INTRACELLULAR SIGNAL TRANSDUCTION OF INDUCIBLE NITRIC OXIDE SYNTHASE EXPRESSION IN THE CENTRAL NERVOUS SYSTEM

我们先前展示了功能诱导的硝酸氧化物合成酶（iNOS）的表达是由干扰素-γ （IFN-γ）在人类神经细胞线NB-39-nu中被诱导的，其mRNA水平是由TNF-α的同时治疗同步诱导的。在目前的研究中，我们研究了在NB-39-nu细胞中IFN-γ和TNF-α上iNOS基因激活的信号转移机制的协同效应。IFN-γ初级NB-39-nu细胞诱导的TNF-α和TNF 2型受体（TNF-R2）作为iNOS表达良好。在另一端， TNF型1受体（TNF 0 R1）不断地在未暴露的细胞中表达，并且在IFN-γ治疗期间，其表达水平没有改变。IFN-γ对iNOS mRNA表达的诱导的TNF-α的影响被证实为反TNF-α的事实，但不是反TNF-β中性化抗体抑制了IFN-γ处理的NB-39-nu细胞中iNOS mRNA的诱导。TNF-R2在iNOS基因激活的信号转移中的参与也得到了以下证据：1）TNF-α alone induces iNOS mRNA expression in the cell stably overexpressing TNF-R2（NB-39-nu/TNF-R2）但控制细胞不能稳定地表达β-GAL（NB-39-nu/β-GAL）和2）在NB-39-nu细胞中首次检测到iNOS mRNA，IFN-γ和TNF-α治疗后12小时，NB-39-nu/TNF-R2细胞在TNF-α治疗后可在6小时内检测到iNOS mRNA。NF-D2 k-D2 B抑制剂在NB-39-nu/TNF-R2细胞中明显抑制的TNF-α刺激的iNOS mRNA表达的添加。因此，IFN-γ可能在TNF信号转换机的激活中参与，以及TNF-α激活NF-β D2 k-β-β通过TNF-α信号可能发挥一个重要的作用，以促进NB-39-nu细胞对IFN-γ和TNF-α的刺激。These Findings may provide a new intracellular signal transduction Mechanism for the iNOS gene regulation in human neuronal cell.

We previously showed that the expression of functional inducible nitric oxide synthase (iNOS) was induced by interferon-γ (IFN-γ) in a human neuroblastoma cell line NB-39-nu, and its mRNA level was synergistically induced by simultaneous treatment of TNF-α. In the present study, we examined the signal transduction mechanism of the synergistic effect of IFN-γ and TNF-α on iNOS gene activation in NB-39 -nu cells. IFN-γ primed NB-39-nu cells induced TNF-α and TNF type 2 receptor (TNF-R2) as well as iNOS expressions. On the other hand, TNF type 1 receptor (TNF0R1) was continuously expressed in untreated cells, and its expression level did not change during the further treatment with IFN-γ. The involvement of TNF-α in the induction of iNOS mRNA expression by IFN-γ was evidenced by the fact that anti-TNF-α but not anti-TNF-β neutralizing antibody inhibits the induction of iNOS mRNA in IFN-γ-treated NB-39-nu cells. The involvement of TNF-R2 in the signal transduction for iNOS gene activation was also evidenced by followings: 1) TNF-α alone induces iNOS mRNA expression in the cells stably overexpressing TNF-R2 (NB-39-nu/TNF-R2) but not in control cells stably expressing β-GAL (NB-39-nu/β-GAL), and 2) although iNOS mRNA firstly detected in NB-39-nu cells at 12 hr after IFN-γ and TNF-α treatment, NB-39-nu/TNF-R2 cells could express iNOS mRNA at 6 hr after TNF-α alone treatment. The addition of NF-ィイD2kィエD2B inhibitor significantly suppressed TNF-α stimulated iNOS mRNA expression in NB-39-nu/TNF-R2 cells. Thus, IFN-γ may involved in the activation of TNF signal transduction machinery, and the NF-ィイD2kィエD2B activation by TNF-α through TNF-R2 signaling might play an important role for induction of iNOS expression in NB-39-nu cells upon stimulation with IFN-γ and TNF-α. These findings may provide a new intracelluar signal transduction mechanism for the iNOS gene regulation in human neuronal cells.