De novo decorin gene expression suppresses the malignant phenotype in human colon cancer cells

Expression of decorin and biglycan by rabbit articular chondrocytes. Effects of cytokines and phenotypic modulation

In this study, the levels of mRNAs coding for aggrecan, decorin and biglycan in rabbit articular chondrocytes were investigated, using both monolayer and 3D-alginate cultures treated with TGF-beta 1 and IL-1 beta. The cells were shown to express higher amounts of proteoglycan messages, specially the aggrecan, in gels than in monolayers. TGF-beta 1 increased aggrecan mRNA in both systems, whereas biglycan message was elevated only in alginate. It markedly decreased decorin expression in monolayer, either in primary or passaged cultures. In contrast, IL-1 beta had a weak inhibitory effect on both decorin and biglycan expression. Subculturing induced a dramatic decrease of aggrecan mRNA, while that of decorin augmented. Biglycan expression transiently increased after two passages, whereas it declined in further subcultures. Passaged chondrocytes transferred to alginate re-expressed high levels of aggrecan, decorin and biglycan. The data point to the influence of morphology, proliferative state and environment of the articular chondrocytes on their biosynthetic responses to cytokines. Although these immature cells do not fully reflect the adult chondrocytes present in the cartilage, this study may help in understanding the behaviour of these cells in osteoarticular diseases, where the surrounding extracellular matrix is profoundly altered.

Transforming growth factor-beta gene expression in avian Low Score Normal pectoral muscle

The avian Low Score Normal (LSN) genetic muscle weakness is phenotypically characterized by a reduction in the ability of birds to right themselves from a supine position. In previous studies, LSN birds exhibited elevated levels of decorin transcript and protein at embryonic Day 20 and a large increase in collagen crosslinking at 6 wk posthatch. Transforming growth factor-beta (TGF-beta) expression has been reported to control decorin expression. Steady state levels of TGF-beta1 and TGF-beta2 transcripts were determined in ovo and posthatch in order to initiate an investigation of the mechanism underlying decorin expression. On embryonic Day 20 through 1 wk posthatch, TGF-beta2 transcript levels were elevated, whereas an increase in TGF-beta1 was only noted at 1 d posthatch. These data suggest that the increase in decorin expression may be associated with a modification in a TGF-beta signal transduction pathway.

Decorin activates the epidermal growth factor receptor and elevates cytosolic Ca2+ in A431 carcinoma cells

Several independent lines of evidence have implicated decorin, a small leucine-rich proteoglycan, in the inhibition of cell proliferation. However, the mechanism by which decorin mediates its effect on cell proliferation is unclear. Here we report, for the first time, decorin-mediated increases in intracellular Ca2+ levels of single A431 cells. The effects of decorin persisted in the absence of extracellular Ca2+ but were blocked by AG1478, an epidermal growth factor (EGF)-specific tyrosine kinase inhibitor, and by down-regulation of the EGF receptor. The effects of decorin were not mimicked by the structurally homologous protein, biglycan. Our results indicate a novel action of decorin on the EGF receptor, which results in mobilization of intracellular Ca2+ providing a possible mechanism by which decorin causes growth suppression.

Decorin suppresses tumor cell growth by activating the epidermal growth factor receptor

Decorin, a small leucine-rich proteoglycan, is capable of suppressing the growth of various tumor cell lines when expressed ectopically. In this report, we investigated the biochemical mechanism by which decorin inhibits cell cycle progression. In A431 squamous carcinoma cells, decorin proteoglycan or protein core induced a marked growth suppression, when either exogenously added or endogenously produced by a transgene. Decorin caused rapid phosphorylation of the EGF receptor and a concurrent activation of mitogen-activated protein (MAP) kinase signal pathway. This led to a protracted induction of endogenous p21, a potent inhibitor of cyclin-dependent kinases, and ultimate cell cycle arrest. Biglycan, a related proteoglycan, had no effect. Moreover, decorin activated the EGF receptor/MAP kinase/ p21 axis in cell lines of various histogenetic backgrounds. These results provide the first evidence that EGF and decorin converge functionally to regulate the cell cycle through activation of a common pathway which ultimately leads to growth suppression.

Receptor-mediated endocytosis of decorin: involvement of leucine-rich repeat structures

Decorin, a small dermatan sulfate proteoglycan, is characterized by a core protein with central leucine-rich repeat structures and a single glycosaminoglycan chain. It is catabolized by receptor-mediated uptake and subsequent intralysosomal degradation. In the present study, the localization of the receptor binding site(s) along the core protein was investigated. Various recombinant decorin fragments were consistently able to inhibit the endocytosis of wild-type decorin. The most potent inhibitory peptides were those which encompassed the central Leu125-Val230 region, i.e., the fifth to eighth leucine-rich repeat, or at least a part of it. The peptide Leu125-Val230 bound directly to the 51-kDa endocytosis receptor, and Fab fragments of antibodies against this peptide inhibited the endocytosis of decorin in a dose-dependent manner. Decorin constructs expressed in human 293 cells and comprising the full-length coding region or lacking sequences N- and/or C-terminally of the Leu125-Val230 region were all endocytosed with similar clearance rates. These data suggest that the N- and C-terminal domains of the core protein are not required for endocytosis. The receptor binding site is rather represented by contiguous leucine-rich repeat structures of the central part of the core protein. This conclusion is supported by competition experiments with biglycan, a structurally related small proteoglycan.

Alterations in sarcomere structure, collagen organization, mitochondrial activity, and protein metabolism in the avian low score normal muscle weakness

Skeletal muscle fibers are surrounded by an extracellular matrix. The extracellular matrix is composed of glycoproteins, collagen, and proteoglycans. Proteoglycans have been suggested to play an important functional role in tissue differentiation. However, an understanding of how the extracellular matrix affects skeletal muscle development and function is largely unknown. In the avian genetic muscle weakness, low score normal (LSN), a late embryonic increase in the expression of decorin is followed by a subsequent increase in collagen crosslinking. The sarcomere organization, collagen fibril diameter and organization were investigated using transmission electron microscopy. Measurements were made at 20 days of embryonic development and 6 weeks posthatch. These studies showed changes in sarcomere organization and deterioration of muscle fibril structure in the LSN pectoral muscle. In vitro satellite cell cultures were developed and assayed for mitochondrial activity, and protein synthesis and degradation. In these analyses, mitochondrial activity from LSN satellite cells was significantly higher than those from normal pectoral muscle satellite cells. Protein synthesis rates between the normal and LSN satellite cell-derived myotubes were similar, but protein degradation rates were higher in the LSN cultures. Based on the reported functions of decorin as a regulator of cell proliferation and collagen fibril organization, it is possible that the late embryonic increase in decorin may be influencing the alterations in LSN sarcomere and collagen organization.

Differences in decorin and biglycan expression in patients with gastric ulcer healing

BACKGROUND

The small interstitial proteoglycans decorin and biglycan have been shown to interact with various extracellular matrix molecules and with transforming growth factor-beta. These interactions are proposed to be important for tissue repair, as the former interactions may affect the diameter and spacing of collagen fibrils, and the latter interaction the proliferation and differentiation of cells embedded in the matrix. The aim of this study is to localize these proteoglycans in the stomach and to investigate their suitability as potential markers of extracellular matrix activity in gastric lesions.

METHODS

Immunohistochemical techniques and in situ hybridization were used to study the phenotypic expression of these two proteoglycans in routinely processed specimens of human stomach tissue from 8 patients with gastric ulcer and 10 healthy control persons.

RESULTS

In normal gastric tissue, immunostaining for both proteoglycans was found in the interstitium, with a more pronounced staining in the pylorus region than in the corpus area. In addition, biglycan showed a strong staining of parietal cells. In specimens of healing gastric ulcers a larger deposition of decorin throughout scar tissue could be shown, and a higher expression of decorin was also found by in situ hybridization. Biglycan was only found at the edges of the lesions.

CONCLUSION

This study shows for the first time the presence of decorin and biglycan in human gastric mucosa. We also showed that these proteoglycans may be involved in the gastric ulcer healing processes.

Critical role of glutamate in a central leucine-rich repeat of decorin for interaction with type I collagen

The chondroitin/dermatan sulfate proteoglycan decorin is known to interact via its core protein with fibrillar collagens, thereby influencing the kinetics of fibril formation and the final diameter of the fibrils. To define the binding site(s) for type I collagen along the core protein, which is mainly composed of leucine-rich repeat structures, decorin cDNAs were constructed and expressed in human kidney 293 cells. The constructs encoded (i) C-terminally truncated molecules, (ii) core proteins with deletions of selected leucine-rich repeats, or (iii) various point mutations. The deletion of the sixth leucine-rich repeat Met176-Lys201 and the mutation E180K drastically interfered with the binding to reconstituted type I collagen fibrils. In contrast, the deletion of the seventh repeat Leu202-Ser222 led at the most to a marginally impaired binding, although the secretion of this proteoglycan was abnormally low. Decorin with two other point mutations in the sixth leucine-rich repeat, Lys187 --> Gln and Lys200 --> Gln, respectively, bound type I collagen either normally or even better than the normal recombinant proteoglycan. These data suggest that a major collagen-binding site of decorin is located within the sixth leucine-rich repeat and that glutamate-180 within this repeat is of special importance for ionic interactions between the two matrix components.

Ectopic expression of decorin protein core causes a generalized growth suppression in neoplastic cells of various histogenetic origin and requires endogenous p21, an inhibitor of cyclin-dependent kinases

Decorin belongs to a family of secreted, small, leucine-rich proteoglycans that affect matrix assembly and cellular growth. Ectopic expression of decorin proteoglycan or protein core as a mutated form lacking any glycosaminoglycan side chains induced growth suppression in neoplastic cells of various histogenetic origins, including tumor cells derived from gastrointestinal, genital, skeletal, cutaneous, or bone marrow tissues. Exogenously added recombinant decorin also suppressed overall growth of the parental cell lines. In all stably-transfected clones, growth retardation was specifically associated with induction of the potent cyclin-dependent kinase inhibitor p21, but not p27, and subsequent translocation of p21 protein into the nuclei of decorin-expressing cells. This led to a greater proportion of the cells arrested in G1 phase of the cell cycle. These changes were independent of functional p53 or retinoblastoma protein. De novo expression of decorin in HCT116 human colon carcinoma cells harboring a disrupted p21 gene failed to induce growth suppression, in contrast to the wild-type cells in which p21 and growth arrest could be induced. These findings indicate that ectopic production of decorin protein core can retard the growth of a variety of tumor cells and that endogenous p21 is a required downstream effector of this biological axis.

Biglycan gene promoter activity in osteosarcoma cells is regulated by cyclic AMP

The pericellular proteoglycan biglycan is among the major secretory products of osteoblasts and articular chondrocytes but the regulatory agents and signal transduction pathways that ultimately lead to alterations in biglycan gene expression are poorly defined. We report here on the transcriptional up-regulation of biglycan in MG-63 osteosarcoma cells by agents that increase intracellular cAMP levels. Transfection of these cells with biglycan promoter luciferase reporter fusion genes and subsequent treatment with forskolin or the cAMP analog 8-Bromo-cAMP resulted in an up to 3.8-fold stimulation of biglycan promoter activity. This effect could be prevented with the compound KT5720, a specific inhibitor of the cAMP-dependent protein kinase. Up-regulation of transcription is also reflected at the level of mRNA expression, since biglycan mRNA steady state levels in MG-63 cells increased approximately 2-fold after 24 hours of forskolin treatment. These data suggest that elevated levels of intracellular cAMP increase transcription from the biglycan promoter in bone cells and implicate for the first time the cAMP/protein kinase A signal transduction pathway in the regulation of biglycan gene expression.

Decorin and collagen type I gene expression in avian low score normal pectoral muscle

The avian Low Score Normal (LSN) genetic muscle weakness is phenotypically characterized by a reduction in the ability of the birds to right themselves from a supine position. Compared to normal skeletal muscle, LSN muscle has normal myosin isoform switching and cell-cell recognition, elevated glycosaminoglycan and decorin levels at embryonic Day 20, and a large increase in collagen crosslinking at 6 wk posthatch. To begin to determine the biological mechanism involved in the elevated decorin protein concentration at embryonic Day 20, the steady-state levels of transcripts encoding both decorin and collagen Type I at embryonic Days 14, 19, and 20, and at 1 d and 6 wk posthatch were measured. On embryonic Day 20, collagen Type I transcripts were not different from the control but there was a significant elevation in decorin transcript levels. At 1 d and 6 wk posthatch, transcript levels of decorin and collagen Type I were not different between LSN and controls. The change in decorin transcript steady-state levels is limited to late embryonic development and suggests an alteration in a signal transduction pathway regulating decorin transcription.

Expression of small extracellular chondroitin/dermatan sulfate proteoglycans is differentially regulated in human endothelial cells

We have examined the expression of the small extracellular chondroitin/dermatan sulfate proteoglycans (CS/DS PGs), biglycan, decorin, and PG-100, which is the proteoglycan form of colony stimulating factor-1, in the human endothelial cell line EA.hy 926. We have also examined whether modulation of the phenotype of EA.hy 926 cells by tumor necrosis factor-alpha (TNF-alpha) is associated with specific changes in the synthesis of these PGs. We demonstrate that EA.hy 926 cells, when they form monolayer cultures typical of macrovascular endothelial cells, express and synthesize detectable amounts of biglycan and PG-100, but not decorin. On SDS-polyacrylamide gel electrophoresis both PGs behave like proteins of the relative molecular weight of approximately 250,000. TNF-alpha that changed the morphology of the cells from a polygonal shape into a spindle shape and that also stimulated the detachment of the cells from culture dish, markedly decreased the net synthesis of biglycan, whereas the net synthesis of PG-100 was increased. These changes were parallel with those observed at the mRNA level of the corresponding PGs. The proportions of the different sulfated CS/DS disaccharide units of PGs were not affected by TNF-alpha. Several other growth factors/cytokines, such as interferon-gamma, fibroblast growth factors-2 (FGF-2) and -7 (FGF-7), interleukin-1beta, and transforming growth factor-beta, unlike TNF-alpha, modulated neither the morphology nor the biglycan expression of EA.hy 926 cells under the conditions used in the experiments. However, PG-100 expression was increased also in response to FGF-2 and -7 and transforming growth factor-beta. None of the above cytokines, including TNF-alpha, was able to induce decorin expression in the cells. Our results indicate that the regulatory elements controlling the expression of the small extracellular CS/DS PGs in human endothelial cells are different.

Reversal of in vivo drug resistance by the transforming growth factor-beta inhibitor decorin

Transforming growth factor-beta (TGF-beta) has been implicated in the in vivo resistance of the EMT-6/CTX and EMT-6/ CDDP murine mammary tumors. Both of these tumors have a higher number of intratumoral vessels than the EMT-6/ parent tumor. Animals bearing the resistant tumors have higher plasma levels of TGF-beta than animals bearing the parent tumors; however, upon treatment with cytotoxic therapies there is a greater rise in plasma TGF-beta levels in animals bearing the parent tumor than in animals bearing the resistant tumors. In situ hybridization for TGF-beta mRNA and immunohistochemical staining for TGF-beta protein showed that the resistant tumor levels of this growth factor are higher than those of the parent tumor prior to treatment; however, after cytotoxic therapy the increase in TGF-beta is greater in the parent tumor than in the resistant tumors. Treatment of tumor-bearing animals with the naturally occurring TGF-beta inhibitor decorin did not alter the sensitivity of the parent tumor to cyclophosphamide or to CDDP as determined by tumor cell survival assay. However, administration of decorin increased the sensitivity of the EMT-6/CTX tumor to cyclophosphamide and of the EMT-6/CDDP tumor to CDDP so that the drug resistance of these tumors was nearly ablated. A similar pattern was observed in the drug response of the bone marrow granulocyte-macrophage colony-stimulating factor of animals bearing each of the 3 tumors.

Targeted disruption of decorin leads to abnormal collagen fibril morphology and skin fragility

Decorin is a member of the expanding group of widely distributed small leucine-rich proteoglycans that are expected to play important functions in tissue assembly. We report that mice harboring a targeted disruption of the decorin gene are viable but have fragile skin with markedly reduced tensile strength. Ultrastructural analysis revealed abnormal collagen morphology in skin and tendon, with coarser and irregular fiber outlines. Quantitative scanning transmission EM of individual collagen fibrils showed abrupt increases and decreases in mass along their axes. thereby accounting for the irregular outlines and size variability observed in cross-sections. The data indicate uncontrolled lateral fusion of collagen fibrils in the decorindeficient mice and provide an explanation for the reduced tensile strength of the skin. These findings demonstrate a fundamental role for decorin in regulating collagen fiber formation in vivo.

The family of the small leucine-rich proteoglycans: key regulators of matrix assembly and cellular growth

The focus of this review is on conceptual and functional advances in our understanding of the small leucine-rich proteoglycans. These molecules belong to an expanding gene class whose distinctive feature is a structural motif, called the leucine-rich repeat, found in an increasing number of intracellular and extracellular proteins with diverse biological attributes. Three-dimensional modeling of their prototype protein core proposes a flexible, arch-shaped binding surface suitable for strong and distinctive interactions with ligand proteins. Changes in the properties of individual proteoglycans derive from amino acid substitutions in the less conserved surface residues, changes in the number and length of the leucine-rich repeats, and/or variation in glycosylation. These proteoglycans are tissue organizers, orienting and ordering collagen fibrils during ontogeny and in pathological processes such as wound healing, tissue repair, and tumor stroma formation. These properties are rooted in their bifunctional character: the protein moiety binding collagen fibrils at strategic loci, the microscopic gaps between staggered fibrils, and the highly charged glycosaminoglycans extending out to regulate interfibrillar distances and thereby establishing the exact topology of fibrillar collagens in tissues. These proteoglycans also interact with soluble growth factors, modulate their functional activity, and bind to cell surface receptors. The latter interaction affects cell cycle progression in a variety of cellular systems and could explain the purported changes in the expression of these gene products around the invasive neoplastic cells and in regenerating tissues.

Identification of a bimodal regulatory element encompassing a canonical AP-1 binding site in the proximal promoter region of the human decorin gene

We have previously described a tumor necrosis factor alpha (TNF-alpha) response element, located between residues -188 and -140 of the human decorin promoter, that mediates the inhibitory effect of TNF-alpha on decorin gene expression (Mauviel, A., Santra, M., Chen, Y.-Q., Uitto, J., and Iozzo, R. V. (1995) J. Biol. Chem. 270, 11692-11700). In this report, we demonstrate that interleukin 1 (IL-1), a pleiotropic cytokine that shares a wide variety of biological properties with TNF-alpha, uses the same cis element to up-regulate decorin gene expression. Specifically, IL-1 enhances the expression of the human decorin gene, and this effect is mediated by activation of the corresponding promoter, as shown in transient cell transfection experiments using decorin promoter-chloramphenicol acetyl transferase reporter gene constructs. Additional transfection experiments with various 5'-deletion promoter-chloramphenicol acetyltransferase constructs demonstrate that both the inhibitory effect of TNF-alpha and the stimulatory effect of IL-1 are mediated by a 48-base pair segment of the promoter, between residues -188 and -140. This region, which contains a canonical AP-1 binding site, TGAGTCA, allows an antagonistic effect of these two cytokines on the decorin promoter activity. When cloned upstream of the thymidine kinase promoter, this promoter fragment requires the AP-1 sequence to be responsive to IL-1. Supershift assays with various AP-1 antibodies identified c-Jun, Jun-B, and Fra-1 as components of the complex binding to the decorin promoter. Overexpression of c-jun, an oncogene encoding the c-Jun/AP-1 transcription factor, reduces the basal activity of both decorin and -188/-140 thymidine kinase promoter constructs. In contrast, blockage of c-jun expression with an antisense c-jun construct potentiates the stimulatory effect of IL-1 and reverses the response to TNF-alpha. These data indicate that the region between residues -188 and -140 of the human decorin promoter functions as a bimodal regulatory element and allows transcriptional repression by c-Jun/AP-1 complexes.

Decorin-induced growth suppression is associated with up-regulation of p21, an inhibitor of cyclin-dependent kinases

The secreted proteoglycan decorin has been implicated in the negative control of cell proliferation primarily by virtue of its ability to block transforming growth factor-beta. Moreover, decorin expression is markedly up-regulated during quiescence but suppressed upon viral transformation, whereas de novo decorin expression in colon carcinoma cells abrogates the malignant phenotype by arresting the cells in the G1 phase of the cell cycle. Here we show that this decorin-induced growth arrest is associated with up-regulation of p21 mRNA and protein in a transforming growth factor-beta- and p53-independent pathway. The augmented p21 protein is present as a multimeric complex with various cyclins and cyclin-dependent kinases in the nuclei of decorin-expressing cells, thereby leading to suppression of cyclin-dependent kinase activity and block of cell division. Through the usage of decorin-specific antisense oligodeoxynucleotide treatment, we demonstrate that the expression of decorin is closely linked to that of p21 and that abrogation of decorin leads to suppression of p21 and restoration of cell division. Collectively, our results provide a plausible mechanism by which decorin may contribute to retard and suppress the growth of tumor cells in vivo.

Transcriptional regulation of the human biglycan gene

The small leucine-rich proteoglycan biglycan is involved in several physiological and pathophysiological processes through the ability of its core protein to interact with other extracellular matrix molecules and transforming growth factor-beta (TGF-beta). To learn more about the regulation of biglycan core protein expression, we have cloned and sequenced 1218 base pairs from the 5'-flanking region of the human biglycan gene, demonstrated functional promoter activity, and investigated the molecular mechanisms through which various agents modulate its transcriptional activity. Sequencing revealed the presence of several cis-acting elements including multiple AP-2 sites and interleukin-6 response elements, a NF-kappaB site, a TGF-beta negative element, and an E-box. The TATA and CAAT box-lacking promoter possesses many features of a growth-related gene, e.g. a GC-rich immediate 5' region, many Sp1 sites, and the use of multiple transcriptional start sites. Transient transfections of the tumor cell lines MG-63, SK-UT-1, and T47D with various biglycan 5'-flanking region-luciferase reporter gene constructs showed that the proximal 78 base pairs are sufficient for full promoter activity. Several agents among them interleukin-6, and tumor necrosis factor-alpha. were capable of altering biglycan promoter activity. However, in MG-63 cells, TGF-beta1 failed to increase either activity of the biglycan promoter constructs or specific transcription from the endogenous biglycan gene. Since TGF-beta1 also did not alter the stability of cytoplasmic biglycan mRNA as determined from Northern analysis after inhibition of transcription with 5,6-dichloro-1beta-D-ribofuranosylbenzimidazole, an as yet unidentified nuclear post-transcriptional mechanism was considered responsible for the TGF-beta effect in this cell type. These results might help to elucidate the molecular pathways leading to pathological alterations of biglycan expression observed in atherosclerosis, glomerulonephritis, and fibrosis.

Deficient expression of the small proteoglycan decorin in a case of severe/lethal osteogenesis imperfecta

In osteogenesis imperfecta (OI) the effects of mutations in type I collagen genes generally reflect their nature and localization. Unrelated individuals sharing identical mutations present, in general, similar clinical phenotypes. However, in some such cases the clinical phenotype differs. This variable clinical expression could be the result of abnormalities in other connective tissue proteins. Since decorin is a component of connective tissue, binds to type I collagen fibrils and plays a role in matrix assembly, we studied decorin production in skin fibroblasts from OI patients. Cultured fibroblasts from one patient with extremely severe osteogenesis imperfecta (classified as type II/III) who has an alpha 1(I)gly415ser mutation were found to secrete barely detectable amounts of decorin into culture medium. Western blotting using antibodies raised against decorin confirmed the reduction of the decorin core protein and Northern blot analysis showed decorin mRNA levels below the limit of detection. Cells from a patient, with a less severe phenotype, bearing a mutation in the same position of the triple helix (alpha 1(I)gly415) expressed decorin normally. The different clinical phenotypes could be due to the differing genetic backgrounds of the patients so it is tempting to conclude that in our most severely affected patient the absence of decorin aggravates the clinical phenotype.