He Bin, Weber Georg F
Department of Radiation Oncology, New England Medical Center, Boston, MA, USA.
Eur J Biochem. 2003 May;270(10):2174-85. doi: 10.1046/j.1432-1033.2003.03574.x.
The transcription factor NF-kappaB is activated in cellular stress responses. This requires rapid regulation of its function, which is accomplished, in part, by various modes of phosphorylation. Even though diverse DNA binding subunits of NF-kappaB proteins may transactivate from distinct recognition sequences, the differential regulation of transcription from the large number of NF-kappaB responsive sites in various gene promoters and enhancers has been incompletely understood. The cyclic GMP-dependent kinase (PKG) is an important mediator of signal transduction that may induce gene expression through cAMP response element binding protein (CREB) and through other, yet undefined, mechanisms. We have previously characterized a signal transduction pathway that leads to activation-induced cell death in T-lymphocytes and involves the activation of PKG. Here we demonstrate that the NF-kappaB proteins p65, p49 (also called p52), and p50 are specific substrates for this kinase. PKG dose-dependently increases the transactivating activity of p65 from the NF-kappaB consensus sequence. It also mediates dose-dependently an increase in transcriptional activity by p49 or p50 from a unique CCAAT/enhance binding protein (C/EBP)-associated NF-kappaB site, but not from the consensus site. Phosphorylation of p65, p50, or p49 does not alter their subcellular distribution. Because the release of cytosolic p65/p50 heterodimers into the nucleus is by itself insufficient to differentiate all the numerous NF-kappaB promoter sequences, phosphorylation of the DNA-binding subunits reveals a form of differential regulation of NF-kappaB activity and it implies a novel pathway for PKG-induced gene transcription. These observations may bear on mechanisms of programmed cell death in T-lymphocytes. They may also be relevant to ongoing efforts to induce cancer cell apoptosis through activation of PKG.
转录因子核因子-κB（NF-κB）在细胞应激反应中被激活。这需要对其功能进行快速调节，而这部分是通过各种磷酸化模式来实现的。尽管NF-κB蛋白的多种DNA结合亚基可能从不同的识别序列进行反式激活，但对于各种基因启动子和增强子中大量NF-κB反应位点转录的差异调节尚未完全了解。环磷酸鸟苷依赖性激酶（PKG）是信号转导的重要介质，它可能通过环磷酸腺苷反应元件结合蛋白（CREB）以及其他尚未明确的机制诱导基因表达。我们之前已经描述了一条导致T淋巴细胞激活诱导细胞死亡并涉及PKG激活的信号转导途径。在此我们证明，NF-κB蛋白p65、p49（也称为p52）和p50是这种激酶的特异性底物。PKG以剂量依赖性方式增加p65从NF-κB共有序列的反式激活活性。它还以剂量依赖性方式介导p49或p50从一个独特的CCAAT/增强子结合蛋白（C/EBP）相关的NF-κB位点增加转录活性，但从共有序列则不然。p65、p50或p49的磷酸化不会改变它们的亚细胞分布。由于胞质p65/p50异二聚体释放到细胞核本身不足以区分所有众多的NF-κB启动子序列，DNA结合亚基的磷酸化揭示了一种NF-κB活性的差异调节形式，这意味着PKG诱导基因转录的一条新途径。这些观察结果可能与T淋巴细胞程序性细胞死亡的机制有关。它们也可能与目前通过激活PKG诱导癌细胞凋亡的努力相关。
