Regulation of proteolytic activity in tissues

Effects of fibronectin cleaved by neuropsin on cell adhesion and migration

Neuropsin is a serine protease cloned from the mouse hippocampus. Since neuropsin is a secreted protein which effectively cleaves fibronectin, it may affect cell adhesion or cell migration by modulating the content and/or chemical characteriscs of fibronectin in extracellular matrix (ECM). In adhesion assays, alpha5B2 cells expressing integrin alpha5beta1 bound less effectively to fibronectin teated with neuropsin than intact fibronectin. In Boyden chamber chemotaxis assays, the fibronectin-induced migration of alpha5B2 cells was not affected by neuropsin treatment. These findings suggest that neuropsin regulates the local microenvironment by modulating the interaction between cells and fibronectin in ECM.

Fiber type-specific expression of major proteolytic systems in fast- to slow-transforming rabbit muscle

The present study investigates the role of two major proteolytic systems in transforming rabbit and rat muscles. The fast-to-slow transformation of rabbit muscle by chronic low-frequency stimulation (CLFS) induces fast-to-slow transitions of intact, mature fibers and replacement of degenerating fibers by newly formed slow fibers. Ubiquitination, an indicator of the ATP-dependent proteasome system, and calpain activity were measured in homogenates of control and stimulated extensor digitorum longus muscles. Calpain activity increased similarly (approximately 2-fold) in stimulated rat and rabbit muscles. CLFS had no effect on protein ubiquitination in rat muscle but led to elevations in ubiquitin protein conjugates in rabbit muscle. Immunohistochemistry was used to study the distribution of micro-calpain and m-calpain and of ubiquitinated proteins in myosin heavy chain-based fiber types. The findings suggest that both proteolytic systems are involved in fiber transformation and replacement. Transforming mature fibers displayed increases in micro-calpain and accumulation of ubiquitin protein conjugates. The majority of these fibers were identified as type IIA. Enhanced ubiquitination was also observed in degenerating and necrotic fibers. Such fibers additionally displayed elevated m-calpain levels. Conversely, p94, the skeletal muscle-specific calpain, decayed rapidly after stimulation onset and was hardly detectable after 4 days of CLFS.

Expression and enzymatic activity of human disintegrin and metalloproteinase ADAM19/meltrin beta

The adamalysins are involved in proteolysis, adhesion, fusion, and intracellular signaling. Human ADAM19/adamalysin-19 (A disintegrin and metalloproteinase 19) was identified from primary dendritic cell cDNA libraries. It has a signal sequence, a pro-domain with a "cysteine-switch" residue, a metalloproteinase domain with a zinc-binding site, a disintegrin, a cysteine-rich domain, an epidermal-growth-factor-like domain, a transmembrane domain, and a cytoplasmic domain with putative SH3 ligand binding sites. Its mRNA was expressed in the placenta, heart, bladder, lymph nodes, and leukocytes, colorectal adenocarcinoma SW 480, and other organs/cells. The hADAM19 recombinant protein was expressed in human cells. It formed a complex with and cleaved alpha-2 macroglobulin (alpha2-M). Its proteolytic activity was blocked by 1,10-phenanthroline, EDTA, EGTA, and a synthetic matrix metalloproteinase (MMP) inhibitor and not by the tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2. It did not cleave the MMP substrates tested, e.g., type I collagen and gelatin, casein, and four peptide substrates. Thus, hADAM19 is an active metalloproteinase and may have a specific substrate profile.

Characterization of a novel heterodimeric cathepsin L-like protease and cDNA encoding the catalytic subunit of the protease in embryos of Artemia franciscana

Embryos and larvae of the brine shrimp, Artemia franciscana, contain a novel cathepsin L-like cysteine protease (ACP) composed of 28.5- and 31.5-kDa subunits. Both subunits of the ACP are glycosylated, and seven isoforms of the protease were identified by isoelectric focusing with pI values ranging from 4.6 to 6.2. Several clones containing sequences coding for the 28.5-kDa subunit of the ACP were isolated from an Artemia embryo cDNA library in lambda ZAP II. One clone of 1229 bp, with an open reading frame of 1014 bp, was sequenced and found to contain 50-65% amino acid sequence identity with several members of the cathepsin L subfamily of cysteine proteases. The mature protein predicted from this sequence consisted of 217 amino acids with a mass of 23.5 kDa prior to post-translational modifications. The mature protein showed 68.6% amino acid sequence identity with human cathepsin L and 73.9% identity with cathepsin L-like proteases from Sarcophaga. peregrina and Drosophila melanogaster. The full-length cDNA clone analyzed in this study (pCP-3b) was renamed AFCATL1 (A. franciscana Cathepsin L1) and the sequence has been deposited in the Genbank database, accession number AF147207. Northern blot analyses identified a single transcript of about 1.4 kb in both embryos and young larvae of Artemia. Southern blot analyses of Artemia genomic DNA treated with various restriction endonucleases indicated a single gene for the ACP. The catalytic subunit of the ACP was tightly associated with a 31.5-kDa protein, which may localize the protease to nonlysosomal sites in embryos and larvae.Key words: cathepsin L, proteases, embryos, development, Artemia.

A new broad-spectrum protease inhibitor from the entomopathogenic bacterium Photorhabdus luminescens

A new protease inhibitor was purified to apparent homogeneity from a culture medium of Photorhabdus luminescens by ammonium sulfate precipitation and preparative isoelectric focusing followed by affinity chromatography. Ph. luminescens, a bacterium symbiotically associated with the insect-parasitic nematode Heterorhabditis bacteriophora, exists in two morphologically distinguishable phases (primary and secondary). It appears that only the secondary-phase bacterium produces this protease inhibitor. The protease inhibitor has an M:(r) of approximately 12000 as determined by SDS-PAGE. Its activity is stable over a pH range of 3.5-11 and at temperatures below 50 degrees C. The N-terminal 16 amino acids of the protease inhibitor were determined as STGIVTFKND(X)GEDIV and have a very high sequence homology with the N-terminal region of an endogenous inhibitor (IA-1) from the fruiting bodies of an edible mushroom, Pleurotus ostreatus. The purified protease inhibitor inactivated the homologous protease with an almost 1:1 stoichiometry. It also inhibited proteases from a related insect-nematode-symbiotic bacterium, Xenorhabdus nematophila. Interestingly, when present at a molar ratio of 5 to 1, this new protease inhibitor completely inactivated the activity of both trypsin and elastase. The activity of proteinase A and cathepsin G was partially inhibited by this bacterial protease inhibitor, but it had no effect on chymotrypsin, subtilisin, thermolysin and cathepsins B and D. The newly isolated protease inhibitor from the secondary-phase bacteria and its specific inhibition of its own protease provides an explanation as to why previous investigators failed to detect the presence of protease activity in the secondary-phase bacteria. The functional implications of the protease inhibitor are also discussed in relation to the physiology of nematode-symbiotic bacteria.

Stability studies on the cathepsin L proteinase of the helminth parasite, Fasciola hepatica

Fasciola hepatica, the liver fluke, secretes a cathepsin L cysteine proteinase. The enzyme is active over the pH range 5-9 and is remarkably stable at 37 degrees C, pH 7.0, in contrast to mammalian cathepsin Ls that are active in the acidic pH range and are inactivated within 15 min at neutral pH. The liver fluke proteinase is also very tolerant of organic solvents, particularly dimethylformamide. However, it is completely inactivated by 1 mM Hg(2+) and adversely affected by other heavy metals and divalent cations. Addition of glycerol and EDTA enhanced the liver fluke enzyme's stability at 50 degrees C, while glucose and glycerol protected the enzyme from inactivation by repeated freeze-thawing. The high stability of liver fluke cathepsin L suggests that it may have potential for use in bioindustrial applications.

Synthetic inhibitor of matrix metalloproteinases (batimastat) reduces prostate cancer growth in an orthotopic rat model

BACKGROUND

Increased concentrations of metalloproteinases are associated with the invasive and metastatic behavior of several human malignant tumors. Normally, enzymatic activity is tightly regulated by nonspecific mechanisms and specific inhibitors. The aim of the study was to determine the potential of a synthetic metalloproteinase inhibitor, batimastat, to show its in vitro effect on MatLyLu cancer cells and its in vivo effect on tumor growth in orthotopic cancer (R3327 Dunning tumor) in rats.

METHODS

In vitro, a dose response curve of batimastat was generated over 4 days using the MTT assay. Prostate cancer was injected in vivo in male Copenhagen rats by inoculating R3327 Dunning tumor cells (MatLyLu) into the ventral prostatic lobe of 30 rats. Each of 10 rats received batimastat (30 mg/kg body weight) or vehicle administered once a day by i.p. application beginning the day of cell inoculation. Ten rats remained untreated. The effect on local tumor growth was evaluated by measuring tumor weights 20 days after tumor cell inoculation.

RESULTS

Significant inhibition of tumor cell proliferation in vitro occurred at 400 and 4,000 ng/ml batimastat. After orthotopic cell inoculation, tumors grew to mean weights of 18.9 g in the control group without treatment, to 22.3 g in the vehicle group, and to 11.1 g in the treated group. In comparison to the control group and to the vehicle group, tumor weights increased significantly less under treatment with batimastat.

CONCLUSIONS

Batimastat is able to reduce tumor growth in the standard prostate cancer model. Using this model, activity against cancer progression of future inhibitory agents can be reliably assessed.

Purification of recombinant flavanone 3beta-hydroxylase from petunia hybrida and assignment of the primary site of proteolytic degradation

Flavanone 3beta-hydroxylase catalyzes the Fe(II)/oxoglutarate-dependent hydroxylation of (2S)-flavanones to (2R,3R)-dihydroflavonols in the course of flavonol/anthocyanin or catechin biosynthesis. The enzyme from Petunia hybrida consists of a 41,655-Da polypeptide that is prone to rapid proteolysis in crude plant extracts as well as on expression in Escherichia coli, and commercial protease inhibitors were inefficient in stopping the degradation. To pinpoint the primary site of proteolysis and to improve the activity yields, two revised schemes of purification were developed for the recombinant polypeptides. Applying a four-step protocol based on extraction and ion-exchange chromatography at pH 7.5, the primary, catalytically inactive proteolytic enzyme fragment (1.1 mg) was isolated and shown to cross-react on Western blotting as one homogeneous band of about 38 kDa. Mass spectrometric analysis assigned a mass of 37,820 +/- 100 Da to this fragment, and partial sequencing revealed an unblocked amino terminus identical to that of the native 3beta-hydroxylase. Thus, the native enzyme had been degraded by proteolysis of a small carboxy-terminal portion, and the primary site of cleavage must be assigned most likely to the Glu 337-Leu 338 bond, accounting for a loss of about 3800 Da. Alternatively, the enzyme degradation was greatly reduced when the extraction of recombinant bacteria was carried out with phosphate buffer at pH 5.5 followed by size exlusion and anion-exchange chromatography. This rapid, two-step purification resulted in a homogeneous 3beta-hydroxylase of high specific acitivity (about 32 mkat/kg) at roughly 5% yield, and the procedure is a major breakthrough in mechanistic investigations of this class of labile dioxygenases.

Lysosomal cysteine proteases: more than scavengers

Lysosomal cysteine proteases were believed to be mainly involved in intracellular protein degradation. Under special conditions they have been found outside lysosomes resulting in pathological conditions. With the discovery of a series of new cathepsins with restricted tissue distributions, it has become evident that these enzymes must be involved in a range of specific cellular tasks much broader than as simple housekeeping enzymes. It is therefore timely to review and discuss the various physiological roles of mammalian lysosomal papain-like cysteine proteases as well as their mechanisms of action and the regulation of their activity.

Primary structure and properties of the cathepsin G/chymotrypsin inhibitor from the larval hemolymph of Apis mellifera

A member of the Ascaris inhibitor family exhibiting anti-cathepsin G and anti-chymotrypsin activity was purified from the larval hemolymph of the honey bee (Apis mellifera). Three forms of the inhibitor, designated AMCI 1-3, were isolated using gel filtration and anion-exchange chromatographies followed by reverse-phase HPLC. The amino-acid analyses indicated that AMCI-1 and AMCI-2 have an identical composition whereas AMCI-3 is shorter by two residues (Thr, Arg). All three forms contain as many as 10 cysteine residues and lack tryptophan, tyrosine, and histidine. The sequence of the isoinhibitors showed that the major form (AMCI-1) consisting of 56 amino-acid residues was a single-chain protein of molecular mass 5972 Da, whereas the other two forms were two-chain proteins with a very high residue identity. The AMCI-2 appeared to be derived from AMCI-1, as a result of the Lys24-Thr25 peptide bond splitting, while AMCI-3 was truncated at its N-terminus by the dipeptide Thr25-Arg26. The association constants for the binding of bovine alpha-chymotrypsin to all purified forms of the inhibitor were high and nearly identical, ranging from 4.8 x 10(10) M-1 for AMCI-1 to 2.7 x 10(9) M-1 for AMCI-3. The sensitivity of cathepsin G to inhibition by each inhibitor was different. Only the association constant for the interaction of this enzyme with AMCI-1 was high (2 x 10(8) M-1) whereas those for AMCI-2 and AMCI-3 were significantly lower, and appeared to be 3.7 x 10(7) M-1 and 4.5 x 10(6) M-1, respectively. The reactive site of the inhibitor, as identified by cathepsin G degradation and chemical modification, was found to be at Met30-Gln31. A search in the Protein Sequence Swiss-Prot databank revealed a significant degree of identity (44%) between the primary structure of AMCI and the trypsin isoinhibitor from Ascaris sp (ATI). On the basis of the cysteine residues alignment, the position of the reactive site as well as some sequence homology, the cathepsin G/chymotrypsin inhibitor from larval hemolymph of the honey bee may be considered to be a member of the Ascaris inhibitor family.

Cathepsin S and cruzipain are inhibited by equistatin from Actinia equina

Cathepsin S has been isolated for the first time from human tissue. It has a molecular mass of 24 kDa and an isoelectric point in the range of 8.2 to 8.6. The enzyme is inhibited by equistatin, which belongs to the thyropins, a new family of protein inhibitors, with an inhibition constant of Ki = 0.40 +/- 0.07 nM. Cruzipain, a cathepsin L-like enzyme sharing a 130 amino acid long C-terminal extension, is also strongly inhibited by equistatin (Ki = 0.028 +/- 0.006 nM). Together with previously reported data, these results further indicate that a functional heterogeneity exists among thyropin inhibitors, as demonstrated by their interaction with cathepsin S and cruzipain.

Bikunin present in human peritoneal fluid is in part derived from the interaction of serum with peritoneal mesothelial cells

We recently reported that peritoneal fluid mainly contains two proteoglycans; one is the interstitial proteoglycan referred to as decorin, and the other an uncharacterized small chondroitin sulfate proteoglycan. In the present study, we have used a two-step process to isolate the small chondroitin sulfate proteoglycan free of decorin. The purified molecule ran as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with apparent molecular mass 50 kd made up of a chondroitin-4-sulfate glycosaminoglycan chain and a 30-kd core protein. NH2-terminal analysis of the core protein showed significant sequence homology with bikunin, a component of the human inter-alpha-trypsin inhibitor (IalphaI) family. A Western blot analysis using anti-human inter-alpha-trypsin inhibitor confirmed the identity of the small chondroitin sulfate proteoglycan as bikunin, and a trypsin inhibitor counterstain assay confirmed its anti-trypsin activity. Examination of serum from patients receiving continuous peritoneal dialysis suggests that free bikunin in peritoneal fluid may be the result of leakage of serum proteins into the peritoneum. Our findings further show that the interaction of serum with peritoneal mesothelial cells offers a new and novel explanation for the presence of bikunin in peritoneal fluid.

Non-homology knowledge-based prediction of the papain prosegment folding pattern: a description of plausible folding and activation mechanisms

BACKGROUND

A detailed knowledge of three-dimensional conformations is necessary in order to understand the close relationship between protein structure and function. Among current methodologies, homology modeling is an important tool for obtaining reliable geometries and it provides a direct alternative to X-ray or NMR techniques. In contrast, predictive methods with no three-dimensional template (non-homology) still require further validation and systematization.

RESULTS

Here, we present a non-homology knowledge-based strategy for the structural prediction of the proregion of a cysteine proteinase zymogen. This method analyzes individual sequences and multiple alignments of homologous sequences, making use of different published algorithms and incorporating all available structure-related information to obtain improved predictions. Our strategy yielded acceptable secondary structure and general three-dimensional assignments when compared with crystallographic data from homologous proteins.

CONCLUSIONS

We discuss our successes and failures as a contribution to non-homology prediction development. In addition, based on the information analyzed and generated in this work, we propose plausible folding and activation mechanisms for thiol-proteinase precursors that attempt to shed light on the molecular basis of prosegment functions.

Detection and characterization, using fluoresceincadaverine, of amine acceptor protein substrates accessible to active transglutaminase expressed by rabbit articular chondrocytes

The purpose of this study was to investigate the implication of transglutaminases in the biology of articular chondrocytes. Transglutaminase activity measurements performed on cell lysates showed that a transglutaminase was present in chondrocytes in primary culture and that it was strongly activated by limited proteolysis. In chondrocytes dedifferentiated by subculture or retinoic acid treatment, this transglutaminase appeared to be downregulated, while type II transglutaminase expression was induced. However, protein levels, mRNA steady-state levels or transglutaminase activity in whole-cell lysates do not necessarily reflect the activity present in living cells, as it is strongly regulated. Therefore, Fluoresceincadaverine, a fluorescent polyamine, was used for detecting amine acceptor protein substrates accessible to active transglutaminase in living cells. After incubation of chondrocytes with Fluoresceincadaverine, dedifferentiated cells exhibited an extracellular labelling, while chondrocytes in primary culture did not, unless thrombin was added to the culture medium. In contrast, Fluoresceincadaverine labelling was not detected in the cytosol, although the transglutaminases were also partly cytosolic. By confocal microscopy and Western blot analysis of labelled cells in culture, fibronectin was shown to be the main substrate for both transglutaminases. The transglutaminases present in articular chondrocytes may, therefore, contribute to the organization and the stabilization of their extracellular matrix.

Characterization of recombinant and brain neuropsin, a plasticity-related serine protease

Activity-dependent changes in neuropsin gene expression in the hippocampus implies an involvement of neuropsin in neural plasticity. Since the deduced amino acid sequence of the gene contained the complete triplet (His-Asp-Ser) of the serine protease domain, the protein was postulated to have proteolytic activity. Recombinant full-length neuropsin produced in the baculovirus/insect cell system was enzymatically inactive but was readily converted to active enzyme by endoprotease processing. The activational processing of prototype neuropsin involved the specific cleavage of the Lys32-Ile33 bond near its N terminus. Native neuropsin that was purified with a purity of 1,100-fold from mouse brain had enzymatic characteristics identical to those of active-type recombinant neuropsin. Both brain and recombinant neuropsin had amidolytic activities cleaving Arg-X and Lys-X bonds in the synthetic chromogenic substrates, and the highest specific activity was found against Boc-Val-Pro-Arg-4-methylcoumaryl-7-amide. The active-type recombinant neuropsin effectively cleaved fibronectin, an extracellular matrix protein. Taken together, these results indicate that this protease, which is enzymatically novel, has significant limbic effects by changing the extracellular matrix environment.

Activation of extracellular matrix metalloproteinases in equine laminitis

Samples of connective tissue obtained from the hoof of six laminitic and eight non-laminitic adult horses were analysed zymographically to investigate whether connective tissue matrix metalloproteinases are activated or induced during laminitis. The activity or matrix metalloproteinases was substantially greater in the tissues from the laminitic horses than in the tissues from the non-laminitic horses. A comparison of the collagenolytic activity in the laminitic and control tissues showed that collagenolytic activities corresponding to the 92 kDa (P < 0.001), 72 kDa (P < 0.01) and 66 kDa (P < 0.01) bands were induced in the laminitic tissues.

Effects of simulated solar radiation on type I and type III collagens, collagenase (MMP-1) and stromelysin (MMP-3) gene expression in human dermal fibroblasts cultured in collagen gels

Understanding the mechanisms responsible for photodamage to the skin is most important for dermatology. 3-D cultures have been used as tools to mimic the in vivo situation for several years. We irradiated such a system containing human dermal fibroblasts cultured in collagen gels, a well-known model considered to be a dermal equivalent, which reproduces the interaction between cells and the surrounding extracellular matrix. The effects of solar irradiation (315-800 nm) on the steady-state levels of the mRNAs of extracellular matrix components (type I and III collagens) and their degrading enzymes (interstitial collagenase, MMP-1 and stromelysin 1, MMP-3) were measured. Exposure to low levels of solar radiation (0-10 J cm-2 in the UVA, i.e. suberythemal UVA doses) caused a transient decrease in type I procollagen mRNA, an increase in MMP-mRNA, and no change in type III procollagen mRNA steady-state levels. These results describe the early changes in the connective tissue of the skin following exposure to low-level solar stimulation, and may help explain the long-term changes in photodamaged skin.

Expression of matrix metalloproteinases and their inhibitors in aneurysms and normal aorta

BACKGROUND

Abdominal aortic aneurysms (AAAs) are characterized by degradation of collagen and elastin resulting from increases in matrix metalloproteinase (MMP) activity. Previous authors have identified isolated increases in expression of specific MMPs in AAAs, but none have compared relative levels of expression of particular MMPs to one another or to those of their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). This study proposes to quantify relative mRNA levels for interstitial collagenase (MMP-1), 72 kd type IV collagenase (MMP-2), 92 kd type IV collagenase (MMP-9), TIMP-1, and TIMP-2 in normal aorta (NA) and AAA to provide insight as to the relative importance of each in aneurysm formation.

METHODS

Competitive polymerase chain reactions (PCRs) with gene-specific external standards and cDNA derived from AAAs (n = 8; mean age, 67.4 years) and NA (n = 5; mean age, 40.6 years) were used to quantify mRNA levels. Results were normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels, determined by means of competitive PCR, and compared by means of Mann-Whitney statistics.

RESULTS

Significant increases in MMP mRNA expression in AAA over NA were observed for MMP-1 (3.64 versus 0.3, p = 0.007), MMP-9 (78.03 versus 3.35, p = 0.003), TIMP-1 (835.32 versus 477.2, p = 0.027), and TIMP-2 (18.09 versus 4.14, p = 0.003). The ratio of MMP to TIMP mRNA levels was higher in AAA than NA (0.135 versus 0.045, p = 0.018).

CONCLUSIONS

Increases in expression of MMP-1, MMP-9, and MMP/TIMP ratios may result in increased proteolysis and matrix degradation, which characterize AAAs. MMP-9 appears to be the predominant metalloproteinase expressed in AAA, because its mRNA levels were more than 20 times and 2 times higher than those of MMP-1 and MMP-2, respectively. TIMP-1 mRNA levels were in molar excess to those of any of the metalloproteinases studied.

Analytical aspects regarding the measurement of metalloproteinases and their inhibitors in blood

OBJECTIVE

Both in vitro and in vivo investigations have shown that the balance between matrix metalloproteinases (MMP) and the tissue inhibitors of metalloproteinases (TIMP) seems to be important in physiological and pathological processes which involve tissue remodeling and repair.

DESIGN AND METHODS

In order to investigate the analytical reliability of new commercial ELISA tests. BIOTRAK test kits (Amersham Int.) were used for the determination of metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), and the MMP-1/TIMP-1 complex in blood.

RESULTS

The detection limits and the precision data were in the usual ranges of ELISA tests so that concentrations found in blood could be determined reliably. Since all three analytes were lower in heparin plasma than in serum or EDTA plasma, heparin plasma was selected as the specimen of choice. Measurement of diluted samples gave higher values than those of undiluted native plasma samples because the inhibitory effects of specific/unspecific inhibitors or other matrix components were apparently reduced. To obtain comparable data from different laboratories, the predilution of samples must be defined. We recommend to use diluted plasma samples of 1:5, 1:21, and 1:11 for the determination of MMP-1, TIMP-1, and the complex MMP-1/TIMP1, respectively. The preliminary upper 95% reference limits measured under these conditions in healthy subjects (40 females: 40 males) were 14.4 micrograms/L for MMP-1 in females, 20 micrograms/L for MMP-1 in males. 1668 micrograms/L for TIMP-1 and 116 micrograms/L for the complex MMP-1/TIMP-1.

CONCLUSION

The study has shown that the BIOTRAK test combinations for MMP-1, TIMP-1, and MMP-1/TIMP-1 complex allow a reliable measurement of the analyte concentrations in heparin plasma. In order to avoid preanalytical misinterpretations only heparin plasma samples in defined dilutions should be used.

Changes in rat corneal matrix metalloproteinases and serine proteinases under vitamin A deficiency

PURPOSE

Vitamin A deficiency alters the transparency of the cornea due to epithelial cell keratinization and increases the susceptibility of the cornea to ulceration. The purpose of this study was to determine the effect of vitamin A deficiency on rat corneal matrix metalloproteinases and serine proteinases.

METHODS

Four dietary groups of male WAG/RijMCW rats were prepared: (1) Vitamin A deficient rats were raised on a casein-based retinoid deficient diet; (2) Retinol repleted rats were raised on the retinoid deficient diet. On the eighty-sixth day on this diet, the rats were fed retinyl palmitate and then given free access to the retinyl palmitate-supplemented control diet; (3) The weight-matched, pair-fed rats were restricted in their intake of the retinyl palmitate-supplemented diet so that their weight gain matched that of the A-rats; (4) The non-restricted rats were given free access to the retinyl palmitate-supplemented diet. The animals were killed at the late plateau stage for weight of the deficiency (102-106 days). Zymography was used to study proteinases in the corneal extracts.

RESULTS

Vitamin A deficient and control rat corneas contain multiple matrix metalloproteinases and serine proteinases. The matrix metalloproteinases at 90/92 kDa (gelatinase B) and 66/63/57 kDa (gelatinase A) were significantly decreased in the corneas of the vitamin A deficient rats relative to the control corneas. Corneas from the four groups of rats contained 76, 45, 38, 28 and 22 kDa proteinases that cleaved casein. Only the vitamin A deficient corneas contained a 50 kDa casein cleaving enzyme. The 76, 45, 38 and 28 kDa serine proteinases were significantly lower in the vitamin A deficient corneas. The major 22 kDa enzyme was not altered by the deficiency. All casein cleaving proteinases were inhibited by phenylmethylsulfonyl fluoride and chymostatin except for a minor 76 kDa band. The activity of this band was not altered by inhibitors for the other classes of proteinases, ethylenediaminetetraacetic acid, E-64 or pepstatin. The concentrations of the 61, 52 and 40 kDa plasminogen activators were not altered by the deficiency.

CONCLUSIONS

Alterations in corneal proteinases under vitamin A deficiency conditions may be involved in the characteristic changes observed in the cornea under vitamin A deficiency conditions: decreased exfoliation of epithelial cells, increased levels of keratofibrils in the corneal keratocytes, increased stromal keratocyte degradation and increased susceptibility towards ulceration.

Thiocalsin: a thioredoxin-linked, substrate-specific protease dependent on calcium

We describe a protease, named "thiocalsin," that is activated by calcium but only after reductive activation by thioredoxin, a small protein with a redox-active disulfide group that functions widely in regulation. Thiocalsin appeared to be a 14-kDa serine protease that functions independently of calmodulin. The enzyme, purified from germinating wheat grain, specifically cleaved the major indigenous storage proteins, gliadins and glutenins, after they too had been reduced, preferentially by thioredoxin. The disulfide groups of the enzyme, as well as its protein substrates, were reduced by thioredoxin via NADPH and the associated enzyme, NADP-thioredoxin reductase. The results broaden the roles of thioredoxin and calcium and suggest a joint function in activating thiocalsin, thereby providing amino acids for germination and seedling development.