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J Keski-Oja

Publications and source records attributed to J Keski-Oja.

At least 19 recordsLinked to original sources
PubMed2001

Regulation of membrane-type matrix metalloproteinase 1 activity by dynamin-mediated endocytosis.

Membrane-type matrix metalloproteinase 1 (MT1-MMP) plays a critical role in extracellular matrix remodeling under both physiological and pathological conditions. However, the mechanisms controlling its activity on the cell surface remain poorly understood. In this study, we demonstrate that MT1-MMP is regulated by endocytosis. First, we determined that Con A induces proMMP-2 activation in HT1080 cells by shifting endogenous MT1-MMP from intracellular compartments to cell surface. This phenotype was mimicked by the cytoplasmic truncation mutant MT1 Delta C with more robust pro-MMP-2 activation and cell surface expression than wild-type MT1-MMP in transfected cells. MT1 Delta C was subsequently shown to be resistant to Con A treatment whereas MT1-MMP remains competent, suggesting that Con A regulates MT1-MMP activity through cytoplasmic domain-dependent trafficking. Indeed, MT1-MMP was colocalized with clathrin on the plasma membrane and with endosomal antigen 1 in endosomes. Internalization experiments revealed that MT1-MMP is internalized rapidly in clathrin-coated vesicles whereas MT1 Delta C remains on cell surface. Coexpression of a dominant negative mutant of dynamin, K44A, resulted in elevation of MT1-MMP activity by interfering with the endocytic process. Thus, MT1-MMP is regulated by dynamin-dependent endocytosis in clathrin-coated pits through its cytoplasmic domain.

Animals↗
PubMed2001

Promoter characterization of the human and mouse epilysin (MMP-28) genes.

Epilysin (MMP-28) is a recently cloned member of the matrix metalloproteinase family (Lohi et al., J. Biol. Chem. 276 (2001) 10134). It is expressed at highest levels in the skin by basal and suprabasal keratinocytes, and in testis by developing germ cells. To characterize the epilysin promoter, we isolated a 3.0 kb fragment of human genomic DNA containing 5'-flanking sequence of the epilysin gene, and a corresponding 660 bp fragment from the mouse. The 5'-flanking sequences contain no typical TATA-boxes or CCAAT sequences close to the translation initiation sites. RNase protection assay revealed that two transcription start sites are utilized in the human epilysin gene, situated 210 and 230 bp upstream from the translation start site. The promoter contains a GT-box, situated 300 bp upstream from the translation start site, with homology to the consensus binding site for transcription factors of the Sp family. This site is perfectly conserved between the human and mouse promoters. For reporter gene assays a series of constructs with fragments of increasing length of the epilysin promoter were coupled to the firefly luciferase gene. Reporter gene assays indicated that deletion or mutation of the GT-box dramatically reduces the transcriptional activity both in keratinocytes and in spermatogonia. Gel mobility shift assays showed that several nuclear proteins bind specifically to this sequence. Supershift assays with antibodies specific for members of the Sp family identified Sp1 and Sp3 as components of these protein/DNA complexes and hence as possible regulators of the epilysin gene. Our results indicate that the epilysin promoter has distinctive structural and functional features, which may control the unique expression and regulation patterns of the epilysin gene.

Animals↗
PubMed2001

Endostatin-induced modulation of plasminogen activation with concomitant loss of focal adhesions and actin stress fibers in cultured human endothelial cells.

Endostatin, a M(r) 20,000 fragment of collagen XVIII, is able to inhibit angiogenesis and induce apoptosis in endothelial cells in vivo. We analyzed the effectsof recombinant endostatin on human microvascular endothelial cells, focusing on pericellular plasminogen activation and its targeting by the focal adhesion-associated cytoskeletal structures. Analysis of the proteolytic plasminogen activator system revealed that endostatin modulates the distribution of soluble and cell surface-associated urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor, type 1 (PAI-1). Casein zymographic and immunoprecipitation analyses indicated that endostatin exerts its effects by decreasing the levels of soluble uPA and PAI-1 and their complexes in a dose-dependent manner. Immunofluorescence analysis of cell surface-associated uPA indicated that endostatin treatment caused the redistribution of receptor-bound uPA from focal contacts, resulting in diffuse cell surface staining. In accordance with this observation, immunofluorescence staining of the urokinase receptor revealed that endostatin treatment removed uPAR from focal adhesions. Accordingly, endostatin caused a rapid disassembly of focal adhesions as observed by immunofluorescence analysis of the focal adhesion proteins vinculin and paxillin. A prominent change in the cytoskeletal architecture was observed as the actin stress fiber network was dissociated in response to endostatin treatment. The effect of focal adhesion disassembly was reversible, persisting from 1 h up to 6 h. Our results suggest that the antiangiogenic activity of endostatin involves the modulation of focal adhesions and actin stress fibers and the down-regulation of the urokinase plasminogen activator system.

Actins↗
PubMed2001

Latency, activation, and binding proteins of TGF-beta.

The TGF-beta superfamily of growth factors consists of an increasing number of different polypeptide modulators of cell growth, differentiation, and morphogenesis. Three mammalian isoforms have been molecularly cloned. Numerous ways to regulate the expression of the TGF-beta genes have been identified. TGF-betas are, for example, subject to regulation by retinoids, steroid hormones, and vitamin D. A characteristic feature in the biology of TGF-betas is that they are usually secreted from cells in latent forms. The large latent complex consists of the small latent complex (TGF-beta and its propeptide) and a high molecular weight protease resistant binding protein, latent TGF-beta binding protein (LTBP). LTBPs are required for the proper folding and secretion of TGF-beta. TGF-beta is not just secreted from cultured cells but is deposited via LTBPs to the pericellular space, namely to the extracellular matrix. Release of these complexes and activation by proteases is under tight regulation and provides a means to rapidly increase local concentrations of TGF-beta. Biological events, where enhanced or focal proteolysis and activation of latent TGF-beta takes place, include cell invasion, tissue remodeling, and wound healing.

Animals↗
PubMed2001

Activation of paracrine TGF-beta1 signaling upon stimulation and degranulation of rat serosal mast cells: a novel function for chymase.

As a source of transforming growth factor beta1 (TGF-beta1), mast cells have been implicated as potential effector cells in many pathological processes. However, the mechanisms by which mast cells express, secrete, and activate TGF-beta1 have remained vague. We show here by means of RT-PCR, immunoblotting, and immunocytochemistry that isolated rat peritoneal mast cells synthesize and store large latent TGF-beta1 in their chymase 1-containing secretory granules. Mast cell stimulation and degranulation results in rapid secretion of the latent TGF-beta1, which is converted by chymase 1 into an active form recognized by the type II TGF-beta serine/threonine kinase receptor (TbetaRII). Thus, mast cells secrete active TGF-beta1 by a unique secretory mechanism in which latent TGF-beta1 and the activating enzyme chymase 1 are coreleased. The activation of latent TGF-beta1 specifically by chymase was verified using recombinant human latent TGF-beta1 and recombinant human chymase. In isolated TbetaRI- and TbetaRII-expressing peritoneal macrophages, the activated TGF-beta1 induces the expression of the plasminogen activator inhibitor 1 (PAI-1), whereas in the mast cells, the levels of TbetaRI, TbetaRII, and PAI-1 expression were below detection. Selective stimulation of mast cells in vivo in the rat peritoneal cavity leads to rapid overexpression of TGF-beta1 in peritoneal mast cells and of TbetaRs in peritoneal macrophages. These data strongly suggest that mast cells can act as potent paracrine effector cells both by secreting active TGF-beta1 and by enhancing its response in target cells.

Animals↗
PubMed2001

Latent TGF-beta binding protein LTBP-1 contains three potential extracellular matrix interacting domains.

Latent TGF-beta binding proteins (LTBPs) are components of the extracellular matrix (ECM). They belong to the fibrillin/LTBP-superfamily, and are high molecular weight glycoproteins characterized by EGF-like repeats and 8-Cys repeats. Most LTBPs associate with the small latent forms of TGF-beta. Their roles include to facilitate the secretion of latent TGF-beta and to target it to the ECM. In order to identify new matrix-binding domains of LTBP-1 and to characterize their association with the extracellular matrix, we have produced (in a mammalian expression system) partly overlapping recombinant fragments of its shorter form, LTBP-1S, and analyzed the binding of the purified fusion proteins to extracellular matrices of cultured human dermal and lung fibroblasts. Recombinant fragments from three different regions of the N- and C-termini showed affinity to the matrix. These interacting regions contain either the first (hybrid), second or fourth 8-Cys domains of the LTBP-1S molecule. They bound independently to the matrix. Each of them had an ability to inhibit the association of native exogenous LTBP-1 with fibroblast extracellular matrix. The interactions of the LTBP-1 fragments with the extracellular matrix resisted treatment with sodium deoxycholate, suggesting strong, possibly covalent binding. The binding occurred in a time- and dose-dependent fashion. The N-terminal fragments bound more readily to the matrices. With all fragments the binding took place both with intact fibroblast matrices and with matrices isolated by sodium deoxycholate. When using CHO cell layers, which form sparse matrices, only the N-terminal fragment of LTBP-1 was efficiently incorporated. The association of the binding fragments with isolated matrices was enhanced by soluble, cell-derived factors. The current data suggest that LTBP-1 contains three different domains with an ability to associate with the extracellular matrix.

Animals↗
PubMed2001

Novel non-TGF-beta-binding splice variant of LTBP-4 in human cells and tissues provides means to decrease TGF-beta deposition.

Small latent TGF-beta consists of latency associated peptide (LAP) bound to the 25 kDa TGF-beta by noncovalent interactions. Small latent TGF-beta is secreted from cells and deposited into the extracellular matrix as covalent complexes with its binding proteins, LTBPs. Four LTBPs have been molecularly cloned and their structures contain repetitive sequences. The 3rd 8-Cys repeats of LTBP-1, -3 and -4 are able to associate with small latent TGF-beta. We analyzed by RT-PCR the expression of LTBPs 1-4 in a panel of cultured human cell lines including fibroblasts of different origin, endothelial cells and immortalized keratinocytes. LTBPs were expressed in an overlapping manner, but differences in their expression levels were detected. SV-40 transformed human embryonic lung fibroblasts contained less of the mRNAs for the LTBPs, suggesting that malignant transformation leads to decrease in LTBP expression. A novel alternatively spliced form of LTBP-4 lacking the 3rd 8-Cys repeat (LTBP-4delta8-Cys3rd) was identified. LTBP-4delta8-Cys3rd does not bind TGF-beta and it was found to be expressed in the same tissues as the full length LTBP-4. The exon-intron structure of LTBP-4 around the 3rd 8-Cys repeat was similar to those of LTBP-2 and -3. LTBP-4delta8-Cys3rd was produced by alternative splicing over two exons. In addition, HL-60 promyelocytic leukemia cells expressed a splice variant lacking only one exon of this region. The expression of the non-TGF-beta-binding variant of LTBP-4 may be important for the regulation of TGF-beta deposition in tissues. Since LTBPs are a part of the extracellular matrix microfibrils, the LTBP-4delta8-Cys3rd protein may also be involved in various structural functions not related to TGF-beta signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Regulation of membrane-type-1 matrix metalloproteinase activity by its cytoplasmic domain.

Membrane-type-1 matrix metalloproteinase (MT1-MMP) has transmembrane and cytoplasmic domains, which target it to invasive fronts. We analyzed the role of the cytoplasmic tail by expressing wild type MT1-MMP and three mutants with progressively truncated C termini in human Bowes melanoma cells. We examined gelatinase A activation and the localization and processing of recombinant proteins in stable cell clones using gelatin zymography, immunoblotting, and immunofluorescence. Cell invasion was analyzed in vitro by Matrigel invasion assays. Gelatinase A was activated in all cell clones. However, the localization of MT1-MMP to the leading edge of migrating cells and cell invasion through Matrigel were strongly enhanced only in cells expressing either wild type or truncated MT1-MMP lacking 6 C-terminal amino acid residues (Delta577). Truncations of 10 or 16 amino acid residues in the cytoplasmic domain (Delta567 and Delta573, respectively) disturbed MT1-MMP localization. The expression of wild type and Delta577 MT1-MMPs induced also their cleavage to 43-kDa cell surface forms and the release of soluble, approximately 20-kDa N-terminal fragments containing the catalytic center. A synthetic MMP inhibitor but not a gelatinase inhibitor prevented the processing, suggesting that autocatalytic cleavage occurs. Purified soluble MT1-MMP was also autoproteolytically processed to 43- and 20-kDa forms in vitro. Our results indicate that the cytoplasmic domain has an important role in cell invasion by controlling both the targeting and degradation/turnover of MT1-MMP.

Cloning, Molecular↗
PubMed2000

Structural analysis and promoter characterization of the human membrane-type matrix metalloproteinase-1 (MT1-MMP) gene.

Membrane type-1 matrix metalloproteinase (MT1-MMP) degrades extracellular matrix components directly and indirectly by activation of other matrix metalloproteinases (MMPs). In the present study, we have isolated and characterized the human MT1-MMP gene and its promoter. The gene consists of 10 exons and nine introns spanning more than 10 kilobases (kb). The locations of two exon-intron splicing sites are distinct from the preserved positions among other known MMP genes. Primer extension and RNAse and S1 nuclease protection analyses indicated that there are four major and several minor transcription start sites. The 5'-flanking sequence of the gene contains putative regulatory elements, including one Sp-1 site and four CCAAT-boxes, whereas there is no TATA-box. The Sp-1 binding site was functional, as shown by gel shift and supershift analyses. Transfection studies with promoter constructs containing 0.1 to 7.2 kb of 5'-flanking sequence coupled to a luciferase reporter gene indicated that the promoter contains additional positive and negative regulatory sequences. Deletion of the Sp-1 binding site by site-directed mutagenesis reduced luciferase activity by about 90%, demonstrating the crucial role of this element in maintaining MT1-MMP transcription. Our findings indicate that the human MT1-MMP promoter has distinctive structural and functional features compared with other MMP genes, which may lead to a unique expression pattern and regulation during physiological and pathological processes.

Base Sequence↗
PubMed2000

Expression and purification of soluble and inactive mutant forms of membrane type 1 matrix metalloproteinase.

Membrane type 1 matrix metalloproteinase (MT1-MMP) is a membrane-bound proteinase and a cell-surface receptor and activator of gelatinase A in normal and neoplastic cells. We have expressed and purified a soluble deletion mutant of MT1-MMP lacking the transmembrane and cytoplasmic domains and an inactive mutant of the soluble MT1-MMP, where the active-site glutamic acid(240) was substituted by alanine (E240A). A baculovirus transfer vector coding for amino acids 21-539 of MT1-MMP (DeltaTM) and a similar vector coding for the mutation (E240ADeltaTM) were constructed for expression in insect cells. Both DeltaTM and E240ADeltaTM were secreted to the culture medium of infected High Five insect cells. They were then purified by cation-exchange followed by gel-filtration chromatography. DeltaTM was able to cleave denatured type I collagen and fibronectin and activate MMP-2/gelatinase-A, while E240ADeltaTM had only low proteolytic activity against denatured collagen I. The current expression and purification protocol should prove useful for the production of large amounts of enzymatically active soluble MT1-MMP.

Amino Acid Substitution↗
PubMed2000

Specific sequence motif of 8-Cys repeats of TGF-beta binding proteins, LTBPs, creates a hydrophobic interaction surface for binding of small latent TGF-beta.

Transforming growth factor (TGF)-betas are secreted in large latent complexes consisting of TGF-beta, its N-terminal latency-associated peptide (LAP) propeptide, and latent TGF-beta binding protein (LTBP). LTBPs are required for secretion and subsequent deposition of TGF-beta into the extracellular matrix. TGF-beta1 associates with the 3(rd) 8-Cys repeat of LTBP-1 by LAP. All LTBPs, as well as fibrillins, contain multiple 8-Cys repeats. We analyzed the abilities of fibrillins and LTBPs to bind latent TGF-beta by their 8-Cys repeats. 8-Cys repeat was found to interact with TGF-beta1*LAP by direct cysteine bridging. LTBP-1 and LTBP-3 bound efficiently all TGF-beta isoforms, LTBP-4 had a much weaker binding capacity, whereas LTBP-2 as well as fibrillins -1 and -2 were negative. A short, specific TGF-beta binding motif was identified in the TGF-beta binding 8-Cys repeats. Deletion of this motif in the 3(rd) 8-Cys repeat of LTBP-1 resulted in loss of TGF-beta*LAP binding ability, while its inclusion in non-TGF-beta binding 3(rd) 8-Cys repeat of LTBP-2 resulted in TGF-beta binding. Molecular modeling of the 8-Cys repeats revealed a hydrophobic interaction surface and lack of three stabilizing hydrogen bonds introduced by the TGF-beta binding motif necessary for the formation of the TGF-beta*LAP - 8-Cys repeat complex inside the cells.

Amino Acid Motifs↗
PubMed2000

Impaired migration and delayed differentiation of pancreatic islet cells in mice lacking EGF-receptors.

Pancreatic acini and islets are believed to differentiate from common ductal precursors through a process requiring various growth factors. Epidermal growth factor receptor (EGF-R) is expressed throughout the developing pancreas. We have analyzed here the pancreatic phenotype of EGF-R deficient (-/-) mice, which generally die from epithelial immaturity within the first postnatal week. The pancreata appeared macroscopically normal. The most striking feature of the EGF-R (-/-) islets was that instead of forming circular clusters, the islet cells were mainly located in streak-like structures directly associated with pancreatic ducts. Based on BrdU-labelling, proliferation of the neonatal EGF-R (-/-) beta-cells was significantly reduced (2.6+/-0.4 versus 5.8+/-0.9%, P<0.01) and the difference persisted even at 7-11 days of age. Analysis of embryonic pancreata revealed impaired branching morphogenesis and delayed islet cell differentiation in the EGF-R (-/-) mice. Islet development was analyzed further in organ cultures of E12.5 pancreata. The proportion of insulin-positive cells was significantly lower in the EGF-R (-/-) explants (27+/-6 versus 48+/-8%, P<0.01), indicating delayed differentiation of the beta cells. Branching of the epithelium into ducts was also impaired. Matrix metalloproteinase (MMP-2 and MMP-9) activity was reduced 20% in EGF-R (-/-) late-gestation pancreata, as measured by gelatinase assays. Furthermore, the levels of secreted plasminogen activator inhibitor-1 (PAI-1) were markedly higher, while no apparent differences were seen in the levels of active uPA and tPa between EGF-R (-/-) and wild-type pancreata. Our findings suggest that the perturbation of EGF-R-mediated signalling can lead to a generalized proliferation defect of the pancreatic epithelia associated with a delay in beta cell development and disturbed migration of the developing islet cells as they differentiate from their precursors. Upregulated PAI-1 production and decreased gelatinolytic activity correlated to this migration defect. An intact EGF-R pathway appears to be a prerequisite for normal pancreatic development.

Animals↗
PubMed2000

1alpha,25-dihydroxyvitamin D3 and its analogues down-regulate cell invasion-associated proteases in cultured malignant cells.

Vitamin D and its derivatives (deltanoids) are potent regulators of cell proliferation and differentiation. Targeted production of proteolytic enzymes like serine proteases and metalloproteinases is an important part of the invasive process of cancer cells. Treatment with 1 alpha25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] decreases the invasive properties of breast carcinoma cells. Here we have analyzed the effects of 1alpha,25(OH)2D3 and its synthetic analogues on the secretion and cell surface association of the components of the plasminogen activator (PA) system and on the secretion of certain matrix metalloproteinases (MMPs) and their inhibitors in MDA-MB-231 breast carcinoma cells. Deltanoids were able to decrease the secretion of urokinase PA and tissue-type PA activity in a dose-dependent manner and to increase PA inhibitor 1 secretion, leading to reduced total PA activity. CB1093 was the most potent analogue, effective at concentrations several logarithms lower than 1alpha,25(OH)2D3. Transient transfection of different urokinase PA promoter reporter constructs to HT-1080 fibrosarcoma indicator cells indicated that vitamin D-responsive sequences were located between nucleotides -2350 and -1870 in the 5' region of the promoter. Treatment of MDA-MB-231 cells with 1alpha,25(OH)2D3 or other deltanoids also resulted in decreased MMP-9 levels in association with increased tissue inhibitor of MMP 1 activity. Membrane-type 1-MMP expression or proteolytic processing were not appreciably affected by deltanoids. Vitamin D and its analogues caused a decrease in Matrigel invasion assays of MDA-MB-231 cells. Cancer cell invasion is associated with coordinated secretion of proteolytic enzymes and their inhibitors. Vitamin D and its derivatives can evidently influence invasive processes by two means: (a) decreasing the expression and activity of cell invasion-associated serine proteases and metalloproteinases; and (b) inducing their inhibitors.

Alitretinoin↗
PubMed1999

Independent promoters regulate the expression of two amino terminally distinct forms of latent transforming growth factor-beta binding protein-1 (LTBP-1) in a cell type-specific manner.

Latent transforming growth factor-beta (TGF-beta)-binding proteins (LTBPs) are components of the extracellular matrix and large latent TGF-beta complexes are secreted by various cells. Human LTBP-1 is known to exist in different forms. LTBP-1L (long) has an amino-terminal extension, which is not found in the smaller LTBP-1S isoform. To study the formation and transcriptional regulation of LTBP-1S and LTBP-1L isoforms, we determined the nucleotide sequences of their 5'-flanking regions. The upstream regions of both isoforms are devoid of TATA boxes but contain other putative binding sites for several transcription factors. Genomic sequencing revealed that LTBP-1L transcript is alternatively spliced to an internal splice acceptor inside exon 1 of LTBP-1S and thus defined the genomic organization of the isoforms. Reporter gene analysis of upstream regions indicated the presence of independent, functional promoters, which regulate the transcription of the isoforms by cell-specific manner. Deletion analyses of the promoter regions revealed specific elements modulating their basal and cell type-specific expression. In SV-40 virus-transformed WI-38 lung fibroblasts a regulatory element repressed the transcription of LTBP-1S by a cell-specific manner. In amniotic epithelial cells, transcription of the LTBP-1S reporter gene construct was down-regulated by a distal upstream element. mRNA levels of the isoforms of LTBP-1 were stimulated in response to TGF-beta1 in WI-38 cells. However, since TGF-beta1 failed to stimulate the transcription of LTBP-1 reporter gene constructs, TGF-beta1 may mediate the induction of the isoforms by post-transcriptional mechanisms. Chromosomal localization of the LTBP-1 gene was refined to 2p22-24.

Base Sequence↗
PubMed1999

Latent transforming growth factor-beta binding proteins (LTBPs)--structural extracellular matrix proteins for targeting TGF-beta action.

Growth factors of the transforming growth factor-beta family are potent regulators of the extracellular matrix formation, in addition to their immunomodulatory and regulatory roles for cell growth. TGF-beta s are secreted from cells as latent complexes containing TGF-beta and its propeptide, LAP (latency-associated peptide). In most cells LAP is covalently linked to an additional protein, latent TGF-beta binding protein (LTBP), forming the large latent complex. LTBPs are required for efficient secretion and correct folding of TGF-beta s. The secreted large latent complexes associate covalently with the extracellular matrix via the N-termini of the LTBPs. LTBPs belong to the fibrillin-LTBP family of extracellular matrix proteins, which have a typical repeated domain structure consisting mostly of epidermal growth factor (EGF)-like repeats and characteristic eight cysteine (8-Cys) repeats. Currently four different LTBPs and two fibrillins have been identified. LTBPs contain multiple proteinase sensitive sites, providing means to solubilize the large latent complex from the extracellular matrix structures. LTBPs are now known to exist both as soluble molecules and in association with the extracellular matrix. An important consequence of this is LTBP-mediated deposition and targeting of latent, activatable TGF-beta into extracellular matrices and connective tissues. LTBPs have a dual function, they are required both for the secretion of the small latent TGF-beta complex as well as directing bound latent TGF-beta to extracellular matrix microfibrils. However, it is not known at present whether LTBPs are capable of forming microfibrils independently, or whether they are a part of the fibrillin-containing fibrils. Most LTBPs possess RGD-sequences, which may have a role in their interactions with the cell surface. At least LTBP-1 is chemotactic to smooth muscle cells, and is involved in vascular remodelling. Analyses of the expressed LTBPs have revealed considerable variations throughout the molecules, generated both by alternative splicing and utilization of multiple promoter regions. The significance of this structural diversity is mostly unclear at present.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Expression of collagenases-1 and -3 and their inhibitors TIMP-1 and -3 correlates with the level of invasion in malignant melanomas.

Since proteolysis of the dermal collagenous matrix and basement membranes is required for local invasive growth and early metastasis formation of cutaneous melanomas, we have analysed the activities/expression levels of certain metalloproteinases in melanomas and cultured melanoma cells by in situ hybridization and Northern analysis. In addition to collagenases-1 and -3 that have been implicated in invasive growth behaviour of various malignant tumours, we analysed the levels of 72-kDa gelatinase and its activators MT1-MMP and TIMP-2 in cultured melanoma cells. The lesions examined included three cases of lentigo maligna and 28 cases of Clark grade I-V melanomas. The premalignant as well as the grade I tumours were consistently negative for collagenase-1 and -3 and TIMP-1 and -3. The collagenases were predominantly expressed in the cancer cells of Clark grade III and IV tumours. TIMP-1 and -3 were abundantly expressed in the cancer and/or stromal cells of grade III and IV melanomas, while TIMP-2 protein was detected also in melanomas representing lower invasive potential. Northern analysis of seven melanoma cell lines showed that the expression of collagenase-1 and TIMPs-1 and -3 was associated with 72-kDa gelatinase positivity. All melanoma cell lines were positive for MT1-MMP and TIMP-2 mRNAs. Our results suggest that overexpression of collagenases-1 and -3 and TIMPs-1 and -3 is induced during melanoma progression. Expression of TIMPs may reflect host response to tumour invasion in an effort to control MMP activity and preserve extracellular matrix integrity.

Adult↗