de Wit H, Dokter W H, Koopmans S B, Lummen C, van der Leij M, Smit J W, Vellenga E
Department of Internal Medicine, University of Groningen, The Netherlands.
Leukemia. 1998 Mar;12(3):363-70. doi: 10.1038/sj.leu.2400950.
The transcription factor NF-kappaB plays an important role in the regulated expression of cytokines in human monocytes. A p100 subunit of NF-kappaB has IkappaB-like properties by sequestering the p65 transactivating subunit in the cytosol of cells. In transient transfection assays we demonstrated that p100 has an inhibitory effect on the NF-kappaB-dependent IL-6 promoter activity. In view of this finding, we studied the regulation of the p100 subunit in human monocytes in response to LPS, the inflammatory cytokines IL-1beta and TNF-alpha and lymphokines. The results demonstrate that LPS, IL-1beta, and TNF-alpha induce p100 expression at mRNA and protein level while IFN-gamma, IL-3 and IL-4/IL-10 have no effect. The induction of p100 expression was shown to be mediated by a two-fold increase in the p100 transcription rate and a two-fold increase in p100 mRNA stability. Furthermore the p100 mediated upregulation was dependent on a tyrosine kinase dependent pathway rather than the protein kinase C pathway. NF-kappaB is a complex of either p50 homodimers or a p50/p65 heterodimer. The latter is known to strongly autoregulate p100 transcription. We therefore examined the composition of NF-kappaB induced by LPS vs the different lymphokines. LPS-induced NF-kappaB showed a distinct p65 supershift whereas the composition of NF-kappaB induced by different lymphokines did not show a change in p65. We conclude that the p100 subunit of the transcription factor NF-kappaB is induced by different inflammatory mediators while lymphokines fail to induce p100 expression which may be caused by the induction of NF-kappaB predominantly consisting of p50 homodimers.
转录因子核因子-κB（NF-κB）在人类单核细胞中细胞因子的调控表达中发挥重要作用。NF-κB的p100亚基通过在细胞质中隔离p65反式激活亚基而具有类IκB的特性。在瞬时转染实验中，我们证明p100对NF-κB依赖的白细胞介素-6（IL-6）启动子活性具有抑制作用。鉴于这一发现，我们研究了人类单核细胞中p100亚基对脂多糖（LPS）、炎性细胞因子白细胞介素-1β（IL-1β）和肿瘤坏死因子-α（TNF-α）以及淋巴因子的反应调控。结果表明，LPS、IL-1β和TNF-α在mRNA和蛋白质水平诱导p100表达，而干扰素-γ（IFN-γ）、IL-3和IL-4/IL-10则无此作用。p100表达的诱导被证明是由p100转录速率增加两倍和p100 mRNA稳定性增加两倍介导的。此外，p1介导的上调依赖于酪氨酸激酶依赖的途径，而不是蛋白激酶C途径。NF-κB是由p50同二聚体或p50/p65异二聚体组成的复合物。已知后者强烈自调控p100转录。因此，我们研究了LPS与不同淋巴因子诱导的NF-κB的组成。LPS诱导的NF-κB显示出明显的p65超迁移条带，而不同淋巴因子诱导的NF-κB的组成在p65上没有变化。我们得出结论，转录因子NF-κB的p100亚基由不同的炎性介质诱导，而淋巴因子未能诱导p100表达，这可能是由于主要由p50同二聚体组成的NF-κB的诱导所致。
