Reduced lysyl oxidase activity in skin fibroblasts from patients with Menkes'' syndrome.

Lysyl oxidase activity against both collagen and elastin substrates has been examined in the culture medium of skin fibroblasts derived from unrelated patients with Menkes' syndrome and from control subjects. The medium of three Menkes' fibroblast lines showed 3--30% of the activity present in the medium of control fibroblasts, against a purified collagen substrate. Lysyl oxidase activity in the culture medium of two of the Menkes' fibroblast lines was also examined by using a crude aortic-elastin substrate and was similarly decreased in comparison with that in the medium of control fibroblasts. Lysyl oxidase activity in the medium of a fourth fibroblast line, derived from a foetus with Menkes' syndrome, was 42% of that in the medium of control fibroblasts derived from a 1-day-old baby against a collagen substrate, and 26% of that in control fibroblast medium against an elastin substrate. The copper content of the cell layers of the Menkes' fibroblast cultures was elevated in comparison with normal fibroblast cultures, as has previously been reported to be characteristic of such cells. It is suggested that the decrease in lysyl oxidase activity would help to explain the connective tissue defects observed in Menkes' syndrome, and that this reduction, in conjunction with the elevated concentrations of cellular copper, would support the hypothesis that a functional intracellular copper deficiency exists in Menkes' syndrome.     

Secretion of lysyl oxidase by cultured human skin fibroblasts and effects of monensin, nigericin, tunicamycin and colchicine

Lysyl oxidase is an extracellular enzyme that initiates crosslink formation in the major connective tissue proteins, the collagens and elastin. This enzyme activity accumulated in a fresh medium of cultured human skin fibroblasts for at least 24 h, but the accumulation was distinctly non-linear after the first 12 h. Most of the total enzyme activity was present in the medium, the activity found in the cell layer representing about 30% of the total activity at 4 h, and about 10-15% at 24 h. The bulk of the cell-layer-associated activity appeared to be extracellular, as more than half was lost upon trypsinization. Culturing of the cells for 8 h in the presence of either monensin or nigericin, ionophores known to inhibit the secretion of many proteins at the level of the Golgi complex, markedly reduced the accumulation of lysyl oxidase activity in the medium. Monensin was particularly effective, as it produced a distinct inhibition even at a 10 nM concentration, reaching 50% at 30 nM. Both ionophores also reduced enzyme activity in the cell layer, whereas no definite decrease was seen in the activity of the trypsinized cells. The effect of monensin was evidently not due to any general toxicity on the part of the drug, since even a 500 nM concentration gave no inhibition of the incorporation of [3H]leucine into total protein. Tunicamycin also reduced lysyl oxidase activity in the medium and to a lesser extent in the cell layer, but the effective dose, 1-10 micrograms/ml, also inhibited the incorporation of [3H]leucine into total protein. The reduced enzyme activity may therefore not be due to a direct effect of tunicamycin on the glycosylation of the lysyl oxidase protein itself but may be mediated through other actions of the drug. Colchicine caused no inhibition in lysyl oxidase activity secretion even at a 10 microM concentration, although it has been reported to inhibit collagen secretion at doses more than one order of magnitude lower.     

A Fluorometric Assay for Detection of Lysyl Oxidase Enzyme Activity in Biological Samples

Lysyl oxidase catalyzes the final known enzymatic step required for collagen and elastin cross-linking in the biosynthesis of normal mature functional insoluble extracellular matrices. In addition, lysyl oxidase has been identified as a possible tumor suppressor. Lysyl oxidase activity in biological samples is traditionally and most reliably assessed by tritium release end-point assays using radiolabeled collagen or elastin substrates involving laborious vacuum distillation of the released tritiated water. In addition, a less sensitive fluorometric method exists that employs nonpeptidyl amine lysyl oxidase substrates and measures hydrogen peroxide production with horseradish peroxidase coupled to homovanillate oxidation. The present study describes a more sensitive fluorescent assay for lysyl oxidase activity that utilizes 1,5-diaminopentane as substrate, and released hydrogen peroxide is detected using Amplex red in horseradish peroxidase-coupled reactions. This method allows the detection of 40 ng of enzyme per 2 ml assay at 37 degrees C and is 7.5 times more sensitive than the currently available fluorometric assay for enzyme activity. This method eliminates the interference that occurs in some biological samples and can be successfully used to detect lysyl oxidase activity in cell culture experiments.     

Lysyl oxidase activates the transcription activity of human collagene III promoter. Possible involvement of Ku antigen

Lysyl oxidase is an extracellular enzyme that controls the maturation of collagen and elastin. Lysyl oxidase and collagen III often show similar expression patterns in fibrotic tissues. Therefore, we investigated the influence of lysyl oxidase overexpression on the promoter activity of human COL3A1 gene. Our results showed that when COS-7 cells overexpressed the mature form of lysyl oxidase, the activity of the human COL3A1 promoter was increased up to an average of 12 times when tested by luciferase reporter assay. The effect was specific, because other promoters were not affected. Moreover, lysyl oxidase effect was abolished by beta-aminopropionitrile, a specific inhibitor of its catalytic activity. Electrophoretic mobility shift assay showed a binding activity in the region from -101 to -77 that was significantly increased by lysyl oxidase overexpression. The binding was specifically competed by the cold probe, and the mutagenesis of this region abolished both the binding activity in gel retardation and lysyl oxidase stimulation of COL3A1 promoter in transfection experiments. We identified the binding activity as Ku antigen in its two components: Ku80 and Ku70. This study suggests a new coordinated mechanism by which lysyl oxidase might control the development of fibrosis.     

Inhibition of lysyl oxidase by disulfhydryls, diamines and sulfhydryl-amines.

Lysyl oxidase is the enzyme responsible for the oxidative deamination of lysine and hydroxylysine residues in collagen and elastin. Lysyl oxidase activity is irreversibly inhibited by disulfhydryls and diamines while the sulfhydryl-amine, penicillamine, inhibits reversibly. Monosulfhydryls or monoamines do not inhibit significantly. All inhibitors tested react directly with the enzyme. The disulfhydryls do not inhibit through thiolytic cleavage as an equivalent amount of β-mercaptoethanol does not produce significant inhibition (1). The possibility of adduct formation between these bifunctional inhibitors and aldehyde or pyridoxine derived cofactors within the enzyme is discussed.     

The propeptide domain of lysyl oxidase induces phenotypic reversion of ras-transformed cells

Lysyl oxidase is an extracellular enzyme critical for the normal biosynthesis of collagens and elastin. In addition, lysyl oxidase reverts ras-mediated transformation, and lysyl oxidase expression is down-regulated in human cancers. Since suramin inhibits growth factor signaling pathways and induces lysyl oxidase in ras-transformed NIH3T3 cells (RS485 cells), we sought to investigate the effects of suramin on the phenotype of transformed cells and the role of lysyl oxidase in mediating these effects. Suramin treatment resulted in a more normal phenotype as judged by growth rate, cell cycle parameters, and morphology. beta-aminopropionitrile, the selective inhibitor of lysyl oxidase enzyme activity, was remarkably unable to block suramin-induced reversion. By contrast, ectopic antisense lysyl oxidase demonstrated that lysyl oxidase gene expression mediated phenotypic reversion. Since lysyl oxidase is synthesized as a 50 kDa precursor and processed to a 30 kDa active enzyme and 18 kDa propeptide, the effects of these two products on the transformed phenotype of RS485 cells were then directly assessed in the absence of suramin. Here we report, for the first time, that the lysyl oxidase propeptide, and not the lysyl oxidase enzyme, inhibits ras-dependent transformation as determined by effects on cell proliferation assays, growth in soft agar, and Akt-dependent induction of NF-kappaB activity. Thus, the lysyl oxidase propeptide, which is released during extracellular proteolytic processing of pro-lysyl oxidase, functions to inhibit ras-dependent cell transformation.     

Lysyl oxidase and P-ATPase-7A expression during embryonic development in the rat

Lysyl oxidase activity is critical for the assembly and cross-linking of extracellular matrix proteins, such as collagen and elastin. Moreover, lysyl oxidase activity is sensitive to changes in copper status and genetic perturbations in copper transport, e.g., mutations in the P-type ATPase gene, ATP7A, associated with cellular copper transport. Lysyl oxidase may also serve as a vehicle for copper transport from extracellular matrix cells. Herein, we demonstrate that sufficient lysyl oxidase functional activity is present in the rat embryo at gestation day (GD) 9 to be detected in conventional enzyme assays. Estimation of embryonic lysyl oxidase functional activity, however, required partial purification in order to remove inhibitors. From GD 9 to GD 15, lysyl oxidase activity was relatively constant when expressed per unit of protein or DNA. In contrast, the steady-state levels of lysyl oxidase and ATP7A mRNA, measured by RT-PCR and expressed relative to total RNA and cyclophilin mRNA, increased approximately fourfold from GD 9 to 15. The pattern of temporal expression for ATP7A was consistent with its possible role in copper delivery to lysyl oxidase.     

Cloning, sequence analysis, and characterization of the 'lysyl oxidase' from Pichia pastoris

Lysyl oxidase from Pichia pastoris has been successfully overexpressed. EPR and resonance Raman experiments have shown that copper and TPQ are present, respectively. Lysyl oxidase from P. pastoris has a similar substrate specificity to the mammalian enzyme (both have been shown to oxidize peptidyl lysine residues) and is 30% identical to the human kidney diamine oxidase (the highest of any non-mammalian source). This enzyme also has a relatively broad substrate specificity compared to other amine oxidases. Molecular modeling data suggest that the substrate channel in lysyl oxidase from P. pastoris permits greater active site access than observed in structurally-characterized amine oxidases. This larger channel may account for the diversity of substrates that are turned over by this enzyme.     

Mutant cells defective in poly(ADP-ribose) synthesis due to stable alterations in enzyme activity or substrate availability

We used two different approaches to develop cell lines deficient in poly(ADP-ribose) synthesis to help determine the role of this reaction in cellular functions. One approach to this problem was to develop cell lines deficient in enzyme activity; the other approach was to develop cell lines capable of growing with such low nicotinamide adenine dinucleotide (NAD) levels so as to effectively limit substrate availability for poly(ADP-ribose) synthesis. The selection strategy for obtaining cells deficient in activity of poly(ADP-ribose) polymerase was based on the ability of this enzyme to deplete cellular NAD in response to high levels of DNA damage. Using this approach, we first obtained cell lines having 37-82% enzyme activity compared to their parental cells. We now report the development and characterization of two cell lines which were obtained from cells having 37% enzyme activity by two additional rounds of further mutagenization and selection procedures. These new cell lines contain 5-11% enzyme activity compared to the parental V79 cells. In pursuit of the second strategy, to obtain cells which limit poly(ADP-ribose) synthesis by substrate restriction, we have now isolated spontaneous mutants from V79 cells which can grow stably in the absence of free nicotinamide or any of its analogs. These cell lines maintain NAD levels in the range of 1.5-3% of that found in their parental V79 cells grown in complete medium. The pathway of NAD biosynthesis in these NAD-deficient cells is not yet known. Further characterization of these lines showed that under conditions that restricted poly(ADP-ribose) synthesis, they all had prolonged doubling times and increased frequencies of sister chromatid exchanges.     

Collagen cross-linking. Purification and substrate specificity of lysyl oxidase.

Lysyl oxidase is a specific amine oxidase that catalyzes the formation of aldehyde cross-link intermediates in collagen and elastin. In this study, lysyl oxidase from embryonic chick cartilage was purified to constant specific activity and a single protein band on sodium dodecyl sulfate acrylamide gel electrophoresis. This band had an apparent molecular weight of 62,000. The eluted protein cross-reacted with inhibiting antisera developed against highly purified lysyl oxidase. The highly purified enzyme was active with both insoluble elastin and embryonic chick skin or bone collagen precipitated as reconstituted, native fibrils. There was low activity with nonhydroxylated collagen, collagen monomers, or native fibrils isolated from lathyritic calvaria. The maximum number of aldehyde intermediates formed per molecule of collagen that became insoluble was two. These results indicate that lysyl oxidase has maximum activity on ordered aggregates of collagen molecules that may be overlapping associations of only a few collagen molecules across. Formation of aldehyde intermediates and cross-links during fibril formation may facilitate the biosynthesis of stable collagen fibrils and contribute to increased fibril tensile strength in vivo.     

Lysyl oxidase deficiency in lung and fibroblasts from mice with hereditary emphysema.

Lysyl oxidase activity was measured in the lungs and from cultured fibroblasts of Blotchy mice. A marked decrease in lysyl oxidase activity was observed in lungs of affected mice as compared to normal litter mates. Fibroblasts cultured from Blotchy mice were also deficient in lysyl oxidase, producing less than half of normal enzyme levels. Normal and Blotchy fibroblasts which had been maintained in culture for several months and had undergone spontaneous transformation, continued to show the same magnitude of difference in lysyl oxidase levels. The data suggest that the deficiency of lysyl oxidase is inherent in Blotchy fibroblasts and support the idea that the deficiency of this enzyme is the metabolic lesion that leads to the connective tissue defects observed in these animals.     

Superoxide dismutase during glucose repression of Hansenula polymorpha CBS 4732

Hansenula polymorpha CBS 4732 was studied during cultivation on methanol and different glucose concentrations. Activities of Cu/Zn and Mn superoxide dismutase, catalase and methanol oxidase were investigated. During cultivation on methanol, increased superoxide dismutase and catalase activities and an induced methanol oxidase were achieved. Transfer of a methanol grown culture to medium with a high glucose concentration caused growth inhibition, low consumption of carbon, nitrogen and phosphate substrates, methanol oxidase inactivation as well as decrease of catalase activity (21.8 +/- 0.61 deltaE240 x min(-1) x mg protein(-1)). At the same time, a high value for superoxide dismutase enzyme was found (42.9 +/- 0.98 U x mg protein(-1), 25% of which was represented by Mn superoxide dismutase and 75% - by the Cu/Zn type). During derepression methanol oxidase was negligible (0.005 +/- 0.0001 U x mg protein(-1)), catalase tended to be the same as in the repressed culture, while superoxide dismutase activity increased considerably (63.67 +/- 1.72 U x mg protein(-1), 69% belonging to the Cu/Zn containing enzyme). Apparently, the cycle of growth inhibition and reactivation of Hansenula polymorpha CBS 4732 cells is strongly connected with the activity of the enzyme superoxide dismutase.     

Characterization of cytochrome-c oxidase mutants in human fibroblasts

Skin fibroblasts were selected as having cytochrome-c oxidase deficiency by activity measurements in whole cells. Each cell line was cultured in sufficient amount to isolate mitochondria for biochemical characterization. Cytochrome-c oxidase was then examined by activity measurements, by heme determination and by polypeptide analysis using antibodies specific to the enzyme subunits. The cytochrome-c oxidase activity in the different cell lines ranged from 9% to 54% of that of normal fibroblasts. Heme determinations and polypeptide analysis established that the lowered cytochrome-c oxidase activity was due to reduced amounts of the complex in the mitochondrial inner membrane. In all cases, there was defective assembly of the enzyme, with the amounts of mitochondrially coded and nuclear coded subunits being reduced proportionally. These studies show that fibroblasts can be used for prenatal diagnosis of mitochondrial diseases and are a useful system in which to study mitochondrial biogenesis.     

Multiple bone morphogenetic protein 1-related mammalian metalloproteinases process pro-lysyl oxidase at the correct physiological site and control lysyl oxidase activation in mouse embryo fibroblast cultures

Lysyl oxidase catalyzes the final enzymatic step required for collagen and elastin cross-linking in extracellular matrix biosynthesis. Pro-lysyl oxidase is processed by procollagen C-proteinase activity, which also removes the C-propeptides of procollagens I-III. The Bmp1 gene encodes two procollagen C-proteinases: bone morphogenetic protein 1 (BMP-1) and mammalian Tolloid (mTLD). Mammalian Tolloid-like (mTLL)-1 and -2 are two genetically distinct BMP-1-related proteinases, and mTLL-1 has been shown to have procollagen C-proteinase activity. The present study is the first to directly compare pro-lysyl oxidase processing by these four related proteinases. In vitro assays with purified recombinant enzymes show that all four proteinases productively cleave pro-lysyl oxidase at the correct physiological site but that BMP-1 is 3-, 15-, and 20-fold more efficient than mTLL-1, mTLL-2, and mTLD, respectively. To more directly assess the roles of BMP-1 and mTLL-1 in lysyl oxidase activation by connective tissue cells, fibroblasts cultured from Bmp1-null, Tll1-null, and Bmp1/Tll1 double null mouse embryos, thus lacking BMP-1/mTLD, mTLL-1, or all three enzymes, respectively, were assayed for lysyl oxidase enzyme activity and for accumulation of pro-lysyl oxidase and mature approximately 30-kDa lysyl oxidase. Wild type cells or cells singly null for Bmp1 or Tll1 all produced both pro-lysyl oxidase and processed lysyl oxidase at similar levels, indicating apparently normal levels of processing, consistent with enzyme activity data. In contrast, double null Bmp1/Tll1 cells produced predominantly unprocessed 50-kDa pro-lysyl oxidase and had lysyl oxidase enzyme activity diminished by 70% compared with wild type, Bmp1-null, and Tll1-null cells. Thus, the combination of BMP-1/mTLD and mTLL-1 is shown to be responsible for the majority of processing leading to activation of lysyl oxidase by murine embryonic fibroblasts, whereas in vitro studies identify pro-lysyl oxidase as the first known substrate for mTLL-2.     

Properties of highly purified lysyl oxidase from embryonic chick cartilage.

Lysyl oxidase the enzyme which oxidately deaminates lysine residues in collagen and elastin, was purified from embryonic chick cartialge by employing an affinity column of lathyritic rat skin collagen coupled to Sepharose, followed by separation on DEAE-cellulose. An enzyme preparation was obtained which was pure as shown by polyacrylamide gel electrophoresis. The specific activity was 1800-fold higher than that of the original extract. The pure enzyme utilized both collagen and elastin substrate. Furthermore, the ratios of enzyme activity with elastin substrate versus that with collagen substrate were the same at all stages of purity. Only one protein band was found after polyacrylamide gel electrophoresis of the pure lysyl oxidase in sodium dodecyl sulfate and mercaptoethanol. The molecular weight was estimated to be 28000. It was found that the enzyme contained a large number of cysteine and tyrosine residues. Evidence was obtained for molecular heterogeneity of lysyl oxidase. The enzyme eluted from DEAE-cellulsoe in at least four distinct regions. When the peaks were rechromatographed separately, they eluted at salt concentrations similar to those of the original chromatogram. However, the substrate specificity and the electrophoretic mobility on polyacrylamide gel were the same for all enzyme fractions.     

Measurement of medium lysyl oxidase activity in aorta smooth muscle cells. Effects of multiple medium changes and inhibition of protein synthesis

Cultures of rabbit aortic smooth muscle (RSM) cells are a valuable model system for studying production and metabolism of connective tissue components. This report describes various assay procedures for lysyl oxidase, the enzyme responsible for deaminating lysine residues to give aldehyde cross-link precursors, in culture medium from these cells. Studies of the medium enzyme from second-passage RSM cells indicate that approximately 40% of the total enzyme activity in the flask of cells is in the medium. The medium enzyme levels are replenished quite rapidly following refeeding, and enzyme levels in the medium appear to be feedback controlled. The mechanism for this control is unknown at present. Multiple refeeding experiments in which the medium was changed every 2-4 h for up to 40 h indicate that these cells are cap]able of producing large amounts of enzyme and are capable of altering enzyme production and secretion quite rapidly in response to changes in their environment. Protein synthesis inhibitor studies with cycloheximide suggest that the major portion of the enzyme released into the medium following refeeding is newly synthesized although a pool of latent enzyme is also present. As in intact tissue, extraction of the enzyme from the cell layer requires strong denaturing reagents such as 4 M urea. These results suggest that the production of lysyl oxidase is closely regulated and is very responsive to changes in the external environment of the cells. This cell culture system appears to be an excellent one to study the production of lysyl oxidase and its role in connective tissue fibrillogenesis.     

Purification and properties of four species of lysyl oxidase from bovine aorta

Lysyl oxidase of bovine aorta was resolved into four enzymically active species by elution from DEAE-cellulose with a salt gradient in 6m-urea, consistent with purification results obtained with enzyme of other tissues [Stassen (1976) Biochim. Biophys. Acta438, 49-60]. In the present study, each of the four peaks of activity was purified to apparent homogeneity by subsequent chromatography on gel-filtration media in 6m-urea. Each enzyme is eluted as a species with mol.wt. approx. 30000 under these conditions, although lysyl oxidase polymerizes to a series of multimers with molecular weights ranging up to 1000000 in the absence of urea. The apparent subunit molecular weight of each enzyme species determined by electrophoresis in sodium dodecyl sulphate and 8m-urea is approx. 32000-33000. The amino acid compositions of the purified forms of lysyl oxidase are similar to each other, although sufficient differences exist to conclude that each is a unique molecular species. Incorporation of alpha-toluenesulphonyl fluoride into the purification scheme does not alter the resolution of enzyme into four species, suggesting that proteolysis during isolation is not the basis of the heterogeneity. The similar sensitivities of each form of enzyme to chelating agents and to semicarbazide and isoniazid indicate that each requires the participation of a metal ion, presumably Cu(2+), and of a carbonyl compound for enzyme function. The present study describes a method for the purification of multiple species of lysyl oxidase and reveals that significant chemical differences exist between the different enzyme forms.     

sn-glycerol-3-phosphate oxidase and alcohol tolerance inDrosophila melanogaster larvae

The role of sn-glycerol-3-phosphate oxidase (GPO; EC 1.1.99.5) in the variation of ethanol tolerance in Drosophila melanogaster was assessed in isofemale lines derived from individuals collected at the Chateau Tahbilk Winery and Wandin North Orchard of Victoria, Australia. When fed an undefined medium (semolina-treacle) with 6% ethanol (v/v), larvae of lines with high GPO activities survived better than did larvae of lines with low GPO activities. Although GPO was induced to higher activity levels by dietary ethanol in larvae of all the test lines, GPO activity was greater in lines representing the area outside the wine cellar. This implied that the cellar environment selected against individuals with high levels of GPO. These data do not explain the established difference in tolerance between cellar and outside populations. The GPO activities of lines were not dependent upon the activities of the lipogenic enzyme, glycerol-3-phosphate dehydrogenase; the major ethanol-degrading enzyme, alcohol dehydrogenase; or the citric acid cycle enzyme, fumarase. Thus, GPO activity is an important component of the metabolic mechanism of ethanol tolerance in larvae, but the mode of action of GPO has not been defined.