Differential effects of p-nitrophenyl-D-xylosides on mouse blastocysts and uterine epithelial cells

Aglycone Ebselen and β-d-Xyloside Primed Glycosaminoglycans Co-contribute to Ebselen β-d-Xyloside-Induced Cytotoxicity

Most β-d-xylosides with hydrophobic aglycones are nontoxic primers for glycosaminoglycan assembly in animal cells. However, when Ebselen was conjugated to d-xylose, d-glucose, d-galactose, and d-lactose (8A-D), only Ebselen β-d-xyloside (8A) showed significant cytotoxicity in human cancer cells. The following facts indicated that the aglycone Ebselen and β-d-xyloside primed glycosaminoglycans co-contributed to the observed cytotoxicity: 1. Ebselen induced S phase cell cycle arrest, whereas 8A induced G2/M cell cycle arrest; 2. 8A augmented early and late phase cancer cell apoptosis significantly compared to that of Ebselen and 8B-D; 3. Both 8A and phenyl-β-d-xyloside primed glycosaminoglycans with similar disaccharide compositions in CHO-pgsA745 cells; 4. Glycosaminoglycans could be detected inside of cells only when treated with 8A, indicating Ebselen contributed to the unique property of intracellular localization of the primed glycosaminoglycans. Thus, 8A represents a lead compound for the development of novel antitumor strategy by targeting glycosaminoglycans.

Xyloside-primed Chondroitin Sulfate/Dermatan Sulfate from Breast Carcinoma Cells with a Defined Disaccharide Composition Has Cytotoxic Effects in Vitro

We previously reported that the xyloside 2-(6-hydroxynaphthyl) β-d-xylopyranoside (XylNapOH), in contrast to 2-naphthyl β-d-xylopyranoside (XylNap), specifically reduces tumor growth both in vitro and in vivo Although there are indications that this could be mediated by the xyloside-primed glycosaminoglycans (GAGs) and that these differ in composition depending on xyloside and cell type, detailed knowledge regarding a structure-function relationship is lacking. In this study we isolated XylNapOH- and XylNap-primed GAGs from a breast carcinoma cell line, HCC70, and a breast fibroblast cell line, CCD-1095Sk, and demonstrated that both XylNapOH- and XylNap-primed chondroitin sulfate/dermatan sulfate GAGs derived from HCC70 cells had a cytotoxic effect on HCC70 cells and CCD-1095Sk cells. The cytotoxic effect appeared to be mediated by induction of apoptosis and was inhibited in a concentration-dependent manner by the XylNap-primed heparan sulfate GAGs. In contrast, neither the chondroitin sulfate/dermatan sulfate nor the heparan sulfate derived from CCD-1095Sk cells primed on XylNapOH or XylNap had any effect on the growth of HCC70 cells or CCD-105Sk cells. These observations were related to the disaccharide composition of the XylNapOH- and XylNap-primed GAGs, which differed between the two cell lines but was similar when the GAGs were derived from the same cell line. To our knowledge this is the first report on cytotoxic effects mediated by chondroitin sulfate/dermatan sulfate.

Border patrol: insights into the unique role of perlecan/heparan sulfate proteoglycan 2 at cell and tissue borders

The extracellular matrix proteoglycan (ECM) perlecan, also known as heparan sulfate proteoglycan 2 or HSPG2, is one of the largest (>200 nm) and oldest (>550 M years) extracellular matrix molecules. In vertebrates, perlecan's five-domain structure contains numerous independently folding modules with sequence similarities to other ECM proteins, all connected like cars into one long, diverse complex train following a unique N-terminal domain I decorated with three long glycosaminoglycan chains, and an additional glycosaminoglycan attachment site in the C-terminal domain V. In lower invertebrates, perlecan is not typically a proteoglycan, possessing the majority of the core protein modules, but lacking domain I where the attachment sites for glycosaminoglycan chains are located. This suggests that uniting the heparan sulfate binding growth factor functions of domain I and the core protein functions of the rest of the molecule in domains II-V occurred later in evolution for a new functional purpose. In this review, we surveyed several decades of pertinent literature to ask a fundamental question: Why did nature design this protein uniquely as an extraordinarily long multifunctional proteoglycan with a single promoter regulating expression, rather than separating these functions into individual proteins that could be independently regulated? We arrived at the conclusion that the concentration of perlecan at functional borders separating tissues and tissue layers is an ancient key function of the core protein. The addition of the heparan sulfate chains in domain I likely occurred as an additional means of binding the core protein to other ECM proteins in territorial matrices and basement membranes, and as a means to reserve growth factors in an on-site depot to assist with rapid repair of those borders when compromised, such as would occur during wounding. We propose a function for perlecan that extends its role from that of an extracellular scaffold, as we previously suggested, to that of a critical agent for establishing and patrolling tissue borders in complex tissues in metazoans. We also propose that understanding these unique functions of the individual portions of the perlecan molecule can provide new insights and tools for engineering of complex multi-layered tissues including providing the necessary cues for establishing neotissue borders.

The heparin-binding domain of HB-EGF mediates localization to sites of cell-cell contact and prevents HB-EGF proteolytic release

Heparin-binding EGF-like growth factor (HB-EGF) is a ligand for EGF receptor (EGFR) and possesses the ability to signal in juxtacrine, autocrine and/or paracrine mode, with these alternatives being governed by the degree of proteolytic release of the ligand. Although the spatial range of diffusion of released HB-EGF is restricted by binding heparan-sulfate proteoglycans (HSPGs) in the extracellular matrix and/or cellular glycocalyx, ascertaining mechanisms governing non-released HB-EGF localization is also important for understanding its effects. We have employed a new method for independently tracking the localization of the extracellular EGF-like domain of HB-EGF and the cytoplasmic C-terminus. A striking observation was the absence of the HB-EGF transmembrane pro-form from the leading edge of COS-7 cells in a wound-closure assay; instead, this protein localized in regions of cell-cell contact. A battery of detailed experiments found that this localization derives from a trans interaction between extracellular HSPGs and the HB-EGF heparin-binding domain, and that disruption of this interaction leads to increased release of soluble ligand and a switch in cell phenotype from juxtacrine-induced growth inhibition to autocrine-induced proliferation. Our results indicate that extracellular HSPGs serve to sequester the transmembrane pro-form of HB-EGF at the point of cell-cell contact, and that this plays a role in governing the balance between juxtacrine versus autocrine and paracrine signaling.

Heparanase improves mouse embryo implantation

OBJECTIVE

To improve mouse embryonic implantation by recombinant heparanase supplementation. Heparanase, an endoglycosidase-degrading heparan sulfate proteoglycan, may have a role in embryonic implantation because of its enzymatic, angiogenic, and adhesive properties. Increasing endometrial receptivity could improve one of the most difficult pathologies in human fertility.

DESIGN

Comparison between mouse blastocysts obtained after 24-hour incubation of morulae with or without heparanase.

SETTING

Experimental laboratory in a medical center.

ANIMAL(S)

Mice.

INTERVENTION(S)

Morulae were flushed from CB6F1 female mice and incubated for 24 hours at 37 degrees C in M16 medium supplemented with 0.1 mg/mL heparanase (n = 203), with albumin (n = 60), or with medium alone (n = 258).

MAIN OUTCOME MEASURE(S)

Blastocysts were evaluated by heparanase immunostaining (n = 10), activity assay (n = 283), and transfer to foster mice uterine horns (n = 228). The number of implantation sites was compared.

RESULT(S)

Immunostaining demonstrated that heparanase is constitutively expressed in mouse morulae and blastocyts. Heparanase supplementation resulted in increased staining and enzymatic activity in blastocyts. Implantation rates for the heparanase, M16 medium, and albumin groups, were 36.9%, 17.8%, and 20%, respectively (P<.01).

CONCLUSION(S)

Heparanase was found to be constitutively expressed by blastocyst-stage embryos. Moreover, the amount of heparanase was markedly increased by incubation of morulae with recombinant heparanase, evaluated by immunostaining and enzymatic activity. Heparanase supplementation resulted in approximately a twofold increase in embryo implantation rate in vivo. Taken together, these data suggest that heparanase is actively involved in embryo implantation.

Immune-responsive gene 1 is a novel target of progesterone receptor and plays a critical role during implantation in the mouse

The steroid hormone progesterone (P) is a critical regulator of uterine receptivity during blastocyst implantation. The hormone acts through nuclear P receptors (PRs) to modulate the expression of specific gene networks in various uterine cell types. To identify the P-regulated pathways underlying uterine receptivity, we previously used oligonucleotide microarrays to analyze uterine mRNA profiles at the time of implantation in response to RU486, a PR antagonist. We reported that the mRNA corresponding to the immune-responsive gene 1 (Irg1), a previously described lipopolysaccharide-inducible gene, is one of the several mRNAs that are markedly down-regulated by RU486 in the preimplantation uterus. In the present study, we performed in situ hybridization to show that P stimulates Irg1 mRNA synthesis in the luminal epithelial cells of uteri of ovariectomized wild-type but not PR knockout mice. We also report that Irg1 mRNA was induced in the luminal epithelium of pregnant uterus between d 3 and 5, overlapping the window of implantation. To investigate the function of Irg1 during implantation, we administered sense or antisense oligodeoxynucleotides into preimplantation mouse uteri. Treatment with antisense oligodeoxynucleotides led to suppression in Irg1 mRNA expression without affecting unrelated mRNAs in the pregnant uterus. This intervention was also accompanied by impairment in embryo implantation, indicating that the phenotype is linked to the suppression of Irg1 mRNA. Collectively, our studies identified Irg1 as a novel target of PR in the pregnant uterus and also revealed that it is a critical regulator of the early events leading to implantation.

Expression of heparin/heparan sulfate interacting protein/ribosomal protein l29 during the estrous cycle and early pregnancy in the mouse

Using a variety of approaches, we have examined the expression of the heparin/heparan sulfate (Hp/HS) interacting protein/ribosomal protein L29 (HIP/RPL29) in mouse uteri during the estrous cycle and early pregnancy. HIP/RPL29 selectively binds heparin and HS and may promote HS-dependent embryo adhesion. HIP/RPL29 was prominently expressed in both luminal and glandular epithelia under almost all conditions, including the phase of embryo attachment. In contrast, differences were noted in HIP/RPL29 expression in the stromal compartment both during the estrous cycle and during early pregnancy. Most notably, HIP/RPL29 accumulated in decidua, where it displayed a pattern complementary to that of pericellular deposition of the HS proteoglycan, perlecan. HIP/RPL29 protein was detected in implanted embryos at both initial and later stages of implantation; however, embryonic HIP/RPL29 mRNA accumulation was more pronounced at later stages (Day 7.5 postcoitum). In situ hybridization revealed similar spatial changes for HIP/RPL29 mRNA during these different physiological states. Whereas differences in the spatial pattern of HIP/RPL29 protein and mRNA expression were demonstrable, little change was detected in the level of HIP/RPL29 mRNA or protein in total endometrial extracts. Mouse blastocysts attached, but did not outgrow, on surfaces coated with recombinant murine HIP/RPL29. Surprisingly, soluble glycosaminoglycans including heparin, low molecular weight heparin, or chondroitin sulfate were not able to inhibit embryo attachment to HIP/RPL29-coated surfaces. These latter observations indicate that embryonic cell surface components other than HS proteoglycans can promote binding to HIP/RPL29 expressed by uterine cells.

EXT genes are differentially expressed in bone and cartilage during mouse embryogenesis

Hereditary multiple exostoses (HME) is a genetically heterogeneous disease characterized by the development of bony protuberances at the ends of all long bones. Genetic analyses have revealed HME to be a multigenic disorder linked to three loci on chromosomes 8q24 (EXT1), 11p11-13 (EXT2), and 19p (EXT3). The EXT1 and EXT2 genes have been cloned and defined as glycosyltransferases involved in the synthesis of heparan sulfate. EST database analysis has demonstrated additional gene family members, EXT-like genes (EXTL1, EXTL2, and EXTL3), not associated with a HME locus. The mouse homologs of EXT1 and EXT2 have also been cloned and shown to be 99% and 95% identical to their human counterparts, respectively. Here, we report the identification of the mouse EXTL1 gene and show it is 74% identical to the human EXTL1 gene. Expression studies of all three mouse EXT genes throughout various stages of embryonic development were carried out and whole-mount in situ hybridization in the developing limb buds showed high levels of expression of all three EXT genes. However, in situ hybridization of sectioned embryos revealed remarkable differences in expression profiles of EXT1, EXT2, and EXTL1. The identical expression patterns found for the EXT1 and EXT2 genes support the recent observation that both proteins form a glycosyltransferase complex. We suggest a model for exostoses formation based on the involvement of EXT1 and EXT2 in the Indian hedgehog/parathyroid hormone-related peptide (PTHrP) signaling pathway, an important regulator of the chondrocyte maturation process.

Role of proteoglycans on testosterone synthesis by purified Leydig cells from immature and mature rats

In order to characterize an involvement of proteoglycans (PG) in the regulation of Leydig cell function, we have examined the effects of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis and para-nitrophenyl-beta-D-galactoside (PNPG), an inefficient structural analogue, on testosterone production by purified Leydig cells from immature and mature rats, in the presence or not of various concentrations of hCG during 24 h. Whatever the age, the addition of PNPX induces a decrease of [35S] and [3H] incorporations into cell layer associated-PG; these latter being less numerous (-50 and -25%, respectively in immature and mature rat), and less sulfated (-40%) when compared to control Leydig cells. In immature Leydig cells, the inhibition of PG synthesis decreases both the basal and weakly stimulable-hCG or -(Bu)2cAMP or -LH testosterone synthesis. In mature Leydig cells, the PG inhibition has no effect on testosterone production both in the absence of hCG and in the presence of weak amounts of hCG but increases it in the presence of subsaturating hCG concentrations. Whatever the age, the inhibition of PG synthesis is ineffective in the presence of saturating amounts of either hCG or (Bu)2cAMP. These effects are maintained in the presence of MIX, PMA, but are not observed in the presence of 22R-hydroxycholesterol. Therefore, our results suggest that in rat Leydig cells, the inhibition of PG synthesis affects the signal transduction at a step distal to cyclic AMP and more precisely, the cholesterol supply to the mitochondria by acting on its cellular distribution (free and esterified cholesterol).

Mucin and proteoglycan functions in embryo implantation

Embryo implantation is a complex series of events that involves changes in pattern of expression of embryonic as well as uterine cell surface components. In the case of the embryo, these changes are driven by the developmental program. In the case of the uterus, these changes are triggered by both maternal hormonal influences as well as embryo-derived factors. Aspects of the implantation process vary among species; however, interaction between the external surface of the embryonic trophectoderm and the apical surface of the lumenal uterine epithelium is a common event. Progress is being made in defining the molecular players in these cell surface interactions. Large-molecular-weight mucin glycoproteins such as MUC1 are present at the apical surface of the uterine epithelium under most conditions. Under most circumstances, these mucins appear to protect the mucosal surface from infection and the action of degradative enzymes. These mucins are antiadhesive and also appear to represent a barrier to embryo attachment. Consistent with this model, reduction of mucin expression is observed in uterine lumenal epithelia in many species. Nonetheless, mucin expression persists in the human uterus during the proposed receptive phase. It is possible that mucin loss is localized to implantation sites in humans. Alternatively, mucins may function differently within the context of human implantation than in other species. Studies primarily performed in mice indicate that heparan sulfate proteoglycans, in particular, perlecan, appears on the exterior trophectodermal surface coincident with the acquisition of attachment competence. Various in vitro studies indicate that heparan sulfate proteoglycans support embryo attachment activity that may represent an early event in embryo-uterine interaction. Uterine epithelia cells express several complementary heparan sulfate-binding proteins that may participate in these attachment processes. Use of molecular genetic approaches in mouse models, as well as careful studies of the expression and function of these molecules in the context of implantation in various species are beginning to shed light on the key molecular events of implantation.

A peptide sequence of heparin/heparan sulfate (HP/HS)-interacting protein supports selective, high affinity binding of HP/HS and cell attachment

We previously have identified a novel cell surface heparan sulfate/heparin (HS/HP)-interacting protein (HIP) found in human uterine epithelia and a variety of other human epithelial and endothelial cells and cell lines (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823; Rohde, L. H., Julian, J., Babaknia, A., and Carson, D. D. (1996) J. Biol. Chem. 271, 11824-11830). The amino acid sequence predicted for HIP revealed a potential HS/HP-binding motif. In the present studies, a synthetic peptide corresponding to this putative HS/HP-binding motif, HIP peptide, was synthesized and examined with regard to its HS/HP binding and cell attachment promoting activity. Results using solid phase binding assays demonstrate that HIP peptide binds HS/HP with high selectivity and has high affinity for bulk HP (50% saturation congruent with 300 nM) and even higher affinity for a subset of polysaccharides found in commercial [3H]HP (half-saturation congruent with 10 nM). Moreover, HIP peptide binds subsets of cell and extracellular matrix-associated HS and dermatan sulfate expressed by RL95 cells, a human uterine adenocarcinoma cell line. HIP peptide also binds a similar fraction of HS as well as dermatan sulfate expressed by JAR cells, a human choriocarcinoma cell line. In contrast to binding of cell- or extracellular matrix-associated HS, HIP peptide does not bind secreted or released forms of HS or DS from either RL95 or JAR cells to a significant extent. HS species that bind to HIP peptide are generally larger, have a higher negative charge density, and have a larger proportion of di- and trisulfated disaccharide units than HS species that do not bind to HIP peptide, demonstrating structural differences among these polysaccharides. This same peptide supports HS-dependent JAR cell attachment. Collectively, these data demonstrate that a linear peptide sequence found within HIP can account, at least in part, for the HS/HP binding and cell adhesion promoting activities of this protein.

The heparin-binding lectin from ovine placenta: purification and identification as histone H4

The heparin-binding lectin complex from ovine placental cotyledons was purified by affinity chromatography on heparin-agarose column. It showed three protein bands, which had molecular weights of 13000, 15000 and 17000 by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the presence of DNA by agarose gel electrophoresis. The protein components of the complex were separated by reverse-phase HPLC. The minimum inhibitory concentrations of glycosaminoglycans were significantly different for the lectin complex and the separated proteins, suggesting affinity changes upon DNA binding. The haemagglutinating activity specificity allowed the characterization of the fraction with a molecular weight of 13000 as the heparin-binding lectin. This protein was identified as histone H4 by internal sequencing, thus showing that this is the histone responsible for the heparin-binding property of the complex. The accompanying proteins were tentatively identified as histones H2A and H2B.

Expression of heparan sulfate proteoglycan (perlecan) in the mouse blastocyst is regulated during normal and delayed implantation

Previous studies have shown that expression of the heparan sulfate proteoglycan, perlecan, on the external trophectodermal cell surfaces of mouse blastocysts increases during acquisition of attachment competence. However, it is not clear if this change in perlecan protein expression also is reflected at the level of perlecan mRNA expression. In the present investigation, the spatial and temporal patterns of perlecan mRNA expression in the mouse embryo during the periimplantation period were examined by in situ hybridization and reverse transcriptase-polymerase chain reaction. In addition, a delayed implantation model was used to determine the expression of perlecan mRNA and protein in dormant and estrogen-activated hatched blastocysts. The results demonstrate that perlecan mRNA expression is low in morulae, but increases in Day 4 blastocysts, attaining maximal expression in Day 4.5 attachment-competent blastocysts. In contrast, perlecan mRNA is detected in both the dormant and estrogen-activated delayed blastocysts; however, within 12 hr of blastocyst activation by estrogen, both perlecan protein and heparan sulfate chain expression markedly increase. Taken together, these results suggest that during normal development perlecan mRNA expression increases with the acquisition of attachment competence. Moreover, perlecan protein expression also is attenuated during delayed implantation and appears to increase in response to nidatory estrogen, perhaps via the increased translation of preexisting perlecan mRNA.

Cell surface expression of HIP, a novel heparin/heparan sulfate binding protein, of human uterine epithelial cells and cell lines

Previous studies established that uterine epithelial cells and cell lines express cell surface heparin/heparan sulfate (HP/HS)-binding proteins (Wilson, O., Jacobs, A. L., Stewart, S., and Carson, D. D. (1990) J. Cell. Physiol. 143, 60-67; Raboudi, N., Julian, J., Rohde, L. H., and Carson, D. D. (1992) J. Biol. Chem. 267, 11930-11939). The accompanying paper (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823) describes the cloning of a full-length cDNA corresponding to a candidate cell surface HP/HS interacting protein, HIP, expressed by a variety of human epithelia. A synthetic peptide was synthesized corresponding to an amino acid sequence predicted from the cDNA sequence and used to prepare a rabbit polyclonal antibody. This antibody reacted with a protein with an apparent Mr of 24,000 by SDS-polyacrylamide gel electrophoresis that was highly enriched in the 100,000 x g particulate fraction of RL95 cells. This molecular weight is similar to that of the protein expressed by 3T3 cells transfected with HIP cDNA. HIP was solubilized from this particulate fraction with NaCl concentrations > or = 0.8 M demonstrating a peripheral association consistent with the lack of a membrane spanning domain in the predicted cDNA sequence. HIP was not released by heparinase digestion suggesting that the association is not via membrane-bound HS proteoglycans. NaCl-solubilized HIP bound to heparin-agarose in physiological saline and eluted with NaCl concentrations of 0.75 M and above. Furthermore, incubation of 125I-HP with transblots of the NaCl-solubilized HIP preparations separated by two-dimensional gel electrophoresis demonstrated direct binding of HP to HIP. Indirect immunofluorescence studies demonstrated that HIP is expressed on the surfaces of intact RL95 cells. Binding of HIP antibodies to RL95 cell surfaces at 4 degrees C was saturable and blocked by preincubation with the peptide antigen. Single cell suspensions of RL95 cells formed large aggregates when incubated with antibodies directed against HIP but not irrelevant antibodies. Finally, indirect immunofluorescence studies demonstrate that HIP is expressed in both lumenal and glandular epithelium of normal human endometrium throughout the menstrual cycle. In addition, HIP expression increases in the predecidual cells of post-ovulatory day 13-15 stroma. Collectively, these data indicate that HIP is a membrane-associated HP-binding protein expressed on the surface of normal human uterine epithelia and uterine epithelial cell lines.

Identification of a novel glycosaminoglycan core-like molecule. II. Alpha-GalNAc-capped xylosides can be made by many cell types

The accompanying article (Manzi, A., Salimath, P. V., Spiro, R. C., Keifer, P. A., and Freeze, H. H. (1995) J. Biol. Chem. 270, 9154-9163) reported the complete structure of a novel molecule made by human melanoma cells incubated with 1 mM 4-methylumbelliferyl-beta Xyl (Xyl beta MU). The product resembles a common pentasaccharide core region found in chondroitin/dermatan sulfate glycosaminoglycans, except that a terminal alpha-Gal-NAc residue is found in a location normally occupied by beta-GalNAc in these chains or alpha-GlcNAc in heparan sulfate chains. In this paper we show that several other human cancer cell lines and Chinese hamster ovary cells also make alpha-GalNAc-capped xylosides. The [6-3H]galactose-labeled Xyl beta MU product binds to immobilized alpha-GalNAc-specific lectin from Helix pomatia and the binding is competed by GalNAc, but not by Glc. Binding to the lectin is destroyed by digestion with alpha-N-acetylgalactosaminidase, but not beta-hexosaminidase. The nature of the aglycone influences the amount and relative proportion of this material made, with p-nitrophenyl-beta-xyloside being a better promoter of alpha-GalNAc-terminated product than Xyl beta MU. This novel oligosaccharide accounts for 45-65% of xyloside-based products made by both human melanoma and Chinese hamster ovary cells when they are incubated with 30 microM Xyl beta MU, but at 1 mM both the total amount and the proportion decreases to only 5-10%. In both cell lines this product is replaced by a corresponding amount of Sia alpha 2,3Gal beta 4Xyl beta MU. Preferential synthesis of the alpha-GalNAc-capped material at very low xyloside concentration argues that it is a normal biosynthetic product and not an experimental artifact. This pentasaccharide may be a previously unrecognized intermediate in glycosaminoglycan chain biosynthesis. Since this alpha-GalNAc residue occurs at a position that determines whether chondroitin or heparan chains are added to the acceptor, it may influence the timing, type, and extent of further chain elongation.

Inhibition of proteoglycan synthesis induces an increase in follicle stimulating hormone (FSH)-stimulated estradiol production by immature rat Sertoli cells

In order to define the possible involvement of proteoglycans (PG) in the regulation of Sertoli cell functions, we have examined the effect of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis, on follicle stimulating hormone (FSH)-dependent estradiol production by immature rat Sertoli cells. Addition of PNPX to the culture medium induced a dose-dependent inhibition of 35S-labeled PG synthesis in Sertoli cells both in the medium and the cell layer. Simultaneously there was a drastic increase in 35S-labeled secreted glycosaminoglycans. By 1 mM PNPX, syntheses of chondroitin sulfate proteoglycans released into culture medium and of heparan sulfate proteoglycans associated with the cell layer were 35% of values from untreated cells. Simultaneously, PNPX induced a twofold (mean of seven experiments, range 17-250%) enhancement of FSH (100 ng/ml)-stimulated estradiol production. In each individual experiment, there was an inverse relationship between the amplitude of PNPX-induced increase in FSH responsiveness and the FSH capability to stimulate basal estradiol production in cultured rat Sertoli cells. The effect of PNPX on FSH-stimulated aromatase activity was not mimicked by para-nitrophenyl-beta-D-galactoside, a structural analog of PNPX that has no effect on PG synthesis. The (Bu)2cAMP-stimulated estradiol synthesis was not modified in the presence of PNPX. Moreover, PNPX enhancement of FSH-stimulated estradiol synthesis disappeared when Sertoli cells were cultured in the presence of 1-methyl-3-isobutylxanthine, an inhibitor of phosphodiesterase activity. These findings suggest that inhibition of PG synthesis under PNPX conditions did not affect signal transduction steps distal to cAMP but rather decreased the phosphodiesterase activity in Sertoli cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell surface glycoconjugates as modulators of embryo attachment to uterine epithelial cells

Attachment of mammalian embryos to the uterine wall involves the coordinated development of both the embryo and the uterine epithelium to an attachment-competent state. This coordination is achieved directly or indirectly through the actions of ovarian steroids. Acquisition of attachment competence is proposed to reflect two processes. The first is the loss of non-adhesive glycoproteins at the cell surface of embryos, e.g. zona pellucida subunits, as well as uterine epithelial cells, e.g. mucin glycoproteins. The second process is the functional expression of complementary adhesion-promoting molecules at these cell surfaces. A series of studies indicates that heparan sulfate proteoglycans and their corresponding binding sites can play an important role in the initial stage of embryo attachment to the uterine surface.

Alpha- and beta-xylosides modulate the synthesis of fibronectin and thrombospondin-1 by endothelial cells

We have previously shown that both p-nitrophenyl-alpha-D-xylopyranoside (alpha-xyloside) and p-nitrophenyl-beta-D-xylopyranoside (beta-xyloside) inhibit endothelial morphogenesis in vitro. In order to determine the mechanism for this inhibition, we have now investigated the effects of these compounds on the synthesis of proteoglycans and proteins by bovine aortic endothelial cells. Consistent with their well-recognised modes of action, beta-xyloside, but not alpha-xyloside, enhanced the secretion of free glycosaminoglycans into the medium. Furthermore, although both xylosides inhibited proteoglycan deposition into the cell layer/matrix, only beta-xyloside altered the nature of the proteoglycans synthesised by the cells. Both alpha- and beta-xylosides markedly inhibited total protein synthesis by endothelial cells in the absence of any effect on cell growth. This inhibition was time- and dose-dependent and was not due to the enzymatic release of p-nitrophenol by the cells. The synthesis of fibronectin and thrombospondin-1 were specifically and differentially modulated by both alpha- and beta-xylosides. That is, xylosides markedly reduced fibronectin levels relative to other proteins in both the medium and the cell layer/matrix. In contrast, the relative levels of thrombospondin-1 were increased in the xyloside-treated cultures both in terms of mRNA and protein. These studies demonstrate novel effects of xylosides on protein synthesis. Furthermore, they suggest that the inhibition of endothelial morphogenesis by xylosides may be due to the actions of these compounds on the synthesis of specific proteins.

Implantation and decidualization in rodents

This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.

Heparin-like glycosaminoglycans participate in binding of a human trophoblastic cell line (JAR) to a human uterine epithelial cell line (RL95)

In vitro studies in our laboratory have indicated that heparan sulfate proteoglycans (HSPGs) play an important role in murine embryo implantation. In order to investigate the potential function of HSPGs in human implantation, two human cell lines (RL95 and JAR) were used to model uterine epithelium and embryonal trophectoderm, respectively. A heterologous cell-cell adhesion assay was developed to determine if binding of JAR cells to RL95 cells was heparan sulfate-dependent. Labeled, single cell suspensions of JAR cells attached to confluent monolayers of RL95 cells in a dose- and time-dependent manner. Heparin-like glycosaminoglycans and JAR cell proteoglycans competitively inhibited JAR cell adhesion to RL95 cells by 50% or more. A panel of chemically modified heparins were used to demonstrate that O-sulfation and amino group substitution were critical for inhibition of cell-cell adhesion. Treatment with chlorate, an inhibitor of ATP-sulfurylase, resulted in a 56% reduction in cell-cell binding compared to untreated controls. Heparinase and chondroitinase ABC markedly inhibited JAR-RL95 binding, while chondroitinase AC had no significant effect. These observations indicated that HSPGs as well as dermatan sulfate-containing proteoglycans participated in cell-cell binding. Collectively, these results indicate that initial binding interactions between JAR and RL95 cells is mediated by cell surface glycosaminoglycans (GAGs) with heparin-like properties (i.e., heparan sulfate and dermatan sulfate). These observations are consistent with an important role for HS and heparin-like GAGs as well as their corresponding binding sites in early stages of human trophoblast-uterine epithelial cell binding.

Altered proteoglycan synthesis via the false acceptor pathway can be dissociated from beta-D-xyloside inhibition of proliferation

beta-D-Xylosides have been used to perturb proteoglycan (PG) synthesis to elucidate the function of PGs in a number of cellular processes, including proliferation, migration, and differentiation. This study was designed to examine whether specific xylosides affect the proliferation of several different cell types and, if so, whether this effect is dependent on altered PG synthesis via the false acceptor pathway. Both methylumbelliferyl beta-D-xylopyranoside and p-nitrophenyl beta-D-xylopyranoside (PNP beta-xyloside) inhibit cell proliferation and modulate PG synthesis; however, the alpha form of PNP xyloside which does not perturb PG synthesis inhibits the proliferation of cultured cells on a molar basis equally as well as the beta form. Conversely, beta-methyl xylopyranoside stimulates the synthesis of free glycosaminoglycan chains equally as well as PNP beta-xyloside and yet has no measurable effect on cell proliferation at comparable doses, indicating that cells can grow normally while experiencing disruption of their proteoglycan metabolism. At doses ranging from 0.5 to 5 mM, PNP beta-xyloside arrests cells in the G1 phase of the cell cycle at the same time point as serum starvation. It also delays the exist of cycling cells from the S phase. This treatment is not cytotoxic and is rapidly reversed by the replacement of PNP beta-xyloside containing medium with control medium. Dimethyl sulfoxide, the most commonly used solvent for beta-xyloside in proteoglycan studies, potentiates the inhibitory effect of PNP beta-xyloside on cell proliferation. These results indicate that the perturbation of PG synthesis via the false acceptor pathway can be uncoupled from control of cell proliferation.

Expression of externally-disposed heparin/heparan sulfate binding sites by uterine epithelial cells

A class of high-affinity binding sites that preferentially bind heparin/heparan sulfate have been identified on the external surfaces of mouse uterine epithelial cells cultured in vitro. [3H]Heparin binding to these surfaces was time-dependent, saturable, and was blocked specifically by the inclusion of unlabeled heparin or endogenous heparan sulfate in the incubation medium. A variety of other glycosaminoglycans did not compete for these binding sites. The presence of sulfate on heparin influenced, but was not essential for, recognition of the polysaccharide by the cell surface binding sites. [3H]-Heparin bound to the cell surface was displaceable by unlabeled heparin, but not chondroitin sulfate. Treatment of intact cells on ice with trypsin markedly reduced [3H]heparin binding, indicating that a large fraction of the surface binding sites were associated with proteins. Scatchard analyses revealed a class of externally disposed binding sites for heparin/heparan sulfate exhibiting an apparent Kd of approximately 50 nM and present at a level of 1.3 x 10(6) sites per cell. Approximately 9-14% of the binding sites were detectable at the apical surface of cells cultured under polarized conditions in vitro. Detachment of cells from the substratum with EDTA stimulated [3H]heparin binding to cell surfaces. These observations suggested that most of the binding sites were basally distributed and were not primarily associated with the extracellular matrix. Collectively, these observations indicate that specific interactions with heparin/heparan sulfate containing molecules can take place at both the apical and basal cell surfaces of uterine epithelial cells. This may have important consequences with regard to embryo-uterine and epithelial-basal lamina interactions.

A calcium-binding, asparagine-linked oligosaccharide is involved in skeleton formation in the sea urchin embryo

We have previously identified a 130-kD cell surface protein that is involved in calcium uptake and skeleton formation by gastrula stage embryos of the sea urchin Strongylocentrotus purpuratus (Carson et al., 1985. Cell. 41:639-648). A monoclonal antibody designated mAb 1223 specifically recognizes the 130-kD protein and inhibits Ca+2 uptake and growth of the CaCO3 spicules produced by embryonic primary mesenchyme cells cultured in vitro. In this report, we demonstrate that the epitope recognized by mAb 1223 is located on an anionic, asparagine-linked oligosaccharide chain on the 130-kD protein. Combined enzymatic and chemical treatments indicate that the 1223 oligosaccharide contains fucose and sialic acid that is likely to be O-acetylated. Moreover, we show that the oligosaccharide chain containing the 1223 epitope specifically binds divalent cations, including Ca+2. We propose that one function of this negatively charged oligosaccharide moiety on the surfaces of primary mesenchyme cells is to facilitate binding and sequestration of Ca+2 ions from the blastocoelic fluid before internalization and subsequent deposition into the growing CaCO3 skeleton.