ISG15 counteracts Listeria monocytogenes infection.
Bottom Line: ISG15 is an interferon-stimulated, linear di-ubiquitin-like protein, with anti-viral activity.We made use of stable isotope labeling in tissue culture (SILAC) to identify ISGylated proteins that could be responsible for the protective effect.Strikingly, infection or overexpression of ISG15 leads to ISGylation of ER and Golgi proteins, which correlates with increased secretion of cytokines known to counteract infection.
Affiliation: Unité, Institut Pasteur, Paris, France.
ISG15 is an interferon-stimulated, linear di-ubiquitin-like protein, with anti-viral activity. The role of ISG15 during bacterial infection remains elusive. We show that ISG15 expression in nonphagocytic cells is dramatically induced upon Listeria infection. Surprisingly this induction can be type I interferon independent and depends on the cytosolic surveillance pathway, which senses bacterial DNA and signals through STING, TBK1, IRF3 and IRF7. Most importantly, we observed that ISG15 expression restricts Listeria infection in vitro and in vivo. We made use of stable isotope labeling in tissue culture (SILAC) to identify ISGylated proteins that could be responsible for the protective effect. Strikingly, infection or overexpression of ISG15 leads to ISGylation of ER and Golgi proteins, which correlates with increased secretion of cytokines known to counteract infection. Together, our data reveal a previously uncharacterized ISG15-dependent restriction of Listeria infection, reinforcing the view that ISG15 is a key component of the innate immune response.
No MeSH data available.
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Mentions: In order to determine which pathway was essential for ISG15 induction, we performed an siRNA screen of innate immune molecules that are known to be involved in bacterial sensing (Figure 2C). As for the experiments described above, we used HeLa cells for the siRNA screen. Although HeLa cells are reported to lack STING (Burdette and Vance, 2013), the ATCC line we worked with expressed STING mRNA, as evidenced by qRT-PCR. We were able to specifically extinguish this signal with siRNA (Figure 2—figure supplement 2). Our data showed that the ISG15 signal was clearly dependent on IRF3, IRF7, STING, and TBK1, implicating the CSP. In further support of an interferon-independent signal, depleting STAT1, which is a critical mediator of type I and III interferon signaling did not abrogate the ISG15 signal (Figure 2C). In non-immune cells interferon induction has been linked to sensing of triphosphorylated RNA by RIG-I (Abdullah et al., 2012; Hagmann et al., 2013); however, in our experimental conditions, RIG-I did not seem to be required for the ISG15 signal. Instead, it seems that direct ISG15 induction occurs through a pathway similar to the CSP in macrophages.
No MeSH data available.