Identification of a new membrane-bound heparan sulphate proteoglycan

Combined genetic-pharmacologic inactivation of tightly linked ADAMTS proteases in temporally specific windows uncovers distinct roles for versican proteolysis and glypican-6 in cardiac development

Extracellular matrix remodeling mechanisms are understudied in cardiac development and congenital heart defects. We show that matrix-degrading metalloproteases ADAMTS1 and ADAMTS5, are extensively co-expressed during mouse cardiac development. The mouse mutants of each gene have mild cardiac anomalies, however, their combined genetic inactivation to elicit cooperative roles is precluded by tight gene linkage. Therefore, we coupled Adamts1 inactivation with pharmacologic ADAMTS5 blockade to uncover stage-specific cooperative roles and investigated their potential substrates in mouse cardiac development. ADAMTS5 blockade was achieved in Adamts1 null mouse embryos using an activity-blocking monoclonal antibody during distinct developmental windows spanning myocardial compaction or cardiac septation and outflow tract rotation. Synchrotron imaging, RNA in situ hybridization, immunofluorescence microscopy and electron microscopy were used to determine the impact on cardiac development and compared to Gpc6 and ADAMTS-cleavage resistant versican mutants. Mass spectrometry-based N-terminomics was used to seek relevant substrates. Combined inactivation of ADAMTS1 and ADAMTS5 prior to 12.5 days of gestation led to dramatic accumulation of versican-rich cardiac jelly and inhibited formation of compact and trabecular myocardium, which was also observed in mice with ADAMTS cleavage-resistant versican. Combined inactivation after 12.5 days impaired outflow tract development and ventricular septal closure, generating a tetralogy of Fallot-like defect. N-terminomics of combined ADAMTS knockout and control hearts identified a cleaved glypican-6 peptide only in the controls. ADAMTS1 and ADAMTS5 expression in cells was associated with specific glypican-6 cleavages. Paradoxically, combined ADAMTS1 and ADAMTS5 inactivation reduced cardiac glypican-6 and outflow tract Gpc6 transcription. Notably, Gpc6-/- hearts demonstrated similar rotational defects as combined ADAMTS inactivated hearts and both had reduced hedgehog signaling. Thus, versican proteolysis in cardiac jelly at the canonical Glu441-Ala442 site is cooperatively mediated by ADAMTS1 and ADAMTS5 and required for proper ventricular cardiomyogenesis, whereas, reduced glypican-6 after combined ADAMTS inactivation impairs hedgehog signaling, leading to outflow tract malrotation.

Association of Sonic Hedgehog with the extracellular matrix requires its zinc-coordination center

Background

Sonic Hedgehog (Shh) has a catalytic cleft characteristic for zinc metallopeptidases and has significant sequence similarities with some bacterial peptidoglycan metallopeptidases defining a subgroup within the M15A family that, besides having the characteristic zinc coordination motif, can bind two calcium ions. Extracellular matrix (ECM) components in animals include heparan-sulfate proteoglycans, which are analogs of bacterial peptidoglycan and are involved in the extracellular distribution of Shh.

Results

We found that the zinc-coordination center of Shh is required for its association to the ECM as well as for non-cell autonomous signaling. Association with the ECM requires the presence of at least 0.1 μM zinc and is prevented by mutations affecting critical conserved catalytical residues. Consistent with the presence of a conserved calcium binding domain, we find that extracellular calcium inhibits ECM association of Shh.

Conclusions

Our results indicate that the putative intrinsic peptidase activity of Shh is required for non-cell autonomous signaling, possibly by enzymatically altering ECM characteristics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00359-5.

Recombinant immunotoxin targeting GPC3 is cytotoxic to H446 small cell lung cancer cells

Glypican-3 (GPC3) is a cell membrane glycoprotein that regulates cell growth and proliferation. Aberrant expression or distribution of GPC3 underlies developmental abnormalities and the development of solid tumours. The strongest evidence for the participation of GPC3 in carcinogenesis stems from studies on hepatocellular carcinoma and lung squamous cell carcinoma. To the best of our knowledge, the role of the GPC3 protein and its potential therapeutic application have never been studied in small cell lung carcinoma (SCLC), despite the known involvement of associated pathways and the high mortality caused by this disease. Therefore, the aim of the present study was to examine GPC3 targeting for SCLC immunotherapy. An immunotoxin carrying an anti-GPC3 antibody (hGC33) and Pseudomonas aeruginosa exotoxin A 38 (PE38) was generated. This hGC33-PE38 protein was overexpressed in E. coli and purified. ADP-ribosylation activity was tested in vitro against eukaryotic translation elongation factor 2. Cell internalisation ability was confirmed by confocal microscopy. Cytotoxicity was analysed by treating liver cancer (HepG2, SNU-398 and SNU-449) and lung cancer (NCI-H510A, NCI-H446, A549 and SK-MES1) cell lines with hGC33-PE38 and estimating viable cells number. A BrdU assay was employed to verify anti-proliferative activity of hGC33-PE38 on treated cells. Fluorescence-activated cell sorting was used for the detection of cell membrane-bound GPC3. The hGC33-PE38 immunotoxin displayed enzymatic activity comparable to native PE38. The protein was efficiently internalised by GPC3-positive cells. Moreover, hGC33-PE38 was cytotoxic to HepG2 cells but had no effect on known GPC3-negative cell lines. The H446 cells were sensitive to hGC33-PE38 (IC₅₀, 70.6±4.6 ng/ml), whereas H510A cells were resistant. Cell surface-bound GPC3 was abundant on the membranes of H446 cells, but absent on H510A. Altogether, the present findings suggested that GPC3 could be considered as a potential therapeutic target for SCLC immunotherapy.

Heparan Sulfate Proteoglycans Biosynthesis and Post Synthesis Mechanisms Combine Few Enzymes and Few Core Proteins to Generate Extensive Structural and Functional Diversity

Glycosylation is a common and widespread post-translational modification that affects a large majority of proteins. Of these, a small minority, about 20, are specifically modified by the addition of heparan sulfate, a linear polysaccharide from the glycosaminoglycan family. The resulting molecules, heparan sulfate proteoglycans, nevertheless play a fundamental role in most biological functions by interacting with a myriad of proteins. This large functional repertoire stems from the ubiquitous presence of these molecules within the tissue and a tremendous structural variety of the heparan sulfate chains, generated through both biosynthesis and post synthesis mechanisms. The present review focusses on how proteoglycans are “gagosylated” and acquire structural complexity through the concerted action of Golgi-localized biosynthesis enzymes and extracellular modifying enzymes. It examines, in particular, the possibility that these enzymes form complexes of different modes of organization, leading to the synthesis of various oligosaccharide sequences.

Persistent Polyfunctional Chimeric Antigen Receptor T Cells That Target Glypican 3 Eliminate Orthotopic Hepatocellular Carcinomas in Mice

BACKGROUND AND AIMS

Glypican 3 (GPC3) is an oncofetal antigen involved in Wnt-dependent cell proliferation that is highly expressed in hepatocellular carcinoma (HCC). We investigated whether the functions of chimeric antigen receptors (CARs) that target GPC3 are affected by their antibody-binding properties.

METHODS

We collected peripheral blood mononuclear cells from healthy donors and patients with HCC and used them to create CAR T cells, based on the humanized YP7 (hYP7) and HN3 antibodies, which have high affinities for the C-lobe and N-lobe of GPC3, respectively. NOD/SCID/IL-2Rgcnull (NSG) mice were given intraperitoneal injections of luciferase-expressing (Luc) Hep3B or HepG2 cells and after xenograft tumors formed, mice were given injections of saline or untransduced T cells (mock control), or CAR (HN3) T cells or CAR (hYP7) T cells. In other NOD/SCID/IL-2Rgcnull (NSG) mice, HepG2-Luc or Hep3B-Luc cells were injected into liver, and after orthotopic tumors formed, mice were given 1 injection of CAR (hYP7) T cells or CD19 CAR T cells (control). We developed droplet digital polymerase chain reaction and genome sequencing methods to analyze persistent CAR T cells in mice.

RESULTS

Injections of CAR (hYP7) T cells eliminated tumors in 66% of mice by week 3, whereas CAR (HN3) T cells did not reduce tumor burden. Mice given CAR (hYP7) T cells remained tumor free after re-challenge with additional Hep3B cells. The CAR T cells induced perforin- and granzyme-mediated apoptosis and reduced levels of active β-catenin in HCC cells. Mice injected with CAR (hYP7) T cells had persistent expansion of T cells and subsets of polyfunctional CAR T cells via antigen-induced selection. These T cells were observed in the tumor microenvironment and spleen for up to 7 weeks after CAR T-cell administration. Integration sites in pre-infusion CAR (HN3) and CAR (hYP7) T cells were randomly distributed, whereas integration into NUPL1 was detected in 3.9% of CAR (hYP7) T cells 5 weeks after injection into tumor-bearing mice and 18.1% of CAR (hYP7) T cells at week 7. There was no common site of integration in CAR (HN3) or CD19 CAR T cells from tumor-bearing mice.

CONCLUSIONS

In mice with xenograft or orthoptic liver tumors, CAR (hYP7) T cells eliminate GPC3-positive HCC cells, possibly by inducing perforin- and granzyme-mediated apoptosis or reducing Wnt signaling in tumor cells. GPC3-targeted CAR T cells might be developed for treatment of patients with HCC.

An investigation of genetic polymorphisms in heparan sulfate proteoglycan core proteins and key modification enzymes in an Australian Caucasian multiple sclerosis population

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease affecting the central nervous system in young adults. Heparan sulfate proteoglycans (HSPGs) are ubiquitous to the cell surface and the extracellular matrix. HSPG biosynthesis is a complex process involving enzymatic attachment of heparan sulfate (HS) chains to a core protein. HS side chains mediate specific ligand and growth factor interactions directing cellular processes including cell adhesion, migration and differentiation. Two main families of HSPGs exist, the syndecans (SDC1-4) and glypicans (GPC1-6). The SDCs are transmembrane proteins, while the GPC family are GPI linked to the cell surface. SDC1 has well-documented interactions with numerous signalling pathways. Genome-wide association studies (GWAS) have identified regions of the genome associated with MS including a region on chromosome 13 containing GPC5 and GPC6. International studies have revealed significant associations between this region and disease development. The exostosin-1 (EXT1) and sulfatase-1 (SULF1) are key enzymes contributing to the generation of HS chains. EXT1, with documented tumour suppressor properties, is involved in the initiation and polymerisation of the growing HS chain. SULF1 removes 6-O-sulfate groups from HS chains, affecting protein-ligand interactions and subsequent downstream signalling with HS modification potentially having significant effects on MS progression. In this study, we identified significant associations between single nucleotide polymorphisms in SDC1, GPC5 and GPC6 and MS in an Australian Caucasian case-control population. Further significant associations in these genes were identified when the population was stratified by sex and disease subtype. No association was found for EXT1 or SULF1.

Signaling network involved in the GPC3-induced inhibition of breast cancer progression: role of canonical Wnt pathway

PURPOSE

We have shown that GPC3 overexpression in breast cancer cells inhibits in vivo tumor progression, by acting as a metastatic suppressor. GPC3-overexpressing cells are less clonogenic, viable and motile, while their homotypic adhesion is increased. We have presented evidences indicating that GPC3 inhibits canonical Wnt and Akt pathways, while non-canonical Wnt and p38MAPK cascades are activated. In this study, we aimed to investigate whether GPC3-induced Wnt signaling inhibition modulates breast cancer cell properties as well as to describe the interactions among pathways modulated by GPC3.

METHODS

Fluorescence microscopy, qRT-PCR microarray, gene reporter assay and Western blotting were performed to determine gene expression levels, signaling pathway activities and molecule localization. Lithium was employed to activate canonical Wnt pathway and treated LM3-GPC3 cell viability, migration, cytoskeleton organization and homotypic adhesion were assessed using MTS, wound healing, phalloidin staining and suspension growth assays, respectively.

RESULTS

We provide new data demonstrating that GPC3 blocks-also at a transcriptional level-both autocrine and paracrine canonical Wnt activities, and that this inhibition is required for GPC3 to modulate migration and homotypic adhesion. Our results indicate that GPC3 is secreted into the extracellular media, suggesting that secreted GPC3 competes with Wnt factors or interacts with them and thus prevents Wnt binding to Fz receptors. We also describe the complex network of interactions among GPC3-modulated signaling pathways.

CONCLUSION

GPC3 is operating through an intricate molecular signaling network. From the balance of these interactions, the inhibition of breast metastatic spread induced by GPC3 emerges.

Combining expression of GPC3 in tumors and CD16 on NK cells from peripheral blood to identify patients responding to codrituzumab

Background

Codrituzumab, a monoclonal antibody targeting an oncofetal protein glypican-3 (GPC3) expressed on cell surface of hepatocellular carcinoma (HCC) induces antibody-dependent cellular cytotoxicity (ADCC) and inhibits tumor growth in preclinical studies. Based on this mechanism, tumor GPC3 expression and CD16 expression on NK cells, which are the effector cells of ADCC, were investigated to correlate with codrituzumab's clinical efficacy in patients with advanced HCC.

Results

Joint analyses of the two biomarkers revealed that both high levels of GPC3 and CD16 were required for patients to benefit from codrituzumab; lack of either one of them would lead to a loss of the therapeutic effect.

Conclusions

These results suggest the combination of tumor GPC3 expression and CD16 expression on NK cells from peripheral blood at baseline as a composite biomarker to select HCC patients for codrituzumab.

Impact

The conclusion warrants a future study in an HCC population with both high GPC3 expression and high levels of CD16 at baseline to establish codrituzumab's therapeutic benefit in HCC.

Methods

Data from a phase II clinical trial of codrituzumab were used for the analyses. GPC3 expression in baseline tumor biopsies was determined by immunohistochemistry (IHC) analysis, and baseline CD16 expression on NK cells were quantified by peripheral blood lymphocyte immunophenotyping. According to high or low expression of GPC3 and CD16, different patient subgroups were formed; for each subgroup, overall survival of patients having high codrituzumab exposure was compared to that of patients receiving placebo.

Mass spectrometry-based proteomics revealed Glypican-1 as a novel ADAM17 substrate

ADAM17 (a disintegrin and metalloproteinase 17) is a plasma membrane metalloprotease involved in proteolytic release of the extracellular domain of many cell surface molecules, a process known as ectodomain shedding. Through this process, ADAM17 is implicated in several aspects of tumor growth and metastasis in a broad range of tumors, including head and neck squamous cell carcinomas (HNSCC). In this study, mass spectrometry-based proteomics approaches revealed glypican-1 (GPC1) as a new substrate for ADAM17, and its shedding was confirmed to be metalloprotease-dependent, induced by a pleiotropic agent (PMA) and physiologic ligand (EGF), and inhibited by marimastat. In addition, immunoblotting analysis of GPC1 in the extracellular media from control and ADAM17shRNA pointed to a direct involvement of ADAM17 in the cleavage of GPC1. Moreover, mass spectrometry-based interactome analysis of GPC1 revealed biological functions and pathways related mainly to cellular movement, adhesion and proliferation, which were events also modulated by up regulation of full length and cleavage GPC1. Altogether, we showed that GPC1 is a novel ADAM17 substrate, thus the function of GPC1 may be modulated by proteolysis signaling.

BIOLOGICAL SIGNIFICANCE

Inhibition of metalloproteases as a therapeutic approach has failed because there is limited knowledge of the degradome of individual proteases as well as the cellular function of cleaved substrates. Using different proteomic techniques, this study uncovered novel substrates that can be modulated by ADAM17 in oral squamous cell carcinoma cell line. Glypican-1 was validated as a novel substrate for ADAM17, with important function in adhesion, proliferation and migration of carcinoma cells. Therefore, this study opens new avenues regarding the proteolysis-mediated function of GPC1 by ADAM17.

Immunotoxin targeting glypican-3 regresses liver cancer via dual inhibition of Wnt signalling and protein synthesis

Glypican-3 is a cell surface glycoprotein that associates with Wnt in liver cancer. We develop two antibodies targeting glypican-3, HN3 and YP7. The first antibody recognizes a functional epitope and inhibits Wnt signalling, whereas the second antibody recognizes a C-terminal epitope but does not inhibit Wnt signalling. Both are fused to a fragment of Pseudomonas exotoxin A (PE38) to create immunotoxins. Interestingly, the immunotoxin based on HN3 (HN3-PE38) has superior antitumor activity as compared with YP7 (YP7-PE38) both in vitro and in vivo. Intravenous administration of HN3-PE38 alone, or in combination with chemotherapy, induces regression of Hep3B and HepG2 liver tumour xenografts in mice. This study establishes glypican-3 as a promising candidate for immunotoxin-based liver cancer therapy. Our results demonstrate immunotoxin-induced tumour regression via dual mechanisms: inactivation of cancer signalling via the antibody and inhibition of protein synthesis via the toxin.

Evaluation of antiglypican-3 therapy as a promising target for amelioration of hepatic tissue damage in hepatocellular carcinoma

In Egypt, hepatocellular carcinoma (HCC) was predicted to continue to rise over the next few decades causing a national problem. Meanwhile, glypican-3 (GPC3), a highly expressed glypican, has emerged as a potential target for HCC immunotherapy. Therefore, we aimed to identify the impact of blocking GPC3 on liver damage in HCC as well as a possible mechanism. Fifty four HCC patients, 20 cirrhotic patients and 10 healthy subjects were recruited. Serum levels of GPC3, sulfatase-2 (SULF-2), heparan sulfate proteoglycan (HSPG), insulin-like growth factor-II (IGF-II) were measured by ELISA. In parallel, HCC was induced in 40 male Sprague-Dawley rats in presence/absence of antiGPC-3. Liver impairment was detected by investigating liver sections stained with hematoxylin/eosin and serum α-fetoprotein (AFP). Liver homogenates of GPC3, SULF-2, and HSPG were measured by ELISA. Gene expression of caspase-3 and IGF-II were assayed by RT-PCR. HCC patients showed significant elevated serum levels of GPC3, IGF-II and SULF-2 accompanied by decreased HSPG. However, treatment of HCC rats with antiGPC-3 significantly reduced serum AFP and showed nearly normal hepatocytes. In addition, antiGPC-3 significantly reduced elevated liver homogenates protein levels of GPC3 and SULF-2 and gene expression of IGF-II and caspase-3. antiGPC-3 restored the reduced hepatic HSPG. antiGPC-3 showed anti-tumor activity as well as hepatoprotective effects. antiGPC-3-chemoprotective effect can be explained by forced reduction of IGF-II expression, restoration of HSPGs, deactivation of SULF-2 and reduction of gene expression of caspase-3. Targeting GPC3 is a promising therapeutic approach for HCC.

Critical analysis of the potential of targeting GPC3 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide. The treatment options for patients with advanced HCC are limited, and novel treatment strategies are required urgently. Glypican-3 (GPC3), a member of the glypican family of heparan sulfate proteoglycans, is overexpressed in 72%−81% of HCC cases, and is correlated with a poor prognosis. GPC3 regulates both stimulatory and inhibitory signals, and plays a key role in regulating cancer cell growth. GPC3 is released into the serum, and so might be a useful diagnostic marker for HCC. GPC3 is also used as an immunotherapeutic target in HCC. A Phase I study of a humanized anti-GPC3 monoclonal antibody, GC33, revealed a good safety profile and potential antitumor activity, and a Phase II trial is currently ongoing. In addition, the authors’ investigator-initiated Phase I study of a GPC3-derived peptide vaccine showed good safety and tolerability, and demonstrated that the GPC3 peptide-specific cytotoxic T-lymphocyte frequency in peripheral blood correlated with overall survival in HCC patients. A sponsor-initiated Phase I clinical trial of a three-peptide cocktail vaccine, which includes a GPC3-derived peptide, is also underway. GPC3 is currently recognized as a promising therapeutic target and diagnostic marker for HCC. This review introduces the recent progress in GPC3 research, from biology to clinical impact.

Golgi protein 73, not Glypican-3, may be a tumor marker complementary to α-Fetoprotein for hepatocellular carcinoma diagnosis

BACKGROUND AND AIM

This study aimed to evaluate the effectiveness of serum Golgi protein 73 (GP73) and Glypican-3 (GPC-3) as tumor markers for diagnosis of hepatocellular carcinoma (HCC).

METHODS

A total of 257 subjects were enrolled and consisted of 61 healthy controls, 32 hepatitis B virus carriers, 80 cirrhosis patients, and 84 HCC patients. Diagnosis was performed based on established clinical procedure. Serum GP73, GPC-3, and α-fetoprotein were measured. Receiving operating characteristic (ROC) curves were plotted to determine the sensitivity and specificity of each serum marker and their combinations.

RESULT

Serum GP73 levels were significantly increased in HCC patients. No significant differences were observed between GP73 and α-fetoprotein (AFP) as markers for HCC diagnosis. However, GP73 was more sensitive than AFP in the diagnosis of small HCC. A combination of GP73 and AFP tests increased the sensitivity and specificity for HCC diagnosis. The area under the ROC curve (AUC) of combined test was 0.93 compared with 0.88 for GP73 and 0.90 for AFP alone. GPC-3 tests were negative in all 84 HCC patients. The AUC for GPC-3 is 0.43, indicating that serum GPC-3 was not an effective tumor marker for HCC diagnosis.

CONCLUSION

Serum GP73 is a potential tumor marker for HCC diagnosis, especially for differential diagnosis of small HCC and cirrhosis. The combination of GP73 and AFP is more sensitive than AFP alone. Serum GPC-3 does not appear to be an effective tumor marker for HCC diagnosis.

Analysis of cytotoxic T lymphocytes from a patient with hepatocellular carcinoma who showed a clinical response to vaccination with a glypican‑3‑derived peptide

Glypican-3 (GPC3), which is a carcinoembryonic antigen, is overexpressed in human hepatocellular carcinoma (HCC). Previously, we performed a phase I clinical trial of GPC3-derived peptide vaccination in patients with advanced HCC, and reported that GPC3 peptide vaccination is safe and has clinical efficacy. Moreover, we proposed that a peptide-specific CTL response is a predictive marker of overall survival in patients with HCC who receive peptide vaccination. In this study, we established GPC3-derived peptide-specific CTL clones from the PBMCs of an HLA-A ^* 02:07-positive patient with HCC who was vaccinated with an HLA-A2-restricted GPC3 peptide vaccine and showed a clinical response in the phase I clinical trial. Established CTL clones were analyzed using the IFN-γ ELISPOT assay and a cytotoxicity assay. GPC3 peptide-specific CTL clones were established successfully from the PBMCs of the patient. One CTL clone showed cytotoxicity against cancer cell lines that expressed endogenously the GPC3 peptide. The results suggest that CTLs have high avidity, and that natural antigen-specific killing activity against tumor cells can be induced in a patient with HCC who shows a clinical response to vaccination with the GPC3 _144–152 peptide.

Suppression of glypican 3 inhibits growth of hepatocellular carcinoma cells through up-regulation of TGF-β2

Glypican 3 (GPC3) is a valuable diagnostic marker and a potential therapeutic target in hepatocellular carcinoma (HCC). To evaluate the efficacy of targeting GPC3 at the translational level, we used RNA interference to examine the biologic and molecular effects of GPC3 suppression in HCC cells in vitro and in vivo. Transfection of Huh7 and HepG2 cells with GPC3-specific small interfering RNA (siRNA) inhibited cell proliferation (P < .001) together with cell cycle arrest at the G(1) phase, down-regulation of antiapoptotic protein (Bcl-2, Bcl-xL, and Mcl-1), and replicative senescence. Gene expression analysis revealed that GPC3 suppression significantly correlated with transforming growth factor beta receptor (TGFBR) pathway (P = 4.57e-5) and upregulated TGF-β2 at both RNA and protein levels. The effects of GPC3 suppression by siRNA can be recapitulated by addition of human recombinant TGF-β2 to HCC cells in culture, suggesting the possible involvement of TGF-β2 in growth inhibition of HCC cells. Cotransfection of siRNA-GPC3 with siRNA-TGF-β2 partially attenuated the effects of GPC3 suppression on cell proliferation, cell cycle progression, apoptosis, and replicative senescence, confirming the involvement of TGF-β2 in siRNA-GPC3-mediated growth suppression. In vivo, GPC3 suppression significantly inhibited the growth of orthotopic xenografts of Huh7 and HepG2 cells (P < .05), accompanied by increased TGF-β2 expression, reduced cell proliferation (observed by proliferating cell nuclear antigen staining), and enhanced apoptosis (by TUNEL staining). In conclusion, molecular targeting of GPC3 at the translational level offers an effective option for the clinical management of GPC3-positive HCC patients.

Glypican-5 stimulates rhabdomyosarcoma cell proliferation by activating Hedgehog signaling

Binding between the Hedgehog ligand and its receptor Patched 1 is stabilized by Glypican-5.

Glypican-5 (GPC5) is one of the six members of the glypican family. It has been previously reported that GPC5 stimulates the proliferation of rhabdomyosarcoma cells. In this study, we show that this stimulatory activity of GPC5 is a result of its ability to promote Hedgehog (Hh) signaling. We have previously shown that GPC3, another member of the glypican family, inhibits Hh signaling by competing with Patched 1 (Ptc1) for Hh binding. Furthermore, we showed that GPC3 binds to Hh through its core protein but not to Ptc1. In this paper, we demonstrate that GPC5 increases the binding of Sonic Hh to Ptc1. We also show that GPC5 binds to both Hh and Ptc1 through its glycosaminoglycan chains and that, unlike GPC3, GPC5 localizes to the primary cilia. Interestingly, we found that the heparan sulfate chains of GPC5 display a significantly higher degree of sulfation than those of GPC3. Based on these results, we propose that GPC5 stimulates Hh signaling by facilitating/stabilizing the interaction between Hh and Ptc1.

Optimization of tissue processing for immunohistochemistry for the detection of human glypican-3

Glypican-3 (GPC3) is frequently upregulated in hepatocellular carcinoma (HCC) and data on the expression profile in HCC might be useful for therapeutic decision-making and prognostic prediction. This study was performed using HepG2 xenograft tissues to optimize the tissue processing method for GPC3 immunohistochemistry. The optimization was conducted in terms of using GPC3 immunohistochemistry for biological study of GPC3 (Experiment 1) and as a diagnostic tool (Experiment 2). In Experiment 1, GPC3 immunoreactivity (IR) and tissue architecture were compared among differently fixed and embedded specimens. In Experiment 2, using conventional formalin-fixed paraffin-embedded (FFPE) procedures, the effects of different fixation times and antigen retrieval treatments were assessed. In Experiment 1, the periodate-lysine-paraformaldehyde (PLP)-fixed and AMeX method-embedded (PLP-AMeX) specimen showed superior immunoreactivity and excellent tissue architecture preservation. In contrast, the other specimens, especially frozen specimens, resulted in poor IR. In Experiment 2, specimens fixed for 24h showed better IR than those fixed for 7 days and the most remarkable improvement in IR was achieved after protease treatment. These findings indicate that with GPC3 immunohistochemistry for biological studies, the PLP-AMeX specimen is preferable. For diagnostics using FFPE specimens, the fixation time should not be too long and protease should be used for the antigen retrieval treatment.

Glypican-3 reexpression regulates apoptosis in murine adenocarcinoma mammary cells modulating PI3K/Akt and p38MAPK signaling pathways

Glypican-3 (GPC3) is a proteoglycan involved in proliferation and cell survival. Several reports demonstrated that GPC3 is downregulated in some tumors, such as breast cancer. Previously, we determined that GPC3 reexpression in the murine mammary adenocarcinoma LM3 cells induced an impairment of their invasive and metastatic capacities, associated with a decrease of their motility and an increase of their cell death. We demonstrated that GPC3 inhibits canonical Wnt signaling, as well as it activates non canonical pathway. Now, we identified signaling pathways responsible for the pro-apoptotic role of GPC3 in LM3 cells. We found for the first time that GPC3 inhibits the PI3K/Akt anti-apoptotic pathway while it stimulates the p38MAPK stress-activated one. We report a concomitant modulation of CDK inhibitors as well as of pro- and anti-apoptotic molecules. Our results provide new clues regarding the mechanism involved in the modulation induced by GPC3 of mammary tumor cell growth and survival.

The expression profile of glypican-3 and its relation to macrophage population in human hepatocellular carcinoma

BACKGROUND

Glypican-3 (GPC3) is frequently upregulated in hepatocellular carcinoma (HCC). Analysis of GPC3-deficient mice implies GPC3 involvement in macrophage-lineage cells.

AIM

In this study, we first assessed the association of GPC3 expression with the macrophage population in liver tissues from 30 HCC patients using immunohistochemistry.

METHODS

The GPC3 expression was categorized into three patterns - one with GPC3-negative staining and two with GPC3-positive staining (one with unclear membrane staining and one with clear membrane staining, designated GPC3+/C). The number of macrophages that were stained with resident macrophage (rMvarphi) or pan-macrophage (pMvarphi) markers was counted for each GPC3 expression pattern.

RESULTS

GPC3 immunoreactivity was observed in 76.7% of the HCC specimens. No significant differences were observed in the number of rMvarphi marker-positive cells among the three expression patterns. In contrast, the GPC3+/C pattern showed a significantly higher number of pMvarphi-positive cells compared with the other two patterns, most of which tended to take on the morphology of migrating macrophages. A second experiment conducted to compare macrophage infiltration between the xenograft tissues of a GPC3-transfected HCC cell line and its parent GPC3-nonexpressing cell line revealed that the increase in macrophages was stimulated by membrane expression of GPC3.

CONCLUSION

The observations suggest that the increased macrophages in the GPC3+/C pattern are likely to be recruited macrophages, not resident macrophages, and that the expression of GPC3 in the membrane is involved in macrophage recruitment.

Glypican 3-expressing gastric carcinoma: distinct subgroup unifying hepatoid, clear-cell, and alpha-fetoprotein-producing gastric carcinomas

Gypican-3 (GPC3) has been recognized as an oncofetal protein in hepatic neoplasms and yolk sac tumors. To characterize a distinct subgroup of gastric carcinoma (GC) expressing GPC3 (GPC3-GC), primary and metastatic GC tissues were evaluated by immunohistochemistry with special focus on their related entities: hepatoid, clear-cell, and alpha-fetoprotein-producing GC. GPC3-GC was defined as focal GPC3-GC when 10-49% of neoplastic cells were positive, and as diffuse GPC3-GC when more than 50% of cells were positive. Among 926 GC cases, 101 (11%) were GPC3-GC, of which 45 were diffuse and 56 were focal GPC3-GC. Specific histological patterns, such as the hepatoid and clear-cell patterns, were frequently observed in diffuse GPC3-GC (38 and 49%, respectively) and in focal GPC3-GC (4 and 25%, respectively), whereas these patterns were extremely rare in GPC3-negative GC. Immunoreactive alpha-fetoprotein was only identified in GPC3-GC (38% of diffuse and 14% of focal GPC3-GC). Both diffuse and focal GPC3-GC showed nodal metastasis more frequently (67 and 55%, respectively) than GPC3-negative GC (34%), and the diffuse GPC3-GC had significantly more T2-4 and M1 stage cases. GPC3 immunostaining was present in 57 out of 61 nodal metastases (93%) and in all four liver metastases examined. Importantly, diffuse GPC3 expression was observed in the liver metastasis, even if the primary tumor was focal GPC3-GC. GPC3-GC is a distinctive group of GC, which unifies hepatoid, clear-cell, and alpha-fetoprotein-producing GC. GPC3 is expected to be a target of forthcoming immunotherapy for a patient bearing this specific type of GC.

Glypican-3 regulates migration, adhesion and actin cytoskeleton organization in mammary tumor cells through Wnt signaling modulation

Glypican-3 (GPC3) is a proteoglycan involved in migration, proliferation and cell survival modulation in several tissues. There are many reports demonstrating a downregulation of GPC3 expression in some human tumors, including mesothelioma, ovarian and breast cancer. Previously, we determined that GPC3 reexpression in the murine mammary adenocarcinoma LM3 cells induced an impairment of their in vivo invasive and metastatic capacities together with a higher susceptibility to in vitro apoptosis. Currently, the signaling mechanism of GPC3 is not clear. First, it was speculated that GPC3 regulates the insulin-like growth factor (IGF) signaling system. This hypothesis, however, has been strongly challenged. Recently, several reports indicated that at least in some cell types GPC3 serves as a selective regulator of Wnt signaling. Here we provide new data demonstrating that GPC3 regulates Wnt pathway in the metastatic adenocarcinoma mammary LM3 cell line. We found that GPC3 is able to inhibit canonical Wnt signals involved in cell proliferation and survival, as well as it is able to activate non canonical pathway, which directs cell morphology and migration. This is the first report indicating that breast tumor cell malignant properties can be reverted, at least in part, by GPC3 modulation of Wnt signaling. Our results are consistent with the potential role of GPC3 as a metastasis suppressor.

Anti-glypican 3 antibody as a potential antitumor agent for human liver cancer

Human glypican 3 (GPC3) is preferentially expressed in the tumor tissues of liver cancer patients. In this study, we obtained a monoclonal antibody (mAb) against the COOH-terminal part of GPC3, which induced antibody-dependent cellular cytotoxicity (ADCC). The mAb, designated GC33, exhibited marked tumor growth inhibition of s.c. transplanted Hep G2 and HuH-7 xenografts that expressed GPC3 but did not inhibit growth of the SK-HEP-1 that was negative for GPC3. GC33 was efficacious even in an orthotopic model; it markedly reduced the blood alpha-fetoprotein levels of mice intrahepatically transplanted with Hep G2 cells. Humanized GC33 (hGC33) was as efficacious as GC33 against the Hep G2 xenograft, but hGC33 lacking carbohydrate moieties caused neither ADCC nor tumor growth inhibition. Depletion of CD56+ cells from human peripheral blood mononuclear cells markedly abrogated the ADCC caused by hGC33. The results show that the antitumor activity of hGC33 is mainly attributable to ADCC, and in human, natural killer cell-mediated ADCC is one possible mechanism of the antitumor effects by GC33. hGC33 will provide a novel treatment option for liver cancer patients with GPC3-positive tumors.

Alpha-fetoprotein and other tumour-associated antigens for immunotherapy of hepatocellular cancer

BACKGROUND

Hepatocellular carcinoma (HCC) is a leading cause of cancer death, with few treatment options for advanced disease.

OBJECTIVES

Here, we review the aetiology of HCC and focus on recent data on tumour-associated antigens (TAA) for HCC, their functions and potential use as immunological targets for immune-based therapy for HCC. In addition, we examine some aspects of antigen presentation within the liver.

RESULTS/CONCLUSIONS

alpha-Fetoprotein (AFP) has been investigated for many years as a TAA, and has been tested in recent clinical trials. More recently, additional TAA have been identified and new therapeutic approaches have been investigated which may be testable clinically in this difficult disease setting.

Glypican-3-mediated oncogenesis involves the Insulin-like growth factor-signaling pathway

Glypican-3 (gpc3) is the gene responsible for Simpson-Golabi-Behmel overgrowth syndrome. Previously, we have shown that GPC3 is overexpressed in hepatocellular carcinoma (HCC). In this study, we demonstrated the mechanisms for GPC3-mediated oncogenesis. Firstly, GPC3 overexpression in NIH3T3 cells gave to cancer cell phenotypes including growing in serum-free medium and forming colonies in soft agar, or on the other way, GPC3 knockdown in HuH-7 cells decreased oncogenecity. We further demonstrated that GPC3 bound specifically through its N-terminal proline-rich region to both Insulin-like growth factor (IGF)-II and IGF-1R. GPC3 stimulated the phosphorylation of IGF-1R and the downstream signaling molecule extracellular signal-regulated kinase (ERK) in an IGF-II-dependent way. Also, GPC3 knockdown in HCC cells decreased the phosphorylation of both IGF-1R and ERK. Therefore, GPC3 confers oncogenecity through the interaction between IGF-II and its receptor, and the subsequent activation of the IGF-signaling pathway. This data are novel to the current understanding of the role of GPC3 in HCC and will be important in future developments of cancer therapy.

Processing by convertases is not required for glypican-3-induced stimulation of hepatocellular carcinoma growth

Glypicans are a family of heparan sulfate proteoglycans that are bound to the cell surface by a lipid anchor. Six members of this family have been identified in mammals (GPC1-GPC6). Glypicans act as regulators of the activity of various cytokines, including Wnts, Hedgehogs, and bone morphogenetic proteins. It has been reported that processing by a convertase is required for GPC3 activity during convergent extension in zebrafish embryos, for GPC3-induced regulation of Wnt signaling, and for the binding of GPC3 to Wnt5a. In our laboratory, we have recently demonstrated that GPC3 promotes the growth of hepatocellular carcinomas (HCCs) by stimulating canonical Wnt signaling. Because there is increasing evidence indicating that the structural requirements for GPC3 activity are cell type specific, we decided to investigate whether GPC3 needs to be processed by convertases to stimulate cell proliferation and Wnt signaling in HCC cells. We report here that a mutant GPC3 that cannot be processed by convertases is still able to play its stimulatory role in Wnt activity and HCC growth.

Effects of Syndecan-1 and Glypican on Muscle Cell Proliferation and Differentiation: Implications for Possible Functions During Myogenesis

The heparan sulfate proteoglycans, syndecan-1 and glypican, are low-affinity receptors for fibroblast growth factor 2 (FGF2). Because FGF2 is a potent stimulator of skeletal muscle cell proliferation and a strong inhibitor of differentiation, it is likely that changes in syndecan-1 and glypican expression will affect myogenesis as both, in part, regulate FGF-dependent signaling. In the current study, expression vector constructs containing either syndecan-1 or glypican were transfected into turkey myogenic satellite cells resulting in the overexpression of these genes. The amount of expression of each of these genes was measured by semiquantitative reverse transcriptase polymerase chain reaction. The satellite cell cultures overexpressing syndecan-1 were unable to fuse to form multinucleated myotubes after differentiation was induced. The syndecan-1-transfected cells maintained a rounded morphology typical of cells during proliferation. In contrast, the satellite cells transfected with glypican formed larger myotubes. These results suggest that both syndecan-1 and glypican play pivotal, but different, roles in both muscle cell proliferation and differentiation.

Identification of Soluble NH2-Terminal Fragment of Glypican-3 as a Serological Marker for Early-Stage Hepatocellular Carcinoma

For detection of hepatocellular carcinoma (HCC) in patients with liver cirrhosis, serum alpha-fetoprotein has been widely used, but its sensitivity has not been satisfactory, especially in small, well-differentiated HCC, and complementary serum marker has been clinically required. Glypican-3 (GPC3), a heparan sulfate proteoglycan anchored to the plasma membrane, is a good candidate marker of HCC because it is an oncofetal protein overexpressed in HCC at both the mRNA and protein levels. In this study, we demonstrated that its NH(2)-terminal portion [soluble GPC3 (sGPC3)] is cleaved between Arg(358) and Ser(359) of GPC3 and that sGPC3 can be specifically detected in the sera of patients with HCC. Serum levels of sGPC3 were 4.84 +/- 8.91 ng/ml in HCC, significantly higher than the levels seen in liver cirrhosis (1.09 +/- 0.74 ng/ml; P < 0.01) and healthy controls (0.65 +/- 0.32 ng/ml; P < 0.001). In well- or moderately-differentiated HCC, sGPC3 was superior to alpha-fetoprotein in sensitivity, and a combination measurement of both markers improved overall sensitivity from 50% to 72%. These results indicate that sGPC3 is a novel serological marker essential for the early detection of HCC.

Glypican-3 is involved in cellular protection against mitoxantrone in gastric carcinoma cells

Elevated expression of the heparan sulphate proteoglycan glypican-3 (GPC3) was found on mRNA and protein levels in the atypical multidrug-resistant gastric carcinoma cell line EPG85-257RNOV, which was established by in vitro selection against mitoxantrone. In order to elucidate a putative role of GPC3 in the drug-resistant phenotype, the mitoxantrone-resistant cell line EPG85-257RNOV was transfected with an expression vector construct carrying an anti-GPC3 hammerhead ribozyme. It could be demonstrated that in anti-GPC3 ribozyme-transfected cell clones, the GPC3-specific mRNA and corresponding protein expression levels were decreased to levels that are similar to those observed in nonresistant, parental cells. The anti-GPC3 ribozyme-containing clones reduced the mitoxantrone resistance level up to 21% of the original resistance and the crossresistance against etoposide to 33% of the original value. This reversal of drug resistance was accompanied by an increased cellular mitoxantrone accumulation in the anti-GPC3 ribozyme-expressing cells. In conclusion, it was verified that GPC3 is involved in the cellular protection against mitoxantrone in the atypical multidrug-resistant gastric carcinoma cell line EPG85-257RNOV.

Glypican-3: a novel serum and histochemical marker for hepatocellular carcinoma

BACKGROUND & AIMS

Early detection of hepatocellular carcinoma (HCC) is critical for successful treatment. However, the differential diagnosis between HCC and benign hepatic lesions is sometimes difficult and new biochemical markers for HCC are required. It has been reported that glypican-3 (GPC3) messenger RNA (mRNA) is significantly increased in most HCCs compared with benign liver lesions or normal liver. The goal of this study is to determine whether GPC3 is also overexpressed at the protein level and whether GPC3 is detectable in the serum of patients with HCC.

METHODS

GPC3 was assessed in liver tissue sections by immunohistochemistry and in serum by enzyme-linked immunosorbent assay. Serum alpha-fetoprotein (AFP) level was also measured in the same patients.

RESULTS

Immunohistochemical studies showed that GPC3 is expressed in 72% of HCCs (21 of 29), whereas it is not detectable in hepatocytes from normal liver and benign liver diseases. Consistent with this, GPC3 was undetectable in the serum of healthy donors and patients with hepatitis, but its levels were significantly increased in 18 of 34 patients (53%) with HCC. In addition, only 1 of 20 patients with hepatitis plus liver cirrhosis displayed elevated levels of serum GPC3. Interestingly, in most cases, there was no correlation between GPC3 and AFP values. Thus, at least 1 of the 2 markers was elevated in 82% of the patients with HCC.

CONCLUSIONS

GPC3 is specifically overexpressed in most HCCs and is elevated in the serum of a large proportion of patients with HCC. The simultaneous determination of GPC3 and AFP may significantly increase the sensitivity for diagnosis of HCC.

Inhibition of invasion and metastasis by glypican-3 in a syngeneic breast cancer model

Glypican-3 (GPC3), a proteoglycan bound to the cell membrane through a GPI anchor, is widely expressed in the embryo but down regulated in most adult tissues, with some exceptions as mammary cells. GPC3 is involved in the regulation of cell proliferation and survival in specific cell types. LM3, a murine mammary tumor cell line unable to express GPC3, was stably transfected with the rat GPC3 gene to analyze its role in tumor progression. Upon injection into syngeneic BALB/c mice LM3-GPC3 clones showed less local invasiveness and developed fewer spontaneous and experimental lung metastasis than controls. GPC3-expressing cells were more sensitive to apoptosis induced by serum depletion, exhibited a delay in the first steps of spreading and were less motile than controls. On the other hand, LM3-GPC3 cells were significantly more adherent to FN than control ones. We observed that GPC3 transfectants presented a higher expression of E-cadherin and beta-catenin, molecules whose down regulation has been associated with tumor progression. Exogenous TGF-beta increased MMP-9 activity in both control and GPC3-expressing cells, but did not modulate MMP-2. Contrarily, GPC3 expression prevented the increase of MMP-2 activity induced by IGF-II. Our results suggest that GPC3 has a protective role against mammary cancer progression.

Glypican-3 is overexpressed in human hepatocellular carcinoma

To identify candidate genes that could be used as diagnostic and therapeutic targets for hepatocellular carcinoma (HCC), we searched for the genes that are overexpressed in HCC by combining representational difference analysis and microarray. Genes such as glypican-3 (GPC3), insulin-like growth factor 2, long-chain fatty-acid-coenzyme A ligase 4, farnesyl diphosphate synthase were frequently identified in our screening. Northern blot analysis with these four genes confirmed their overexpression in HCC. Among them we found that GPC3 transcript is upregulated in six out of seven cases of HCC. Immunoblot and immunohistochemical staining using polyclonal anti-GPC3 antibodies further confirmed that GPC3 protein is indeed increased in HCC tumor samples. We also found that GPC3 is secreted into culture media from cell lines derived from HCC. We conclude that GPC3 is a good molecular marker for HCC.

The role of glypicans in mammalian development

Glypicans are a family of heparan sulfate proteoglycans that are bound to the cell surface by a glycosyl-phosphatidylinositol anchor. Six members of this family have been identified in mammals. In general, glypicans are highly expressed during development, and their expression pattern suggests that they are involved in morphogenesis. One member of this family, glypican-3, is mutated in the Simpson-Golabi-Behmel syndrome. This syndrome is characterized by overgrowth and various developmental abnormalities that indicate that glypican-3 inhibits proliferation and cell survival in the embryo. It has consequently been proposed that glypicans can regulate the activity of several growth factors that play a critical role in morphogenesis.

GPC3 mutation analysis in a spectrum of patients with overgrowth expands the phenotype of Simpson-Golabi-Behmel syndrome

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked overgrowth syndrome caused by deletions in glypican 3 (GPC3). SGBS is characterized by pre- and postnatal overgrowth, a characteristic facial appearance, and a spectrum of congenital malformations which overlaps that of other overgrowth syndromes. We performed GPC3 deletion screening on 80 male patients with somatic overgrowth in the following categories: SGBS (n = 19), possible SGBS (n = 26), including families in which individuals had previously been diagnosed with other overgrowth syndromes, and Wiedemann-Beckwith syndrome (WBS) (n = 35). Using exon-specific PCR and Southern blot analysis, we identified seven GPC3 deletions. In most cases a clear X-linked family history was not present. In two cases, GPC3 deletions were identified in patients belonging to pedigrees published previously as other overgrowth syndromes: one with a diagnosis of Sotos syndrome and the other Perlman syndrome with nephroblastomatosis. A third patient developed hepatoblastoma, a tumor type not previously described in SGBS. No GPC3 deletions were identified among the WBS patients. Direct sequencing of all GPC3 exons in the remaining 13 SGBS patients without GPC3 deletions did not identify any further mutations, raising the possibility of alternative silencing mechanisms and/or other genes in the pathogenesis of SGBS. Our results validate the clinical specificity of the facial appearance, skeletal/hand anomalies, and supernumerary nipples in patients with GPC3 deletions. Our data also suggest that nephroblastomatosis and hepatoblastoma are included in the phenotypic spectrum of GPC3 deletions and SGBS, underscoring the importance of tumor surveillance in these children.

Regulation of urokinase/urokinase receptor interaction by heparin-like glycosaminoglycans

We show here that the interaction between the urokinase-type plasminogen activator and its receptor, which plays a critical role in cell invasion, is regulated by heparan sulfate present on the cell surface and in the extracellular matrix. Heparan sulfate oligomers showing a composition close to the dimeric repeats of heparin (glucosamine-NSO(3)(6-OSO(3))-iduronic acid(2-OSO(3))) n = 5 and n > 5, where iduronic acid may alternate with glucuronic acid, exhibit affinity for urokinase plasminogen activator and confer specificity on urokinase/urokinase receptor interaction. Cell surface clearance of heparan sulfate reduces the affinity of such interaction with a parallel decrease of specific urokinase binding in the presence of an unaltered expression of receptor. Transfection of human urokinase plasminogen activator receptor in normal Chinese hamster ovary fibroblasts and in Chinese hamster ovary cells defective for the synthesis of sulfated glycosaminoglycans results in specific urokinase/receptor interaction only in nondefective cells. Heparan sulfate/urokinase and receptor/urokinase interactions exhibit similar K(d) values. We concluded that heparan sulfate functions as an adaptor molecule that confers specificity on urokinase/receptor binding.

Proteoglycans in the developing brain: new conceptual insights for old proteins

Proteoglycans are a heterogeneous class of proteins bearing sulfated glycosaminoglycans. Some of the proteoglycans have distinct core protein structures, and others display similarities and thus may be grouped into families such as the syndecans, the glypicans, or the hyalectans (or lecticans). Proteoglycans can be found in almost all tissues being present in the extracellular matrix, on cellular surfaces, or in intracellular granules. In recent years, brain proteoglycans have attracted growing interest due to their highly regulated spatiotemporal expression during nervous system development and maturation. There is increasing evidence that different proteoglycans act as regulators of cell migration, axonal pathfinding, synaptogenesis, and structural plasticity. This review summarizes the most recent data on structures and functions of brain proteoglycans and focuses on new physiological concepts for their potential roles in the developing central nervous system.

Expression of GPC3, an X-linked recessive overgrowth gene, is silenced in malignant mesothelioma

Gene expression changes in rat asbestos-induced malignant mesothelioma (MM) cells were investigated by differential mRNA display. A mRNA transcript identified by this approach was abundant in normal rat mesothelial cells but not expressed in rat MM cell lines. Northern blot analysis confirmed that this transcript is uniformly silenced in rat MM cell lines and primary tumors. Nucleotide sequence analysis revealed that this transcript is encoded by the rat glypican 3 gene (GPC3), whose human homolog is mutated in the Simpson-Golabi-Behmel overgrowth syndrome. Allelic loss at the GPC3 locus was infrequent (6.9%) in MM cell lines, and no mutations were found. GPC3 transcript levels were markedly decreased in 16 of 18 primary tumors and 17 of 22 human MM cell lines. Most of the cell lines were shown to have aberrant methylation of the GPC3 promoter region. In two of four human MM cell lines tested, GPC3 expression was restored after 2-deoxy 5-azacytidine (DAC)-mediated demethylation of its promoter region. Ectopic expression of GPC3 inhibited in vitro colony formation of human MM cells. Collectively, these data suggest that down-regulation of GPC3 is a common occurrence in MM and that GPC3, an X-linked recessive overgrowth gene, may encode a negative regulator of mesothelial cell growth.

Heparan sulfate chains with antimitogenic properties arise from mesangial cell-surface proteoglycans

Heparan sulfate (HS) chains accumulate in both the medium and the cell layer of mesangial cell cultures. When given in fresh medium to quiescent cultures at naturally occurring concentrations, they suppress entry into the cell cycle and progression to DNA synthesis. We have attempted to identify the proteoglycan (PG) source of the antimitogenic HS chains from mesangial cell layers (HS(c)) and medium (HS(c)). When cells were labeled for 16 hours with [35S]sulfate, 25% of the label was found in intracellular HS chains and 5% in extracellular HSPGs. Cell-surface HSPGs accounted for the remaining 70% of the label associated with cell-layer HS and were released by either trypsin or 2% Triton X-100. About 20% of this cell-surface fraction was released by treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), and probably represents glypican-like PG; glypican mRNA was present in the cells. The remainder of this fraction could be incorporated into liposomes, indicating the presence of hydrophobic transmembrane regions suggestive of syndecans. Upon purification and deglycosylation, an antiserum to rat liver HSPGs that reacts primarily with syndecan-2 showed a strong signal corresponding to this protein and three weaker bands that may represent additional syndecans. mRNAs for syndecan-1, -2, and -4 were present in the cultures. Syndecan-1 and -2 mRNAs were increased 30 minutes after stimulation of quiescent rat mesangial cells (RMCs) with serum. Heparin, HS(c), and HS(m) all prevented this increase. Syndecan-4 mRNA was not affected by serum, heparin, or HS. In pulse-chase experiments, the amount of 35S appearing in the cellular protein-free HS fraction was accounted for almost entirely by cell-surface PGs, as matrix-associated label was a minor contribution at the end of the pulse-labeling. The appearance of [35S]HS in cell extracts was unaffected by phospholipase C treatment, indicating that turnover of the newly labeled syndecan fraction is the source of the antimitogenic HS chains.

Glypican-6, a new member of the glypican family of cell surface heparan sulfate proteoglycans

The glypicans compose a family of glycosylphosphatidylinositol-anchored heparan sulfate proteoglycans. Mutations in dally, a gene encoding a Drosophila glypican, and in GPC3, the gene for human glypican-3, implicate glypicans in the control of cell growth and division. So far, five members of the glypican family have been identified in vertebrates. By sequencing expressed sequence tag clones and products of rapid amplifications of cDNA ends, we identified a sixth member of the glypican family. The glypican-6 mRNA encodes a protein of 555 amino acids that is most homologous to glypican-4 (identity of 63%). Expression of this protein in Namalwa cells shows a core protein of approximately 60 kDa that is substituted with heparan sulfate only. GPC6, the gene encoding human glypican-6, contains nine exons. Like GPC5, the gene encoding glypican-5, GPC6 maps to chromosome 13q32. Clustering of the GPC5/GPC6 genes on chromosome 13q32 is strongly reminiscent of the clustering of the GPC3/GPC4 genes on chromosome Xq26 and suggests GPCs arose from a series of gene and genome duplications. Based on similarities in sequence and gene organization, glypican-1, glypican-2, glypican-4, and glypican-6 appear to define a subfamily of glypicans, differing from the subfamily comprising so far glypican-3 and glypican-5. Northern blottings indicate that glypican-6 mRNA is widespread, with prominent expressions in human fetal kidney and adult ovary. In situ hybridization studies localize glypican-6 to mesenchymal tissues in the developing mouse embryo. High expressions occur in smooth muscle cells lining the aorta and other major blood vessels and in mesenchymal cells of the intestine, kidney, lung, tooth, and gonad. Growth factor signaling in these tissues might in part be regulated by the presence of glypican-6 on the cell surface.

Glypican-3-deficient mice exhibit developmental overgrowth and some of the abnormalities typical of Simpson-Golabi-Behmel syndrome

Glypicans are a family of heparan sulfate proteoglycans that are linked to the cell surface through a glycosyl-phosphatidylinositol anchor. One member of this family, glypican-3 (Gpc3), is mutated in patients with the Simpson-Golabi-Behmel syndrome (SGBS). These patients display pre- and postnatal overgrowth, and a varying range of dysmorphisms. The clinical features of SGBS are very similar to the more extensively studied Beckwith-Wiedemann syndrome (BWS). Since BWS has been associated with biallelic expression of insulin-like growth factor II (IGF-II), it has been proposed that GPC3 is a negative regulator of IGF-II. However, there is still no biochemical evidence indicating that GPC3 plays such a role.Here, we report that GPC3-deficient mice exhibit several of the clinical features observed in SGBS patients, including developmental overgrowth, perinatal death, cystic and dyplastic kidneys, and abnormal lung development. A proportion of the mutant mice also display mandibular hypoplasia and an imperforate vagina. In the particular case of the kidney, we demonstrate that there is an early and persistent developmental abnormality of the ureteric bud/collecting system due to increased proliferation of cells in this tissue element. The degree of developmental overgrowth of the GPC3-deficient mice is similar to that of mice deficient in IGF receptor type 2 (IGF2R), a well characterized negative regulator of IGF-II. Unlike the IGF2R-deficient mice, however, the levels of IGF-II in GPC3 knockouts are similar to those of the normal littermates.

Mammalian homologues of the Drosophila slit protein are ligands of the heparan sulfate proteoglycan glypican-1 in brain

Using an affinity matrix in which a recombinant glypican-Fc fusion protein expressed in 293 cells was coupled to protein A-Sepharose, we have isolated from rat brain at least two proteins that were detected by SDS-polyacrylamide gel electrophoresis as a single 200-kDa silver-stained band, from which 16 partial peptide sequences were obtained by nano-electrospray tandem mass spectrometry. Mouse expressed sequence tags containing two of these peptides were employed for oligonucleotide design and synthesis of probes by polymerase chain reaction and enabled us to isolate from a rat brain cDNA library a 4.1-kilobase clone that encoded two of our peptide sequences and represented the N-terminal portion of a protein containing a signal peptide and three leucine-rich repeats. Comparisons with recently published sequences also showed that our peptides were derived from proteins that are members of the Slit/MEGF protein family, which share a number of structural features such as N-terminal leucine-rich repeats and C-terminal epidermal growth factor-like motifs, and in Drosophila Slit is necessary for the development of midline glia and commissural axon pathways. All of the five known rat and human Slit proteins contain 1523-1534 amino acids, and our peptide sequences correspond best to those present in human Slit-1 and Slit-2. Binding of these ligands to the glypican-Fc fusion protein requires the presence of the heparan sulfate chains, but the interaction appears to be relatively specific for glypican-1 insofar as no other identified heparin-binding proteins were isolated using our affinity matrix. Northern analysis demonstrated the presence of two mRNA species of 8. 6 and 7.5 kilobase pairs using probes based on both N- and C-terminal sequences, and in situ hybridization histochemistry showed that these glypican-1 ligands are synthesized by neurons, such as hippocampal pyramidal cells and cerebellar granule cells, where we have previously also demonstrated glypican-1 mRNA and immunoreactivity. Our results therefore indicate that Slit family proteins are functional ligands of glypican-1 in nervous tissue and suggest that their interactions may be critical for certain stages of central nervous system histogenesis.

Glypican-1 is a VEGF165 binding proteoglycan that acts as an extracellular chaperone for VEGF165

Glypican-1 is a member of a family of glycosylphosphatidylinositol anchored cell surface heparan sulfate proteoglycans implicated in the control of cellular growth and differentiation. The 165-amino acid form of vascular endothelial growth factor (VEGF165) is a mitogen for endothelial cells and a potent angiogenic factor in vivo. Heparin binds to VEGF165 and enhances its binding to VEGF receptors. However, native HSPGs that bind VEGF165 and modulate its receptor binding have not been identified. Among the glypicans, glypican-1 is the only member that is expressed in the vascular system. We have therefore examined whether glypican-1 can interact with VEGF165. Glypican-1 from rat myoblasts binds specifically to VEGF165 but not to VEGF121. The binding has an apparent dissociation constant of 3 x 10(-10) M. The binding of glypican-1 to VEGF165 is mediated by the heparan sulfate chains of glypican-1, because heparinase treatment abolishes this interaction. Only an excess of heparin or heparan sulfates but not other types of glycosaminoglycans inhibited this interaction. VEGF165 interacts specifically not only with rat myoblast glypican-1 but also with human endothelial cell-derived glypican-1. The binding of 125I-VEGF165 to heparinase-treated human vascular endothelial cells is reduced following heparinase treatment, and addition of glypican-1 restores the binding. Glypican-1 also potentiates the binding of 125I-VEGF165 to a soluble extracellular domain of the VEGF receptor KDR/flk-1. Furthermore, we show that glypican-1 acts as an extracellular chaperone that can restore the receptor binding ability of VEGF165, which has been damaged by oxidation. Taken together, these results suggest that glypican-1 may play an important role in the control of angiogenesis by regulating the activity of VEGF165, a regulation that may be critical under conditions such as wound repair, in which oxidizing agents that can impair the activity of VEGF are produced, and in situations were the concentrations of active VEGF are limiting.

GPC4, the gene for human K-glypican, flanks GPC3 on xq26: deletion of the GPC3-GPC4 gene cluster in one family with Simpson-Golabi-Behmel syndrome

The glypicans constitute a growing family of cell surface heparan sulfate proteoglycans that may play a role in the control of cell division and growth regulation. Recently, deletions and translocations involving GPC3 (the gene for glypican-3, localized on Xq26) have been identified in patients with Simpson-Golabi-Behmel syndrome (SGBS). This X-linked syndrome is characterized by pre- and postnatal overgrowth, visceral and skeletal abnormalities, and a high risk for the development of embryonal tumors, mostly Wilms tumor and neuroblastoma. In the present report we show that the gene for human K-glypican/glypican-4 (GPC4) also maps to Xq26, centromeric to GPC3. The glypican-4 protein is encoded by nine exons. Establishment of a BAC/PAC contig physically linking GPC4 and GPC3 indicates that these two genes are arranged in a tandem array, the 5' end of GPC4 flanking the 3' end of GPC3. Unlike the glypican-3 message, the glypican-4 message is nearly ubiquitous. Analysis of DNA samples from eight patients with diagnosis of SGBS identified one individual with a deletion that involves the entire GPC4 gene and the last two exons of GPC3. The tight clustering of GPC3 and GPC4, with deletions that occasionally affect both genes, may be relevant for explaining the variability of the SGBS phenotype.