Disruption of Microtubules Sensitizes the DNA Damage-induced Apoptosis Through Inhibiting Nuclear Factor kappaB (NF-kappaB) DNA-binding Activity

The massive reorganization of microtubule network involves in transcriptional regulation of several genes by controlling transcriptional factor, nuclear factor-kappa B (NF-kappaB) activity. The exact molecular mechanism by which microtubule rearrangement leads to NF-kappaB activation largely remains to be identified. However microtubule disrupting agents may possibly act in synergy or antagonism against apoptotic cell death in response to conventional chemotherapy targeting DNA damage such as adriamycin or comptothecin in cancer cells. Interestingly pretreatment of microtubule disrupting agents (colchicine, vinblastine and nocodazole) was observed to lead to paradoxical suppression of DNA damage-induced NF-kappaB binding activity, even though these could enhance NF-kappaB signaling in the absence of other stimuli. Moreover this suppressed NF-kappaB binding activity subsequently resulted in synergic apoptotic response, as evident by the combination with Adr and low doses of microtubule disrupting agents was able to potentiate the cytotoxic action through caspase-dependent pathway. Taken together, these results suggested that inhibition of microtubule network chemosensitizes the cancer cells to die by apoptosis through suppressing NF-kappaB DNA binding activity. Therefore, our study provided a possible anti-cancer mechanism of microtubule disrupting agent to overcome resistance against to chemotherapy such as DNA damaging agent.

Diclofenac inhibits IFN-gamma plus lipopolysaccharide-induced iNOS gene expression via suppression of NF-kappaB activation in RAW 264.7 macrophages

Diclofenac, a phenylacetic acid derivative, is a widely used non-steroidal anti-inflammatory drug (NSAID) to provide effective relief of inflammation and pain. Nitric oxide (NO) synthesized by inducible nitric oxide synthase (iNOS) has been implicated as a mediator of inflammation. We examined the inhibitory effects of diclofenac on the induction of iNOS in RAW 264.7 macrophages which were activated with lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). Treatment of RAW 264.7 cells with diclofenac and other NSAIDs (aspirin and indomethacin) significantly inhibited NO production and iNOS protein expression induced by LPS plus IFN-gamma. Also, diclofenac but not aspirin and indomethacin, inhibited iNOS mRNA expression and nuclear factor-kappa B (NF-kappaB) binding activity concentration-dependently. Furthermore, transfection of RAW 264.7 cells with iNOS promoter linked to a CAT reporter gene revealed that only diclofenac inhibited the iNOS promoter activity induced by LPS plus IFN-gamma through the NF-kappaB sites of iNOS promoter. Taken together, these suggest that diclofenac may exert its anti-inflammatory effect by inhibiting iNOS gene expression at the transcriptional level through suppression of NF-kappaB activation.

Role of NF- kappaB binding sites in the regulation of inducible nitric oxide synthase by tyrosine kinase

In macrophages, lipopolysaccharide (LPS) alone or in combination with interferon- gamma (IFN- gamma) has been shown to release a nitric oxide (NO) through the increase of the transcription of the inducible nitric oxide synthase (iNOS) gene. To investigate the exact intracellular signaling pathway of the regulation of iNOS gene transcription by LPS plus IFN- gamma, the effects of protein tyrosine kinase (PTK) inhibitor and protein kinase C (PKC) inhibitors on NO production, iNOS mRNA expression, nuclear factor- kappaB (NF- kappaB) binding activity and the promoter activity of iNOS gene containing two NF- kappaB sites have been examined in a mouse macrophage RAW 264.7 cells. LPS or IFN- gamma, stimulated NO production, and their effect was enhanced synergistically by mixture of LPS and IFN- gamma. The PTK inhibitor such as tyrphostin reduced LPS plus IFN- gamma-induced NO production, iNOS mRNA expression and NF- kappaB binding activity. In contrast, PKC inhibitors such as H-7, Ro-318220 and staurosporine did not show any effect on them. In addition, transfection of RAW 264.7 cells with iNOS promoter linked to a CAT reporter gene revealed that tyrphostin inhibited the iNOS promoter activity through the NF- kappaB binding site, whereas PKC inhibitors did not. Taken together, these suggest that PTK, but not PKC pathway, is involved in the regulation of the iNOS gene transcription through the NF- kappaB sites of iNOS promoter in RAW 264.7 macrophages by LPS plus IFN- gamma.