Antibiofilm activity of polyethylene glycol-quercetin nanoparticles-loaded gelatin-N,O-carboxymethyl chitosan composite nanogels against Staphylococcus epidermidis

BACKGROUND

Biofilms, such as those from Staphylococcus epidermidis, are generally insensitive to traditional antimicrobial agents, making it difficult to inhibit their formation. Although quercetin has excellent antibiofilm effects, its clinical applications are limited by the lack of sustained and targeted release at the site of S. epidermidis infection.

OBJECTIVES

Polyethylene glycol-quercetin nanoparticles (PQ-NPs)-loaded gelatin-N,O-carboxymethyl chitosan (N,O-CMCS) composite nanogels were prepared and assessed for the on-demand release potential for reducing S. epidermidis biofilm formation.

METHODS

The formation mechanism, physicochemical characterization, and antibiofilm activity of PQ-nanogels against S. epidermidis were studied.

RESULTS

Physicochemical characterization confirmed that PQ-nanogels had been prepared by the electrostatic interactions between gelatin and N,O-CMCS with sodium tripolyphosphate. The PQ-nanogels exhibited obvious pH and gelatinase-responsive to achieve on-demand release in the micro-environment (pH 5.5 and gelatinase) of S. epidermidis. In addition, PQ-nanogels had excellent antibiofilm activity, and the potential antibiofilm mechanism may enhance its antibiofilm activity by reducing its relative biofilm formation, surface hydrophobicity, exopolysaccharides production, and eDNA production.

CONCLUSIONS

This study will guide the development of the dual responsiveness (pH and gelatinase) of nanogels to achieve on-demand release for reducing S. epidermidis biofilm formation.

Non-thermal plasma causes Pseudomonas aeruginosa biofilm release to planktonic form and inhibits production of Las-B elastase, protease and pyocyanin

The increasing risk of antibiotic failure in the treatment of Pseudomonas aeruginosa infections is largely related to the production of a wide range of virulence factors. The use of non-thermal plasma (NTP) is a promising alternative to antimicrobial treatment. Nevertheless, there is still a lack of knowledge about the effects of NTP on the virulence factors production. We evaluated the ability of four NTP-affected P. aeruginosa strains to re-form biofilm and produce Las-B elastase, proteases, lipases, haemolysins, gelatinase or pyocyanin. Highly strains-dependent inhibitory activity of NTP against extracellular virulence factors production was observed. Las-B elastase activity was reduced up to 82% after 15-min NTP treatment, protease activity and pyocyanin production by biofilm cells was completely inhibited after 60 min, in contrast to lipases and gelatinase production, which remained unchanged. However, for all strains tested, a notable reduction in biofilm re-development ability was depicted using spinning disc confocal microscopy. In addition, NTP exposure of mature biofilms caused disruption of biofilm cells and their dispersion into the environment, as shown by transmission electron microscopy. This appears to be a key step that could help overcome the high resistance of P. aeruginosa and its eventual elimination, for example in combination with antibiotics still highly effective against planktonic cells.

Fibroblast activation protein-alpha and dipeptidyl peptidase IV (CD26): cell-surface proteases that activate cell signaling and are potential targets for cancer therapy

Fibroblast activation protein-alpha (FAP-alpha) and dipeptidyl peptidase IV (DPPIV) are serine proteases with post-prolyl peptidase activities that can modify tumor cell behavior. FAP-alpha and DPPIV can form heteromeric complexes with each other and may function coordinately to modulate the growth, differentiation, adhesion, and metastasis of tumor cells. This review is focused on FAP-alpha and summarizes a series of studies showing that elevated expression of FAP-alpha results in profound changes in growth and malignant behavior of tumor cells. Depending on the model system investigated, FAP-alpha expression causes dramatic promotion or suppression of tumor growth. In the case of tumor promotion, FAP-alpha expression can drive tumor growth by increasing angiogenesis and by decreasing the anti-tumor response of the immune system. In the case of tumor suppression, FAP-alpha can decrease tumorigenicity of mouse melanoma cells and restore contact inhibition and growth factor dependence even when it is catalytically inactive, implying that protein-protein interactions mediate these effects. Understanding how FAP-alpha activates cell signaling is critical to determining how FAP-alpha mediates growth promotion versus growth suppression in the different model systems and ultimately in human cancer patients. In particular, the roles of FAP-alpha protease activity and FAP-alpha complex formation with DPPIV and other surface molecules in activating cell signaling need to be elucidated since these represent potential targets for therapeutic intervention.

Reduction of experimental laser-induced choroidal neovascularization by orally administered BPHA, a selective metalloproteinase inhibitor

BACKGROUND

N-Biphenyl sulfonyl-phenylalanine hydroxamic acid (BPHA), a synthetic, selective matrix metalloproteinase (MMP)-2, -9, -14 inhibitor, has been reported to show significant antiangiogenic activity without unpleasant adverse effects. After film in situ zymography (FIZ) and conventional zymography were performed to detect MMP in experimental choroidal neovascularizations (CNVs), we studied the reducible effect of BPHA on CNVs.

METHODS

Using FIZ, the gelatinolytic activity of MMPand BPHA-reduction on gelatinolysis were examined in diode-laser-induced CNV lesions in a total of 22 male Brown Norway rats. The MMP subtypes were studied in the CNV lesions of three rats using conventional zymography. Vehicle solution only or 25-, 50-, or 100 mg/kg-body-weight of BPHA was administered orally twice daily for 14 days after the laser photocoagulation in 18 rats, respectively. Fluorescein angiograms were taken, and the late hyperfluorescence of CNVs was given scores by three researchers using four grades. The thickness of CNV lesions was studied histologically.

RESULTS

In laser-induced CNVs, the gelatinolytic activity of MMP and reduction of gelatinolysis by BPHA were observed on FIZ, and MMP-2 and proMMP-2 were identified by conventional zymography. The scores given to the late dye leakage and staining on angiograms were lower in the BPHA-treated groups ( p<0.01) than in the controls, and the effect appeared to be dose-dependent. Similarly, the CNV lesions in the BPHA-treated groups were less thick than in the controls ( p<0.01).

CONCLUSIONS

MMP-2 played a role in laser-induced CNV development, and administration of BPHA reduced the experimental CNVs.

Membrane type 1 matrix metalloproteinase and gelatinase A synergistically degrade type 1 collagen in a cell model

A fibrosarcoma cell line transfected with the matrix metalloproteinase MT1 MMP showed an enhanced ability to degrade 14C-labelled collagen films. As previously shown for proMMP 2 activation, TIMP 1 was an ineffective inhibitor of the process of collagenolysis whereas TIMP 2 was efficient and completely prevented collagen degradation. In the presence of the calcium ionophore, ionomycin, proteolytic processing of MT1 MMP was restricted and collagenolysis did not occur indicating that the 63 kDa form of the enzyme is not a functional collagenase. The collagenolytic activity of MT1 MMP was shown to be enhanced by the addition of proMMP 2, but TIMP 1 inhibition remained poor relative to that of TIMP 2. The study demonstrated that synergy between two non-conventional collagenases effectively degrades insoluble pericellular collagen. Due to the membrane localisation of MT1 MMP, this could potentially occur in a highly localised manner.

Role of matrix metalloproteinases and their tissue inhibitors in the regulation of coronary cell migration

The migration of vascular cells is regulated by matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs). Because the activation of adventitial fibroblasts has been implicated in coronary repair, we have examined regional differences in cell outgrowth and the synthesis of MMPs/TIMPs in different layers of porcine coronary arteries. Coronary medial explants demonstrated significantly slower cell outgrowth than coronary adventitia in culture (P<0.001). These observations were paralleled by the predominant expression of TIMP-1 and -2 in the media (14-fold and 37-fold higher than in adventitia, respectively, P<0.001), whereas higher gelatinolytic activities (MMP-2 and -9) were released from adventitial explants. Smooth muscle cell outgrowth from the media was regulated by endogenous TIMPs, since TIMP inhibition (recombinant MMP-2 or neutralizing anti-TIMP antibodies) facilitated cell outgrowth (P<0.001). In contrast, the addition of recombinant TIMP-1 or -2 decreased adventitial cell outgrowth. In the coculture experiments, the presence of coronary media retarded adventitial cell outgrowth, whereas medial damage abrogated these effects, allowing for fibroblast migration (P<0.001). In conclusion, this study demonstrated differential migratory properties and distinct MMP/TIMP synthesis by coronary fibroblasts and smooth muscle cells. Endogenous TIMPs in the media may play an important role in maintaining coronary arterial wall homeostasis, whereas high levels of matrix-degrading activities confer the "invasive" characteristics of adventitial fibroblasts.

Expression of matrix metalloprotease-2-cleaved laminin-5 in breast remodeling stimulated by sex steroids

The extracellular matrix plays an important role in breast remodeling. We have shown that matrix metalloprotease-2 (MMP2) cleaves laminin-5 (Ln-5), a basement membrane component, generating a fragment called gamma2x. Human breast epithelial cells, while constitutively immobile on intact Ln-5, acquire a motile phenotype on MMP2-cleaved Ln-5. We hypothesize that this mechanism may underlie cell mobilization across the basement membrane during branching morphogenesis in breast development regulated by sex steroids. We report that the expression of MMP2 and cleavage of Ln-5 correlate well with tissue remodeling and epithelial rearrangement of the breast both in vivo and in vitro. Thus, the Ln-5 gamma2x fragment was detected by immunoblotting in sexually mature, pregnant, and postweaning, but not in prepubertal or lactating mammary glands. Furthermore, cleaved Ln-5, as well as MMP2, became detectable in remodeling glands from sexually immature rats treated with sex steroids. In rat mammary gland explants, epithelial reorganization and luminal cell morphological changes were induced by the addition of exogenous MMP2, in parallel to the appearance of cleaved Ln-5. Similar effects were observed in epithelial monolayers plated on human Ln-5 and exposed to MMP2. These results suggest that cleavage of Ln-5 by MMP2 might be regulated by sex steroids and that it may contribute to breast remodeling under physiological and possibly pathological conditions.

Matrix metalloproteinases generate angiostatin: effects on neovascularization

Angiostatin, a cleavage product of plasminogen, has been shown to inhibit endothelial cell proliferation and metastatic tumor cell growth. Recently, the production of angiostatin has been correlated with tumor-associated macrophage production of elastolytic metalloproteinases in a murine model of Lewis lung cell carcinoma. In this report we demonstrate that purified murine and human matrix metalloproteinases generate biologically functional angiostatin from plasminogen. Macrophage elastase (MMP-12 or MME) proved to be the most efficient angiostatin-producing MMP. MME was followed by gelatinases and then the stomelysins in catalytic efficiency; interstitial collagenases had little capacity to generate angiostatin. Both recombinant angiostatin and angiostatin generated from recombinant MME-treated plasminogen inhibited human microvascular endothelial cell proliferation and differentiation in vitro. Finally, employing macrophages isolated from MME-deficient mice and their wild-type littermates, we demonstrate that MME is required for the generation of angiostatin that inhibits the proliferation of human microvascular endothelial cells.

Proteoglycan turnover in the sclera of normal and experimentally myopic chick eyes

PURPOSE

The turnover of chick scleral proteoglycans from control and form-vision deprived (myopic) eyes was compared in vivo and in explant cultures to determine whether proteoglycan degradation is altered during the development of myopia and to characterize the mechanism of proteoglycan turnover in the sclera.

METHODS

Seven-day-old chicks were radiolabeled via an intraperitoneal injection of 35SO4, and monocular form deprivation was induced 48 hours later. After 1, 2, and 3 weeks of form deprivation, birds were killed, and the amount of 35SO4-proteoglycans remaining in different scleral regions was measured in control and deprived eyes. Posterior sclera were also radiolabeled in organ culture containing 35SO4, and radiolabeled scleral proteoglycans were chased into unlabeled medium for 0 to 11 days. 35SO4-labeled proteoglycans within the scleral matrix and those released into the medium were characterized by Sepharose CL-2B chromatography and western blot analysis.

RESULTS

The biological half-life of scleral proteoglycans was significantly shorter within the posterior pole of form-deprived eyes (t1/2 = 7.212 days) compared with the same region of control eyes (t1/2 = 9.619 days; P < 0.001), whereas no differences in turnover rates were seen in the anterior sclera or equatorial sclera. When posterior scleral punches were placed in organ culture, 35SO4-labeled proteoglycan turnover rates were similar for control and form-deprived eyes. Chromatographic and western blot analyses indicated that approximately 80% of the total 35SO4 within the posterior sclera is incorporated into the aggrecan. Western blot analyses of aggrecan core protein released into the medium by control and form-deprived scleral punches indicated that the core protein was degraded into a series of smaller fragments of Mr = 102 to 220 kDa. A specific antiserum (anti-FVDIPEN) detected the presence of a 50-kDa C-terminal aggrecan fragment released into the medium, which was generated by the action of the matrix metalloproteinase gelatinase A and/or stromelysin.

CONCLUSIONS

The turnover rate of 35SO4-labeled scleral proteoglycans is vision dependent and is accelerated in the posterior sclera of chick eyes during the development of experimental myopia. The loss of proteoglycans from the scleral matrix involves proteolytic cleavage at various sites along the aggrecan core protein through the action, at least in part, of gelatinase A and/or stromelysin.

Remodeling of collagen matrix by human tumor cells requires activation and cell surface association of matrix metalloproteinase-2

We assessed the functional significance of tumor cell-associated matrix metalloproteinase (MMP)-2 in extracellular matrix remodeling compared with that of the soluble enzyme by evaluating the contraction of three-dimensional collagen lattices by human glioma U251.3 and fibrosarcoma HT-1080 cell lines. In this model, the constitutive synthesis and activation of the MMP-2 proenzyme were modulated by stable transfections of tumor cells with cDNA encoding membrane type 1-MMP (MT1-MMP). The efficiency of transfected cells in contracting collagen lattices was shown to be dependent on the MT1-MMP-mediated activation of MMP-2 accompanied by cell surface association of activated MMP-2, on the cell-matrix interactions controlled by collagen-specific integrins, and on the integrity of actin and microtubule cytoskeletons. Each one of these mechanisms was essential but was not sufficient by itself in accomplishing gel contraction by MT1-MMP-transfected cells. Both MMP-2 activation and gel contraction by transfected glioma cells were inhibited by tissue inhibitor of metalloproteinase (TIMP)-2 and the recombinant COOH-terminal domain of MMP-2. However, the kinetics and mechanisms of their inhibitory effects were different, because TIMP-2 and the COOH-terminal domain of MMP-2 preferentially inhibited the MT1-MMP-dependent and autocatalytic steps of MMP-2 activation, respectively. By contrast, TIMP-1, an efficient inhibitor of soluble MMP-2 activity, failed to affect gel contraction. In addition, soluble MMP-2 activated by either organomercurials or cells was not able to induce the contraction of collagen lattices when added to transfected cells. Therefore, soluble activated MMP-2, sensitive to TIMP-1 inhibition, does not mediate collagen gel contraction by tumor cells, whereas the activity of cell surface-associated MMP-2 plays a critical role in remodeling of the extracellular matrix in vitro. These mechanisms of functional and spatial regulation of MMP-2 may also be applicable to different aspects of tissue reorganization in vivo, including cell migration and invasion, angiogenesis, and wound healing.

Neuronal matrix metalloproteinase-2 degrades and inactivates a neurite-inhibiting chondroitin sulfate proteoglycan

Chondroitin sulfate proteoglycans (CSPGs) are implicated in the regulation of axonal growth. We previously reported that the neurite-promoting activity of laminin is inhibited by association with a Schwann cell-derived CSPG and that endoneurial laminin may be inhibited by this CSPG as well [Zuo J, Hernandez YJ, Muir D (1998) Chondroitin sulfate proteoglycan with neurite-inhibiting activity is upregulated after peripheral nerve injury. J Neurobiol 34:41-54]. Mechanisms regulating axonal growth were studied by using an in vitro bioassay in which regenerating embryonic dorsal root ganglionic neurons (DRGn) were grown on sections of normal adult nerve. DRGn achieved slow neuritic growth on sections of normal nerve, which was reduced significantly by treatment with metalloproteinase inhibitors. Similar results were obtained on a synthetic substratum composed of laminin and inhibitory CSPG. DRGn expressed the matrix metalloproteinase, MMP-2, which was transported to the growth cone. Recombinant MMP-2 inactivated the neurite-inhibiting CSPG without hindering the neurite-promoting potential of laminin. Similarly, neuritic growth by DRGn cultured on normal nerve sections was increased markedly by first treating the nerve sections with MMP-2. The proteolytic deinhibition by MMP-2 was equivalent to and nonadditive with that achieved by chondroitinase, suggesting that both enzymes inactivated inhibitory CSPG. Additionally, the increases in neuritic growth resulting from treating nerve sections with MMP-2 or chondroitinase were blocked by anti-laminin antibodies. From these results we conclude that MMP-2 provides a mechanism for the deinhibition of laminin in the endoneurial basal lamina and may play an important role in the regeneration of peripheral nerve.

Disruption of angiogenesis by PEX, a noncatalytic metalloproteinase fragment with integrin binding activity

Angiogenesis depends on both cell adhesion and proteolytic mechanisms. In fact, matrix metalloproteinase 2 (MMP-2) and integrin alphavbeta3 are functionally associated on the surface of angiogenic blood vessels. A fragment of MMP-2, which comprises the C-terminal hemopexin-like domain, termed PEX, prevents this enzyme binding to alphavbeta3 and blocks cell surface collagenolytic activity. PEX blocks MMP-2 activity on the chick chorioallantoic membrane where it disrupts angiogenesis and tumor growth. Importantly, a naturally occurring form of PEX can be detected in vivo in conjunction with alphavbeta3 expression in tumors and during developmental retinal neovascularization. Levels of PEX in these vascularized tissues suggest that it interacts with endothelial cell alphavbeta3 where it serves as a natural inhibitor of MMP-2 activity, thereby regulating the invasive behavior of new blood vessels.

Metastatic ability of MXT mouse mammary subpopulations correlates with clonal expression and/or membrane-association of gelatinase A

We have developed a novel murine mammary tumor system with variants representing different stages of tumor progression. The MXT-s parental cell line was established from a urethane-induced and hormone-sensitive mammary tumor. MXT-s parental cells are highly tumorigenic but poorly metastatic. MXT clones and variants were selected by either in vitro or in vivo procedures, and they differ in metastatic ability and 17 beta-estradiol dependency for tumor growth. The MXT-c1.1 and MXT-B2 cell lines produced lung metastasis after intravenous injection into 100% of syngenic mice, but only MXT-c1.1 cells were highly metastatic from intramammary tumors. The fingerprints obtained by arbitrarily primed-polymerase chain reaction demonstrated that the metastatic variants and clones had a common genetic background and resulted from clonal selection from the parental cell line. We studied whether the matrix metalloproteinase (MMP) profile is correlated with tumor progression and metastatic ability in the MXT tumor system. Gelatinases A and B were assayed in the cells, both by enzyme activity and mRNA expression. Gelatinase A was expressed in MXT-c1.1 cells, whereas MXT-B2 cells did not express either MMP. In contrast, the mammary fat pad tumors expressed both gelatinases. Membrane Type 1-MMP transcripts were also detected in MXT cells and tumors. Because the mRNA levels of gelatinase. A were low in MXT-B2 tumors, we suggested that exogenous gelatinase A bound the cell membranes of MXT-B2 cells in vivo. Indirect evidence was obtained in vitro by treatment of MXT-B2 cells with NIH/3T3 fibroblast-conditioned medium. After this treatment, we detected a gelatinolytic activity at M(r) 68,000 in the cell-membrane extract of MXT-B2 cells and an increase in migratory ability through type IV collagen matrices. On the other hand, Ha-ras gene dosage correlated positively with metastatic ability but not with either gelatinase A or gelatinase B expression. No significant differences were observed in the expression of stromelysin-1 and tissue inhibitors of MMP. Thus, in the MXT tumor system, the expression of gelatinase A or its cell association and Ha-ras gene dosage independently contribute to the metastatic phenotype.

Degradation of T-kininogen by cathepsin D and matrix metalloproteinases

Cathepsin D, matrix metalloproteinase (MMP)-2, MMP-3 (stromelysin), and MMP-9 were isolated from rat granulomatous tissues. HT1080 human fibrosarcoma cells and rheumatoid synovial cell CM. At acidic conditions, cathepsin D cleaved T-kininogen into small peptides and released Met-T-kinin-Leu (kinin precursor), but failed to release kinin. MMP-3 cleaved T-kininogen into a 57 kDa fragment as measured by SDS-PAGE and Western blot analysis using anti-T-kininogen antiserum. On the other hand, no degradation of T-kininogen occurred during incubation with MMP-2 or MMP-9100/1) at pH 7.5 for 7 h.

Breast cancer; tumor neovasculature and the effect of tissue inhibitor of metalloproteinases-1 (TIMP-1) on angiogenesis

Microvessel density has been proposed as a prognostic factor in breast carcinoma. In paired samples of human breast carcinoma and the adjacent non-neoplastic tissue, proliferating microvessels were associated with in situ ductal and lobular carcinomas. In invasive carcinomas, the microvessels were located within the tumor stroma. Recombinant tissue inhibitor of metalloproteinases-1 (rTIMP-1) was produced in a baculovirus system to examine its effect on angiogenesis. When present as a molecule of 29 kDa, rTIMP-1 inhibited matrix metalloproteinase (MMP) activity. However, a 66 kDa aggregate of TIMP-1 did not block MMP activity, although it inhibited in vitro angiogenesis as the 29 kDa form did. Studies have been initiated to characterize the effects of overexpression of TIMP-1 on breast carcinoma cells. Preliminary findings show TIMP-1 mediated changes in morphology and downregulation of MMP activity. These findings suggest that the angiogenesis inhibitory activity of TIMP-1 is unrelated to its antimetalloproteinase activity and that TIMP-1 may affect cellular function in different ways.

Augmentation by eosinophils of gelatinase activity in the airway mucosa: comparative effects as a putative mediator of epithelial injury

1. We have studied the release of gelatin-degrading enzymes from isolated sheets of bronchial mucosa in the presence and absence of eosinophils. 2. Isolated sheets of bovine bronchial mucosa released gelatin-degrading activity in similar amounts from both the apical and basolateral aspects of the tissue. Gelatinolytic activity could not be increased by treatment of the mucosal sheets with calcium ionophore, A23187. 3. The activity of the released gelatinases could be inhibited by chelation of divalent cations or by the matrix metalloproteinase inhibitors, BB-94 and BB-250. However, inhibitors of serine proteinases, or of cysteine proteinases were without effect. In zymography, major bands of gelatin-degrading activity consistent with gelatinases A and B were identified. 4. Addition of guinea-pig eosinophils to the basolateral aspect of bronchial mucosa for 60 min resulted in an increase in the gelatinolytic activity of the conditioned medium, irrespective of whether the eosinophils were stimulated with ionophore A23187 or not. However, only ionophore-stimulated eosinophils reacted to produce sufficient tissue damage to increase the transepithelial flux of serum albumin. 5. Purified eosinophils were a poor source of gelatinolytic activity, indicating that when interacting with the bronchial mucosa their effect is to increase the apparent release and/or activation of gelatinases derived from the airway mucosa. 6. After organomercurial activation, recombinant human progelatinase A increased the permeability of the bronchial mucosa to mannitol. However, the activity of enzyme and duration of exposure required to do this were greater than the amounts of gelatinase activity detected during eosinophil-mediated injury. Sheets of airway mucosa were also resistant to injury evoked by high concentrations of hydrogen peroxide or plasmin. 7. Collectively, these results suggest that if gelatinases are involved in eosinophil-mediated injury and repair of the bronchial mucosa, they require other mediators to act in concert to bring about outright epithelial cell detachment. This does not preclude the possibility that gelatinases are crucial in rendering the airway mucosa hyperfragile.

Plasminogen activators augment endothelial cell organization in vitro by two distinct pathways

Endothelial cell differentiation into capillary structures is a complex process that requires the concerted effects of several extracellular matrix proteases, including plasminogen activators. Here, the role of tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) was evaluated in an in vitro model of endothelial morphogenesis involving organization of human umbilical vein endothelial cells into tubular structures when they are cultured on the basement membrane preparation, Matrigel. Both uPA and tPA were detected in HUVEC cultures on Matrigel, and inhibitors of plasminogen activators or of serine proteases decreased the extent of the tube network formed by the cells. The decrease resulting from serine protease inhibitors was additive to that from matrix metalloproteinase inhibitors which have previously been shown to decrease tube formation in this model, suggesting that the two classes of proteases modulate tube formation by distinct mechanisms. Plasminogen activator inhibitor (PAI)-1 decreased tube formation by 50% when added up to 4.5 h after the initiation of an 18 h assay and caused 25% inhibition when added 9.5 h after culture initiation, indicating that the effects of plasminogen activators are not limited to an early event in the differentiation process. Steady-state expression of mRNA for uPA increased during the first several hours of culture on Matrigel, further supporting a role for PA activity throughout the process of tube formation. These findings suggested that PAs may affect multiple events during tube-forming activity. A fucosylated peptide comprising the amino-terminal domain of uPA that binds to the uPA receptor (uPAR) but lacking proteolytic activity enhanced tube formation. In contrast, a defucosylated form of the same peptide had no effect. Since fucosylation of this fragment has been shown to be essential in other models of cell stimulation by uPA-uPAR interaction, these data support the hypothesis that uPA enhances endothelial morphogenesis both through proteolytic activity and via uPAR occupancy. Plasminogen activators could facilitate angiogenesis in vivo.

Gelatinase A activity directly modulates melanoma cell adhesion and spreading

Interaction of cells with the extracellular matrix (ECM) plays an important role in the regulation of cell behavior. Formation of adhesive contacts leads to transduction of signals into the cell and results in altered gene expression and modulation of the cellular phenotype. Specific adhesive interactions of the fibronectin and vitronectin receptors with their ligands in the matrix modulates expression of ECM-degrading metalloproteases. These proteases are involved in the acquisition of the invasive phenotype by a number of cell types. The activity of matrix metalloproteases (MMPs) is reduced by endogenous inhibitors referred to as tissue inhibitors of metalloproteases (TIMPs). Alterations in the balance between the activity of MMPs and TIMPs alters cellular invasion through effects on matrix degradation. In this study we demonstrate that inhibition of endogenous gelatinase A activity in A2058 human melanoma cells results in enhanced cellular adhesion. To further explore this phenomenon, we have used retroviral infection vectors to control the amount of the MMP inhibitor TIMP-2 in human melanoma A2058 cells. Altering the production of TIMP-2 modulates not only proteolysis of the extracellular matrix, but also the adhesive and spreading properties of the cells and results in altered cell morphology. These effects of TIMP-2 appear to be mediated by inhibition of gelatinase A activity. We conclude that gelatinase A, in addition to contributing to proteolysis of ECM components, also functions to proteolyse cell surface components that mediate attachment of A2058 cells to the ECM. Thus, gelatinase A may function to modulate cell attachment and facilitate cell migration and invasion.

Activity of ternary gelatinase A-TIMP-2-matrix metallo-proteinase complexes

The progelatinase A-TIMP-2 complex behaves like a Janus. Like TIMP (tissue inhibitor of metalloproteinases) it inhibits active matrix metalloproteinases, and activation with 4-aminophenylmercury acetate leads to a gelatinolytic activity. This activity, however, amounts only to less than 10% of that of free gelatinase A not complexed with TIMP-2. When the progelatinase A-TIMP-2 complex inhibits an active matrix metalloproteinase, a ternary complex is generated. After activation with 4-aminophenylmercury acetate this ternary complex displays a more than tenfold proteolytic activity compared to activated gelatinase A-TIMP-2 complex, thus reaching the activity of free gelatinase A. The activity of the ternary complex is nearly independent from the bound matrix metalloproteinase. When the progelatinase A-TIMP-2 complex is activated at first with 4-aminophenylmercury acetate the generation of the ternary complex is made impossible and not such a significant enhancement of activity is observed. These results suggest that gelatinase A-TIMP-2 complex may be a matrix metalloproteinase of the 'second step': It starts its proteolytic attack after it has switched off the activity of other matrix metalloproteinases.