Department of Biochemistry, School of Medicine, University of Washington, Seattle, WA 98195-7350, USA.
DNA Repair (Amst). 2012 May 1;11(5):488-501. doi: 10.1016/j.dnarep.2012.02.004. Epub 2012 Apr 6.
Cockayne syndrome is a segmental progeria most often caused by mutations in the CSB gene encoding a SWI/SNF-like ATPase required for transcription-coupled DNA repair (TCR). Over 43Mya before marmosets diverged from humans, a piggyBac3 (PGBD3) transposable element integrated into intron 5 of the CSB gene. As a result, primate CSB genes now generate both CSB protein and a conserved CSB-PGBD3 fusion protein in which the first 5 exons of CSB are alternatively spliced to the PGBD3 transposase. Using a host cell reactivation assay, we show that the fusion protein inhibits TCR of oxidative damage but facilitates TCR of UV damage. We also show by microarray analysis that expression of the fusion protein alone in CSB-null UV-sensitive syndrome (UVSS) cells induces an interferon-like response that resembles both the innate antiviral response and the prolonged interferon response normally maintained by unphosphorylated STAT1 (U-STAT1); moreover, as might be expected based on conservation of the fusion protein, this potentially cytotoxic interferon-like response is largely reversed by coexpression of functional CSB protein. Interestingly, expression of CSB and the CSB-PGBD3 fusion protein together, but neither alone, upregulates the insulin growth factor binding protein IGFBP5 and downregulates IGFBP7, suggesting that the fusion protein may also confer a metabolic advantage, perhaps in the presence of DNA damage. Finally, we show that the fusion protein binds in vitro to members of a dispersed family of 900 internally deleted piggyBac elements known as MER85s, providing a potential mechanism by which the fusion protein could exert widespread effects on gene expression. Our data suggest that the CSB-PGBD3 fusion protein is important in both health and disease, and could play a role in Cockayne syndrome.
科凯恩综合征是一种节段性早衰症，通常由编码转录偶联 DNA 修复（TCR）所需的 SWI/SNF 样 ATP 酶的 CSB 基因突变引起。在狨猴与人类分化的 4300 万年前，一个 piggyBac3（PGBD3）转座元件就已经整合到 CSB 基因的内含子 5 中。因此，灵长类 CSB 基因现在产生 CSB 蛋白和一种保守的 CSB-PGBD3 融合蛋白，其中 CSB 的前 5 个外显子被选择性剪接到 PGBD3 转座酶上。通过宿主细胞再激活测定，我们发现融合蛋白抑制氧化损伤的 TCR，但促进 UV 损伤的 TCR。我们还通过微阵列分析表明，融合蛋白单独在 CSB 缺失的 UV 敏感综合征（UVSS）细胞中的表达会诱导类似于先天抗病毒反应和未磷酸化 STAT1（U-STAT1）正常维持的延长干扰素反应的干扰素样反应；此外，基于融合蛋白的保守性，这种潜在的细胞毒性干扰素样反应很大程度上可以通过共表达功能性 CSB 蛋白来逆转。有趣的是，CSB 和 CSB-PGBD3 融合蛋白的共同表达，而不是单独表达，上调胰岛素生长因子结合蛋白 IGFBP5 并下调 IGFBP7，这表明融合蛋白也可能赋予代谢优势，也许在存在 DNA 损伤的情况下。最后，我们证明融合蛋白在体外与已知的分散的 900 个内部缺失的 piggyBac 元件家族的成员结合，称为 MER85s，这为融合蛋白如何对基因表达产生广泛影响提供了一种潜在的机制。我们的数据表明，CSB-PGBD3 融合蛋白在健康和疾病中都很重要，并且可能在科凯恩综合征中发挥作用。
