Okumura Fumihiko, Lenschow Deborah J, Zhang Dong-Er
Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
J Biol Chem. 2008 Sep 5;283(36):24484-8. doi: 10.1074/jbc.M803795200. Epub 2008 Jul 7.
The expression of the ubiquitin-like molecule ISG15 (UCRP) and protein modification by ISG15 (ISGylation) are strongly activated by interferon, genotoxic stress, and pathogen infection, suggesting that ISG15 plays an important role in innate immune responses. Inducible nitric-oxide synthase (iNOS) is induced by the similar stimuli as ISG15 and enhances the production of nitric oxide (NO), a pleiotropic free radical with antipathogen activity. Here, we report that cysteine residues (Cys-76 and -143 in mouse, Cys-78 in human) of ISG15 can be modified by NO, and the NO modification of ISG15 decreases the dimerization of ISG15. The mutation of the cysteine residue of ISG15 to serine improves total ISGylation. The NO synthase inhibitor S-ethylisothiourea reduces endogenous ISGylation. Furthermore, ectopic expression of iNOS enhanced total ISGylation. Together, these results suggest that nitrosylation of ISG15 enhances target protein ISGylation. This is the first report of a relationship between ISGylation and nitrosylation.
类泛素分子ISG15（UCRP）的表达以及ISG15介导的蛋白质修饰（ISGylation）可被干扰素、基因毒性应激和病原体感染强烈激活，这表明ISG15在先天免疫反应中发挥重要作用。诱导型一氧化氮合酶（iNOS）与ISG15受相似刺激诱导，并增强一氧化氮（NO）的生成，NO是一种具有抗病原体活性的多效性自由基。在此，我们报告ISG15的半胱氨酸残基（小鼠中的Cys-76和-143，人类中的Cys-78）可被NO修饰，且ISG15的NO修饰会降低ISG15的二聚化。将ISG15的半胱氨酸残基突变为丝氨酸可提高总的ISGylation水平。NO合酶抑制剂S-乙基异硫脲可降低内源性ISGylation。此外，iNOS的异位表达增强了总的ISGylation。总之，这些结果表明ISG15的亚硝基化增强了靶蛋白的ISGylation。这是关于ISGylation与亚硝基化之间关系的首次报道。
