keratan-sulfate and Osteosarcoma

The small leucine-rich repeat proteoglycans (SLRPs) constitute a group of structurally and functionally related molecules that participate in the organization of the extracellular matrix ECM and have important effects on cell behavior. Osteosarcomas are heterogeneous bone tumors whose common characteristic is the production of an abundant nonmineralized (ECM)-osteoid. The scope of this minireview is to briefly present the current state of knowledge on the role of the SLRPs in osteosarcoma pathogenesis, with special emphasis on the recently described in osteosarcoma, proteoglycan lumican.

Topics: Animals; Biglycan; Cell Movement; Cell Proliferation; Chondroitin Sulfate Proteoglycans; Decorin; Extracellular Matrix; Extracellular Matrix Proteins; Humans; Keratan Sulfate; Lumican; Osteosarcoma; Proteoglycans; Signal Transduction

Human osteosarcoma cell lines were recently shown to express and secrete the small leucine rich proteoglycan (SLRP) lumican, with the ability to regulate the growth and motility of these cells. In this study, lumican-deficient Saos 2 cells were demonstrated to have increased adhesive capability onto fibronectin (FN) (p≤0.01). Upon neutralization of endogenous transforming growth factor β2 (TGF-β2) activity, no difference in the ability of lumican siRNA-transfected and scramble siRNA-transfected Saos 2 cells to adhere onto FN was detected (p=NS). Exogenous TGF-β2 was shown to stimulate Saos 2 cell adhesion to FN (p≤0.01). These results therefore, suggest that the inverse correlation existing between lumican expression and Saos 2 cell adhesion is dependent on active TGF-β2 signaling. Furthermore, the significant increase in Smad 2 activation present in lumican-deficient cells (p≤0.01) was annulled in the presence of the anti-TGF-β2 peptide, demonstrating that lumican is an upstream regulator of the TGF-β2/Smad 2 signaling cascade. Crucial to FN-dependent adhesion, β1 integrin expression and pFAK activation were likewise identified as downstream TGF-β2 effectors regulated by lumican expression. In conclusion, this study demonstrates a novel out-in signaling circuit in human osteosarcoma cells: secreted to extracellular matrix lumican is an endogenous inhibitor of TGF-β2 activity, resulting in downstream effector modulation including pSmad 2, integrin β1 and pFAK to regulate osteosarcoma adhesion.

Topics: Cell Adhesion; Cell Line, Tumor; Chondroitin Sulfate Proteoglycans; Enzyme Activation; Fibronectins; Focal Adhesion Kinase 2; Humans; Integrin beta1; Keratan Sulfate; Lumican; Osteosarcoma; Peptide Fragments; RNA, Small Interfering; Signal Transduction; Smad2 Protein; Transcriptional Activation; Transforming Growth Factor beta2

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.

Topics: Cell Differentiation; Cell Division; Cell Line, Tumor; Cell Movement; Cell Proliferation; Chondroitin Sulfate Proteoglycans; Cyclin-Dependent Kinase Inhibitor p21; Down-Regulation; Humans; Keratan Sulfate; Lumican; Osteosarcoma; RNA, Messenger; RNA, Small Interfering; Transfection

Topics: Aggrecans; Animals; Carbohydrate Conformation; Carbohydrate Sequence; Cells, Cultured; Centrifugation, Density Gradient; Chromatography, High Pressure Liquid; Chromatography, Ion Exchange; Electrophoresis, Polyacrylamide Gel; Extracellular Matrix Proteins; Glycosaminoglycans; Isotope Labeling; Keratan Sulfate; Lectins, C-Type; Molecular Sequence Data; Oligosaccharides; Osteosarcoma; Proteoglycans; Rats; Sulfates; Sulfur Radioisotopes; Tumor Cells, Cultured