Thornton A M, Ogryzko V V, Dent A, Sharf R, Levi B Z, Kanno Y, Staudt L M, Howard B H, Ozato K
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
J Immunol. 1996 Dec 1;157(11):5145-54.
Type I (alpha,beta) and type II (gamma) IFNs elicit antiproliferative and antiviral activities through two distinct transcription pathways involving 1) IRF family proteins and ISGF3, and 2) STAT1. We have employed a dominant negative strategy to study the role of IRF family proteins in eliciting the biologic activities of IFN. A truncated IRF protein retaining the DNA-binding domain (DBD) of ICSBP (a member of the IRF family) was stably transfected into U937 monocytic cells. Clones expressing DBD had markedly reduced ISRE-binding activity and were defective in expressing several type I IFN-inducible genes. STAT1 was one such type I IFN-inducible gene whose expression was also inhibited in DBD clones. As a result, the expression of several IFN-gamma-inducible genes was also inhibited in these clones, indicating functional coupling of the type I and type II IFN transcription pathways. Furthermore, DBD clones grew more slowly than control clones and were refractory to antiproliferative effects of both types of IFNs. We found that IFN treatment of U937 cells leads to a G1 arrest and an increase in underphosphorylated retinoblastoma gene product. However, IFN treatment did not change the cell cycle profile, nor retinoblastoma gene product phosphorylation state in DBD clones. These data indicate that expression of DBD disrupts cell cycle regulatory mechanisms. Combined with the previously noted failure of DBD clones to elicit antiviral activity, the present work shows that IRF family proteins play an integral part in growth control activities of IFNs.
I型（α、β）和II型（γ）干扰素通过两条不同的转录途径引发抗增殖和抗病毒活性，这两条途径涉及：1）干扰素调节因子（IRF）家族蛋白和干扰素刺激基因因子3（ISGF3）；2）信号转导和转录激活因子1（STAT1）。我们采用显性负性策略来研究IRF家族蛋白在引发干扰素生物学活性中的作用。将保留干扰素共识序列结合蛋白（ICSBP，IRF家族成员之一）的DNA结合结构域（DBD）的截短IRF蛋白稳定转染至U937单核细胞中。表达DBD的克隆的干扰素刺激反应元件（ISRE）结合活性显著降低，并且在表达几个I型干扰素诱导基因方面存在缺陷。STAT1就是这样一个I型干扰素诱导基因，其在DBD克隆中的表达也受到抑制。结果，几个γ干扰素诱导基因在这些克隆中的表达也受到抑制，这表明I型和II型干扰素转录途径存在功能偶联。此外，DBD克隆的生长比对照克隆更慢，并且对两种类型干扰素的抗增殖作用均不敏感。我们发现，用干扰素处理U937细胞会导致G1期停滞，并使视网膜母细胞瘤基因产物的低磷酸化水平增加。然而，干扰素处理并未改变DBD克隆的细胞周期分布，也未改变视网膜母细胞瘤基因产物的磷酸化状态。这些数据表明，DBD的表达破坏了细胞周期调控机制。结合之前提到的DBD克隆无法引发抗病毒活性，目前的研究表明IRF家族蛋白在干扰素的生长控制活性中发挥着不可或缺的作用。
