Hematopoietic progenitor cells of transgenic mice with increased copper/zinc‐superoxide dismutase activity are resistant to tumor necrosis factor

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Abstract
The mechanism of growth inhibition mediated by tumor necrosis factor (TNF) is unclear. Since recent data strongly suggested that generation of superoxide is a key step in cytotoxicity of TNF, we reasoned that cells expressing high levels of enzymes that degrade superoxide radicals would be resistant to TNF. Therefore, we examined the TNF‐sensitivity of bone marrow progenitor cells of transgenic mice that expressed the gene for human copper zinc‐superoxide dismutase (CuZn‐SOD). The CuZn‐SOD is a key enzyme in the metabolism of superoxide radicals. Heterozygous and homozygous transgenic mice had 3‐ and 5‐fold increased levels of CuZn‐SOD activity, respectively. Bone marrow cells of transgenic and nontransgenic mice were plated in soft gel culture with TNF (0.01–100 ng/ml). TNF inhibited myeloid colony formation supported by either granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) or G‐CSF from nontransgenic mice in a dose‐dependent manner. In contrast, the myeloid clonal growth of homozygote transgenic mice was not inhibited by TNF at concentrations up to 100 ng/ml. As expected, the effects of TNF on erythroid clonogenic cells, which do not produce superoxide, and the action of transforming growth factor‐β on myeloid progenitor cells, were similar in both transgenic and nontransgenic mice. These results suggest that the mechanism of TNF‐mediated growth inhibition of hematopoietic cells occurs through production of superoxide.