Civil A, Rensink I, Aarden L A, Verweij C L
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Department of Autoimmune Diseases, 1066 CX Amsterdam, The Netherlands.
J Biol Chem. 1999 Nov 26;274(48):34369-74. doi: 10.1074/jbc.274.48.34369.
Activation of T cells through the antigen-specific T-cell receptor in combination with a costimulatory signal results in efficient cytokine gene transcription. The CD28-induced signal represents a major costimulatory signal for T cells. A CD28 response element, named CD28RE, was first identified in the interleukin-2 (IL-2) promoter region. Here we demonstrate that the NF-kappaB sequence in the IL-6 promoter functions as a CD28 response element. Mutations in this sequence rendered the IL-6 promoter unresponsive to CD28 costimulation. Moreover, this element could replace the IL-2 CD28RE in conferring CD28 responsiveness to the IL-2 promoter. In analogy to the known CD28 response elements IL-2 CD28RE, IL-8 CD28RE, and the human immunodeficiency virus-1 (HIV-1) NF-kappaB motif, the IL-6 NF-kappaB motif efficiently bound c-Rel, c-Rel/NFKB1, and the recently identified inducible T-cell factor NF-MATp35. However, the IL-6 NF-kappaB sequence together with the IL-8 CD28RE and HIV-1 NF-kappaB sequence differed from the IL-2 CD28RE in the binding of NF-kappaB/Rel family proteins. Although the IL-2 CD28RE exerted selective binding with c-Rel and c-Rel/NFKB1, the other CD28REs allowed efficient binding of a wide range of NF-kappaB/Rel family proteins. The difference in binding specificity correlated with the capacity of the distinct CD28 response elements to function in the context of the IL-6 promoter in response to T-cell activation. Domain swapping experiments revealed that the IL-8 CD28RE and HIV-1 NF-kappaB motif conferred similar responsiveness as the genuine IL-6 NF-kappaB motif in the transcriptional activation of the IL-6 promoter upon CD28 costimulation. In contrast, replacement of the IL-6 NF-kappaB sequence by the IL-2 CD28RE motif strongly reduced the responsiveness of the IL-6 promoter. These data indicate that despite the sequence similarity, two different classes of CD28 responsive elements exist that differ in their NF-kappaB binding capacity and the ability to confer CD28 costimulatory responsiveness toward a heterologous promoter.
通过抗原特异性T细胞受体并结合共刺激信号激活T细胞，可导致有效的细胞因子基因转录。CD28诱导的信号是T细胞的主要共刺激信号。一个名为CD28RE的CD28反应元件首先在白细胞介素-2（IL-2）启动子区域被鉴定出来。在此我们证明，IL-6启动子中的NF-κB序列作为一个CD28反应元件发挥作用。该序列中的突变使IL-6启动子对CD28共刺激无反应。此外，这个元件可以取代IL-2 CD28RE，赋予IL-2启动子对CD28的反应性。与已知的CD28反应元件IL-2 CD28RE、IL-8 CD28RE以及人类免疫缺陷病毒-1（HIV-1）NF-κB基序类似，IL-6 NF-κB基序能有效结合c-Rel、c-Rel/NFKB1以及最近鉴定出的诱导性T细胞因子NF-MATp35。然而，IL-6 NF-κB序列与IL-8 CD28RE和HIV-1 NF-κB序列在NF-κB/Rel家族蛋白的结合上与IL-2 CD28RE不同。虽然IL-2 CD28RE与c-Rel和c-Rel/NFKB1有选择性结合，但其他CD28RE允许广泛的NF-κB/Rel家族蛋白有效结合。结合特异性的差异与不同的CD28反应元件在T细胞激活时在IL-6启动子背景下发挥作用的能力相关。结构域交换实验表明，在CD28共刺激时，IL-8 CD28RE和HIV-1 NF-κB基序在IL-6启动子的转录激活中赋予与真正的IL-6 NF-κB基序相似的反应性。相反，用IL-2 CD28RE基序取代IL-6 NF-κB序列会强烈降低IL-6启动子的反应性。这些数据表明，尽管序列相似，但存在两类不同的CD28反应元件，它们在NF-κB结合能力以及赋予异源启动子对CD28共刺激反应性的能力方面存在差异。
