Ebola virus disease (EVD) is characterized by immune dysregulation and damaging hyperinflammation. We aimed to characterize the signaling pathways and regulatory mechanisms dysregulated during EVD. To avoid hyperinflammation, innate immune signaling is regulated by post-translational modifications (PTMs), including protein phosphorylation. Here, we show that the protein tyrosine phosphatase nonreceptor type 13 (PTPN13) negatively regulates Interferon (IFN)-β while also positively regulating the neutrophil chemoattractant CXCL1. Using vectors encoding IRF3 with mutations on phosphorylation sites, we identified Y292 on IRF3 as a PTPN13 target of dephosphorylation. Knockout of PTPN13 increased IRF3 phosphorylation and expression of IFNβ and IFN-stimulated genes (ISGs) following poly(I:C) stimulation. Intriguingly, depletion of PTPN13 during Ebola virus (EBOV) infection resulted in decreased IFNβ and ISG induction at later time points post-infection, which correlated with increased viral titers. We identified PTPN13-mediated dephosphorylation of the viral protein VP35 as one potential mechanism inhibiting virus replication. Additionally, the induction of inflammatory chemokines, including CXCL1, decreased in PTPN13 knockout cells late during EBOV infection. These effects could be explained by increased phosphorylation of the regulatory p85 subunit of PI3K. Dephosphorylation of p85 promotes its degradation, subsequently enhancing PI3K kinase activity and downstream signaling via AKT. Together, our study suggests that PTPN13 is involved in immune regulation and efficient antiviral responses by dephosphorylation of IRF3, EBOV-VP35 and PI3K-p85.
Warren et al. (Tue,) studied this question.