Response of stratified cultures of human keratinocytes to disruption of proteoglycan synthesis by p-nitrophenyl-beta-D-xylopyranoside

Perturbation of the heparin/heparin-sulfate interactome of human breast cancer cells modulates pro-tumourigenic effects associated with PI3K/Akt and MAPK/ERK signalling

Heparansulfate-proteoglycans (HSPGs) interact via their polyanionic heparansulfate (HS) side chains with a variety of proteins on the cell surface or within the extracellular matrix membrane. The large number of heparin/HS binding proteins form a highly interconnected functional network, which has been termed as the heparin/HS interactome and is functionally linked to physiological and pathological processes. The aim of this study was to investigate the global effect of these protein-HSPG interactions on the tumourigenicity of two breast cancer cell lines (MCF-7 and MDA-MB-231). Cancer cells were cultured in serum-free medium and treated with a concentration of heparin which was capable of modulating HS/ligand interaction. Microarray analysis of MCF-7 cells cultured under these conditions showed that expression of 105 of 1,357 genes potentially related to the pathogenesis of breast neoplasm was significantly altered by heparin treatment. The changes in gene expression correlated with a less tumourigenic phenotype, including reduction of cell adhesive, invasive and migratory properties. These effects were associated with an inhibition of the PI3K/Akt and Raf/MEK/ERK signalling pathways. The modulatory effect of heparin on HS-associated activity was confirmed with one example of heparin/HS interactomes, transforming growth factor β (TGFβ). The innate TGFβ activity of MCF-7 cells was reduced by heparin treatment, with specific interruption of the TGFβ-Smad signalling pathway. The pro-tumourigenic contribution of the heparin/HS interactomes was verified in cells in which HSPG synthesis was blocked using β-xyloside. In conclusion, the interaction between cell surface HPSGs and innate heparin/HS interactomes makes a significant contribution to the tumourigenicity.

Transcriptional profiling identifies genes induced by hepatocyte-derived extracellular matrix in metastatic human colorectal cancer cell lines

The milieu of the liver, and in particular hepatocyte-derived extracellular matrix (hECM), is a critical factor regulating development of liver metastases of colorectal cancer (CRC) cells. The present study has investigated genes altered by hECM in CRC cells and particularly by heparan sulfate chains of hepatocyte proteoglycans. Gene profiling analysis shows that after 2 days on hECM, 226 genes are up-regulated more than 2-fold in strongly metastatic SM cells, including genes involved in growth arrest and apoptosis, signal transduction, cell migration, proliferation, communication and angiogenesis, with activation of the erbB signaling network and p53 effectors. Genes down-regulated by hECM include genes involved in lipogenesis and the S phase of the cell cycle. Further studies exploring the kinetics of gene expression after 4 and 7 days culture on hECM show induction of EGF family members and of stem cell markers. In particular, hECM, but not collagen, increases mRNA expression of HB-EGF and colon stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5). Expression of these genes is not induced by hECM depleted of the heparan sulfate chains of proteoglycans. Lastly, a specific cell population positive for cancer stem cell (CSC) markers LGR5, epCAM and CD133, but negative for CD44, appears after 7 days culture on hECM, a population which is reduced by 50 % in cells grown on heparan sulfated-depleted hECM. Collectively, the data suggest that hECM induces growth factors and receptors regulating proliferation of metastatic CRC in the liver and offers a growth advantage for specific populations expressing CSC markers.

Heparan sulfate-dependent ERK activation contributes to the overexpression of fibrotic proteins and enhanced contraction by scleroderma fibroblasts

OBJECTIVE

To investigate the contribution of heparan sulfate proteoglycan and Ras/MEK/ERK to the overexpression of profibrotic proteins and the enhanced contractile ability of dermal fibroblasts from patients with systemic sclerosis (SSc; scleroderma).

METHODS

The effects of the MEK/ERK inhibitor U0126, the heparan sulfate side chain formation inhibitor beta-xyloside, and soluble heparin on the overexpression of profibrotic genes were compared in fibroblasts from lesional skin of patients with diffuse SSc and fibroblasts from healthy control subjects. Identified protein expressions were compared with the contractile abilities of fibroblasts while they resided within a collagen lattice. Forces generated were measured using a culture force monitor.

RESULTS

Inhibiting MEK/ERK with U0126 significantly reduced expression of a cohort of proadhesive and procontractile proteins that normally are overexpressed by scleroderma fibroblasts, including integrin alpha4 and integrin beta1. Antagonizing heparan sulfate side chain formation with beta-xyloside or the addition of soluble heparin prevented ERK activation, in addition to reducing the expression of these proadhesive/contractile proteins. Treatment with either U0126, beta-xyloside, or heparin resulted in a reduction in the overall peak contractile force generated by dermal fibroblasts. Blocking platelet-derived growth factor receptor with Gleevec (imatinib mesylate) reduced overall contractile ability and the elevated syndecan 4 expression and ERK activation in SSc fibroblasts.

CONCLUSION

The results of this study suggest that heparan sulfate-dependent ERK activation contributes to the enhanced contractile ability demonstrated by dermal fibroblasts from lesional skin of patients with scleroderma. These results are consistent with the notion that the MEK/ERK procontractile pathway is dysregulated in scleroderma dermal fibroblasts. Additionally, the results suggest that antagonizing the MEK/ERK pathway is likely to modulate heparan sulfate proteoglycan activity, which in turn may have a profound effect on the fibrotic response in SSc.

Serglycin proteoglycan is sorted into zymogen granules of rat pancreatic acinar cells

Serglycin is known as a secretory granule proteoglyean in hematopoietic cells. In this study we identified a high-molecular-weight molecule in aggregated content proteins of zymogen granules of pancreatic acinar cells. The amino acid composition of the isolated protein showed high similarity to serglycin proteoglycan core protein. To confirm the expression of serglycin proteoglycan in pancreatic acinar cells we cloned the rat pancreas cDNA of serglycin core protein and detected the serglycin mRNA in pancreas tissue and AR4-2J cells by reverse transcription-PCR. In AR4-2J cells, transfected with serglycin fused to green fluorescent protein (EGFP), serglycin localized within a web-like pattern in the perinuclear space as well as with a punctate pattern distributed in the cytoplasm. The perinuclear structures colocalized with the Golgi membrane-associated protein p115 and the punctate structures with the secretory enzyme procarboxypeptidase A, indicating that the serglycin-EGFP fusion protein travels through compartments of the secretory pathway and is sorted into secretory granules. Using an antiserum against serglycin core protein immunofluorescence as well as immunogold electron microscopy analysis conrirmed the subcellular distribution of serglycin proteoglycan in zymogen granules of pancreatic acinar cells. To prevent glycosylation of serglycin core protein we incubated AR4-2J cells with 2 mM p-nitrophenyl-beta-D-xylopyranoside (PNP-xyloside), which serves as alternate substrate for glycosaminoglycan chain attachment. Furthermore, we deleted the serine/glycine repeat region in the serglycin core protein. In both approaches the transfected serglycin-EGFP fusion protein could be detected predominantly in perinuclear Golgi membrane structures, while in control cells the serglycin fusion protein was mostly sorted into the secretory granules. Additionally, we show that sorting of secretory enzymes like amylase

The folded modules of aggrecan G3 domain exert two separable functions in glycosaminoglycan modification and product secretion

Aggrecan is the major proteoglycan in the extracellular matrix of cartilage. A notable exception is nanomelic cartilage, which lacks aggrecan in its matrix. The example of nanomelia and other evidence leads us to believe that the G3 domain plays an important role in aggrecan processing, and it has indeed been confirmed that G3 allows glycosaminoglycan (GAG) chain attachment and product secretion. However, it is not clear how G3, which contains at least a carbohydrate recognition domain (CRD) and a complement binding protein (CBP) motif, plays these two functional roles. The present study was designed to dissect the mechanisms of this phenomenon and specially 1) to determine the effects of various cysteine residues in GAG modification and product secretion as well as 2) to investigate which of the two processing events is the critical step in the product processing. Our studies demonstrated that removal of the two amino-terminal cysteines in the CRD motif and the single cysteine in the amino terminus of CBP inhibited secretion of CRD and CBP. Use of the double mutant CRD construct also allowed us to observe a deviation from the usual strict coupling of GAG modification and product secretion steps. The presence of a small chondroitin sulfate fragment overcame the secretion-inhibitory effects once the small chondroitin sulfate fragment was modified by GAG.

Interactions of fibrillin-1 with heparin/heparan sulfate, implications for microfibrillar assembly

Fibrillin-1 is a major constituent of the 10-12 nm extracellular microfibrils. Here we identify, characterize, and localize heparin/heparan sulfate-binding sites in fibrillin-1 and report on the role of such glycosaminoglycans in the assembly of fibrillin-1. By using different binding assays, we localize two calcium-independent heparin-binding sites to the N-terminal (Arg(45)-Thr(450)) and C-terminal (Asp(1528)-Arg(2731)) domains of fibrillin-1. A calcium-dependent-binding site was localized to the central (Asp(1028)-Thr(1486)) region of fibrillin-1. Heparin binding to these sites can be inhibited by a highly sulfated and iduronated form of heparan sulfate but not by chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate, demonstrating that the heparin binding regions represent binding domains for heparan sulfate. When heparin or heparan sulfate was added to cultures of skin fibroblasts, the assembly of fibrillin-1 into a microfibrillar network was significantly reduced. Western blot analysis demonstrated that this effect was not due to a reduced amount of fibrillin-1 secreted into the culture medium. Inhibition of the attachment of glycosaminoglycans to core proteins of proteoglycans by beta-d-xylosides resulted in a significant reduction of the fibrillin-1 network. These studies suggest that binding of fibrillin-1 to proteoglycan-associated heparan sulfate chains is an important step in the assembly of microfibrils.

The mechanism of cell death in human cultured colon adenocarcinoma cell line COLO 201 induced by beta-D-N-acetylglucosaminyl-p-nitrophenol

COLO 201, human colon adenocarcinoma cells were incubated with artificial primers, p-nitrophenyl-glycoside derivatives at 1.0 mmol (mM) in the medium containing 10% fetal bovine serum to detect sugar chain elongation. However, when p-nitrophenyl-beta-N-acetylglucosamine (beta-GlcNAc-PNP) was added, the medium changed color to yellow and the cells were dead. To explain this finding, the cells were incubated with 1.0 mM each of beta-GlcNAc-PNP and 4-methylumbelliferyl-beta-N-acetylglucosamine, then the number of living cells was measured in a time course. In beta-GlcNAc-PNP, the living cells were decreased at 24 hours. The cells were survived with N-acetylglucosamine, whereas in the presence of p-nitrophenol (PNP) the living cells were decreased. It was suggested that PNP released from beta-GlcNAc-PNP induced the cell death. Activity of beta-D-N-acetylglucosaminidase was detected in fetal bovine serum. It was shown that PNP induced the cell death in time-and-dose dependent manner. Genomic DNA from COLO 201 analyzed by agarose gel electrophoresis was fragmentated. PNP analogues were tested for toxicity, and the results suggested that the phenolic OH-group linked to benzene ring and nitro-group linked to the structure in para-form (PNP) was the most effective.

The L1 major capsid protein of human papillomavirus type 11 recombinant virus-like particles interacts with heparin and cell-surface glycosaminoglycans on human keratinocytes

The L1 major capsid protein of human papillomavirus (HPV) type 11, a 55-kDa polypeptide, forms particulate structures resembling native virus with an average particle diameter of 50-60 nm when expressed in the yeast Saccharomyces cerevisiae. We show in this report that these virus-like particles (VLPs) interact with heparin and with cell-surface glycosaminoglycans (GAGs) resembling heparin on keratinocytes and Chinese hamster ovary cells. The binding of VLPs to heparin is shown to exhibit an affinity comparable to that of other identified heparin-binding proteins. Immobilized heparin chromatography and surface plasmon resonance were used to show that this interaction can be specifically inhibited by free heparin and dextran sulfate and that the effectiveness of the inhibitor is related to its molecular weight and charge density. Sequence comparison of nine human L1 types revealed a conserved region of the carboxyl terminus containing clustered basic amino acids that bear resemblance to proposed heparin-binding motifs in unrelated proteins. Specific enzymatic cleavage of this region eliminated binding to both immobilized heparin and human keratinocyte (HaCaT) cells. Removal of heparan sulfate GAGs on keratinocytes by treatment with heparinase or heparitinase resulted in an 80-90% reduction of VLP binding, whereas treatment of cells with laminin, a substrate for alpha6 integrin receptors, provided minimal inhibition. Cells treated with chlorate or substituted beta-D-xylosides, resulting in undersulfation or secretion of GAG chains, also showed a reduced affinity for VLPs. Similarly, binding of VLPs to a Chinese hamster ovary cell mutant deficient in GAG synthesis was shown to be only 10% that observed for wild type cells. This report establishes for the first time that the carboxyl-terminal portion of HPV L1 interacts with heparin, and that this region appears to be crucial for interaction with the cell surface.

CD44 expression on epidermal melanocytes

We examined CD44 expression on melanocytes to begin to understand what role CD44 might have in the normal behavior of melanocytes and to provide a basis for comparing CD44 expression in melanoma cells. CD44 was expressed on the entire surface of melanocytes and accentuated at the tips of dendritic processes. Two predominant forms of CD44 are expressed on cultured human foreskin melanocytes. One form has the covalent addition of chondroitin sulfate, whereas the other form has no chondroitin sulfate. Both use the hematopoietic, or CD44H, core protein. Using polymerase chain reaction primers that span the site where alternative splicing of CD44 occurs, we found only the cDNA coding CD44H. 12-O-Tetradecanoylphorbol 13-acetate increases the size of the chondroitin sulfate chain(s) attached to CD44 but not the proportion of CD44 molecules that carry chondroitin sulfate. Ninety percent of proteoglycans on melanocytes are chondroitin sulfate proteoglycans, and the CD44 chondroitin sulfate proteoglycan represented 10% of that total. These data show that CD44H is expressed as a "part-time" chondroitin sulfate proteoglycan on normal cultured melanocytes.