Suppression of tumor metastasis by manganese superoxide dismutase is associated with reduced tumorigenicity and elevated fibronectin

We have examined the tumorigenicity and the level of extracellular matrix proteins in fibrosarcoma cells expressing low (SOD-L) and high (SOD- H) MnSOD activities as well as the fibrosarcoma cells transfected with the selectable marker alone (NEO). When the cells derived from each tumor cell line were injected into syngeneic mice, the number of tumor cells required to make a tumor in one-half of the mice (TD₅₀) was markedly increased in MnSOD-transfected cells. The decrease in the tumorigenicity of the MnSOD- transfected cells was associated with an increase in the fibronectin level. These results support the hypothesis that MnSOD is a new type of tumor- suppressor gene.