Division of Hematology/Oncology, Department of Medicine, Weill Cornell Medical College, New York, NY, USA.
Blood. 2011 Sep 29;118(13):3559-69. doi: 10.1182/blood-2011-06-357996. Epub 2011 Aug 9.
The phenotype of germinal center (GC) B cells includes the unique ability to tolerate rapid proliferation and the mutagenic actions of activation induced cytosine deaminase (AICDA). Given the importance of epigenetic patterning in determining cellular phenotypes, we examined DNA methylation and the role of DNA methyltransferases in the formation of GCs. DNA methylation profiling revealed a marked shift in DNA methylation patterning in GC B cells versus resting/naive B cells. This shift included significant differential methylation of 235 genes, with concordant inverse changes in gene expression affecting most notably genes of the NFkB and MAP kinase signaling pathways. GC B cells were predominantly hypomethylated compared with naive B cells and AICDA binding sites were highly overrepresented among hypomethylated loci. GC B cells also exhibited greater DNA methylation heterogeneity than naive B cells. Among DNA methyltransferases (DNMTs), only DNMT1 was significantly up-regulated in GC B cells. Dnmt1 hypomorphic mice displayed deficient GC formation and treatment of mice with the DNA methyltransferase inhibitor decitabine resulted in failure to form GCs after immune stimulation. Notably, the GC B cells of Dnmt1 hypomorphic animals showed evidence of increased DNA damage, suggesting dual roles for DNMT1 in DNA methylation and double strand DNA break repair.
生发中心（GC）B 细胞的表型包括对快速增殖和激活诱导胞嘧啶脱氨酶（AICDA）的致突变作用的独特耐受性。鉴于表观遗传模式在决定细胞表型方面的重要性，我们研究了 DNA 甲基化和 DNA 甲基转移酶在 GC 形成中的作用。DNA 甲基化分析显示，GC B 细胞与静止/幼稚 B 细胞相比，DNA 甲基化模式发生了明显变化。这种转变包括 235 个基因的甲基化差异显著，基因表达的一致性变化影响最显著的是 NFkB 和 MAP 激酶信号通路的基因。与幼稚 B 细胞相比，GC B 细胞主要呈低甲基化状态，AICDA 结合位点在低甲基化位点中高度富集。GC B 细胞也表现出比幼稚 B 细胞更高的 DNA 甲基化异质性。在 DNA 甲基转移酶（DNMTs）中，只有 DNMT1 在 GC B 细胞中显著上调。Dnmt1 条件性敲除小鼠显示 GC 形成缺陷，用 DNA 甲基转移酶抑制剂地西他滨处理小鼠可导致免疫刺激后无法形成 GC。值得注意的是，Dnmt1 条件性敲除动物的 GC B 细胞显示出 DNA 损伤增加的证据，表明 DNMT1 在 DNA 甲基化和双链 DNA 断裂修复中具有双重作用。
