Regulation of thrombomodulin by tumor necrosis factor-alpha: comparison of
transcriptional and posttranscriptional mechanisms
SR Lentz, M Tsiang and JE Sadler
Department of Medicine, Howard Hughes Medical Institute, Washington
University School of Medicine, St Louis, MO 63110.
The procoagulant properties of cultured vascular endothelial cells are
enhanced in response to inflammatory cytokines such as tumor necrosis
factor-alpha (TNF). A major component of this response is a reduction in
expression of thrombomodulin, a cell surface cofactor for the activation of
protein C. Regulation of thrombomodulin expression by TNF has been reported
to occur through multiple mechanisms. To determine the relative roles of
transcriptional and posttranscriptional regulation, the effect of TNF on
the turnover of thrombomodulin protein and mRNA was examined in human and
bovine endothelial cells. Quantitative nuclease S1 protection assays showed
a 70% to 90% reduction in thrombomodulin mRNA within 4 hours of the
addition of 1.0 nmol/L TNF to the culture medium. The decrease in
thrombomodulin mRNA resulted from inhibition of transcription, followed by
rapid degradation of thrombomodulin transcripts (t1/2 less than or equal to
3 hours). In pulse-chase incubations, thrombomodulin synthesis decreased
parallel with mRNA, but the rate of degradation of radiolabeled
thrombomodulin was not significantly altered by TNF. Human thrombomodulin
was degraded with a t1/2 of 8.2 +/- 2.4 hours (SD) or 7.5 +/- 1.3 hours
(SD) in the absence or presence of TNF, respectively. We conclude that TNF
acts primarily to inhibit thrombomodulin transcription. The subsequent
decrease in activity results from the inherent instability of
thrombomodulin mRNA and protein in these cells, and not from the regulation
of thrombomodulin degradation.
Volume 77,
Issue 3,
pp. 542-550,
02/01/1991
Copyright © 1991 by The American Society of Hematology
