LC-MS of FLAG-tagged C-terminal domain of human DUX4

DUX4 activates the first wave of zygotic gene expression in the early embryo. Mis-expression of DUX4 in skeletal muscle causes facioscapulohumeral dystrophy (FSHD), whereas expression in cancers suppresses IFNg-induction of MHC Class I and contributes to immune evasion. We show that the DUX4 protein broadly suppresses immune signaling pathways—including IFNg, IFNb, DDX58, IFIH1 and cGAS mediated pathways. A conserved region containing (L)LxxL(L) motifs in the DUX4 carboxyterminal domain (CTD) was necessary to suppress interferon stimulated genes (ISGs). Co-immunoprecipitation identified DUX4-CTD interaction with multiple immune signaling factors, including STAT1. The DUX4-CTD (L)LxxL(L) region interacts with phosphorylated STAT1, sequesters it in the nucleus, modestly reduces its DNA binding, and prevents STAT1 from inducing ISG transcription. Mouse Dux similarly interacted with STAT1 and suppressed IFNg induction of ISGs. These findings identify an evolved role of the DUXC family in modulating immune signaling pathways with implications for development, cancers, and FSHD.