Regulated splicing produces different forms of dopa decarboxylase in the central nervous system and hypoderm of Drosophila melanogaster

The dopa decarboxylase gene (Ddc) of Drosophila melanogaster is expressed in the hypoderm and the nervous system and promoter elements mediating differential expression in these tissues have been identified (Scholnick et al., 1986). Here we report an additional mode of regulation; the unique primary transcript of the Ddc gene is spliced to form mRNAs in these two tissues which differ by a single internal exon. In vitro mutagenesis and P-element-mediated transformation were employed to manipulate the tissue-specific expression of these RNAs. This approach demonstrated that regulated splicing rather than differential stability causes the tissue-specific expression of these RNAs and allowed the identification of Ddc enzyme isoforms encoded by each mRNA. The Ddc enzyme in the central nervous system differs from the hypodermal Ddc protein by the addition of 33-35 amino acids on the N terminus.

Free radical reduction by thioredoxin reductase at the surface of normal and vitiliginous human keratinocytes

Cell cultures of human keratinocytes contain membrane-associated thioredoxin reductase that is extremely active in reducing radicals on the outer plasma membrane. This enzyme activity was confirmed by its purification from cultures of stratified human keratinocytes by affinity column chromatography. The enzyme was assayed both in vivo and in vitro using a spin-labeled quaternary ammonium compound as the substrate, under saturating conditions in free radical substrate. Specific activities were determined by monitoring the sequential decrease in the amplitude of the electron spin resonance signal per unit of cell protein. The following properties were found: Cultures of adult stratified cells have approximately twice the thioredoxin reductase activity of neonatal cells. The enzyme is inhibited by thioprotein inhibitors (i.e., parachloromecuribenzoate and dinitrochlorobenzene). The activity is regulated by calcium concentrations of the cell culture medium. Stratified keratinocytes are half as active in medium containing 2 mM Ca++ compared with 0.1 mM Ca++ concentration. Product inhibition of the enzyme occurs with oxidized coenzyme NADP+ (i.e., 87% inhibition of enzyme activity over 30 min). The enzyme is heat stable at temperatures of 70 degrees C for 10 min. It is inactivated at 75 degrees C. A comparative study of thioredoxin reductase activity on stratified differentiated and undifferentiated rapidly growing cells was performed. Also, enzyme activity was quantitated for cultured keratinocytes isolated from vitiliginous and normal skin of the same donor. The results of this study, and the connection between this enzyme activity and UV-generated free radicals are reconciled in terms of the mechanism of action and metabolic activity of thioredoxin reductase.

Regulation of the activity of histamine-N-methyltransferase from guinea pig skin by biogenic amines

Histamine-N-methyltransferase, a major histamine-degrading enzyme in the skin, was purified from guinea pig skin about 150-fold. The enzymological characteristics including pH optimum, Km values for substrates, and molecular weight were almost consistent with those reported in the brain. Regulatory mechanism of the enzyme activity by biogenic amines was investigated using the purified specimen. Serotonin, tryptamine, and 5-methoxytryptamine intensely inhibited the activity while tryptophan, melatonin, N-acetylserotonin, tryptophol, and 5-hydroxyindole acetic acid had no significant effects. Dopamine, tyramine, 3-methyltyramine, and phenylethylamine also inhibited the activity while no particular effects were obtained by adrenaline, noradrenaline, tyrosine, and DOPA. Spermidine and cadaverine caused significant but weaker inhibition. These amines acted competitively with respect to histamine, although varying manners were observed with respect to S-adenosyl-L-methionine. From these results, it was concluded that the enzyme activity was inhibited by such compounds in which a certain chemical structure, CH2-CH2-NH2 group neighboring the hydrophobic group, was contained. A possible mechanism of inhibition by the amines is postulated, and possible roles of such compounds in the inflammation by impairing the histamine metabolism is discussed.

Induction of keratinocyte type-I transglutaminase in epithelial cells of the rat

Using immunogold-silver techniques, we have demonstrated that, in rats, type-I (keratinocyte) transglutaminase is expressed primarily in stratified squamous epithelia of the integument, the upper digestive tract, and the lower female genital tract. In these epithelia, the enzyme was found to be present predominantly in the granular layer, but was evident at low levels even in the basal layer, especially in the genital tract. No immunoreactivity was detected in glandular, columnar, or transitional epithelia or in soft tissues. However, considerable enzyme antigenicity was observed in the endometrium and in major ducts of the pancreas and mammary glands of near-term pregnant and early postpartum females. In cultures, substantial immunoreactivity was readily identifiable not only in epidermal, vaginal, and esophageal epithelial cells (immunopositive in vivo), but also in urinary bladder, seminal vesicle, and tracheal epithelial cells (immunonegative in vivo). Primary epithelial outgrowths from bladder and seminal vesicle tissue explants were immunopositive, demonstrating rapid adaptation to the culture environment. These results reveal three distinct levels of regulation of transglutaminase expression in various cell types: during the differentiation of keratinocytes, during pregnancy, being evident principally in the endometrium but detectable elsewhere as well, and during the cultivation of certain epithelia which do not normally express the enzyme in vivo. We conclude that type-I transglutaminase may be a valuable marker for elucidating the regulation of normal epithelial differentiation and squamous metaplasia.

Cysteine proteinases produced by cultured rabbit V2 carcinoma cells and rabbit skin fibroblasts

Rabbit V2 carcinoma cells and normal rabbit skin fibroblasts produced cysteine proteinases with properties similar to those of purified rabbit liver cathepsin B. Both cell types secreted into the culture medium enzymes with an apparent Mr of 43,000, which reacted with synthetic substrates commonly used for cathepsin B. After limited proteolysis with pepsin or treatment at pH 3, the Mr = 43,000 species could be converted into forms with Mr = 34,000 and an increased specific activity. In the intracellular pool of both V2 carcinoma cells and fibroblasts, a cysteine proteinase with the same Mr of cathepsin B (27,000) was found. Despite the similarity in molecular size, substrate specificity and sensitivity to inhibitors, the tumor and fibroblast enzymes were not identical in their stability at pH greater than or equal to 7 and were produced by the 2 cell types in considerably different amounts. In terms of enzyme units and normalized to an equal cell number, the ratios of fibroblast enzyme/tumor enzyme were as follows: secreted 130-150; intracellular, 150-180. The pH stability of the cysteine proteinases was determined quantitatively by measuring the half-life of enzyme activity. At pH 8.0 and 25 degrees C the secreted tumor cysteine proteinase had a half-life of at least 5 hr, whereas the secreted fibroblast enzyme and liver cathepsin B had half-lives of 8.8 min and 4.4 min, respectively.

all-trans-Retinoic acid inhibits the appearance of two phorbol ester-induced ornithine decarboxylase mRNAs in mouse epidermis

Two ornithine decarboxylase mRNA species are seen in mouse epidermis in response to the topical application of the phorbol ester tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA). This induction occurs in a time- and dose-dependent fashion and appears to be relatively specific as alpha-actin mRNA reveals no change with treatment. Both mRNA species are inhibited in a dose-dependent manner by treating mouse skin with all-trans-retinoic acid prior to TPA. These results indicate that these two compounds are active at the transcriptional level.

Association of steroid sulfatase with one of the arylsulfatase C isozymes in human fibroblasts

When arylsulfatase C, a microsomal membrane-bound enzyme, is assayed with its natural substrates, the 3-beta-hydroxysteroid sulfates, it is also known as steroid sulfatase. Whether arylsulfatase C and steroid sulfatase are identical enzymes or not, however, has long been disputed. We now report that two electrophoretic variants of arylsulfatase C occur in normal human fibroblasts: one has a single anodic band of activity, "s," and the other has an additional faster migrating band, "f". The two types, s and "f + s", occur in cells from either sex. When fibroblast strains with the f + s forms of arylsulfatase C were cloned, two types of primary clones were always obtained: s and f + s. A single f band was never seen. When these primary clones were subcloned, however, the arylsulfatase C phenotype remained unchanged: primary s clones gave rise to s subclones and f + s clones to f + s subclones only. Therefore, these forms were clonal in origin and demonstrated a novel inheritance pattern in human cultured cells. The appearance of increasing amounts of the f band was correlated with up to 4-fold increase of arylsulfatase C activity, whereas the steroid sulfatase activity remained constant, thus demonstrating that arylsulfatase C was not identical with steroid sulfatase activity. Polyclonal antibodies raised against the s form immunoprecipitated activities of the s form of arylsulfatase C and steroid sulfatase but not the f form of arylsulfatase C. Therefore, we conclude that only the s form of arylsulfatase C is immunologically related to steroid sulfatase so that arylsulfatase C per se is not necessarily identical with steroid sulfatase. In addition, a novel form of genetic heterogeneity of isozymes in human fibroblasts is demonstrated.

Lipid metabolism in xanthomatous skin of hypercholesterolemic rabbits

The authors studied xanthomatous skin in cholesterol-fed rabbits for changes in lipid content and in activities of enzymes regulating intracellular lipid content. After 80 days of hypercholesterolemic diet, xanthomas were widespread and changes in lipid metabolism were marked. In both tissue homogenates and cell membrane pellets, unesterified cholesterol and phospholipids increased 2-fold to 6-fold, and cholesteryl esters increased about 30-fold. Tissue triglycerides, however, decreased to half the levels found in control skin. Cholesterol esterification rates, measured by activity of acyl coenzyme A: cholesterol acyltransferase, increased moderately to markedly; hydrolase activity against 4-methylumbelliferyl oleate also increased at both acid and neutral pH, but hydrolase activity against cholesterol oleate increased only at acid pH. Thus, hypercholesterolemia caused striking increases in intracellular cholesterol esterification rates, increases in lipase activity at both neutral and acid pH, and increases in cholesteryl ester hydrolase activity at acid pH. Increases in cholesterol-esterifying activity uniformly exceeded increases in cholesteryl ester hydrolytic activity in congruence with net accumulation of cholesteryl ester. Skin xanthoma grade, however, had no consistent relation to the cholesterol esterification rates. Instead, the enzyme data suggested that marked abnormalities of lipid metabolism are diffusely distributed through dermal tissue as a precondition for the focal emergence of xanthomas.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-mediated epidermal ornithine decarboxylase induction and skin tumor promotion by new lipoxygenase inhibitors lacking protein kinase C inhibitory effects

Both 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) and 3,4,2',4'-tetrahydroxychalcone inhibited 12-lipoxygenase of mouse epidermis. The IC50 of AA861 and 3,4,2',4'-tetrahydroxychalcone for epidermal 12-lipoxygenase were 1.9 and 0.2 microM, respectively. These agents showed very weak inhibitory actions on epidermal cyclooxygenase, with the potency of inhibition for cyclooxygenase less than 1/50 of that for lipoxygenase. Induction of epidermal ornithine decarboxylase by 12-O-tetradecanoylphorbol-13-acetate (TPA; 10 nmol/mouse) was potently inhibited by these agents in a dose-dependent manner (1-30 mumol/mouse). TPA (5 nmol/mouse)-induced skin tumor formation was also strongly suppressed by these agents (15 mumol/mouse). Both AA861 and 3,4,2',4'-tetrahydroxychalcone failed to inhibit partially purified epidermal protein kinase C activity. These results support the proposed involvement of lipoxygenase product(s) of arachidonic acid in TPA-induced skin tumor promotion.

Dopaminergic inhibition of tyrosinase activity in hair follicular melanocytes of the mouse

Bromocriptine, a dopamine agonist that blocks the secretion of MSH, inhibits melanogenesis in the hair follicular melanocytes of pubertal C3H-HeAvy mice. However, since this effect cannot be explained by a reduction in circulating alpha-MSH, we have examined the possibility that dopaminergic mechanisms may have a direct inhibitory effect on these melanocytes. Bromocriptine decreased tyrosinase activity in skin explants from 30- to 35-day-old mice that were growing dark hair. This decrease in tyrosinase activity was blocked by dopamine receptor antagonists, haloperidol or spiperone. The specific D2 agonist LY 171555 also inhibited tyrosinase activity in the skin explants in a dose-related manner and the effect was blocked by sulpiride, a D2-receptor antagonist. Neither bromocriptine nor LY 171555 had any effect on tyrosinase activity in skin explants taken from adult mice that were growing yellow hair. The D1-receptor agonist SKF 38393 had no effect on tyrosinase activity in skin explants from either group of mice. The present results support the idea that dopamine D2-receptor agonists have a direct inhibitory effect upon tyrosinase activity of hair follicular melanocytes of the C3H-HeAvy mouse. However, this effect was confined to periods of dark hair growth when the melanocytes produce eumelanin. The D2 agonists were ineffective in reducing tyrosinase activity during adult life when the melanocytes produce predominantly phaeomelanin. This suggests that different control mechanisms may operate in the hair follicular melanocytes during periods of eumelanin and phaeomelanin synthesis.

Competitive inhibition of human skin collagenase by N-benzyloxycarbonyl-L-prolyl-L-alanyl-3-amino-2-oxopropyl-L-leucyl-L- alanylglycine ethyl ester

A 'ketomethylene' peptide, N-benzyloxycarbonyl-L-prolyl-L-alanyl-3-amino- 2-oxopropyl-L-leucyl-L-alanylglycine ethyl ester, was synthesized and shown to be a fairly potent competitive inhibitor of human skin collagenase.

Antenatal diagnosis of recessive dystrophic epidermolysis bullosa: collagenase expression in cultured fibroblasts as a biochemical marker

We performed fetoscopy and skin biopsy on a 19-week fetus at risk for recessive dystrophic epidermolysis bullosa (RDEB). Ultrastructural analysis of the tissue revealed dermolytic blister formation in the skin characteristic of the disease. To develop a biochemical test for use in antenatal diagnosis of RDEB, we established skin fibroblast cultures from the 20-week aborted fetus. The collagenase production by fetal RDEB fibroblast cultures was greater than seen in normal fetal fibroblast cultures. The concentration in culture medium from fetal RDEB cultures was 5.42 +/- 0.74 micrograms/ml (mean +/- SE) compared with 2.24 +/- 1.11 micrograms/ml in normal adult control cultures and 2.05 +/- 0.61 micrograms/ml in cultures from patients with other genetic forms of epidermolysis bullosa (p less than 0.025). In contrast, the concentration of collagenase in the fetal RDEB culture medium was not different from that seen in cell cultures from known patients with RDEB (5.34 +/- 1.12 micrograms/ml). Collagenase activity of the fetal RDEB medium was also increased approximately 3.5-fold. These data indicate that enhanced expression of collagenase by fetal RDEB skin fibroblasts can serve as a biochemical adjunct, and possibly an alternative, to morphologic examination of tissue for antenatal diagnosis.

Effects of 12-o-tetradecanoylphorbol-13-acetate and polyprenoic acid derivative on calcium-activated phospholipid-dependent protein kinase of pig skin

12-o-Tetradecanoylphorbol-13-acetate (TPA) activates calcium-activated, phospholipid-dependent protein kinase (protein kinase C) partially purified in an ion exchange column from pig epidermis. Protein kinase C was activated by TPA in a concentration-dependent manner with simultaneous addition of Ca2+ and phospholipid. Polyprenoic acid derivative (E5166) which is a newly synthesized retinoic acid derivative, inhibited the TPA activation of protein kinase C. This inhibition may explain the mechanisms by which retinoids inhibit TPA-induced tumor promotion.

Characterization of the testicular abnormality in 5 alpha-reductase deficiency

The testes of five phenotypic women (from four families) with 5 alpha-reductase deficiency were studied. In one of the patients, the enzyme deficiency was similar in the testis and epididymis and in fibroblasts cultured from the labia majora. In testes from four of the patients, the concentrations of the 5 alpha-reduced steroids dihydrotestosterone and 3 alpha-androstanediol were less than 10% of those in normal subjects. We conclude that the testis is involved in 5 alpha-reductase deficiency. Impaired spermatogenesis was evident in testicular biopsies from all five subjects, and in two, sperm production, as estimated in testicular homogenates, was less than 10% of normal. The extent to which spermatogenic arrest is due to 5 alpha-reductase deficiency or testicular maldescent is not clear.

Melanocyte-stimulating hormone and the regulation of tyrosinase activity in hair follicular melanocytes of the mouse

Skin tyrosinase activity increases during hair growth in C3H-HeAvy mice and reaches higher levels in young (30- to 35-day-old) mice when the hair follicular melanocytes synthesize the black pigment, eumelanin, than in older (6-month-old) mice when they produce the golden yellow pigment, phaeomelanin. To examine the regulation of the melanocytes at these different stages we have compared the effect of alpha-MSH and other agents that act, through cyclic AMP-dependent mechanisms, on skin tyrosinase activity in both young and old mice during hair growth, initiated by plucking. Daily administration of alpha-MSH, isoprenaline or theophylline increased coat darkness, and skin tyrosinase activity in the younger mice 7-9 days after plucking, but they were ineffective in the older mice. Similarly alpha-MSH, 8-bromo-cyclic AMP or theophylline increased tyrosinase activity in skin explants from the younger mice incubated for up to 24 h but had no effect in explants from older mice. Cyclic GMP had no effect on tyrosinase activity in skin explants from both young and old mice. It is suggested that whereas cyclic AMP-dependent mechanisms may operate to regulate tyrosinase activity in the hair follicular melanocytes of younger mice that produce eumelanin these systems may not operate in the older mice when these melanocytes synthesize phaeomelanin. Phaeomelanin synthesis, unlike that of eumelanin, may not depend upon tyrosinase and its regulation by cyclic AMP and this could explain the low levels of this enzyme in the skin and its failure to respond to alpha-MSH and other activators of the cyclic AMP system during periods of phaeomelanin production.

Comparative effects of topically applied nitrated arenes and their nonnitrated parent arenes on cutaneous and hepatic drug and carcinogen metabolism in neonatal rats

The effect of a single topical application of several nitroarenes (1-nitropyrene, nitropyrenes mixture, nitrobenzo(ghi)perylene mixture, 3-nitrofluoranthene, nitrofluoranthene mixture, and nitroperylene mixture) and their corresponding parent arenes to neonatal rats on hepatic and cutaneous drug and carcinogen metabolism was studied. Topical application of each nitroarene (10 mg/kg) resulted in significant induction of aryl hydrocarbon hydroxylase (AHH), 7-ethoxyresorufin O-deethylase (ERD), and 7-ethoxycoumarin O-deethylase (ECD) activities in both skin (1.5- to 14.6-fold) and liver (1.3- to 41.9-fold). The induction of these enzymes by each of the nitroarenes was significant when compared to control or to their corresponding parent arenes. Among the nitroarenes studied, 1-nitropyrene was the least effective in inducing enzyme activities. The inducibility in both skin and liver by different nitroarenes tested was in the following order: nitrofluoranthenes mixture greater than 3-nitrofluoranthene greater than nitroperylenes mixture greater than nitrobenzo(ghi)perylenes mixture greater than nitropyrenes mixture greater than 1-nitropyrene. The nitrofluoranthenes mixture and the nitroperylenes mixture were almost as effective as 3-methylcholanthrene (3-MC). Parent arenes were either ineffective or significantly less effective than nitrated arenes in inducing hepatic and/or cutaneous monooxygenase activities. Hepatic and/or cutaneous benzphetamine N-demethylase (BPD), NADPH cytochrome c reductase, NADH ferricyanide reductase activities, and the levels of cytochrome P-450 and cytochrome b5, remained unchanged following treatment with either topically applied nitroarenes or arenes. However, a shift of approximately 1 nm to the blue region in the absorption maximum of hepatic cytochrome P-450 was observed in animals treated with nitroarenes. This shift was not evident in the case of 1-nitropyrene. Analysis of benzo(a)pyrene metabolites by high-pressure liquid chromatography revealed a significant enhancement in the production of metabolites by nitroarene-treated rat skin and liver microsomes. Our studies suggest that nitroarenes are inducers of hepatic and cutaneous monooxygenases in neonatal rats after topical administration and that they resemble the 3-MC type of inducers in this regard.

The role of calcium in the regulation of free radical reduction by thioredoxin reductase at the surface of the skin

Membrane associated thioredoxin reductase has been previously shown to reduce free radicals on the outer plasma membranes of human keratinocytes and melanocytes to provide a possible first line of defense against free radical damage at the surface of the skin. Preliminary experiments with cell cultures of human keratinocytes and melanocytes grown in serum-free medium showed that the enzyme activity depends on extracellular calcium concentration in the medium. Thioredoxin reductase activity at the surface of the skin, at the surface of human keratinocytes and melanocytes, and purified thioredoxin reductase from E. coli and adult human keratinocytes all exhibited calcium-dependent allosteric control. Since thioredoxin reductase contains two extremely reactive thiolate groups at the active site with pK values close to neutrality, both of these anions can form covalent complexes with N-ethylmaleimide by nucleophilic attack on the double bond. In our experiments we used spin-labeled maleimide [4-maleimido-tempo] to examine the local environment in the active site of thioredoxin reductase in the presence and absence of calcium. Both spin-labeled thioethers are distinguishable by EPR spectroscopy, with one site being significantly more immobilized than the other. Hence, it has been possible to observe direct evidence for active site closure by calcium. These results suggest that extracellular calcium may play an important role in regulation of thioredoxin reductase activity for the defense mechanism against UV-mediated free radical damage at the surface of human skin.

A comparative study of stearic and lignoceric acid oxidation by human skin fibroblasts

Sensitive assays were developed for long chain and very long chain fatty acid oxidation in human skin fibroblast homogenates. Stearic and lignoceric acids were degraded by the fibroblasts by the beta-oxidation pathway. The cofactor requirements for stearic and lignoceric acid beta-oxidation were very similar but not identical. For example, appreciable lignoceric acid oxidation could be demonstrated only in the presence of alpha-cyclodextrin and was inhibited by Triton X-100. In Zellweger's syndrome, stearic acid beta-oxidation was partially reduced whereas lignoceric acid beta-oxidation was reduced dramatically (less than 12% activity compared to the controls). The results presented suggest that stearic acid beta-oxidation occurs in mitochondria as well as in peroxisomes, but lignoceric acid oxidation occurs entirely in the peroxisomes. We suggest that the beta-oxidation systems for stearic acid and lignoceric acid may be different.

Isolation of a dipeptidyl aminopeptidase, a putative processing enzyme, from skin secretion of Xenopus laevis

A dipeptidyl aminopeptidase has been purified to apparent homogeneity from skin secretion of Xenopus laevis. This enzyme is a glycoprotein with a molecular mass of about 98 kDa. It hydrolyzes a variety of dipeptidyl-p-nitroanilides and oligopeptides containing proline, alanine or glycine as the second amino acid and is inhibited by diisopropylfluorophosphate. The pH optimum was found to be around 8, while at pH 6, substrates were cleaved at about one-third of the maximal rate. This dipeptidyl aminopeptidase has the specificity required for the cleavage of amino-terminal extensions preceding the sequence of caerulein and xenopsin in their respective precursors.

Angiotensin-converting enzyme: characteristics in human skin fibroblasts

Angiotensin-converting enzyme, although most prominent in vascular endothelium, has been identified in numerous tissues. Recent studies have indicated that several hormones, including glucocorticoids and thyroid hormone, may affect the activity of this enzyme. In the present study, angiotensin-converting enzyme was examined in homogenates of cultured human skin fibroblasts. Angiotensin-converting enzyme activity was measured by a radiometric assay using [Glycine-1-14C] Hippuryl-L-histidyl-L-leucine (1.1 mmol/L) as substrate, and was expressed as nmol hippuric acid formed per minute/mg protein. Angiotensin-converting enzyme was identified in all five cell strains tested, and the activity observed was 0.97 +/- 0.18 nmol/min/mg protein (mean +/- SE). The optimum pH was between 6.9 and 7.6, and optimum temperature was 37 degrees C, with loss of activity of 55 degrees C and higher. Buffer strength was optimized at Tris 0.025 mol/L, and 1.0 mol/L NaCl. Activity increased linearly with protein concentration and with time, and the Km = 1.14 mmol/L. The most potent inhibitor of fibroblast ACE was captopril (SQ 14,225) with an IC50 = 10(-10) mol/L; other inhibitors included SQ 20,881, EDTA, and phenanthroline. Competitive substrates included angiotensin-I, substance P, and bradykinin. Four hormones, T3 (10(-9)-10(-7) mol/L), 1,25 (OH)2D3 (10(-8)-10(-7) mol/L), dexamethasone (10(-7)-10(-6) mol/L), and a synthetic androgen, R1881 (10(-8)-10(-7) mol/L) were incubated with cells for 72 hours. In all incubations, there was no significant effect on cellular ACE activity induced by any agent. Angiotensin-converting enzyme activity in serum free media was less than 1% of cell activity and was unaltered by hormone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of human collagenases with a hydroxamic acid affinity column

Human collagenase has been isolated from skin fibroblasts and rheumatoid synovium by using an affinity matrix, prepared by coupling Pro-Leu-Gly-NHOH to agarose. Following the methodology described herein, the skin enzyme was isolated in two steps in 76% yield and the synovial enzyme was purified in three steps in 71% yield. Importantly, each enzyme hydrolyzed collagen into 3/4-1/4 cleavage fragments, indicating that a true collagenase had been isolated. The column was specific for the human enzyme since the collagenase from Clostridium histolyticum did not bind. The affinity ligand was designed according to the formalism proposed by Holmquist and Vallee [Holmquist, B., & Vallee, B. L. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 6216] that effective metalloenzyme inhibitors can be synthesized by coupling a suitable metal-coordinating group to a substrate analogue. In this case, the hydroxamic acid probably coordinates to the active-site metal and the Pro-Leu-Gly moiety is similar to the carboxyl side of the cleavage site of collagen, the enzyme's substrate. The IC50 for N-(benzyloxycarbonyl)-Pro-Leu-Gly-NHOH is 4 X 10(-5) M for both enzymes. The affinity chromatographic procedures described here should aid in future studies on vertebrate collagenases.

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.