Journal
JOURNAL OF LEUKOCYTE BIOLOGY
Volume 100, Issue 6, Pages 1363-1373Publisher
WILEY
DOI: 10.1189/jlb.2VMA1215-577R
Keywords
inflammation; macrophages; nuclear factor kappa B; phosphatidylinositol 4-monophosphate; phospholipase C
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Funding
- National Science Centre (Krakow, Poland) [DEC-2013/08/A/NZ3/00850]
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LPS binds sequentially to CD14 and TLR4/MD2 receptor triggering production of proinflammatory mediators. The LPS-induced signaling is controlled by a plasma membrane lipid PI(4,5)P-2 and its derivatives. Here, we show that stimulation of murine peritoneal macrophages with LPS induces biphasic accumulation of PI(4,5)P-2 with peaks at 10 and 60-90 min that were still seen after silencing of TLR4 expression. In contrast, the PI(4,5)P-2 elevation was abrogated when CD14 was removed from the cell surface. To assess the contribution of CD14 and TLR4 to the LPS-induced PI(4,5)P-2 changes, we used HEK293 transfectants expressing various amounts of CD14 and TLR4. In cells with a low content of CD14 and high of TLR4, no accumulation of PI(4,5)P-2 occurred. With an increasing amount of CD14 and concomitant decrease of TLR4, 2 peaks of PI(4,5)P-2 accumulation appeared, eventually approaching those found in LPS-stimulated cells expressing CD14 alone. Mutation of the signaling domain of TLR4 let us conclude that the receptor activity can modulate PI(4,5)P-2 accumulation in cells when expressed in high amounts compared with CD14. Among the factors limiting PI(4,5)P-2 accumulation are its hydrolysis, phosphorylation, and availability of its precursor, PI(4)P. Inhibition of PLC and PI3K or overexpression of PI4K II alpha that produces PI(4)P promoted PI(4,5)P-2 elevation in LPS-stimulated cells. The elevation of PI(4,5)P-2 was dispensable for TLR4 signaling yet enhanced its magnitude. Taken together, these data suggest that LPS-induced accumulation of PI(4,5)P-2 that maximizes TLR4 signaling is controlled by CD14, whereas TLR4 can fine tune the process by affecting the PI(4,5)P-2 turnover.
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