Thrombospondin-1 is downregulated by anoxia and suppresses tumorigenicity of human glioblastoma cells

Angiogenesis, the sprouting of new capillaries from preexisting blood vesse ls, results hom a disruption of the balance between stimulatory and inhibit ory factors. Here, we show chat anoxia reduces expression of thrombospondin -1 (TSP-1), a natural inhibitor of angiogenesis, in glioblastoma cells. Thi s suggests that reduced oxygen tension can promote angiogenesis not only by stimulating the production of inducers, such as vascular endothelial growt h factor, but also by reducing the production of inhibitors. This downregul ation may significantly contribute to glioblastoma development, since we sh ow that an increase in TSP-1 expression is sufficient to strongly suppress glioblastoma cell tumorigenicity in vivo.