Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America.
PLoS One. 2012;7(1):e29870. doi: 10.1371/journal.pone.0029870. Epub 2012 Jan 17.
Type I interferon (IFN) stimulates expression and conjugation of the ubiquitin-like modifier IFN-stimulated gene 15 (ISG15), thereby restricting replication of a wide variety of viruses. Conjugation of ISG15 is critical for its antiviral activity in mice. HECT domain and RCC1-like domain containing protein 5 (HerC5) mediates global ISGylation in human cells, whereas its closest relative, HerC6, does not. So far, the requirement of HerC5 for ISG15-mediated antiviral activity has remained unclear. One of the main obstacles to address this issue has been that no HerC5 homologue exists in mice, hampering the generation of a good knock-out model. However, mice do express a homologue of HerC6 that, in contrast to human HerC6, can mediate ISGylation.Here we report that the mouse HerC6 N-terminal RCC1-like domain (RLD) allows ISG15 conjugation when replacing the corresponding domain in the human HerC6 homologue. In addition, sequences in the C-terminal HECT domain of mouse HerC6 also appear to facilitate efficient ISGylation. Mouse HerC6 paralleled human HerC5 in localization and IFN-inducibility. Moreover, HerC6 knock-down in mouse cells abolished global ISGylation, whereas its over expression enhanced the IFNβ promoter and conferred antiviral activity against vesicular stomatitis virus and Newcastle disease virus. Together these data indicate that HerC6 is likely the functional counterpart of human HerC5 in mouse cells, suggesting that HerC6(-/-) mice may provide a feasible model to study the role of human HerC5 in antiviral responses.
I 型干扰素 (IFN) 刺激泛素样修饰物 IFN 刺激基因 15 (ISG15) 的表达和缀合，从而限制了多种病毒的复制。ISG15 的缀合对其在小鼠中的抗病毒活性至关重要。HECT 结构域和 RCC1 样结构域包含蛋白 5 (HerC5) 在人细胞中介导全局 ISGylation，而其最接近的同源物 HerC6 则不能。到目前为止，HerC5 对 ISG15 介导的抗病毒活性的要求仍然不清楚。解决这个问题的主要障碍之一是小鼠中不存在 HerC5 同源物，这阻碍了良好敲除模型的产生。然而，小鼠确实表达了 HerC6 的同源物，与人类 HerC6 不同，它可以介导 ISGylation。在这里，我们报告说，当替换人 HerC6 同源物中的相应结构域时，小鼠 HerC6 的 N 端 RCC1 样结构域 (RLD) 允许 ISG15 缀合。此外，小鼠 HerC6 的 C 端 HECT 结构域中的序列似乎也有助于有效的 ISGylation。小鼠 HerC6 在定位和 IFN 诱导方面与人类 HerC5 相似。此外，在小鼠细胞中敲低 HerC6 会消除全局 ISGylation，而其过表达增强了 IFNβ 启动子并赋予了对水疱性口炎病毒和新城疫病毒的抗病毒活性。这些数据表明，HerC6 可能是小鼠细胞中人类 HerC5 的功能对应物，表明 HerC6(-/-) 小鼠可能提供一种可行的模型来研究人类 HerC5 在抗病毒反应中的作用。
