Stroke in Icelandic patients with hereditary amyloid angiopathy is related to a mutation in the cystatin C gene, an inhibitor of cysteine proteases.

Cystatin C is an inhibitor of lysosomal cysteine proteases and consists of 120 amino acids. A variant of cystatin C lacking the first NH2-terminal residues and having one amino acid substitution at position 68 forms amyloid deposits mainly in the walls of brain arteries, causing fatal strokes in Icelandic patients with familial cerebral hemorrhage secondary to a form of an autosomal dominant amyloidosis. To understand the molecular basis of the genetic defect, the gene encoding cystatin C was isolated from genomic DNA libraries made from normal tissue and the brain of an Icelandic patient with hereditary cerebral hemorrhage with amyloidosis (HCHWA-I). The data indicate that the cystatin C gene encodes a polypeptide of 146 amino acids, of which the first 26 correspond to a secretory peptide signal sequence. The gene contains two intervening sequences that interrupt the coding region at amino acids 55 and 93. Comparison with genes encoding salivary cystatins and kininogen proteins show sequence homology and conservation of exon-intron structure. Except for a mutation in the second exon (CAG instead of CTG in the normal gene, resulting in the substitution of glutamine for a leucine residue), the gene cloned from the brain of the Icelandic patient is identical to the normal cystatin C gene. Thus, HCHWA-I is the first familial type of amyloidosis related to a point mutation in a gene encoding for an inhibitor. The mutation in the structural gene encoding cystatin C appears to be the primary defect in this inherited disorder causing amyloid fibril formation and accumulation followed by cerebral hemorrhage.

A regulatory cascade involving retinoic acid, Cbfa1, and matrix metalloproteinases is coupled to the development of a process of perichondrial invasion and osteogenic differentiation during bone formation.

Tissue-remodeling processes are largely mediated by members of the matrix metalloproteinase (MMP) family of endopeptidases whose expression is strictly controlled both spatially and temporally. In this article, we have examined the molecular mechanisms that could contribute to modulate the expression of MMPs like collagenase-3 and MT1-MMP during bone formation. We have found that all-trans retinoic acid (RA), which usually downregulates MMPs, strongly induces collagenase-3 expression in cultures of embryonic metatarsal cartilage rudiments and in chondrocytic cells. This effect is dose and time dependent, requires the de novo synthesis of proteins, and is mediated by RAR-RXR heterodimers. Analysis of the signal transduction mechanisms underlying the upregulating effect of RA on collagenase-3 expression demonstrated that this factor acts through a signaling pathway involving p38 mitogen-activated protein kinase. RA treatment of chondrocytic cells also induces the production of MT1-MMP, a membrane-bound metalloproteinase essential for skeletal formation, which participates in a proteolytic cascade with collagenase-3. The production of these MMPs is concomitant with the development of an RA-induced differentiation program characterized by formation of a mineralized bone matrix, downregulation of chondrocyte markers like type II collagen, and upregulation of osteoblastic markers such as osteocalcin. These effects are attenuated in metatarsal rudiments in which RA induces the invasion of perichondrial osteogenic cells from the perichondrium into the cartilage rudiment. RA treatment also resulted in the upregulation of Cbfa1, a transcription factor responsible for collagenase-3 and osteocalcin induction in osteoblastic cells. The dynamics of Cbfa1, MMPs, and osteocalcin expression is consistent with the fact that these genes could be part of a regulatory cascade initiated by RA and leading to the induction of Cbfa1, which in turn would upregulate the expression of some of their target genes like collagenase-3 and osteocalcin.

Correction: The anti-metastatic activity of collagenase-2 in breast cancer cells is mediated by a signaling pathway involving decorin and miR-21.

The original microRNA hybridization data for this article, which has been available for the scientific community upon request, has now been deposited in the GEO repository under accession number GSE124432.

Microcephalia with mandibular and dental dysplasia in adult Zmpste24-deficient mice.

ZMPSTE24 (also called FACE-1) is a zinc-metalloprotease involved in the post-translational processing of prelamin A to mature lamin A, a major component of the nuclear envelope. Mutations in the ZMPSTE24 gene or in that encoding its substrate prelamin A (LMNA) result in a series of human inherited diseases known collectively as laminopathies and showing regional or systemic manifestations (i.e. the Hutchinson-Gilford progeria syndrome). Typically, patients suffering some laminopathies show craniofacial or mandible anomalies, aberrant dentition or facial features characteristic of aged persons. To analyse whether Zmpste24(-/-) mice reproduce the cranial phenotype observed in humans due to mutations in ZMPSTE24 or LMNA, we conducted a craniometric study based on micro-computer tomography (microCT) images. Furthermore, using simple radiology, microCT, microCT-densitometry and scanning electron microscopy, we analysed the mandible and the teeth from Zmpste24(-/-) mice. Finally, the structure of the lower incisor was investigated using an H&E technique. The results demonstrate that Zmpste24(-/-) mice are microcephalic and show mandibular and dental dysplasia affecting only the mandible teeth. In all cases, the lower incisor of mice lacking Zmpste24 was smaller than in control animals, showed cylindrical morphology and a transverse fissure at the incisal edge, and the pulpal cavity was severely reduced. Structurally, the dental layers were normally arranged but cellular layers were disorganized. The inferior molars showed a reduced cusp size. Taken together, these data strongly suggest that Zmpste24(-/-) mice represent a good model to analyse the craniofacial and teeth malformations characteristic of lamin-related pathologies, and might contribute to a better understanding of the molecular events underlying these diseases.

Clinical impact of the subclonal architecture and mutational complexity in chronic lymphocytic leukemia.

Genome studies of chronic lymphocytic leukemia (CLL) have revealed the remarkable subclonal heterogeneity of the tumors, but the clinical implications of this phenomenon are not well known. We assessed the mutational status of 28 CLL driver genes by deep-targeted next-generation sequencing and copy number alterations (CNA) in 406 previously untreated patients and 48 sequential samples. We detected small subclonal mutations (0.6-25% of cells) in nearly all genes (26/28), and they were the sole alteration in 22% of the mutated cases. CNA tended to be acquired early in the evolution of the disease and remained stable, whereas the mutational heterogeneity increased in a subset of tumors. The prognostic impact of different genes was related to the size of the mutated clone. Combining mutations and CNA, we observed that the accumulation of driver alterations (mutational complexity) gradually shortened the time to first treatment independently of the clonal architecture, IGHV status and Binet stage. Conversely, the overall survival was associated with the increasing subclonal diversity of the tumors but it was related to the age of patients, IGHV and TP53 status of the tumors. In conclusion, our study reveals that both the mutational complexity and subclonal diversity influence the evolution of CLL.

A functional link between the tumour suppressors ARF and p33ING1.

The ARF tumour suppressor protein plays a critical role in the activation of p53 in response to oncogenic stress. ARF can activate p53 through nucleolar sequestration of Mdm2. However, several lines of evidence indicate that this is not the only way of action of ARF, and alternative mechanisms must exist. p33ING1 is a putative tumour suppresor, which induces cell-cycle arrest and apoptosis in a p53-dependent manner. Here, we describe that ARF and p33ING1 can interact in vivo. We also show that the subcellular localization of ING1 can be modulated by ARF protein levels, causing a displacement from nuclear to nucleolar localization. Finally, the ability of p33ING1 to cause cell-cycle arrest and induction of p21CIP1, or Mdm2, is impaired in ARF-deficient primary mouse fibroblasts. Based on these observations, we propose that the interaction with p33ING1 represents a novel mechanism for the tumour suppression function of ARF.

Collagenase 3 is a target of Cbfa1, a transcription factor of the runt gene family involved in bone formation.

Collagenase 3 (MMP-13) is a recently identified member of the matrix metalloproteinase (MMP) gene family that is expressed at high levels in diverse human carcinomas and in articular cartilage from arthritic patients. In addition to its expression in pathological conditions, collagenase 3 has been detected in osteoblasts and hypertrophic chondrocytes during fetal ossification. In this work, we have evaluated the possibility that Cbfa1 (core binding factor 1), a transcription factor playing a major role in the expression of osteoblastic specific genes, is involved in the expression of collagenase 3 during bone formation. We have functionally characterized a Cbfa motif present in the promoter region of collagenase 3 gene and demonstrated, by cotransfection experiments and gel mobility shift assays, that this element is involved in the inducibility of the collagenase 3 promoter by Cbfa1 in osteoblastic and chondrocytic cells. Furthermore, overexpression of Cbfa1 in osteoblastic cells unable to produce collagenase 3 leads to the expression of this gene after stimulation with transforming growth factor beta. Finally, we show that mutant mice deficient in Cbfa1, lacking mature osteoblasts but containing hypertrophic chondrocytes which are also a major source of collagenase 3, do not express this protease during fetal development. These results provide in vivo evidence that collagenase 3 is a target of the transcriptional activator Cbfa1 in these cells. On the basis of these transcriptional regulation studies, together with the potent proteolytic activity of collagenase 3 on diverse collagenous and noncollagenous bone and cartilage components, we proposed that this enzyme may play a key role in the process of bone formation and remodeling.

ADAM 23/MDC3, a human disintegrin that promotes cell adhesion via interaction with the alphavbeta3 integrin through an RGD-independent mechanism.

ADAM 23 (a disintegrin and metalloproteinase domain)/MDC3 (metalloprotease, disintegrin, and cysteine-rich domain) is a member of the disintegrin family of proteins expressed in fetal and adult brain. In this work we show that the disintegrin-like domain of ADAM 23 produced in Escherichia coli and immobilized on culture dishes promotes attachment of different human cells of neural origin, such as neuroblastoma cells (NB100 and SH-S(y)5(y)) or astrocytoma cells (U373 and U87 MG). Analysis of ADAM 23 binding to integrins revealed a specific interaction with alphavbeta3, mediated by a short amino acid sequence present in its putative disintegrin loop. This sequence lacks any RGD motif, which is a common structural determinant supporting alphavbeta3-mediated interactions of diverse proteins, including other disintegrins. alphavbeta3 also supported adhesion of HeLa cells transfected with a full-length cDNA for ADAM 23, extending the results obtained with the recombinant protein containing the disintegrin domain of ADAM 23. On the basis of these results, we propose that ADAM 23, through its disintegrin-like domain, may function as an adhesion molecule involved in alphavbeta3-mediated cell interactions occurring in normal and pathological processes, including progression of malignant tumors from neural origin.

Tagged ATG8-Coding Constructs for the In Vitro and In Vivo Assessment of ATG4 Activity.

Autophagy is a catabolic pathway, which mediates the degradation of cytoplasmic components and sustains many essential cellular functions. More than 30 genes have been involved in different aspects of this essential process in simple eukaryotes as yeast. Among these genes, those coding for members of the Atg4-Atg8 proteolytic system have acquired a high degree of complexity throughout evolution. Contrasting with the situation in unicellular eukaryotes, in which the system is composed by just a single protease (Atg4) and a single substrate (Atg8), evolution has led to the presence of several members for both Atg4 and Atg8 families in multicellular organisms. In human cells, there are four Atg4 proteases and six Atg8 substrates, which have probably evolved to cope with specific requirements for autophagic pathway in more complex scenarios. Despite these considerations, the reasons for the evolutionarily acquired complexity of this proteolytic system are still not completely understood. In this work, we describe two different applications of a relatively simple but useful technique to analyze protease-substrate specificity of this system in mammalian cells. By using the described technique, it is possible to determine the cellular efficiency in the initial cleavage for each of the Atg8 family members in diverse experimental settings both in cultured cells and live laboratory mice.

Matrilysin-2, a new matrix metalloproteinase expressed in human tumors and showing the minimal domain organization required for secretion, latency, and activity.

We have identified a human placenta cDNA coding for a new member of the matrix metalloproteinase (MMP) family. The isolated cDNA encodes a polypeptide of 261 amino acids, the smallest MMP identified to date, which contains several structural features of MMPs including the signal sequence, the prodomain involved in enzyme latency, and the catalytic domain with the zinc-binding site. However, it lacks the hinge region and hemopexin-domain present in most MMPs. According to these structural characteristics, the human MMP described herein has been called matrilysin-2 (MMP-26), because it exclusively shares with matrilysin this minimal domain organization required for secretion, latency, and activity. The amino acid sequence of matrilysin-2 also contains a threonine residue adjacent to the Zn-binding site that has been defined as a specific feature of matrilysin. Chromosomal location of the matrilysin-2 gene showed that it maps to the short arm of chromosome 11, a location distinct to that of other MMP genes. Matrilysin-2 was expressed in Escherichia coli, and, after purification and refolding, the recombinant protein was found to degrade synthetic substrates commonly used for assaying MMPs. Furthermore, this protein hydrolyzed type IV collagen, fibronectin, fibrinogen, and gelatin, which indicated that matrilysin-2 is a potent enzyme with a wide substrate specificity. In addition, it was found that matrilysin-2 is able to activate progelatinase B. Proteolytic activity of matrilysin-2 against all of these substrates was abolished by synthetic inhibitors and by tissue inhibitors of metalloproteinases. Expression analysis revealed that matrilysin-2 is detected not only in placenta and uterus but is widely expressed in malignant tumors from different sources as well as in diverse tumor cell lines. These data together with its broad spectrum of proteolytic activity, suggest that matrilysin-2 may play a role in some of the tissue-remodeling events associated with tumor progression.

Cloning and expression analysis of human bleomycin hydrolase, a cysteine proteinase involved in chemotherapy resistance.

A cDNA encoding human bleomycin hydrolase, a member of the cysteine proteinase family of proteins, has been cloned from a human brain cDNA library. The isolated cDNA contains an open reading frame coding for a polypeptide of 456 amino acids that contains all of the structural features characteristic of cysteine proteinases, including the cysteine, histidine, and asparagine residues that are essential for the catalytic properties of these enzymes. The deduced amino acid sequence for human bleomycin hydrolase shows 92, 40, and about 35% of identities with those determined for rabbit bleomycin hydrolase, yeast bleomycin hydrolase, and bacterial aminopeptidase C, respectively. Northern blot analysis of poly(A)+ RNAs isolated from a variety of human tissues demonstrated that human bleomycin hydrolase is expressed in all examined tissues, which is consistent with a putative role of this protein as a proteolytic enzyme involved in norman cellular protein degradation and turnover. Preliminary expression analysis of bleomycin hydrolase in different human tumors showed increased expression of the enzyme in a series of head and neck carcinomas when compared with paired adjacent normal mucosa. We also observed a variable degree of bleomycin hydrolase expression in different types of lymphoma, with low or undetectable levels in Hodgkin's disease samples and higher levels in Burkitt's lymphomas. These results are consistent with a proposed role for human bleomycin hydrolase in resistance of some tumor to bleomycin chemotherapy.

Identification of the major protein components in breast secretions from women with benign and malignant breast diseases.

The protein composition of breast secretions from 99 premenopausal women with benign or malignant breast diseases and from 70 control women without breast pathologies has been studied by using polyacrylamide gel electrophoresis. These fluids have been classified into two types according to their major polypeptide components. Type I fluids are defined by three major distinctive bands at Mr 44,000, 24,000, and 17,000, while those designated Type II present distinctive bands at Mr 80,000, 15,000, and 14,000. Amino acid sequencing and immunoblotting analysis demonstrated that proteins in Type I secretions correspond to Zn-alpha 2-glycoprotein, apolipoprotein D, and gross cystic disease fluid protein-15, while those from Type II fluids have been identified as lactoferrin, lysozyme, and alpha-lactalbumin. Most women (93%) without breast pathology and most patients (88%) with benign diseases had secretions with a Type I polypeptide pattern. By contrast, a large percentage (57%) of secretions from women with breast carcinoma presented a Type II protein pattern. Further studies with a large number of women will be useful for corroborating the potential clinical interest of breast fluid protein analysis.

Regulation of collagenase-3 expression in human breast carcinomas is mediated by stromal-epithelial cell interactions.

Collagenase-3 (MMP-13) is a recently identified member of the human matrix metalloproteinase gene family that is expressed in breast carcinomas and in articular cartilage from arthritic patients. Here, we have studied the cellular origin of this enzyme in breast carcinomas by in situ RNA hybridization, and we found that collagenase-3 is expressed by stromal cells immediately adjacent to epithelial tumor cells but not by the tumor cells themselves; nor is it expressed by the normal breast glandular epithelium. Consistent with this observation, coculture experiments using human fibroblasts and MCF-7 breast cancer cells revealed that conditioned medium from breast cancer cells stimulated the fibroblastic expression of collagenase-3 mRNA. In contrast, no stimulatory effect was observed when medium from fibroblast cells was added to breast cancer cells. These results strongly suggest that transcription of collagenase-3 in stromal cells is activated by diffusible factors released from epithelial breast cancer cells. A survey of a series of cytokines and growth factors known for their ability to induce collagenase-3 expression in human fibroblasts identified interleukin-1alpha and interleukin-1beta as potential candidates for inducing the expression of this MMP gene in breast carcinomas. According to these results, collagenase-3 should be included among the molecular factors that are detected during the stromal reaction to invasive breast cancer and that, by concerted action, may be essential for tumor growth and progression.

Growth inhibition of human breast cancer cells by 1,25-dihydroxyvitamin D3 is accompanied by induction of apolipoprotein D expression.

We have analyzed the effect of 1,25-dihydroxyvitamin D3 on the expression of the gene encoding apolipoprotein D (apoD), a protein component of the human plasma lipid transport system that is overproduced by a specific subset of breast carcinomas. Northern blot analysis revealed that 1,25-dihydroxyvitamin D3 strongly up-regulated apoD mRNA levels in T-47D human breast cancer cells in a time- and dose-dependent manner. The potency of this vitamin as an inducer of apoD expression was stronger than the effect observed for such steroid hormones as androgens and progesterone, described previously as hormonal up-regulators of apoD expression in these cells. A time course study demonstrated that the induction of apoD mRNA reached a level of 5-fold over the untreated cells after 48 h of incubation in the presence of 10(-7) M 1,25-dihydroxyvitamin D3. A dose-response analysis showed that a 10(-6) M concentration of this vitamin consistently induced a maximal accumulation of 7-fold over the control cells. Similar up-regulatory effects on the apoD gene expression were obtained by treatment of T-47D cells with 1,25-dihydroxyvitamin D3 analogues, including MC 903, which is relatively devoid of hypercalcemic side effects in clinical applications. Western blot analysis revealed that the inductive effect of 1,25-dihydroxyvitamin D3 was also reflected at the protein level as an increase of immunoreactive protein in the conditioned media of vitamin-treated cells. This increased expression of apoD was accompanied by an inhibition of cell growth and morphological changes in T-47D cells. By contrast, we did not detect any inductive effect of 1,25-dihydroxyvitamin D3 on apoD gene expression in MDA-MB-231 cells, which are refractory to the growth-inhibitory effects of this compound. On the basis of these results, we propose 1,25-dihydroxyvitamin D3 as an important regulator of the expression of the apoD gene in breast carcinomas. We also suggest that apoD may be of interest as a biochemical marker of the action of 1,25-dihydroxyvitamin D3 derivatives in current studies using these compounds as inhibitors of breast cancer cell growth or as chemotherapeutic agents in the prevention of breast cancer.

Identification and characterization of human MT5-MMP, a new membrane-bound activator of progelatinase a overexpressed in brain tumors.

A cDNA encoding a new member of the membrane-type (MT) matrix metalloproteinase (MMP) family has been identified and cloned from a human brain cDNA library. The isolated cDNA encodes a polypeptide of 645 amino acids that displays a similar domain organization as other MMPs, including a predomain with the activation locus, a zinc-binding site, and a hemopexin domain. The deduced amino acid sequence contains a COOH-terminal extension, rich in hydrophobic residues and similar in size to the equivalent domains identified in MT-MMPs. Immunofluorescence and Western blot analysis of COS-7 cells transfected with the isolated cDNA revealed that the encoded protein is localized in the plasma membrane. On the basis of these features, this novel human MMP has been called MT5-MMP because it represents the fifth member of the MT-MMP subfamily of MMPs. Fluorescent in situ hybridization experiments showed that the human MT5-MMP gene (MMP-24) maps to 20q11.2, a region frequently amplified in tumors from diverse sources. Northern blot analysis demonstrated that MT5-MMP is predominantly expressed in brain, kidney, pancreas, and lung. In addition, MT5-MMP transcripts were detected at high levels compared to normal brain tissue in a series of brain tumors, including astrocytomas and glioblastomas. The catalytic domain of MT5-MMP, produced in Escherichia coli as a fusion protein with glutathione S-transferase, exhibits a potent proteolytic activity against progelatinase A, leading to the generation of the Mr 62,000 active form of this enzyme. These data suggest that MT5-MMP may contribute to the activation of progelatinase A in tumor tissues, in which it is overexpressed, thereby facilitating tumor progression.

Cathepsin L2, a novel human cysteine proteinase produced by breast and colorectal carcinomas.

We have identified and cloned a new member of the papain family of cysteine proteinases from a human brain cDNA library. The isolated cDNA codes for a polypeptide of 334 amino acids that exhibits all of the structural features characteristic of cysteine proteinases, including the active site cysteine residue essential for peptide hydrolysis. Pairwise comparisons of this amino acid sequence with the remaining human cysteine proteinases identified to date showed a high percentage of identity (78%) with cathepsin L; the percentage of identity with all other members of the family was much lower (<40%). On the basis of these structural characteristics, we have tentatively called this novel protein cathepsin L2. The cDNA encoding the mature cathepsin L2 was expressed in Escherichia coli, and after purification, the recombinant protein was able to degrade the synthetic peptide benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methylcoumarin, which is commonly used as a substrate for cysteine proteinases. Cathepsin L2 proteolytic activity on this substrate was abolished by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane, an inhibitor of cysteine proteinases, thus providing additional evidence that the isolated cDNA encodes a functional cysteine proteinase. Northern blot analysis of polyadenylated RNAs isolated from a variety of human tissues demonstrated that cathepsin L2 is predominantly expressed in the thymus and testis. This finding is in marked contrast with the wide tissue distribution of most cysteine proteinases characterized to date, including cathepsin L, and suggests that cathepsin L2 may play a specialized role in the thymus and testis. Expression analysis of cathepsin L2 in human tumors revealed a widespread expression in colorectal and breast carcinomas but not in normal colon or mammary gland or in peritumoral tissues. Cathepsin L2 was also expressed by colorectal and breast cancer cell lines as well as by some tumors of diverse origin, including ovarian and renal carcinomas. These results open the possibility that this novel enzyme may be involved in tumor processes, as already reported for other cysteine proteinases, including cathepsin L.

Molecular cloning of a novel membrane-type matrix metalloproteinase from a human breast carcinoma.

A new member of the matrix metalloproteinase (MMP) family of enzymes has been cloned from a human breast carcinoma cDNA library. The isolated cDNA contains an open reading frame 1554 bp long, encoding a polypeptide of 518 amino acids. The predicted amino acid sequence displays a similar domain organization as the remaining MMPs, including a prodomain with the activation locus, the zinc-binding site, and the hemopexin domain. In addition, it contains a C-terminal extension, rich in hydrophobic residues and similar in size to those present in the different membrane-type MMPs (MT-MMPs) identified to date. On the basis of these structural characteristics, this novel MMP has been tentatively called MT4-MMP, because it represents the fourth member of this subclass of MMPs characterized mainly by the occurrence of putative transmembrane domain in their amino acid sequences. MT4-MMP also contains a nine-residue insertion between the propeptide and the catalytic domain, which is a common feature of MT-MMPs and stromelysin-3. This amino acid sequence insertion ends with the consensus sequence R-X-R/K-R, which seems to be essential in the activation of these proteinases by furin. Northern blot analysis of polyadenylated RNAs isolated from a variety of human tissues revealed that the MT4-MMP gene (MMP-17) is expressed mainly in the brain, leukocytes, the colon, the ovary, and the testis. The expression of MT4-MMP in leukocytes together with its putative membrane localization suggest that this enzyme could be involved in the activation of membrane-bound precursors of growth factors or inflammatory mediators such as tumor necrosis factor-alpha. In addition, MT4-MMP transcripts were detected in all breast carcinomas, as well as in all breast cancer cell lines analyzed in the present work. On the basis of these expression data in breast tumors, a potential role for human MT4-MMP in the tumoral process is also suggested.

Structure and expression in breast tumors of human TIMP-3, a new member of the metalloproteinase inhibitor family.

A new member of the metalloproteinase inhibitor family of proteins has been cloned from a complementary DNA library derived from a human breast tumor. The isolated complementary DNA contains an open reading frame 633 base pairs long, encoding a polypeptide of 211 amino acids, which has been called tissue inhibitor of metalloproteinase 3 (TIMP-3). This protein displays low sequence similarity to the previously known human TIMPs but shows a high degree of similarity with chicken inhibitor of metalloproteinase 3, a recently described metalloproteinase inhibitor stimulated during oncogenic transformation of chicken fibroblasts and with the ability to promote some phenotypic properties of transformed cells. Northern blot analysis of RNA from human tissues revealed that the TIMP-3 gene is expressed in placenta and uterus but not in liver and ovary. In addition, TIMP-3 transcripts were detected in all breast carcinomas examined. On the basis of these expression data in breast tumors, together with its high degree of structural homology with chicken inhibitor of metalloproteinase 3, a possible role for human TIMP-3 in the regulation of connective tissue turnover and remodeling is proposed.

Human MT6-matrix metalloproteinase: identification, progelatinase A activation, and expression in brain tumors.

The localization of proteolytic enzymes at the cell surface is a widely used strategy for facilitating tumor invasion. In this study, we have cloned a new member of the membrane-type subfamily of matrix metalloproteinases (MT-MMPs), a group of enzymes associated with tumor progression. The cloned cDNA encodes a protein of 562 amino acids with a domain organization similar to that of other MT-MMPs, including a prodomain with a cysteine switch, a catalytic domain with the zinc-binding site, a hemopexin-like domain, and a COOH-terminal extension rich in hydrophobic residues. The predicted protein sequence also contains a short insertion of basic residues located between the propeptide and the catalytic domain and involved in the proteolytic activation of MT-MMPs by furin-like enzymes. Furthermore, immunofluorescence and Western blot analysis of COS-7 cells transfected with the isolated cDNA revealed that the encoded protein is localized at the cell surface. Based on these properties, this novel human matrix metalloproteinase has been called MT6-MMP because it is the sixth identified member of this subfamily of matrix metalloproteinase. Cotransfection of expression plasmids encoding MT6-MMP and progelatinase A resulted in activation of COS-7-secreted progelatinase A, as demonstrated by gelatin zymography. In contrast, transfection of progelatinase A cDNA alone did not lead to the activation of the proenzyme. Northern blot analysis of polyadenylated RNAs isolated from human tissues demonstrated that MT6-MMP is predominantly expressed in leukocytes, lung, and spleen. MT6-MMP was also detected at high levels in SW480 colon carcinoma cells as well as in some anaplastic astrocytomas and glioblastomas, but not in normal colon or brain or in meningiomas. On the basis of these results, we propose that MT6-MMP may facilitate tumor progression through its ability to activate progelatinase A at the membrane of cells from colon carcinomas or brain tumors.

Collagenase-3 expression in breast myofibroblasts as a molecular marker of transition of ductal carcinoma in situ lesions to invasive ductal carcinomas.

Collagenase-3 (matrix metalloproteinase 13; MMP-13), a protease originally identified in breast carcinoma, is characterized by a potent degrading activity against a wide spectrum of extracellular matrix proteins. The aims of this study were to localize and identify the MMP-13-expressing cells in invasive human breast carcinoma and to evaluate the role of MMP-13 in transition to invasive lesions by studying ductal carcinoma in situ (DCIS). We found expression of MMP-13 in stromal fibroblast-like cells in all 21 invasive ductal carcinomas studied and in 4 of 9 invasive lobular carcinomas. In most carcinomas, expression of MMP-13 was limited to small stromal foci in the tumor area. Combined in situ hybridization and immunohistochemistry showed coexpression of alpha-smooth muscle actin immunoreactivity and MMP-13 mRNA in myofibroblasts. In contrast, cytokeratin-positive cancer cells, alpha-smooth muscle actin-positive vascular smooth muscle cells, CD68-positive macrophages, and CD31-positive endothelial cells were all MMP-13 mRNA negative. In situ hybridization for MMP-13 in 17 DCIS lesions revealed expression in 10 cases. Immunohistochemical analysis of all DCIS cases identified microinvasion in 8 of the 17 lesions. Seven of the eight lesions with microinvasion were MMP-13 positive. Further analysis showed that MMP-13 expression was often associated with the microinvasive events. This particular expression pattern was unique for MMP-13 among other MMPs analyzed, including MMP-2, -11, and -14. We conclude that MMP-13 is primarily expressed by myofibroblasts in human breast carcinoma and that expression in DCIS lesions often is associated with microinvasive events. On the basis of these data, we propose that MMP-13 may play an essential role during transition of DCIS lesions to invasive ductal carcinomas.