Expression of Tumor Necrosis Factor-a in Cultured Human Endothelial Cells Stimulated With Lipopolysaccharide or Interleukin-1a

Tumor-necrosis factor-a (TNF-a) is a proinflammatory cytokine with a wide variety of biological effects. The most important source of this cytokine is monocytes/macrophages. It is a potent agonist in the activation of endothelial cells; however, the precise role of endothelial cells as a source of TNF-a is not known. In the present study, we addressed the possibility that TNF-a is produced by cultured human umbilical vein endothelial cells (HUVEC) stimulated with factors such as lipopolysaccharide (LPS) or interleukin-1a (IL-1a). LPS and IL-1a induced expression of TNF-a mRNA in HUVEC. IL-1a induced expression and secretion of TNF-a protein, but LPS did not induce production of TNF-a protein. Most of the TNF-a protein in cell lysate was found in the membrane fraction. The mRNA for TNF-a–converting enzyme (TACE) was expressed in unstimulated HUVEC, and its level was not altered by treatment with LPS or IL-1a. Transfection of HUVEC with full-length cDNA encoding the precursor TNF-a enhanced secretion of TNF-a protein by these cells, and treatment of the cells with a TACE inhibitor reduced the secretion. These results suggest that HUVEC produce TNF-a and have TACE activity. Secreted TNF-a may be involved in autocrine activation of endothelial cells, and TNF-a retained in cell membrane may serve as a juxtacrine system to activate target cells on the endothelial surface. (Arterioscler Thromb Vasc Biol. 2000;20:410-415.)