Cell-free pool of CD14 mediates activation of transcription factor NF-kappa B by lipopolysaccharide in human endothelial cells.

Abstract

Lipopolysaccharide (LPS), a maijor envelope component of Gram-negative bacteria, is the most frequent causative agent of septic shock and disseminated intravascular coagulation. LPS activates both CD14-positive (monocytes, macrophages, polymorphonuclear leukocytes) and CD14-negative (B-cell lines, endothelial cells) cells. CD14, a 55-kDa glycosyl-phosphatidylinositol-anchored membrane protein present on mature myeloid cells, serves as a receptor for LPS in complex with a soluble (serum-derived) LPS-binding protein (LBP). In this report, we show that human umbilical vein endothelial cells (HUVEC), which do not express measurable CD14 protein, become 3000-fold more sensitive to LPS-induced activation in the presence of serum, as measured by activation of the transcription factor NF-KB and expression of mRNA encoding tissue factor, a procoagulant molecule. This enhanced responsiveness of HUVEC is specifically mediated by the cell-free pool of CD14 (soluble CD14, sCD14) found in serum. The role of sCD14 in HUVEC activation by LPS was established by .(l) the blocking effect of monoclonal anti-CD14 antibodies which discriminate between cell-bound and sCD14,(ii) the lack of the serum-enhancing effect after immunodepletion of sCD14, and (iiW) establishing a reconstituted system in which recombinant sCD14 was sufficient to enhance the effects of LPS in the absence of serum and without a requirement for LBP. Thus, this mechanism of endothelial cell activation by LPS involves a cell-free pool of sCD14 most likely shed from CD14-positive cells of the monocytic lineage.

Extracellular Toll-Like Receptor 2 Region Containing Ser40-Ile64 but Not Cys30-Ser39 Is Critical for the Recognition ofStaphylococcus aureus Peptidoglycan

“…The cytoplasmic domains of TLRs homologous to IL-1R have been demonstrated to be essential for signaling leading to NF-B activation (13). Because each TLR is involved in signaling for different bacterial ligands (13, 16, 18 -20, 33, 34) CD14 serves as a functional receptor for LPS and PGN (5,7,35). TLRs have also been demonstrated to be responsible for cellular responsiveness to LPS and PGN (13,18).…”

“…Although CD14 avidly binds LPS and PGN, CD14 alone cannot confer cell responsiveness to bacterial ligands, because CD14 does not possess the intracellular signaling domain. In addition to membrane-bound CD14 (mCD14), consisting of Thr 1 -Ala 356 , the soluble form of CD14 (sCD14) is also able to activate cells in response to bacterial ligands (35). Recombinant sCD14, consisting of the CD14 region Thr 1 -Gly 323 , has been proved to be active (9).…”

Induction of inhibitory factor κBα mRNA in the central nervous system after peripheral lipopolysaccharide administration: Anin situhybridization histochemistry study in the rat

“…Cells inside the BBB, by contrast, are not freely accessible by blood-borne LPS (8) and cytokines [although small amounts of circulating cytokines have been reported to be transported across the BBB (22)]. In addition, receptors for LPS (23,24), tumor necrosis factor ␣ (25), and interleukin 1 (26) have been localized in the endothelial cells of brain vasculature. Moreover, the activation of the NF-B system in these cells suggests that they respond to the peripheral stimulation by producing their own signal molecules, probably cytokines.…”

Inducible expression of an antibiotic peptide gene in lipopolysaccharide-challenged tracheal epithelial cells.

“…CD14 exists in two forms, a glycosyl phosphatidylinositolanchored membrane form characterized from macrophages and a soluble form (23). The soluble form, found in serum, can mediate LPS-stimulated responses in endothelial and epithelial cells (26)(27)(28)(29). In our studies, we found that serum augments a response of TECs to LPS (Fig.…”