EFFECT OF MYCOPHENOLIC-ACID ON TNF-ALPHA-INDUCED EXPRESSION OF CELL-ADHESION MOLECULES IN HUMAN VENOUS ENDOTHELIAL-CELLS IN-VITRO

1 Mycophenolic acid (MPA) is an inhibitor of inosine-5'-monophosphate dehydrogenase and therefore interferes with cellular GTP biosynthesis. Recently, MPA has been used as an antiproliferative and immunosuppres sive agent. In the present study, the effect of MPA on the expression of the endothelial cell adhesion molecules (CAMs), intercellular (I) C AM-1, vascular (V) CAM-1 and endothelial (E)-selectin, was investigate d in tumour necrosis factor-alpha (TNF alpha)-activated cultured human venous endothelial cells (EC). 2 Surface expression of CAMs was measu red by flow cytometry and mRNA expression by Northern blot analysis. T ranscriptional activation of CAMs by the nuclear factor NF-kappa B was determined by an electromobility shift assay. The function of CAMs wa s studied by a static adhesion assay with human monocyte-like undiffer entiated U937 cells. 3 Pretreatment of TNF alpha- (5 ng ml(-1), 12 h) activated EC with MPA (10 mu M, 24 h) increased the binding of U937 ce lls, which had not been treated with MPA, by approximate to 2 fold. MP A-pretreatment of EC did not affect TNF alpha-induced surface expressi on of ICAM-1. However, VCAM-1 and E-selectin were increased 2-3 fold a nd remained elevated up to 24 h, by which time TNF alpha-activated con trol EC had returned to baseline levels of expression. The effect of M PA on the surface expression of CAMs was half-maximal at approximate t o 1 1 mu M and required greater than or equal to 12 h of pretreatment. Guanosine (0.3 mM), a precursor of GTP, did not prevent the effect of MPA on the expression of CAMs in TNF alpha-activated EC. 4 Kinetics o f mRNA expression of CAMs mirrored protein expression: mRNA for ICAM-1 was unaffected, whereas TNF alpha-induced mRNA expression for E-selec tin and VCAM-1 was prolonged and increased by MPA. This effect was not due to increased transcription mediated by the nuclear transcription factor NF-kappa B. However, half-life for E-selectin mRNA was increase d 10 fold by MPA, whereas ICAM-1 mRNA half-life was unchanged. 5 The d ata demonstrate that apart from its antiproliferative effects on lymph ocytes, MPA enhances TNF alpha-induced VCAM-1 and E-selectin surface e xpression on EC by selectively increasing the mRNA-stability of these cell adhesion molecules. This effect of MPA on EC appears to be indepe ndent from inhibition of inosine-5'-monophosphate dehydrogenase.