Isolation of a novel latent transforming growth factor-beta binding protein gene (LTBP-3)

This paper reports the molecular cloning of a novel gene in the mouse that shows structural similarities to the microfibril protein fibrillin and to the latent transforming growth factor-beta (TGF-beta) binding protein (LTBP), a component of the latent TGF-beta complex. The gene was initially isolated during a low stringency polymerase chain reaction screen of a NIH 3T3 cell cDNA library using primers that amplify a human fibrillin-1 epidermal growth factor-like repeat. Three lines of evidence suggest that the mouse gene is a third member of the LTBP gene family, which we designate LTBP-3. First, the deduced polypeptide, which consists of 15 epidermal growth factor-like repeats, 3 TGF binding protein repeats, and 2 proline- and glycine-rich sequences, shows 38.4% identity with LTBP-1 but only 27% identity with fibrillin-1. Second, the gene appears to be co-expressed in developing mouse tissues with TGF-beta. Third, immunoprecipitation studies using mouse preosteoblast MC3T3-E1 cells and a specific anti-peptide polyclonal antiserum reveal that the mouse polypeptide forms a complex with the TGF-beta 1 precursor. Finally, we note that the LTBP-3 gene was recently localized to a distinct genetic locus (Li, X., Yin, W., Perez-Jurado, L., Bonadio, J., and Francke, U. (1995) Mamm. Genome 6, 42-45). Identification of a third binding protein provides further insight into a mechanism by which latent TGF-beta complexes can be targeted to connective tissue matrices and cells.

1,25-Dihydroxyvitamin D3 enhances the expression of transforming growth factor beta 1 and its latent form binding protein in cultured breast carcinoma cells

Transforming growth factor beta s (TGF-beta s) are a family of polypeptide growth factors that regulate cellular growth, phenotype, and differentiation. TGF-beta s are synthesized as latent high molecular weight complexes that include the NH2-terminal remnant of the TGF-beta precursor (latency-associated protein) and, frequently, latent TGF-beta binding protein. After activation, TGF-beta s act as local mediators of hormonal responses in target tissues. TGF-beta functions as a negative growth regulator for both breast cancer cells and normal mammary epithelial cells. Vitamin D3 is growth inhibitory for the estrogen receptor-negative breast cancer cell line BT-20 and regulates TGF-beta expression in cultured keratinocytes. We studied here the effects of vitamin D3 and its analogues on TGF-beta expression and activity in BT-20 cells. It was found that vitamin D3 enhanced both TGF-beta 1 mRNA and secretion of the protein in a time- and dose-dependent manner. Analyses of the vitamin D3 responses in the presence of cycloheximide or actinomycin D indicated that the TGF-beta 1 mRNA induction was dependent on both protein and RNA synthesis. The amounts of latent TGF-beta binding protein were also increased in the conditioned medium but not in the pericellular matrix of vitamin D3-treated cultures. The amounts of active TGF-beta were enhanced in vitamin D3-treated cultures as well, suggesting autocrine or paracrine functions for the secreted growth factor. Some analogues of vitamin D3 (EB 1089, MC 903, and KH 1060) that are known to be potent inhibitors of breast cancer cell growth both in vitro and in vivo had similar or more pronounced inducing effects on TGF-beta 1 mRNA levels. The present results indicate that vitamin D3 and its analogues are potent inducers of both active and latent forms of TGF-beta 1 in BT-20 breast carcinoma cells and provide evidence for coordinated regulation of latent TGF-beta binding protein and TGF-beta 1.

Human mast cell chymase and leukocyte elastase release latent transforming growth factor-beta 1 from the extracellular matrix of cultured human epithelial and endothelial cells

Monolayer cultures of human epithelial and endothelial cells were used to study the association of latent transforming growth factor-beta 1 (TGF-beta 1) to extracellular matrices and its release and activation during matrix degradation. Human umbilical vein endothelial cells and embryonic lung fibroblasts produced relatively high levels of TGF-beta 1, its propeptide (beta 1-latency-associated protein), and latent TGF-beta-binding protein and incorporated latent TGF-beta 1 into their matrices as shown by immunoblotting. Amnion epithelial cells produced lower levels of these proteins. Confluent cultures of epithelial cells were exposed to matrix-degrading proteases and glycosidases. Mast cell chymase, leukocyte elastase, and plasmin efficiently released matrix-bound latent TGF-beta 1 complexes, while chondroitinase ABC and heparitinases were ineffective. The ability of the proteases to activate recombinant latent TGF-beta 1 was tested using growth inhibition assays and a novel sodium deoxycholate-polyacrylamide gel electrophoresis followed by immunoblotting. Sodium deoxycholate solubilized M(r) 25,000 TGF-beta 1 but did not dissociate high M(r) latent TGF-beta 1 complexes, allowing separation of these forms by polyacrylamide gel electrophoresis. Mast cell chymase and leukocyte elastase did not activate latent TGF-beta 1, suggesting that its release from matrix and activation are controlled by different mechanisms. The release of TGF-beta from the matrix by leukocyte and mast cell enzymes may contribute to the accumulation of connective tissue in inflammation.

Localization of transforming growth factor-beta and latent transforming growth factor-beta binding protein in rat kidney

TGF-beta plays an important role in maintaining the renal histological structure, and glomerular and tubular function. TGF-beta is usually secreted in a biologically inactive or latent form with high molecular weight by normal cells. The latent form of TGF-beta is composed of three distinct components: (a) mature TGF-beta (b) TGF-beta latency associated peptide (LAP) (c) latent TGF-beta binding protein (LTBP). LTBP plays a central role in the assembly, secretion and activation of TGF-beta 1. Most cells secrete a large latent TGF-beta with LTBP, while the other cells secrete a small latent TGF-beta without LTBP. However, the precise localization of TGF-beta and LTBP in the kidney is still not known. In the present study, we used the reverse transcription in combination with polymerase chain reaction (RT-PCR) to investigate the precise localization of TGF-beta 1 and LTBP in the microdissected glomeruli, renal tubules and arterioles. Our findings showed that TGF-beta 1 mRNA was detected in all nephron segments, glomeruli, and arterioles. On the other hand, LTBP mRNA was present in the glomeruli and arterioles, while it was absent in every segment of the renal tubules. Moreover, the immunohistochemical study of LTBP showed that the LTBP protein was localized on the glomeruli and arterioles but not on the renal tubules at the same localization as LTBP mRNA. These results indicate that the tubular epithelial cells secrete the small latent TGF-beta 1, while glomerular cells secrete the large latent TGF-beta 1, suggesting that they both have different structures and thus potentially different biological functions.

Mapping of human and murine genes for latent TGF-beta binding protein-2 (LTBP2)

A novel gene, isolated because of structural similarities to fibrillin, was called LTBP2 when its 4.6-kb transcript was found to encode a protein sequence related to the latent TGF-beta binding protein (LTBP1), which is encoded on human chromosome (Chr) 2, region p12-q22. We have assigned the human and murine LTBP2 loci to regions of conserved synteny on human Chr 11 and mouse Chr 19. By PCR analysis of somatic cell hybrid DNA and fluorescence in situ hybridization, LTBP2 was mapped to human Chr band 11q12 and Ltbp2 to mouse Chr band 19B. Differences between inbred strains were discovered by single-strand conformation analysis of PCR products from the 3' untranslated region. Analysis of BXD and AKXL recombinant inbred strains have placed Ltbp2 between D19Rp19 and Ly10 on proximal mouse Chr 19.

Identification and characterization of LTBP-2, a novel latent transforming growth factor-beta-binding protein

Latent transforming growth factor-beta (TGF-beta)-binding protein (LTBP) is a component of the latent TGF-beta complex in human platelets. LTBP is composed of two different cysteine-rich repeat sequences, i.e. epidermal growth factor (EGF)-like repeats and a repeat containing 8 cysteine residues. The overall structure of LTBP is similar to those of the microfibrillar proteins fibrillin-1 and fibrillin-2. Here we report the identification of a novel protein termed LTBP-2, which is structurally related to LTBP. cDNA for LTBP-2 was obtained from human foreskin fibroblast cDNA libraries using a fragment of the LTBP cDNA as a probe. LTBP-2 is composed of 20 EGF-like repeats and four copies of the 8-cysteine repeat. The amino acid sequence of LTBP-2 is 41% identical to that of LTBP and 25% identical to that of fibrillin-1. LTBP-2 is synthesized as a 240-kDa protein by human foreskin fibroblasts and also by COS cells transfected with the isolated LTBP-2 cDNA. Similar to LTBP, a considerable part of LTBP-2 was found to be associated with extracellular matrix. Co-transfection of cDNAs for LTBP-2 and TGF-beta 1 revealed that LTBP-2 forms a high molecular weight complex with the TGF-beta 1 precursor. The LTBP-2 gene was assigned to chromosome 14q24. These results indicate that different forms of latent TGF-beta complexes occur and suggest that the different associated proteins may function to target the complexes to specific sites.

Immunohistochemical localization of transforming growth factor-beta 1, -beta 2, and -beta 3 latency-associated peptide in human cornea

PURPOSE

To study spatial distribution of TGF-beta isoforms (TGF-beta 1, -beta 2, and -beta 3) in the human cornea and to elucidate their biologic roles in corneal maintenance.

METHODS

Frozen sections obtained from eight human autopsy eyes were placed on gelatin-coated slides. After blocking of nonspecific binding sites, the slides were incubated with rabbit polyclonal antibody to the latency-associated peptide (LAP) region of human TGF-beta 1, TGF-beta 2, and TGF-beta 3 precursors, followed by the incubation with biotinylated swine anti-rabbit IgG. Subsequently, a streptavidin-labeled alkaline phosphatase technique was used.

RESULTS

In the corneal region, beta 1-LAP antibody did not stain either epithelium or stroma, beta 2-LAP antibody stained all epithelial cell layers and the corneal stroma, and beta 3-LAP antibody stained the subepithelial region alone. The staining pattern in the limbal region was almost the same as in the corneal region, except in the limbal stroma, which was stained with beta 1-LAP antibody in three of eight samples. In the trabecular meshwork, all samples showed clear staining with beta 2-LAP antibody, whereas beta 1-LAP and beta 2-LAP antibody stained faintly in five of eight and four of eight samples, respectively.

CONCLUSION

beta 2-LAP was found in the corneal epithelium and stroma and beta 3-LAP in the subepithelial region, suggesting that TGF-beta 2 and TGF-beta 3 may play essential roles in normal corneal epithelial maintenance in vivo.

Enhanced expression of transforming growth factor-beta s and transforming growth factor-beta type II receptor in the synovial tissues of patients with rheumatoid arthritis

BACKGROUND

A growing body of evidences suggests that transforming growth factor-beta (TGF-beta) is produced in the synovial fluid of patients with rheumatoid arthritis (RA), and that TGF-beta is an important regulator in the course of the disease. Careful studies on the endogenous synthesis of TGF-beta as well as its receptors are therefore necessary to clarify the possible role of TGF-beta in RA.

EXPERIMENTAL DESIGN

We examined the expressions of latent TGF-beta 1, -beta 2, and -beta 3, the latent TGF-beta 1-binding protein (LTBP) as well as TGF-beta type II receptor (TGF-beta RII) in the synovial biopsy tissues of 21 patients with RA by immunohistochemistry. Five specimens from these cases representing both active and chronic inactive stages were also examined for the corresponding mRNA by in situ hybridization. Northern blot analysis was performed on 3 synovial membranes taken from the RA patients together with a control synovium.

RESULTS

Abundant LTBP, TGF-beta 1, and TGF-beta RII-positive cells as well as less intensively stained TGF-beta 2 and TGF-beta 3-positive cells were found in the synovial layer. These cells were positive for the histocompatibility antigen, HLA-DR. In lymphocyte aggregates, scattered cells positively labeled for LTBP and TGF-beta 1 were found. They stained in a reticular pattern that was similar to that demonstrated by an antibody against human dendritic cells, and also expressed HLA-DR. In situ hybridization revealed markedly increased signals for LTBP and TGF-beta RII mRNA in tissues with an active inflammatory process, when compared with tissues with less active inflammation. However, no clear differences in the levels of expression for any of the TGF-beta isoforms were found. Specimens with pronounced fibrosis, fibroblasts, and surrounding collagen fibers expressed positive immunoreactivities for all TGF-beta isoforms and LTBP. Northern blot analysis on 4 synovial tissues demonstrated positive signals for LTBP and TGF-beta 1 mRNA in all three RA patients in contrast to a normal control, which did not show any signals. An increased expression of TGF-beta RII mRNA was detected in the tissue from one of the patients.

CONCLUSIONS

An abundant expression of TGF-beta 1 and LTBP, as well as TGF-beta RII was seen in most actively proliferating synovial intimal cells, and the level of the expression varied during the course of the disease. We conclude that TGF-beta is involved tightly in the regulation of the inflammatory process, and it is thus possible that the endogenous TGF-beta functions as a self-regulator that induces the remission periods.

Expression of transforming growth factor-beta 1 and its relation to endomysial fibrosis in progressive muscular dystrophy

Progressive muscular dystrophy is characterized by muscle fiber necrosis, regeneration, and endomysial fibrosis. Although absence of dystrophin has been known as the cause of muscle fiber degeneration, pathogenesis of interstitial fibrosis is still unknown. Transforming growth factor-beta 1 (TGF-beta 1) induces accumulation of extracellular matrix in various diseases, such as liver cirrhosis and interstitial pneumonitis. To investigate its function on the pathogenesis of progressive muscular dystrophy, it was necessary to determine the degree of TGF-beta 1 expression and the site of TGF-beta 1 immunoreactivity. In Duchenne muscular dystrophy and most of Becker muscular dystrophy, high TGF-beta 1 immunoreactivity expressed on muscle fibers and extracellular space. In other myopathies with endomysial fibrosis, however, TGF-beta 1 was seldom observed. We also examined the immunoreactivity of the latent TGF-beta binding protein, which is bound to the TGF-beta precursors. In all Duchenne muscular dystrophy and half of Becker muscular dystrophy cases, high latent TGF-beta 1 binding protein immunoreactivity was seen, but in other myopathies its immunoreactivity was seldom seen on muscle fibers or extracellular space. Therefore TGF-beta 1 may play an important role in synthesis and accumulation of extracellular matrix in progressive muscular dystrophy.

TGF-beta 1 in glomerulosclerosis and interstitial fibrosis of adriamycin nephropathy

The role of transforming growth factor-beta 1 (TGF-beta 1) for renal injury was investigated in the chronic model of progressive renal disease in rats induced by the injection of adriamycin. The renal cortical tissues were sampled at weeks 4, 8 and 16 for histological examination, either cortical or glomerular cell culture, and RNA extraction. A progressive increase in fibronectin synthesis was found in metabolically labeled cortical or glomerular culture at week 8 or 16, correlating with the degree of glomerulosclerosis and interstitial fibrosis. TGF-beta bioassay (mink lung epithelial cell assay) showed a progressive increase in latent TGF-beta secretion from cortex and glomeruli, while the amount of active TGF-beta was small. The peak of latent TGF-beta levels at week 16 coincided with the intense TGF-beta 1 staining of inflammatory cells dispersed in the interstitium and glomeruli. Northern blotting demonstrated the difference in the mRNA expression patterns of TGF-beta 1 and latent TGF-beta 1 binding protein (LTBP) in the cortex. TGF-beta 1 mRNA was constantly high throughout the experiment, while LTBP mRNA increased progressively and reached a peak at week 16. Furthermore, mRNA levels of fibronectin, procollagen alpha 2(I), and TGF-beta type II and type III receptors increased progressively in a similar pattern to the renal histological changes. These temporal and spacial relationships between the renal histological changes and the increased expression of TGF-beta 1 and TGF-beta receptors may thus suggest that TGF-beta 1 plays an important role in the process of the renal fibrosis and sclerosis.

Latent transforming growth factor-beta 1 associates to fibroblast extracellular matrix via latent TGF-beta binding protein

The role of latent transforming growth factor-beta (TGF-beta) binding protein (LTBP) in the association of TGF-beta 1 to the extracellular matrix of cultured fibroblasts and HT-1080 fibrosarcoma cells was studied by immunochemical methods. The matrices were isolated from the cells, and the levels of LTBP and TGF-beta 1 were estimated by immunoblotting and immunoprecipitation. LTBP, TGF-beta 1, and its propeptide (latency-associated peptide, LAP) were found to associate to the extracellular matrix. Immunoblotting analysis indicated that treatment of the cells with plasmin resulted in a concomitant time and dose dependent release of both LTBP and TGF-beta 1 from the extracellular matrix to the supernatant. Comparison of molecular weights suggested that plasmin treatment resulted in the cleavage of LTBP from the high molecular weight fibroblast form to a form resembling the low molecular weight LTBP found in platelets. Pulse-chase and immunoprecipitation analysis indicated that both the free form of LTBP and LTBP complexed to latent TGF-beta were efficiently incorporated in the extracellular matrix, from where both complexes were slowly released to the culture medium. Addition of plasmin to the chase solution resulted, however, in a rapid release of LTBP from the matrix. Fibroblast derived LTBP was found to associate to the matrix of HT-1080 cells in a plasmin sensitive manner as shown by immunoprecipitation analysis. These results suggest that the latent form of TGF-beta 1 associates with the extracellular matrix via LTBP, and that the release of latent TGF-beta 1 from the matrix is a consequence of proteolytic cleavage(s) of LTBP.

Assignment of the gene encoding the latent TGF-beta 1-binding protein (LTBP1) to human chromosome 2, region p12-->q22

Latent transforming growth factor beta 1-binding protein (LTBP1) is an important component of the large latent TGF-beta 1 complex. It plays a role in the assembly and secretion of the latent TGF-beta 1. In this paper we have used a cDNA probe for LTBP1 to determine the chromosomal localization of the human gene. Using a panel of well-defined human x rodent somatic cell hybrid lines, LTBP1 could be assigned to chromosome 2. Further sublocalization of the gene to 2p12-->q22 was achieved using three hybrid lines which contain partially over-lapping fragments of chromosome 2.

Identification and expression of two forms of the human transforming growth factor-beta-binding protein endoglin with distinct cytoplasmic regions

Endoglin is an homodimeric membrane antigen with capacity to bind transforming growth factor-beta (TGF-beta) and whose expression is up-regulated on myeloid cells upon differentiation to macrophages. We have isolated full-length cDNA clones from a lambda gt 10 library, prepared from phorbol 12-myristate 13-acetate-differentiated HL60 cells by screening with an endoglin-specific cDNA probe from endothelial cells. Sequencing of the largest clone (3073 bp), revealed that the leader sequence contains 25 residues and that the 586 amino acids of the extracellular and transmembrane domains were identical to those described for endothelial endoglin. However, the cytoplasmic tail encoded by this cDNA clone contains only 14 amino acids as opposed to the 47 residues previously reported, suggesting the existence of two alternative endoglin variants. The expression of these isoforms was demonstrated by polymerase chain reaction analyses on endothelial cells, myelomonocytic cell lines HL-60 and U-937, and placenta. Independent cDNA constructs corresponding to both forms were transfected into mouse fibroblasts leading to the expression of two distinct endoglin molecules. Both forms were shown to bind TGF-beta 1 and, when overexpressed in transfected mouse fibroblasts, to form disulfide-linked homodimers, indicating that the cysteine residues present in the extracellular domain are responsible for the dimerization.

A 60-kD protein mediates the binding of transforming growth factor-beta to cell surface and extracellular matrix proteoglycans

The biological activity of many cytokines is regulated by binding proteins present at the cell surface, in extracellular matrices or in soluble phase. We describe here a TGF-beta binding protein that is both an extracellular matrix and a cell surface protein. When intact extracellular matrices of HEP-G2 cells were affinity cross-linked with 125I-TGF-beta 1, two major binding components were seen: a 250-kD, proteoglycan-like molecule, presumed to be betaglycan, and a 60-kD protein. The 60-kD TGF-beta-binding protein was also present at the cell surface. It could be released from the cell surface by treating cells with high salt, heparin, chondroitin sulfate, heparitinase, or chondroitinase, indicating that it is bound to heparan sulfate and chondroitin sulfate proteoglycans. The 60-kD protein bound TGF-beta 1 with an apparent dissociation constant of 1.6 nM, and there were 30,000 binding sites per cell at the cell surface. In addition to the HEP-G2 cells and another hepatoma cell line, the 60-kD protein was also found in a human colon carcinoma (HT-29) cell line but not in rat kidney (NRK-49F) or human fibroblast (HUT-12) cell lines. The 60-kD protein could be extracted from cells containing it and transferred to the surface of previously negative cells. The 60-kD protein may serve to regulate the binding of TGF-beta to its signal transducing receptors by targeting TGF-beta to appropriate locations in the microenvironment of cells.

Induction of transforming growth factor-beta during cardiac allograft rejection

The polypeptides of the transforming growth factor-beta (TGF-beta) family are potent endogenous immuno-regulators. Using a rat cardiac allograft transplant model, we investigated the expression of the precursor forms of TGF-beta 1, TGF-beta 2, and TGF-beta 3 and the latent TGF-beta binding protein (LTBP) by immunohistochemistry. The activity of TGF-beta in the extracts from transplanted as well as normal hearts was measured using a bioassay, and Northern blot analysis was performed on RNA extracts. The transplanted hearts were analyzed both during acute rejection up to 6 days and during chronic rejection up to 6 mo after transplantation and compared with normal controls. The animals of the chronic rejection group received cyclosporin A for immunosuppression. The TGF-beta bioactivity dramatically increased in the transplanted allografts during the chronic rejection process compared to the normal hearts, and so did the immunostaining as well as the mRNA levels for TGF-beta 1 and, to a lesser extent, the immunostaining for TGF-beta 2. TGF-beta 3 expression remained unchanged and was only found in the myocardium in trace amounts. During the acute rejection process up to 6 days after transplantation, TGF-beta immunoreactivity increased only slightly, whereas the TGF-beta mRNA was severalfold increased. Control animals treated with cyclosporin A showed a similar pattern at day 6 with regard to TGF-beta expression. LTBP was induced simultaneously with TGF-beta 1 and occurred within interstitial spaces of the myocardium. The TGF-beta was produced by macrophage-like infiltrating lymphocytes. In conclusion, highly elevated levels of TGF-beta and LTBP were found during chronic rejection of cardiac allografts in rats. The induction of TGF-beta may counteract the rejection process and could be useful for new therapeutic approaches in the prevention of allograft rejection.

Lack of the latent transforming growth factor beta binding protein in malignant, but not benign prostatic tissue

Transforming growth factor beta (TGF-beta) is a family of proteins which act as a potent growth inhibitor for most cell types including epithelial cells. TGF-beta is synthesized as latent high molecular weight complexes, composed of TGF-beta, the NH2-terminal part of the TGF-beta precursor and the third molecule, the latent TGF-beta binding protein (LTBP). We here ascertain that TGF-beta is expressed in human prostatic cancer tissue as well as in cystectomized prostatic tissue and in materials from transurethral resections with benign prostatic hyperplasia, analyzed by immunohistochemistry. TGF-beta is observed in both epithelial cells and stromal cells. No significant correlation was obtained between TGF-beta expression in tumor cells and their degree of differentiation. However, analysis by immunohistochemistry using antibodies against LTBP revealed that specimens from histopathologically verified human prostatic cancer are mostly negative for this molecule, although it is expressed in cystectomized prostatic and benign prostatic hyperplasia tissues. These results indicate that in cystectomized prostatic and benign prostatic hyperplasia tissues, TGF-beta may be produced in a complex associated with LTBP; whereas in prostatic carcinoma, TGF-beta is produced without associating with LTBP. The biological significance of the production of TGF-beta in relation to LTBP and the possible association with prognosis are discussed.

Genomic organization of the sequence coding for fibrillin, the defective gene product in Marfan syndrome

Marfan syndrome results from mutations in an extracellular matrix glycoprotein, fibrillin. Previous studies have characterized approximately 6.9-kb of the estimated 10-kb fibrillin transcript. We have now completed the primary structure of fibrillin, elucidated the exon/intron organization of the gene and derived a physical map of the genetic locus. Pre-fibrillin consists of 2,871 amino acids which, excluding the signal peptide, are arranged into five structurally distinct regions. The largest of these regions comprises about 75% of the entire protein and consists of numerous repeated cysteine-rich sequences homologous to the peptide motifs of the epidermal growth factor (EGF) and transforming growth factor-beta binding protein (TGF-bp). Forty-three of the forty-six EGF-like repeats contain a calcium binding consensus sequence (EGF-CB) conceivably mediating protein-protein interactions. Fibrillin exhibits a few additional cysteine-rich modules that are apparently unique to this macromolecule and may represent evolutionary variants of the EGF-CB and TGF-bp motifs. Almost all of the cysteine-rich repeats are encoded by single exons; consequently, the fibrillin gene is relatively large (approximately 110-kb) and highly fragmented (65 exons). This study provides the first comprehensive analysis of the fibrillin gene and relevant information for the full characterization of Marfan syndrome mutations.

Ca2+ binding of latent transforming growth factor-beta 1 binding protein

Latent transforming growth factor-beta 1 binding protein (LTBP) is a constituent of the latent high molecular weight complex of TGF-beta 1 in human platelets. In the present communication, we show that LTBP binds Ca2+ in its free form as well as in the latent TGF-beta 1 complex. The binding of Ca2+ induces a structural change which protects the molecule against proteolysis and changes its elution position when analyzed by anion exchange chromatography. The in vitro activation of TGF-beta 1 is not influenced by the presence of Ca2+. The possible significance of Ca2+ binding of LTBP is discussed.

Role of the latent TGF-beta binding protein in the activation of latent TGF-beta by co-cultures of endothelial and smooth muscle cells

Transforming growth factor beta (TGF-beta) is released from cells in a latent form consisting of the mature growth factor associated with an aminoterminal propeptide and latent TGF-beta binding protein (LTBP). The endogenous activation of latent TGF-beta has been described in co-cultures of endothelial and smooth muscle cells. However, the mechanism of this activation remains unknown. Antibodies to native platelet LTBP and to a peptide fragment of LTBP inhibit in a dose-dependent manner the activation of latent TGF-beta normally observed when endothelial cells are cocultured with smooth muscle cells. Inhibition of latent TGF-beta activation was also observed when cells were co-cultured in the presence of an excess of free LTBP. These data represent the first demonstration of a function for the LTBP in the extracellular regulation of TGF-beta activity and indicate that LTBP participates in the activation of latent TGF-beta, perhaps by concentrating the latent growth factor on the cell surface where activation occurs.

Immunoelectron microscopic localization of transforming growth factor beta 1 and latent transforming growth factor beta 1 binding protein in human gastrointestinal carcinomas: qualitative difference between cancer cells and stromal cells

Transforming growth factor beta 1 (TGF-beta 1) is secreted as an inactive complex associated with latent TGF-beta 1 binding protein (LTBP). Tissue localization of these proteins has not been fully understood in human pathological conditions. We examined the immunohistochemical localization of TGF-beta 1 precursor (proTGF-beta 1) and LTBP in carcinomas and granulation tissue in the human gastrointestinal tract at the light and electron microscopic levels. In normal tissue, endothelial cells and granulocytes sporadically showed immunoreactivity for proTGF-beta 1, while epithelial cells were all negative. In cancer tissue, both cancer cells and stromal cells (fibroblasts, macrophages, and endothelial cells) were positive for proTGF-beta 1, more frequently in diffuse-type gastric carcinomas than in differentiated-type adenocarcinomas. Immunoelectron microscopy revealed that proTGF-beta 1 was localized in rough endoplasmic reticulum and perinuclear cisternae in fibroblasts, macrophages, and endothelial cells in cancer stroma and in fibrous granulation tissue. In contrast, the intracellular localization of proTGF-beta 1 in carcinoma cells was predominantly observed in the cytosol (cytoplasmic matrix). This finding suggests disarranged or blocked intracellular transportation of proTGF-beta 1 in cancer cells. The immunoreactivity for LTBP was not observed in the normal epithelial cells. It was localized in cancer stroma, not in cancer cells. Ultrastructurally, LTBP was located in the extracellular matrix around fibroblasts and smooth muscle cells. The intracellular immunoreactivity for LTBP was observed in rough endoplasmic reticulum of fibroblasts and smooth muscle cells, the same as in granulation tissue. These results suggest that gastrointestinal carcinoma cells produce no or a small amount of LTBP in vivo. Our investigation suggests that extensive fibrosis in both cancer stroma and granulation tissues may be promoted by TGF-beta 1 mainly secreted from stromal cells.

Transforming growth factor-beta 1, -beta 2, and -beta 3 secreted by a human glioblastoma cell line. Identification of small and different forms of large latent complexes

Transforming growth factor-beta 1 (TGF-beta 1) has been found to occur as latent high molecular weight complexes, with or without an associated component denoted latent TGF-beta 1-binding protein (LTBP). We show here that a human glioblastoma cell line (U-1240 MG) secretes all isoforms of TGF-beta s found in mammalian cells (TGF-beta 1, -beta 2, and -beta 3). Approximately 26% of the secreted TGF-beta is in an active form. Latent TGF-beta s were partially purified from medium conditioned by the U-1240 MG cell line using anion exchange chromatography. Analysis of the different fractions by immunoblotting using antisera against precursor parts of the different TGF-beta isoforms, and against LTBP, revealed that not only TGF-beta 1 but also other isoforms of TGF-beta may occur in high molecular weight forms containing LTBP. In addition, each one of the TGF-beta isoforms occurred in smaller forms not containing LTBP. Interestingly, each of the TGF-beta isoforms was also seen in complexes of about 210 kDa containing associated component(s) distinct from LTBP. These results indicate that each of the different isoforms of TGF-beta is synthesized and secreted by this glioblastoma cell line in several different high molecular weight latent forms; the biological importance of the various latent TGF-beta complexes is discussed.

Transforming growth factor beta 1-specific binding proteins on human vascular endothelial cells

Transforming growth factor beta (TGF beta) regulates the growth of human umbilical vein endothelial cells (HUVEC) differently depending on the isoform of TGF beta and the culture conditions. The cells are resistant to growth inhibition by TGF beta when the cells are cultured on substratum coated with gelatin. However, the proliferation of HUVEC cultured on substratum without a gelatin coating is inhibited by TGF beta, depending on the isoform and concentration of TGF beta. Binding assays with 125I-TGF beta 1 reveal that HUVEC contain a single class of high-affinity (Kd = 4.4 pM) TGF beta 1 binding sites with 8500 sites per cell. Affinity cross-linking studies demonstrate that HUVEC express 180 and 80 kDa TGF beta 1 binding sites that do not bind TGF beta 2. The reduction and the removal of glycosaminoglycans does not affect the electrophoretic mobility of the 180-kDa binding protein cross-linked with 125I-TGF beta 1. Therefore, the 180-kDa TGF beta 1 binding protein is not related to the type III TGF beta receptor, but might be a novel TGF beta 1-specific receptor/binding protein expressed on vascular endothelial cells. The expression of TGF beta 1 binding sites is not affected by the presence or absence of the gelatin coating on the culture substratum. The data suggest that a gelatin coating does not regulate the susceptibility of HUVEC to TGF beta 1 at the level of the receptor/binding proteins, and that growth inhibition of HUVEC by TGF beta 1 is linked to the regulation of extracellular matrices required for the interaction between the cells and the substratum.

The 260-kDa transforming growth factor (TGF)-beta binding protein in rat glomeruli is a complex comprised of 170- and 85-kDa TGF-beta binding proteins

In a previous study (MacKay, K., Robbins, A. R., Bruce, M. D., and Danielpour, D. (1990) J. Biol. Chem. 265, 9351-9356) we showed that rat glomeruli contain transforming growth factor (TGF)-beta 1 binding proteins with apparent molecular masses of 260, 170, and 85 kDa (Gl-260, Gl-170, Gl-85) as determined by electrophoresis under nonreducing conditions. We demonstrate here that Gl-260 is a complex of 170- and 85-kDa TGF-beta binding proteins. Under denaturing conditions the integrity of Gl-260 is maintained through the cross-linking of one monomer of the disulfide-linked TGF-beta 1 homodimer to Gl-85 and of the other monomer to the 100-kDa subunit of Gl-170. In addition, some Gl-260 complexes are maintained by direct cross-linking of Gl-85 to the 100-kDa subunit of Gl-170. One-dimensional peptide maps of Gl-85 and the 100-kDa subunit of Gl-170 indicate that they have distinctly different ligand binding domains. In contrast, peptide maps of Gl-85 and the type II receptor of normal rat kidney fibroblasts are similar. The biological responses of isolated glomeruli to TGF-beta appear to parallel those of cultured glomerular cells which are without detectable Gl-170 and Gl-260 binding proteins.

[The effect of microinjection of anti-TGF beta-1 antibodies on the early development of Xenopus laevis]

In order to testify the function of the TGF beta related protein, we microinjected the antibodies against the TGF beta-1 to one blastomere of two-cell stage embryos. Dosages of antibodies injected were 24-36 ng, 12 -18 ng, 6-9 ng and 1.5-2.25 ng. Malformed embryos with exposed yolk mass were produced. They were designated as YE-1, YE-2 and YE-3 according to the degree of malformation which was found to be related to the dosage of antibodies injected to the blastomere. These malformed embryos could normally develop to blastula, but the yolk mass was exposed on the injection half during gastrulation. In the group with the highest dosage, the most seriously affected embryos belong to the YE-1. For most of them, no muscle tissue could be found from head to tail in the injection half, the development of mesoderm seemed to be thoroughly inhibited. YE-2 was the group with decreased dosage, small block of muscle tissue was usually observed in the injection half. YE-3 was the least affected group with the injection half containing blocks of muscle tissue similar to that of the non-injection half. The different groups of malformations seemed to be related to the degree and range of interference on gastrulation. In the group with highest dosage, the gastrulation of the entire injection half seemed to be prohibited, and YE-1 was produced. In the groups with lower dosages, only part of injection half was interfered, and YE-3 v and YE-3 d were resulted. From the results mentioned above, we concluded that TGF beta-related protein are not only present in the early embryos of Xenopus laevis, but also may be concerned with mesoderm induction.

[Immunohistochemical studies on the TGF beta-related protein in the early development of Xenopus laevis]

By the method of immunocytochemistry, using the polyclonal antibodies raised against the 1-29 N-terminal residues of TGF beta-1, we found that the protein could bind to the antibodies was present in the early embryos of Xenopus. The protein was named TGF beta-related protein. It was distributed mainly in the endoderm from blastula (stg. 7) to late neurula. In the blastula (stg. 8), the protein was localized in the vegetal hemisphere near the floor of the blastocoel [Plate I, Fig. 1]. In the early gastrula (stg. 10.5) [Plate I, Fig. 2], it was localized in the central part of the vegetal hemisphere. In late gastrula (stg. 12), it was mainly distributed around the gastrocoel [Plate I, Fig. 3], but the fluorescence in endoderm cells (ventral part beneath the gastrocoel) was stronger than in the mesoderm cells (dorsal part of the gastrocoel). In the early neurula (stg. 14), the whole endoderm displayed strong fluorescence and the part of dorsal mesoderm (presumptive somite & notochord) close to endoderm was also found to be positively stained [Plate I, Fig. 4,5], but the part close to neural plate was negative. In The late neurula (stg. 20) [Plate I, Fig. 6], it was found in the central area of yolk mass (endoderm cells). No positive stain was detected in the unfertilized egg, embryos earlier than stage and later than stage 20/21.2+ protein in early development.