UP-REGULATION OF THROMBOMODULIN IN HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS INVITRO

Previous studies have shown that thrombomodulin (TM) on endothelial cells is down-regulated by endotoxin, interleukin-1β (IL-1β), and tumor necrosis factor (TNF). This loss of anti-coagulant potential is thought to be related to the hypercoagulable state in sepsis, inflammation, and cancer. The current studies describe up-regulation of TM in human umbilical vein endothelial cells (HUVECs) by several compounds as judged by increased surface cofactor activity, surface TM antigen, and TM mRNA levels. Surface TM activity was increased by active phorbol esters (10-8 M, 24-48 h), analogs of cAMP (1-10 mM, 4 h), and forskolin (10-6 M, 24-48 h). Up-regulation of TM in HUVECs by 4β-phorbol 12-myristate 13-acetate (PMA) and dibutyryl cAMP (dBcAMP) was due to de novo synthesis of TM protein resulting from increased TM mRNA levels. The results suggest that protein kinase C and protein kinase A may be involved in cellular regulatory mechanisms for TM expression. In addition, PMA effects on surface TM activity are biphasic, with an initial reduction followed by a significant enhacement. Hence, we propose that compounds capable of increasing intracellular cAMP concentrations in HUVECs may be useful in preventing thrombosis by increasing the anti-thrombotic properties of endothelial cells. © 1990 Copyright, 1990 by the Journal of Biochemistry.