Tumor necrosis factor-α downregulates protein S secretion in human microvascular and umbilical vein endothelial cells but not in the HepG-2 heoatoma cell line

Abstract

Protein S deficiency, which is associated with thrombosis, can either be inherited or acquired. Recently, we reported that a decrease in free protein S was observed in 19 of 25 persons with HIV/AIDS. The proinflammatory cytokine, tumor necrosis factor-α (TNF-α), has been reported to be elevated in human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) patients and has been shown to induce a procoagulant state on the surface of endothelial cells. We report here that recombinant TNF-α (rTNF-α) downregulated protein S synthesis in the SV-40T transfected human microvascular endothelial cell line (HMEC-1) model system by approximately 70% and in primary human umbilical vein and dermal microvascular endothelial cell cultures by approximately 50%. Using the HMEC-1 model. Northern blot analysis showed a decrease in protein S RNA at 24 hours that was corroborated by Western blot analysis and enzyme-linked immunosorbent assay (ELISA) quantification. Evidence supporting the specificity of the TNF-α effect included the following: (1) TNF-α downregulation of protein S was completely blocked by TNF neutralizing antibody; (2) the effect was transient, and protein S was restored to near normal levels after TNF was removed from cell cultures; (3) an antibody directed to the TNF RI (55-kD receptor) was shown to mimic the action of TNF-α on HMEC-1 cells; and (4) other proinflammatory cytokines, interleukin (IL)-1, IL-6, and TGF-β, had no effect on protein S secretion. However, TNF-α showed no regulatory control over protein S synthesis in the human hepatocellular carcinoma cell line HepG-2. We suggest that TNF-α downregulation of protein S may be a mechanism for localized procoagulant activity and thrombosis recently reported in some AIDS patients with associated protein S deficiency.