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Extracellular Ca 2+ suppresses endotoxin‐inducible tissue factor activation in monocytic THP‐1 cells
Author(s) -
Chu Arthur J.,
Fox Melissa J.,
Prasad Jai K.
Publication year - 2000
Publication title -
cell biochemistry and function
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 61
eISSN - 1099-0844
pISSN - 0263-6484
DOI - 10.1002/(sici)1099-0844(200001/03)18:1<67::aid-cbf852>3.0.co;2-n
Subject(s) - tissue factor , thp1 cell line , ex vivo , extracellular , chemistry , receptor , microbiology and biotechnology , cd14 , coagulation , in vitro , cell culture , biology , biochemistry , medicine , genetics
Background Monocytic tissue factor (TF), an initiator of extrinsic blood coagulation, is often activated under various inflammatory conditions including endotoxemia. This activation could be a contributing factor to the manifestation of disseminated intravascular coagulation following septic shock. Hypothesis We herein determine if extracellular Ca 2+ ([Ca 2+ ] ex ) regulates bacterial endotoxin (LPS)‐inducible monocytic TF activation. Methods We have employed a model monocytic cell line (THP‐1) to explore the mode of action of [Ca 2+ ] ex on the modulation of LPS‐induced TF activation. TF activity was measured by a single stage clotting assay, while TF expression as well as LPS recognition and its receptor expression were studied in immunofluorescent approaches. Results LPS‐induced TF activation was inversely correlated to [Ca 2+ ] ex . Upon exposure of THP‐1 cells to LPS (1·5 μg ml −1 ) for 6 h in the Hanks' medium without CaCl 2 , TF was activated by nearly 10‐fold. TF activation appreciably decreased with the increasing [Ca 2+ ] ex . No more than 3·5‐fold TF activation was detected at 5 m m [Ca 2+ ] ex . Consistent with the significantly lower degree of TF activation, LPS‐induced TF expression at 5 m m [Ca 2+ ] ex was 60 per cent less than that without [Ca 2+ ] ex . FACScan analysis showed that LPS recognition was significantly blocked at 5 m m [Ca 2+ ] ex which however had no effect on the expression of CD14 and CD11b, the proposed major LPS receptors. Moreover, LPS binding in vitro was significantly inhibited by 5 m m CaCl 2 . Conclusion Our results demonstrate that [Ca 2+ ] ex blocked LPS recognition without affecting its receptor expression on THP‐1 monocytes. This insensitivity to LPS thereby resulted in the depressed inducible monocytic TF expression and activation. Copyright © 2000 John Wiley & Sons, Ltd.