Advanced glycation endproducts stimulate the MAP-kinase pathway in tubulus cell line LLC-PK1

Advanced glycation endproducts (AGEs) are suggested to play an important role in diabetic nephropathy. They induce specific cellular responses such as the release of cytokines in different cell lines. The effect of AGEs on signal transduction pathways was investigated in the renal tubulus cell line LLC-PK1. Using a serine-phosphate-specific antibody AGE-induced cellular responses associated with phosphorylation/dephosphorylation events were demonstrated. In particular, the p42MAP kinase and its downstream target, the AP-1 complex, are shown to be activated by AGE-BSA but not by BSA. In contrast, only partial phosphorylation is observed for the p70S6-kinase. Thus, AGEs appear to induce specific signal transduction pathways.     

Stability of metallothionein isoforms by capillary zone electrophoresis

Advanced glyco-oxidation end products (AGEs) generate oxygen free radicals that potentiate the development of atherosclerosis. Thus, AGEs may potentiate the aggregation of human platelets through oxidative stress. AGE-bovine serum albumin (BSA) and AGE-poly-L-lysine were evaluated for aggregation of human platelets. Superoxide in platelet-rich plasma (PRP) was measured using lucigenin-derived chemiluminescence. The platelet aggregation induced by ADP or U46619 was potentiated by preincubation with AGE-BSA, by 40% and by 59%, P < .05, respectively, vs BSA. Aggregation was increased by AGEs in a dose-dependent manner. The production of superoxide was significantly greater in PRP incubated with AGE-BSA vs BSA. The other Maillard reaction products, such as Amadori-, pentosidine-, and carboxymethyl lysine (CML)-BSA had no effect. Superoxide dismutase or indomethacin abolished the enhancing effect of AGEs on the platelet aggregation. AGEs potentiate platelet aggregation possibly with superoxide anions and prostanoids. AGE-induced potentiation of platelet aggregation may be involved in the development of atherosclerosis.     

Proteinases in renal cell death

The role of proteinases in renal proximal tubule (RPT) cellular death was examined using specific inhibitors of proteinases. Rabbit RPT suspensions were incubated with antimycin A for 1 h or tetrafluoroethyl-L-cysteine (TFEC) for 4 h in the absence or presence of the specific cysteine proteinase inhibitor L-trans-epoxysuccinyl-leucylamido (4-guanidino)butane (E-64), the serine proteinase inhibitors N-p-tosyl-L-lysine chloromethyl ketone (TLCK) or 3,4-dichloroisocoumarin (DCS), the serine and cysteine proteinase inhibitors leupeptin or antipain, or the aspartic proteinase inhibitor pepstatin. E-64 and pepstatin decreased lactate dehydrogenase (LDH) release, a marker of cell death, from RPT exposed either to antimycin A or TFEC. TLCK, DCS, leupeptin, or antipain did not decrease antimycin A- or TFEC-induced cell death. Bromohydroquinone- or t-butylhydroperoxide-induced cell death was not decreased by any of the proteinase inhibitors. Loss of lysosomal membrane potential, indicated by neutral red release, occurred prior to the onset of antimycin A-induced cell death. Extensive inhibition of lysosomal cathepsins B and L by E-64 was correlated with cytoprotection. However, E-64 was only protective after some cell death had occurred. These results suggest that lysosomal cysteine and aspartic proteinases, but not serine proteinases, play a role in RPT cell death induced by antimycin A or TFEC. The observation that E-64 was only protective after some cell death had occurred suggests that lysosomal cathepsins are released from dying cells and subsequently attack the remaining viable cells.     

Degradation of serum albumin by rat liver and kidney lysosomes

Lysosomes were isolated from the livers and from the kidneys of rats treated or not treated with the cysteine proteinase inhibitor leupeptin, and the levels of the intralysosomal serum albumin of the leupeptin-treated rats were compared with those of the saline-treated control rats. Leupeptin caused an intralysosomal accumulation of albumin in vivo because of its potent inhibition of lysosomal protein degradation. In fact, the lysosomes isolated from the livers and kidneys of leupeptin-treated rats almost completely lost their ability to degrade rat albumin in vitro. These findings show that the lysosomes are subcellular sites of the degradation of unlabeled serum albumin in these tissues. They also suggest that cysteine proteinases sensitive to leupeptin are involved in the lysosomal degradation of albumin. Albumin was degraded by total lysosomal enzymes in vitro. It was also degraded by the lysosomal extract being devoid of cathepsins H and J, prepared from rat kidney. The degradation of albumin by total lysosomal enzymes in vitro was greatly suppressed by a cysteine proteinase inhibitor, cystatin alpha, with no inhibition of cathepsins B and L. It was slightly suppressed by N-(L-3-trans-propylcarbamoyloxirane-2-carbonyl)-L-isoleucyl-L-prol ine (CA-074), a selective inhibitor of cathepsin B, and by pepstatin, an inhibitor of cathepsin D, whereas it was markedly suppressed by a combination of cystatin alpha and either CA-074 or pepstatin. These and associated findings show that cystatin alpha-sensitive cysteine proteinase(s), which is distinct from cathepsins B, H, L, and J, and cathepsins B and D are involved in the lysosomal degradation of albumin.     

Inhibitory effect of albumin-derived advanced glycosylation products on PMA-induced superoxide anion production by rat macrophages

Advanced glycosylation end products (AGE) are implicated in many of the complications of diabetes. In the same way, infectious diseases are frequently associated with this disease. An impaired respiratory burst in macrophages may be a cause of infectious complications in diabetic patients. To establish a possible mechanism of this altered cell function, we have analyzed the effect of AGE-modified proteins on PMA-dependent superoxide anion production (O2.-) from normal rat peritoneal macrophages. We have used AGE-modified bovine serum albumin (AGE-BSA) prepared by incubation with glucose. AGE-BSA partially inhibits the phorbol ester-dependent superoxide production by macrophages in vitro. The specificity of this inhibitory effect is demonstrated by the fact that aminoguanidine, an inhibitor of the formation of AGE products, fully prevents the effect of AGE-BSA in vitro. Macrophages from diabetic rats shown an inhibition on PMA dependent-O2.- production. However, the treatment in vivo with aminoguanidine produced a cancelation of the inhibitory effect observed in the diabetic state. These data suggest that AGE-modified proteins could be implicated in the impairment of macrophage respiratory burst in diabetes.     

Effects of glycated protein on the expression of very late antigen 5 (VLA5), a fibronectin receptor, of cultured rat mesangial cells

Advanced glycosylation end products are believed to play a role in the increase in extracellular matrix in diabetic glomerulosclerosis via a pathway involving a mesangial cell fibronectin receptor. In the present study, I assessed cultured rat mesangial cells for the presence of mRNA for VLA5, one of the fibronectin receptors. Using these cells, I also evaluated the effects of glycated proteins on the expression of VLA5 and fibronectin. Mesangial cells of Wistar rats were cultured in RPMI 1640 containing 20% FCS. The cells were incubated for 72 hr in a medium containing 50 mg/ml of nonglycated BSA or in a medium containing 50 mg/ml glycated BSA (AGE-BSA). Immunostaining and Northern blot analyses showed that the cells incubated with AGE-BSA exhibited a decrease in VLA5 protein and related mRNA, but showed an increase in the synthesis of fibronectin and related mRNA. On the other hand, non-glycated BSA did not induce these changes in the expression of VLA5 or fibronectin in the mesanginal cells. Northern blot analysis for VLA5 mRNA was also conducted using mesangial cells cultured in a medium with a high glucose concentration (30 mM). However, the high glucose condition did not have any effect on the expression of VLA5 protein or related mRNA. These results suggest that glycated proteins may regulate fibronectin synthesis in mesangial cells by modifying the expression of fibronectin receptors, such as the inhibition of VLA5 synthesis that acts as negative feedback of fibronectin synthesis.     

Tumor-associated cysteine proteinase activities in human melanoma cells and fibroblasts of different origin

Specific catalytic activities of cysteine proteinases including cathepsins B (EC 3.4.22.1) and L (EC 3.4.22.15) in human melanoma cell lines SK-MEL-28, SK-MEL-30, MEL-HO and in fibroblasts of different origin are reported. Cell line-specific pH profiles of these cysteine proteinases were determined fluorometrically with benzyloxycarbonyl-phenylalanyl-arginine-amidomethylcoumarine (Z-Phe-Arg-AMC) under saturated conditions. Single activities of cathepsins B and L were inactivated by urea and by benzyloxycarbonyl-phenylalanyl-phenylalanine-diazomethylketone (Z-Phe-Phe-CHN2) in order to describe the activities of these enzymes separately. The melanoma cell line MEL-HO, which originated from a primary lesion, showed highest activity of an unknown cysteine proteinase. This enzyme is not inactivated by urea and Z-Phe-Phe-CHN2 and has a Michaelis constant (K(M) value) of approximately 1 mM. The specific characteristics suggest that it is a tumor-associated cathepsin B. In addition, high invasive subpopulations of SK-MEL-28 and SK-MEL-30 cell lines isolated by an invasion assay showed higher proteinase activities than the low invasive subpopulations. Furthermore, in fibroblasts originating from melanoma tissue cysteine proteinase activities were increased compared to normal skin fibroblasts. In conclusion, these results indicate that these cysteine proteinases shown here are tumor-associated proteinases, possibly facilitating invasion and dissemination of melanoma cells.     

Functional defects in lysosomal enzymes in autosomal dominant polycystic kidney disease (ADPKD): abnormalities in synthesis, molecular processing, polarity, and secretion

The phenotype of autosomal dominant polycystic kidney disease (ADPKD) is characterized by basement membrane abnormalities, hyperproliferation, and alterations in epithelial cell polarity. Since proteinases have been implicated in matrix degradation and growth factor activation, lysosomal enzymes were compared in normal and ADPKD tissues and cell cultures. Acidic proteolytic activity (azocasein) was reduced in ADPKD, and specific enzymatic assays detected disease-dependent decreases in the specific activities of beta-galactosidase, beta-hexosaminidase, and cathepsins, B, L, and H. Cathepsin D-specific activities were unchanged. Lucifer yellow fluorescence in ADPKD cells was consistent with an alteration in heterogeneity of lysosomal enzyme content in ADPKD rather than a decrease in total lysosomal number. Western analysis, metabolic labeling, and immunoprecipitation analysis confirmed decreases in the expression and synthesis of the major normal molecular immunoreactive species of beta-galactosidase and cathepsins B and H in ADPKD tissue and cells but no changes in cathepsin D. In addition, ADPKD-specific high-molecular-weight species of cathepsin H were seen and abnormal forms of cathepsin B and beta-galactosidase were common in ADPKD, suggesting abnormal molecular processing and posttranslational modifications. In addition, immunolocalization studies showed abnormal apical plasma-membrane localization of cathepsins B and H in ADPKD cyst epithelial cells, consistent with a protein sorting defect in ADPKD. Increased extracellular secretion of lysosomal enzymes was also measured in ADPKD cultured cells and in filter-grown epithelia shown to be predominantly directed to the basal compartment. These results demonstrate that lysosomal enzyme alterations in ADPKD may play a role in aberrant processing of the basement membrane. Alterations in the polarized secretion of lysosomal enzymes by ADPKD epithelia in vitro were also detected. Whereas all normal epithelia cells secreted lysosomal enzymes predominantly to the apical medium compartments, basally directed secretion was increased in all ADPKD epithelia and attained an overall reversal of polarity for cathepsins B + L. It is concluded that alterations in lysosomal enzyme function in ADPKD are the result of alterations in synthesis, molecular processing, and polarized secretion of specific enzymes and may have impact on proliferative and basement membrane abnormalities in this genetic disease. These results are consistent with a fundamental defect in protein processing sorting, and trafficking in ADPKD.     

Brain aging in normotensive and hypertensive strains of rats. III. A quantitative study of cerebrovasculature

The mechanism of degradation of fructose-1,6-bisphosphate aldolase from rabbit muscle by the lysosomal proteinase cathepsin B was determined. Treatment of aldolase with cathepsin B destroys up to 90% of activity with fructose 1,6-bisphosphate as substrate, but activity with fructose 1-phosphate is slightly increased. Cathepsin L, another lysosomal thiol proteinase, and papain are also potent inactivators of aldolase, whereas inactivation is not caused by cathepsins D or H even at high concentrations, or by cathepsin B inhibited by leupeptin or iodoacetate. The cathepsin-B-treated aldolase shows no detectable change in subunit molecular weight, oligomer molecular weight or subunit interactions. Cathepsin B cleaves dipeptides from the C-terminus of th aldolase subunits. Four dipeptides are released sequentially: Ala-Tyr, Asn-His, Ile-Ser and Leu-Phe, and a maximum of five additional dipeptides may be released. There are indications that this peptidyldipeptidase activity of cathepsin B may be an important aspect of its action on protein substrates generally.     

In vitro transcription of Myxococcus xanthus genes with RNA polymerase containing sigmaA, the major sigma factor in growing cells

Long-term incubation of proteins with glucose leads to advanced glycation end products (AGEs) with fluorescence and a brown color. We recently demonstrated immunologically the intracellular AGE accumulation in smooth muscle cell (SMC)-derived foam cells in advanced atherosclerotic lesions. To understand the mechanism of AGE accumulation in these foam cells, we have now characterized the interaction of AGE proteins with rabbit-cultured arterial SMCs. In experiments at 4 degrees C, 125I-labeled AGE-bovine serum albumin (AGE-BSA) showed a dose-dependent saturable binding to SMCs with an apparent dissociation constant (Kd) of 4.0 microg/ml. In experiments at 37 degrees C, AGE-BSA underwent receptor-mediated endocytosis and subsequent lysosomal degradation. The endocytic uptake of 125I-AGE-BSA was effectively inhibited by unlabeled AGE proteins such as AGE-BSA and AGE-hemoglobin, but not by acetylated LDL and oxidized LDL, well-known ligands for the macrophage scavenger receptor (MSR). Moreover, the binding of 125I-AGE-BSA to SMCs was affected neither by amphoterin, a ligand for one type of the AGE receptor, named RAGE, nor by 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole-hexanoic acid-BSA, a ligand for the other AGE receptors, p60 and p90. This indicates that the endocytic uptake of AGE proteins by SMCs is mediated by an AGE receptor distinct from MSR, RAGE, p60, and p90. To examine the functional role of this AGE receptor, the migratory effects of AGE-BSA on these SMCs were tested. Incubation with 1-50 microg/ml of AGE-BSA for 14 h resulted in significant dose-dependent cell migration. The AGE-BSA-induced SMC migration was chemotactic in nature and was significantly inhibited (approximately 80%) by an antibody against transforming growth factor-beta (TGF-beta), and the amount of TGF-beta secreted into the culture medium from SMC by AGE-BSA was sevenfold higher than that of control, indicating that TGF-beta is involved in the AGE-induced SMC chemotaxis. These data suggest that AGE may play a role in SMC migration in advanced atherosclerotic lesions.     

Lipid peroxidation parameters and activities of lysosomal enzymes in patients with diabetes mellitus

The processes of lipid peroxidation and activities of lysosomal enzymes were studied in 56 patients with type I and II diabetes mellitus. The rate of lipid peroxidation of red cell membranes was assessed from the activities of enzymatic (NADPH-dependent) and nonenzymatic (ascorbate-dependent) lipid peroxidation, from accumulation of acylhydroperoxides, intermolecular joints, and from spontaneous red cell hemolysis. Activities of lysosomal enzymes (cathepsins, acid DNAse, and beta-galactosidase) were measured in leukoconcentrate. The activity of enzymatic system of lipid peroxidation and acylhydroperoxide content in red cell membranes were found increased. In parallel with this, a deficiency in leukocytic lysosomes of beta-galactosidase and DNAse was revealed. The detected metabolic disturbances may be regarded as one of the pathogenetic mechanisms of development of diabetic angiopathies. A relationship was revealed between changes in lipid peroxidation parameters and activities of lysosomal enzymes, on the one hand, and diabetes mellitus type and duration, on the other.     

Accumulation of pyrraline-modified albumin in phagocytes due to reduced degradation by lysosomal enzymes

Previous studies suggested that the interaction between proteins modified by advanced glycation end products (AGEs) and cells, such as macrophages, may be involved in diabetic angiopathy. Pyrraline is one of the AGEs and known to be elevated in plasma of diabetic rats and humans, and is present in vascular lesions of diabetic and elderly subjects. We examined whether modification of albumin by pyrraline influences its degradation by macrophage-like cell line, P388D1 cells. Degradation of pyrraline-modified albumin by these cells was diminished, causing accumulation of the albumin in these cells. The susceptibility of pyrraline-modified albumin to lysosomal proteolytic enzymes was reduced by approximately 40% in vitro, while lysosomal activity in the cells per se was not affected. This phenomenon was also observed when human monocytes were used instead of P388D1 cells. Our results suggest that accumulation of pyrraline-modified albumin in P388D1 cells is due to the reduced susceptibility of the protein to lysosomal enzymatic degradation. Such alterations in the interaction between AGEs-modified protein and phagocytes may contribute to angiopathy in elderly subjects and patients with diabetes.     

PAF-antagonists with lipid structure. 6. Alkylpropandiol lipids with acyl- and ether- structures at the C-3 position and heterocyclic head groups; synthesis, characterization and structure-activity relationship

OBJECTIVE: To investigate whether nonenzymatic glycated end products (AGEs) have effects on the expression and bioactivity of plasminogen activator inhibitor-1 (PAI-1), one of the seripin proteinases, which lead to extracellular matrix (ECM) degradation in cultured human mesangial cells. METHODS: Human mesangial cells (HMC) were cultured. Cell proliferation, fibronectin production, mRNA expression and bioactivity of PAI-1 were determined after exposure to AGE-BSA for 24 hours and 48 hours in vitro. RESULTS: HMC stimulated by AGE-BSA exhibited inhibition in HMC proliferation, increase in fibronectin production, and PAI-1 bioactivity. These changes were pronounced with prolongation of experimental time. PAI-1 mRNA expression increased significantly at 24 hr (0.45% +/- 0.06% vs 0.65% +/- 0.08%, P < 0.05), however more marked increase of PAI-1 mRNA expression at 48 hr (0.51 +/- 0.08% vs 0.92 +/- 0.10%, P < 0.01). CONCLUSIONS: Increase of mRNA expression and bioactivity of PAI-1 induced by AGEs decreased ECM degradation and play an important role in the pathogenesis of ECM accumulation and glomerulosclerosis.     

Advanced glycation end products in vitreous: Structural and functional implications for diabetic vitreopathy

PURPOSE: Advanced glycation end products (AGEs) form irreversible cross-links with many macromolecules and have been shown to accumulate in tissues at an accelerated rate in diabetes. In the present study, AGE formation in vitreous was examined in patients of various ages and in patients with diabetes. Ex vivo investigations were performed on bovine vitreous incubated in glucose to determine AGE formation and cross-linking of vitreous collagen. METHODS: By means of an AGE-specific enzyme-linked immunosorbent assay (ELISA), AGE formation was investigated in vitreous samples obtained after pars plana vitrectomy in patients with and without diabetes. In addition, vitreous AGEs were investigated in bovine vitreous collagen after incubation in high glucose, high glucose with aminoguanidine, or normal saline for as long as 8 weeks. AGEs and AGE cross-linking was subsequently determined by quantitative and qualitative assays. RESULTS: There was a significant correlation between AGEs and increasing age in patients without diabetes (r = 0.74). Furthermore, a comparison between age-matched diabetic and nondiabetic vitreous showed a significantly higher level of AGEs in the patients with diabetes (P < 0.005). Collagen purified from bovine vitreous incubated in 0.5 M glucose showed an increase in AGE formation when observed in dot blot analysis, immunogold labeling, and AGE ELISA. Furthermore, there was increased cross-linking of collagen in the glucose-incubated vitreous, when observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein separation. This cross-linking was effectively inhibited by coincubation with 10 mM aminoguanidine. CONCLUSIONS: This study suggests that AGEs may form in vitreous with increasing age. This process seems to be accelerated in the presence of diabetes and as a consequence of exposure to high glucose. Advanced glycation and AGE cross-linking of the vitreous collagen network may help to explain the vitreous abnormalities characteristic of diabetes.     

The state of lysosomes and protein turnover in rat liver. Effect of excess vitamin A

Administration of excess vitamin A to rats induces labilization of liver lysosomal membranes, as shown by the release of lysosomal cathepsins upon tissue homogenization. The effect of lysosomal labilization on liver protein turnover was investigated. The apparent turnover rate of liver proteins in the hypervitaminotic animals, as measured by a double isotope-labeling technique (Glass and Doyle (1972) J, Biol. Chem, 247, 5234-5242), was found to be the same as that in control animals. Neutral and alkaline fructose-1, 6-biphosphatase [EC 3.3.3.11] activities in the liver were also found to be unchanged in hypervitaminosis A. These data indicate that the rate of intracellular protein degradation is not determined by the level of "free cathepsins. Protein synthesis in the livers of the hypervitaminotic animals was partially imparied, as shown by the shift of polysomal profiles toward lighter aggregates.     

A comparative study on the synthesis of the natriuretic hormone dopamine in OK and LLC-PK1 cells

The Vmax values (in nmol/mg protein/15 min) for AAAD in OK cells (0.94 +/- 0.08) were found to be significantly (P < 0.01) lower than those observed in LLC-PK1 cells (4.37 +/- 0.08). However, in both cell lines decarboxylation reaction was a saturable process with similar K(m) values (OK cells = 1.1 mM (0.3, 1.8); LLC-PK1 cells = 1.8 mM (1.6, 2.1)). Contrariwise to OK cells, decarboxylation of L-DOPA to dopamine in LLC-PK1 cells followed a linear (7.6 +/- 0.1 pmol/mg protein/min) non-saturable kinetics till 120 min of incubation. The formation of dopamine from increasing concentrations of L-DOPA (10 to 500 microM) followed a non-linear kinetics in both cell lines; the process of L-DOPA decarboxylation was saturated at low concentrations of L-DOPA with an apparent K(m) value of 11 microM (0.2, 22.6) in OK cells and 27.4 microM (11.1, 43.7) in LLC-PK1 cells. The formation of dopamine in LLC-PK1 cells (Vmax = 2097 +/- 113 pmol/mg protein/6 min) was 13.7-fold that occurred in OK cells (Vmax = 153 +/- 10 pmol/mg protein/6 min). In conclusion, LLC-PK1 cells appear to be endowed with a greater ability to form dopamine from exogenous L-DOPA when compared to OK cells.     

Cross-class inhibition of the cysteine proteinases cathepsins K, L, and S by the serpin squamous cell carcinoma antigen 1: a kinetic analysis

The human squamous cell carcinoma antigens (SCCA) 1 and 2 are tandemly arrayed genes that encode two high-molecular-weight serine proteinase inhibitors (serpins). Although these proteins are 92% identical, differences in their reactive site loops suggest that they inhibit different types of proteinases. Our previous studies show that SCCA2 inhibits chymotrypsin-like serine proteinases [Schick et al. (1997) J. Biol. Chem. 272, 1849-1855]. We now show that, unlike SCCA2, SCCA1 lacks inhibitory activity against any of the more common types of serine proteinases but is a potent cross-class inhibitor of the archetypal lysosomal cysteine proteinases cathepsins K, L, and S. Kinetic analysis revealed that SCCA1 interacted with cathepsins K, L, and S at 1:1 stoichiometry and with second-order rate constants >/= 1 x 10(5) M-1 s-1. These rate constants were comparable to those obtained with the prototypical physiological cysteine proteinase inhibitor, cystatin C. Also relative to cystatin C, SCCA1 was a more potent inhibitor of cathepsin K-mediated elastolytic activity by forming longer lived inhibitor-proteinase complexes. The t1/2 of SCCA1-cathepsin S complexes was >1155 min, whereas that of cystatin C-cathepsin complexes was 55 min. Cleavage between the Gly and Ser residues of the reactive site loop and detection of a stable SCCA1-cathepsin S complex by sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggested that the serpin interacted with the cysteine proteinase in a manner similar to that observed for typical serpin-serine proteinase interactions. These data suggest that, contingent upon their reactive site loop sequences, mammalian serpins, in general, utilize their dynamic tertiary structure to trap proteinases from more than one mechanistic class and that SCCA1, in particular, may be involved in a novel inhibitory pathway aimed at regulating a powerful array of lysosomal cysteine proteinases.     

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A 7-, 14-, and 21-day course of injections of the lysosomotropic drug chloroquine in a dose of 50-mg/kg per day causes a more than two-fold decrease of T3 concentration and insignificant changes in the level of T4 and thyrotropin in the blood serum of rats. In the series with 14- and 21-day courses of chloroquine injections, inhibition of the thiol cathepsins B and L with simultaneous activation of the aspartic proteinase cathepsin D occurred. Permeability of the lysosomal membranes for all hydrolases under study considerably increased after a 7-day course of chloroquine but reduced subsequently to the control level in longer treatment. The possible mechanisms of changes in the spectrum of lysosomal proteinases and functional activity of the thyroid are discussed.     

Human cathepsin F. Molecular cloning, functional expression, tissue localization, and enzymatic characterization

A cDNA for a novel human papain-like cysteine protease, designated cathepsin F, has been cloned from a lambdagt10-skeletal muscle cDNA library. The nucleotide sequence encoded a polypeptide of 302 amino acids composed of an 88-residue propeptide and a 214-residue mature protein. Protein sequence comparisons revealed 58% homology with cathepsin W; about 42-43% with cathepsins L, K, S, H, and O; and 38% with cathepsin B. Sequence comparisons of the propeptides indicated that cathepsin F and cathepsin W may form a new cathepsin subgroup. Northern blot analysis showed high expression levels in heart, skeletal muscle, brain, testis, and ovary; moderate levels in prostate, placenta, liver, and colon; and no detectable expression in peripheral leukocytes and thymus. The precursor polypeptide of human recombinant cathepsin F, produced in Pichia pastoris, was processed to its active mature form autocatalytically or by incubation with pepsin. Mature cathepsin F was highly active with comparable specific activities toward synthetic substrates as reported for cathepsin L. The protease had a broad pH optimum between 5.2 and 6.8. Similar to cathepsin L, its pH stability at cytosolic pH (7.2) was short, with a half-life of approximately 2 min. This may suggest a function in an acidic cellular compartment. Transient expression of T7-tagged cathepsin F in COS-7 cells revealed a vesicular distribution of the gene product in the juxtanuclear region of the cells. However, contrary to all known cathepsins, the open reading frame of the cathepsin F cDNA did not encode a signal sequence, thus suggesting that the protease is targeted to the lysosomal compartment via an N-terminal signal peptide-independent lysosomal targeting pathway.     

Inhibition of trypanosomal cysteine proteinases by their propeptides

The ability of the prodomains of trypanosomal cysteine proteinases to inhibit their active form was studied using a set of 23 overlapping 15-mer peptides covering the whole prosequence of congopain, the major cysteine proteinase of Trypanosoma congolense. Three consecutive peptides with a common 5-mer sequence YHNGA were competitive inhibitors of congopain. A shorter synthetic peptide consisting of this 5-mer sequence flanked by two Ala residues (AYHNGAA) also inhibited purified congopain. No residue critical for inhibition was identified in this sequence, but a significant improvement in Ki value was obtained upon N-terminal elongation. Procongopain-derived peptides did not inhibit lysosomal cathepsins B and L but did inhibit native cruzipain (from Dm28c clone epimastigotes), the major cysteine proteinase of Trypanosoma cruzi, the proregion of which also contains the sequence YHNGA. The positioning of the YHNGA inhibitory sequence within the prosegment of trypanosomal proteinases is similar to that covering the active site in the prosegment of cysteine proteinases, the three-dimensional structure of which has been resolved. This strongly suggests that trypanosomal proteinases, despite their long C-terminal extension, have a prosegment that folds similarly to that in related mammal and plant cysteine proteinases, resulting in reverse binding within the active site. Such reverse binding could also occur for short procongopain-derived inhibitory peptides, based on their resistance to proteolysis and their ability to retain inhibitory activity after prolonged incubation. In contrast, homologous peptides in related cysteine proteinases did not inhibit trypanosomal proteinases and were rapidly cleaved by these enzymes.