Inhibition of basal and tumor necrosis factor-enhanced binding of murine tumor cells to murine endothelium by transforming growth factor-β 1

Abstract The adherence of cells to microvascular endothelium is important in a number of processes, including inflammatory responses and metastasis. It has been demonstrated that in human models, cytokines such as TNF, IL-1, IFN-γ increase the adhesiveness of endothelium for cells of the immune and inflammatory system by stimulating the expression of cell adhesion molecules on endothelial cell surfaces. We and others have shown similar cytokine-induced endothelial adhesiveness for tumor cells in murine and human models. In contrast to the effect of those modulators, transforming growth factor-β (TGF-β) has been shown to inhibit the binding of human neutrophils and T lymphocytes to human endothelium, although the mechanism of TGF-β action remains unknown. Little is known about the effect of TGF-β on tumor cell-endothelial interaction. In the present study, we demonstrate that TGF-β inhibits basal and TNF-enhanced binding of murine P815 mastocytoma cells to murine microvascular endothelium (MME). The alterations in MME mediated by TGF-β, also lead to the inhibition of adherence of murine splenocytes, thymocytes, and human lymphoblastoid cells but do not inhibit adherence of murine B16 melanoma cells. The effect of TGF-β is transient and inhibition of the endothelial adhesive phenotype is strongest 12 to 24 h after addition of the factor to MME. The TGF-β-mediated inhibition of P815 basal binding to endothelium is dependent on protein synthesis because cycloheximide reverses the TGF-β effect. TGF-β does not appear to activate classical signal transduction pathways. Inhibitors of G proteins do not abolish TGF-β action, protein kinase C and protein kinase A activators elicit an effect opposite to that of the factor, TGF-β does not increase intracellular cAMP levels, and finally calcium-mobilizing agents do not mimic, but rather inhibit the effect of TGF-β. However, TGF-β-mediated inhibition of both basal binding and TNF-enhanced P815 binding to MME is completely abolished in the presence of the protein phosphatase inhibitor okadaic acid which suggests that TGF-β may elicit its effect by stimulating protein phosphatase activity.