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PubMed1996

Influence of osteogenic protein-1 (OP-1;BMP-7) and transforming growth factor-beta 1 on bone formation in vitro.

The bone morphogenetic proteins (BMPs) and transforming growth factor-beta s (TGF-beta s), are a group of structurally related proteins which have been shown to stimulate bone formation in vivo. Since these proteins are concentrated in the organic matrix of bone and would be released during bone resorption, they are likely to have a profound effect on the remodeling bone and may provide a link between bone resorption and bone formation. We are using primary cultures of fetal rat calvarial cells (FRCC) to study the independent and combined effects of OP-1/BMP-7 and TGF-beta 1 on bone cells at different stages of differentiation in order to identify responding cell populations and target genes. We have confirmed prior reports that OP-1 stimulates, while TGF-beta 1 inhibits, osteogenic differentiation in this system. The increase in both number and size of the mineralized nodules induced by OP-1 was accompanied by increased expression of alkaline phosphatase and type I collagen with an induction of bone sialoprotein (BSP) suggesting that OP-1 stimulates both differentiation and clonal expansion of osteoblastic cells. Interestingly, TGF-beta 1 abrogated OP-1 induced nodule formation. Despite these opposing effects on osteogenic differentiation, TGF-beta 1 (Wrana et al, 1991) and OP-1 both stimulated a rapid induction of osteopontin (OPN) mRNA in confluent FRCC cultures enriched in pre-osteoblastic cells. In contrast, when OP-1 was added to nodule-forming cultures which are enriched in osteoblastic cells, there was only a weak induction of OPN. Moreover, while the expression of one marker for mature osteoblasts (BSP) was refractory to OP-1, another (osteocalcin) was markedly stimulated. Thus OP-1 has selective effects on bone matrix protein expression that are dependent on the differentiated state of the cells.

Alkaline Phosphatase↗
PubMed1999

Localization of secreted protein acidic and rich in cysteine (SPARC) expression in the rat eye.

Secreted protein acidic and rich in cysteine (SPARC) is a secreted glycoprotein protein which modulates cell shape and cell-matrix interactions and has been implicated in the regulation of angiogenesis, vascular permeability and cataract formation. In situ hybridization and immunohistochemical studies for SPARC were performed to determine the cell and tissue distribution of SPARC in rat eye. Studies demonstrated SPARC mRNA and protein co-localization at all sites. In the retina SPARC mRNA and protein were localized predominantly to the Müller and ganglion cells. Within the choroid, SPARC was found in vascular endothelial cells and fibroblasts; in the sclera SPARC was present in blood vessels and fibroblasts. SPARC was also present in the non-pigmented epithelial cells of the ciliary body, and in the epithelium of the lens capsule and cornea. The demonstrated anatomical distribution of SPARC in the rat eye is consistent with several of the biological functions ascribed to this matricellular protein and provides a rational basis for its examination in pathological conditions.

Animals↗
PubMed2000

A study of SPARC and vitronectin localization and expression in pediatric and adult gliomas: high SPARC secretion correlates with decreased migration on vitronectin.

SPARC is a secreted glycoprotein that interacts with extracellular matrix (ECM) proteins to promote de-adhesion of cells from the matrix, thereby inducing a biological state conducive to cell migration. We have demonstrated that SPARC is highly expressed in gliomas (grades II-IV) and promotes glioma invasion in vitro. Therefore, the protein itself or its mechanisms of action might become therapeutic targets to arrest glioma invasion. Vitronectin is an ECM protein found in the blood vessel basement membranes and may promote glioma invasion along these structures. It binds to SPARC in vitro. However, it is not known whether SPARC and vitronectin colocalize and/or interact to contribute to brain tumor cell migration in vivo. In this study, we immuno-histochemically determined if the grade I juvenile pilocytic astrocytomas (JPAs) also express SPARC, if vitronectin is expressed in grades I, II, and IV astrocytomas, and if the proteins colocalize in brain tumors in vivo. We performed western blot analyses to determine if different grades of tumors had different intracellular and/or secreted levels of SPARC and vitronectin. We performed migration assays to determine whether vitronectin is a permissive substrate for glioma migration, and whether the extent of migration correlates with the level of secreted SPARC. Our data demonstrated that JPAs expressed SPARC and secreted significantly higher levels than glioblastomas multiforme (GBMs). Vitronectin was absent from well-preserved tumor but present in areas of disrupted tumor, such as degeneration and/or necrosis. SPARC and vitronectin colocalized only in regions of angiogenesis. We observed that the extent of migration on vitronectin inversely correlated with the level of secreted SPARC: the higher the level, the lesser the migration. These data suggest that the outcome of SPARC - ECM interactions may depend on local SPARC concentrations. The high levels of SPARC secreted by the JPAs, paradoxically, may be more prohibitive for migration on vitronectin than the lower levels secreted by the GBMs. This may account, in part, for the lack of JPA invasion into brain tissue along blood vessel membranes.

Adult↗
PubMed2006

Novel function of alternatively activated macrophages: stabilin-1-mediated clearance of SPARC.

The matricellular protein SPARC (secreted protein acidic and rich in cysteine) has been implicated in development, differentiation, response to injury, and tumor biology by virtue of its regulation of extracellular matrix production/assembly and its antiadhesive and antiproliferative effects on different cell types. Despite numerous biological activities described for SPARC, cell surface receptors for this protein have not been identified. By phage display and in vitro-binding assays, we now show that SPARC interacts with stabilin-1, a scavenger receptor expressed by tissue macrophages and sinusoidal endothelial cells. The interaction is mediated by the extracellular epidermal growth factor-like region of stabilin-1 containing the sequence FHGTAC. Using FACS analysis and confocal microscopy, we demonstrate that stabilin-1 internalizes and targets SPARC to an endosomal pathway in Chinese hamster ovary cells stably transfected with this receptor. In human macrophages, stabilin-1 expression is required for receptor-mediated endocytosis of SPARC. SPARC was efficiently endocytosed by alternatively activated macrophages stimulated by IL-4 and dexamethasone, but not solely by Th1 or Th2 cytokines. A time course of ligand exposure to alternatively activated macrophages revealed that stabilin-1-mediated endocytosis of SPARC was followed by its targeting for degradation, similar to the targeting of acetylated low density lipoprotein, another stabilin-1 ligand. We propose that alternatively activated macrophages coordinate extracellular matrix remodeling, angiogenesis, and tumor progression via stabilin-1-mediated endocytosis of SPARC and thereby regulate its extracellular concentration.

Animals↗
PubMed1999

SPARC: a potential diagnostic marker of invasive meningiomas.

SPARC, a secreted, extracellular matrix-associated protein implicated in the modulation of cell adhesion and migration, was evaluated as a marker for invasive meningiomas. Although the majority of meningiomas are clinically and morphologically benign, approximately 10% progress into atypical and malignant tumors, according to the standard criteria. However, a subset of meningiomas presents as histomorphologically benign tumors (WHO grade I), but they are clinically invasive. It has been suggested that these tumors should be classified as malignant, and that the patients may require adjuvant therapy and closer follow up. Unfortunately, a significant number of these tumors may not be recognized because the surgical specimen used to assess the grade of a tumor lacks the infiltrative interface with the brain, which is currently necessary to determine its invasive character. Therefore, a marker of heightened invasiveness would greatly facilitate the identification of this subset of patients. In this study, the immunohistochemical expression of SPARC in benign, noninvasive primary meningiomas was compared with its expression in invasive, aggressive, primary and recurrent meningiomas. SPARC was not expressed in the 9 benign, noninvasive tumors, but was highly expressed in the 20 invasive tumors, regardless of the grade. The findings suggest that SPARC is a potential diagnostic marker of invasive meningiomas and is capable of distinguishing the histomorphologically benign noninvasive from the histomorphologically benign but invasive meningiomas, in the absence of the infiltrative interface.

Biomarkers, Tumor↗
PubMed1999

Rat embryo fibroblasts transformed by c-Jun display highly metastatic and angiogenic activities in vivo and deregulate gene expression of both angiogenic and antiangiogenic factors.

The comparative tumorigenicity in rats and nude mice of cell lines derived from FR3T3 and transformed by either c-jun, ras, SV40 lt, or bovine papilloma virus type 1 (BPV1) oncogenes was investigated. c-Jun-transformed cells were as tumorigenic and metastatic as Ras-transformed cells. Latencies were short, and numerous pulmonary metastases were observed in all injected animals. In contrast, tumors induced by s.c. injection of SV40-transformed cells developed slower, and none of the animals who received injections i.v. presented with metastases. BPV1-transformed cells had an intermediate tumorigenic and metastatic activity. Microvessels present in the different tumors were revealed by immunostaining with Griffonia (Bandeiraea) Simplicifolia lectin 1. Tumors obtained with c-Jun-transformed cells exhibited more neovascularization than those induced by the other oncogenes. By comparison to FR3T3 cells or SV40- or BPV1-transformed cells, c-Jun-transformed fibroblasts repress the antiangiogenic thrombospondin-1 and SPARC genes, whereas we found that they express higher levels of gene expression of the angiogenic vascular endothelial growth factor. Finally, as compared with cells before passage in animals, thrombospondin-1, SPARC, and VEGF gene expression was also deregulated in cell lines isolated from primary tumors induced by BPV1-transformants. Our results indicate that the high transforming potential of c-Jun, evidenced as soon as transformation is established in vitro, correlates with deregulation of gene expression of both angiogenic and antiangiogenic factors leading to rapid neovascularization of tumors.

Animals↗
PubMedDate not supplied

Role of endothelin in the human craniofacial morphogenesis.

Human craniofacial morphogenesis is a complex biological event: it is mediated by several factors and different types tissue interaction. Recent studies on animal models have led to an improved understanding of human craniofacial malformations. In particular, the endothelins, peptides that are involved in various biological functions in many tissues and organs, have been shown to play a crucial role in the development of the first branchial-arch-derived structures in mice [Kurihara et al., Nature 368:703-710, 1994]. We previously reported the identification and localization of endothelin-1 (ET-1) and its receptors in human fetal jaw [Barni et al., Dev Biol 168:373-377, 1995]. In the present study, the gene expression of ET-1 and its receptors were demonstrated in human jaw from 11-12-week-old fetuses. By using in situ hybridization, mRNA for ET-1 was localized in the epithelial cells of the oral mucosa: mRNA for ET receptors (ETA and ETB subtypes) was expressed in the mesenchyme. In situ binding experiments confirmed the presence of ETA and ETB receptors in the cells involved in the osteogenesis of the mandible. Furthermore, ET-1 was able to stimulate thymidine uptake and the expression of the oncoprotein c-fos in the same cell types. Our results indicate that ET-1 may play a putative role in epithelium-mesenchyme interaction during human craniofacial morphogenesis. Our findings are in complete accord with those of the most recent works by Yanagisawa [Yanagisawa H et al., 1998] and Clouthier [Clouthier et al., Development 125:813-824, 1998]. They most probably confirm the primary role of ET-1 in the development of the pharyngeal arches.

Bone and Bones↗
PubMed1999

Cell cycle-dependent nuclear location of the matricellular protein SPARC: association with the nuclear matrix.

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that inhibits cellular adhesion and proliferation. In this study, we report the detection of SPARC in the interphase nuclei of embryonic chicken cells in vivo. Differential partitioning of SPARC was also noted in the cytoplasm of these cells during discrete stages of M-phase: cells in metaphase and anaphase exhibited strong cytoplasmic immunoreactivity, whereas cells in telophase were devoid of labeling. Immunocytochemical analysis of embryonic chicken cells in vitro likewise showed the presence of SPARC in the nucleus. Furthermore, elution of soluble proteins and DNA from these cells indicated that SPARC might be a component of the nuclear matrix. We subsequently examined cultured bovine aortic endothelial cells, which initially appeared to express SPARC only in the cytoplasm. However, after elution of soluble proteins and chromatin, we also detected SPARC in the nuclear matrix of these cells. Embryonic chicken cells incubated with recombinant SPARC were seen to take up the protein and to translocate it to the nucleus progressively over a period of 17 h. These observations provide new information about SPARC, generally recognized as a secreted glycoprotein that mediates interactions between cells and components of the extracellular matrix. The evidence presented in this study indicates that SPARC might subserve analogous functions in the nuclear matrix.

Animals↗
PubMed1999

Loss of insulin-like growth factor I receptor-dependent expression of p107 and cyclin A in cells that lack the extracellular matrix protein secreted protein acidic and rich in cysteine.

The extracellular matrix-associated glycoprotein secreted protein acidic and rich in cysteine (SPARC) has been implicated in the control of cell proliferation during tissue remodeling, wound healing, and malignant development. Here, we describe a novel mechanism through which SPARC influences cell cycle progression in embryonic fibroblasts derived from Sparc-nullizygous (-/-) mice. SPARC-deficient cells were indistinguishable from wild-type cells in their ability to initiate DNA synthesis after treatment with either fetal bovine serum or platelet-derived growth factor. In contrast, Sparc -/- cells responded poorly to activation of the insulin-like growth factor receptor (IGFI-R) by insulin. This defect was traced to reduced expression of the IGFI-R in Sparc -/- cells. Consistent with impaired cell cycle progression through S-phase, insulin-stimulated Sparc -/- cells also revealed reduced expression of two key regulators of S phase progression (cyclin A and thymidine kinase), whereas expression of the G1 phase progression regulators cmyc or cyclin D1 was unaffected. An examination of the status of retinoblastoma family pocket proteins in Sparc -/- cells revealed a selective and dramatic reduction in levels of the retinoblastoma-related protein p107. Exogenous platelet-derived growth factor restored expression of the IGFI-R and IGFI-R dependent DNA synthesis as well as induction of cyclin A, thymidine kinase, and p107 in insulin-stimulated Sparc -/- cells. These results suggest that SPARC-dependent matrix to cell interactions contribute to the regulation of p107 and cyclin A through IGFI-R dependent pathway(s).

Animals↗
PubMed2000

Increased expression of osteonectin/SPARC mRNA and protein in age-related human cataracts and spatial expression in the normal human lens.

PURPOSE: We have previously reported increased levels of Osteonectin/SPARC transcript in age-related cataractous compared to normal human lenses. The purpose of the present study was to evaluate the corresponding levels of osteonectin/SPARC protein in age-related cataractous relative to normal lenses and to evaluate the levels of osteonectin/SPARC transcript in specific types of age-related human cataracts. The spatial expression of osteonectin/SPARC was also evaluated in normal human lenses. METHODS: Specific types of age-related cataracts were collected and graded. Normal human lenses were microdissected into epithelia and fibers. Osteonectin/SPARC protein levels were monitored by Western immunoblotting, and transcript levels were evaluated by reverse transcriptase polymerase chain reaction (RT-PCR). Osteonectin/SPARC expression patterns were examined by RT-PCR and by immunostaining. RESULTS: Higher levels of osteonectin/SPARC protein were detected in age-related cataractous relative to normal human lenses. Increased levels of osteonectin/SPARC transcript were also detected in posterior-subcapsular and nuclear cataractous lenses relative to normal lenses. Osteonectin/SPARC transcripts were detected in the lens epithelium but not fibers. Osteonectin/SPARC protein levels were highest in the peripheral lens epithelium. CONCLUSIONS: Consistent with our previous studies on osteonectin/SPARC mRNA levels, osteonectin/SPARC protein levels were also elevated in cataractous compared to normal human lenses. Increased levels of osteonectin/SPARC mRNA were also found in nuclear and posterior-subcapsular cataracts relative to normal lenses. Osteonectin/SPARC expression is confined to the lens epithelium, and osteonectin/SPARC levels are highest in the peripheral lens epithelium.

Adolescent↗
PubMed2000

Osteonectin/SPARC secreted by RPE and localized to the outer plexiform layer of the monkey retina.

PURPOSE: Osteonectin/SPARC is a secreted protein that has been implicated in ocular disease. Deletion of osteonectin/SPARC causes age-onset cataract in mice and the cataractous human lens has increased expression of osteonectin/SPARC. In this study, the expression and localization of osteonectin/SPARC in the monkey retina were determined as was secretion by cultured human retinal pigment epithelial (RPE) cells. METHODS: Adult Rhesus monkey eyes (Macaca mulatta) were dissected, and 5-mm macula and peripheral retina punches were obtained. Supernatants were collected from cultured human RPE cells. Subcellular fractionation of whole monkey retina was also performed. Osteonectin/SPARC expression and/or secretion was monitored by Northern and Western blot analyses, and localization was determined by immunocytochemistry. RESULTS: Outside of the retina osteonectin/SPARC mRNA is broadly expressed in many human tissues. Northern blot analysis shows that in the retina osteonectin/SPARC is expressed almost exclusively by the macular RPE/choroid. Western blot analysis revealed osteonectin/SPARC in both the macula and the peripheral neural retina but only in trace amounts in the RPE/choroid. In subcellular fractions of the whole retina, osteonectin/SPARC was detected, mainly in the soluble fraction but also in the membrane and nuclear fractions. Immunohistochemical analysis localized osteonectin/SPARC specifically to the outer plexiform layer. Western blot analysis of conditioned medium from human RPE cells cultured on porous substrates indicated that osteonectin/SPARC is secreted in large amounts from both the apical and basal sides of the RPE. CONCLUSIONS: Collectively these data provide evidence that osteonectin/SPARC is synthesized in the macular RPE, secreted, and subsequently transported to the outer plexiform layer. The expression pattern of osteonectin/SPARC in the subcellular retinal fractions is consistent with a soluble protein that is transported and internalized.

Animals↗
PubMed2001

Expression of SPARC/osteonectin/BM4O in the human gut: predominance in the stroma of the remodeling distal intestine.

SPARC is a glycoprotein of the extracellular matrix that exhibits a number of biological functions such as disruption of cell adhesion and modulation of matrix metalloprotease expression. These properties, in concert with the expression of the molecule during development, repair, and neoplastic progression, suggest that SPARC has an important role in remodeling in a variety of tissues. However, the role of SPARC in the intestine is unclear since the development expression and tissular origin of SPARC in this organ appears to be species-dependent. As a first step to investigate the function of SPARC in the tissues of the intestine, we have analyzed its expression at the protein and mRNA levels in the human fetal and adult small intestinal and colonic mucosa as well as in intestinal cell models. Our results show that SPARC expression is differentially regulated during development and along the length of the human intestine. In the colon, SPARC was predominantly found at the epithelial-mesenchymal interface at the fetal stage, below detection levels in the normal adult, but re-expressed in the stroma of colonic tumors. In the small intestine, low levels of SPARC expression were observed at an early stage of morphogenesis (between 9 and 11 weeks) but expression was not detected at subsequent developmental stages nor was it induced in the mucosa of Crohn's disease. While SPARC appeared to be produced mainly by mesenchymal and stromal cells in the intact intestine it was not detected in colon cancer cells. Taken together, these results indicate that SPARC is subject to an onco-fetal pattern of expression in the stroma of the colonic mucosa while its expression is much more restricted in the small intestine, suggesting a differential involvement of this molecule in the extracellular matrix remodeling occurring along the length of the developing and diseased human intestinal mucosa.

Base Sequence↗
PubMed2001

Vitamin D control of osteoblast function and bone extracellular matrix mineralization.

Vitamin D is the major regulator of calcium homeostasis and protects the organism from calcium deficiency via effects on the intestine, kidney, parathyroid gland, and bone. Disturbances in the vitamin D endocrine system (e.g., vitamin D-dependent rickets type I and type II), result in profound effects on the mineralization of bone. Recent studies with vitamin D receptor knockout mice also show effects on bone. It is questioned whether vitamin D has a direct effect on bone formation and mineralization. In rickets and particular vitamin D receptor knockout mice, calcium supplementation restores bone mineralization. However, the vitamin D receptor is present in osteoblasts, and vitamin D affects the expression of various genes in osteoblasts. This review focuses on the role of vitamin D in the control of osteoblast function and discusses the current knowledge of the direct effects of vitamin D on mineralization. Moreover, the role of vitamin D metabolism and the mechanism of action of vitamin D and interaction with other hormones and factors are discussed.

Alkaline Phosphatase↗
PubMed2002

Increased circulating concentrations of the counteradhesive proteins SPARC and thrombospondin-1 in systemic sclerosis (scleroderma). Relationship to platelet and endothelial cell activation.

OBJECTIVE: To determine whether circulating concentrations of the counteradhesive proteins SPARC (secreted protein acidic and rich in cysteine) and thrombospondin-1 (TSP-1) are elevated in scleroderma (systemic sclerosis, SSc). The relationship of these counteradhesive proteins to measures of platelet and endothelial cell activation was examined. METHODS: Plasma from 45 patients with SSc (26 limited form, 19 diffuse) and 22 age and sex matched controls was assayed for SPARC, TSP-1, beta-thromboglobulin (betaTG), and platelet factor 4 (PF4), 2 distinct platelet a-granule products, and soluble E-selectin, a marker of endothelial cell activation. RESULTS: The mean (+/- SE) SPARC concentration was greater in patients with limited SSc (124.0 +/- 9.6 ng/ml) compared to controls (66.8 +/- 8.0 ng/ml) (p = 0.0005), whereas in patients with diffuse SSc (74.1 +/- 7.9 ng/ml) it was not. Elevated SPARC concentrations in the limited SSc group could not be ascribed to either platelet or endothelial cell activation. TSP-1 concentrations were also increased in SSc patients (n = 29) compared to controls (n = 11) (2.98 +/- 0.12 vs 2.4 +/- 0.21 log transformed ng/ml; p < 0.02). Unlike SPARC, TSP-1 concentrations correlated with both betaTG (r = 0.57, p = 0.0014) and PF4 (r = 0.41, p = 0.026) levels, indicating that increased TSP-1 could, in part, be explained through elevated platelet a-granule release in SSc patients. Plasma levels of betaTG, PF4, and E-selectin were each similarly elevated (p < 0.003) in patients with both limited and diffuse SSc compared to controls. CONCLUSION: That circulating SPARC and TSP-1 are elevated in patients with SSc raises the possibility that counteradhesive proteins, which regulate vascular organization and remodeling, might contribute to the pathogenesis of SSc vasculopathy.

Adult↗
PubMed2002

SPARC is a key Schwannian-derived inhibitor controlling neuroblastoma tumor angiogenesis.

Neuroblastoma (NB), a common pediatric neoplasm, consists of two main cell populations: neuroblastic/ganglionic cells and Schwann cells. NB tumors with abundant Schwannian stroma display a more benign clinical behavior than stroma-poor tumors. Recent studies suggest that Schwann cells influence NB tumor growth via secreted factors that induce differentiation, suppress proliferation, and inhibit angiogenesis. Two angiogenesis inhibitors, pigment epithelium-derived factor and tissue inhibitor of metalloproteinase-2, have been detected in Schwann cell secretions. Here, we isolated another Schwann cell-derived secreted inhibitor of angiogenesis, a 43-kDa protein identified as SPARC (secreted protein acidic and rich in cysteine), an extracellular matrix protein. We found SPARC to be critical for the antiangiogenic phenotype of cultured Schwann cells. We also show that purified SPARC potently inhibits angiogenesis and significantly impairs NB tumor growth in vivo. SPARC may be an effective candidate for the treatment of children with clinically aggressive, Schwannian stroma-poor NB tumors.

Adult↗
PubMed2003

Effects of the matricellular protein SPARC on human retinal pigment epithelial cell behavior.

PURPOSE: To determine the effects of the matricellular protein SPARC (Secreted Protein, Acidic and Rich in Cysteine) on human retinal pigment epithelial (HRPE) cell behavior in vitro. METHODS: Proliferation and migration assays were performed on HRPE cells exposed to various concentrations of SPARC. Additionally, HRPE cells were seeded on top of collagen matrices (a 2D model of the retinal scarring disorder known as proliferative vitreoretinopathy or PVR) and were exposed to SPARC over a 7 day period. Changes in matrix contraction were recorded. RESULTS: HRPE cell proliferation was significantly inhibited at 1 and 10 microg/ml SPARC (p<0.01). SPARC protein did not stimulate HRPE cell migration at any of the concentrations used. SPARC did not significantly affect fibronectin-induced HRPE cell migration at SPARC concentrations up to 10 microg/ml. HRPE cell-seeded collagen matrices demonstrated a significant inhibition of matrix contraction by 1 and 10 microg/ml SPARC (t-test; p<0.02 and 0.001, respectively) compared to controls. CONCLUSIONS: SPARC protein has anti-proliferative effects on HRPE cells in vitro. In addition, SPARC appears to have an inhibitory effect on HRPE-mediated contraction of 2D collagen matrices. These results are consistent with an important role for SPARC in modulating cell behavior in vitro and may indicate a role for SPARC in modifying HRPE cell activities during the development of PVR and other proliferative retinal diseases.

Adult↗