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Dietzel E, Weiskirchen S, Floehr J, Horiguchi M, Todorovic V, Rifkin DB, Jahnen-Dechent W, Weiskirchen R. Latent TGF-β binding protein-1 deficiency decreases female fertility. Biochem Biophys Res Commun 2016; 482:1387-1392. [PMID: 27956181 DOI: 10.1016/j.bbrc.2016.12.046] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 12/07/2016] [Indexed: 11/19/2022]
Abstract
The four latent transforming growth factor-β (TGF-β) binding proteins LTBP1-4 are extracellular matrix-associated proteins playing a critical role in the activation of TGF-β. The LTBP1 gene forms two major transcript variants (i.e. Ltbp1S and Ltbp1L) that are derived from different promoters. We have previously shown the importance of LTBP1 in vivo by using three different Ltbp1 null mice that were either deleted for exons 1 and 2 (Ltbp1L knockout), exon 5 (Ltbp1ΔEx5), or exon 8 (Ltbp1ΔEx8). While the Ltbp1L knockout and the Ltbp1ΔEx8 are perinatal lethal and die of cardiovascular abnormalities, the Ltbp1ΔEx5 is viable because it expresses a short form of Ltbp1L that lacks 55 amino acids (Δ55 variant of Ltbp1) formed by splicing out exon 5, while lacking the Ltbp1S variant. Since only the Ltbp1ΔEx5 mouse is viable, we have used this model to address aspects of puberty, fertility, age-dependent reproduction, and ovary function. We report for the first time a function of LTBP1 in female reproduction. The Ltbp1ΔEx5 females showed impaired fertility associated with delayed sexual maturity (p = 0.0074) and ovarian cyst formation in females older than 40 weeks (p = 0.0204).
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Affiliation(s)
- Eileen Dietzel
- Helmholtz-Institute for Biomedical Engineering, Biointerface Laboratory, RWTH Aachen University, Medical Faculty, 52074 Aachen, Germany.
| | - Sabine Weiskirchen
- Institute of Molecular Pathobiochemistry, Experimental Gene Therapy and Clinical Chemistry, RWTH Aachen University, Medical Faculty, 52074 Aachen, Germany
| | - Julia Floehr
- Helmholtz-Institute for Biomedical Engineering, Biointerface Laboratory, RWTH Aachen University, Medical Faculty, 52074 Aachen, Germany
| | - Masahito Horiguchi
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Vesna Todorovic
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA; Department of Medicine, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Daniel B Rifkin
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA; Department of Medicine, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Willi Jahnen-Dechent
- Helmholtz-Institute for Biomedical Engineering, Biointerface Laboratory, RWTH Aachen University, Medical Faculty, 52074 Aachen, Germany
| | - Ralf Weiskirchen
- Institute of Molecular Pathobiochemistry, Experimental Gene Therapy and Clinical Chemistry, RWTH Aachen University, Medical Faculty, 52074 Aachen, Germany.
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2
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Troilo H, Steer R, Collins RF, Kielty CM, Baldock C. Independent multimerization of Latent TGFβ Binding Protein-1 stabilized by cross-linking and enhanced by heparan sulfate. Sci Rep 2016; 6:34347. [PMID: 27677855 PMCID: PMC5039643 DOI: 10.1038/srep34347] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 09/08/2016] [Indexed: 11/09/2022] Open
Abstract
TGFβ plays key roles in fibrosis and cancer progression, and latency is conferred by covalent linkage to latent TGFβ binding proteins (LTBPs). LTBP1 is essential for TGFβ folding, secretion, matrix localization and activation but little is known about its structure due to its inherent size and flexibility. Here we show that LTBP1 adopts an extended conformation with stable matrix-binding N-terminus, extended central array of 11 calcium-binding EGF domains and flexible TGFβ-binding C-terminus. Moreover we demonstrate that LTBP1 forms short filament-like structures independent of other matrix components. The termini bind to each other to facilitate linear extension of the filament, while the N-terminal region can serve as a branch-point. Multimerization is enhanced in the presence of heparin and stabilized by the matrix cross-linking enzyme transglutaminase-2. These assemblies will extend the span of LTBP1 to potentially allow simultaneous N-terminal matrix and C-terminal fibrillin interactions providing tethering for TGFβ activation by mechanical force.
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Affiliation(s)
- Helen Troilo
- The Wellcome Trust Centre for Cell-Matrix Research is within the School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Ruth Steer
- The Wellcome Trust Centre for Cell-Matrix Research is within the School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Richard F Collins
- The Wellcome Trust Centre for Cell-Matrix Research is within the School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Cay M Kielty
- The Wellcome Trust Centre for Cell-Matrix Research is within the School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Clair Baldock
- The Wellcome Trust Centre for Cell-Matrix Research is within the School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
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3
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Horiguchi M, Todorovic V, Hadjiolova K, Weiskirchen R, Rifkin DB. Abrogation of both short and long forms of latent transforming growth factor-β binding protein-1 causes defective cardiovascular development and is perinatally lethal. Matrix Biol 2015; 43:61-70. [PMID: 25805620 DOI: 10.1016/j.matbio.2015.03.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 03/12/2015] [Accepted: 03/12/2015] [Indexed: 12/30/2022]
Abstract
Latent transforming growth factor-β binding protein-1 (LTBP-1) is an extracellular protein that is structurally similar to fibrillin and has an important role in controlling transforming growth factor-β (TGF-β) signaling by storing the cytokine in the extracellular matrix and by being involved in the conversion of the latent growth factor to its active form. LTBP-1 is found as both short (LTBP-1S) and long (LTBP-1L) forms, which are derived through the use of separate promoters. There is controversy regarding the importance of LTBP-1L, as Ltbp1L knockout mice showed multiple cardiovascular defects but the complete null mice did not. Here, we describe a third line of Ltbp1 knockout mice generated utilizing a conditional knockout strategy that ablated expression of both L and S forms of LTBP-1. These mice show severe developmental cardiovascular abnormalities and die perinatally; thus these animals display a phenotype similar to previously reported Ltbp1L knockout mice. We reinvestigated the other "complete" knockout line and found that these mice express a splice variant of LTBP-1L and, therefore, are not complete Ltbp1 knockouts. Our results clarify the phenotypes of Ltbp1 null mice and re-emphasize the importance of LTBP-1 in vivo.
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Affiliation(s)
- Masahito Horiguchi
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Vesna Todorovic
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA; Department of Medicine, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Krassimira Hadjiolova
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA
| | - Ralf Weiskirchen
- Institute of Molecular Pathobiochemistry, Experimental Gene Therapy and Clinical Chemistry, RWTH University Hospital Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany
| | - Daniel B Rifkin
- Department of Cell Biology, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA; Department of Medicine, New York University Langone School of Medicine, 550 First Avenue, New York, NY 10016, USA.
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4
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Pathogenesis of Varicose Veins. J Vasc Interv Radiol 2012; 23:33-9; quiz 40. [DOI: 10.1016/j.jvir.2011.09.010] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Revised: 08/31/2011] [Accepted: 09/09/2011] [Indexed: 01/24/2023] Open
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5
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Expression of mRNA isoforms of latent transforming growth factor-β binding protein-1 in coronary atherosclerosis and human tissues. Biochem Genet 2010; 49:213-25. [PMID: 21161366 DOI: 10.1007/s10528-010-9400-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2010] [Accepted: 09/17/2010] [Indexed: 10/18/2022]
Abstract
Latent transforming growth factor-β binding protein-1 (LTBP1) has been implicated in the control of secretion, localization, and activation of TGFβ (transforming growth factor-β). We developed a quantitative reverse-transcriptase polymerase chain reaction (Q-RT-PCR) assay using an RNA internal standard to examine the expression of three alternatively spliced isoforms of LTBP1 (LTBP1Δ41, LTBP1Δ53, and LTBP1Δ55) in a variety of human tissues. The assays were also used to determine the expression of LTBP1L and LTBP1S isoforms and total LTBP1. The Q-RT-PCR assays were highly reproducible and showed that in most tissues LTBP1Δ55 and LTBP1L were minor components of LTBP1. The proportion of LTBP1Δ41 ranged from 2% of total LTBP1 mRNA in early coronary atherosclerotic lesions to 54% in advanced lesions.
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6
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Ek W, Strömstedt L, Wahlberg P, Siegel P, Andersson L, Carlborg O. Genetic analysis of metabolic traits in an intercross between body weight-selected chicken lines. Physiol Genomics 2010; 42:20-2. [PMID: 20332184 DOI: 10.1152/physiolgenomics.00149.2009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A network of four interacting loci has been reported previously to influence growth in two lines of chickens divergently selected for body weight at 56 days of age. Located on chromosomes 3 (Growth4), 4 (Growth6), 7 (Growth9), and 20 (Growth12), they explained nearly half of the difference in body weight at selection age between the two lines. The original study reported effects on body weight and fat deposition, but no attempts were made to explore the effects of the network on other phenotypes measured in the F(2) population. In this study we conducted further analyses to evaluate the specific effects of the four-locus network on other metabolic traits as well as refining results from the original study by including a larger number of genetic markers in the quantitative trait locus (QTL) regions. We confirm the previously described effect of the epistatic network on body weight and show that the network increases the total amount of muscle and fat as well as the weight of the internal organs. The network as a whole did not change the relative content of any studied organs or tissues in the body. There was, however, a significant interaction between the loci on chromosomes 3 and 7 that changed the relative proportion of abdominal fat and breast muscle in the chicken by increasing abdominal fat weight without a corresponding increase in muscle mass.
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Affiliation(s)
- Weronica Ek
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden.
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7
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Drews F, Knöbel S, Moser M, Muhlack KG, Mohren S, Stoll C, Bosio A, Gressner AM, Weiskirchen R. Disruption of the latent transforming growth factor-beta binding protein-1 gene causes alteration in facial structure and influences TGF-beta bioavailability. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1783:34-48. [PMID: 17950478 DOI: 10.1016/j.bbamcr.2007.08.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 08/06/2007] [Accepted: 08/13/2007] [Indexed: 11/16/2022]
Abstract
Latent transforming growth factor-beta binding proteins are a family of extracellular matrix proteins comprising four isoforms (LTBP-1, -2, -3, -4) with different structures, tissue expression patterns and affinity for TGF-beta. So far, respective knockout models have highlighted some essential functions for LTBP-2, LTBP-3 and LTBP-4, while the physiological significance of LTBP-1 is only superficially known. Here we report for the first time the generation and characterization of a mouse model lacking both the long and short LTBP-1 isoform. Surprisingly, respective mice are viable and fertile. However, detailed X-ray analysis of the skull revealed a modified facial profile. In addition, the gene disruption induces a reduced biological activity of TGF-beta that became evident in an experimental model of hepatic fibrogenesis in which the LTBP-1 knockout animals were less prone to hepatic fibrogenesis. Furthermore, comparative cDNA microarray gene expression profiling of cultured hepatic stellate cells confirmed that respective nulls were less receptive to cellular activation and transdifferentiation into myofibroblasts. Therefore, we conclude that LTBP-1 has essential functions in the control of TGF-beta activation.
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Affiliation(s)
- Falko Drews
- Institute of Clinical Chemistry and Pathobiochemistry, RWTH University Hospital Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany
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8
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McAlinden A, Havlioglu N, Sandell LJ. Regulation of protein diversity by alternative pre-mRNA splicing with specific focus on chondrogenesis. ACTA ACUST UNITED AC 2004; 72:51-68. [PMID: 15054904 DOI: 10.1002/bdrc.20004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Analysis of the human genome has dramatically demonstrated that the majority of protein diversity is generated by alternative splicing of pre-mRNA. This powerful and versatile mechanism controls the synthesis of functionally different protein isoforms that may be required during specific stages of development from a single gene. Consequently, ubiquitous and/or tissue-specific RNA splicing factors that regulate this splicing mechanism provide the basis for defining phenotypic characteristics of cells during differentiation. In this review, we will introduce the basic mechanisms of pre-mRNA alternative splicing, describe how this process is regulated by specific RNA splicing factors, and relate this to various systems of cell differentiation. Chondrogenesis, a well-defined differentiation pathway necessary for skeletogenesis, will be discussed in detail, with focus on some of the alternatively-spliced proteins known to be expressed during cartilage development. We propose a heuristic view that, ultimately, it is the regulation of these RNA splicing factors that determines the differentiation status of a cell. Studying regulation at the level of pre-mRNA alternative splicing will provide invaluable insights into how many developmental mechanisms are controlled, thus enabling us to manipulate a system to select for a specific differentiation pathway.
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Affiliation(s)
- Audrey McAlinden
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
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9
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Noguera I, Obata H, Gualandris A, Cowin P, Rifkin DB. Molecular cloning of the mouse Ltbp-1 gene reveals tissue specific expression of alternatively spliced forms. Gene 2003; 308:31-41. [PMID: 12711388 DOI: 10.1016/s0378-1119(03)00463-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Latent transforming growth factor binding proteins (Ltbp-1, -2, -3 and -4) and fibrillins (Fbn-1 and -2) are structurally related cysteine-rich extracellular matrix proteins that localize to the 10 nm microfibrils. Ltbp-1 is thought to promote the secretion and proper folding of the small latent transforming growth factor beta (TGF-beta) complex (TGF-beta plus its propeptide) and is implicated in sequestering it in the extracellular matrix. Here we report the isolation of the mouse Ltbp-1 complementary DNA (cDNA) and gene. The longer form of the Ltbp-1 cDNA encodes a predicted 1713 amino acid protein containing 18 epidermal growth factor-like repeats, four 8-cysteine domains and several motifs that suggest interactions with alpha(IV)beta(1) and alpha(9)beta(1) integrins. Northern blotting analyses indicate that long and short Ltbp-1 transcripts are widely expressed in adult mouse tissues and most abundantly expressed in heart. Ltbp-1 is a single copy gene that maps to chromosome 17, band E (1-3) and encompasses more than 212 kb. The Ltbp-1 gene contains 34 exons and shows a similar organization to the LTBP-2 gene, suggesting that these genes originated from a common ancestral gene.
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Affiliation(s)
- Irene Noguera
- Department of Cell Biology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA
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10
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Abstract
Latent transforming growth factor beta binding protein-1 (LTBP-1) is important in regulating the localization and activation of transforming growth factor beta. In this paper is reported the isolation of the full-length Xenopus LTBP-1 cDNA from screening a neurula embryo cDNA library. Sequence analysis of XLTBP-1 cDNA revealed an open reading frame of 4518 bp encoding a 1398 amino acid protein with a molecular mass of 154.1 kDa and an isoelectric point of 4.65. The Xenopus XLTBP-1 shares 61 and 65% amino acid identity with the mouse and human LTBP-1, respectively. It contains 17 epidermal growth factor-like motifs and four eight-cysteine repeats (8-Cys). RNase protection assay revealed that XLTBP-1 is a maternal and zygotic gene, while whole-mount in situ hybridization analysis performed on embryos at different stages showed that during early Xenopus development, XLTBP-1 mRNA is expressed in the Spemann organizer, prechordal and chordal mesoderm, and later on in the organizer derived tissues. These findings suggest an important role for XLTBP-1 in embryo axis formation.
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Affiliation(s)
- Natalina Quarto
- Dipartimento di Chimica Biologica, Facoltà di Scienze dell'Università di Napoli, Federico II, Napoli, Italy.
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11
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Mangasser-Stephan K, Gartung C, Lahme B, Gressner AM. Expression of isoforms and splice variants of the latent transforming growth factor beta binding protein (LTBP) in cultured human liver myofibroblasts. LIVER 2001; 21:105-13. [PMID: 11318979 DOI: 10.1034/j.1600-0676.2001.021002105.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND/AIMS The activation of hepatic stellate cells (HSC) to extracellular matrix (ECM) producing myofibroblasts (MFB) is the key pathogenetic event in human liver fibrogenesis. Latent transforming growth factor beta binding protein (LTBP), a component of the profibrogenic large latent transforming growth factor (TGF)-beta complex, is suggested to be important for secretion, latency, storage and activation of TGF-beta in the ECM. This study was performed to identify the expression profile of all hitherto known LTBP isoforms and LTBP splice variants in conjunction with that of TGF-beta isoforms in cultured human liver MFB. METHODS Cultured human MFB were analyzed for TGF-beta and LTBP using reverse-transcription polymerase chain reaction (RT-PCR), sequence analysis, immunofluorescence staining, metabolic labeling, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA). RESULTS Transcripts of all three TGF-beta isoforms, of all four LTBP isoforms and of nearly all splice variants of LTBP-1 and LTBP-4 so far known were detected. Metabolic labeling followed by immunoprecipitation with anti-LTBP-1 antibody revealed the synthesis of LTBP proteins. Secretion of free LTBP and LTBP integrated into the large latent TGF-beta complex was demonstrated by size-exclusion chromatography. Co-localization of LTBP-1 and -2 with fibronectin and collagen type I was observed by double immunofluorescence staining. CONCLUSION The expression of a complete profile of hitherto known LTBP proteins by cultured human MFB suggests a role in modulating the bioactivity of TGF-beta in the diseased liver.
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Affiliation(s)
- K Mangasser-Stephan
- Institute of Clinical Chemistry and Pathobiochemistry, Central Laboratory, RWTH-University Hospital, Aachen, Germany
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12
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Abstract
The TGF-beta superfamily of growth factors consists of an increasing number of different polypeptide modulators of cell growth, differentiation, and morphogenesis. Three mammalian isoforms have been molecularly cloned. Numerous ways to regulate the expression of the TGF-beta genes have been identified. TGF-betas are, for example, subject to regulation by retinoids, steroid hormones, and vitamin D. A characteristic feature in the biology of TGF-betas is that they are usually secreted from cells in latent forms. The large latent complex consists of the small latent complex (TGF-beta and its propeptide) and a high molecular weight protease resistant binding protein, latent TGF-beta binding protein (LTBP). LTBPs are required for the proper folding and secretion of TGF-beta. TGF-beta is not just secreted from cultured cells but is deposited via LTBPs to the pericellular space, namely to the extracellular matrix. Release of these complexes and activation by proteases is under tight regulation and provides a means to rapidly increase local concentrations of TGF-beta. Biological events, where enhanced or focal proteolysis and activation of latent TGF-beta takes place, include cell invasion, tissue remodeling, and wound healing.
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Affiliation(s)
- K Koli
- Department of Virology, Haartman Institute, University of Helsinki, FIN-00014 Helsinki, Finland.
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13
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Norman SA, Rhodes SN, Treasurywala S, Hoelzinger DB, Rankin Shapiro J, Scheck AC. Identification of transforming growth factor-?1-binding protein overexpression in carmustine-resistant glioma cells by MRNA differential display. Cancer 2000. [DOI: 10.1002/1097-0142(20000815)89:4<850::aid-cncr18>3.0.co;2-b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Koski C, Saharinen J, Keski-Oja J. Independent promoters regulate the expression of two amino terminally distinct forms of latent transforming growth factor-beta binding protein-1 (LTBP-1) in a cell type-specific manner. J Biol Chem 1999; 274:32619-30. [PMID: 10551816 DOI: 10.1074/jbc.274.46.32619] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Latent transforming growth factor-beta (TGF-beta)-binding proteins (LTBPs) are components of the extracellular matrix and large latent TGF-beta complexes are secreted by various cells. Human LTBP-1 is known to exist in different forms. LTBP-1L (long) has an amino-terminal extension, which is not found in the smaller LTBP-1S isoform. To study the formation and transcriptional regulation of LTBP-1S and LTBP-1L isoforms, we determined the nucleotide sequences of their 5'-flanking regions. The upstream regions of both isoforms are devoid of TATA boxes but contain other putative binding sites for several transcription factors. Genomic sequencing revealed that LTBP-1L transcript is alternatively spliced to an internal splice acceptor inside exon 1 of LTBP-1S and thus defined the genomic organization of the isoforms. Reporter gene analysis of upstream regions indicated the presence of independent, functional promoters, which regulate the transcription of the isoforms by cell-specific manner. Deletion analyses of the promoter regions revealed specific elements modulating their basal and cell type-specific expression. In SV-40 virus-transformed WI-38 lung fibroblasts a regulatory element repressed the transcription of LTBP-1S by a cell-specific manner. In amniotic epithelial cells, transcription of the LTBP-1S reporter gene construct was down-regulated by a distal upstream element. mRNA levels of the isoforms of LTBP-1 were stimulated in response to TGF-beta1 in WI-38 cells. However, since TGF-beta1 failed to stimulate the transcription of LTBP-1 reporter gene constructs, TGF-beta1 may mediate the induction of the isoforms by post-transcriptional mechanisms. Chromosomal localization of the LTBP-1 gene was refined to 2p22-24.
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Affiliation(s)
- C Koski
- Department of Virology, The Haartman Institute, University of Helsinki, FIN-00014 Helsinki, Finland
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Saharinen J, Hyytiäinen M, Taipale J, Keski-Oja J. Latent transforming growth factor-beta binding proteins (LTBPs)--structural extracellular matrix proteins for targeting TGF-beta action. Cytokine Growth Factor Rev 1999; 10:99-117. [PMID: 10743502 DOI: 10.1016/s1359-6101(99)00010-6] [Citation(s) in RCA: 215] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Growth factors of the transforming growth factor-beta family are potent regulators of the extracellular matrix formation, in addition to their immunomodulatory and regulatory roles for cell growth. TGF-beta s are secreted from cells as latent complexes containing TGF-beta and its propeptide, LAP (latency-associated peptide). In most cells LAP is covalently linked to an additional protein, latent TGF-beta binding protein (LTBP), forming the large latent complex. LTBPs are required for efficient secretion and correct folding of TGF-beta s. The secreted large latent complexes associate covalently with the extracellular matrix via the N-termini of the LTBPs. LTBPs belong to the fibrillin-LTBP family of extracellular matrix proteins, which have a typical repeated domain structure consisting mostly of epidermal growth factor (EGF)-like repeats and characteristic eight cysteine (8-Cys) repeats. Currently four different LTBPs and two fibrillins have been identified. LTBPs contain multiple proteinase sensitive sites, providing means to solubilize the large latent complex from the extracellular matrix structures. LTBPs are now known to exist both as soluble molecules and in association with the extracellular matrix. An important consequence of this is LTBP-mediated deposition and targeting of latent, activatable TGF-beta into extracellular matrices and connective tissues. LTBPs have a dual function, they are required both for the secretion of the small latent TGF-beta complex as well as directing bound latent TGF-beta to extracellular matrix microfibrils. However, it is not known at present whether LTBPs are capable of forming microfibrils independently, or whether they are a part of the fibrillin-containing fibrils. Most LTBPs possess RGD-sequences, which may have a role in their interactions with the cell surface. At least LTBP-1 is chemotactic to smooth muscle cells, and is involved in vascular remodelling. Analyses of the expressed LTBPs have revealed considerable variations throughout the molecules, generated both by alternative splicing and utilization of multiple promoter regions. The significance of this structural diversity is mostly unclear at present.
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Affiliation(s)
- J Saharinen
- Department of Virology, Haartman Institute, University of Helsinki, Finland
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