Mechanism of Action of Interferon-gamma

干扰素(IFN)通过与细胞受体相互作用来激活基因表达的方法正在积极研究中。已有研究表明，尽管存在正常的物种特异性屏障，但细胞内的人干扰素-γ可以激活小鼠细胞的特征反应，这可能是由于受体造成的。这种作用不是由于诱导合成小鼠干扰素或肿瘤坏死因子所致。将要进行的实验将确定其他次级调解人是否会对此负责。如果不是，则将研究细胞内干扰素-γ激活基因表达的替代机制，以及这种反应与干扰素-γ作用的正常生理途径之间的关系。为了研究次级介质的作用，我们将在瞬时或在可调节启动子的作用下，或在脂质体融合的情况下，检测细胞内表达干扰素-γ的细胞对MHC-II类基因表达的诱导。中和性抗体和蛋白质合成抑制剂将被添加到这些细胞中，以阻止次级介质的作用或产生。为了研究细胞内干扰素-γ激活反应的机制，将进行一项研究，以确定与游离干扰素-γ相互作用的细胞质蛋白。干扰素-γ分子的突变将被用来探索C-末端结构域在正常的细胞外和细胞内活动中的作用。干扰素通过受体介导的信号转导在靶细胞上发挥作用，如诱导特定基因表达。这项拟议的工作包含了一个非传统的概念，即细胞外配体可以具有细胞内功能。提出的实验将探索一种假设，即干扰素直接作用于特定基因，可能是在细胞核内。从这项研究中获得的信息可能被证明适用于其他细胞因子和生长因子使用的信号机制。

The means by which interferons (IFNs) activate gene expression through interaction with cellular receptors is being actively investigated. It has been shown that intracellular human IFN-gamma can activate characteristic responses in murine cells despite the normal species-specificity barrier presumed to be due to the receptor. This effect is not due to induced synthesis of murine IFNs or TNF. Experiments to be performed will determine whether other secondary mediators could be responsible. If they are not, alternative mechanisms by which intracellular IFN-gamma may activate gene expression and the relationship between this response and the normal physiological pathway for IFN-gamma action will be investigated. To examine the role of secondary mediators, the induction of MHC class II mRNA expression in cells will be assayed in cells expressing intracellular IFN-gamma transiently or under a regulatable promoter, or after delivery of IFN-gamma protein by liposome fusion. Neutralizing antibodies and inhibitors of protein synthesis will be added to such cells to block the action or production of secondary mediators. To examine mechanisms by which intracellular IFN-gamma can activate responses, a search will be made to identify cytoplasmic proteins which interact with free IFN- gamma. Mutations of the IFN-gamma molecule will be used to explore the role of C-terminal domains in both normal extracellular and intracellular activity. The "comon wisdom" is that inteferons exert their effects, such as induction of specific gene expression, on target cells via receptor-mediated signal transduction. The proposed work embraces an unconventional concept, i.e., that an extracellular ligand can have an intracellular function. The experiments proposed will explore the hypothesis that IFN acts directly, possibly within the nucleus, to turn on specific genes. The information obtained from this study could turn out to be applicable to signaling mechanisms used by other cytokines and growth factors.