Paclitaxel-induced immune suppression is associated with NF-kappa B activation via conventional PKC isotypes in lipopolysaccharide-stimulated 70Z/3 pre-B-lymphocyte tumor cells

Paclitaxel, a potent antitumor agent, has been shown to be lipopolysacchari de (LPS) mimetic in mice, stimulating signaling pathways and gene expressio n indistinguishably from LPS. In the present study, we showed the intracell ular signaling pathway of paclitaxel-induced nuclear factor-kappaB (NF-kapp aB) activation and its suppressive effect on LPS-induced signaling in murin e 70Z/3 pre-B cells. Stimulation of 70Z/3 cells with LPS for 30 min caused activation of NF-kappaB in the nuclei by detection of DNA-protein binding s pecific to NF-kappaB. Similarly, paclitaxel also produced a marked and dose -related NF-kappaB activation. However, pretreatment of cells with 10 muM p aclitaxel for 18 h resulted in complete inhibition of LPS-mediated NF-kappa B activation. Interestingly, the activity of I kappaB kinase (IKK-beta), wh ich plays an essential role in NF-kappaB activation through I kappaB phosph orylation, was largely enhanced in paclitaxel-treated cells, detected as I kappaB alpha phosphorylation. Because protein kinase C (PKC) is implicated in the activation of NF-kappaB via IKK-beta, the effect of paclitaxel on PK C activation was also measured. It was shown that NF-kappaB nuclear translo cation and DNA binding in response to paclitaxel was completely blocked by the conventional PKC inhibitor, Go 6976. Moreover, immunoblotting analysis with paclitaxel-treated cell extract demonstrated that the conventional PKC isotype PKC-alpha was found to be involved in the regulation of paclitaxel -induced NF-kappaB activation, as determined by electrophoretic mobility sh ift of PKC. Therefore, these data suggest that paclitaxel may activate IKK- beta via conventional PKC isotypes, resulting in NF-kappaB activation and, finally, desensitization of LPS-inducible signaling pathway in 70Z/3 pre-B cells.