CD14 is not involved in Rhodobacter sphaeroides diphosphoryl lipid A inhibition of tumor necrosis factor alpha and nitric oxide induction by taxol in murine macrophages.
Taxol, a microtubule stabilizer with anticancer activity, mimics the actions of lipopolysaccharide (LPS) on murine macrophages in vitro. Recently, it was shown that taxol-induced macrophage activation was inhibited by the LPS antagonist Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA). To investigate the mechanisms of taxol-induced macrophage activation, the present study focused on the interaction of LPS, RsDPLA, and taxol in the activation of and binding to macrophages. Taxol alone induced murine C3H/He macrophages to secrete tumor necrosis factor alpha (TNF) and to produce nitric oxide (NO) with kinetics similar to that of LPS. Macrophages from LPS-hyporesponsive C3H/HeJ mice, in contrast, did not yield any detectable TNF and NO production in response to LPS or taxol. RsDPLA inhibited taxol-induced TNF and NO production from C3H/He macrophages in a dose-dependent manner. The inhibition by RsDPLA was specific for LPS and taxol in that RsDPLA did not inhibit heat-killed Listeria monocytogenes- or zymosan-induced TNF production. Polymyxin B blocked the inhibitory effect of RsDPLA on taxol-induced TNF production. The inhibitory activity of RsDPLA appeared to be reversible since macrophages still responded to taxol in inducing TNF production after the RsDPLA was washed out with phosphate-buffered saline prior to the addition of taxol. Taxol-induced TNF production was not inhibited by colchicine, vinblastine, or 10-deacetylbaccatine III. A mutant cell line, J7.DEF3, defective in expression of a CD14 antigen, responded equally well to taxol by producing TNF as did the parent J774.1 cells. This suggested that the activation of macrophages by taxol does not require CD14. Taxol-induced TNF production by the mutant cells was also inhibited by RsDPLA. 125I-labeled LPS and 3H-labeled taxol was reported to bind to J774.1 cells predominantly via CD14 and microtubules, respectively. The binding of 125I-labeled LPS to J7.DEF3 cells was about 30 to 40% of that to J774.1 cells. The binding of 125I-LPS to J774.1 cells was inhibited by unlabeled LPS and RsDPLA but not by taxol. On the other hand, 3H-labeled taxol bound to both J774.1 cells and J7.DEF3 cells in similar time- and dose-dependent manners. The binding of [3H]taxol to these cells was inhibited by taxol but not by LPS or RsDPLA. Although the binding studies failed to examine cross competition for binding to macrophages, a possible explanation of these results is that LPS, RsDPLA, and taxol share the same molecule(s) on murine macrophages for their functional receptor(s), which is neither CD14 nor tubulin.
Kirikae
F
F
Department of Microbiology, Jichi Medical School, Tochigi-ken, Japan.
Kirikae
T
T
Qureshi
N
N
Takayama
K
K
Morrison
D C
DC
Nakano
M
M
D000818:Animals; D015703:Antigens, CD / Q000502:physiology*; D015214:Antigens, Differentiation, Myelomonocytic / Q000502:physiology*; D001665:Binding Sites; D003078:Colchicine / Q000494:pharmacology; D005260:Female; D008050:Lipid A / Q000031:analogs & derivatives* / Q000494:pharmacology; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects*; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D009569:Nitric Oxide / Q000096:biosynthesis*; D017239:Paclitaxel / Q000494:pharmacology*; D011112:Polymyxin B / Q000494:pharmacology; D012242:Rhodobacter sphaeroides; D043823:Taxoids; D014315:Triterpenes / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*; D014747:Vinblastine / Q000494:pharmacology; D015054:Zymosan / Q000494:pharmacology
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D008050:Lipid A; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D043823:Taxoids; D014315:Triterpenes; D014409:Tumor Necrosis Factor-alpha; C049596:diphosphoryl lipid A; D009569:Nitric Oxide; C042213:10-deacetylbaccatine III; D014747:Vinblastine; D015054:Zymosan; D011112:Polymyxin B; D017239:Paclitaxel; D003078:Colchicine