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Biomedical subjects

S N Vogel

Publications and source records attributed to S N Vogel.

At least 19 recordsLinked to original sources
PubMed1996

Differential dysregulation of nitric oxide production in macrophages with targeted disruptions in IFN regulatory factor-1 and -2 genes.

Recent studies have reported that IFN regulatory factor-1 (IRF-1) regulates nitric oxide (NO.) production in murine macrophages (M phi). Since IRF-2 recognizes the same consensus sequence as IRF-1, we postulated that IRF-2 may also regulate NO.. Therefore, the ability of M phi from INF-2 homozygous (IRF-2-/-) and heterozygous (IRF-2+/-) knockout mice to produce NO. following LPS and/or IFN-gamma stimulation was compared with the responses of IRF-1-/-, IRF-1+/-, and C57BL/6+/+ M phi. IRF-2-/- M phi produced less LPS-induced NO2- than IRF-2+/- or C57BL/6 M phi. LPS and IFN-gamma synergized to increase NO2- production from IRF-2-/- M phi to approximately 50% of IRF-2+/- and C57BL/6 levels. Unexpectedly, IRF-2-/-, IRF-2+/- and C57BL/6 M phi produced comparable levels of inducible NO synthase mRNA in response to treatment with LPS and IFN-gamma. IRF-1-/- M phi produced barely detectable NO2- and low, but detectable, inducible NO. synthase mRNA in response to IFN-gamma and LPS. These results indicate that IRF-1 and IRF-2 differ in their mechanism of NO. regulation and that IRF-2 regulates inducible NO. synthase post-transcriptionally.

Animals↗
PubMed1996

Heat shock mimics glucocorticoid effects on IFN-gamma-induced Fc gamma RI and Ia messenger RNA expression in mouse peritoneal macrophages.

Glucocorticoids activate or repress the expression of different genes. In murine macrophages, glucocorticoids exert opposing effects on the IFN-gamma-induced expression of Fc gamma RI and Ia mRNA and cell surface expression; they enhance IFN-gamma-induced Fc gamma RI mRNA and protein expression, yet inhibit IFN-gamma-induced Ia mRNA and protein expression. Recently, in transfected cell lines, heat shock (HS) has been shown to promote nuclear accumulation of the glucocorticoid receptor (GR), resulting in potentiation of certain GR-mediated responses. In this study, we compared the effects of HS and dexamethasone (DEX) treatment on the IFN-gamma induction of Fc gamma RI and Ia mRNA in murine primary peritoneal macrophages. Our results show that HS exerted the same opposing effects on these IFN-gamma-responsive genes as DEX at 37 degrees C. The glucocorticoid antagonist RU 486 blocked both DEX and HS-induced enhancement of IFN-gamma induction of Fc gamma RI, suggesting a common GR-mediated mechanism. While RU 486 also reversed DEX-induced repression of Ia mRNA expression, supporting a GR-mediated action, it did not affect HS-mediated repression, raising the possibility of a ligand-independent HS response pathway.

Animals↗
PubMed1996

Paclitaxel (Taxol)-induced NF-kappaB translocation in murine macrophages.

Interaction of bacterial lipopolysaccharide (LPS) with macrophages results in the induction of a cascade of cytokines that mediate the varied effects of LPS. An early intracellular signaling event that follows receptor engagement is the activation of transcription factor NF-kappaB. Nf-kappaB has been shown to be important for the induction of many LPS-inducible cytokine genes, including tumor necrosis factor alpha, interleukin-1beta, and interleukin-6. Previously, we and others have shown that the antitumor agent paclitaxel (Taxol) is able to mimic bacterial LPS in its ability to activate murine macrophages. In this report, we have extended these findings by demonstrating that paclitaxel, like LPS, is able to stimulate the translocation of primarily p50-p65 heterodimers of NF-kappaB to the nucleus. This activation is dose dependent and requires a concentration of > or =5 microM paclitaxel. The kinetics of NF-kappaB activation by paclitaxel are slower than those of LPS: by 15 min poststimulation, LPS-induced NF-kappaB activation was readily detected, whereas the paclitaxel-induced NF-kappaB activation was minimal. Moreover, paclitaxel- and protein-free LPS-induced translocation of NF-kappaB was seen only in macrophages derived from LPS-responsive C3H/OuJ mice and not from the LPS-hyporesponsive C3H/HeJ mice, a finding that is consistent with those of previous genetic studies linking paclitaxel responsiveness to the Lps gene. Finally, the LPS structural antagonist Rhodobacter sphaeroides diphosphoryl lipid A inhibited both LPS-and paclitaxel-induced NF-kappaB activation, suggesting a common receptor component in this activation.

Animals↗
PubMed1996

Biochemical characterization and protein kinase C dependency of monokine-inducing activities of Toxoplasma gondii.

Previous reports have indicated that the early induction of interleukin-12 (IL-12), tumor necrosis factor alpha (TNF-alpha), IL-1beta, and IL-10 is crucial for the establishment and regulation of host cell-mediated immunity to the intracellular protozoan parasite Toxoplasma gondii. In this study, we demonstrate that a soluble tachyzoite extract (soluble tachyzoite antigen) can trigger the expression of these four monokines by murine inflammatory macrophages. Further characterization revealed that the parasite molecules in soluble tachyzoite antigen responsible for monokine induction are heat stable at 100 degree C but differ in sensitivity to protease digestion. Thus, the tachyzoite factors that stimulate TNF-alpha and IL-to expression were found to be more resistant to treatment with proteinase K than those responsible for IL-12 and IL-10 induction. Similarly, while the factors responsible for the induction of all four monokines were found to be sensitive to periodate oxidation, the TNF-alpha-stimulating activity was partially resistant to treatment with the compound at a low concentration (1 mM). A further dichotomy in monokine induction signals was inferred from experiments with isoquinoline sulfonamide protein kinase inhibitors. The latter work suggested that the pathways for TNF-alpha and IL-1beta are protein kinase C dependent, while expression of IL-12 and expression of IL-10 share distinct signal transduction mechanisms involving other kinases. Together, these data argue that monokine induction by T. gondii is mediated by glycoproteins that may belong to distinct groups in terms of their biochemical properties and intracellular signaling pathways.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Effect of liposome-mediated macrophage depletion on LPS-induced cytokine gene expression and radioprotection.

Tissue-specific cytokine mRNA expression was examined in mice that received LPS. In the liver, IL-6, IL-10, IL-12 (p40), and TNF-alpha were induced by 30 min after injection with LPS. In the spleen, IL-6 and TNF-alpha were induced by 30 min after LPS challenge, while increases in IL-10 and IL-12 (p40) were delayed in onset. GM-CSF, IFN-gamma, and IL-12 (p35) were not induced in the liver or spleen until 60 to 90 min after LPS injection. Mice were depleted of macrophages in their liver and spleen by i.v. injection of liposome-encapsulated dichloromethylene bisphosphonate (Cl2MBP). Induction of IL-1 beta, IL-6, IL-10, and IL-12 (p40) mRNA by LPS was reduced by > 95% in the liver of macrophage-depleted mice, implicating macrophages as the primary producers of these cytokines. Macrophage depletion resulted in a 50 to 75% reduction in TNF-alpha mRNA in the liver. The results from Cl2MBP-liposome-treated mice also suggested that splenic macrophages were the primary producers of LPS-induced IL-1 beta, IL-6, IL-12 (p40), and IL-1 receptor antagonist (IL-1ra) mRNA, but not IL-10 and TNF-alpha mRNA. Mice treated with Cl2MBP-liposomes were more susceptible to ionizing irradiation than control mice, whether or not they were administered a radioprotective dose of LPS. These findings suggest that depletion of liver and splenic macrophages results in a dysregulation of basal and LPS-induced cytokine responses that can be associated with an altered biologic response.

Animals↗
PubMed1995

Defective ceramide response in C3H/HeJ (Lpsd) macrophages.

Lipid second messengers are gaining recognition as important mediators of extracellular signals. One such lipid, ceramide, generated from membrane sphingomyelin following stimulation with TNF-alpha, IL-1 beta, or IFN-gamma, activates ceramide-activated kinase (CAK). A recent study demonstrated that LPS activated CAK without generating ceramide, suggesting that the LPS stimulation of cells mimics the second messenger function of ceramide. To compare ceramide to LPS signaling, we assessed the ability of LPS-responsive (Lpsn) and LPS-hyporesponsive (Lpsd) macrophages to respond directly to ceramide for enhanced expression of LPS-inducible genes. In contrast to macrophages from C3H/Ouj (Lpsn) mice, C3H/Hej (Lpsd) macrophages failed to respond to cellpermeable analogues of ceramide (C2,C6,C16) or sphingomyelinase. These results suggest that a common critical molecule, encoded by the Lps gene, regulates both ceramide and LPS signaling pathways.

Alleles↗
PubMed1995

The serine/threonine phosphatase inhibitor, calyculin A, inhibits and dissociates macrophage responses to lipopolysaccharide.

LPS-stimulated macrophages (M phi) produce inflammatory mediators that are largely responsible for the pathophysiology associated with septic shock. M phi respond to LPS with rapid protein phosphorylation and dephosphorylation on serine, threonine, and tyrosine residues. If these events are critical for the cellular response to LPS, the kinases and/or phosphatases involved may be vulnerable targets for pharmacologic intervention. Recent studies demonstrated that tyrosine kinase inhibitors block LPS-induced tyrosine phosphorylation of MAP kinases as well as TNF-alpha and IL-1 beta production. To investigate a role for serine/threonine phosphatases, we evaluated the effect of calyculin A, a potent serine/threonine phosphatase inhibitor, on LPS stimulation of murine M phi. Pretreatment of M phi with calyculin A inhibited LPS-induced expression of six immediate-early genes: TNF-alpha, IL-1 beta, IFN-beta, IP-10, IRF-1, and TNFR-2. Calyculin A added 1.5 h after LPS treatment greatly reduced accumulation of IP-10, IRF-1, and TNFR-2 mRNA, but not TNF-alpha, IL-1 beta, and IFN-beta mRNA. Calyculin A, in the absence or presence of LPS, resulted in sustained tyrosine phosphorylation of the MAP kinases. These findings suggest that an "early" serine/threonine phosphatase activity is essential for LPS stimulation of M phi and that the activation of MAP kinases is not sufficient for the induction of these immediate-early genes. The requirement for a "late" phosphatase activity for expression of a subset of LPS-inducible genes dissociates at least two regulatory pathways in LPS signal transduction.

Animals↗
PubMed1995

Differential expression of interferon regulatory factor 1 (IRF-1), IRF-2, and interferon consensus sequence binding protein genes in lipopolysaccharide (LPS)-responsive and LPS-hyporesponsive macrophages.

Macrophages secrete interferon (IFN), as well as other cytokines, following lipopolysaccharide (LPS) stimulation. The interferon regulatory factors (IRFs) comprise a family of DNA-binding proteins that have been implicated in the transcriptional regulation of IFN and certain IFN-inducible genes. We therefore characterized basal and LPS-inducible levels of IRF-1, IRF-2, and interferon consensus sequence binding protein (ICSBP) mRNA in LPS-responsive macrophages and compared the expression of these genes in macrophages that typify two murine models of LPS hyporesponsiveness. In the first model, the LPS-hyporesponsive phenotype of the C3H/HeJ mouse is genetically determined and maps to the Lps locus on mouse chromosome 4. In the second model, normally LPS-responsive macrophages acquire a transient LPS-hyporesponsive phenotype following a prior exposure to LPS, a phenomenon referred to as "endotoxin tolerance." Using reverse transcription PCR, we detected basal levels of IRF-1 mRNA in LPS-responsive (Lpsn) macrophages that were approximately 15 times higher than those found in LPS-hyporesponsive (Lpsd) macrophages. Conversely, Lpsd macrophages expressed basal levels of IRF-2 mRNA that were approximately 18 times higher than those expressed in Lpsn macrophages. LPS stimulation resulted in a dose- and time-dependent accumulation of IRF-1, IRF-2, and ICSBP mRNA only in Lpsn macrophages. Cycloheximide inhibited the accumulation of LPS-stimulated IRF-2 and ICSBP mRNA, but not IRF-1 mRNA, thus designating IRF-1 an immediate-early, LPS-inducible gene. Finally, macrophages rendered tolerant to endotoxin expressed elevated but nonmaximal mRNA levels for all three transcription factors that are not reinduced upon secondary challenge with LPS. Thus, the IRFs may represent yet an additional molecular pathway in the complex response to LPS.

Animals↗
PubMed1995

Exogenous tumor necrosis factor alpha and interleukin-1 alpha increase resistance to Salmonella typhimurium: efficacy is influenced by the Ity and Lps loci.

Interleukin-1 alpha (IL-1 alpha) or tumor necrosis factor alpha (TNF-alpha) administered prior to infection with Salmonella typhimurium increases survival in mice that are Ityr, not in susceptible Lpsd or Itys mice. Combined IL-1 alpha and TNF-alpha pretreatment results in greater survival than that seen with either cytokine alone in Ityr mice. Treatment after infection with TNF-alpha and/or IL-1 alpha increases the mean time to death but not the survival fraction of Lpsd mice and was ineffective in either Ityr or Itys mice.

Animals↗
PubMed1995

LPS and Taxol activate Lyn kinase autophosphorylation in Lps(n), but not in Lpsd), macrophages.

BACKGROUND: The anti-tumor agent, Taxol, has been shown in murine macrophages to stimulate tumor necrosis factor (TNF), modulate TNF receptors, induce a large panel of immediate-early genes, and induce protein tyrosine phosphorylation indistinguishably from LPS. These data, coupled with the finding that lipid A antagonists block Taxol-induced stimulation, support the hypothesis that these two structurally unrelated compounds activate a common, receptor-associated signaling apparatus. A very early event in LPS signaling of human monocytes is activation of lyn kinase activity. We therefore sought to evaluate the activation of lyn kinase by LPS and Taxol in LPS-responsive (Lps(n)) and LPS-hyporesponsive (Lps(d)) macrophages. MATERIALS AND METHODS: C3H/OuJ (Lps(n)) and C3H/HeJ (Lps(d)) macrophages were stimulated by LPS or Taxol. Cell lysates were subjected to immunoprecipitation with anti-lyn antibody, gel electrophoresis, and in vitro kinase assays. Autoradiography and Phosphor-Imager analysis were carried out to detect incorporation of 32P into lyn protein. RESULTS: Within seconds of stimulation, LPS and Taxol induce in Lps(n) macrophages a depression of autophosphorylation, followed within minutes by autophosphorylation of both p53 and p56 lyn species. Lps(d) macrophages respond to LPS and Taxol with the initial decrease in activity, but fail to respond to LPS with autophosphorylation, and respond only to a limited extent upon Taxol stimulation. Tyrosine phosphatase inhibitors exerted inhibitory effects on LPS stimulation of lyn autophosphorylation. CONCLUSIONS: Decreased lyn kinase activity within seconds and autophosphorylation within minutes of LPS or Taxol stimulation in Lps(n) macrophages strongly supports the hypothesis that LPS and Taxol share a common signaling pathway. The finding that C3H/HeJ macrophages respond to LPS and Taxol with a normal depression of lyn activity, but fail to autophosphorylate lyn normally in response to LPS or Taxol, suggests that the Lps(d) defect is distal to LPS-receptor interaction. Finally, the inhibitory effect of tyrosine phosphatase inhibitors on LPS-induced lyn autophosphorylation suggests that tyrosine phosphatase(s) may participate in the regulation of lyn kinase activity.

Antineoplastic Agents, Phytogenic↗
PubMed1995

Dissection of LPS-induced signaling pathways in murine macrophages using LPS analogs, LPS mimetics, and agents unrelated to LPS.

The model in Figure 3 summarizes the data presented above. Using the induction of the select panel of LPS-inducible genes and the phosphorylation on tyrosine of specific MAP kinases, we have been able to dissociate three signaling pathways shared by LPS and its analogs and mimetics: a pathway that leads to tyrosine phosphorylation, one that leads to the induction of a gene subset including TNF alpha, TNFR-2, and IL-1 beta, and a pathway that results in induction of IP-10, D3, and D8 gene expression. It is still unclear if macrophage activation by non-LPS products occurs entirely through distinct yet redundant pathways or if other signaling receptors ultimately tie into the same intermediate pathways. This approach may identify particular stimuli as tools to induce specific pathways leading to select gene subsets and/or tyrosine kinase activation and, perhaps, identify a pathway deficient in C3H/HeJ macrophages.

Animals↗
PubMed1994

Activation of LPS-inducible genes by the antitumor agent 5,6-dimethylxanthenone-4-acetic acid in primary murine macrophages. Dissection of signaling pathways leading to gene induction and tyrosine phosphorylation.

The synthetic flavone analogue 5,6-dimethylxanthenone-4-acetic acid (5,6-MeXAA) has shown promise as an antitumor agent and is currently a candidate for clinical trials. Because 5,6-MeXAA has been shown in a murine macrophage and a human myelomonocytic cell line to induce TNF-alpha mRNA and to activate macrophages to become tumoricidal, actions that are shared with bacterial LPS, we sought to determine the level of LPS mimetic activity exhibited by this low m.w. macrophage-activating agent. To elucidate its mechanisms of action, the capacity to induce a panel of LPS-inducible genes was assessed. 5,6-MeXAA was found to induce a subset of LPS-inducible genes within the panel in both Lpsn and Lpsd primary murine macrophages. Of the six LPS-inducible genes examined, there was marked induction of IP-10, D8, and D3; low induction of TNF-alpha gene expression; and insignificant induction of TNFR-2 and IL-1 beta genes. 5,6-MeXAA was also found to be a potent inducer of IFNs in macrophages of both strains, and of increased expression of the genes that encode the IFN regulatory factors IRF-1, IRF-2, and ICSBP. In contrast with LPS, 5,6-MeXAA failed to induce significantly any of the 40- to 45-kDa tyrosine phosphoproteins induced by LPS. These data suggest that 5,6-MeXAA shares with LPS certain biochemical pathways that lead to gene induction and allow for the additional dissection of the relationship of tyrosine phosphorylation and the expression of specific genes.

Animals↗
PubMed1994

Endotoxin-induced early gene expression in C3H/HeJ (Lpsd) macrophages.

C3H/HeJ (Lpsd) macrophages have been shown to respond to certain LPSs, especially from rough mutant bacteria. C3H/OuJ (Lpsn) macrophages are induced by wild-type LPS, rough LPS, or lipid A to express many genes, including TNF-alpha, TNFR-2, IL-1 beta, IP-10, D3, and D8. C3H/HeJ macrophages failed to induce any of these genes when cultured with wild-type LPS or synthetic lipid A, even when pretreated with IFN-gamma. However, rough mutant Salmonella minnesota Ra, Rc, and Rd LPS, and Escherichia coli D31 m3 Rd LPS induced Lpsd macrophages to express a subset of genes within the gene panel. Because bioactive preparations contained trace quantities of endotoxin protein(s), a deoxycholate-modified, phenol-water method was used to repurify rough LPS into an aqueous phase, and extract endotoxin proteins into a phenol phase. Repurified LPS failed to stimulate Lpsd macrophages; however, phenol fractions were approximately 10% as potent in Lpsd macrophages as crude rough LPS. Full potency was restored in C3H/HeJ macrophages when aqueous phase LPS and phenol-phase proteins were co-precipitated, suggesting that LPS and endotoxin proteins interact synergistically. Endotoxin proteins alone induced TNF-alpha, TNFR-2, and IL-1 beta, but not IP-10, D3, and D8 genes in both Lpsd and Lpsn macrophages. Tyrosine phosphorylation of three 41- to 47-kDa proteins was induced by endotoxin proteins, but not by LPS, in Lpsd macrophages. Thus, endotoxin proteins seem to activate a signaling pathway(s) that converges (distal to the Lps gene product) with a subset of LPS-signaling pathways.

Animals↗
PubMed1994

CD14-mediated translocation of nuclear factor-kappa B induced by lipopolysaccharide does not require tyrosine kinase activity.

During the course of serious bacterial infections, lipopolysaccharide (LPS) is believed to interact with macrophage receptors, resulting in the generation of inflammatory mediators and systemic symptoms including hemodynamic instability and shock. CD14, a glycosylphosphatidylinositol-linked antigen, functions as an LPS signaling receptor. A critical issue concerns the mechanism by which CD14, which has no transmembrane domain, transduces its signal following LPS binding. Recently, investigators have hypothesized that CD14-mediated signaling is effected through a receptor-associated tyrosine kinase (TK), suggesting a multicomponent receptor model of LPS signaling. Wild-type Chinese hamster ovary (CHO)-K1 cells can be activated by endotoxin to release arachidonate following transfection with human CD14 (CHO/CD14). Nuclear translocation of cytosolic NF-kappa B is correlated with a number of LPS-inducible responses. We sought to determine if this pathway were present in CHO/CD14 cells and to elucidate the relationship of NF-kappa B activation to the CD14 receptor system. LPS-stimulated translocation of NF-kappa B in CHO/CD14 cells resembled the same response in the murine macrophage-like cell line RAW 264.7. Protein synthesis inhibitors and corticosteroids, which suppress arachidonate release and the synthesis of proinflammatory cytokines, had no effect on translocation of NF-kappa B in CHO/CD14 or RAW 264.7 cells, demonstrating that NF-kappa B translocation is an early event. Although TK activity was consistently observed by immunoblotting extracts from activated RAW 264.7 cells, LPS-induced phosphotyrosine residues were not observed from similarly treated CHO/CD14 cells. Furthermore, the TK inhibitors herbimycin A and genistein failed to inhibit translocation of NF-kappa B in CHO/CD14 or RAW 264.7 cells, although both of these agents inhibited LPS-induced TK activity in RAW 264.7 cells. These results imply that TK activity is not obligatory for CD14-mediated signal transduction to occur in response to LPS.

Animals↗
PubMed1994

Molecular interactions between interferon consensus sequence binding protein and members of the interferon regulatory factor family.

Interferon (IFN) consensus sequence binding protein (ICSBP) is a transcription factor expressed mostly in the cells of the immune system. ICSBP belongs to the IFN regulatory factor (IRF) family, which also includes IRF-1, IRF-2, and the IFN-alpha-stimulated gene factor 3 gamma (ISGF3 gamma). We show here that ICSBP forms a complex with IRF-1 or IRF-2 both in vivo and in vitro and, in the presence or absence of the target DNA, with the IFN-stimulated response element (ISRE). Further, electrophoretic mobility shift assays show that this interaction greatly enhances the otherwise very low binding affinity of ICSBP to the ISRE. We show, on the other hand, that ICSBP inhibits binding of the IFN-alpha-stimulated gene factor 3 gamma to the ISRE. Through these interactions ICSBP is likely to exert complex modulatory functions in the regulation of IFN-stimulated genes.

Base Sequence↗
PubMed1994

Regulation of IFN-gamma-induced nuclear expression of IFN consensus sequence binding protein in murine peritoneal macrophages.

IFNs are well characterized macrophage-activating agents. Their varied effects are largely mediated via the induction of many genes, whose products act in concert to induce macrophage differentiation. Homologous DNA sequences have been found upstream of the promoter in many of these IFN-inducible genes and bind a family of trans-acting proteins. Interferon consensus sequence binding protein (ICSBP) is one member of this family of interferon regulatory factors (IRF) and is structurally related within the DNA-binding domain to the other members, IRF-1, IRF-2, and ISGF3 gamma. ISCBP mRNA levels become elevated in response to IFN-gamma; however, little is known about the regulation of ICSBP expression at the protein level. In this study, anti-ICSBP peptide Abs were used to quantify and localize ICSBP in murine peritoneal exudate macrophages. Western blot analysis of cytoplasmic and nuclear extracts from treated and control cells revealed ICSBP to be induced by IFN-gamma and not by IFN-alpha and to exist primarily in the nucleus. The regulation of ICSBP induction by IFN-gamma was consistent with the characteristics found at the mRNA level; inhibition by IFN-alpha or glucocorticoids and the requirement for protein kinase C (as determined pharmacologically). The time course of IFN-gamma-induced ICSBP showed an induction of protein that required approximately 12 h to reach maximal levels. Induced ICSBP was relatively stable, exhibiting a half-life of approximately 48 h. Indirect immunofluorescence also demonstrated ICSBP to be an IFN-gamma-inducible protein that is strongly localized to the nucleus.

Amino Acid Sequence↗
PubMed1994

Taxol provides a second signal for murine macrophage tumoricidal activity.

The anticancer drug, taxol, blocks cell division by stabilizing microtubules. However, taxol has distinct cell-cycle-independent effects. For example, taxol and bacterial LPS induce strikingly similar responses in murine macrophages. Here we report that taxol, like LPS, provides a "second" signal for murine macrophage activation to tumoricidal activity. Tumoricidal activity was determined by the release of 51Cr from prelabeled P815 mastocytoma target cells. Taxol or LPS alone weakly induced C3H/OuJ (Lpsn) murine macrophages to kill P815 mastocytoma cells, and tumoricidal activity was not induced by the classic "priming" signal, IFN-gamma. However, combinations of taxol or LPS with IFN-gamma synergized to activate macrophages to lyse tumor cells. Taxol activation of macrophages required an intact LPS signaling pathway, as taxol did not induce IFN-gamma-treated C3H/HeJ (Lpsd) macrophages to lyse target cells. In normal (Lpsn) murine macrophages, IFN-gamma, LPS, or taxol alone induced low or moderate levels of nitric oxide synthase gene expression and nitric oxide secretion. However, this gene and cytostatic metabolite were induced synergistically by combinations of taxol or LPS with IFN-gamma. Secretion of nitric oxide correlated with tumor cell killing, and taxol-activated macrophages failed to kill tumor targets in the presence of NG-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthase. The data illustrate the potential for taxol to activate macrophage mediated-antitumor mechanisms in addition to its better characterized role as an anti-mitotic agent.

Amino Acid Oxidoreductases↗