responsible for kinin release. One of the acid proteinase was identified as cathepsin D from SDS-polyacrylamide gel electrophoresis and Western-blot analysis, using anti-rat liver cathepsin D IgG. Cathepsin D alone could not release T-kinin, but T-kinin-containing peptides. The T-kinin-containing peptides were separated into two peptides by reverse-phase high-performance liquid chromatography. From determination of its amino acid composition and its immunoreactivity toward anti-bradykinin antiserum, one of the T-kinin-containing peptides was identified as T-kinin-Leu.

Identification of latent procathepsin H in microsomal lumen: characterization of proteolytic processing and enzyme activation

Procathepsin H in kidney and liver microsomal lumen was identified to have a molecular mass of 41 kDa by immunoblot analysis. The proenzyme was then concentrated by applying the microsomal contents to a concanavalin A-Sepharose column. When the concanavalin A-adsorbed fraction was incubated at pH 4.0 at 20 degrees C, the activity measured with synthetic substrate increased 3.5 times over that of the control after 24 h incubation. Immunoblot analysis showed that acidic treatment caused the disappearance of procathepsin H. Thus the proenzyme might be processed to the mature enzyme under acidic conditions. The marked increase of enzymatic activity and the conversion of proenzyme were completely blocked with pepstatin which is a potent inhibitor of aspartic proteases. These results suggested that a protease for processing procathepsin H might be cathepsin D, a major lysosomal aspartic protease. Therefore, procathepsin H seems to be synthesized first in the enzymatically inactive form in endoplasmic reticulum and successively converted into the active form in lysosomes during biosynthesis.

Identification of a precursor form of cathepsin D in microsomal lumen: characterization of enzymatic activation and proteolytic

A precursor form of cathepsin D with 45 kDa was demonstrated in the rat liver microsomal lumen by immunoblotting analysis. The microsomal fraction containing procathepsin D which passed through a pepstatin-Sepharose resin showed no appreciable activity of cathepsin D. The in vitro incubation of this fraction at pH 3.0 resulted in a gradual increase of proteolytic activity toward hemoglobin as substrate and also, the proteolytic conversion of procathepsin D to the mature form was concomitantly observed. The proteolytic processing step was sensitive to pepstatin. These results suggest that procathepsin D is inactive in the endoplasmic reticulum and may be converted to the active forms by autoproteolytic processing mechanism at acidic pH during biosynthesis.

Biochemical and immunochemical similarity between erythrocyte membrane aspartic proteinase and cathepsin E

An aspartic proteinase previously thought to be unique to erythrocyte membranes, termed "EMAP", has been shown to be closely related to cathepsin E. Enzymic comparison revealed that these two enzymes resembled each other in molecular weight, susceptibility to pepstatin and chromatographic behaviors on DEAE-Sephacel and Mono P chromatofocusing columns. They were immunoprecipitated by antiserum against human EMAP in a similar way. Immunochemical similarity between the two enzymes was also substantiated by immunoblot analysis.

Study of cathepsin A, B and D activities in the skin wound edges. Its application to the differential diagnosis between vital and postmortem wounds

The aims of the authors in this paper has been to check the diagnostic ability of the Cathepsin A, B and D concentrations in the skin wound edges to the differential diagnosis between vital and postmortem wounds. We have studied 56 domestic pigs grouped in seven experimental series consisting of 8 animals in each, according to the time (0, 5, 15, 30 min and 1, 3 and 6 h) after the injury. The enzymatic activities were investigated following the methods by Bowen and Davison Biochem. J., 131 (1973) 417-419, Suhar and Marks J. Biochem., 101 (1979) 23-30 and by Anson (modified by Yamamoto, Eur. J. Biochem., 95 (1979) 459-467) for Cathepsin A, B and D, respectively. For the differential diagnosis between vital and postmortem wounds, our results showed that the most useful markers studied are the Cathepsin A and D activities, Cathepsin D that of the first one.

Cytochrome P-450 and NADPH-cytochrome P-450 reductase are degraded in the autolysosomes in rat liver

We have investigated the degradation in rat liver of two typical endoplasmic reticulum (ER) membrane proteins, phenobarbital (PB)-inducible cytochrome P-450 (P-450[PB]) and NADPH-cytochrome P-450 reductase (FP2). Autolysosomes, almost completely free from contamination by the other organelles such as ER, were prepared from leupeptin-treated rat livers according to the method of Furuno et al. (Furuno, K., T. Ishikawa, and K. Kato, 1982, J. Biochem., 91:1943-1950). Quantitative immunoblot analysis showed that these two proteins were found in large amounts in the autolysosomes regardless of PB treatment. The specific content of P-450 (PB) in the autolysosomes changed along with that in the microsomes during and after PB treatment, whereas hardly any P-450(PB) was detected in the cytosol fraction throughout the experiment. We also found a marked increase in the autolysosomal proteins 3 d after cessation of PB treatment when microsomal proteins are degraded most rapidly. Ferritin immunoelectron microscopy revealed directly that when the limiting membranes of the premature autolysosomes were partially broken the smooth vesicles segregated within the autolysosomes were heavily stained with ferritin anti-P-450(PB) conjugates. Thus, for the first time, we could present convincing evidence that P-450(PB) and FP2 are segregated to be degraded in the autolysosomes.