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

Curcumin relieves arecoline-induced oral submucous fibrosis via inhibiting the LTBP2/NF-κB axis

BACKGROUND

Submucosal fibrosis (OSF) of the oral cavity is a chronic scarring disease. Arecoline (Are) is the driving factor for the occurrence and deterioration of OSF. Curcumin plays a vital anti-inflammatory role in Are-induced OSF development. However, its potential pharmacological mechanism needs to be elucidated.

METHODS

The relative molecular level was measured via qRT-PCR or Western blot. MTT assay, transwell assay and flow cytometry detected cell proliferation, migration, and apoptosis. The correlation between hypoxia-inducible factor-1α (HIF-1α) and LTBP2 promoter was confirmed through dual-luciferase reporter assay. ELISA was performed to detect inflammatory cytokines levels.

RESULTS

Curcumin alleviated Are-induced oral mucosal fibroblast cells fibrosis by reducing oral mucosa fibroblasts viability, promoting cell apoptosis, suppressing cell migration, and down-regulating the levels of fibrosis markers and inflammatory factors. Curcumin relieved Are-induced OSF via inhibiting HIF-1α. Mechanically, HIF-1α bound to the promoter of LTBP2 to transcriptionally activated LTBP2. LTBP2 knockdown relieved Are-induced OSF, and curcumin down-regulated LTBP2 via inhibiting HIF-1α to relieve Are-induced OSF. Moreover, curcumin decreased NF-κB signal associated proteins via inhibiting LTBP2 to relieve Are-induced OSF.

CONCLUSION

Curcumin reduced the transcription level of LTBP2 by inhibiting HIF-1α, thereby inactivating NF-κB pathway to alleviate Are-induced OSF.

Mitochondrial calcium uptake regulates tumour progression in embryonal rhabdomyosarcoma

Embryonal rhabdomyosarcoma (ERMS) is characterised by a failure of cells to complete skeletal muscle differentiation. Although ERMS cells are vulnerable to oxidative stress, the relevance of mitochondrial calcium homoeostasis in oncogenesis is unclear. Here, we show that ERMS cell lines as well as primary tumours exhibit elevated expression of the mitochondrial calcium uniporter (MCU). MCU knockdown resulted in impaired mitochondrial calcium uptake and a reduction in mitochondrial reactive oxygen species (mROS) levels. Phenotypically, MCU knockdown cells exhibited reduced cellular proliferation and motility, with an increased propensity to differentiate in vitro and in vivo. RNA-sequencing of MCU knockdown cells revealed a significant reduction in genes involved in TGFβ signalling that play prominent roles in oncogenesis and inhibition of myogenic differentiation. Interestingly, modulation of mROS production impacted TGFβ signalling. Our study elucidates mechanisms by which mitochondrial calcium dysregulation promotes tumour progression and suggests that targeting the MCU complex to restore mitochondrial calcium homoeostasis could be a therapeutic avenue in ERMS.

Quantitative proteomic profiling of extracellular matrix and site-specific collagen post-translational modifications in an in vitro model of lung fibrosis

Lung fibrosis is characterized by excessive deposition of extracellular matrix (ECM), in particular collagens, by fibroblasts in the interstitium. Transforming growth factor-β1 (TGF-β1) alters the expression of many extracellular matrix (ECM) components produced by fibroblasts, but such changes in ECM composition as well as modulation of collagen post-translational modification (PTM) levels have not been comprehensively investigated. Here, we performed mass spectrometry (MS)-based proteomics analyses to assess changes in the ECM deposited by cultured lung fibroblasts from idiopathic pulmonary fibrosis (IPF) patients upon stimulation with transforming growth factor β1 (TGF-β1). In addition to the ECM changes commonly associated with lung fibrosis, MS-based label-free quantification revealed profound effects on enzymes involved in ECM crosslinking and turnover as well as multiple positive and negative feedback mechanisms of TGF-β1 signaling. Notably, the ECM changes observed in this in vitro model correlated significantly with ECM changes observed in patient samples. Because collagens are subject to multiple PTMs with major implications in disease, we implemented a new bioinformatic platform to analyze MS data that allows for the comprehensive mapping and site-specific quantitation of collagen PTMs in crude ECM preparations. These analyses yielded a comprehensive map of prolyl and lysyl hydroxylations as well as lysyl glycosylations for 15 collagen chains. In addition, site-specific PTM analysis revealed novel sites of prolyl-3-hydroxylation and lysyl glycosylation in type I collagen. Interestingly, the results show, for the first time, that TGF-β1 can modulate prolyl-3-hydroxylation and glycosylation in a site-specific manner. Taken together, this proof of concept study not only reveals unanticipated TGF-β1 mediated regulation of collagen PTMs and other ECM components but also lays the foundation for dissecting their key roles in health and disease.

The proteomic data has been deposited to the ProteomeXchange Consortium via the MassIVE partner repository with the data set identifier MSV000082958.

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Quantitative proteomics of TGF-β-induced changes in ECM composition and collagen PTM in pulmonary fibroblasts

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TGF-β promotes crosslinking and turnover as well as complex feedback mechanisms that alter fibroblast ECM homeostasis.

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A novel bioinformatic workflow for MS data analysis enabled global mapping and quantitation of known and novel collagen PTMs

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Quantitative assessment of prolyl-3-hydroxylation site occupancy and lysine-O-glycosylation microheterogeneity

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TGF-β1 modulates collagen PTMs in a site-specific manner that may favor collagen accumulation in lung fibrosis

LTBP2 is secreted from lung myofibroblasts and is a potential biomarker for idiopathic pulmonary fibrosis

Although differentiation of lung fibroblasts into α-smooth muscle actin (αSMA)-positive myofibroblasts is important in the progression of idiopathic pulmonary fibrosis (IPF), few biomarkers reflecting the fibrotic process have been discovered. We performed microarray analyses between FACS-sorted steady-state fibroblasts (lineage (CD45, TER-119, CD324, CD31, LYVE-1, and CD146)-negative and PDGFRα-positive cells) from untreated mouse lungs and myofibroblasts (lineage-negative, Sca-1-negative, and CD49e-positive cells) from bleomycin-treated mouse lungs. Amongst several genes up-regulated in the FACS-sorted myofibroblasts, we focussed on Ltbp2, the gene encoding latent transforming growth factor-β (TGF-β) binding protein-2 (LTBP2), because of the signal similarity to Acta2, which encodes αSMA, in the clustering analysis. The up-regulation was reproduced at the mRNA and protein levels in human lung myofibroblasts induced by TGF-β1. LTBP2 staining in IPF lungs was broadly positive in the fibrotic interstitium, mainly as an extracellular matrix (ECM) protein; however, some of the αSMA-positive myofibroblasts were also stained. Serum LTBP2 concentrations, evaluated using ELISA, in IPF patients were significantly higher than those in healthy volunteers (mean: 21.4 compared with 12.4 ng/ml) and showed a negative correlation with % predicted forced vital capacity (r = -0.369). The Cox hazard model demonstrated that serum LTBP2 could predict the prognosis of IPF patients (hazard ratio for death by respiratory events: 1.040, 95% confidence interval: 1.026-1.054), which was validated using the bootstrap method with 1000-fold replication. LTBP2 is a potential prognostic blood biomarker that may reflect the level of differentiation of lung fibroblasts into myofibroblasts in IPF.

Proteomic profiling identifies markers for inflammation-related tumor-fibroblast interaction

Background

Cancer associated fibroblasts are activated in the tumor microenvironment and contribute to tumor progression, angiogenesis, extracellular matrix remodeling, and inflammation.

Methods

To identify proteins characteristic for fibroblasts in colorectal cancer we used liquid chromatography-tandem mass spectrometry to derive protein abundance from whole-tissue homogenates of human colorectal cancer/normal mucosa pairs. Alterations of protein levels were determined by two-sided t test with greater than threefold difference and an FDR of < 0.05. Public available datasets were used to predict proteins of stromal origin and link protein with mRNA regulation. Immunohistochemistry confirmed the localization of selected proteins.

Results

We identified a set of 24 proteins associated with inflammation, matrix organization, TGFβ receptor signaling and angiogenesis mainly originating from the stroma. Most prominent were increased abundance of SerpinB5 in the parenchyme and latent transforming growth factor β-binding protein, thrombospondin-B2, and secreted protein acidic-and-cysteine-rich in the stroma. Extracellular matrix remodeling involved collagens type VIII, XII, XIV, and VI as well as lysyl-oxidase-2. In silico analysis of mRNA levels demonstrated altered expression in the tumor and the adjacent normal tissue as compared to mucosa of healthy individuals indicating that inflammatory activation affected the surrounding tissue. Immunohistochemistry of 26 tumor specimen confirmed upregulation of SerpinB5, thrombospondin B2 and secreted protein acidic-and-cysteine-rich.

Conclusions

This study demonstrates the feasibility of detecting tumor- and compartment-specific protein-signatures that are functionally meaningful by proteomic profiling of whole-tissue extracts together with mining of RNA expression datasets. The results provide the basis for further exploration of inflammation-related stromal markers in larger patient cohorts and experimental models.

Presentation of a keratocystic odontogenic tumor with agenesis: a case report

Introduction

We analyzed the etiopathogenetic, clinical, radiographic, and histopathologic aspects of keratocystic odontogenic tumors, particularly in association with dental anomalies of number, with the aim of providing useful information for their correct diagnosis, treatment, and prognosis within a multidisciplinary approach.

Case presentation

A 14-year-old Caucasian girl presented for observation of bilateral agenesis of the upper incisors, which was diagnosed by orthopantomography. Approximately one year after starting orthodontic treatment, the patient went to the emergency department because of a phlegmonous tumefaction of the lateroposterior upper left maxillary region. Diagnostic orthopantomography and axial computed tomography scan results of the facial skeleton revealed a large lesion occupying the left maxillary sinus, rhizolysis of dental elements 26 and 27, and dislocation of dental element 28. The lesion and infected sinus mucosa were removed through surgical antral-cystectomy with the Caldwell-Luc approach. Histological examination of the lesion confirmed the suspected diagnosis of keratocystic odontogenic tumor. The 12-month follow-up orthopantomography and computed tomography scan results showed good trabecular bone formation in the lesion area. The 24-month follow-up results showed optimal healing in the area of the lesion, positive pulp vitality tests for teeth 26 and 27, and good periodontal tissue healing, as verified through periodontal probing.

Conclusions

Combined with our observations from a careful review of the literature, the results of the case study suggest that keratocystic odontogenic tumor and dental agenesis probably do not develop through a common genetic cause. More likely, they are caused by related environmental factors. Management of this case required the multidisciplinary collaboration of different specializations and careful planning to devise a correct therapeutic protocol and reach a favorable prognosis.

The role of quantitative mass spectrometry in the discovery of pancreatic cancer biomarkers for translational science

In the post-genomic era, it has become evident that genetic changes alone are not sufficient to understand most disease processes including pancreatic cancer. Genome sequencing has revealed a complex set of genetic alterations in pancreatic cancer such as point mutations, chromosomal losses, gene amplifications and telomere shortening that drive cancerous growth through specific signaling pathways. Proteome-based approaches are important complements to genomic data and provide crucial information of the target driver molecules and their post-translational modifications. By applying quantitative mass spectrometry, this is an alternative way to identify biomarkers for early diagnosis and personalized medicine. We review the current quantitative mass spectrometric technologies and analyses that have been developed and applied in the last decade in the context of pancreatic cancer. Examples of candidate biomarkers that have been identified from these pancreas studies include among others, asporin, CD9, CXC chemokine ligand 7, fibronectin 1, galectin-1, gelsolin, intercellular adhesion molecule 1, insulin-like growth factor binding protein 2, metalloproteinase inhibitor 1, stromal cell derived factor 4, and transforming growth factor beta-induced protein. Many of these proteins are involved in various steps in pancreatic tumor progression including cell proliferation, adhesion, migration, invasion, metastasis, immune response and angiogenesis. These new protein candidates may provide essential information for the development of protein diagnostics and targeted therapies. We further argue that new strategies must be advanced and established for the integration of proteomic, transcriptomic and genomic data, in order to enhance biomarker translation. Large scale studies with meta data processing will pave the way for novel and unexpected correlations within pancreatic cancer, that will benefit the patient, with targeted treatment.

Cutis laxa: intersection of elastic fiber biogenesis, TGFβ signaling, the secretory pathway and metabolism

Cutis laxa (CL), a disease characterized by redundant and inelastic skin, displays extensive locus heterogeneity. Together with geroderma osteodysplasticum and arterial tortuosity syndrome, which show phenotypic overlap with CL, eleven CL-related genes have been identified to date, which encode proteins within 3 groups. Elastin, fibulin-4, fibulin-5 and latent transforming growth factor-β-binding protein 4 are secreted proteins which form elastic fibers and are involved in the sequestration and subsequent activation of transforming growth factor-β (TGFβ). Proteins within the second group, localized to the secretory pathway, perform transport and membrane trafficking functions necessary for the modification and secretion of elastic fiber components. Key proteins include a subunit of the vacuolar-type proton pump, which ensures the efficient secretion of tropoelastin, the precursor or elastin. A copper transporter is required for the activity of lysyl oxidases, which crosslink collagen and elastin. A Rab6-interacting goglin recruits kinesin motors to Golgi-vesicles facilitating the transport from the Golgi to the plasma membrane. The Rab and Ras interactor 2 regulates the activity of Rab5, a small guanosine triphosphatase essential for the endocytosis of various cell surface receptors, including integrins. Proteins of the third group related to CL perform metabolic functions within the mitochondria, inhibiting the accumulation of reactive oxygen species. Two of these proteins catalyze subsequent steps in the conversion of glutamate to proline. The third transports dehydroascorbate into mitochondria. Recent studies on CL-related proteins highlight the intricate connections among membrane trafficking, metabolism, extracellular matrix assembly, and TGFβ signaling.

LTBP-2 acts as a novel marker in human heart failure - a preliminary study

BACKGROUND

We have observed increased expression of latent TGF-β binding protein (LTBP)-2 mRNA in human failing hearts. This study was aimed to further confirm LTBP-2 act as a novel marker in human acute heart failure.

METHODS AND RESULTS

We demonstrated that median level of LTBP-2 in myocardial samples from heart failure patients was significantly elevated, and TGF-β1 significantly promoted LTBP-2 expression in neonatal rat cardiomyocytes. To investigate the potential of LTBP-2 as a biomarker to diagnose heart failure with reduced ejection fraction (HFREF), another cohort of 133 consecutive patients with dyspnea were enrolled. In receiver operating characteristic (ROC) curve analyses to detect HFREF, LTBP-2 achieved an area under curve (AUC) of 0.67 (95% confidence intervals (CI) 0.58-0.75), comparable to the diagnostic ability of NT-proBNP 0.68 (95% CI 0.59-0.77).

CONCLUSION

The serum LTBP-2 levels might act as a promising biomarker in HFREF.

Identification of novel accessible proteins bearing diagnostic and therapeutic potential in human pancreatic ductal adenocarcinoma

Pancreas ductal adenocarcinoma (PDAC) remains a deadly malignancy with poor early diagnostic and no effective therapy. Although several proteomic studies have performed comparative analysis between normal and malignant tissues, there is a lack of clear characterization of proteins that could be of clinical value. Systemically reachable ("potentially accessible") proteins, suitable for imaging technologies and targeted therapies represent a major group of interest. The current study explores potentially accessible proteins overexpressed in PDAC, employing innovative proteomics technologies. In the discovery phase, potentially accessible proteins from fresh human normal and PDAC tissues were ex vivo biotinylated, isolated and identified using 2D-nano-HPLC-MS/MS method. The analysis revealed 422 up-regulated proteins in the tumor, of which 83 (including protein isoforms) were evaluated as potentially accessible. Eleven selected candidates were further confirmed as up-regulated using Western blot and multiple reaction monitoring protein quantification. Of these, transforming growth factor beta-induced (TGFBI), latent transforming growth factor beta binding 2 (LTBP2), and asporin (ASPN) were further investigated by employing large scale immunohistochemistry-based validations. They were found to be significantly expressed in a large group of clinical PDAC samples compared to corresponding normal and inflammatory tissues. In conclusion, TGFBI, LTBP2, and ASPN are novel, overexpressed, and potentially accessible proteins in human PDAC. They bear the potential to be of clinical value for diagnostic and therapeutic applications and merit further studies using in vivo models.

Independent regulation of short and long forms of latent TGF-beta binding protein (LTBP)-4 in cultured fibroblasts and human tissues

Transforming growth factor (TGF)-beta is secreted and targeted into the extracellular matrix (ECM) in association with one of the latent TGF-beta binding proteins (LTBPs). Activation of these latent complexes is an important regulatory step in TGF-beta signaling. LTBPs target the growth factor into the ECM and expose it to activating mechanisms. Disruption of LTBP-4 gene causes severe developmental abnormalities in both humans and mice. Transcripts for two N-terminally distinct LTBP-4 variants, LTBP-4S (short) and -4L (long), have been identified. In the current work, we have characterized differences in the expression, processing, and ECM targeting of these LTBP-4 variants. Heart and skeletal muscle displayed expression of both variants, while liver expressed mainly LTBP-4L and lung as well as small intestine LTBP-4S. This tissue-specific expression pattern was found to originate from control of transcription by two independent promoters. Furthermore, LTBP-4S and -4L proteins were secreted and processed differently. During secretion, LTBP-4L was complexed with TGF-beta1, whereas the majority of LTBP-4S was secreted in a free form. In addition, LTBP-4S was incorporated into the ECM, while full-length LTBP-4L was not readily detectable in the ECM. These data suggest that LTBP-4 functions are modified by tissue-specific expression of the two N-terminally distinct variants, which in addition exhibit significant differences in cellular processing and targeting, that is, this provides a basis for understanding molecular diversity in LTBP-4 structure and function.

Induction of human LTBP-3 promoter activity by TGF-beta1 is mediated by Smad3/4 and AP-1 binding elements

Latent TGF-beta binding proteins (LTBPs) are extracellular matrix glycoproteins, which are essential for the targeting and activation of TGF-betas. LTBP-3 regulates the bioavailability of TGF-beta especially in the bone. To understand the regulation of LTBP-3 expression, we have isolated and characterized the promoter region of human LTBP-3 gene. The GC-rich TATA-less promoter contained several transcription initiation sites and putative binding sites for multiple sequence specific transcription factors including Sp1, AP-1, c-Ets, MZF-1, Runx1 and members of the GATA-family. Reporter gene analyses of the promoter indicated that it was more active in MG-63 than in Saos-2 osteosarcoma cells, suggesting that it is regulated as the endogenous gene. TGF-beta1 stimulated the transcriptional activity of LTBP-3 promoter in MG-63 cells, while certain other bone-derived growth factors and hormones were ineffective. TGF-beta1 increased LTBP-3 mRNA levels accordingly. Analyses of deletion constructs of the promoter and mutational deletion of specific transcription factor binding sites indicated that Smad3/4 and AP-1 binding sites mediated the TGF-beta1 response. The involvement of AP-1 activity was further indicated by decreased TGF-beta responsiveness of the LTBP-3 promoter in the presence of a MEK/Erk signaling pathway inhibitor. Our results suggest an important new role for TGF-beta1 in the regulation of its binding protein, LTBP-3.

Gene expression profiling of normal human pulmonary fibroblasts following coculture with non-small-cell lung cancer cells reveals alterations related to matrix degradation, angiogenesis, cell growth and survival

Increasing evidence supports a major role for the microenvironment in carcinoma formation and progression. The influence of the stroma is partly mediated by signalling between epithelial tumor cells and neighboring fibroblasts. However, the molecular mechanisms underlying these interactions are largely unknown. To mimic the initial steps of invasive carcinoma in which tumor cells come in contact with normal stromal cells, we used a coculture model of non-small-cell lung cancer tumor cells and normal pulmonary fibroblasts. Using DNA filter arrays, we first analysed the overall modification of gene expression profile after a 24 h period of coculture. Next, we focused our interest on the transcriptome of the purified fibroblastic fraction of coculture using both DNA filter arrays and a laboratory-made DNA microarray. These experiments allowed the identification of a set of modulated genes coding for growth and survival factors, angiogenic factors, proteases and protease inhibitors, transmembrane receptors, kinases and transcription regulators that can potentially affect the regulation of matrix degradation, angiogenesis, invasion, cell growth and survival. This study represents to our knowledge the first attempt to dissect early global gene transcription occurring in a tumor-stroma coculture model and should help to understand better some of the molecular mechanisms involved in heterotypic signalling between epithelial tumor cells and fibroblasts.

Beta(2)-adrenoceptor stimulation enhances latent transforming growth factor-beta-binding protein-1 and transforming growth factor-beta1 expression in rat hippocampus after transient forebrain ischemia

A protective capacity of transforming growth factor-beta1 (TGF-beta1) against various insults inducing neurone cell death in vitro and in vivo has been well established. We have recently shown the rapid up-regulation and persistent expression of TGF-beta1 in surviving CA1 pyramidal cells after cerebral ischemia suggesting an endogenous mechanism of neuroprotection by this multifunctional cytokine. In the present study, we demonstrated that intraperitoneal administration of clenbuterol, a lipophilic beta(2)-adrenoceptor agonist, caused an increase in TGF-beta1 expression in non-ischemic rats and further enhanced TGF-beta1 protein levels in rat CA1 pyramidal neurones after transient forebrain ischemia. In the hippocampus neuroprotection by clenbuterol (0.5 mg/kg) was accompanied by increased TGF-beta1 immunoreactivity as early as 3 h, and remained elevated up to 2 days after ischemia. The corresponding increased TGF-beta1 mRNA levels after ischemia were not further enhanced by clenbuterol, suggesting post-transcriptional regulation of TGF-beta1 protein after beta(2)-adrenoceptor stimulation. In saline-treated rats latent TGF-beta-binding protein-1 (LTBP-1) immunoreactivity was moderately elevated 3 and 6 h after ischemia, and returned to control levels after 1 day of reperfusion. In parallel with the up-regulation of TGF-beta1 immunoreactivity, LTBP-1 levels in the hippocampus were considerably increased by clenbuterol from 3 h to 2 days after ischemia. Our data demonstrate a concomitant increase in LTBP-1 and TGF-beta1 expression in the ischemic hippocampus after stimulation of beta(2)-adrenoceptors.

Role of transforming growth factor-beta1 and its latent form binding protein in pseudoexfoliation syndrome

Pseudoexfoliation (PEX) syndrome is a common and clinically important systemic condition characterized by the pathologic production and accumulation of an abnormal fibrillar extracellular material in many intra- and extraocular tissues. Recent evidence suggests that it is a type of elastosis associated with the excess synthesis of elastic microfibrillar components such as fibrillin-1. Since transforming growth factor (TGF)-beta is a major modulator of extracellular matrix formation, the potential involvement of TGF-beta and its latent form binding protein (LTBP) in this aberrant matrix process was investigated. The expression of various isoforms of TGF-beta and LTBP was investigated in the anterior segment tissues of PEX and control eyes on the protein and mRNA level by light and electron microscopic immunohistochemistry, in situ hybridization, and semiquantitative RT-PCR. TGF-beta1 and TGF-beta2 levels were measured in aqueous humor and serum of PEX and control patients by ELISA. Cultures of Tenon's capsule fibroblasts were established to study the effect of TGF-beta1 on fibrillin-1 mRNA expression by Northern blot analysis. Significantly increased concentrations of both total and active TGF-beta1 were measured in the aqueous humor of PEX eyes without and with glaucoma as compared to control eyes, whereas levels of TGF-beta2 were not significantly different. The expression of TGF-beta1, LTBP-1, and LTBP-2, but not TGF-beta2, was markedly increased in anterior segment tissues of PEX eyes, particularly in the non-pigmented epithelium of the ciliary body, on both the mRNA and the protein level. Latent TGF-beta1 staining was consistently associated with PEX material deposits and could be released by proteolytic processing. Double immunolabeling revealed clear co-localization of LTBP-1 and -2 with latent TGF-beta1 and with fibrillin-1 on PEX fibrils. The expression of mRNA coding for fibrillin-1 was up-regulated in vitro by TGF-beta1. This study provides evidence for a significant role of TGF-beta1 and the LTBPs 1 and 2 in PEX syndrome. The results suggest that increased levels of latent and active TGF-beta1 in the aqueous humor of PEX patients, derived from enhanced local synthesis and activation, promote the buildup of the abnormal extracellular elastic material characteristic of PEX syndrome. They further support a dual role for LTBPs, both as integral structural components of PEX fibers and as a means of matrix anchorage of latent TGF-beta1, representing one possible mechanism for the regulation of TGF-beta1 activity in PEX eyes. Future therapeutic strategies might focus on TGF-beta1 antagonistic approaches.

Elastic fiber proteins in the glomerular mesangium in vivo and in cell culture

BACKGROUND

Glomerular capillaries of the mammalian kidney are exposed to high intraluminal hydrostatic pressures and require elastic constraint to maintain size, shape, and integrity. Previous morphological and functional studies indicated that the extracellular matrices of glomeruli, that is, basement membrane and mesangial matrix, contribute to glomerular resilience and mechanical stability. Immunofluorescence microscopy findings demonstrated elastic fiber components to be located in the renal vasculature, including glomeruli. The aim of this study was to clarify the exact glomerular localization, composition, and cellular production of these proteins.

METHODS

We examined the renal distribution of the elastic fiber proteins fibrillin-1, emilin, microfibril-associated glycoproteins (MAGPs) 1 and 2, latent transforming growth factor-binding protein-1 (LTBP-1), and elastin using immunohistology and immunoelectron microscopy of human, rat, and mouse kidneys. In mesangial cell cultures, we also studied the expression and extracellular deposition of such proteins by use of Northern blotting and immunocytochemistry.

RESULTS

Fibrillin-1, emilin, MAGPs 1 and 2, and LTBP-1 were present in glomeruli of mouse, rat, and human kidney, where they were located predominantly in the mesangial extracellular matrix underlying glomerular endothelium and basement membrane. Several of these proteins, as well as elastin, were also expressed in the renal vasculature. While elastin localized to the glomerular vascular pole in afferent and efferent arterioles extending to Bowman's capsule, it was not found in the glomerular capillary tuft. Cultured mesangial cells of rat, mouse, and human kidneys expressed mRNAs of fibrillin-1, emilin, MAGP-2, and elastin, and the respective proteins localized within and outside of mesangial cells, as shown by immunocytochemistry. mRNA expression of fibrillin-1, emilin, and elastin was strong in quiescent mesangial cells; their gene expression was further up-regulated by transforming growth factor-beta1, while it was transiently reduced when cells were exposed to mitogenic 10% fetal calf serum and platelet-derived growth factor.

CONCLUSIONS

These findings demonstrate that specific elastic fiber proteins are produced and secreted by mesangial cells. This process is regulated by growth factors. Their abundance in the extracellular matrix of the mesangium is in keeping with the concept that elastic fiber proteins contribute to the mechanical stability and elastic strength of the glomerular capillary tuft.

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.

TGF-beta signaling in A549 lung carcinoma cells: lipid second messengers

Transforming growth factor-beta (TGF-beta) is a potent inducer of numerous extracellular matrix components, largely through a transcriptional mechanism. To define the postreceptor signaling pathways used by TGF-beta in the induction of extracellular matrix gene expression, we have utilized the human lung carcinoma cell line, A549, in transfection experiments with the TGF-beta inducible reporter construct, p3TP-Lux. Previous work from this laboratory using pharmacologic agents suggested that a phosphatidylcholine-specific phospholipase C and protein kinase C may be involved in early aspects of TGF-beta signaling. Here we provide evidence that TGF-beta induces a rapid and transient increase in diacylglycerol (DAG) production. When cells transfected with the p3TP-Lux reporter plasmid are simultaneously treated with TGF-beta and a DAG kinase inhibitor, we observed a higher level of luciferase than with TGF-beta alone. We also find elevated levels of phosphocholine in cells following TGF-beta treatment. Further, exogenously added bacterial phosphatidylcholine phospholipase C (PC-PLC) is capable of inducing expression of the p3TP-Lux reporter to the same extent as TGF-beta indicating that the bacterial PC-PLC can mimic the TGF-beta effect. In contrast, neither hexanoyl sphingosine (a ceramide analogue) nor arachadonic acid induce expression of the p3TP-Lux reporter. Measurements with the fluorescent, calcium-sensitive dye, FURA2, indicated that there was no change in intracellular calcium in response to TGF-beta. Furthermore, buffering intracellular calcium with the calcium chelating agent BAPTA/AM failed to block TGF-beta induction of the p3TP-Lux reporter. Thus the TGF-beta signaling pathway appears to involve the production of diacylglycerol but is independent of calcium.

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.

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

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.