Held Tobias, Basler Michael, Knobeloch Klaus-Peter, Groettrup Marcus
Division of Immunology, Department of Biology, University of Konstanz, Konstanz, Germany.
Biotechnology Institute Thurgau at the University of Konstanz, Kreuzlingen, Switzerland.
Eur J Immunol. 2021 Jan;51(1):138-150. doi: 10.1002/eji.202048646. Epub 2020 Aug 5.
The IFN stimulated gene 15 (ISG15) encodes a 15-kDa ubiquitin-like protein, that is induced by type I IFNs and is conjugated to the bulk of newly synthesized polypeptides at the ribosome. ISG15 functions as an antiviral molecule possibly by being covalently conjugated to viral proteins and disturbing virus particle assembly. Here, we have investigated the effect of ISGylation on degradation and antigen presentation of viral and cellular proteins. ISGylation did not induce proteasomal degradation of bulk ISG15 target proteins neither after overexpressing ISG15 nor after induction by IFN-β. The MHC class I cell surface expression of splenocytes derived from ISG15-deficient mice or mice lacking the catalytic activity of the major de-ISGylating enzyme USP18 was unaltered as compared to WT mice. Fusion of ubiquitin or FAT10 to the long-lived nucleoprotein (NP) of lymphocytic choriomeningitis virus accelerated the proteasomal degradation of NP while fusion to ISG15 did not detectably speed up NP degradation. Nevertheless, MHC-I restricted presentation of two epitopes of NP were markedly enhanced when it was fused to ISG15 similarly to fusion with ubiquitin or FAT10. Thus, we provide evidence that ISG15 can enhance the presentation of antigens on MHC-I most likely by promoting co-translational antigen processing.
干扰素刺激基因15（ISG15）编码一种15千道尔顿的类泛素蛋白，它由I型干扰素诱导产生，并在核糖体上与大量新合成的多肽结合。ISG15可能通过与病毒蛋白共价结合并干扰病毒颗粒组装而发挥抗病毒分子的作用。在这里，我们研究了ISGylation对病毒和细胞蛋白降解及抗原呈递的影响。无论是过表达ISG15后，还是IFN-β诱导后，ISGylation均未诱导大量ISG15靶蛋白的蛋白酶体降解。与野生型小鼠相比，来自ISG15缺陷小鼠或缺乏主要去ISGyl化酶USP18催化活性的小鼠的脾细胞的MHC I类细胞表面表达未发生改变。将泛素或FAT10与淋巴细胞性脉络丛脑膜炎病毒的长寿命核蛋白（NP）融合可加速NP的蛋白酶体降解，而与ISG15融合则未检测到明显加快NP降解。然而，当NP与ISG15融合时，类似于与泛素或FAT10融合，MHC-I限制的NP两个表位的呈递明显增强。因此，我们提供证据表明，ISG15最有可能通过促进共翻译抗原加工来增强MHC-I上的抗原呈递。
