Ig Enhancers Increase RNA Polymerase II Stalling at Somatic Hypermutation Target Sequences.
Ig Enhancers Increase RNA Polymerase II Stalling at Somatic Hypermutation Target Sequences.
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DOI：
10.4049/jimmunol.2100923
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发表时间：
2022-01-01
期刊：
影响因子：
--
通讯作者：
Alinikula J
中科院分区：
文献类型：
--
作者：
Tarsalainen A;Maman Y;Meng FL;Kyläniemi MK;Soikkeli A;Budzyńska P;McDonald JJ;Šenigl F;Alt FW;Schatz DG;Alinikula J
体细胞超突变（SHM）在活化的B细胞中驱动免疫球蛋白（Ig）基因的遗传多样性，并支持对抗原亲和力增加的抗体的产生。SHM通过Ig基因的增强子（DIVACs；多样化激活子）靶向Ig基因，但增强子如何介导这种活性尚不清楚。我们在鸡DT40 B细胞中发现，高活性的DIVACs增加了突变基因中RNA聚合酶2 （Pol2）的磷酸化和Pol2的占用，但很少或没有增加伸长能力的Pol2或产生全长转录本，这表明Pol2的积累停滞了。DIVAC在人类拉莫斯伯基特淋巴瘤细胞中也有类似的效果。divac诱导的失速与突变靶基因中单链DNA气泡检测的增加弱相关。我们没有发现反义转录的证据，也没有发现DIVAC通过改变突变基因中H3K27ac或组蛋白变体H3.3的水平起作用。这些研究结果表明，在SHM的情况下，Pol2延迟和顺式作用靶向元件之间存在联系，从而确定了基因组中SHM位点特异性靶向的机制基础。我们的研究结果表明，DIVAC元件使靶基因成为艾滋病介导突变的合适平台，而不需要增加转录输出。
Somatic hypermutation (SHM) drives the genetic diversity of immunoglobulin (Ig) genes in activated B cells and supports the generation of antibodies with increased affinity for antigen. SHM is targeted to Ig genes by their enhancers (DIVACs; diversification activators), but how the enhancers mediate this activity is unknown. We show using chicken DT40 B cells that highly active DIVACs increase the phosphorylation of RNA polymerase 2 (Pol2) and Pol2 occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol2 or production of full-length transcripts, indicating accumulation of stalled Pol2. DIVAC has similar effect also in human Ramos Burkitt lymphoma cells. The DIVAC-induced stalling is weakly associated with an increase in the detection of single-stranded DNA bubbles in the mutating target gene. We did not find evidence for antisense transcription, or that DIVAC functions by altering levels of H3K27ac or the histone variant H3.3 in the mutating gene. These findings argue for a connection between Pol2 stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVAC elements render the target gene a suitable platform for AID-mediated mutation without a requirement for increasing transcriptional output.
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