The function of multiple IκB:NF-κB complexes in the resistance of cancer cells to Taxol-induced apoptosis
The function of multiple IκB:NF-κB complexes in the resistance of cancer cells to Taxol-induced apoptosis
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DOI：
10.1038/sj.onc.1205848
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发表时间：
2002-09-19
期刊：
影响因子：
8
通讯作者：
Chiao, PJ
中科院分区：
文献类型：
--
作者：
Dong, QG;Sclabas, GM;Chiao, PJ
Rel/NF-kappaB转录因子通过调控特定基因的表达在细胞凋亡和肿瘤发生中起关键作用。为了确定RelA的组成性活性在肿瘤发生中的作用，我们产生了表达IkappaBalpha的显性负突变体（IkappaBalphaM）的胰腺肿瘤细胞系。在本报告中，我们表明，抑制组成型NF-κ B活性，无论是通过异位表达的IkappaBalphaM或通过处理细胞与蛋白酶体抑制剂PS-341，它阻止细胞内降解的IB α蛋白，下调表达的bcl-xl。我们鉴定了bcl-xl启动子中两个假定的NF-κ B结合位点（κ B/A和B），并发现这两个位点与不同的NF-κ B蛋白相互作用。p65/p50异二聚体与κ B/A位点相互作用，而p50/p50同二聚体与κ B/B位点相互作用。bcl-xl启动子报告基因分析显示NF-κ B依赖的转录激活主要由kappaB/A位点介导，表明bcl-xl是RelA/ p50调控的下游靶基因之一。IkappaBalphaM和PS-341都完全消除NF-κ B DNA结合活性;然而，PS-341，而不是IkappaBalphaM的异位表达，使细胞对紫杉醇诱导的凋亡敏感。这是由于紫杉醇介导的RelA通过IkappaB β的磷酸化和降解的再活化以及NF-κ B调节的bcl-xl基因在这些癌细胞中的再表达，因为bcl-xl基因的异位表达赋予PS-341致敏细胞对紫杉醇诱导的细胞凋亡的抗性。这些结果证明了各种NF-κ B/IkappaB复合物在调节抗凋亡基因响应凋亡刺激中的重要功能，并且它们提高了NF-κ B：IkappaB α和NF-κ B：IkappaB β复合物受不同上游激活剂调节的可能性，并且NF-κ B在胰腺肿瘤发生中起关键作用。
The Rel/NF-kappaB transcription factors play a key role in the regulation of apoptosis and in tumorigenesis by controlling the expressions of specific genes. To determine the role of the constitutive activity of RelA in tumorigenesis, we generated pancreatic tumor cell lines that express a dominant negative mutant Of IkappaBalpha (IkappaBalphaM). In this report, we show that the inhibition of constitutive NF-kappaB activity, either by ectopic expression Of IkappaBalphaM or by treating the cells with a proteasome inhibitor PS-341 which blocks intracellular degradation Of IBalpha proteins, downregulates the expression of bcl-xl. We identified two putative NF-kappaB binding sites (kappaB/A and B) in the bcl-xl promoter and found that these two sites interact with different NF-kappaB proteins. p65/p50 heterodimer interacts with kappaB/A site whereas p50/p50 homodimer interacts with kappaB/B. The bcl-xl promoter reporter gene assays reveal that NF-kappaB dependent transcriptional activation is mainly mediated by kappaB/A site, indicating that bcl-xl is one of the downstream target genes regulated by RelA/ p50. Both IkappaBalphaM and PS-341 completely abolish NF-kappaB DNA binding activity; however, PS-341, but not ectopic expression Of IkappaBalphaM, sensitized cells to apoptosis induced by Taxol. This is due to the Taxol-mediated reactivation of RelA through phosphorylation and degradation Of IkappaBbeta and the re-expression of NF-kappaB regulated bcl-xl gene in these cancer cells as ectopic expression of the bcl-xl gene confers resistance to Taxol-induced apoptosis in PS-341 sensitized cells. These results demonstrate the important function of various NF-kappaB/IkappaB complexes in regulating anti-apoptotic genes in response to apoptotic stimuli, and they raise the possibility that NF-kappaB:IkappaBalpha and NF-kappaB:IkappaBbeta complexes are regulated by different upstream activators, and that NF-kappaB plays a key role in pancreatic tumorigenesis.