发布: 2017年05月20日第7卷第10期 DOI: 10.21769/BioProtoc.2295 浏览次数: 14532
评审: Alka MehraFabienne C. FieselShahzada KhanAnonymous reviewer(s)
Abstract
While the activation of the transcription factor interferon regulatory factor 5 (IRF5) is critical for the induction of innate immune responses, it also contributes to the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE). IRF5 phosphorylation is a hallmark of its activation in the Toll-like receptor (TLR) pathway, where active IRF5 induces type I interferon and proinflammatory cytokine genes. By using the phosphate-binding molecule Phos-tag, without either radioisotopes or phospho-specific antibodies, the protocol described here enables detection of the phosphorylation of both human and murine IRF5, as well as that of other proteins.
Keywords: IRF5 (IRF5)Background
In the TLR-MyD88 pathway, IRF5 is activated through post-translational modifications such as ubiquitination and phosphorylation, and then active IRF5 translocates into the nucleus and induces its target genes (Takaoka et al., 2005; Balkhi et al., 2008; Tamura et al., 2008; Hayden and Ghosh, 2014). Regarding the activation status of IRF5 in SLE, it has been reported that IRF5 accumulates in the nucleus in monocytes of SLE patients (Stone et al., 2012). Furthermore, we recently showed in an SLE murine model that IRF5 hyperactivation (e.g., elevated phosphorylation) leads to the development of an SLE-like disease (Ban et al., 2016). Therefore, analyzing the activation status of IRF5 is important for studying SLE as well as innate immune responses. Phosphorylation is central to the activation of IRF5, as numerous studies have revealed the functional phosphorylation sites of IRF5 by site-directed mutagenesis and/or mass spectrometry (Barnes et al., 2002; Lin et al., 2005; Chen et al., 2008; Chang Foreman et al., 2012; Lopez-Pelaez et al., 2014; Ren et al., 2014). However, antibodies specific for these phosphorylation sites are not commercially available. In addition, phosphorylated IRF5 is normally not separated from non-phosphorylated IRF5 using standard SDS-PAGE. We thus utilized the functional molecule Phos-tag, which binds specifically to the phosphate group via metal ions (Kinoshita et al., 2006). Without using radioisotopes or phospho-specific antibodies, this protocol enables the detection of multiple phosphorylations of the IRF5 protein as up-shifted bands in the resulting immunoblot analysis (Figure 1). This protocol can be applied for detecting the phosphorylation of other proteins if a specific antibody for the total protein of the target protein is available.
Figure 1. Schematic of Phos-tag immunoblot analysis. Phos-tag binds specifically to a phosphate group on the target protein via metal ions, such as Zn2+ or Mn2+. Non-phosphorylated and phosphorylated forms of the target protein (IRF5 in this figure) are separated by SDS-PAGE using acrylamide conjugated with Phos-tag, and then detected by immunoblot analysis using an appropriate specific antibody. The mobility shift of the phosphorylated protein is caused by trapping of its phosphate groups by the polyacrylamide gel-conjugated Phos-tag. Thus, multiple phosphorylations of IRF5 appear as different up-shifted bands, whose mobility shift increases with the phosphorylation level of each IRF5 molecule.
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文章信息
版权信息
© 2017 The Authors; exclusive licensee Bio-protocol LLC.
如何引用
Sato, G. R., Ban, T. and Tamura, T. (2017). Phos-tag Immunoblot Analysis for Detecting IRF5 Phosphorylation. Bio-protocol 7(10): e2295. DOI: 10.21769/BioProtoc.2295.
分类
细胞生物学 > 细胞信号传导 > 磷酸化
生物化学 > 蛋白质 > 修饰
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