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

ABSTRACT: 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.

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Myoblast

DISEASE(S): Facioscapulohumeral Muscular Dystrophy

SUBMITTER: Sean Bennett

LAB HEAD: Stephen J. Tapscott

PROVIDER: PXD029215 | Pride | 2023-05-10

REPOSITORIES: Pride

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Project description:DUX4 is a double homeodomain transcription factor whose misexpression in the muscle causes facioscapulohumeral muscular dystrophy (FSHD). The transcriptional activity of DUX4 has been extensively characterized, and is thought to be the primary driver of FSHD pathogenesis. Yet, DUX4 expression lowers the protein level of an RNA quality control factor, UPF1, without affecting its transcript level, hinting at post-transcriptional regulatory activity downstream of DUX4 expression. How extensive the post-transcriptional activity of DUX4 is, and how relevant it is to FSHD pathogenesis, is unknown. In order to gain insight into DUX4-induced post-transcriptional gene regulation, we measured transcript and protein levels in DUX4 expressing cells via RNA-seq and SILAC-based quantitative mass spectrometry, respectively. We show that DUX4 transcriptional targets are robustly translated, including those genes previously identified as potential FSHD biomarkers. However, comparing the overall pattern of gene expression changes for RNA versus protein reveals striking differences in the most highly activated pathways, with the former showing changes in RNA processing and splicing, and the latter affecting the humoral immune response, proteolysis and exocytosis, among other pathways. Consistent with a misregulation of exocytosis, fluorescence imaging shows fragmented golgi apparatus in DUX4-expressing cells. Of the genes that showed discordant RNA and protein expression levels, post-transcriptional buffering was particularly evident for genes involved in stress response and may explain why DUX4-expressing cells succumb to toxicity despite robust transcriptional activation of stress response genes. Moreover, several genes involved in RNA decay including UPF1, UPF3B, SMG6 and XRN1 showed downregulation at the protein level, which may explain the massive inhibition of RNA quality control in DUX4-expressing cells. These results highlight the importance of considering post-transcriptional gene regulation in DUX4-expressing cells in order to fully understand the FSHD disease process.

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

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