Thrombospondin is synthesized and secreted by human osteoblasts and osteosarcoma cells

Abstract

In this study we have shown by both immunofluorescence and immunoprecipitation techniques that human osteoblasts and osteosarcoma cells synthesize and secrete thrombospondin, a 450-kDa glycoprotein initially found in platelets. Immunofluorescence with a mouse monoclonal antibody to human platelet thrombospondin yielded specific granular staining within the cytoplasm of human osteoblasts. SDS/polyacrylamide gel electrophoresis analysis of immunoprecipitates obtained with polyclonal and monoclonal anti-thrombospondin antibodies allows the identification of thrombospondin in the cellular lysates and the culture media of biosynthetically labelled osteoblasts and osteosarcoma cells. Kinetic and dose/response studies of osteoblasts and of two osteosarcoma cell lines (MG-63, SaOs-2) were performed to assess the ability of these cells to adhere to thrombospondin and type-I collagen. Thrombospondin promoted the attachment of human osteoblasts whereas it inhibited the adhesion of MG-63 and SaOs-2 cells, both when it was directly adsorbed to plastic and when it was bound to type-I collagen. Therefore osteoblasts and osteosarcoma cells may be valuable tools to study the role of thrombospondin in cell adhesion.Thrornbospondin is a platelet a-granule glycoprotein which is secreted in response to thrombin [I]. The secreted thrombospondin binds to the surface of activated platelets [2] and is involved in platelet aggregation [3,4]. This glycoprotein is also synthesized by a wide range of cultured cells including fibroblasts [5, 61, endothelial [7, 81, squamous carcinoma [9] and smooth muscle cells [ 5 ] , monocytes and macrophages [lo], and is incorporated into their extracellular matrices [5,6]. The exact physiological function(s) of thrombospondin in these cells is unknown; however, there is growing evidence that it is involved in cell adhesion [9, 11, 121. Thrombospondin has a molecular mass of 450 kDa and is composed of three equivalent disulphide-linked chains of 150-160 kDa [13]. Each thrombospondin chain is made up of several protease-resistant domains, which bind specifically to heparin, fibrinogen, fibronectin, collagen, histidine-rich glycoprotein and plasminogen (for review see [14]). We have recently demonstrated that thrombospondin also forms a specific complex with osteonectin [15], a bone-related protein which is present in human platelets [16]. These findings, taken together with the fact that thrombospondin is secreted by several cultured cell lines, prompted us to examine whether or not it is also present in bone.

Antisense‐mediated reduction in thrombospondin‐1 expression reduces cell motility in malignant glioma cells

“…TSP-1 is synthesized and secreted by many types of human tumors, including squamous carcinoma, melanoma, glioma, 15 osteosarcoma 16 and breast adenocarcinoma. [17][18][19][20] Malignant progression in some cell lines is associated with reduced TSP expression.…”

Thrombospondin‐4 is expressed by early osteogenic tissues in the chick embryo

“…However, TSP-2 binds heparin with lower affinity than TSP-1 (O' Rourke et al, 1992), and thus may impart different properties to the matrix, or interact differently with cell surfaces. Osteoblasts derived from adult human bone attach to platelet TSP-1 (Robey et al, 1989), and the MG-63 osteosarcoma cell line undergoes partial spreading on TSP-1 through heparin and RGD-peptide dependent mechanisms (Clezardin et al, 1989(Clezardin et al, , 1991Adams and Lawler, 1993b). The carboxyl-terminal domain of TSP-4 expressed as a bacterial fusion protein supports cell attachment, but displays lower adhesive activity than the corresponding domain of TSP-1 (Adams and Lawler, 1994).…”

Comparative profiling of plasma proteome from breast cancer patients reveals thrombospondin-1 and BRWD3 as serological biomarkers

“…Recently, it has been reported that there is a direct correlation between plasma levels of THBS1 and breast cancer stages with higher levels being found in women with metastatic breast cancer (Byrne et al, 2007), with which our study on 84 plasma samples is highly consistent. THBS1 is synthesized and secreted by many cultured human tumor cell lines derived from squamous carcinoma, melanoma, glioma (Varani et al, 1989), osteosarcoma (Clezardin et al, 1989), and breast adenocarcinoma (Incardona et al, 1993). THBS1 could be found commonly in malignant breast tissues, especially in the stromal vicinity of the tumor cells.…”