| 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. © 1994 Wiley-Liss, Inc. |
