Role of protein kinase C-delta in the regulation of collagen gene expression in scleroderma fibroblasts.

Working with cultured dermal fibroblasts derived from control individuals and patients with systemic sclerosis (SSc), we have examined the effects of protein kinase C-delta (PKC-delta) on type I collagen biosynthesis and steady-state levels of COL1A1 and COL3A1 mRNAs. Rottlerin, a specific inhibitor of PKC-delta, exerted a powerful, dose-dependent inhibition of type I and type III collagen gene expression in normal and SSc cells. Optimal rottlerin concentrations caused a 70-90% inhibition of type I collagen production, a >80% reduction in COL1A1 mRNA, and a >70% reduction in COL3A1 mRNA in both cell types. In vitro nuclear transcription assays and transient transfections with COL1A1 promoter deletion constructs demonstrated that rottlerin profoundly reduced COL1A1 transcription and that this effect required a 129-bp promoter region encompassing nucleotides -804 to -675. This COL1A1 segment imparted rottlerin sensitivity to a heterologous promoter. Cotransfections of COL1A1 promoter constructs with a dominant-negative PKC-delta expression plasmid showed that suppression of this kinase silenced COL1A1 promoter activity. The results indicate that PKC-delta participates in the upregulation of collagen gene transcription in SSc and suggest that treatment with PKC-delta inhibitors could suppress fibrosis in this disease.

Signaling events required for transforming growth factor-beta stimulation of connective tissue growth factor expression by cultured human lung fibroblasts.

It is possible that many of the fibrogenic effects of transforming growth factor-beta (TGF-beta) are mediated by connective tissue growth factor (CTGF). In the present work, we show that TGF-beta1 produces a 5- to 6-fold increase in CTGF expression by cultured human lung fibroblasts that is due mainly to increased transcription. The half-life of CTGF mRNA is 1.96 h, consistent with its role as a cytokine. In addition to requiring Smad activity, based upon the effects of specific inhibitors, the TGF-beta intracellular signaling pathway requires the activity of a phosphatidylcholine-specific phospholipase C, a protein kinase C, and one or more tyrosine kinases. It is also likely that the pathway requires a member of the Ras superfamily of small GTPases, but not trimeric G proteins. Pharmacologic inhibition of TGF-beta stimulation of CTGF expression may be an effective therapeutic approach to a variety of undesirable fibrotic reactions.

Extracellular matrix and nuclear localization of beta ig-h3 in human bladder smooth muscle and fibroblast cells.

The extracellular matrix (ECM) plays an essential role in bladder structure and function. In this study, expression of beta ig-h3, a recently identified extracellular matrix protein, was investigated in human bladder tissue, and human bladder smooth-muscle (SMC) and fibroblast cells in vitro. SMCs secreted greater than three times the level of this protein compared with fibroblasts. The relative levels of beta ig-h3 mRNA in the two cell types reflected the protein expression. Immunohistochemical analysis demonstrated protein deposition in the ECM as well as cytoplasmic localization and, unexpectedly, nuclei. Anti-beta ig-h3 antibodies also stained the matrix surrounding the detrusor SMCs and nuclei of bladder fibroblasts, SMCs, and urothelium in intact bladder tissue. Western blot analyses of medium and matrix fractions obtained from cells in vitro revealed protein of approximately 70-74 kDa, whereas nuclear extracts contained a 65-kDa reactive protein band. We propose that although this protein is a structural component of bladder ECM, its nuclear localization suggests that it has other regulatory and/or structural functions.

Inhibition of type I collagen gene expression in normal and systemic sclerosis fibroblasts by a specific inhibitor of geranylgeranyl transferase I.

OBJECTIVE: To examine the effects of specific inhibition of geranylgeranyl transferase I on the expression of types I and III collagen genes in normal and systemic sclerosis (SSc) dermal fibroblasts in vitro. METHODS: Fibroblasts from 2 normal subjects and 4 SSc patients were incubated with 2-10 microM of GGTI-298, a specific geranylgeranyl transferase inhibitor. Type I collagen and fibronectin production were determined by enzyme-linked immunosorbent assay. Steady-state messenger RNA (mRNA) levels for alpha1(I), alpha2(I), and alpha1(III) collagens and fibronectin were assessed by Northern hybridization, and the transcription of the alpha1(I) collagen gene was examined by transient transfections with a reporter construct containing -5.3 kb of the gene. RESULTS: GGTI-298 caused a dose-dependent inhibition of type I collagen production and a reduction in the steady-state levels of alpha1(I), alpha2(I), and alpha1(III) mRNA in normal and SSc cells. A 60-70% inhibition of type I collagen production and a 70-80% reduction in the mRNA levels for alpha1(I), alpha2(I), and alpha1(III) were observed at 10 microM GGTI-298. In contrast, the expression of fibronectin, cyclooxygenase 1, and GAPDH was not affected. The effects on alpha1(I) collagen mRNA resulted from a profound reduction in transcription of the alpha1(I) collagen gene promoter. GGTI-298 did not affect cellular viability or morphology. CONCLUSION: These results demonstrate that specific inhibition of geranylgeranyl prenylation causes a potent and selective inhibition of expression of the genes encoding types I and III collagens, without affecting cellular viability. The findings indicate that inhibition of geranylgeranyl prenylation should be further studied as a potential therapeutic approach for SSc and other fibrosing diseases.

Expression of betaig-h3 by human bronchial smooth muscle cells: localization To the extracellular matrix and nucleus.

Bronchial smooth muscle cells play a central role in normal lung physiology by controlling airway tone. In addition, airway smooth muscle hyperplasia and hypertrophy are important factors in the pathophysiology of asthma. In this study, expression of betaig-h3, a recently identified component of the extracellular matrix (ECM), was investigated in primary human bronchial smooth muscle (HBSM) cells. Northern blot analysis demonstrated that treatment of cultured HBSM cells with transforming growth factor-beta1 resulted in a 4- to 5-fold increase in the steady-state level of betaig-h3 messenger RNA. Western blot analysis of secreted proteins using monospecific antibodies generated against peptide sequences found in the N- and C-terminal regions of the protein identified several isoforms having apparent mass of 70-74 kD. Immunohistochemical analysis of human lung localized betaig-h3 to the vascular and airway ECM, and particularly to the septal tips of alveolar ducts and alveoli, suggesting that it may have a morphogenetic role. Analysis of cultured HBSM cells identified betaig-h3 in both the ECM as well as the cytoplasm, and surprisingly also in the nucleus. These results demonstrate that betaig-h3 is produced by resident lung cells, is a component of lung ECM, and may play an important role in lung structure and function. The presence of this protein in nuclei suggests that it may have regulatory functions in addition to its role as a structural component of lung ECM.

TGF-beta1 stimulation of fibronectin transcription in cultured human lung fibroblasts requires active geranylgeranyl transferase I, phosphatidylcholine-specific phospholipase C, protein kinase C-delta, and p38, but not erk1/erk2.

The cytokine transforming growth factor-beta (TGF-beta) has multiple effects on a variety of cell types, modulating cell growth and differentiation as well as extracellular matrix deposition and degradation. In the present work, we demonstrate that TGF-beta1 produces a fourfold increase in transcription of the fibronectin gene in cultured human fetal lung fibroblasts with only a small increase in mRNA stability resulting in a significant increase in fibronectin mRNA steady state level. A corresponding increase in production of fibronectin protein accompanied the increase in mRNA. Through the use of specific inhibitors, we demonstrate that geranylgeranylated, but not farnesylated or acylated protein(s), protein kinase C-delta, phosphatidylcholine-specific phospholipse C, tyrosine kinase activity, and stress-activated protein kinase p38 are required for this TGF-beta1 effect. Trimeric G proteins and mitogen-activated protein kinases erk1 and erk2 do not appear to be involved. While these results emphasize the complexities involved in the control of extracellular matrix synthesis by TGF-beta, they also identify reaction sites that may be amenable to pharmacologic modulation. Such modulation could be of great advantage in the treatment of a wide variety of undesirable fibrotic reactions.

Signaling pathway by which TGF-beta1 increases expression of latent TGF-beta binding protein-2 at the transcriptional level.

The cytokine transforming growth factor-beta has multiple effects on a wide variety of cell types. These effects include modulation of growth and regulation of gene transcription. In the present work, we demonstrate that TGF-beta1 increases transcription of the latent transforming growth factor-beta binding protein-2 ( LTBP-2) gene in cultured human fetal lung fibroblasts leading to a significant increase in LTBP-2 mRNA steady state level. The stability of LTBP-2 mRNA was not appreciably altered. A corresponding increase in production of LTBP-2 protein accompanied the increase in mRNA. Through the use of specific inhibitors, we demonstrate that a member of the Ras super family and a protein kinase C, probably of the atypical (non-diacylglycerol, non-Ca++ dependent) class are likely to be components in the signaling pathway. However, phospholipases, G proteins and extracellular-signal regulated kinases do not appear to be involved. These results combined with previous findings on elastin regulation by TGF-beta1 (Kucich et al. (1997). Am. J. Respir. Cell Mol. Biol., 17: 10-16) demonstrate that TGF-beta1 can coordinately increase the steady state levels of mRNAs encoding components of the elastic fiber, but through diverse mechanisms. In contrast to LTBP-2, increased elastin expression is achieved by message stabilization. Furthermore, the TGF-beta1 signaling pathways differ and while the pathway leading to increased LTBP-2 transcription shares components with those modulating transcription of other genes, it is unlikely to be precisely congruent with any other previously described one.

Requirement for geranylgeranyl transferase I and acyl transferase in the TGF-beta-stimulated pathway leading to elastin mRNA stabilization.

The TGF-betas are multipotent in their biological activity, modulating cell growth and differentiation as well as extracellular matrix deposition and degradation. Most of these activities involve modulation of gene transcription. However, TGF-beta1 has been shown previously to substantially increase the expression of elastin by stabilization of tropoelastin mRNA through a signaling pathway which involves a phosphatidylcholine-specific phospholipase and a protein kinase C. The present results, through the use of specific inhibitors of geranylgeranyl transferase I, farnesyl transferase, and acyl transferase, demonstrate that geranylgeranylated and acylated, but not farnesyslated protein(s) is required for this TGF-beta1 effect. In addition, the general tyrosine kinase inhibitor genistein completely blocked this TGF-beta1 effect. The results suggest that the TGF-beta1 signaling pathway requires not only receptor ser/thr kinase activity, but also tyrosine kinase and small GTPase activities.

Thrombin and human plasma kallikrein inhibition during simulated extracorporeal circulation block platelet and neutrophil activation.

Cardiopulmonary bypass causes hemorrhagic complications, and initiates a chemical and cellular inflammatory response. Contact of blood with synthetic surfaces leads to qualitative and quantitative alterations in platelets, neutrophils, complement, and contact systems. Despite the fact that cardiopulmonary bypass is carried out in the presence of high doses of heparin, there is significant activation of both platelets and neutrophils. Thrombin is protected on cell and fibrin surfaces from antithrombin, even in the presence of high doses of heparin (approximately 5 U/ml). We therefore studied the effect of a small (Mr = 497), highly effective (Ki = 41 pM), reversible tripeptide inhibitor of thrombin, DUP 714 (1 microM), in a well characterized model of simulated extracorporeal circulation. In the absence of DUP 714, platelet counts decreased by 75% 5 min after the start of extracorporeal bypass and increased to 48% at 120 min of recirculation. DUP 714 significantly preserved platelet counts, decreased plasma levels of platelet beta-thromboglobulin levels, but did not prevent a decrease in sensitivity of platelets to adenosine diphosphate. Kallikrein-C1-inhibitor and C1-C1-inhibitor complexes increased progressively from 0.32 U/ml to 0.67 U/ml and from 4.45 U/ml to 7.25 U/ml, respectively, during 120 min of recirculation without DUP 714. Addition of DUP 714 significantly inhibited kallikrein-C1-inhibitor complex formation but did not affect C1-C1-inhibitor complexes. In the absence of DUP 714, human neutrophil elastase levels rose from a baseline of 0.01 +/- 0.00 microg/ml to 1.18 +/- 0.21 microg/ml during 120 min of recirculation. Human neutrophil elastase release at 120 min was significantly inhibited in the presence of DUP 714 to 37% of the value with heparin alone. These results indicated that addition of this novel thrombin (and kallikrein) inhibitor to heparin preserved platelet counts, decreased platelet secretion, and provided the additional benefit of partially blocking neutrophil activation during simulated extracorporeal circulation.

Molecular analysis of collagens in bladder fibrosis.

PURPOSE: Fibrosis of bladder tissue is characterized by an abnormal deposition of connective tissue within different layers of the bladder wall, resulting in a low volume, high pressure vesical which may ultimately contribute to renal scarring and failure. These bladders are functionally referred to as "non-compliant" and may result from different etiologies: neurogenic, which encompasses myelodysplasia and spinal cord injury, or non-neurogenic, owing to obstruction or radiation therapy. To examine the molecular mechanisms responsible for this fibrosis, we have analyzed a well-characterized pediatric patient population for alteration(s) in collagen types I and III regulation at the protein and nucleic acid levels. MATERIALS AND METHODS: Immunohistochemical localization of collagen subtypes (I, III, and IV) was carried out using type specific monoclonal antibodies. Total collagen was determined by hydroxyproline analysis, and subtype specific expression of collagenous proteins, following cyanogen bromide extraction procedures, was quantified by competitive ELISA. Total RNA was extracted by guanidinium/phenol/chloroform, and slot blot hybridization analyses with radiolabeled human cDNA probes were quantified by densitometry of resulting autoradiograms. RESULTS: Connective tissue infiltration of detrusor smooth muscle bundles was specific for type III collagen. Protein analyses demonstrated: 1) an increase in total collagen, 2) a statistically significant increase in the type III: type I collagen ratio, and 3), an absolute increase in type III collagen protein in non-compliant bladder tissue. At the mRNA level, there was a coordinate increase in both collagen I and III steady-state mRNAs in non-neurogenic bladder tissue, whereas neurogenic bladder tissue was characterized by an increase in the type III: type I mRNA transcript ratio. CONCLUSIONS: These data suggest that regulation of collagen synthesis in bladder fibrosis is complex and is characterized by both transcriptional and post-transcriptional mechanisms, depending upon the etiology of the fibrosis.

Mechanical forces alter extracellular matrix synthesis by human periodontal ligament fibroblasts.

Periodontal ligament fibroblasts (PDLFs) are a heterogeneous population of cells that are involved in the normal maintenance, repair and regeneration of both the ligament and adjacent hard tissues. Additionally, the ability of these cells to respond to mechanical stimulation suggests that they have a central role in mediating the osseous remodeling that underlies physiological and orthodontic tooth movement. To characterize their role further in this process, the current study evaluated the effect of tensional stress on the biosynthesis of extracellular matrix (ECM) proteins by human PDLFs. Cell strains were established from extracted human premolars and third molars. Cells exposed to 5% biaxial deformation (strain) at a frequency of 30 times/min for 24 hr exhibited statistically significant increases in type I collagen and fibronectin synthesis, and a statistically significant decrease in tropoelastin production relative to unstretched controls. Cells exposed to 10% strain exhibited similar responses for fibronectin and tropoelastin while the amount of type I collagen synthesized by stretched cells did not differ from control levels. These results indicate that mechanical stimulation of PDLFs alters type I collagen, tropoelastin and fibronectin production and that these cells are differentially responsive to varying levels of mechanical stress. The ability of these cells to alter ECM protein synthesis in response to specific magnitudes of tensional stress may in part explain how PDLFs regulate ligament and hard tissue remodeling.

Stabilization of elastin mRNA by TGF-beta: initial characterization of signaling pathway.

The cytokine transforming growth factor-beta (TGF-beta) has multiple effects on a wide variety of cell types. These effects include modulation of growth and regulation of gene transcription. In a few instances, TGF-beta has also been shown to regulate gene expression posttranscriptionally by altering message stability, but the pathway by which this activity is executed remains largely unknown. In the present work, we demonstrate that TGF-beta 1 has no effect on transcription of the elastin gene in cultured human fetal lung fibroblasts, but does stabilize elastin messenger RNA (mRNA), leading to a dramatic increase in the steady-state level of elastin mRNA. A corresponding increase in production of tropoelastin accompanies the increase in elastin mRNA. Through the use of specific inhibitors, we demonstrate that phosphatidylcholine (PC)-specific phospholipase C (PLC) and protein kinase C (PKC) are involved in mediating the elastin message stabilization. In contrast, G proteins and extracellularly regulated kinases do not appear to be involved. These results suggest that although the TGF-beta signaling pathway leading to message stabilization shares components with that modulating transcription, the message-stabilization pathway also contains diverse other elements.

Expression of microfibrillar proteins by bovine bladder urothelium.

OBJECTIVES: To determine the occurrence and potential function of proteins composing elastic microfibrils in the developing bovine bladder. METHODS: Monospecific antibodies, generated against two well-characterized microfibrillar proteins, microfibril-associated glycoprotein (MAGP) and fibrillin-1 (FBN1), were used in immunohistochemical analysis of full-thickness frozen sections of fetal bovine bladder. The localization of these two antibodies was compared with that of anti-type IV collagen antibody. Adjacent serial sections were stained for routine light microscopy. Cultured urothelial cells were fixed in 3.7% formaldehyde and permeabilized with 0.5% Triton X-100 before immunoanalysis. Control reactions used either preimmune serum or a monoclonal antibody to a nonmatrix protein. Poly(A+) ribonucleic acid was isolated from cultured urothelial cells and subjected to Northern analysis using specific complementary deoxyribonucleic acid probes for MAGP and FBN1. RESULTS: Both MAGP and FBN1 are expressed by the urothelium and are found in association with the underlying basement membrane, as visualized by their co-localization with type IV collagen. Furthermore, urothelial cells in culture continue to express both microfibrillar proteins. CONCLUSIONS: The developing bovine urothelium expresses major microfibrillar protein components. The role of these microfibrils in the urothelium remains to be determined, but they may have an important anchoring function.

MR889, a neutrophil elastase inhibitor, in patients with chronic obstructive pulmonary disease: a double-blind, randomized, placebo-controlled clinical trial.

We investigated whether MR889, a synthetic cyclic thiolic elastase inhibitor, administered for a period of 4 weeks to chronic obstructive pulmonary disease (COPD) patients, is well-tolerated, and whether it modifies biochemical indices of lung destruction. The study was a double-blind, randomized, placebo-controlled clinical trial in COPD patients. Thirty subjects were administered MR889 orally at a dose of 500 mg b.i.d. for 4 weeks, and 30 received placebo following the same schedule. In addition to safety parameters, MR889 efficacy was checked by a pretreatment/postreatment evaluation of levels of plasma elastin-derived peptides and urinary desmosine. There were no statistically significant differences between pretreatment and posttreatment efficacy parameter levels either in the control group or in the treated group. However, in a subset of treated patients with a short disease duration, the level of urinary desmosine dropped significantly with respect to pretreatment values (p = 0.004). We conclude that MR889 is safe to administer to COPD patients for a period of at least 4 weeks. During this time, MR889 does not modify biochemical markers of lung destruction in unselected COPD patients. Nevertheless, a subset of treated patients with fairly short disease duration showed a post-treatment reduction of desmosine urine levels, thus justifying the need for further studies to prove the efficacy of MR889 in modulating indices of lung destruction in COPD.

Molecular cloning of the microfibrillar protein MFAP3 and assignment of the gene to human chromosome 5q32-q33.2.

Microfibrils having a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues, but characterization of these microfibrils is incomplete. To further our understanding of the gene structure of proteins composing the microfibrils and to identify their chromosomal location, we have cloned and characterized another microfibril protein, designated microfibril-associated protein-3 (MFAP3). The human gene encoding MFAP3 has a very simple structure, containing only two translated exons encoding a protein of 362 amino acids. Monospecific antibodies prepared against the recombinantly expressed protein reacted with the microfibrils found in ocular zonules. MFAP3 does not appear to share homology with any other known protein. The gene was found to be located on chromosome 5q32-q33.2, near the locus 5q21-q31 reported for the fibrillin gene, FBN2, which has been linked to congenital contractural arachnodactyly. MFAP3 is a candidate gene for heritable diseases affecting microfibrils.

Selective kallikrein inhibitors alter human neutrophil elastase release during extracorporeal circulation.

Cardiopulmonary bypass causes hemorrhagic complications and initiates a biochemical and cellular "whole body inflammatory response." This study investigates whether a variety of selective inhibitors of the contact pathway of intrinsic coagulation modulate complement and neutrophil activation during simulated extracorporeal circulation. After 60 min of recirculation in the presence of the slow tight-binding boronic acid inhibitor, Bz-Pro-Phe-boroArg-OH (10.7 microM), complete inhibition of kallikrein-C1-inhibitor complex formation and marked inhibition of C1-C1-inhibitor complex formation and the release of human neutrophil elastase were observed. Arg15-aprotinin (3.1 microM), Ala357,Arg358 alpha 1-antitrypsin (2.6 microM), and soybean trypsin inhibitor (48.0 microM) either completely or partially inhibited the generation of kallikrein-C1-inhibitor complexes but were less effective inhibitors of human neutrophil elastase release. The second-order rate constants for the inhibition of kallikrein in purified systems are consistent with the order of effectiveness of the inhibitors in blocking human neutrophil elastase release in heparinized blood. Our results suggest that low-molecular-weight selective inhibitors of kallikrein may be effective agents in the attenuation of the contact-mediated inflammatory response in cardiopulmonary bypass.

Analysis of amelogenin proteins using monospecific antibodies to defined sequences.

Amelogenins are the predominant proteins found in the developing enamel matrix and are believed to play a crucial role in normal mineralization. Although the amelogenin gene is found as a single copy in all species in which it has been examined, multiple amelogenin polypeptides ranging in size from 5 to 25 kDa are obtained upon extraction of developing enamel matrix, making identification and characterization of individual components difficult. This heterogeneity may be ascribed to transcription of divergent genes located on the X and Y chromosomes, alternative splicing of the primary transcripts, physiologic degradative processing, and artefactual degradation. In order to characterize individual components, antibodies were produced to the following peptides: (1) QPLQPMQPMQPLQPLQPL (corresponding to the repeat sequence encoded only in the bovine X chromosome gene), (2) IRHPPLPP (corresponding to a unique sequence generated by alternative splicing found in leucine-rich amelogenin peptide (LRAP), (3) LPDLPLEAWPATDKTKREEVD corresponding to the amelogenin carboxy-terminus. Amelogenin proteins obtained from fetal bovine molars were subjected to SDS PAGE and Western electrotransfer, and immuno-ultrastructural analysis. These analyses demonstrated that: (1) the distribution of amelogenin polypeptides isolated from male fetuses differed appreciably from that of females, (2) the LRAP junctional peptide sequence can be specifically identified, and (3) the LRAP peptide can be immunolocalized in the enamel matrix of both males and females.

Alpha 1-antitrypsin Pittsburgh (Met358-->Arg) inhibits the contact pathway of intrinsic coagulation and alters the release of human neutrophil elastase during simulated extracorporeal circulation.

Cardiopulmonary bypass prolongs bleeding time, increases postoperative blood loss, and triggers activation of plasma proteolytic enzyme systems and blood cells referred to as the "whole body inflammatory response". Contact of blood with synthetic surfaces leads to qualitative and quantitative alterations in platelets, neutrophils, contact and complement systems. Contact and complement pathway proteins both induce neutrophil activation. alpha 1-antitrypsin Pittsburgh (Met358-->Arg), a mutant of alpha 1-antitrypsin, is a potent inhibitor of plasma kallikrein and thrombin. We investigated whether this recombinant mutant protein inhibited platelet activation, as well as contact and/or complement-induced neutrophil activation during simulated extracorporeal circulation. Arg358 alpha 1-antitrypsin did not prevent the 34% drop in platelet count at 5 min of recirculation, did not block the 50% decrease in ADP-induced platelet aggregation at 120 min of recirculation, nor inhibit the release of 6.06 +/- 1.07 micrograms/ml beta-thromboglobulin at 120 min of recirculation suggesting that the inhibitor had little effect on platelet activation. However, Arg358 alpha 1-antitrypsin totally blocked kallikrein-C1-inhibitor complex formation but not C1-C1-inhibitor complex formation. Most importantly, Arg358 alpha 1-antitrypsin decreased the release of 1.11 +/- 0.16 micrograms/ml human neutrophil elastase by 43%. The attenuation of neutrophil activation in the absence of an effect on complement activation via the classical pathway, supports the concept that kallikrein is a major mediator of neutrophil degranulation during cardiopulmonary bypass.

Microfibril-associated glycoprotein: characterization of the bovine gene and of the recombinantly expressed protein.

Microfibrils having a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues. Because isolation of native proteins composing the microfibrils has proven difficult, information on structure/function relationships is limited. In order to extend our understanding of the 31-kDa microfibril-associated glycoprotein (MAGP), the bovine gene has been cloned and characterized and the protein has been expressed in a eukaryotic system. The compact coding portion of the gene is contained in 4.5 kbp of genomic DNA and does not appear to share any domain motifs with other known proteins. The size, amino acid composition, and sequence of the amino terminus of the secreted recombinant protein (rMAGP) all agree with values predicted by the nucleotide sequence of the cDNA used in the expression vector. The rMAGP reacts with a monospecific antibody prepared against a defined amino acid sequence of the natural molecule and reacts specifically with recombinantly produced tropoelastin, suggesting that rMAGP will be a useful reagent with which to study its interaction with other extracellular matrix components.