Heparan sulfate proteoglycan of human colon: partial molecular cloning, cellular expression, and mapping of the gene (HSPG2) to the short arm of human chromosome 1

Expanding genetic and clinical aspects of Schwartz-Jampel syndrome: A report of two cases with literature review

Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterized by muscle stiffness (myotonia) and chondrodysplasia. This disease is caused by biallelic loss of function mutations in the HSPG2 gene, which encodes the core protein of perlecan. This study aims to investigate causative variants in two sisters born to consanguineous Iranian parents. Both patients were presented with myotonia and a mask-like face; moreover, they showed a less common symptom, gastrointestinal bleeding, which is not typical of SJS and has only been reported in one patient. Regarding the crucial role of perlecan in vascular structure and mucosal stability, bleeding disorders could be expected in perlecan dysfunctions. In addition to the case study, a comprehensive literature review was conducted to gather information on similar genetic variants, associated clinical features, and possible disease mechanisms. Results of this study contribute to our understanding of the genetic and clinical aspects of Schwartz-Jampel syndrome, and more importantly, the manifestation of gastrointestinal bleeding in patients with Schwartz-Jampel syndrome.

Modular Proteoglycan Perlecan/HSPG2: Mutations, Phenotypes, and Functions

Heparan sulfate proteoglycan 2 (HSPG2) is an essential, highly conserved gene whose expression influences many developmental processes including the formation of the heart and brain. The gene is widely expressed throughout the musculoskeletal system including cartilage, bone marrow and skeletal muscle. The HSPG2 gene product, perlecan is a multifunctional proteoglycan that preserves the integrity of extracellular matrices, patrols tissue borders, and controls various signaling pathways affecting cellular phenotype. Given HSPG2's expression pattern and its role in so many fundamental processes, it is not surprising that relatively few gene mutations have been identified in viable organisms. Mutations to the perlecan gene are rare, with effects ranging from a relatively mild condition to a more severe and perinatally lethal form. This review will summarize the important studies characterizing mutations and variants of HSPG2 and discuss how these genomic modifications affect expression, function and phenotype. Additionally, this review will describe the clinical findings of reported HSPG2 mutations and their observed phenotypes. Finally, the evolutionary aspects that link gene integrity to function are discussed, including key findings from both in vivo animal studies and in vitro systems. We also hope to facilitate discussion about perlecan/HSPG2 and its role in normal physiology, to explain how mutation can lead to pathology, and to point out how this information can suggest pathways for future mechanistic studies.

Novel HSPG2 mutations causing Schwartz‑Jampel syndrome type 1 in a Chinese family: A case report

Schwartz-Jampel syndrome type 1 (SJS1) is a rare autosomal recessive disease caused by mutations in the gene heparan sulfate proteoglycan 2 (HSPG2; also known as basement membrane‑specific heparin sulfate). In the present study, a 10‑year‑old female SJS1 proband from a Chinese family, who was diagnosed by X‑ray and physical examination, was recruited. The key clinical features of the patient with SJS1 included short stature, joint contractures, pigeon breast, and myotonia that led to progressive stiffness of the face and limbs; barely discernible kyphosis was also noted. Genetic testing using whole exome sequencing and Sanger sequencing was performed for the proband and family members. A total of 2 novel mutations (c.8788G>A; p.Glu2930Lys and c.11671+5G>A) in the HSPG2 gene were identified in the proband. The family members harboring 1 heterozygous mutation in HSPG2 did not exhibit any skeletal abnormalities. The results of the present study suggested that the compound heterozygous mutations in HSPG2 may be responsible the induction of SJS1, and demonstrated the genotype‑phenotype associations between mutations in the HSPG2 gene and clinical characteristics of SJS1.

The Basement Membrane Proteoglycans Perlecan and Agrin: Something Old, Something New

Several members of the proteoglycan family are integral components of basement membranes; other proteoglycan family members interact with or bind to molecular residents of the basement membrane. Proteoglycans are polyfunctional molecules, for they derive their inherent bioactivity from the amino acid motifs embedded in the core protein structure as well as the glycosaminoglycan (GAG) chains that are covalently attached to the core protein. The presence of the covalently attached GAG chains significantly expands the "partnering" potential of proteoglycans, permitting them to interact with a broad spectrum of targets, including growth factors, cytokines, chemokines, and morphogens. Thus proteoglycans in the basement membrane are poised to exert diverse effects on the cells intimately associated with basement membranes.

The role of perlecan and endorepellin in the control of tumor angiogenesis and endothelial cell autophagy

During tumor growth and angiogenesis there is a dynamic remodeling of tissue architecture often accompanied by the release of extracellular matrix constituents full of biological activity. One of the key constituents of the tumor microenvironment is the large heparan sulfate proteoglycan perlecan. This proteoglycan, strategically located at cell surfaces and within basement membranes, is a well-defined pro-angiogenic molecule when intact. However, when partially processed by proteases released during cancer remodeling and invasion, the C-terminal fragment of perlecan, known as endorepellin, has opposite effects than its parent molecule. Endorepellin is a potent inhibitor of angiogenesis by exerting a dual receptor antagonism by simultaneously engaging VEGFR2 and α2β1 integrin. Signaling through the α2β1 integrin leads to actin disassembly and block of endothelial cell migration, necessary for capillary morphogenesis. Signaling through the VEGFR2 induces dephosphorylation of the receptor via activation of SHP-1 and suppression of downstream proangiogenic effectors, especially attenuating VEGFA expression. A novel and emerging role of endorepellin is its ability to evoke autophagy by activating Peg3 and various canonical autophagic markers. This effect is specific for endothelial cells as these are the primary cells expressing both VEGFR2 and α2β1 integrin. Thus, an endogenous fragment of a ubiquitous proteoglycan can regulate both angiogenesis and autophagy through a dual receptor antagonism. The biological properties of this natural endogenous protein place endorepellin as a potential therapeutic agent against cancer or diseases where angiogenesis is prominent.

Transcriptional complexity of the HSPG2 gene in the human mast cell line, HMC-1

The mammalian HSPG2 gene encodes the proteoglycan protein core perlecan, which has important functions in biology including cell adhesion via integrins, binding to the extracellular matrix via various protein-protein interactions and binding of growth factors via the heparan sulfate chains decorating the N-terminal domain I. Here we show that, in the human mast cell line HMC-1, the transcription of this gene results in a population of mRNA that is processed in such a way to provide a relative increase of transcripts corresponding to domain V or the C-terminus compared to transcripts from either domain III or the N-terminal domain I. This paper also presents evidence of splicing of the HSPG2 gene in HMC-1 cells at exons 2/3 and after comparing this sequence with those published in various databases, a model is postulated to explain what might be happening in these cells with regard to the transcription of the HSPG2 gene. As domain V of perlecan contains the α2β1 integrin binding site that modulates angiogenesis, we hypothesize that the transcriptional control of the HSPG2 gene in mast cells to synthesize these transcripts supports their stimulatory and specific role in wound healing and tissue regeneration.

Preliminary results in a study regarding the relationship between perlecan gene polymorphism and spinal muscular atrophy type I disease

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by weakness and atrophy of proximal muscles. Despite the fact that the disease transmission suggests an autosomal recessive trait, the wide spectrum of clinical manifestations indicates that other genes may contribute to the SMA phenotype. To identify possible modifier genes, the aim of our study was to investigate the relationship between BamH1 perlecan gene polymorphism and SMA type I, the classical severe form of the disease. We genotyped 40 patients with SMA type I disease and 50 subjects without personal or heredo-colateral neuromuscular problems, using the polymerase chain reaction-restriction fragment length polymorphism method. After statistical analysis of the observed genotypes, a significant difference (p = 0.03) could be observed regarding the incidence of TT genotype and T allele in boys with SMA type I compared with affected girls. However, this result cannot be assessed because of the small and unequal number of subjects. We concluded that there might be no association between perlecan gene polymorphism and SMA type I disease.

Novel interactions of perlecan: unraveling perlecan's role in angiogenesis

Perlecan, a highly conserved and ubiquitous basement membrane heparan sulfate proteoglycan, is essential for life, inasmuch as its absence results in embryonic lethality in mice and C. elegans, and neonatal lethality in humans. Perlecan plays an essential role in vasculogenesis and chondrogenesis, as well as in pathological states where these processes are maladapted. Although a large body of evidence supports a pro-angiogenic role for perlecan, recent findings suggests that portions of the perlecan protein core can be antiangiogenic, requiring a further evaluation of the functioning of this complex molecule. This review is focused on the genetics of mammalian and nonmammalian perlecan, the elucidation of its novel interacting partners and its role in angiogenesis. By more fully understanding perlecan's functioning in angiogenesis, we may gain invaluable insight that could lead to therapeutic interventions in cancer and other pathologic states.

Prostate cancer and Hedgehog signalling pathway

The Hedgehog (Hh) family of intercellular signalling proteins have come to be recognised as key mediators in many fundamental processes in embryonic development. Their activities are central to the growth, patterning and morphogenesis of many different regions within the bodies of vertebrates. In some contexts, Hh signals act as morphogens in the dose-dependent induction of distinct cell fates within a target field, in others as mitogens in the regulation of cell proliferation or as inducing factors controlling the form of a developing organ. These diverse functions of Hh proteins raise many intriguing questions about their mode of action. Various studies have now demonstrated the function of Hh signalling in the control of cell proliferation, especially for stem cells and stem-like progenitors. Abnormal activation of the Hh pathway has been demonstrated in a variety of human tumours. Hh pathway activity in these tumours is required for cancer cell proliferation and tumour growth. Recent studies have uncovered the role for Hh signalling in advanced prostate cancer and demonstrated that autocrine signalling by tumour cells is required for proliferation, viability and invasive behaviour. Thus, Hh signalling represents a novel pathway in prostate cancer that offers opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring.

Biomarker discovery from pancreatic cancer secretome using a differential proteomic approach

Quantitative proteomics can be used as a screening tool for identification of differentially expressed proteins as potential biomarkers for cancers. Candidate biomarkers from such studies can subsequently be tested using other techniques for use in early detection of cancers. Here we demonstrate the use of stable isotope labeling with amino acids in cell culture (SILAC) method to compare the secreted proteins (secretome) from pancreatic cancer-derived cells with that from non-neoplastic pancreatic ductal cells. We identified 145 differentially secreted proteins (>1.5-fold change), several of which were previously reported as either up-regulated (e.g. cathepsin D, macrophage colony stimulation factor, and fibronectin receptor) or down-regulated (e.g. profilin 1 and IGFBP-7) proteins in pancreatic cancer, confirming the validity of our approach. In addition, we identified several proteins that have not been correlated previously with pancreatic cancer including perlecan (HSPG2), CD9 antigen, fibronectin receptor (integrin beta1), and a novel cytokine designated as predicted osteoblast protein (FAM3C). The differential expression of a subset of these novel proteins was validated by Western blot analysis. In addition, overexpression of several proteins not described previously to be elevated in human pancreatic cancer (CD9, perlecan, SDF4, apoE, and fibronectin receptor) was confirmed by immunohistochemical labeling using pancreatic cancer tissue microarrays suggesting that these could be further pursued as potential biomarkers. Lastly the protein expression data from SILAC were compared with mRNA expression data obtained using gene expression microarrays for the two cell lines (Panc1 and human pancreatic duct epithelial), and a correlation coefficient (r) of 0.28 was obtained, confirming previously reported poor associations between RNA and protein expression studies.

Perlecan and tumor angiogenesis

Perlecan is a major heparan sulfate proteoglycan (HSPG) of basement membranes (BMs) and connective tissues. The core protein of perlecan is divided into five domains based on sequence homology to other known proteins. Commonly, the N-terminal domain I of mammalian perlecan is substituted with three HS chains that can bind a number of matrix molecules, cytokines, and growth factors. Perlecan is essential for metazoan life, as shown by genetic manipulations of nematodes, insects, and mice. There are also known human mutations that can be lethal. In vertebrates, new functions of perlecan emerged with the acquisition of a closed vascular system and skeletal connective tissues. Many of perlecan's functions may be related to the binding and presentation of growth factors to high-affinity tyrosine kinase (TK) receptors. Data are accumulating, as discussed here, that similar growth factor-mediated processes may have unwanted promoting effects on tumor cell proliferation and tumor angiogenesis. Understanding of these attributes at the molecular level may offer opportunities for therapeutic intervention.

Antibody response against perlecan and collagen types IV and VI in chronic renal allograft rejection in the rat

Chronic rejection is the leading cause of late renal transplant failure. Various structural lesions are observed in grafts undergoing chronic rejection including glomerular basement membrane (GBM) duplications. The well-established Fisher (F344) to Lewis (LEW) rat renal transplant model for chronic rejection was used to assess the presence and role of the humoral immune response against graft antigens during chronic rejection. LEW recipients of F344 allografts develop transplant glomerulopathy and produce IgG1 antibodies directed against F344 GBM preparations that are detectable 3 weeks after transplantation. Glomerular IgG1 deposition was observed that in vitro co-localized with a rabbit anti-rat GBM antiserum in rejecting F344 grafts; elution experiments of isolated glomeruli yielded IgG1 antibodies reactive in vitro with F344 GBM, but not LEW GBM. Prevention of acute rejection by transient treatment of the recipients with cyclosporin A completely abrogated the production of anti-GBM antibodies. Using proteomic techniques we identified the antigens recognized by the LEW posttransplant sera as being the heparan sulfate proteoglycan perlecan and the alpha1 chain of collagen type VI in association with the alpha5 chain of collagen type IV. In conclusion, LEW recipients of F344 kidney grafts produce IgG1 antibodies against donor type perlecan and alpha1(VI)/alpha5(IV) collagen and develop transplant glomerulopathy. These data implicate an important role for the humoral immune response in the development of glomerulopathy during chronic rejection.

Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene

Perlecan is a large heparan sulfate (HS) proteoglycan present in all basement membranes and in some other tissues such as cartilage, and is implicated in cell growth and differentiation. Mice lacking the perlecan gene (Hspg2) have a severe chondrodysplasia with dyssegmental ossification of the spine and show radiographic, clinical and chondro-osseous morphology similar to a lethal autosomal recessive disorder in humans termed dyssegmental dysplasia, Silverman-Handmaker type (DDSH; MIM 224410). Here we report a homozygous, 89-bp duplication in exon 34 of HSPG2 in a pair of siblings with DDSH born to consanguineous parents, and heterozygous point mutations in the 5' donor site of intron 52 and in the middle of exon 73 in a third, unrelated patient, causing skipping of the entire exons 52 and 73 of the HSPG2 transcript, respectively. These mutations are predicted to cause a frameshift, resulting in a truncated protein core. The cartilage matrix from these patients stained poorly with antibody specific for perlecan, but there was staining of intracellular inclusion bodies. Biochemically, truncated perlecan was not secreted by the patient fibroblasts, but was degraded to smaller fragments within the cells. Thus, DDSH is caused by a functional null mutation of HSPG2. Our findings demonstrate the critical role of perlecan in cartilage development.

Role of Proteoglycans in Tumor Progression

Data is now starting to accumulate on the differential expression of PGs in tumor cells of various invasive/metastatic potential. This is not so surprising if one considers the key functions that PGs play in the regulation of cell proliferation, adhesion and motility. However, characterization of PG expression in individual tumor types still awaits further detailed studies. Data on melanomas clearly indicate that PG phenotype is both specific and also promiscuous in a sense that ectopic expression of certain tissue specific PGs can occur in various tumors. Expression of a metastatic phenotype-specific splice variants of CD44 provides an example for the possible marker-function of PG. This also raises the hope that some PGs could be used as diagnostic/prognostic tools in pathology or even as a therapeutic targets against tumor dissemination. On the other hand, specific glycanation inhibitors may also be used for the modulation of tumor PG exist and the invasive phenotype.

Oxidized low density lipoproteins regulate synthesis of monkey aortic smooth muscle cell proteoglycans that have enhanced native low density lipoprotein binding properties

Oxidized low density lipoproteins (Ox-LDL) affect several biological processes involved in atherogenesis. However, it is not known whether Ox-LDL can regulate proteoglycan expression and thus affect arterial wall lipoprotein retention. This study evaluated whether Ox-LDL, as compared with native LDL, regulates proteoglycan expression by monkey arterial smooth muscle cells in vitro and whether proteoglycans synthesized in the presence of Ox-LDL exhibit altered lipoprotein binding properties. Ox-LDL stimulated glycosaminoglycan synthesis, as measured by (35)SO(4) incorporation, by 30-50% over that of native LDL. The effect was maximal after 72 h of exposure to 5 microg/ml of Ox-LDL. The molecular sizes of versican, biglycan, and decorin increased in response to Ox-LDL, as indicated by size exclusion chromatography and SDS-polyacrylamide gel electrophoresis. These effects could be mimicked by the lipid extract of Ox-LDL. These size increases were largely due to chain elongation and not to alterations in the ratio of (35)SO(4) to [(3)H]glucosamine incorporation. Affinity chromatography indicated that Ox-LDL stimulated the synthesis of proteoglycans with high affinity for native LDL. Ox-LDL also specifically stimulated mRNA expression for biglycan (but not versican or decorin), which was correlated with increased expression of secreted biglycan. Thus, Ox-LDL may influence lipoprotein retention by regulating synthesis of biglycan and also by altering glycosaminoglycan synthesis of vascular proteoglycans so as to enhance lipoprotein binding properties.

Glomerular heparan sulfate alterations: mechanisms and relevance for proteinuria

Heparan sulfate (HS) is the anionic polysaccharide side chain of HS proteoglycans (HSPGs) present in basement membranes, in extracellular matrix, and on cell surfaces. Recently, agrin was identified as a major HSPG present in the glomerular basement membrane (GBM). An increased permeability of the GBM for proteins after digestion of HS by heparitinase or after antibody binding to HS demonstrated the importance of HS for the permselective properties of the GBM. With recently developed antibodies directed against the GBM HSPG (agrin) core protein and the HS side chain, we demonstrated a decrease in HS staining in the GBM in different human proteinuric glomerulopathies, such as systemic lupus erythematosus (SLE), minimal change disease, membranous glomerulonephritis, and diabetic nephropathy, whereas the staining of the agrin core protein remained unaltered. This suggested changes in the HS side chains of HSPG in proteinuric glomerular diseases. To gain more insight into the mechanisms responsible for this observation, we studied GBM HS(PG) expression in experimental models of proteinuria. Similar HS changes were found in murine lupus nephritis, adriamycin nephropathy, and active Heymann nephritis. In these models, an inverse correlation was found between HS staining in the GBM and proteinuria. From these investigations, four new and different mechanisms have emerged. First, in lupus nephritis, HS was found to be masked by nucleosomes complexed to antinuclear autoantibodies. This masking was due to the binding of cationic moieties on the N-terminal parts of the core histones to anionic determinants in HS. Second, in adriamycin nephropathy, glomerular HS was depolymerized by reactive oxygen species (ROS), mainly hydroxyl radicals, which could be prevented by scavengers both in vitro (exposure of HS to ROS) and in vivo. Third, in vivo renal perfusion of purified elastase led to a decrease of HS in the GBM caused by proteolytic cleavage of the agrin core protein near the attachment sites of HS by the HS-bound enzyme. Fourth, in streptozotocin-induced diabetic nephropathy and during culture of glomerular cells under high glucose conditions, evidence was obtained that hyperglycemia led to a down-regulation of HS synthesis, accompanied by a reduction in the degree of HS sulfation.

There is binding of collagen IV to beta 1 integrin during early skin basement membrane assembly

This study is concerned with the mechanism of basement membrane assembly in an in vitro 3-dimensional skin-culture system. Dermal fibroblasts alone can synthesize collagen IV, perlecan, and nidogen, but cannot assemble them into a basement membrane. When keratinocytes are added to the culture, however, linear assembly of collagen IV, perlecan, and nidogen is noted at the epidermo-dermal interface. Northern blots and in situ hybridization showed that perlecan and nidogen mRNAs derive exclusively from fibroblasts, while the alpha 2 (IV) collagen chain is expressed by both keratinocytes and fibroblasts, although the major source is in the mesenchyma (80%). Prior to the development of the lamina densa, collagen IV colocalizes with beta 1 integrins, most likely alpha 1 beta 1 and alpha 2 beta 1, which are known receptors for this collagen. Blocking experiments with the AIIB2 mAb (anti-beta 1 integrin subunit) and by peptide inhibition with the CB3(IV) collagen fragment disrupted the assembly of collagen IV. This study suggests that the initiation of basement-membrane formation involves binding of collagen IV molecules to keratinocyte cell-matrix integrins. These complexes act as nucleation sites for further polymerization of collagen IV molecules mostly derived from fibroblasts, by a process of self-assembly.

Matrix proteoglycans: from molecular design to cellular function

The proteoglycan superfamily now contains more than 30 full-time molecules that fulfill a variety of biological functions. Proteoglycans act as tissue organizers, influence cell growth and the maturation of specialized tissues, play a role as biological filters and modulate growth-factor activities, regulate collagen fibrillogenesis and skin tensile strength, affect tumor cell growth and invasion, and influence corneal transparency and neurite outgrowth. Additional roles, derived from studies of mutant animals, indicate that certain proteoglycans are essential to life whereas others might be redundant. The review focuses on the most recent genetic and molecular biological studies of the matrix proteoglycans, broadly defined as proteoglycans secreted into the pericellular matrix. Special emphasis is placed on the molecular organization of the protein core, the utilization of protein modules, the gene structure and transcriptional control, and the functional roles of the various proteoglycans. When possible, proteoglycans have been grouped into distinct gene families and subfamilies offering a simplified nomenclature based on their protein core design. The structure-function relationship of some paradigmatic proteoglycans is discussed in depth and novel aspects of their biology are examined.

Developmental expression of perlecan during murine embryogenesis

Perlecan is a modular heparan sulfate proteoglycan that is an intrinsic constituent of all basement membranes and extracellular matrices. Because of its strategic position and unique structure, perlecan has been implicated in modulating the activity of various growth factors required for normal development and tissue homeostasis. To gain insights into the potential function of perlecan in vivo, we examined the spatiotemporal distribution of its mRNA and protein core during murine embryogenesis. We utilized a new affinity-purified antibody that recognizes specifically the protein core of perlecan together with an in situ RT-PCR approach to perform a systematic analysis of perlecan expression and deposition during murine ontogeny. Perlecan appeared early (E10.5) in tissues of vasculogenesis including heart, pericardium, and major blood vessels. Its early expression coincided with the development of the cardiovascular system. Subsequently (E11-13), the greatest deposition of perlecan occurred within the developing cartilage, especially the cartilage undergoing endochondral ossification, where it remained elevated throughout all the developmental stages, and up to adulthood. Interestingly, the mRNA levels of perlecan were always higher in all the vascularized tissues, principally within endothelial cells, while chondrocytes displayed relatively low mRNA levels. This suggests a higher biosynthesis and turnover rates in the blood vessels vis-à-vis those of cartilaginous and other mesenchymal tissues. During later stages of development (E13-17.5) perlecan mRNA levels progressively increased and its expression correlated with the onset of tissue differentiation of various parenchymal organs including the developing kidneys, lungs, liver, spleen, and gastrointestinal tract. The central nervous system showed no perlecan expression with the exception of the calvaria and choroid plexus. Collectively, the results indicate that perlecan may play crucial roles not only in vasculogenesis but also in the maturation and maintenance of differentiated tissues, including cartilage.

Enterocytic differentiation correlates with changes in the fine structure and sulfation of perlecan in HT29 human colon carcinoma cells

Undifferentiated HT29 and differentiated HT29G-human colon carcinoma cells have been used to study the changes in proteoglycan production and structure associated with enterocytic cell differentiation. Differentiated cells incorporate twice as much sulfate than undifferentiated cells when labeled with [35S]sulfate. Both cell lines produce a heparan sulfate proteoglycan which was purified by ion-exchange. The heparan sulfate proteoglycan from differentiated HT29G- cells is larger and more homogeneous in size than that produced by undifferentiated HT29 cells. No differences in the core protein structure were observed. The detailed structural analysis of the heparan sulfate chains revealed that the structure of these chains follows the standard rules for these glycosaminoglycans with N-sulfated domains and N-acetylated domains. The main finding was that differentiated HT29G- cells have a degree of higher sulfation than HT29 cells. These differences were found to affect primarily 6-O-sulfated positions.

Evidence for the existence of multiple heparan sulfate proteoglycans in the human glomerular basement membrane and mesangial matrix

Heparan sulfate proteoglycans (HSPGs) are essential components of the glomerular basement membrane (GBM) carrying a strong anionic charge. A well-characterized extracellular HSPG is perlecan, ubiquitously expressed in basement membranes. A cDNA construct encoding domains I and II of human perlecan was expressed as a fusion protein with glutathione S-transferase. This fusion protein was used to generate monoclonal antibody 95J10. We compared the staining pattern of 95J10 with that of M215, a previously prepared mAb that recognizes HSPG isolated from human GBM. In kidney cortex, the anti-perlecan mAb 95J10 showed a strong staining of the mesangium, Bowman's capsule, the tubular basement membrane, and stained the GBM only slightly. In contrast, M215 predominantly stained the GBM in a linear fashion. Immunoelectron microscopy supported these results, showing concentrations of perlecan in some regions of the GBM, whereas the unidentified M215 antigen was homogenously distributed throughout the GBM. In other human tissues, both antibodies also produced a different staining pattern. Furthermore, a polyclonal antiserum recognizing HSPG isolated from the GBM did not recognize perlecan from EHS tumors. These results provide evidence for the presence of another HSPG in the GBM that is immunologically distinct from perlecan. The absence of perlecan splice variants in the kidney suggests that this component is encoded by a different gene than perlecan. Given its marked expression in the GBM, this component could be a determining factor in the maintenance of selective glomerular permeability.

Structural and functional characterization of the human perlecan gene promoter. Transcriptional activation by transforming growth factor-beta via a nuclear factor 1-binding element

Perlecan, a modular heparan sulfate proteoglycan of basement membranes and cell surfaces, plays a crucial role in regulating the assembly of extracellular matrices and the binding of nutrients and growth factors to target cells. To achieve a molecular understanding of perlecan gene regulation, we isolated the 5'-flanking region and investigated its functional promoter activity and its response to cytokines. Transient cell transfection assays, using plasmid constructs harboring the perlecan promoter linked to the chloramphenicol acetyltransferase reporter gene, demonstrated that the largest approximately 2.5-kilobase construct contained maximal promoter activity. This promoter region was functionally active in a variety of cells of diverse histogenetic origin, thus corroborating the widespread expression of this gene product. Stepwise 5' deletion analyses demonstrated that the -461-base pair (bp) proximal promoter retained approximately 90% of the total activity, and internal deletions confirmed that the most proximal sequence was essential for proper promoter activity. Nanomolar amounts of transforming growth factor-beta induced 2-3-fold perlecan mRNA and protein core levels in normal human skin fibroblasts, and this induction was transcriptionally regulated; in contrast, tumor necrosis factor-alpha had no effect and was incapable of counteracting the effects of TGF-beta. Using additional 5' deletions and DNase footprinting analyses, we mapped the TGF-beta responsive region to a sequence of 177 bp contained between -461 and -285. This region harbored a 14-bp element similar to a TGF-beta-responsive element present in the promoters of collagen alpha1(I), alpha2(I), elastin, and growth hormone. Electrophoretic mobility shift assays and mutational analyses demonstrated that the perlecan TGF-beta-responsive element bound specifically to TGF-beta-inducible nuclear proteins with high affinity for NF-1 member(s) of transcription factors.

Altered Proteoglycan Gene Expression in Human Biliary Cirrhosis

Proteoglycans play key roles in the physiological assembly of extracellular matrices and in the modulation of growth factor activities. During liver regeneration there is a profound remodelling of the connective tissue network with a concurrent alteration in proteoglycan gene expression. In the present study we have analyzed in detail the biochemical and molecular properties of the proteoglycans associated with biliary cirrhosis. The three major proteoglycans of human liver, namely decorin, syndecan and perlecan, were markedly elevated in the cirrhotic parenchyma as compared to normal liver tissue. Particularly elevated (eight fold) was the perlecan. This proteoglycan had not only heparan sulfate but also chondroitin and dermatan sulfate. Reverse transcriptase PCR revealed a marked enhancement of decorin and syndecan expression and detectable message for perlecan was found only in the cirrhotic liver. These results indicate that significant proteoglycan alterations are associated with the development of biliary cirrhosis and provide basis for future studies aimed at the characterization of the molecular events involved in the regulation of extracellular matrix deposition in this common human disease.

Expression and characterization of human perlecan domains I and II synthesized by baculovirus-infected insect cells

We present the in vitro expression and purification of N-terminal fragments of human perlecan in insect cells. Three tailored fragments of human perlecan cDNA were introduced into the polyhedrin locus of baculovirus expression vectors (BEVs) encoding amino acids 1-196 (domain I), 1-404 (domain I + IIa) and 1-506 (domain I + IIab). The integrity of the BEVs was checked by DNA sequencing, polymerase chain reaction, restriction enzyme analysis and Southern blotting. Northern hybridization and metabolic labeling with [35S]methionine showed that expression of the perlecan-(1-404)- and the -(1-506)- peptide was successful, but in the case of the perlecan-(1-196)-peptide no recombinant protein was produced. Immunoblotting showed that both the (1-404)-peptide and (1-506)-peptide are recognized by 95J10, a monoclonal antibody that was previously raised against perlecan-(24-404)-peptide expressed in Escherichia coli. Gel permeation and anion-exchange chromatography were applied to purify the recombinant proteins. Glycosaminoglycans were demonstrated to be present. Deglycosylation with chondroitinase ABC showed that the perlecan-(1-404)-peptide was glycosylated with chondroitin sulfate residues. Consistent with these results, glycosaminoglycans isolated from the perlecan-(1-404)-peptide were identified as chondroitin sulfate by agarose gel electrophoresis. Furthermore the perlecan-(1-404)-peptide showed affinity to immobilized basic fibroblast growth factor. The availability of baculovirus-derived recombinant perlecan fragments will facilitate domain-specific investigation of the structural and functional properties of perlecan in the future.

Distinct rat aortic smooth muscle cells differ in versican/PG-M expression

Smooth muscle cells (SMCs) with distinct phenotypes are present in blood vessels, and distinct culture types appear when SMCs are maintained in vitro. For example, cultured SMCs from rat adult media grow as bipolar cells, which differ in gene expression from the predominantly cobblestone-shaped SMCs from rat pup aortas and rat neointimas that we call pi SMCs. Since proteoglycans are present at different concentrations in the normal intima and media and are elevated in atherosclerotic plaque, we sought to determine whether pi and adult medial SMC types synthesize different or unique proteoglycans that are characteristic of each phenotype. [35S]sulfate-labeled proteoglycans were purified by ion-exchange chromatography. An adult medial SMC line synthesized a large proteoglycan (0.2 Kav on Sepharose CL-2B) that was not detectable in a pi SMC line. Digestion of this proteoglycan with chondroitin ABC lyase revealed three core glycoproteins of 330, 370, and 450 kD. By Western blot analysis, the two smallest of these reacted with two antibodies to the human fibroblast proteoglycan versican. RNAs hybridizing to versican probes were found only in adult medial-type SMCs, including an adult medial type clone from pup aorta, by Northern blot analysis. Both SMC types synthesize RNAs that hybridize to probes for other proteoglycans, such as perlecan, biglycan, and decorin. We conclude that rat pi SMC cultures, unlike monkey, human, and rat adult medial SMC cultures, express little or no versican. This difference in expression may be responsible for the different morphologies and growth properties of the two cell types.

The biology of perlecan: the multifaceted heparan sulphate proteoglycan of basement membranes and pericellular matrices

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Perlecan: a gem of a proteoglycan

Perlecan, the main proteoglycan of basement membranes and pericellular spaces, is one of the largest single-chain polypeptides of vertebrate animals. The five modules of perlecan are collated from protein building blocks evolutionarily related to molecules involved in nutrient metabolism, mitogenesis and adhesion. These structural motifs, when translated into multimeric functional units, could be effectively utilized by diverse tissues during development, remodelling or neoplastic growth. The protein is highly conserved across species and the available data indicate that this modular proteoglycan has evolved from ancient ancestors by gene duplication and exon shuffling. The discovery of a related molecule in the nematode C. elegans, and the development of skeletal muscle abnormalities in this animal when the perlecan-like molecule is truncated, opens new avenues of research.

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon. Furthermore, a transforming growth factor beta (TGF-beta)-negative element is present in the promotor region of decorin gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Structural characterization of the complete human perlecan gene and its promoter

The complete intron-exon organization of the gene encoding human perlecan (HSPG2), the major heparan sulfate proteoglycan of basement membranes, has been elucidated, and specific exons have been assigned to coding sequences for the modular domains of the protein core. The gene was composed of 94 exons, spanning > 120 kbp of genomic DNA. The exon arrangement was analyzed vis-à-vis the modular structure of the perlecan, which harbors protein domains homologous to the low density lipoprotein receptor, laminin, epidermal growth factor, and neural cell adhesion molecule. The exon size and the intron phases were highly conserved when compared to the corresponding domains of the homologous genes, suggesting that most of this modular proteoglycan has evolved from a common ancestor by gene duplication or exon shuffling. The 5' flanking region revealed a structural organization characteristic of housekeeping and growth control-related genes. It lacked canonical TATA or CAAT boxes, but it contained several GC boxes with binding sites for the transcription factors SP1 and ETF. Consistent with the lack of a TATA element, the perlecan gene contained multiple transcription initiation sites distributed over 80 bp of genomic DNA. These results offer insights into the evolution of this chimeric molecule and provide the molecular basis for understanding the transcriptional control of this important gene.

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteoglycans of basement membranes

Proteoglycans carrying either heparan sulfate and/or chondroitin sulfate side chains are typical constituents of basement membranes. The most prominent proteoglycan (perlecan) consists of a 400-500 kDa core protein and three heparan sulfate chains. Electron microscopy and cDNA sequencing show a complex and elongated domain structure for the core protein which in part is homologous to that of the laminin A chain. This structure may be varied by alternative splicing and proteolysis. Integration into basement membranes probably occurs by heparan sulfate binding to laminin and collagen IV, core protein binding to nidogen and by limited self assembly. The proteoglycan is in addition a cell-adhesive protein which is recognized by beta 1 integrins. Several more proteoglycans with smaller core proteins (10-160 kDa) apparently exist in basement membranes but are less well characterized. Biological functions include control of filtration through basement membranes and binding of growth factors and protease inhibitors.

Perlecan, the large low-density proteoglycan of basement membranes: structure and variant forms

The complete primary structure of perlecan, the large low-density proteoglycan of basement membranes, has been deduced by cDNA cloning for the mouse and more recently the human gene products. Mouse perlecan contains a 396 kDa core protein with five distinct domains: a heparan sulfate attachment domain, a LDL receptor-like domain, two different laminin-like domains and an N-CAM-like domain. These domains are conserved to a striking degree between mouse and human, including alternate splicing of the N-CAM domain to generate variations of perlecan. These variant sequences also appear to be highly conserved between mouse and human. The strong conservation of these domains, including highly repetitive elements and potential alternative splices, suggest they have vital functions.

Mapping of the versican proteoglycan gene (CSPG2) to the long arm of human chromosome 5 (5q12-5q14)

Versican is a major chondroitin sulfate proteoglycan of vascularized connective tissues whose eponym reflects its functional versatility in macromolecular affinity and interactions. In this report we have localized the versican gene (CSPG2) to the long arm of human chromosome 5 by utilizing a combination of somatic cell hybrids, Southern blotting, polymerase chain reaction, and chromosomal in situ hybridization. The proteoglycan gene segregated concordantly with hybrid cell lines containing the long arm of chromosome 5, comprising the 5q12-q14 band regions. To refine this locus further, we screened a chromosome 5-specific library and isolated several genomic clones encoding a portion of the 5' end of versican. One of these genomic clones was used as a probe for in situ hybridization of human chromosome metaphases. The results corroborated the data obtained using somatic cell hybrids and further refined the assignment of the versican gene to the narrow band region of 5q12-5q14, with the primary site likely to be 5q13.2. The availability of novel genomic clones and the mapping data presented here will make possible the identification of any defect genetically linked to this proteoglycan gene.

Establishment of a cell line from the EHS tumor: biosynthesis of basement membrane constituents and characterization of a hybrid proteoglycan containing heparan and chondroitin sulfate chains

We have established a continuous cell line from the Engelbreth-Holm-Swarm (EHS) tumor, a transplantable murine neoplasm that has been extensively utilized to investigate basement membrane constituents. The EHS-derived cells, designated BAM cells, have been subcultured for over 40 passages and have maintained phenotypic and biological properties of the parent EHS tumor cells. BAM cells have retained an epithelioid morphology and the ability to induce EHS-like tumors in mice. Biochemical and immunochemical studies demonstrated that BAM cells synthesize laminin A and B chains, collagen type IV, entactin and the basement membrane specific heparan sulfate proteoglycan. Interestingly, the proteoglycan synthesized by BAM cells was a hybrid molecule containing 2-3 heparan sulfate chains of 25-35 kDa and 1 chondroitin sulfate chain of approximately 17 kDa attached to a 400-kDa protein core. This cell line will be useful to investigations concerning biosynthesis of basement membrane constituents and will be a valuable source of extracellular matrix for testing cellular properties such as attachment, locomotion and differentiation.

Human basement membrane heparan sulfate proteoglycan core protein: a 467-kD protein containing multiple domains resembling elements of the low density lipoprotein receptor, laminin, neural cell adhesion molecules, and epidermal growth factor

The primary structure of the large human basement membrane heparan sulfate proteoglycan (HSPG) core protein was determined from cDNA clones. The cDNA sequence codes for a 467-kD protein with a 21-residue signal peptide. Analysis of the amino acid sequence showed that the protein consists of five domains. The amino-terminal domain I contains three putative heparan sulfate attachment sites; domain II has four LDL receptor-like repeats; domain III contains repeats similar to those in the short arms of laminin; domain IV has lg-like repeats resembling those in neural cell adhesion molecules; and domain V contains sequences resembling repeats in the G domain of the laminin A chain and repeats in the EGF. The domain structure of the human basement membrane HSPG core protein suggests that this mosaic protein has evolved through shuffling of at least four different functional elements previously identified in other proteins and through duplication of these elements to form the functional domains. Comparison of the human amino acid sequence with a partial amino acid sequence from the corresponding mouse protein (Noonan, D. M., E. A. Horigan, S. R. Ledbetter, G. Vogeli, M. Sasaki, Y. Yamada, and J. R. Hassell. 1988. J. Biol. Chem. 263:16379-16387) shows a major difference between the species in domain IV, which contains the Ig repeats: seven additional repeats are found in the human protein inserted in the middle of the second repeat in the mouse sequence. This suggests either alternative splicing or a very recent duplication event in evolution. The multidomain structure of the basement membrane HSPG implies a versatile role for this protein. The heparan sulfate chains presumably participate in the selective permeability of basement membranes and, additionally, the core protein may be involved in a number of biological functions such as cell binding, LDL-metabolism, basement membrane assembly, calcium binding, and growth- and neurite-promoting activities.

Human clathrin heavy chain (CLTC): partial molecular cloning, expression, and mapping of the gene to human chromosome 17q11-qter

The nucleotide sequence of a 916-bp human cDNA clone isolated from a human colon lambda gt11 cDNA library was determined. Sequence analysis showed this cDNA to have 88% homology to the nucleotide sequence of the heavy chain of rat clathrin. The deduced amino acid sequence was 98.7% identical to the rat sequence, a change of only four amino acids. The mRNA identified in both human and rat cells with the human clathrin clone revealed transcripts of approximately 6.5 kb, which is consistent with the predicted 180 kDa molecular weight of the clathrin heavy chain. Southern analysis of human/rodent somatic cell hybrids localized the human clathrin heavy chain gene (CLTC) to chromosome 17. Additional analyses using panels of human/rodent somatic cell hybrids with specific chromosomal translocations and deletions mapped the human clathrin heavy chain gene locus to 17q11-qter.