Glypicans: a growing trend

Evaluation of antitumor potential of an anti-glypican-1 monoclonal antibody in preclinical lung cancer models reveals a distinct mechanism of action

Aim

The main objective of this study was to investigate the antitumor effect of a mouse anti-human glypican-1 (GPC1) monoclonal antibody (mAb) on non-small cell lung carcinoma (NSCLC) and associated molecular mechanisms.

Methods

The anti-proliferative and anti-migratory activities of anti-GPC1 mAb were examined in A549 and H460 NSCLC cells and LL97A lung fibroblasts. The inhibitory effect of anti-GPC1 mAb on tumor growth was evaluated in an orthotopic lung tumor model.

Results

The in vitro study showed that anti-GPC1 mAb profoundly inhibited the anchorage-independent growth of A549 and H460 NSCLC cells and exhibited relatively high cytotoxic activities towards LL97A lung fibroblasts, A549/LL97A and H460/LL97A coculture spheroids. Moreover, anti-GPC1 mAb significantly decreased the expression of phospho-Src (p-Src; Tyr416), p-Akt (Ser473) and β-catenin in the co-cultured LL97A lung fibroblasts, and the expression of phospho-mitogen-activated protein kinase kinase (p-MEK; Ser217/221) and phospho-90 kDa ribosomal s6 kinase (p-p90RSK; Ser380) in co-cultured A549 cells. When anti-GPC1 mAb was administered to tumor-bearing mice, the inhibitory effect of anti-GPC1 mAb on the orthotopic lung tumor growth was not statistically significant. Nonetheless, results of Western blot analysis showed significant decrease in the phosphorylation of fibroblast growth factor receptor 1 (FGFR1) at Tyr766, Src at Tyr416, extracellular signal-regulated kinase (ERK) at Thr202/Tyr204, 90 kDa ribosomal S6 kinase (RSK) at Ser380, glycogen synthase kinases 3α (GSK3α) at Ser21 and GSK3β at Ser9 in tumor tissues. These data implicate that anti-GPC1 mAb treatment impairs the interaction between tumor cells and tumor associated fibroblasts by attenuating the paracrine FGFR signal transduction.

Conclusions

The relatively potent cytotoxicity of anti-GPC1 mAb in lung fibroblasts and its potential inhibitory effect on the paracrine FGFR signal transduction warrant further studies on the combined use of this mAb with targeted therapeutics to improve therapeutic outcomes in lung cancer.

Early diabetic kidney disease: Focus on the glycocalyx

The incidence of diabetic kidney disease (DKD) is sharply increasing worldwide. Microalbuminuria is the primary clinical marker used to identify DKD, and its initiating step in diabetes is glomerular endothelial cell dysfunction, particularly glycocalyx impairment. The glycocalyx found on the surface of glomerular endothelial cells, is a dynamic hydrated layer structure composed of pro-teoglycans, glycoproteins, and some adsorbed soluble components. It reinforces the negative charge barrier, transduces the shear stress, and mediates the interaction of blood corpuscles and podocytes with endothelial cells. In the high-glucose environment of diabetes, excessive reactive oxygen species and proinflammatory cytokines can damage the endothelial glycocalyx (EG) both directly and indirectly, which induces the production of microalbuminuria. Further research is required to elucidate the role of the podocyte glycocalyx, which may, together with endothelial cells, form a line of defense against albumin filtration. Interestingly, recent research has confirmed that the negative charge barrier function of the glycocalyx found in the glomerular basement membrane and its repulsion effect on albumin is limited. Therefore, to improve the early diagnosis and treatment of DKD, the potential mechanisms of EG degradation must be analyzed and more responsive and controllable targets must be explored. The content of this review will provide insights for future research.

Recombinant thrombomodulin may protect cardiac capillary endothelial glycocalyx through promoting Glypican-1 expression under experimental endotoxemia

Introduction

Myocardial dysfunction occurs in patients with sepsis due to vascular endothelial injury. Recombinant human thrombomodulin (rhTM) attenuates vascular endothelial injuries through endothelial glycocalyx (eGC) protection.

Hypothesis

We hypothesized that rhTM attenuates myocardial dysfunction via the inhibition of vascular endothelial injury during sepsis.

Methods

Ten-week-old male C57BL6 mice were injected intraperitoneally with 20 mg/kg of lipopolysaccharide (LPS). In rhTM-treated mice, rhTM was injected intraperitoneally at 3 and 24 h after LPS injection. Saline was injected intraperitoneally as control. To assess for eGC injury, intensity score was measured 48 h after the LPS injection. To confirm vascular endothelial injuries, ultrastructural analysis was performed using scanning (SEM) and transmission electron microscopy (TEM).

Results

The survival rate of the rhTM group at 48 h after LPS injection was significantly higher than that of the control group (68% vs. 17%, p < 0.05). The serum level of troponin I in the rhTM group was lower than that in the control (2.2 ± 0.4 ng/dL vs 9.4 ± 1.1 ng/dL, p < 0.05). The expression of interleukin-6 (IL-6) was attenuated in the rhTM-treated group than in the control (65.3 ± 15.3 ng/mL vs 226.3 ± 19.4 ng/mL, p < 0.05). The serum concentration of syndecan-1, a marker of glycocalyx damage, was significantly decreased 48 h post-administration of LPS in the rhTM-treated group than in the control group. In ultrastructural analysis using SEM and TEM, eGC peeled off from the surface of the capillary lumen in the control. Conversely, the eGC injury was attenuated in the rhTM group. Gene set enrichment analysis revealed that osteomodulin, osteoglycin proline/arginine-rich end leucine-rich repeat protein, and glypican-1, which are proteoglycans, were preserved by rhTM treatment. Their protein expression was retained in endothelial cells.

Conclusion

rhTM attenuates sepsis-induced myocardial dysfunction via eGC protection.

Running Promotes Transformation of Brain Astrocytes Into Neuroprotective Reactive Astrocytes and Synaptic Formation by Targeting Gpc6 Through the STAT3 Pathway

Ischemic stroke is caused by cerebral ischemia upon the blockage of an artery, which results in a high disability rate. Little is known regarding the mechanism of astrocyte function in cerebral ischemia. We aimed to determine the effects of running on the transformation of astrocytes, and subsequent synapse formation. A study of middle cerebral artery occlusion (MCAO) after running in vivo showed that running can promote the transformation of astrocytes toward the neuroprotective phenotype. Our findings of oxygen-glucose deprived astrocytes in vitro after running revealed that these astrocytes transformed into the neuroprotective phenotype, and that the expression of STAT3 and Gpc6 was increased. We confirmed that mechanistically, running can target Gpc6 through the STAT3 pathway and then regulate the number of synapses. We concluded that running promotes synapse proliferation by polarizing astrocytes toward the neuroprotective phenotype and ultimately leads to nerve regeneration.

Cellular repressor of E1A-stimulated genes regulates vascular endothelial cell migration by the ILK/AKT/mTOR/VEGF(165) signaling pathway

The migration of vascular endothelial cells plays a critical role in a variety of vascular physiological and pathological processes, such as embryonic development, angiogenesis, wound healing, re-endothelialization, and vascular remodeling. This study clarified the role and mechanism of a new vascular homeostasis regulator, Cellular repressor of E1A-stimulated genes (CREG), in the migration of primary human umbilical vein endothelial cells (HUVECs). A wound healing assay and transwell migration model showed that upregulation of CREG expression induced HUVEC migration and it was positively correlated with the expression of vascular endothelial growth factor. Furthermore, wild type integrin-linked kinase reversed the poor mobility of CREG knock-down HUVECs; in contrast, kinase-dead integrin-linked kinase weakened the migration of HUVECs. We also studied the effect of CREG on HUVEC migration by the addition of an mTOR inhibitor, recombinant vascular endothelial growth factor(165), neutralizing antibody of vascular endothelial growth factor(165) and AKT siRNA, and we concluded that CREG induces endothelial cell migration by activating the integrin-linked kinase/AKT/mTOR/VEGF(165) signaling pathway.

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.

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.

In vivo footprinting analysis of the Glypican 3 (GPC3) promoter region in neuroblastoma cells

Glypican 3 (GPC3) is an X-linked gene that has its peak expression during development and is down-regulated in all studied tissues after birth. We have shown that GPC3 was expressed in neuroblastoma and Wilms' tumor. To understand the mechanisms regulating the transcription of this gene in neuroblastoma cells, we have focused our study on the identification of putative transcription factors binding the promoter. In this report we performed in vivo dimethylsulfate, UV type C irradiation and DNaseI footprinting analyses coupled with ligation-mediated PCR on nearly 1000 bp of promoter in two neuroblastoma cell lines, SJNB-7 (expressing GPC3) and SK-N-FI (not expressing GPC3). Nucleosome signature footprints were observed in the most distal part of the studied region in both cell lines. We detected eight large differentially protected regions, suggesting the presence of binding proteins in both cell lines but more DNA-protein interactions in GPC3-expressing cells. Sp1 was previously shown to be able to bind some of these regions. Here by combining electromobility shift assays and chromatin immunoprecipitations we showed that the transcription factor NFY was part of the DNA-protein complex found in footprinted regions upstream of the described minimal promoter. These studies performed on chromatin in situ suggest that NFY and yet unknown cell type-specific factors may play an important role in the regulation of GPC3.

Cigarette smoke disrupts VEGF165-VEGFR-2 receptor signaling complex in rat lungs and patients with COPD: morphological impact of VEGFR-2 inhibition

VEGF is fundamental in the development and maintenance of the vasculature. VEGF(165) signaling through VEGF receptor (VEGFR)-2/kinase insert domain receptor (KDR) is a highly regulated process involving the formation of a tertiary complex with glypican (GYP)-1 and neuropilin (NRP)-1. Both VEGF and VEGFR-2 expression are reduced in emphysematous lungs; however, the mechanism of regulation of VEGF(165) signaling through the VEGFR-2 complex in response to cigarette smoke exposure in vivo, and in smokers with and without chronic obstructive pulmonary disease (COPD), is still unknown. We hypothesized that cigarette smoke exposure disrupts the VEGF(165)-VEGFR-2 complex, a potential mechanism in the pathogenesis of emphysema. We show that cigarette smoke exposure reduces NRP-1 and GYP-1 as well as VEGF and VEGFR-2 levels in rat lungs and that VEGF, VEGFR-2, GYP-1, and NRP-1 expression in the lungs of both smokers and patients with COPD are also reduced compared with nonsmokers. Moreover, our data suggest that specific inhibition of VEGFR-2 alone with NVP-AAD777 would appear not to result in emphysema in the adult rat lung. As both VEGF(165) and VEGFR-2 expression are reduced in emphysematous lungs, decreased GYP-1 and NRP-1 expression may yet further disrupt VEGF(165)-VEGFR-2 signaling. Whether or not this by itself is critical for inducing endothelial cell apoptosis and decreased vascularization of the lung seen in emphysema patients is still unclear at present. However, targeted therapies to restore VEGF(165)-VEGFR-2 complex may promote endothelial cell survival and help to ameliorate emphysema.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a clinically heterogeneous overgrowth syndrome associated with an increased risk for embryonal tumor development. BWS provides an ideal model system to study epigenetic mechanisms. This condition is caused by a variety of genetic or epigenetic alterations within two domains of imprinted growth regulatory genes on human chromosome 11p15. Molecular studies of BWS have provided important data with respect to epigenotype/genotype-phenotype correlations; for example, alterations of Domain 1 are associated with the highest risk for tumor development, specifically Wilms' tumor. Further, the elucidation of the molecular basis for monozygotic twinning in BWS defined a critical period for imprint maintenance during pre-implantation embryonic development. In the future, such molecular studies in BWS will permit enhanced medical management and targeted genetic counseling.

The loss of glypican-3 induces alterations in Wnt signaling

Loss-of-function mutations of the GPC3 gene are the cause of the human Simpson-Golabi-Behmel syndrome. Based on the overgrowth phenotype of the Simpson-Golabi-Behmel syndrome patients and the key role played by the insulin-like growth factor (IGF) signaling system in regulating embryonic growth, it was speculated that GPC3 regulates IGF signaling. In order to test the validity of this hypothesis, we mated GPC3 knockout mice with insulin receptor substrate-1 (IRS-1) nullizygous mice. We found that GPC3 regulates organism growth independent of IRS-1, suggesting that GPC3 does not modulate IGF signaling. Instead, we found that GPC3 knockout mice exhibit alterations in the Wnt signaling pathway, which is also associated with the regulation of cell proliferation. In particular, the loss of GPC3 led to the inhibition of the non-canonical Wnt/JNK signaling pathway, while concomitantly causing the activation of canonical Wnt/beta-catenin signaling. These in vivo findings were confirmed in vitro upon the ectopic overexpression of GPC3 in mesothelioma cells. In these cells, the GPC3-induced increase in JNK activity was associated with an enhanced response to Wnt5a. Most interestingly, the heparan sulfate chains of GPC3 were not required for its stimulatory activity on Wnt5a signaling and for the formation of GPC3-Wnt5a complexes. We propose that at least in some cell types GPC3 serves as a selective regulator of Wnt signaling, by potentiating non-canonical Wnt signaling, while inhibiting the canonical Wnt signaling pathway.

Methylation analysis of the glypican 3 gene in embryonal tumours

We have previously shown that the glypican 3 (GPC3) gene was expressed in neuroblastoma (NB) and Wilms' tumour (WT), two embryonal tumours. GPC3 is an X-linked gene that has its peak expression during development and that is downregulated in all investigated tissues after birth. GPC3 expression could be involved in the aetiology of embryonal tumours such as NB and WT. Methylation is known to play a role in gene silencing, notably in chromosome X inactivation. Southern blot- and PCR-based methylation assays were used to assess the methylation status of the GPC3 promoter on genomic DNA from both normal and embryonal tumour cells. In normal cells, the promoter was not methylated in males and partially methylated in females. Our results suggest that DNA methylation of the promoter region is not essential for the transcriptional repression of the GPC3 gene and that the methylation observed in females is probably linked to the inactive X chromosome. In tumour samples, methylation abnormalities have been found exclusively in female NB samples (loss of methylation) and mainly in male WT samples (gain of methylation). Overall, methylation did not significantly correlate with the expression status of GPC3. Although promoter methylation is likely to affect the expression status of the gene, our results suggest that the deregulation of GPC3 transcriptional expression seen in NB and WT involves other regulatory levels.

Heparan Sulfate Proteoglycan Is a Mechanosensor on Endothelial Cells

The objective of this study was to test whether a glycosaminoglycan component of the surface glycocalyx layer is a fluid shear stress sensor on endothelial cells (ECs). Because enhanced nitric oxide (NO) production in response to fluid shear stress is a characteristic and physiologically important response of ECs, we evaluated NO x (NO 2 − and NO 3 − ) production in response to fluid shear stress after enzymatic removal of heparan sulfate, the dominant glycosaminoglycan of the EC glycocalyx, from cultured ECs. The significant NO x production induced by steady shear stress (20 dyne/cm 2 ) was inhibited completely by pretreatment with 15 mU/mL heparinase III (E.C.4.2.2.8) for 2 hours. Oscillatory shear stress (10±15 dyne/cm 2 ) induced an even greater NO x production than steady shear stress that was completely inhibited by pretreatment with heparinase III. Addition of bradykinin (BK) induced significant NO x production that was not inhibited by heparinase pretreatment, demonstrating that the cells were still able to produce abundant NO after heparinase treatment. Fluorescent imaging with a heparan sulfate antibody revealed that heparinase III treatments removed a substantial fraction of the heparan sulfate bound to the surfaces of ECs. In summary, these experiments demonstrate that a heparan sulfate component of the EC glycocalyx participates in mechanosensing that mediates NO production in response to shear stress. The full text of this article is available online at http://www.circresaha.org.

The Simpson-Golabi-Behmel gene, GPC3, is not involved in sporadic Wilms tumorigenesis

Many genes have been implicated in Wilms tumor; however, only one gene, WT1, has a proven role in the development of this embryonal tumor. Wilms tumor occurs in a number of congenital syndromes including the Simpson-Golabi-Behmel syndrome (SGBS) which has phenotypic overlap with another Wilms tumor-predisposing syndrome Wiedemann-Beckwith syndrome. The putative function and expression pattern of the SGBS gene, glypican 3 (GPC3), makes it an attractive candidate Wilms tumor gene. We, therefore, hypothesized that Wilms tumors from non-SGBS patients may harbor somatic mutations of GPC3. Mutation analysis of 64 Wilms tumors was performed. One case of a tumor-specific deletion of the entire GPC3 gene and several polymorphisms were identified. GPC3 expression was evaluated in 36 Wilms tumors and 29/36 expressed GPC3. Surprisingly, we did not find evidence of functional mutations of GPC3 in sporadic Wilms tumor suggesting that GPC3 is not often directly involved in Wilms tumorigenesis.

Overgrowth

The predominant influences on fetal growth are maternal and placental factors. Post-natal growth is regulated by a complex interaction between genetic, environmental and hormonal influences. The role of the growth hormone insulin-like growth factor (GH-IGF) system is explored, including the emerging role of IGF-2 in fetal growth. Increasing understanding of the genetics of overgrowth and short stature syndromes is contributing greatly to basic understanding of growth regulation. A range of prenatal overgrowth syndromes is discussed, including those associated with neonatal hyperinsulinism and hypoglycaemia.Post-natal overgrowth may be caused by a diverse range of normal variant conditions, endocrine disorders, chromosomal abnormalities and other genetic syndromes. An approach to diagnosis is presented and major conditions discussed in detail. Sex-steroid therapy for height limitation continues to be a controversial area with uncertainty about height prediction, benefits achieved and possible long-term side-effects.

Pathological significance of vascular endothelial growth factor A isoform expression in human cancer

Vascular endothelial growth factor (VEGF) is a highly specific factor for vascular endothelial cells. Five VEGF-A isoforms (splice variants 121, 145, 165, 189 and 206) are generated as a result of alternative splicing from a single VEGF-A gene. These differ in their molecular weights and in biological properties such as their ability to bind to cell-surface heparan sulfate proteoglycans. Deregulated VEGF-A expression contributes to the development of solid tumors by promoting tumor angiogenesis. More specifically, VEGF-A189 expression is related to angiogenesis and prognosis in certain human solid tumors. VEGF-A189 expression is also related to the xenotransplantability of human cancers into immunodeficient mice in vivo. Consequently, inhibition of VEGF-A or VEGF-A189 signaling regulates the development and metastasis of a variety of tumors. This review focuses on recent studies of the mechanisms by which VEGF-A regulates angiogenesis in the cancer stroma and on our recent findings concerning the potential mechanisms of VEGF-A189 expression on tumor growth and metastasis.

The contribution of in vivo manipulation of gene expression to the understanding of the function of glypicans

The name glypican identifies a family of heparan sulfate proteoglycans that are linked to the cell surface by a glycosylphosphatidylinositol anchor. Members of this family have been identified in Drosophila, zebrafish, and mammals. The interest in the study of glypicans has increased in the last few years as a result of the discovery that the glypican-3 gene (GPC-3) is mutated in an overgrowth and dysmorphic syndrome. Despite the increased interest, our knowledge about the function of glypicans is still limited, since the molecular basis for the role of glypican-3 in the regulation of body size remains unknown. The in vivo manipulation of glypican expression in lower organisms, however, has demonstrated that these proteoglycans can modulate cellular responses to Wnts and bone morphogenetic factors. Future studies should investigate whether the phenotype of GPC-3-deficient individuals is also due to altered modulation of cellular responses to these factors.

Febrile convulsions, ataxia, developmental delay, and obesity: a new syndrome?

We describe the association of recurrent complicated febrile convulsions, developmental delay, ataxia, and obesity in three unrelated girls. The three girls, aged 3 to 4 years, were all born to healthy, nonconsanguineous parents and have normal siblings. Their birth weight was appropriate for gestational age. They are not dysmorphic and have normal head circumference. Development is delayed; they all walked with an ataxic gait after the age of 2 years and started speaking at 3 years. Their growth charts are remarkably alike: they initially had a normal growth curve and around 24 months of age started to gain weight excessively. They all continue to suffer from complicated febrile seizures, which started before 12 months of age, and are resistant to prophylactic anticonvulsants. Metabolic evaluation is normal. They have normal magnetic resonance images and electroencephalograms. Fragile X and Prader-Willi syndromes were ruled out. We suggest that this is a new mental retardation syndrome that should be considered in children with recurrent febrile convulsions, developmental delay, and obesity. In a recent study, mutations in the beta4 calcium channel were identified in the mutant epileptic mouse that presents with epilepsy, mental retardation, and ataxia. We hypothesize that a calcium channel gene may be involved in this syndrome.

Characterization of a human preadipocyte cell strain with high capacity for adipose differentiation

OBJECTIVE

To develop and to characterize a human preadipocyte cell strain with high capacity for adipose differentiation serving as a model for studying human adipocyte development and metabolism in vitro.

METHODS

Cells were derived from the stromal cells fraction of subcutaneous adipose tissue of an infant with Simpson-Golabi-Behmel syndrome (SGBS). Adipose differentiation was induced under serum-free culture conditions by exposure to 10 nM insulin, 200 pM triiodothyronine, 1 microM cortisol and 2 microM BRL 49653, a PPAR gamma agonist.

RESULTS

During the differentiation process SGBS cells developed a gene expression pattern similar to that found in differentiating human preadipocytes with a characteristic increase in fat cell-specific mRNAs encoding lipoprotein lipase (LPL), glycero-3-phosphate dehydrogenase (GPDH), GLUT4, leptin and others. Differentiated SGBS cells exhibited an increase in glucose uptake upon insulin stimulation and in glycerol release upon catecholamine exposure. SGBS adipocytes were morphologically, biochemically and functionally identical to in vitro differentiated adipocytes from healthy subjects. However, while preadipocytes from healthy control infants rapidly lost their capacity to differentiate after a few cell divisions in culture, SGBS cells maintained their differentiation capacity over many generations: upon appropriate stimulation 95% of SGBS cells of generation 30 developed into adipocytes. A mutation in the glypican 3 gene was not detected in the patient. Thus, it remains unclear whether the molecular alteration in SGBS cells is also responsible for the high differentiation capacity and further investigations are required.

CONCLUSION

The human cell strain described here provides an almost unlimited source of human preadipocytes with high capacity for adipose differentiation and may, therefore, represent a unique tool for studying human fat cell development and metabolism. International Journal of Obesity (2001) 25, 8-15

Glypican-4 is an FGF2-binding heparan sulfate proteoglycan expressed in neural precursor cells

FGF2 is a crucial mitogen for neural precursor cells in the developing cerebral cortex. Heparan sulfate proteoglycans (HSPGs) are thought to play a role in cortical neurogenesis by regulating the action of FGF2 on neural precursor cells. In this article, we present data indicating that glypican-4 (K-glypican), a GPI-anchored cell surface HSPG, is involved in these processes. In the developing mouse brain, glypican-4 mRNA is expressed predominantly in the ventricular zone of the telencephalon. Neither the outer layers of the telencephalic wall nor the ventricular zone of other parts of the developing brain express significant levels of glypican-4, with the exception of the ventricular zone of the tectum. In cultures of E13 rat cortical precursor cells, glypican-4 is expressed in cells immunoreactive for nestin and the D1.1 antigen, markers of neural precursor cells. Glypican-4 expression was not detected in early postmitotic or fully differentiated neurons. Recombinant glypican-4 produced in immortalized neural precursor cells binds FGF2 through its heparan sulfate chains and suppressed the mitogenic effect of FGF2 on E13 cortical precursor cells. The spatiotemporal expression pattern of glypican-4 in the developing cerebral wall significantly overlaps with that of FGF2. These results suggest that glypican-4 plays a critical role in the regulation of FGF2 action during cortical neurogenesis.

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 pattern alterations of syndecans and glypican-1 in normal and pathological trophoblast

Syndecans (syn-1, -2, -3, -4) and glypican-1 are proteoglycans expressed during development in association with changes in tissue organization and differentiation. They participate in the modulation of growth factor actions and in cell-cell and cell-matrix adhesion. The expression of syn-1, -2, -3, -4, and glypican-1 has been studied in normal human placenta and in gestational trophoblastic disease such as hydatidiform mole, invasive mole, and choriocarcinoma, using immunohistochemistry and western blots. Syndecan-3 was not expressed in normal or pathological tissues. During normal gestation, the other proteoglycans showed a specific staining pattern, which for some was modified during pregnancy. For instance, syn-1 was only expressed in syncytiotrophoblast; syn-4 was mainly localized in the villous and extravillous cytotrophoblast in the first trimester, whereas at term it was expressed in the syncytiotrophoblast. The most striking results are the altered expression patterns of syndecans and glypican-1 in pathological tissues. These proteoglycans showed a progressive decrease of immunostaining related to the increase of severity of trophoblastic disease, in particular in invasive mole and choriocarcinoma. In addition, dysregulation in the localization of the expression patterns was observed for syn-2 and -4. Because changes in syndecan expression enable cells to become more or less responsive to their micro-environment, the down-regulation and/or dysregulation of syndecans in relation to the degree of severity of trophoblastic diseases provides new insights into the progression of these pathologies.

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.

Heparan Sulfate Proteoglycan Expression Is Induced During Early Erythroid Differentiation of Multipotent Hematopoietic Stem Cells

Heparan sulfate (HS) proteoglycans of bone marrow (BM) stromal cells and their extracellular matrix are important components of the microenvironment of hematopoietic tissues and are involved in the interaction of hematopoietic stem and stromal cells. Although previous studies have emphasized the role of HS proteoglycan synthesis by BM stromal cells, we have recently shown that the human hematopoietic progenitor cell line TF-1 also expressed an HS proteoglycan. Immunochemical, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern blot analysis of this HS proteoglycan showed that it was not related to the syndecan family of HS proteoglycans or to glypican. To answer the question of whether the expression of HS proteoglycans is associated with the differentiation state of hematopoietic progenitor cells, we have analyzed the proteoglycan synthesis of several murine and human hematopoietic progenitor cell lines. Proteoglycans were isolated from metabolically labeled cells and purified by several chromatographic steps. Isolation and characterization of proteoglycans from the cell lines HEL and ELM-D, which like TF-1 cells have an immature erythroid phenotype, showed that these cells synthesize the same HS proteoglycan, previously detected in TF-1 cells, as a major proteoglycan. In contrast, cell lines of the myeloid lineage, like the myeloblastic/promyelocytic cell lines B1 and B2, do not express HS proteoglycans. Taken together, our data strongly suggest that expression of this HS proteoglycan in hematopoietic progenitor cell lines is associated with the erythroid lineage. To prove this association we have analyzed the proteoglycan expression in the nonleukemic multipotent stem cell line FDCP-Mix-A4 after induction of erythroid or granulocytic differentiation. Our data show that HS proteoglycan expression is induced during early erythroid differentiation of multipotent hematopoietic stem cells. In contrast, during granulocytic differentiation, no expression of HS proteoglycans was observed.

Heparan Sulfate Proteoglycan Expression Is Induced During Early Erythroid Differentiation of Multipotent Hematopoietic Stem Cells

Heparan sulfate (HS) proteoglycans of bone marrow (BM) stromal cells and their extracellular matrix are important components of the microenvironment of hematopoietic tissues and are involved in the interaction of hematopoietic stem and stromal cells. Although previous studies have emphasized the role of HS proteoglycan synthesis by BM stromal cells, we have recently shown that the human hematopoietic progenitor cell line TF-1 also expressed an HS proteoglycan. Immunochemical, reverse transcriptase-polymerase chain reaction (RT-PCR), and Northern blot analysis of this HS proteoglycan showed that it was not related to the syndecan family of HS proteoglycans or to glypican. To answer the question of whether the expression of HS proteoglycans is associated with the differentiation state of hematopoietic progenitor cells, we have analyzed the proteoglycan synthesis of several murine and human hematopoietic progenitor cell lines. Proteoglycans were isolated from metabolically labeled cells and purified by several chromatographic steps. Isolation and characterization of proteoglycans from the cell lines HEL and ELM-D, which like TF-1 cells have an immature erythroid phenotype, showed that these cells synthesize the same HS proteoglycan, previously detected in TF-1 cells, as a major proteoglycan. In contrast, cell lines of the myeloid lineage, like the myeloblastic/promyelocytic cell lines B1 and B2, do not express HS proteoglycans. Taken together, our data strongly suggest that expression of this HS proteoglycan in hematopoietic progenitor cell lines is associated with the erythroid lineage. To prove this association we have analyzed the proteoglycan expression in the nonleukemic multipotent stem cell line FDCP-Mix-A4 after induction of erythroid or granulocytic differentiation. Our data show that HS proteoglycan expression is induced during early erythroid differentiation of multipotent hematopoietic stem cells. In contrast, during granulocytic differentiation, no expression of HS proteoglycans was observed.

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.

Clinical and molecular aspects of the Simpson-Golabi-Behmel syndrome

The Simpson-Golabi-Behmel syndrome (SGBS) is an overgrowth/multiple congenital anomalies/dysplasia syndrome caused by a mutant X-linked gene. The spectrum of its clinical manifestations is broad, varying from very mild forms in carrier females to infantile lethal forms in affected males. A typically affected male will show tall stature, "coarse" face, supernumerary nipples, congenital heart defect, and generalized muscular hypotonia. Mental development is normal in most cases. There is an increased risk of neoplasia in infancy, especially Wilms tumor. The SGBS gene spans 500 kilobases in the Xq26 region and contains eight exons. It encodes an extracellular proteoglycan, designated glypican 3 (GPC3), capable of interacting with the insulin-like growth factor IGF2. At present, only deletions of various sizes have been found in a number of affected families.

OCI-5/GPC3, a glypican encoded by a gene that is mutated in the Simpson-Golabi-Behmel overgrowth syndrome, induces apoptosis in a cell line-specific manner

OCI-5/GPC3 is a member of the glypican family. Glypicans are heparan sulfate proteoglycans that are bound to the cell surface through a glycosyl-phosphatidylinositol anchor. It has recently been shown that the OCI-5/GPC3 gene is mutated in patients with the Simpson-Golabi-Behmel Syndrome (SGBS), an X-linked disorder characterized by pre- and postnatal overgrowth and various visceral and skeletal dysmorphisms. Some of these dysmorphisms could be the result of deficient growth inhibition or apoptosis in certain cell types during development. Here we present evidence indicating that OCI-5/GPC3 induces apoptosis in cell lines derived from mesothelioma (II14) and breast cancer (MCF-7). This induction, however, is cell line specific since it is not observed in NIH 3T3 fibroblasts or HT-29 colorectal tumor cells. We also show that the apoptosis-inducing activity in II14 and MCF-7 cells requires the anchoring of OCI-5/GPC3 to the cell membrane. The glycosaminoglycan chains, on the other hand, are not required. MCF-7 cells can be rescued from OCI-5/GPC3-induced cell death by insulin-like growth factor 2. This factor has been implicated in Beckwith-Wiedemann, an overgrowth syndrome that has many similarities with SGBS. The discovery that OCI-5/GPC3 is able to induce apoptosis in a cell line- specific manner provides an insight into the mechanism that, at least in part, is responsible for the phenotype of SGBS patients.

Diagnosing Friedreich's ataxia

Clinical diagnosis is still of the utmost importance and following our review of cases diagnosed using the strict criteria, 100% were homozygous for the expansion. However, now that there is a relatively simple direct genetic test, the diagnosis can be considered in more unusual cases. Genetic testing has been shown to be of value in establishing the correct diagnosis and in directing the appropriate screening tests, including cardiological assessment and blood sugar estimation. Perhaps the most interesting development following identification of the gene is the rapid progress in our understanding of the protein. If, as seems likely, it turns out to be a mitochondrial protein involved in iron transport, it gives cause for hope of effective treatment.

A patient with Simpson-Golabi-Behmel syndrome and hepatocellular carcinoma

Simpson-Golabi-Behmel syndrome (SGBS) is an X linked disorder characterised by pre- and postnatal overgrowth, coarse facial features, and visceral and skeletal abnormalities. Like other overgrowth syndromes, in the SGBS there is an increased risk for developing neoplasia, mainly embryonic, such as Wilms tumour. We report a 3 year old male patient with SGBS and hepatocellular carcinoma, a previously undescribed tumour associated with the syndrome.

Mouse mutant embryos overexpressing IGF-II exhibit phenotypic features of the Beckwith-Wiedemann and Simpson-Golabi-Behmel syndromes

In mice, the imprinted Igf2 gene (expressed from the paternal allele), which encodes a growth-promoting factor (IGF-II), is linked closely to the reciprocally imprinted H19 locus on chromosome 7. Also imprinted (expressed from the maternal allele) is the Igf2r gene on chromsome 17 encoding the type 2 IGF receptor that is involved in degradation of excess IGF-II. Double mutant embryos carrying a deletion around the H19 region and also a targeted Igf2r allele, both inherited maternally, have extremely high levels of IGF-II (7- and 11-fold higher than normal in tissues and serum, respectively) as a result of biallelic Igf2 expression (imprint relaxation by deletion of H19-associated sequence) in combination with lack of the IGF2R-mediated IGF-II turnover. This excess of IGF-II causes somatic overgrowth, visceromegaly, placentomegaly, omphalocele, and cardiac and adrenal defects, which are also features of the Beckwith-Wiedemann syndrome (BWS), a genetically complex human disorder associated with chromosomal abnormalities in the 11p15.5 region where the IGF2 gene resides. In addition, the double mutant mouse embryos exhibit skeletal defects and cleft palate, which are manifestations observed frequently in the Simpson-Golabi-Behmel syndrome, another overgrowth disorder overlapping phenotypically, but not genetically, with BWS.

Imprinting in clusters: lessons from Beckwith-Wiedemann syndrome

Imprinted genes in mammals can be clustered in the genome. This raises important questions about mechanistic and functional relationships between imprinted genes in a cluster. The insulin-like growth factor II (IGF2) gene is paternally expressed and is surrounded by maternally expressed genes. Loss of imprinting of IGF2 is the most common molecular defect found in the human foetal overgrowth syndrome, Beckwith-Wiedemann syndrome (BWS). Transgenic experiments in the mouse establish that overexpression of IGF2 can result in most of the symptoms of BWS. However, mutations, translocations, or methylation defects in BWS have so far been found in three of the linked maternally expressed genes. We present a model where the paternal growth enhancer IGF2 is surrounded by multiple maternal suppressors, and mutations, or epigenetic alterations, in any of these suppressors could cause BWS. In addition, the precise phenotypic spectrum of BWS might depend on which maternally expressed gene is mutated.

Large scale deletions in the GPC3 gene may account for a minority of cases of Simpson-Golabi-Behmel syndrome

AIMS OF THE STUDY

To identify the proportion and type of deletions present in the glypican 3 (GPC3) gene in a group of patients with Simpson-Golabi-Behmel syndrome (SGBS).

SUBJECTS AND METHODS

PCR analysis using primer pairs which amplify fragments from each of the eight exons of the GPC3 gene was carried out in a series of 18 families with SGBS (approximately half of reported cases).

RESULTS

Deletions were detected in only five families (one reported previously). We found deletions in all exons of the gene except exon 3.

CONCLUSIONS

Our results suggest that large scale deletions may be less common in SGBS than was originally thought. One patient, with an exon 4 and 5 deletion, lacked the characteristic facial dysmorphic features. This raises the possibility of involvement of GPC3 gene defects in a wider range of overgrowth disorders.

OCI-5/rat glypican-3 binds to fibroblast growth factor-2 but not to insulin-like growth factor-2

OCI-5 encodes the rat homologue of glypican-3, a membrane-bound heparan sulfate proteoglycan that is mutated in the Simpson-Golabi-Behmel overgrowth syndrome. OCI-5 and glypican-3 are 95% identical. It has been recently suggested that glypican-3 interacts with insulin-like growth factor-2 (IGF-2) and that this interaction regulates IGF-2 activity. We report here that we have transfected OCI-5 into two different cell lines, and we have not been able to detect an interaction between the OCI-5 proteoglycan produced by the transfected cells and IGF-2. On the other hand, we have found that OCI-5 interacts with FGF-2, as has already been shown for glypican-1. This interaction is mediated by the heparan sulfate chains of OCI-5 because it can be inhibited by heparin or by heparitinase.

Characterization of glypican-5 and chromosomal localization of human GPC5, a new member of the glypican gene family

The four vertebrate glypican-related integral membrane proteoglycans identified so far constitute a discrete family of heparan sulfate proteoglycans that are linked to the cell surface via glycosyl phosphatidylinositol. In addition to the GPI anchor and substitution with heparan sulfate, the members of this family show significant sequence homology and share a unique and characteristic cysteine motif. Starting from an EST entry that showed significant sequence similarity to MXR7 and OCI-5 (coding, respectively, for human and rat glypican-3), we have isolated a human cDNA coding for glypican-5, a novel member of this proteoglycan family. The gene for this novel glypican (GPC5) maps to 13q32. In the adult, it is primarily expressed in brain tissue.

Genomic imprinting: nature and clinical relevance

Molecular genetic techniques allow investigators to trace chromosomes and genes from parent to child and, in a single individual, from tissue to tissue. These techniques have uncovered a new type of gene control in which the allele from one parent is expressed and the allele from the other parent is not. This differential expression is called genomic imprinting. It may lead to phenotypic differences when inheritance is from the mother versus the father. Genomic imprinting has been observed in a number of disorders having to do with growth, behavior, and abnormal cell growth. It is important to be aware that such a phenomenon exists and to consider it when making diagnoses and determining therapy.

Increased expression of the insulin-like growth factor-II gene in Wilms' tumor is not dependent on loss of genomic imprinting or loss of heterozygosity

Loss of imprinting of insulin-like growth factor-II gene (IGF2) and/or loss of heterozygosity at the 11p15 loci have been postulated to be responsible for IGF2 overexpression in Wilms' tumor. In order to delineate the mechanism of IGF2 overexpression in Wilms' tumors, we have genotyped the 11p15-11p13 chromosomal region and determined allelic expression of IGF2 and H19 in both tumor tissue and in normal adjacent kidney tissue from 40 patients with Wilms' tumor. In five of the eight subjects informative for the ApaI IGF2 polymorphism, loss of imprinting of IGF2 was observed in both normal and tumor tissues. A significant increase (>5-fold) in IGF2 expression in tumor tissues compared to the normal adjacent kidney tissue was observed regardless of the IGF2 imprinting or the chromosome 11p15 heterozygosity status. In each case, the overexpression of IGF2 in the tumors was accompanied by activation of all four IGF2 promoters. Our data indicate that alterations of IGF2 imprinting occurred in normal adjacent kidney tissue before tumorigenesis and that the IGF2 overexpression in Wilms' tumor tissue occurs through a loss of heterozygosity- or loss of imprinting-independent process.

Essentials of growth diagnosis

There is more to growth than GH. Growth disorders can be approached expeditiously by assessing the relationships among height, weight, BA and height velocity. Undernutrition is indicated by low weight for height; diabetes mellitus, hyperthyroidism, and electrolyte disturbances are the major endocrine considerations. Short stature results from intrinsically short, delayed, or attenuated growth patterns. Excessive stature results from intrinsically tall, advanced, or accelerated growth patterns. Each of these patterns causing linear growth abnormalities has a distinct differential diagnosis that variously includes endocrine, metabolic, genetic, and systemic disorders.