Involvement of protein kinase C during taxol-induced activation of murine peritoneal macrophages.
Taxol has been known to block cell division by stabilizing microtubules with promising anticancer activity. However, taxol has distinct cell cycle-independent effects. Recently, this novel drug has been shown to provide a second signal for murine macrophage activation to tumoricidal activity via L-arginine-dependent nitric oxide (NO) synthesis. To investigate the mechanism of taxol-induced NO synthesis, we evaluated the ability of protein kinase C (PKC) inhibitors such as staurosporine (STSN) or polymyxin B to block taxol-induced effects. Taxol alone had only a small effect, whereas taxol in combination with rIFN-gamma markedly increased NO synthesis in a dose-dependent manner. STSN and polymyxin B decreased NO synthesis, which had been induced by rIFN-gamma plus taxol. Furthermore, prolonged incubation of the cells with phorbol ester, which down-regulates PKC activity, abolished synergistic cooperative effect of taxol with rIFN-gamma on NO synthesis. Synergy between IFN-gamma and taxol was mainly dependent on taxol-induced TNF-alpha secretion because not only the increase of inducible NO synthase (iNOS) gene expression by rIFN-gamma plus taxol was associated with the increased expression of TNF-alpha gene but also taxol-induced NO production was decreased by the treatment of anti-murine TNF-alpha neutralizing Abs. STSN and polymyxin B potently inhibited taxol-induced TNF-alpha secretion and TNF-alpha gene expression as well as iNOS gene expression by rIFN-gamma plus taxol. However, rIFN-gamma plus TNF-alpha-induced NO synthesis was not blocked by STSN or polymyxin B. This result indicates that TNF-alpha-induced signaling for induction of NO synthesis is not dependent on PKC activation, and further suggests that the point at which TNF-alpha acts on the NO synthesis from rIFN-gamma-primed macrophages lies next to the point of PKC activation. In conclusion, the present results strongly suggest that the capacity of taxol to increase NO synthesis from rIFN-gamma-primed macrophages is the result of taxol-induced TNF-alpha secretion via the signal transduction pathway of PKC activation.
Jun
C D
CD
Department of Microbiology and Immunology, Wonkwang University School of Medicine, Iksan, Korea.
Choi
B M
BM
Kim
H M
HM
Chung
H T
HT
D000199:Actins / Q000235:genetics; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects* / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000096:biosynthesis; D017239:Paclitaxel / Q000494:pharmacology*; D011112:Polymyxin B / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D011994:Recombinant Proteins; D019311:Staurosporine; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
D000199:Actins; D000470:Alkaloids; D017931:DNA Primers; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; D011493:Protein Kinase C; D019311:Staurosporine; D011112:Polymyxin B; D017239:Paclitaxel