Centre for Hematology, Department of Medicine, Imperial College London, W12 0NN London, United Kingdom; and.
Division of Cancer, Department of Surgery and Cancer, Imperial College London, W12 0NN London, United Kingdom.
J Immunol. 2019 Jun 15;202(12):3423-3433. doi: 10.4049/jimmunol.1801618. Epub 2019 May 13.
Induction of programmed DNA damage and its recognition and repair are fundamental for B cell development. The ssDNA-binding protein SSB1 has been described in human cells as essential for the recognition and repair of DNA damage. To study its relevance for B cells, we recently developed and conditional mice. Although SSB1 loss did not affect B cell development, cells exhibited compensatory expression of its homolog SSB2. We have now generated mice and show in this study that SSB2 is also dispensable for B cell development and DNA damage response activation. In contrast to the single loss of or , however, combined SSB1/2 deficiency caused a defect in early B cell development. We relate this to the sensitivity of B cell precursors as mature B cells largely tolerated their loss. Toxicity of combined genetic SSB1/2 loss can be rescued by ectopic expression of either SSB1 or SSB2, mimicked by expression of SSB1 ssDNA-binding mutants, and attenuated by BCL2-mediated suppression of apoptosis. SSB1/2 loss in B cell precursors further caused increased exposure of ssDNA associated with disruption of genome fragile sites, inefficient cell cycle progression, and increased DNA damage if apoptosis is suppressed. As such, our results establish SSB1/2 as safeguards of B cell development and unveil their differential requirement in immature and mature B lymphocytes.
诱导程序性 DNA 损伤及其识别和修复是 B 细胞发育的基础。在人类细胞中，单链 DNA 结合蛋白 SSB1 被描述为识别和修复 DNA 损伤所必需的。为了研究其与 B 细胞的相关性，我们最近开发了和条件性缺失小鼠。尽管 SSB1 缺失不影响 B 细胞的发育，但缺失细胞表现出其同源物 SSB2 的代偿性表达。我们现在已经生成了 SSB2 缺失小鼠，并在这项研究中表明，SSB2 对于 B 细胞发育和 DNA 损伤反应的激活也是可有可无的。与或的单一缺失相反，然而，SSB1/2 的联合缺失导致早期 B 细胞发育缺陷。我们将其与 B 细胞前体的敏感性联系起来，因为成熟的 B 细胞在很大程度上可以耐受它们的缺失。联合遗传 SSB1/2 缺失的毒性可以通过 SSB1 或 SSB2 的异位表达来挽救，这可以通过表达 SSB1 的单链 DNA 结合突变体来模拟，并通过 BCL2 介导的凋亡抑制来减弱。B 细胞前体中的 SSB1/2 缺失进一步导致与基因组脆弱位点破坏相关的 ssDNA 暴露增加、细胞周期进程效率降低和 DNA 损伤增加，如果抑制凋亡。因此，我们的研究结果确立了 SSB1/2 是 B 细胞发育的保障，并揭示了它们在不成熟和成熟 B 淋巴细胞中的不同需求。
