Integrated analyses of genome-wide DNA occupancy and expression profiling identify key genes and pathways involved in cellular transformation by Marek's disease oncoprotein, Meq

Marek’s disease (MD) is an economically significant disease in chickens caused by the highly oncogenic Marek’s disease virus (MDV). A major unanswered question is the mechanism of MDV-induced tumor formation. Meq, a bZIP transcription factor discovered in the 1990s, is critically involved in viral oncogenicity but only a few of its host target genes have been described impeding our understanding of MDV-induced tumorigenesis. Using ChIP-seq and microarray analysis, a high confidence list of Meq-binding sites in the chicken genome and a global transcriptome of Meq-responsive genes was generated. Meq binding sites were found to be enriched in the promoter regions of up-regulated genes, but not in those of down-regulated genes. ChIP-seq was also performed for c-Jun, a known heterodimeric partner of Meq. Close location of binding sites of Meq and c-Jun was noted, suggesting cooperativity between these two factors in modulating transcription. Pathway analysis indicated that Meq transcriptionally regulates many genes that are part of several signaling pathways include the ERK/MAPK, Jak-STAT, and ErbB pathways that are critical for oncogenesis and/or include signaling mediators involved in apoptosis. Meq activates oncogenic signaling cascades by transcriptionally activating major kinases in the ERK/MAPK pathway and simultaneously repressing phosphatases, as verified using inhibitors of MEK and ERK1/2 in a cell proliferation assay. This study provides significant insights into the mechanistic basis of Meq-dependent cell transformation. Overall design: Transcript profiling of DF-1 (a chicken embryo fibroblast cell line) and Meq-DF-1 clone 5G (DF-1 stably expressing Meq driven by the CMV promoter) using Affymetrix chicken GeneChips

马立克氏病（MD）作为一种对鸡养殖业具有显著经济影响的疾病，其病原体为高度恶性的马立克氏病病毒（MDV）。关于MDV诱导肿瘤形成的机制，仍存在一个关键的未解之谜。Meq，一种于20世纪90年代发现的bZIP转录因子，在病毒的致癌性中扮演着至关重要的角色，但其宿主靶基因的描述却寥寥无几，这阻碍了我们对于MDV诱导肿瘤发生机制的理解。通过ChIP-seq和微阵列分析，我们生成了一份高置信度的Meq结合位点列表以及Meq响应基因的全转录组。研究发现，Meq结合位点在上调基因的启动子区域富集，而在下调基因的启动子区域则未发现。此外，对c-Jun（Meq已知异源二聚体伙伴）也进行了ChIP-seq实验。观察到Meq和c-Jun的结合位点相互靠近，这表明这两个因子在调节转录过程中存在协同作用。通路分析表明，Meq通过转录调控多个基因，这些基因涉及多个信号通路，包括ERK/MAPK、Jak-STAT和ErbB通路，这些通路对于肿瘤发生和/或凋亡过程中的信号介导因子至关重要。Meq通过转录激活ERK/MAPK通路中的主要激酶，并同时抑制磷酸酶，从而激活致癌信号级联反应，这一过程通过使用MEK和ERK1/2抑制剂的细胞增殖实验得到验证。本研究为Meq依赖性细胞转化的机制基础提供了重要的见解。总体设计：利用Affymetrix鸡基因芯片对DF-1（一种鸡胚成纤维细胞系）和Meq-DF-1克隆5G（由CMV启动子驱动稳定表达Meq的DF-1细胞系）进行转录谱分析。