Co-receptor For Growth Factor Research Articles

Abstract 1508: Membrane heparan sulfate proteoglycans work with cadherins to establish the directional orientation of migrating cancer cells

Abstract A role of heparan sulfate proteoglycans (HSPGs) in cancer cell differentiation, proliferation and migration has been recognized and related to their ability to specifically interact with growth factors, morphogens, and extracellular matrix proteins, mainly through sulfated groups on their glycosaminoglycan (GAG) chains. Due to the considerable diversity of HSPGs and of their GAG chains, and to the lack of specific ligands, a precise molecular characterization of the biological role of HSPGs in cancer cells is still lacking. HSPGs, besides working as coreceptors for growth factors and morphogens, may have a determinant and autonomous role in cancer signaling events, regulating cell adhesion, migration, and invasiveness. Being overexpressed and over sulfated in cancer cells, HSPGs may become attractive tumor targets for cancer diagnosis and therapy. We had used the tetra-branched peptide NT4, which binds sulphated GAG chains of HSPGs, to validate HSPGs as potential tumor associated antigens in different human solid tumors. The same NT4 peptide had been tested as a tumor targeting agent for either cancer cell imaging or therapy, in vitro and in vivo [1]. Once identified the sulfated GAG specificity of NT4, the peptide has also been used as a specific tool for studying the role of HSPGs in cancer cell migration and invasiveness, with the aim of proposing HSPG as potential drug targets for interfering with cancer invasiveness and metastatic potential [2,3]. We found that NT4 inhibits adhesion, oriented migration, and colony formation in different human cancer cell lines. We investigated the role of HSPGs in migration of different human cancer cell lines, displaying either single-cell mesenchymal migration (PANC-1 pancreas adenocarcinoma, and MDA-MB-231 breast adenocarcinoma) or collective migration (MCF-7 breast adenocarcinoma). After assessing the expression of HSPG and of E- and N- cadherin in each cell line, their specific cellular distribution was detected by confocal microscopy in migrating cells, in wound healing experiments. We found that distribution of either E- or N- cadherins on the membrane of migrating cells is complementary to that of HSPG. This is particularly clear in collective migration, where HSPGs are exclusively located on the migration front of leader cells, whereas cadherins are only expressed by follower cells. Our results suggest that HSPG may have a crucial role in defining the front of migrating cells, while cadherin-mediated cell-cell contacts on the opposite site, may contribute to inducing protrusion formation at the front of migrating cells, as already suggested [4]. [1]- Brunetti J et al. Sci. Rep. 2015, 5, 17736; [2]- Brunetti J et al. Sci. Rep. 2016, 6, 27174; [3]- Depau L et al. J Med Chem 2020, 63, 15997; [4]- Grimaldi C et al Nat Commun 2020, 11, 5397 Citation Format: Lorenzo Depau, Jlenia Brunetti, Chiara Falciani, Marta Garfì, Maria Francesca Paolocci, Alessandro Pini, Luisa Bracci. Membrane heparan sulfate proteoglycans work with cadherins to establish the directional orientation of migrating cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1508.

Biological and Clinical Implications of the Vascular Endothelial Growth Factor Coreceptor Neuropilin-1 in Human Immunodeficiency Virus.

Plasma vascular endothelial growth factor (VEGF) coreceptor neuropilin-1 (NRP-1) had the largest association with coronary plaque in the Randomized Trial to Prevent Vascular Events in HIV (REPRIEVE) proteomics analysis. With little known about NRP-1 in people with human immunodeficiency virus (PWH), we explored its relation to other proteins in REPRIEVE and validated our findings through a Centers for AIDS Research Network of Integrated Clinical Systems (CNICS) case-cohort study by assessing its relation to host factors and incident cardiovascular disease and cancer. Within REPRIEVE, NRP-1 was associated with proteins involved in angiogenesis, signal transduction, immunoregulation, and cell migration/adhesion. Within CNICS, NRP-1 was associated with key host factors, including older age and male sex. NRP-1 was associated with an increased hazard of multiple cancers but a decreased prostate cancer risk. Finally, NRP-1 was most strongly associated with mortality and type 2 myocardial infarction. These data suggest that NRP-1 is part of a clinically relevant immunoregulatory pathway related to multiple comorbidities in PWH. Clinical Trials Registration. NCT02344290.

Coronary vasculature patterning requires a novel endothelial ErbB2 holoreceptor.

Organogenesis and regeneration require coordination of cellular proliferation, regulated in part by secreted growth factors and cognate receptors, with tissue nutrient supply provided by expansion and patterning of blood vessels. Here we reveal unexpected combinatorial integration of a growth factor co-receptor with a heterodimeric partner and ligand known to regulate angiogenesis and vascular patterning. We show that ErbB2, which can mediate epidermal growth factor (EGF) and neuregulin signalling in multiple tissues, is unexpectedly expressed by endothelial cells where it partners with neuropilin 1 (Nrp1) to form a functional receptor for the vascular guidance molecule semaphorin 3d (Sema3d). Loss of Sema3d leads to improper patterning of the coronary veins, a phenotype recapitulated by endothelial loss of ErbB2. These findings have implications for possible cardiovascular side-effects of anti-ErbB2 therapies commonly used for cancer, and provide an example of integration at the molecular level of pathways involved in tissue growth and vascular patterning.

Renal Heparan Sulfate Proteoglycans Modulate Fibroblast Growth Factor 2 Signaling in Experimental Chronic Transplant Dysfunction

Depending on the glycan structure, proteoglycans can act as coreceptors for growth factors. We hypothesized that proteoglycans and their growth factor ligands orchestrate tissue remodeling in chronic transplant dysfunction. We have previously shown perlecan to be selectively up-regulated in the glomeruli and arteries in a rat renal transplantation model. Using the same model, here we present quantitative RT-PCR profiling data on proteoglycans and growth factors from laser-microdissected glomeruli, arterial tunicae mediae, and neointimae at 12 weeks after transplantation. In glomeruli and neointimae of allografts, selective induction of the matrix heparan sulfate proteoglycan perlecan was observed, along with massive accumulation of fibroblast growth factor 2 (FGF2). Profiling the heparan sulfate polysaccharide side chains revealed conversion from a non-FGF2-binding heparan sulfate phenotype in control and isografted kidneys toward a FGF2-binding phenotype in allografts. In vitro experiments with perlecan-positive rat mesangial cells showed that FGF2-induced proliferation is dependent on sulfation and can be inhibited by exogenously added heparan sulfate. These findings indicate that matrix proteoglycans such as perlecan serve as functional docking platforms for FGF2 in chronic transplant dysfunction. We speculate that heparin-like glycomimetics could be a promising intervention to retard development of glomerulosclerosis and neointima formation in chronic transplant dysfunction.

The cytoplasmic domain of neuropilin-1 regulates focal adhesion turnover

Though the vascular endothelial growth factor coreceptor neuropilin-1 (Nrp1) plays a critical role in vascular development, its precise function is not fully understood. We identified a group of novel binding partners of the cytoplasmic domain of Nrp1 that includes the focal adhesion regulator, Filamin A (FlnA). Endothelial cells (ECs) expressing a Nrp1 mutant devoid of the cytoplasmic domain (nrp1cytoΔ/Δ) migrated significantly slower in response to VEGF relative to the cells expressing wild-type Nrp1 (nrp1+/+ cells). The rate of FA turnover in VEGF-treated nrp1cytoΔ/Δ ECs was an order of magnitude lower in comparison to nrp1+/+ ECs, thus accounting for the slower migration rate of the nrp1cytoΔ/Δ ECs.

Heparan sulfate-protein binding specificity

Heparan sulfate (HS) represents a large class of linear polysaccharides that are required for the function of all mammalian physiological systems. HS is characterized by a repeating disaccharide backbone that is subject to a wide range of modifications, making this class of macromolecules arguably the most information dense in all of biology. The majority of HS functions are associated with the ability to bind and regulate a wide range of proteins. Indeed, recent years have seen an explosion in the discovery of new activities for HS where it is now recognized that this class of glycans functions as co-receptors for growth factors and cytokines, modulates cellular uptake of lipoproteins, regulates protease activity, is critical to amyloid plaque formation, is used by opportunistic pathogens to enter cells, and may even participate in epigenetic regulation. This review will discuss the current state of understanding regarding the specificity of HS-protein binding and will describe the concept that protein binding to HS depends on the overall organization of domains within HS rather than fine structure.

CD138 mRNA expression from peripheral blood of patients with follicular and diffuse large B cell lymphoma: relation to disease progression and treatment response

Syndecans are among those transmembrane PGs which act via their heparan sulphate chains as receptors for different matrix elements (e.g. collagen I–III, fibronectin, thrombospondin, tenascin) and co-receptors for growth factors (e.g. bFGF, aFGF, GM-CSF, IL-3, IFNg). We hypothesized that there is a positive relationship between the expression of syndecan-1 (CD138) and treatment response in non-Hodgkin’s lymphoma. To identify the expression of syndecan-1 (CD138) in cases of non-Hodgkin’s lymphoma and to correlate its expression with treatment response and disease stage, this study was carried out as a cross-sectional study and included 30 patients with non-Hodgkin’s lymphomas attending Suez Canal University Hospital; diagnosis of patients was made by routine histological and immunohistochemical examination. CD138 mRNA expression was assessed by TaqMan technique using real-time PCR method. There was increased expression of CD138 mRNA in patients with follicular lymphoma than in patients with diffuse large B cell lymphoma (6.25 versus 3.46, respectively) (p ≤ 0.05). Syndecan-1 (CD138) mRNA expression from peripheral blood may be a useful marker for follicular lymphoma and can be used as a marker of treatment response in patients with follicular and diffuse large B cell lymphoma.

Neuropilin-1 is expressed by breast cancer stem-like cells and is linked to NF-κB activation and tumor sphere formation

Cancer stem cells (CSCs) initiate tumors and have a high resistance to conventional cancer therapy. Tranilast is an orally active drug of low toxicity that exerts inhibitory effects on breast CSCs. This appears to depend on its aryl hydrocarbon receptor (AHR) agonistic activity, but this receptor has diverse functions and it is unclear how CSCs are inhibited. CSCs generate tumor spheres in low-adherence cultures, and we employed the mammosphere-forming assay as a functional test for breast CSCs. Because NF-κB has a key role in mammosphere formation and CSC-mediated tumor initiation, we examined that pathway. We also examined the role of neuropilin-1 (Nrp1), which is a growth factor coreceptor linked to the tumorigenicity of some CSCs. We found that tranilast concurrently suppressed mammosphere formation, Nrp1 expression and constitutive NF-κB activation. Flow cytometric analysis revealed that a subpopulation of breast cancer cells bearing breast CSC markers also expressed Nrp1. A blocking anti-Nrp1 antibody suppressed mammosphere formation. We examined whether there was a link between Nrp1 and NF-κB activation. The siRNA knockdown of Nrp1 severely suppressed NF-κB activation and mammosphere formation. The phosphorylation of Akt and ERK1/2 was also reduced, but to a lesser extent. We conclude that Nrp1 plays a key role in mammosphere formation and this activity is linked to NF-κB activation. Thus, Nrp1 might be a target for therapy against breast CSCs, and the anticancer drug tranilast suppresses its expression.

Targeted Disruption of Heparan Sulfate Interaction with Hepatocyte and Vascular Endothelial Growth Factors Blocks Normal and Oncogenic Signaling

Hepatocyte growth factor (HGF) and vascular endothelial cell growth factor (VEGF) regulate normal development and homeostasis and drive disease progression in many forms of cancer. Both proteins signal by binding to receptor tyrosine kinases and heparan sulfate (HS) proteoglycans on target cell surfaces. Basic residues comprising the primary HS binding sites on HGF and VEGF provide similar surface charge distributions without underlying structural similarity. Combining three acidic amino acid substitutions in these sites in the HGF isoform NK1 or the VEGF isoform VEGF165 transformed each into potent, selective competitive antagonists of their respective normal and oncogenic signaling pathways. Our findings illustrate the importance of HS in growth factor driven cancer progression and reveal an efficient strategy for therapeutic antagonist development.

MicroRNA-125a inhibits cell growth by targeting glypican-4

Heparan sulfate proteoglycan (HSPG), such as glypican, plays a role as a co-receptor for growth factor to influence cells proliferation. However the mechanism is still vague. Micro-RNAs (miRNAs) regulate cell proliferation. Their capacity to direct the translation and stability of targeted transcripts can dramatically influence cellular physiological function. To explore how the function of glypican is regulated involved in cell proliferation, glypican-4 was chosen with a bioinformatics search identifying targeting seed sequences for miR-125a within the 3'-untranslated regions (3'UTR). Indeed, luciferase constructs containing the 3'UTR of glypican-4 demonstrated around 54% less activity in miR-125a expressing cells relative to the controls. The expression of glypican-4 at both the transcript and protein level was down-regulated by transition trasfection of miR-125a in the human embryonic kidney cell line 293T (HEK293T). Although cell proliferation of HEK293T was not influenced by the silence of glypican-4, DNA synthesis in response to FGF2 in the cells was attenuated by knockdown of glypican-4 using siRNA technique. Further study showed that phosphorylation of ERK(1/2) and AKT was suppressed by overexpressing miR-125a, whereas the suppressed MAPK and AKT signaling could be recovered by anti-miR-125a treatment. Both DNA synthesis and cell proliferation were impaired by the inhibitor of ERK(1/2) signaling. MTT assay demonstrated that the cell proliferation was impaired by miR-125a overexpression, however, rescued by anti-miR-125a in HEK293T cells. These results disclosed new function of miR-125a by targeting gene glypican-4 in cell growth process and illustrated the feasibility of using miRNAs as a therapeutic strategy to suppress cells proliferation.

Association of loss of epithelial syndecan-1 with stage and local metastasis of colorectal adenocarcinomas: An immunohistochemical study of clinically annotated tumors

BackgroundSyndecan-1 is a transmembrane proteoglycan with important roles in cell-cell and cell-extracellular matrix adhesion and as a growth factor co-receptor. Syndecan-1 is highly expressed by normal epithelial cells and loss of expression has been associated with epithelial-mesenchymal transition and the transformed phenotype. Loss of epithelial syndecan-1 has been reported in human colorectal adenocarcinomas, but whether this has prognostic significance remains undecided. Here we have examined syndecan-1 expression and its potential prognostic value with reference to a clinically annotated tissue microarray for human colon adenocarcinomas.MethodsSyndecan-1 expression was examined by immunohistochemistry of a tissue microarray containing cores from 158 colorectal adenocarcinomas and 15 adenomas linked to a Cleveland Clinic, IRB-approved database with a mean clinical follow-up of 38 months. The Kaplan-Meier method was used to analyze the relationship between syndecan-1 expression and patient survival. Potential correlations between syndecan-1 expression and the candidate prognostic biomarker fascin were examined.ResultsSyndecan-1 is expressed at the basolateral borders of normal colonic epithelial cells. On adenocarcinoma cells, syndecan-1 was present around cell membranes and in cytoplasm. In 87% of adenocarcinomas, syndecan-1 was decreased or absent; only 13% of patients had stained for syndecan-1 on more than 75% of tumor cells. Decreased syndecan-1 correlated with a higher TNM stage and lymph node metastasis and was more common in males (p = 0.042), but was not associated with age, tumor location or Ki67 index. Reduced tumor syndecan-1 staining also correlated with upregulation of stromal fascin (p = 0.016). Stromal syndecan-1 was observed in 16.6% of tumors. There was no difference in survival between patients with low or high levels of either tumor or stromal syndecan-1.ConclusionSyndecan-1 immunoreactivity was decreased in the majority of human colon adenocarcinomas in correlation with TNM stage and metastasis to local lymph nodes. In a small fraction of adenocarcinomas, syndecan-1 was upregulated in the local stroma. Syndecan-1 expression status did not correlate with patient survival outcomes. Combined analysis of syndecan-1 in relation to a potential prognostic biomarker, fascin, identified that loss of tumor syndecan-1 correlated significantly with strong stromal fascin staining.

Solution Structure of the Cytoplasmic Domain of Syndecan-3 by Two-dimensional NMR Spectroscopy

Syndecan-3 is a cell-surface heparan sulfate proteoglycan, which performs a variety of functions during cell adhension process. It is also a coreceptor for growth factor, mediating cell-cell and cell-matrix interaction. Syndecan-3 contains a cytoplasmic domain potentially associated with the cytoskeleton. Syndecan-3 is specifically expressed in neuron cell and has related to neuron cell differentiation and development of actin filament in cell migration. Syndecans each have a unique, central, and variable (V) region in their cytoplasmic domains. And that region of syndecan-3 may modulate the interactions of the conserved C1 regions of the cytoplasmic domains by tyrosine phosphorylation. Cytoplasmic domain of syndecan-3 has been synthesized for NMR structural studies. The solution structure of syndecan-3 cytoplasmic domain has been determined by two-dimensional NMR spectroscopy and simulated-annealing calculation. The cytoplasmic domain of the syndecan proteins has a tendency to form a dimmer conformation with a central cavity, however, that of syndecan-3 demonstrated a monomer conformation with a flexible region near C-terminus. The structural information might add knowledge about the structure-function relationships among syndecan proteins.

Role of the Basement Membrane Zone in Skin Development

Patterning of the skin during development requires precise reciprocol signaling between adjacent cells. Over the past two decades, several key studies have demonstrated a critical role for basement membrane zone (BMZ) components during epithelial pattern formation. In contrast to a static cellular glue, these papers provide a firm foundation for the notion that the BMZ actively shapes local cellular responses and tissue morphology. A major component of the BMZ are the integrins, a family of cell-surface receptors that adhere cells to the BMZ and mediate mechanical and chemical signals from it. These signals regulate the activities of growth factor receptors and ion channels, and control remodeling of the intracellular actin cytoskeleton. An early indication of the importance of integrins was in the identification of integrin b4 in the development of junctional epidermolyisis bullosa (Vidal et al., 1995). This suggested that skin integrity critically relied on these adhesion molecules. Later studies demonstrated that the key developmental role that integrins play came from mouse knockout experiments such as those that specifically removed integrin b1 in the skin (Brakebusch et al., 2000). The abnormal BMZ and lack of hair follicle proliferation demonstrated the multiple roles integrin b1 plays during development. Additional studies with other individual integrins such as a6 and av have also reinforced the idea that integrins play an instructive role in tissue morphogenesis apart from adhesion, although the precise mechanism of action is still poorly understood. The trimeric laminin family of proteins that acts as integrin coreceptors also play key roles in adhering cells to the BMZ as well as facilitating integrin signaling. Early reports of the role of laminin 5 (laminin 332) in junctional epidermolysis bullosa suggested it worked in a manner similar to integrin b4 in skin integrity and played an important role in epithelial development (Aberdam et al., 1994). However, additional studies by other groups, including that of Miner and co-workers, suggested the existence of numerous laminin genes and laminin isoforms, and suggested that each may play a key role in the process. Subsequent functional studies have shown the diversity of functions for each of the isoforms during skin development, including laminin 10 (laminin 511) and laminin 1 (laminin 111), in hair follicle morphogenesis. In addition to integrins and laminins, other components of the BMZ aid in regulating organ development by acting as growth factor co-receptors. For example, long after the morphogen fibroblast growth factor was identified, the key role for BMZ components as a fibroblast growth factor coreceptor was identified (Rapraeger et al., 1991). In this landmark paper, heparin sulfate proteoglycan was shown to be an obligate molecule to allow fibroblast growth factor to bind and activate its cognate receptor. This suggested that the orientation of surface glycosaminoglycans could regulate the activity of a morphogen substance. Since this study, similar types of BMZ coreceptor activities have also been shown for other developmental morphogens that regulate muscle, hair and other appendage development, including Wnt and Sonic hedgehog (Shh) ligands. Apart from signaling, BMZ components appear to shape the distance and distribution of key morphogens during epithelial development. In one of several landmark papers, The et al., (1999) demonstrated that the product of the tout-velu gene in Drosophila controls the distance that hedgehog ligand can travel through cells of the tissue, but not the absolute activity of the ligand on its receptor. The tout-velu gene encodes a heparin sulfate polymerase whose function is to modify glycosaminoglycan moeties of heparin sulfate proteoglycans. Subsequent studies in flies and vertebrate cells have identified other genes that regulate the process of cell-surface glycosylation such as sister of tout-velu, brother of tout velu, dally and dally-like and implicate cellular glycosylation in morphogen movement across a cell. Moreover, the vertebrate homologs of these molecules were also shown to be encoded by the EXT family of tumor suppressor genes, implicating morphogen tissue distribution as a novel tumor mechanism.

Transmembrane domains of the syndecan family of growth factor coreceptors display a hierarchy of homotypic and heterotypic interactions

The single-pass transmembrane domains (TMDs) of the syndecan family of cell surface adhesion molecules have been implicated in functional protein-protein interactions. Although each paralog contains a conserved GxxxG dimerization motif, we show here that the syndecan-1 TMD dimerizes weakly, the syndecan-3 and syndecan-4 TMDs each dimerize strongly, and the syndecan-2 TMD dimerizes very strongly. These markedly different levels of self-association suggest that paralog TMDs play different roles in directing functional interactions of each full-length syndecan family member. We further show that each syndecan TMD forms detergent-resistant heteromeric complexes with other paralogs, and that these interactions exhibit selectivity. Although heteromeric interactions among full-length syndecan paralogs have not been reported, we argue that the distinct hierarchy of protein-protein interactions mediated by the syndecan TMDs may give rise to considerable complexity in syndecan function. The demonstration that TMD homodimerization and heterodimerization can be mediated by GxxxG motifs and modulated by sequence context has implications for the signaling mechanisms of other cell surface receptors, including the integrins and the erbB family.

Growth factor–induced shedding of syndecan-1 confers glypican-1 dependence on mitogenic responses of cancer cells

The cell surface heparan sulfate proteoglycan (HSPG) glypican-1 is up-regulated by pancreatic and breast cancer cells, and its removal renders such cells insensitive to many growth factors. We sought to explain why the cell surface HSPG syndecan-1, which is also up-regulated by these cells and is a known growth factor coreceptor, does not compensate for glypican-1 loss. We show that the initial responses of these cells to the growth factor FGF2 are not glypican dependent, but they become so over time as FGF2 induces shedding of syndecan-1. Manipulations that retain syndecan-1 on the cell surface make long-term FGF2 responses glypican independent, whereas those that trigger syndecan-1 shedding make initial FGF2 responses glypican dependent. We further show that syndecan-1 shedding is mediated by matrix metalloproteinase-7 (MMP7), which, being anchored to cells by HSPGs, also causes its own release in a complex with syndecan-1 ectodomains. These results support a specific role for shed syndecan-1 or MMP7–syndecan-1 complexes in tumor progression and add to accumulating evidence that syndecans and glypicans have nonequivalent functions in vivo.

Syndecan-3: a cell-surface heparan sulfate proteoglycan important for chondrocyte proliferation and function during limb skeletogenesis

Syndecans are single-pass integral membrane components that serve as co-receptors for growth factors and cytokines and can elicit signal transduction via their cytoplasmic tails. We review here previous studies from our groups on syndecan-3 biology and function in the growth plates of developing long bones in chick and mouse embryos. Gain- and loss-of-function data indicate that syndecan-3 has important roles in restricting mitotic activity to the proliferative zone of growth plate and may do so in close cooperation and interaction with the signaling molecule Indian hedgehog (IHH). Biochemical and protein-modeling data suggest a dimeric/oligomeric syndecan-3 configuration on the chondrocyte's cell surface. Analyses of embryos misexpressing syndecan-3 or lacking IHH provide further clues on syndecan-3/IHH interdependence and interrelationships. The data and the conclusions reached provide insights into mechanisms fine-tuning chondrocyte proliferation, maturation, and function in the developing and growing skeleton and into how abnormalities in these fundamental mechanisms may subtend human congenital pathologies, including osteochondromas in hereditary multiple exostoses syndrome.

Induction of syndecan-1 expression in stromal fibroblasts promotes proliferation of human breast cancer cells.

Infiltrating carcinomas characteristically elicit a reactive stromal response, and accumulating evidence indicates that tumor stroma fibroblasts reciprocally promote tumor development and growth. The cell surface heparan sulfate proteoglycan, syndecan-1 (Sdc1), is thought to function as a coreceptor for growth factor and extracellular matrix interactions, and Sdc1 expression is induced in reactive stromal cells in both mice and man. Mice with a targeted mutation in Sdc1 show reduced tumor development in response to oncogene expression and altered responses to other pathological stimuli that are associated with the induction of stromal Sdc1. Here, we test the hypothesis that Sdc1 is required for the growth-promoting activities of reactive stroma. We found that when highly invasive carcinoma cells (MDA-MB-231) were placed in contact with mouse embryonic fibroblasts (MEFs) in a coculture model, Sdc1 expression was induced. Sdc1 was not induced by less invasive or normal cell lines (T47D and NMuMG). Furthermore, the growth of MDA-MB-231 cells was enhanced by 42% when cocultured with Sdc1+/+ MEFs compared with Sdc1-/- MEFs. When T47D cells were cocultured with fibroblasts that expressed transfected Sdc1, these Sdc1-positive fibroblasts stimulated growth of the breast epithelial cells by 85% compared with untransfected controls. The growth-promoting effect was completely abolished when fibroblasts were transfected with mutant Sdc1 lacking heparan sulfate attachment sites. In conclusion, we have demonstrated that a growth-promoting loop exists between breast cancer cells and their stroma that depends on the activity of glycanated Sdc1.

Amyloid β Binds Trimers as Well as Monomers of the 75-kDa Neurotrophin Receptor and Activates Receptor Signaling

p75(NTR), a nerve growth factor co-receptor that has been implicated in apoptosis of neurons, is structurally related to Fas and the receptors for tumor necrosis factor-alpha that display ligand independent assembly into trimers. Using embryonic day 17 fetal rat cortical neurons and p75(NTR)-expressing NIH-3T3 cells, we now show that p75(NTR) exists as a trimer as well as a monomer. Furthermore, we have reported and others have confirmed that amyloid beta binds p75(NTR), and that this binding leads to apoptotic cell death. We now report that amyloid beta binds to trimers of p75(NTR) as well as to p75(NTR) monomers but not to the p140(trkA), the nerve growth factor co-receptor that mediates neuronal survival. Furthermore, amyloid beta activates p75(NTR), strongly inducing the transcription of c-Jun mRNA and stimulating the stress-activated c-Jun NH(2)-terminal kinase, as measured by phosphorylation of its substrate (glutathione S-transferase-c-Jun-(1-79)). Our data suggest that p75(NTR) may be present as a preformed trimer that binds amyloid beta to induce receptor activation, and support the hypothesis that p75(NTR) activation by amyloid beta is causally related to Alzheimer's disease.

Heparan sulfate proteoglycans on the cell surface: versatile coordinators of cellular functions

Heparan sulfate proteoglycans are complex molecules composed of a core protein with covalently attached glycosaminoglycan chains. While the protein part determines localization of the proteoglycan on the cell surfaces or in the extracellular matrix, the glycosaminoglycan component, heparan sulfate, mediates interactions with a variety of extracellular ligands such as growth factors and adhesion molecules. Through these interactions, heparan sulfate proteoglycans participate in many events during cell adhesion, migration, proliferation and differentiation. We are determining the multitude of proteoglycan functions, as their intricate roles in many pathways are revealed. They act as coreceptors for growth factors, participate in signalling during cell adhesion, modulate the activity of a broad range of molecules, and partake in many developmental and pathological processes, including tumorigenesis and wound repair. This review concentrates on biological roles of cell surface heparan sulfate proteoglycans, namely syndecans and glypicans, and outlines the progress achieved during the last decade in unraveling the molecular interactions behind proteoglycan functions.

Selective alterations of glycosaminoglycans synthesis and proteoglycan expression in rat cortex and hippocampus in pilocarpine-induced epilepsy

Proteoglycans and glycosaminoglycans are elements of matrix. In the nervous system, glycosaminoglycans modulate neurite outgrowth and are co-receptors for growth factors playing a crucial role in cell differentiation and synaptogenesis. The receptor of protein tyrosine phosphatase β (RPTPβ) is a chondroitin sulphate proteoglycan which plays an important role in neural morphogenesis and axon guidance mechanisms. Pilocarpine-treated rats present status epilepticus, which is followed by a seizure-free period (silent), by a period of spontaneous recurrent seizures (chronic), and the hippocampus of these animals exhibits cell loss and mossy fiber sprouting. Thus, the synthesis of heparan sulphate and chondroitin sulphate and the time course of RPTPβ immunoreactivity were studied in the hippocampus and cerebral cortex during these phases of pilocarpine-induced epilepsy. The results showed decreased synthesis of heparan sulphate during the acute phase and an increased synthesis of chondroitin sulphate during the silent period in the cortex and hippocampus. In control rats RPTPβ immunoreactivity was detected only in glial cells. After 6 h of status epilepticus the RPTPβ immunoreactivity was no longer detectable in the glial cells in both tissues and intense staining became evident in the matrix, surrounding CA3 and dentate gyrus and piriform cortex neurones. In the silent and chronic periods RPTPβ immunoreactivity was mainly detected in neuronal somata and fibers of neurones of hippocampus and cortex. These changes show a selective variation of synthesis and expression of glycosaminoglycans and RPTPβ in relation to epilepsy suggesting a molecular interplay between glia and neurones during seizures.