Human osteosarcoma cells, tumorigenic in nude mice, express β1 integrins and low levels of alkaline phosphatase activity

The interactions between cells and the extracellular matrix (EM) have important effects on tumor invasion and metastasis. Osteosarcoma (OS) is a highly metastatic tumor, secondary lesions occurring early in the natural history of the disease. Despite the clinical relevance of disseminated disease in this neoplasia, the metastatic ability and other features related to the metastatic phenotype have not been extensively investigated in human OS cells. In this study the expression of bone matrix proteins, of their receptors, and the ability to adhere to and grow on some EM components in vitro were examined in human OS cell lines and related to their tumorigenic and metastatic potential in vivo. A significantly higher expression of integrin subunits α₂, α₅ and α₆, a better-organized surface expression of fibronectin and laminin, and a lower alkaline phosphatase (ALP) activity was accompanied by a higher ability to grow in vitro on EM components and to produce tumors in nude mice. On the other hand, no relationship was found between these features and the metastatic ability. Therefore, tumorigenicity of human OS cells might be related to an overexpression of some integrins and to a peculiar expression of some bone matrix proteins, possibly associated with distinct differentiative levels. Further investigations on clinical material will possibly help defining the actual prognostic value of these parameters.