Woodward J G, Omer K W, Stuart P M
Department of Microbiology and Immunology, University of Kentucky Medical Center, Lexington 40536-0084.
J Immunol. 1989 Jun 1;142(11):4062-9.
Although the MHC class II genes are known to be regulated transcriptionally, the relative rates of transcription of the four classical class II genes in different cell types have not been investigated. Using nuclear transcriptional analysis, we have investigated the transcriptional rates of the class II genes in the macrophage cell line WEHI-3, normal bone marrow-derived macrophages, L-929 cells, and two different B cell lymphoma lines. Kinetic analysis of class II transcription in IFN-gamma-treated WEHI-3 cells revealed a 4-h delay, followed by a rapid increase in transcription over the next 20 h. A significant basal level of class II transcription, apparent in bone marrow derived macrophages, was also further enhanced by IFN-gamma treatment. None of the class II genes were transcribed in L cells, whereas all class II genes were transcribed constitutively in the B cell lines. In both B cell lines and macrophages, the four class II genes were found to be transcribed at different rates from one another, but the only gene showing a consistent pattern in multiple experiments was A-alpha, always showing the highest rate. We also investigated the effect of protein synthesis inhibition on class II transcription. Cycloheximide treatment of WEHI-3 cells did not inhibit IFN-gamma-induced transcription of the class II genes within 8 h, suggesting that IFN-gamma acts on pre-existing trans-acting factors, rather than inducing their synthesis. In contrast, treatment of B cells with cycloheximide for 8 h significantly reduced class II transcription, suggesting that, in B cells, continuous synthesis of a labile trans-acting factor is required for constitutive expression. These data support the notion that class II expression in B cells is mediated by trans-acting factors distinct from those found in macrophages.
虽然已知MHC II类基因受转录调控，但尚未对不同细胞类型中四个经典II类基因的相对转录速率进行研究。我们利用核转录分析，研究了II类基因在巨噬细胞系WEHI-3、正常骨髓来源的巨噬细胞、L-929细胞以及两种不同的B细胞淋巴瘤系中的转录速率。对经干扰素-γ处理的WEHI-3细胞中II类转录的动力学分析显示，有4小时的延迟，随后在接下来的20小时内转录迅速增加。在骨髓来源的巨噬细胞中明显存在的显著基础水平的II类转录，也因干扰素-γ处理而进一步增强。II类基因在L细胞中均不转录，而在B细胞系中所有II类基因均组成性转录。在B细胞系和巨噬细胞中，发现四个II类基因彼此转录速率不同，但在多个实验中唯一呈现一致模式的基因是A-α，其转录速率始终最高。我们还研究了蛋白质合成抑制对II类转录的影响。用放线菌酮处理WEHI-3细胞8小时内并未抑制干扰素-γ诱导的II类基因转录，这表明干扰素-γ作用于预先存在的反式作用因子，而非诱导其合成。相反，用放线菌酮处理B细胞8小时显著降低了II类转录，这表明在B细胞中，组成性表达需要持续合成一种不稳定的反式作用因子。这些数据支持这样一种观点，即B细胞中II类表达是由与巨噬细胞中不同的反式作用因子介导的。
