Expression of tumor necrosis factor-α in cultured human endothelial cells stimulated with lipopolysaccharide or interleukin-1α

Tumor-necrosis factor-alpha (TNF-alpha) 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-alpha is not known. In the present study, we addressed the possibility that TNF-alpha is produced by cultured human umbilical vein endothelial cells (HUVEC) stimulated with actors such as lipopolysaccharide (LPS) or interleukin-1 alpha (IL-1 alpha). LPS and IL-1 alpha induced expression of TNF-alpha mRNA in HUVEC. IL-1 alpha induced expression and secretion of TNF-alpha protein, but LPS did not induce production of TNF-alpha protein. Most of the TNF-alpha protein in cell lysate was Found in the membrane fraction. The mRNA for TNF-alpha-converting enzyme (TACE) was expressed in unstimulated HUVEC, and its level was not altered by treatment with LPS or IL-1 alpha. Transfection of HUVEC with full-length cDNA encoding the precursor TNF-alpha enhanced secretion of TNF-alpha protein by these cells, and treatment of the cells with a TACE inhibitor reduced the secretion, These results suggest that HUVEC produce TNF-alpha and have TACE activity. Secreted TNF-alpha may be involved in autocrine activation of endothelial cells, and TNF-alpha retained in cell membrane may serve as a juxtacrine system to activate target cells on the endothelial surface.