SP1-mediated downregulation of ADAMTS3 gene expression in osteosarcoma models

ADAMTS3 is a member of procollagen N-proteinase subfamily of ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) gene family. It has an important function in the procollagen maturation process. The removal of N-peptidases is required for the accurate processing of fibrillar collagens. Otherwise, several disorders can occur that is related with the collagenous tissues. ADAMTS3 mainly maturates type II collagen molecule which is the main component of the bone and cartilage. There are several expression studies about ADAMTS3 gene however its transcriptional regulation has not been lightened up, yet. Here we first time cloned and functionally analyzed the promoter region of ADAMTS3 gene, approximately 1380 bp upstream of the transcription start site. Transient transfection experiments showed that all truncated promoter constructs are active and 171 bp fragment is sufficient to activate gene expression in both Saos-2 and MG63 cells. In silico analysis showed that ADAMTS3 has a TATA-less promoter and contains several SP1/GC box binding motifs and a CpG island. Therefore we mainly investigated the SP1 dependent regulation of ADAMTS3 promoter. SP1 downregulated ADAMTS3 transcriptional activity. As consistent with the transcriptional activity, mRNA, and protein expression levels were also decreased by SP1. On the other hand, functional binding of the SP1 on multiple regions of ADAMTS3 promoter was confirmed by EMSA studies. As ADAMTS3 is responsible for the collagen maturation and biosynthesis, further we investigated the effect of SP1 on type I-II and III collagen gene expressions. We point out that SP1 increased type II and III collagen expression and in contrast decreased type I collagen expression levels in Saos-2 cells. mRNA expression level was decreased for all collagen types in MG63 model. Decrease in the type II collagen expression was also demonstrated at the protein level by SP1. Collectively these results provide first findings for the SP1-related transcriptional regulation of ADAMTS3 and collagen genes in osteosarcoma cell lines.

A disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4) cleaves Reelin in an isoform-dependent manner

Reelin is a glycoprotein essential for brain development and functions. Reelin is subject to specific proteolysis at two distinct (N-t and C-t) sites, and these cleavages significantly diminish Reelin activity. The decrease of Reelin activity is detrimental for brain function, but the protease that catalyzes specific cleavage of Reelin remains elusive. Here we found that a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4) cleaves Reelin in an isoform-specific manner. Among ADAMTS-4 isoforms, p50 cleaves the N-t site only, while p75 cleaves both sites. This is the first report identifying a protease that can specifically cleave Reelin.

[Aggrecanases and osteoarthritis]

Osteoarthritis is mainly caused by the degenerative changes of cartilage and cartilage extracellular matrix, while Aggrecanases degradate Proteoglycans which are the major components of cartilage. This review includes three aspects: (1) We have concluded the major enzymes(ADAMTS-4 and ADAMTS-5) which regulate the metabolism of cartilage extracellular matrix. Meanwhile, we have summarized the structure of aggrecanases(ADAMTS-4 and ADAMTS-5) and introduced the function of each regional structure; (2) We have concluded the way cytokines and glycosaminoglycans regulate the metabolism of aggrecanases, and discussed the regulation and control principle of cytokines and glycosaminoglycan; (3) We have summarized the majority of inhibitors to the aggrecanases, introduced the endogenic inhibitors, and put our emphasis on the extrinsic inhibitors (chelating agents, polypeptides and so on). Through deeper research on the enzymes, it will help us further understand the pathogenesis of osteoarthritis, and open up new avenues to clinical treatment.

Proteolytic activities of human ADAMTS-5: comparative studies with ADAMTS-4

Aggrecanases have been characterized as proteinases that cleave the Glu373-Ala374 bond of the aggrecan core protein, and they are multidomain metalloproteinases belonging to the ADAMTS (adamalysin with thrombospondin type 1 motifs) family. The first aggrecanases discovered were ADAMTS-4 (aggrecanase 1) and ADAMTS-5 (aggrecanase 2). They contain a zinc catalytic domain followed by non-catalytic ancillary domains, including a disintegrin domain, a thrombospondin domain, a cysteine-rich domain, and a spacer domain. In the case of ADAMTS-5, a second thrombospondin domain follows the spacer domain. We previously reported that the non-catalytic domains of ADAMTS-4 influence both its extracellular matrix interaction and proteolytic abilities. Here we report the effects of these domains of ADAMTS-5 on the extracellular matrix interaction and proteolytic activities and compare them with those of ADAMTS-4. Although the spacer domain was critical for ADAMTS-4 localization in the matrix, the cysteine-rich domain influenced ADAMTS-5 localization. Similar to previous reports of other ADAMTS family members, very little proteolytic activity was detected with the ADAMTS-5 catalytic domain alone. The sequential inclusion of each carboxyl-terminal domain enhanced its activity against aggrecan, carboxymethylated transferrin, fibromodulin, decorin, biglycan, and fibronectin. Both ADAMTS-4 and -5 had a broad optimal activity at pH 7.0-9.5. Aggrecanolytic activities were sensitive to the NaCl concentration, but activities on non-aggrecan substrates, e.g. carboxymethylated transferrin, were not affected. Although ADAMTS-4 and ADAMTS-5 had similar general proteolytic activities, the aggrecanase activity of ADAMTS-5 was at least 1,000-fold greater than that of ADAMTS-4 under physiological conditions. Our studies suggest that ADAMTS-5 is a major aggrecanase in cartilage metabolism and pathology.

Substrate Conformation Modulates Aggrecanase (ADAMTS-4) Affinity and Sequence Specificity

Protease-substrate interactions are governed by a variety of structural features. Although the substrate sequence specificities of numerous proteases have been established, "topological specificities," whereby proteases may be classified based on recognition of distinct three-dimensional structural motifs, have not. The aggrecanase members of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family cleave a variety of proteins but do not seem to possess distinct sequence specificities. In the present study, the topological substrate specificity of ADAMTS-4 (aggrecanase-1) was examined using triple-helical or single-stranded poly(Pro) II helical peptides. Substrate topology modulated the affinity and sequence specificity of ADAMTS-4 with K(m) values indicating a preference for triple-helical structure. In turn, non-catalytic ADAMTS-4 domains were critical for hydrolysis of triple-helical and poly(Pro) II helical substrates. Comparison of ADAMTS-4 with MMP-1 (collagenase 1), MMP-13 (collagenase 3), trypsin, and thermolysin using triple-helical peptide (THP) and single-stranded peptide (SSP) substrates demonstrated that all five proteases possessed efficient "triple-helical peptidase" activity and fell into one of two categories: (k(cat)/K(m))(SSP) > (k(cat)/K(m))(THP) (thermolysin, trypsin, and MMP-13) or (k(cat)/K(m))(THP) > or = (k(cat)/K(m))(SSP) and (K(m))(SSP) > (K(m))(THP) (MMP-1 and ADAMTS-4). Overall these results suggest that topological specificity may be a guiding principle for protease behavior and can be utilized to design specific substrates and inhibitors. The triple-helical and single-stranded poly(Pro) II helical peptides represent the first synthetic substrates successfully designed for aggrecanases.

Effects of covalently attached chondroitin sulfate on aggrecan cleavage by ADAMTS-4 and MMP-13

Aggrecan is degraded by several aggrecanase-1 (ADAMTS-4) isoforms differing in the number of sulfated glycosaminoglycan (sGAG)-binding motifs. ADAMTS-4 and MMPs cleave aggrecan more efficiently within the chondroitin sulfate (CS)-rich region than the interglobular domain (IGD). We investigated the influence of CS on aggrecan core protein cleavage by ADAMTS-4 (p68) and (p40) as well as MMP-13, which has no recognizable GAG-binding sites. Chondroitinase ABC-treated cartilage aggrecan was cleaved with ADAMTS-4 (p68) less efficiently than CS-substituted aggrecan within the CS-2 domain. Keratanase-treated aggrecan exhibited reduced IGD cleavage, but when both CS and KS were removed, the IGD cleavage was restored. This result suggests that KS in the IGD may compete with CS for ADAMTS-4 (p68) binding. In the absence of KS, however, p68 binding was shifted to the CS-2 domain. CS-deficient full-length recombinant aggrecan (rbAgg) was produced by chondroitinase ABC treatment, or by expression in the xylosyltransferase-deficient CHO-pgsA745 cell line. When digested with the ADAMTS-4 (p68), each of these preparations exhibited reduced CS-2 domain cleavage compared to CS-substituted CHO-K1 cell-derived aggrecan. Additionally, CS-deficient rbAgg showed increased IGD scission prior to cleavage within the CS-2 domain. ADAMTS-4 (p40) readily cleaved both rbAggs within the IGD, but cleaved poorly within the CS-2 domain, indicating little CS dependence. MMP-13, in contrast, cleaved the CS region and the IGD of both CS-substituted and CS-deficient rbAgg equally well. These data indicate that covalently bound CS enhances ADAMTS-4-mediated cleavage within the CS-rich region. MMP-13 also cleaves preferentially within the CS-region, but by an apparently CS-independent mechanism.

An alternative spliced transcript of ADAMTS4 is present in human synovium from OA patients

The major proteoglycan of articular cartilage aggrecan is a substrate for ADAMTS4. RT-PCR analysis of human osteoarthritic (OA) synovial co-cultures using oligonucleotide primers designed to amplify across the exon 8/9 junction of human ADAMTS4 resulted in the amplification of two products, the expected product and a smaller product missing 161 bp from the 5' end of exon 9, the result of alternative splicing in which exon 8 joins to a cryptic 3' splice site within exon 9. The protein produced would be identical to human ADAMTS4 up to Arg(696), and would have a new C-terminal domain with no commonality with the ADAMTS4 spacer domain. Changes in the C-terminal domain of ADAMTS4 may alter its substrate specificity.

ADAMTS-4 (aggrecanase-1): N-Terminal activation mechanisms

ADAMTS-4 (aggrecanase 1) is synthesized as a latent precursor protein that may require activation through removal of its prodomain before it can exert catalytic activity. We examined various proteinases as well as auto-activation under a wide range of conditions for removal of the prodomain and induction of enzymatic activity. The proprotein convertases, furin, PACE4, and PC5/6 efficiently removed the prodomain through cleavage at Arg(212)/Phe(213), generating an active enzyme. Of a broad range of proteases evaluated, only MMP-9 and trypsin were capable of removing the prodomain. In the presence of mercuric compounds, removal of the prodomain through autocatalysis was not observed, nor was it observed at temperatures from 22 to 65 degrees C, at ionic strengths from 0.1 to 1M, or at acidic/neutral pH. At basic pH 8-10, removal of the prodomain by autocatalysis occurred, generating an active enzyme. In conclusion, the pro-form of ADAMTS-4 is not catalytically active and only a limited number of mechanisms mediate its N-terminal activation.

Domains and Maturation Processes That Regulate the Activity of ADAMTS-2, a Metalloproteinase Cleaving the Aminopropeptide of Fibrillar Procollagens Types I–III and V

Processing of fibrillar collagens is required to generate collagen monomers able to self-assemble into elongated and cylindrical collagen fibrils. ADAMTS-2 belongs to the "A disintegrin and metalloproteinase with thrombospondin type 1 motifs" (ADAMTS) family. It is responsible for most of the processing of the aminopropeptide of type I procollagen in the skin, and it also cleaves type II and type III procollagens. ADAMTS are complex secreted enzymes that are implicated in various physiological and pathological processes. Despite accumulating evidence indicating that their activity is regulated by ancillary domains, additional information is required for a better understanding of the specific function of each domain. We have generated 17 different recombinant forms of bovine ADAMTS-2 and characterized their processing, activity, and cleavage specificity. The results indicated the following: (i) activation of the ADAMTS-2 zymogen involves several cleavages, by proprotein convertases and C-terminal processing, and generates at least seven distinct processed forms; (ii) the C-terminal domain negatively regulates enzyme activity, whereas two thrombospondin type 1 repeats are enhancer regulators; (iii) the 104-kDa form displays the highest aminoprocollagen peptidase activity on procollagen type I; (iv) ADAMTS-2 processes the aminopropeptide of alpha1 type V procollagen homotrimer at the end of the variable domain; and (v) the cleaved sequence (PA) is different from the previously described sites ((P/A)Q) for ADAMTS-2, redefining its cleavage specificity. This finding and the existence of multiple processed forms of ADAMTS-2 strongly suggest that ADAMTS-2 may be involved in function(s) other than processing of fibrillar procollagen types I-III.

Regulated Expression of ADAMTS Family Members in Follicles and Cumulus Oocyte Complexes: Evidence for Specific and Redundant Patterns During Ovulation1

Protease cascades are essential for many biological events, including the LH-induced process of ovulation. ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin-like repeats-1) is expressed and hormonally regulated in the ovary by LH and the progesterone receptor. To determine whether other family members might be expressed and regulated in the rodent ovary, those closely related to ADAMTS1 (ADAMTS4 and ADAMTS5) were analyzed in the mouse ovary by reverse transcription-polymerase chain reaction as well as by Western blot, immunohistochemical, and immunocytochemical analyses using highly specific antibodies. Prior to ovulation, ADAMTS4 and ADAMTS5 were coexpressed in granulosa cells of most follicles, whereas ADAMTS5 was also present in granulosa cells of atretic follicles. Following ovulation, ADAMTS1 and ADAMTS4 (but not ADAMTS5) were expressed in multiple cell types, including those within the highly vascular ovulation cone that marks the site of follicle rupture, endothelial cells of newly forming corpora lutea, and cumulus cells within the ovulated cumulus cell-oocyte complex (COC). Versican, a substrate for ADAMTS1 and ADAMTS4, colocalized with these proteases and hylauronan on the cumulus cell surface. To further characterize induction of these proteases and associated molecules, COCs and granulosa cells were isolated from preovulatory follicles and treated with FSH. In expanded COCs and differentiated granulosa cells, FSH induced expression of ADAMTS4 and versican message and protein, whereas increased levels of ADAMTS1 protein was observed in the media of granulosa cells where it was stabilized by heparin in this in vitro system. These studies provide the first evidence that ADAMTS1, ADAMTS4, and ADAMTS5 are expressed in spatiotemporal patterns that suggest distinct as well as some overlapping functions that relate to the broad expression pattern of versican in granulosa cells of small follicles, expanded COCs, and endothelial cells of the mouse ovary.

Novel Types of Mutation Responsible for the Dermatosparactic Type of Ehlers–Danlos Syndrome (Type VIIC) and Common Polymorphisms in the ADAMTS2 Gene

Ehlers-Danlos syndrome (EDS) type VIIC, or dermatosparactic type, is a recessively inherited connective tissue disorder characterized, among other symptoms, by an extreme skin fragility resulting from mutations inactivating ADAMTS-2, an enzyme excising the aminopropeptide of procollagens type I, II, and III. All previously described mutations create premature stop codons leading to a marked reduction in the level of mRNA. In this study, we analyzed the ADAMTS2 cDNA sequences from five patients displaying clinical and/or biochemical features consistent with a diagnosis of either typical or potentially mild form of EDS type VIIC. Three different alterations were detected in the two patients with typical EDS type VIIC. The first patient was homozygous for a genomic deletion causing an in-frame skipping of exons 3-5 in the transcript. In the second patient, the allele inherited from the mother lacks exon 3, generating a premature stop codon, whereas the paternal allele has a genomic deletion resulting in an in-frame skipping of exons 14-16 at the mRNA level. Although the exons 3-5 or 14-16 encode protein domains that have not been previously recognized as crucial for ADAMTS-2 activity, the aminoprocollagen processing was strongly impaired in vitro and in vivo, providing evidence for the requirement of these domains for proper enzyme function. The three other patients with a phenotype with some resemblance to EDS type VIIC only had silent and functionally neutral variations also frequently found in a normal population.

ADAMTS4 (Aggrecanase-1) Interaction with the C-terminal Domain of Fibronectin Inhibits Proteolysis of Aggrecan

ADAMTS4 (aggrecanase-1), a secreted enzyme belonging to the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) gene family, is considered to play a key role in the degradation of cartilage proteoglycan (aggrecan) in osteoarthritis and rheumatoid arthritis. To clone molecules that bind to ADAMTS4, we screened a human chondrocyte cDNA library by the yeast two-hybrid system using the ADAMTS4 spacer domain as bait and obtained cDNA clones derived from fibronectin. Interaction between ADAMTS4 and fibronectin was demonstrated by chemical cross-linking. A yeast two-hybrid assay and solid-phase binding assay using wild-type fibronectin and ADAMTS4 and their mutants demonstrated that the C-terminal domain of fibronectin is capable of binding to the C-terminal spacer domain of ADAMTS4. Wild-type ADAMTS4 was co-localized with fibronectin as determined by confocal microscopy on the cell surface of stable 293T transfectants expressing ADAMTS4, although ADAMTS4 deletion mutants, including Delta Sp (Delta Arg(693)-Lys(837), lacking the spacer domain), showed negligible localization. The aggrecanase activity of wild-type ADAMTS4 was dose-dependently inhibited by fibronectin (IC(50) = 110 nm), whereas no inhibition was observed with Delta Sp. The C-terminal 40-kDa fibronectin fragment also inhibited the activity of wild-type ADAMTS4 (IC(50) = 170 nm). These data demonstrate for the first time that the aggrecanase activity of ADAMTS4 is inhibited by fibronectin through interaction with their C-terminal domains and suggest that this extracellular regulation mechanism of ADAMTS4 activity may be important for the degradation of aggrecan in arthritic cartilage.

Biosynthetic Processing of the Pro-α1(V)Pro-α2(V)Pro-α3(V) Procollagen Heterotrimer

Type V collagen is a quantitatively minor fibrillar collagen comprised of different chain compositions in different tissues. The most widely distributed form, an alpha1(V)2alpha2(V) heterotrimer, regulates the physical properties of type I/V heterotypic collagen fibrils via partially processed NH2-terminal globular sequences. A less characterized alpha1(V)alpha2(V)alpha3(V) heterotrimer has a much more limited distribution of expression and unknown function(s). We characterized the biosynthetic processing of pro-alpha1(V)2pro-alpha2(V) procollagen previously and showed it to differ in important ways from biosynthetic processing of the major fibrillar procollagens I-III. Here we have successfully produced recombinant pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers. We use these, and mouse embryo fibroblasts doubly homozygous null for the Bmp1 gene, which encodes the metalloproteinase bone morphogenetic protein-1 (BMP-1), and for a gene encoding the closely related metalloproteinase mammalian Tolloid-like 1, to characterize biosynthetic processing of pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers, thus completing characterization of type V collagen biosynthetic processing. Whereas pro-alpha1(V) and pro-alpha2(V) processing in pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers is similar to that which occurs in pro-alpha1(V)2pro-alpha2(V) heterotrimers, the processing of pro-alpha3(V) by BMP-1 occurs at an unexpected site within NH2-terminal globular sequences. We also demonstrate that, despite similarities in NH2-terminal domain structures, pro-alpha2(V) NH2-terminal globular sequences are not cleaved by ADAMTS-2, the metalloproteinase that cleaves the N-propeptides of the major fibrillar procollagen chains.

Proprotein convertase furin interacts with and cleaves pro-ADAMTS4 (Aggrecanase-1) in the trans-Golgi network

A member of the A disintegrin and metalloproteinase domain with thrombospondin type-1 motifs (ADAMTS-4) protease family can efficiently cleave aggrecan at several sites detected in joints of osteoarthritic patients. Although recent studies have shown that removal of the prodomain of ADAMTS4 is critical for its ability to degrade aggrecan, the cellular mechanisms for its processing and trafficking remain unclear. In this study, by using both furin-specific inhibitor and RNA interference technique, we demonstrate that furin plays an important role in the intracellular removal of ADAMTS4 prodomain. Further, we demonstrate that proADAMTS4 can be processed by means of multiple furin recognition sites: (206)RPRR(209), (209)RAKR(212), or (211)KR(212). The processing of proADAMTS4 was completely blocked by brefeldin A treatment, suggesting that processing occurs in the trans-Golgi network. Indeed, ADAMTS4 is co-localized with furin in trans-Golgi network. Interestingly, the pro form of ADAMTS4, not its mature one, co-precipitates with furin, suggesting that furin physically interacts with the prodomain of ADAMTS-4. In addition, our evidence suggests that a furin-independent pathway may also contribute to the activation of ADAMTS4. These results indicate that the activation mechanism for ADAMTS4 can be targeted for therapeutical intervention against this enzyme.

Prospects and limitations of the rational engineering of fibrillar collagens

Recombinant collagens are attractive proteins for a number of biomedical applications. To date, significant progress was made in the large-scale production of nonmodified recombinant collagens; however, engineering of novel collagen-like proteins according to customized specifications has not been addressed. Herein we investigated the possibility of rational engineering of collagen-like proteins with specifically assigned characteristics. We have genetically engineered two DNA constructs encoding multi-D4 collagens defined as collagen-like proteins, consisting primarily of a tandem of the collagen II D4 periods that correspond to the biologically active region. We have also attempted to decrease enzymatic degradation of novel collagen by mutating a matrix metalloproteinase 1 cleavage site present in the D4 period. We demonstrated that the recombinant collagen alpha-chains consisting predominantly of the D4 period but lacking most of the other D periods found in native collagen fold into a typical collagen triple helix, and the novel procollagens are correctly processed by procollagen N-proteinase and procollagen C-proteinase. The nonmutated multi-D4 collagen had a normal melting point of 41 degrees C and a similar carbohydrate content as that of control. In contrast, the mutant multi-D4 collagen had a markedly lower thermostability of 36 degrees C and a significantly higher carbohydrate content. Both collagens were cleaved at multiple sites by matrix metalloproteinase 1, but the rate of hydrolysis of the mutant multi-D4 collagen was lower. These results provide a basis for the rational engineering of collagenous proteins and identifying any undesirable consequences of altering the collagenous amino acid sequences.

Transforming growth factor-beta induces secretion of activated ADAMTS-2. A procollagen III N-proteinase

The metalloproteinase ADAMTS-2 has procollagen I N-proteinase activity capable of cleaving procollagens I and II N-propeptides in vitro, whereas mutations in the ADAMTS-2 gene in dermatosparaxis and Ehlers-Danlos syndrome VIIC show this enzyme to be responsible in vivo for most biosynthetic processing of procollagen I N-propeptides in skin. Yet despite its important role in the regulation of collagen deposition, information regarding regulation and substrate specificity of ADAMTS-2 has remained sparse. Here we demonstrate that ADAMTS-2 can, like the procollagen C-proteinases, be regulated by transforming growth factor-beta 1 (TGF-beta 1), with implications for mechanisms whereby this growth factor effects net increases in formation of extracellular matrix. TGF-beta 1 induced ADAMTS-2 mRNA approximately 8-fold in MG-63 osteosarcoma cells in a dose- and time-dependent, cycloheximide-inhibitable manner, which appeared to operate at the transcriptional level. Secreted ADAMTS-2 protein induced by TGF-beta 1 was 132 kDa and was identical in size to the fully processed, active form of the protease. Biosynthetic processing of ADAMTS-2 to yield the 132-kDa form is shown to be a two-step process involving sequential cleavage by furin-like convertases at two sites. Surprisingly, purified recombinant ADAMTS-2 is shown to cleave procollagen III N-propeptides as effectively as those of procollagens I and II, whereas processing of procollagen III is shown to be decreased in Ehlers-Danlos VIIC. Thus, the dogma that procollagen I and procollagen III N-proteinase activities are provided by separate enzymes appears to be false, whereas the phenotypes of dermatosparaxis and Ehlers-Danlos VIIC may arise from defects in both type I and type III collagen biosynthesis.

The globular domain of the proalpha 1(I) N-propeptide is not required for secretion, processing by procollagen N-proteinase, or fibrillogenesis of type I collagen in mice

The globular domain in the NH(2)-terminal propeptide (N-propeptide) of the proalpha1(I) chain is largely encoded by exon 2 of the Col1a1 gene and has been implicated in a number of processes that are involved in the biogenesis, maturation, and function of type I collagen. These include intracellular chain association, transcellular transport and secretion, proteolytic processing of the precursor, feedback regulation of synthesis, and control of fibrillogenesis. However, none of these proposed functions has been firmly established. To evaluate the function of this procollagen domain we have used a targeted mutagenesis approach to generate mice that lack exon 2 in the Col1a1 gene. Mouse lines were established on both a mixed 129 OlaHsd/Sv and C57BL/6 background and a pure 129 OlaHsd/Sv background. Adult mice on the mixed background are normal in appearance and are fertile. To the extent that they have been studied, procollagen synthesis, secretion, and proteolytic processing are normal in these mice, and collagen fibrillogenesis is only slightly altered. However, breeding of heterozygous mutant mice on the 129 background generated homozygous mutants at only 64% of the expected frequency. These findings suggest that although the N-propeptide is not essential for collagen biogenesis in mice it may play some essential role during embryonic development.

Characterization of ADAMTS14, a novel member of the ADAMTS metalloproteinase family

ADAMTS (a disintegrin-like and metalloproteinase domain with thrombospondin type 1 modules) proteins constitute a family of zinc metalloproteinases which target and process extracellular matrix proteins. We cloned and characterized a novel human ADAMTS gene, ADAMTS14, which is located on human chromosome 10q2. ADAMTS14 exhibits the characteristic multidomain structure of ADAMTS proteins including four thrombospondin modules and shows highest similarity to ADAMTS3 and ADAMTS2. By RT-PCR analysis we demonstrated that ADAMTS14 is expressed in human retina and also at low levels in adult brain, lung and placenta.

Procollagen II amino propeptide processing by ADAMTS-3. Insights on dermatosparaxis

The amino and carboxyl propeptides of procollagens I and II are removed by specific enzymes as a prerequisite for fibril assembly. Null mutations in procollagen I N-propeptidase (ADAMTS-2) cause dermatosparaxis in cattle and the Ehlers-Danlos syndrome (dermatosparactic type) in humans by preventing proteolytic excision of the N-propeptide of procollagen I. We have found that procollagen II is processed normally in dermatosparactic nasal cartilage, suggesting the existence of another N-propeptidase(s). We investigated such a role for ADAMTS-3 in Swarm rat chondrosarcoma RCS-LTC cells, which fail to process the procollagen II N-propeptide. Stable transfection of RCS-LTC cells with bovine ADAMTS-2 or human ADAMTS-3 partially rescued the processing defect, suggesting that ADAMTS-3 has procollagen II N-propeptidase activity. Human skin and skin fibroblasts showed 30-fold higher mRNA levels of ADAMTS-2 than ADAMTS-3, whereas ADAMTS-3 mRNA was 5-fold higher than ADAMTS-2 mRNA in human cartilage. We propose that both ADAMTS-2 and ADAMTS-3 process procollagen II, but ADAMTS-3 is physiologically more relevant, given its preferred expression in cartilage. The findings provide an explanation for the sparing of cartilage in dermatosparaxis and, perhaps, for the relative sparing of some procollagen I-containing tissues.

Human Ehlers-Danlos syndrome type VII C and bovine dermatosparaxis are caused by mutations in the procollagen I N-proteinase gene

Ehlers-Danlos syndrome (EDS) type VIIC is a recessively inherited connective-tissue disorder, characterized by extreme skin fragility, characteristic facies, joint laxity, droopy skin, umbilical hernia, and blue sclera. Like the animal model dermatosparaxis, EDS type VIIC results from the absence of activity of procollagen I N-proteinase (pNPI), the enzyme that excises the N-propeptide of type I and type II procollagens. The pNPI enzyme is a metalloproteinase containing properdin repeats and a cysteine-rich domain with similarities to the disintegrin domain of reprolysins. We used bovine cDNA to isolate human pNPI. The human enzyme exists in two forms: a long version similar to the bovine enzyme and a short version that contains the Zn++-binding catalytic site but lacks the entire C-terminal domain in which the properdin repeats are located. We have identified the mutations that cause EDS type VIIC in the six known affected human individuals and also in one strain of dermatosparactic calf. Five of the individuals with EDS type VIIC were homozygous for a C-->T transition that results in a premature termination codon, Q225X. Four of these five patients were homozygous at three downstream polymorphic sites. The sixth patient was homozygous for a different transition that results in a premature termination codon, W795X. In the dermatosparactic calf, the mutation is a 17-bp deletion that changes the reading frame of the message. These data provide direct evidence that EDS type VIIC and dermatosparaxis result from mutations in the pNPI gene.

cDNA cloning and expression of bovine procollagen I N-proteinase: a new member of the superfamily of zinc-metalloproteinases with binding sites for cells and other matrix components

Procollagen N-proteinase (EC 3.4.24.14) cleaves the amino-propeptides in the processing of type I and type II procollagens to collagens. Deficiencies of the enzyme cause dermatosparaxis in cattle and sheep, and they cause type VIIC Ehlers-Danlos syndrome in humans, heritable disorders characterized by accumulation of pNcollagen and severe skin fragility. Amino acid sequences for the N-proteinase were used to obtain cDNAs from bovine skin. Three overlapping cDNAs had an ORF coding for a protein of 1205 residues. Mammalian cells stably transfected with a complete cDNA secreted an active recombinant enzyme that specifically cleaved type I procollagen. The protein contained zinc-binding sequences of the clan MB of metallopeptidases that includes procollagen C-proteinase/BMP-1. The protein also contained four repeats that are homologous to domains found in thrombospondins and in properdin and that can participate in complex intermolecular interactions such as activation of latent forms of transforming growth factor beta or the binding to sulfatides. Therefore, the enzyme may play a role in development that is independent of its role in collagen biosynthesis. This hypothesis was supported by the observation that in some tissues the levels of mRNA for the enzyme are disproportionately high relative to the apparent rate of collagen biosynthesis.

Characterization and partial amino acid sequencing of a 107-kDa procollagen I N-proteinase purified by affinity chromatography on immobilized type XIV collagen

Procollagen I N-proteinase (EC 3.4.24.14), the enzyme that specifically processes type I and type II procollagens to collagen, was isolated from extracts of fetal calf skin. After two chromatographic steps on concanavalin A-Sepharose and heparin-Sepharose, the semi-purified preparation was used to produce monoclonal antibodies. One reacting antibody was found to recognize not the enzyme itself but type XIV collagen on which the enzyme was bound. This binding, highly sensitive to ionic conditions (plH, salt concentrations) but not affected by non-ionic detergents, was used for affinity chromatography that strongly improved the purification procedure. The enzyme is extensively characterized: 1) it has a molecular mass of 107 kDa as determined by polyacrylamide gel electrophoresis in presence of SDS and of about 130 kDa when estimated by gel filtration on a Sephacryl-S300; 2) in standard assay (pH 7.5, 0.2 M NaCl, 35 degrees C), the activation energy for reaction with amino procollagen type I was 17,000 calories per mole. In the same conditions, Km and Vmax values were, respectively, 435 and 39 nM per hour but varied strongly with pH and salt concentration; 3) the enzyme cleaved the NH2-terminal propeptide of type I procollagen at the specific site, the Pro-Gln bond in the alpha 1 type I procollagen chain; 4) the enzyme contained a high proportion of Gly, Asx, and Glx residues but no Hyp or Hyl; 5) partial amino acid sequences obtained from internal peptides of the enzyme displayed no significant homology with known sequences. The association of procollagen I N-proteinase with a FACIT (fibril-associated collagens with interrupted triple helices) collagen as found here might be of physiological significance.

Characterization of type I procollagen N-proteinase from fetal bovine tendon and skin. Purification of the 500-kilodalton form of the enzyme from bovine tendon

Procollagen N-proteinase (EC 3.4.24.14) is the enzyme that specifically cleaves the NH2-terminal propeptides from type I procollagen. Two forms of N-proteinase with apparent molecular sizes of 300 and 500 kDa were found in partially purified preparations from fetal bovine tendon extracts. The 500-kDa form of enzyme was purified 16,000-fold with a recovery of 8% from the extracts of the tendons by six purification steps. The purified enzyme was a neutral, Ca(2+)-dependent proteinase (5-10 mM) that was inhibited by metal chelators. The 500-kDa enzyme contained unreduced polypeptides of 58, 125, 170, and 190 kDa which were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Electron microscopic study indicated that the enzyme molecules were generally globular and had diameters of 33 +/- 4 nm. Other properties of the 500-kDa enzyme were: 1) the Km for type I procollagen is 35 nM at pH 7.5 and 35 degrees C, and the kcat is 290 h-1; 2) the activation energy for reaction with type I procollagen is 10,050 cal mol-1; 3) the isoelectric point is 3.8; 4) the enzyme cleaves the NH2-terminal propeptides of type II procollagen as well as type I procollagen but not of type III procollagen; and 5) the enzyme specifically cleaves a -Pro-Gln- bond in the pro-alpha 1(I) chain and an -Ala-Gln- bond in the pro-alpha 2(I) chain. The bovine N-proteinase with a mass of 300 kDa was found to be similar to the 500-kDa enzyme and appeared to be a degraded form of the 500-kDa enzyme generated during purification. The N-proteinase from fetal bovine skin extracts also contained 300-kDa and 500-kDa enzyme forms.