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Estradiol (E2)-estrogen receptor (ER) actions are implicated in initiation, growth and progression of hormone-dependent breast cancer. Crosstalk between ERs, epidermal growth factor receptor (EGFR) and/or insulin-like growth factor receptor (IGFR) is critical for the observed resistance to endocrine therapies. Cell surface heparan sulfate proteoglycans (HSPGs) are principal mediators of cancer cell properties and the E2-ER pathway as well as those activated by EGFR and IGFR have significant roles in regulating the expression of certain cell surface HSPGs, such as syndecan-2 (SDC-2), syndecan-4 (SDC-4) and glypican-1. In this study, we therefore evaluated the role of EGFR-IGFR signaling on the constitutive expression and E2-mediated expression of ERs and HSPGs as well as the effect of E2-ERs and IGFR/EGFR-mediated cell migration in ERα+ (MCF-7) and ERβ+ (MDA-MB-231) breast cancer cells using specific intracellular inhibitors of EGFR and IGFR. We report that the expression of ERα is mainly enhanced by IGFR, whereas ERβ expression is mainly coordinated by EGFR. Moreover, constitutive SDC-2 expression in ERα+ and ERβ+ cells is mainly mediated through the IGFR, whereas in ERα+ E2-treated cells EGFR is the active one. In contrast, SDC-4 expression is regulated by IGFR in the presence and absence of E2. E2 also seems to diminish the inhibitory effect of EGFR and IGFR inhibitors in breast cancer cell migration. These data suggest that the coordinated action of ERs with EGFR and/or IGFR is of crucial importance, providing potential targets for designing and developing novel multi-potent agents for endocrine therapies.

Glycosaminoglycans are natural heteropolysaccharides that are present in every mammalian tissue. They are composed of repeating disaccharide units that consist of either sulfated or non-sulfated monosaccharides. Their molecular size and the sulfation type vary depending on the tissue, and their state either as part of proteoglycan or as free chains. In this regard, glycosaminoglycans play important roles in physiological and pathological conditions. During recent years, cell biology studies have revealed that glycosaminoglycans are among the key macromolecules that affect cell properties and functions, acting directly on cell receptors or via interactions with growth factors. The accumulated knowledge regarding the altered structure of glycosaminoglycans in several diseases indicates their importance as biomarkers for disease diagnosis and progression, as well as pharmacological targets. This review summarizes how the fine structural characteristics of glycosaminoglycans, and enzymes involved in their biosynthesis and degradation, are involved in cell signaling, cell function and cancer progression. Prospects for glycosaminoglycan-based therapeutic targeting in cancer are also discussed.

Parathyroid hormone (PTH)(1-34), which has been established to have a dual effect on bone metabolism, was recently found to regulate osteosarcoma cell migration. A significant part of the bone anabolic action of PTH(1-34) is attributed to fibroblast growth factor (FGF)-2 stimulation. Furthermore, it was recently suggested that the FGF-proteoglycan axis may form an extracellular matrix-related regulatory feedback loop that controls osteoblastic lineage cell proliferation and execution of the osteogenic program. In this study, we investigated the possible participation of FGF-2 signaling in PTH(1-34)-dependent osteosarcoma cell migration. FGF-2 treatment of osteosarcoma cells resulted in a significant increase (P ≤ 0.01) in MG63 cell migration, similar to that caused by PTH(1-34). mRNA expression analysis of cells treated with PTH(1-34) showed a strong increase in FGF-2 transcript levels (P = 0.0015). Interestingly, the addition of FGF-2 to MG63 cells led to significant downregulation of small leucine-rich proteoglycan biglycan expression at both the mRNA (P ≤ 0.0001) and protein (60%) levels. In order to examine the significance of biglycan on MG63 cell migration, transfection with short interfering RNA specific for biglycan was performed, resulting in a significant increase (P ≤ 0.01) in the migration capacity of biglycan-deficient MG63 cells. In contrast, exogenous human recombinant biglycan strongly inhibited the migration of these cells (P ≤ 0.01). Finally, a direct correlation between PTH(1-34) action and biglycan expression was established by the finding of a significant decrease (P ≤ 0.01) in biglycan transcript levels in PTH(1-34)-treated cells. To summarize, the present study demonstrates a novel cooperative mechanism of PTH(1-34) and FGF-2 action that results in specific alteration of the biglycan extracellular matrix content to regulate osteosarcoma cell migration.

The expression of proteoglycans (PGs), essential macromolecules of the tumor microenvironment, is markedly altered during malignant transformation and tumor progression. Synthesis of stromal PGs is affected by factors secreted by cancer cells and the unique tumor-modified extracellular matrix may either facilitate or counteract the growth of solid tumors. The emerging theme is that this dual activity has intrinsic tissue specificity. Matrix-accumulated PGs, such as versican, perlecan and small leucine-rich PGs, affect cancer cell signaling, growth and survival, cell adhesion, migration and angiogenesis. Furthermore, expression of cell-surface-associated PGs, such as syndecans and glypicans, is also modulated in both tumor and stromal cells. Cell-surface-associated PGs bind various factors that are involved in cell signaling, thereby affecting cell proliferation, adhesion and motility. An important mechanism of action is offered by a proteolytic processing of cell-surface PGs known as ectodomain shedding of syndecans; this facilitates cancer and endothelial cell motility, protects matrix proteases and provides a chemotactic gradient of mitogens. However, syndecans on stromal cells may be important for stromal cell/cancer cell interplay and may promote stromal cell proliferation, migration and angiogenesis. Finally, abnormal PG expression in cancer and stromal cells may serve as a biomarker for tumor progression and patient survival. Enhanced understanding of the regulation of PG metabolism and the involvement of PGs in cancer may offer a novel approach to cancer therapy by targeting the tumor microenvironment. In this minireview, the implication of PGs in cancer development and progression, as well as their pharmacological targeting in malignancy, are presented and discussed.

Osteosarcoma is the most common primary bone tumour associated with childhood and adolescence. The possible role of the small leucine-rich proteoglycan, lumican, in the growth and metastasis of various cancer types has recently been investigated. In this study, the expression of lumican was examined in moderately differentiated (MG-63) and well-differentiated (Saos 2) human osteosarcoma cell lines of high and low metastatic capability, respectively. Real-time PCR, western blotting with antibodies against the protein core and keratan sulfate, and specific enzymatic digestions were the methods employed. The two human osteosarcoma cell lines were found to express and secrete lumican partly substituted with keratan sulfate glycosaminoglycans. Importantly, the non-metastatic, well-differentiated Saos 2 cells produced lumican at rates that were up to sevenfold higher than those of highly metastatic MG-63 cells. The utilization of short interfering RNA specific for the lumican gene resulted in efficient down-regulation of its mRNA levels in both cell lines. The growth of Saos 2 cells was inhibited by lumican, whereas their migration and chemotactic response to fibronectin were found to be promoted. Lumican expression was negatively correlated with the basal level of Smad 2 activation in these cells, suggesting that lumican may affect the bioavailability of Smad 2 activators. By contrast, these cellular functions of highly aggressive MG-63 cells were demonstrated not to be sensitive to a decrease in their low endogenous lumican levels. These results suggest that lumican expression may be positively correlated with the differentiation and negatively correlated with the progression of osteosarcoma.